International Journal of
Molecular Sciences Article
Bacteria-Templated NiO Nanoparticles/Microstructure for an Enzymeless Glucose Sensor Settu Vaidyanathan 1 , Jong-Yuh Cherng 1, *, An-Cheng Sun 2 and Chien-Yen Chen 3, * 1 2 3
*
Department of Chemistry and Biochemistry, National Chung Cheng University, 168 University Road, Min-Hsiung, Chia-Yi 62102, Taiwan;
[email protected] Department of Chemical Engineering & Materials Science, Yuan Ze University. No. 135 Yuandong Road, Zhongli District, Taoyuan City 320, Taiwan;
[email protected] Department of Earth and Environmental Sciences, National Chung Cheng University, 168 University Road, Min-Hsiung, Chia-Yi 62102, Taiwan Correspondence:
[email protected] (J.-Y.C.);
[email protected] (C.-Y.C.); Tel.: +886-5272-0411 (C.-Y.C.)
Academic Editor: Vladimir Sivakov Received: 3 June 2016; Accepted: 28 June 2016; Published: 11 July 2016
Abstract: The bacterial-induced hollow cylinder NiO (HCNiO) nanomaterial was utilized for the enzymeless (without GOx) detection of glucose in basic conditions. The determination of glucose in 0.05 M NaOH solution with high sensitivity was performed using cyclic voltammetry (CV) and amperometry (i–t). The fundamental electrochemical parameters were analyzed and the obtained values of diffusion coefficient (D), heterogeneous rate constant (ks ), electroactive surface coverage (Γ), and transfer coefficient (alpha-α) are 1.75 ˆ 10´6 cm2 /s, 57.65 M´1 ¨ s´1 , 1.45 ˆ 10´10 mol/cm2 , and 0.52 respectively. The peak current of the i–t method shows two dynamic linear ranges of calibration curves 0.2 to 3.5 µM and 0.5 to 250 µM for the glucose electro-oxidation. The Ni2+ /Ni3+ couple with the HCNiO electrode and the electrocatalytic properties were found to be sensitive to the glucose oxidation. The green chemistry of NiO preparation from bacteria and the high catalytic ability of the oxyhydroxide (NiOOH) is the good choice for the development of a glucose sensor. The best obtained sensitivity and limit of detection (LOD) for this sensor were 3978.9 µA mM´1 ¨ cm´2 and 0.9 µM, respectively. Keywords: hollow cylinder NiO (HCNiO) nanostructure; glassy carbon electrode (GCE); non-enzymatic glucose sensor; electrochemical sensing; electrocatalysis; amperometric sensors
1. Introduction Nowadays, amperometric glucose sensors are relevant for use in blood sugar monitoring with reliable sensitivity and selectivity in the health care industry. In the clinical field it was estimated that 2.8% of the world population, around 171 million people, were affected by diabetes in 2000. It will be projected to be 4.4% by the year 2030, approximately 366 million people [1]. The diagnosis of diabetes has become a far more sophisticated branch of science with increasing self-testing kits. Almost 85% of the entire biosensor market is the commercial glucose biosensor which makes diabetes a model for the development of new biosensors [2]. Biosynthesis of nanoparticles (NPs) using biological molecules and microorganisms has rapidly emerged as nanobiotechnology, i.e., biotechnology combined with nanotechnology [3]. Green nanotechnology could be a best alternative for the nanomaterial synthesis with meticulous nature with the help of variety of biological molecules, such as proteins, carbohydrates, and polyphenols [4]. NPs with different shapes, such as spherical, triangular, octahedral, cluster, and amorphous crystalline have been successfully synthesized using microorganisms. Pseudomonas stutzeri,
Int. J. Mol. Sci. 2016, 17, 1104; doi:10.3390/ijms17071104
www.mdpi.com/journal/ijms
Int. J. Mol. Sci. 2016, 17, 1104
2 of 16
Magnetospirillum, Escherichia coli, Klebsiella aerogenes, and Lactobacillus strains have been used for the bacterial shaped synthesis of silver, gold, cadmium, magnetite, and titanium NPs [5–9]. Most of the studies involved for the glucose sensor are the enzymatic reaction between the glucose and glucose oxidase (GOx). GOx catalyzes the oxidation of glucose to gluconolactone in the presence of redox mediators and metallic NPs coated on the electrode. However, the value of the enzyme, mediator, and electrode are expensive. In addition, electrode fouling might occur due to the thermal environment, pH change, lack of chemical stability, and fair toxicity [10–12]. Hence, the enzymeless glucose sensors are dramatically developed due to the low fabrication cost, overpotential reduction, and low detection limit with selectivity, sensitivity, and stability [13–18]. The noble metals and their oxides used as the redox mediators for the non-enzymatic glucose sensors have been reported [19–25]. Further work for the sensitive determination of glucose by simple and available materials, which have low cost and are less time consuming is required. Nanomaterials of NiO become popular for sensor devices because of its magnetic and heterogeneous electrocatalytic activities [26–30]. Green method is preferable for the preparation of materials in chemical industry, which is cost effective and is safe to the environment and human beings [31]. NPs of HCNiO with unique bacterial morphology were synthesized and used for glucose sensor in this study. Nanomaterials were precipitated due to the urea hydrolysis induced by bacterial metabolism [32,33]. The role of bacteria is to produce urease which catalyzes the hydrolysis of urea to CO3 2´ and NH4+ ions. Those ions result in an increasing pH which favors carboxylate ion (´COO´ ) on the bacterial cell wall to bind with the positive nickel ion providing a nucleation site. The CO3 2´ from urea hydrolysis reacts with nickel ions to form Ni precipitate on the surface of bacterial template. This is the formation of bio-Ni precipitate on the cell-wall structure. The aim of this study is to develop the enzymeless electrode for the glucose detection at lower concentration without any additives, such as enzymes and expensive metallic NPs. The glassy carbon electrode, with the help of bacterial-shaped hollow cylinder NiO (HCNiO) nanomaterial was used as a sensor and its properties were studied. This sensor showed excellent electrocatalytic activity towards the glucose detection, and was investigated by cyclic voltammetry and amperometry i–t techniques. 2. Results and Discussions 2.1. Electrochemical Properties of the HCNiO/GC-Modified Electrode The electrocatalytic activity of the constructed HCNiO/GC electrode was examined in 0.05 M NaOH using CV experiments within the potential range of 0.2 V to 0.7 V. The characteristic shape of the CV curves for HCNiO/GC in an alkaline medium is shown in Figure 1. The HCNiO/GC electrode was pre-dipped in NaOH solution for a while, developed the redox peak for Ni3+ /Ni2+ couple in the initial first scan but, at the same time, the sharp redox peaks were not observed for the freshly-modified electrode due to scarcity of Ni(OH)2 . This indicated that the need of aqueous OH´ for the film formation of the hydrous Ni(II) oxide species and Ni(OH)2 spontaneously on the electrode then leads to NiOOH formation [34–36]. In addition, a basic medium with the suitable concentration, 0.05 M NaOH is essential for the nickel-based material for the enhancement of the catalytic activity for the sensitive oxidation of carbohydrates [37]. The anodic and cathodic peaks at a potential of 0.49 V and 0.41 V are represented by the formation of NiOOH and Ni(OH)2 , respectively, on the solid surface of the HCNiO/GC electrode in the liquid NaOH medium. The deposition of the Ni2+ /Ni3+ redox couple was confirmed by the continuous increment of the anodic and cathodic peak currents during the successive CV scan. This implied that the modified electrode in the hydroxyl group environment produced enough of the redox couple on the surface of electrode, are extremely sensitive for shuttling of electrons between the solid surface and liquid medium [38,39]. The overall scheme (Scheme 1) of the reaction mechanism (Equations (1) and (2)) for Figure 1 is suggested below: NiO ` OH´ Ñ NiOOH ` e´
(1)
Int. J. Mol. Sci. 2016, 17, 1104
3 of 16
Oxidation pOxdq
´ Ý Ñ Ni pOHq2 ` OH´ Ý Ð ÝÝ ÝÝ ÝÝ ÝÝ ÝÝ ÝÝ ÝÝ ÝÝ Ý Ý NiOOH ` H2 O ` e
(2)
Reduction pRedq
Thus, the couple at half-wave potential (Ep/2 ) = 0.45 V and ∆Ep = 0.08 V values exhibited a redox with a quasi-reversible process. During the successive scan the anodic peak current (Ipa ) beyond the +0.6 V increased successively, which may be attributed to the electro-oxidation of OH´ ions to O2 with HO‚ radicals as intermediates. This has also been checked with the increasing OH´ ion concentration of supporting electrolyte for this system. It is observed that the anodic peak potential (Epa ) and cathodic peak potential (Epc ) shifted in the negative direction of potentials (lower), and the peak currents (Ipa and Ipc ) were shifting to higher values when the scan cycle number increased, which might be due to the rapid development of NiOOH by adsorptive behavior of nucleation from Ni(OH)2 . This is the indication of active sites of Ni2+ /Ni3+ produced on the surface of HCNiO/GC electrode, which is in agreement with the similar study of Wang et al. in the Ti/TiO2 nanotube arrays (NTAs)/Ni electrode in 2016, which Int. J. Mol. Sci. 17, the 1104CV scans were performed in 0.1 M NaOH solution [40]. 3 of 16 Ni3+ /Ni2+
Int. J. Mol. Sci. 2016, 17, 1104
3 of 16
Scheme 1. 1. Pictorial representation representation of of the the reaction reaction mechanism. Scheme Pictorial reaction mechanism. mechanism. 54th Cycle (c) 54th Cycle (c) 60 60
40 40
Epa shifting Epa shifting
1st Cycle (a) 1st Cycle (a)
I I/ /μΑ μΑ
2nd Cycle (b) 2nd Cycle (b)
20 20 forward scan forward scan 0 0 backward scan backward scan 54th Cycle 54th Cycle
-20 -20 0.2 0.2
0.3 0.3
Epc shifting Epc shifting
0.4 0.4
0.5 0.5
0.6 0.6
E // V V vs. vs. Ag/AgCl/NaCl Ag/AgCl/NaCl (3 (3 M) M) E
0.7 0.7
Figure 1. Cyclic voltammograms of the HCNiO/GC electrode (a) first cycle; (b) second cycle; and (c) Figure 1. 1. Cyclic electrode (a)(a) first cycle; (b)(b) second cycle; andand (c) Figure Cyclic voltammograms voltammogramsof ofthe theHCNiO/GC HCNiO/GC electrode first cycle; second cycle; −1. 54th cycle in the potential between 0.2 V to 0.7 V in 0.05 M NaOH solution, at a scan rate of 0.05 V·s−1 54th cycle in the between 0.2 V0.2 to 0.7 V in M 0.05 NaOH at a scan at rate of 0.05 V·sof. (c) 54th cycle in potential the potential between V to 0.70.05 V in M solution, NaOH solution, a scan rate 0.05 V¨ s´1 . NiO + OH −− → NiOOH + e−−
NiO + OH → NiOOH + e Oxidation (Oxd)
(Oxd) → NiOOH 2.2. Electrochemical SurfaceNi(OH) Characterization ofOxidation the HCNiO/GC Modified Electrode + OH−− ⎯⎯⎯⎯⎯ +H O + e−−
⎯⎯⎯⎯⎯ → ←⎯⎯⎯⎯ ⎯ Ni(OH)22 + OH ←⎯⎯⎯⎯ Reduction (Red)⎯ NiOOH + H22O + e Reduction (Red)
(1) (1) (2) (2)
2.2.1.Thus, Effect the of Scan Rates the Blankpotential Supporting Electrolyte couple at in half-wave (Ep/2 p/2 0.45 V V and and ∆E ∆Epp == 0.08 0.08 V V values values exhibited exhibited aa Thus, the couple at half-wave potential (E )) == 0.45 3+ 2+ Ni3+/Ni /Ni2+ redox redox with aa quasi-reversible quasi-reversible process. During During the successive successive scan scan the the anodic peak current current Ni After a wellwith production of Ni(OH)2process. /NiOOH couplethe by CV scanning at 0.05 anodic V¨ s´1 , peak the modified (I pa) beyond the +0.6 V increased successively, which may be attributed to the electro-oxidation of (Ipa) beyond the +0.6 V increased successively, which may besolution attributed the electro-oxidation electrode was transferred to a fresh 0.05 M NaOH aqueous for to further studies. Figure of 2 − ions to O2 with HO• radicals as intermediates. This has also been checked with the increasing OH − • OH ions O2 with HO radicals as of intermediates. This has also been checked with scan the increasing shows theto cyclic voltammograms HCNiO/GC-modified electrode at various rates (ν) OH−− ion ion concentration concentration of of supporting supporting electrolyte electrolyte for for this this system. system. It It is is observed observed that that the the anodic anodic peak peak OH potential (E pa) and cathodic peak potential (Epc) shifted in the negative direction of potentials (lower), potential (Epa) and cathodic peak potential (Epc) shifted in the negative direction of potentials (lower), and the the peak peak currents currents (I (Ipa pa and Ipc) were shifting to higher values when the scan cycle number and and Ipc) were shifting to higher values when the scan cycle number increased, which might be due to to the the rapid rapid development development of of NiOOH NiOOH by by adsorptive adsorptive behavior behavior of of increased, which might be due 2+/Ni3+ produced on the surface of nucleation from Ni(OH) 2. This is the indication of active sites of Ni2+ nucleation from Ni(OH)2. This is the indication of active sites of Ni /Ni3+ produced on the surface of HCNiO/GC electrode, which is in agreement with the similar study of Wang et al. in the Ti/TiO2
Int. J. Mol. Sci. 2016, 17, 1104
4 of 16
obtained in 0.05 M NaOH solution. The peak currents of anodic (Ipa ) and cathodic (Ipc ) are linearly proportional to the wide range of scan rates between 50 and 5000 mV¨ s´1 , indicating an immobilized surface-controlled electrode process [41]. This adsorption-controlled process was confirmed by the Int.logarithmic J. Mol. Sci. 2016,(log 17, 1104 4 of 16 and double Ip vs. log ν) plot of CV data with the slope values greater than 0.5 (0.58 0.68 for oxidation and reduction peaks respectively, Figure 2b). In addition, peak currents (Ipa and Ipc ) surface-controlled electrode process [41]. This adsorption-controlled process was confirmed by the are linearly to the square rateswith (ν1/2 the values same range scan0.5 rates shown doubleproportional logarithmic (log Ip vs. log ν)root plotof of scan CV data the) at slope greaterofthan (0.58asand 2 > 0.99 for both anodic and cathodic) exists for the in Figure 2c. Regression squared coefficient, (R 0.68 for oxidation and reduction peaks respectively, Figure 2b). In addition, peak currents (Ipa and 1/2) at the same linearity of Ip vs. ν1/2 , which diffusion controlled process alsoofinvolved. Ipc) plot are linearly proportional toindicated the squarethat rootthe of scan rates (ν range scan rates This as is ´ 2 because the huge availability of OHsquared ion diffusion transport the anodic quiescent electrolyte shown in Figure 2c. Regression coefficient, (R > 0.99from for both and supporting cathodic) exists for thetolinearity plot of p vs. ν1/2, which indicated that and the diffusion controlled process also involved. (liquid) the vicinity of Ielectrode surface film (solid) vice versa (diffusion Ø adsorption), during − ion diffusion transport from the quiescent supporting This is because the huge availability of OH the reaction shown in Equation (3), below [40]. electrolyte (liquid) to the vicinity of electrode surface film (solid) and vice versa (diffusion ↔ adsorption), during the reaction shown in Equation (3), below Adsorption process[40]. pOxdq 3` 2` ´ ÝÝÝ Ý Ñ Ni pOHq2+psolid surfaceq ` OH´ ÝÝ ÝÝ ÝÝ ÝÝ ÝÝ Ý ÝÝ ÝÝ ÝÝ ÝÝ ÝÝ ÝÝ Ý Ý3+Ni OOHpsolid surfaceq ` e paqueous phaseq ÐÝAdsorption process (Oxd) Diffusion process pRed ⎯⎯⎯⎯⎯⎯⎯ →q Ni OOH (solid surface) + e − Ni (OH) 2(solid surface) + OH (−aqueous phase) ←⎯⎯⎯⎯⎯⎯ ⎯ Diffusion process (Red)
2000 300
(a)
(a')
log (Ip / µA)
500 mV/s 1500
I / μA p
200
Epa shifting
100
50 mV/s
-1 ν = 50-5000 mVs
3.0
(b)
2.5
logI pa
logI pc = 0.6 822 logν +
-1.5 -2.0
2 R = 0.99 7
-2.5
I / μA
591 ν + 0.9 5 log 8 7 = 0.5 2 0.9981 R =
2.0
0
1000
(3)
(3)
0.329 1
5
-100
-3.0 0.2
0.3
0.4
0.5
0.6
2.0
0.7
E / V vs. Ag/AgCl/NaCl (3 M)
500
5000 mV/s
1200
Ip / µA
300
Epc shifting
550 mV/s
0
Ip = c -10.1 6
-300
R 2= 98 ν 1/2
-600
0.2
0.3
0.4
0.5
0.6
E / V vs. Ag/AgCl/NaCl (3 M)
0.7
0.8
3.5
-1 mVs 03 .06 57 1/ 2 ν 42 .7 9 95 17 .99 = 2 =0 I pa R
600
-500
3.0
(c) ν = 50-5000
900
0
2.5
log (ν / mVs-1)
0.996 0 + 68
0.9 5
15
25
35
45
.925 2 55
65
75
ν1/2 / (mV/s)1/2
Figure 2. CVs of the conditioned HCNiO/GC electrode in 0.05 M NaOH at different scan rates of
Figure 2. CVs of the conditioned HCNiO/GC electrode in 0.05 M NaOH at different scan rates of inset inset (a’) 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5 V·s−1 and (a) 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, (a’) 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5 V¨ s´1 and−1(a) 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 0.9, 0.95, 1, 1.25, 1.5, 1.75, 2, 2.5, 3, 3.5, 4, 4.5, and 5 V·s (current response from lower to higher, 1, 1.25, 1.5, 1.75, 2, 2.5, 3, 3.5, 4, 4.5, and 5 V¨ s´1 (current response from lower to higher, respectively); respectively); (b) plot of log Ip vs. log ν; and (c) Plot of Ip vs. ν1/2. (b) Plot of log Ip vs. log ν; and (c) Plot of Ip vs. ν1/2 .
However, the amount of Ni(OH)2 spontaneously formed at the surface due to the interaction of − was found to be extremely limited since no obvious redox peaks can be observed in the H 2 O or OHthe However, amount of Ni(OH)2 spontaneously formed at the surface due to the interaction of initial scanfound and attothe applied potential energy than the redox overpotential of the ´ was H2 O or OHCV belower extremely limited since no obvious peaks can be modified observed in electrode. Further reaction processes are occurring, as shown in the Equation (2) in Section 3.1. When the initial CV scan and at the lower applied potential energy than the overpotential of the modified increasing the scan rates, the anodic peak potential (Epa) was shifted to the more positive direction electrode. Further reaction processes are occurring, as shown in the Equation (2) in Section 3.1. When and the cathodic peak (Epc) moved towards the negative potential as shown in Figure 2a and inset a’. increasing the scan anodic peak potential shiftedscan to the more positive direction pa ) was Even though therates, peak the current increased remarkably(Ewith increasing rates, but the ratio of the and the cathodic peak (E ) moved towards the negative potential as shown in Figure 2a and inset a’. pc current (Ipa/Ipc) was above unity. It indicates that the Ni(II) to Ni(III) hydrous anodic to cathodic peak Even oxide though the peak current increased remarkably with increasing of the transformation process is a quasi-reversible reaction [42,43]. scan This rates, is duebut to the the ratio charge – ions between the positively-charged Ni, unity. Na, and negatively-charged OHto in hydrous the anodicinteraction to cathodic peak current (Ipa /Ipc ) was above It indicates that the Ni(II) Ni(III) [44].process is a quasi-reversible reaction [42,43]. This is due to the charge interaction oxide environment transformation
between the positively-charged Ni, Na, and negatively-charged OH– ions in the environment [44].
Int. J. Mol. Sci. 2016, 17, 1104
5 of 16
J. Mol.of Sci.Scan 2016, 17, 1104 and Electrocatalytic Effect in the Basic Glucose Solution 2.2.2.Int. Effect Rates
5 of 16
Figure 3 shows theRates effect ofElectrocatalytic glucose addition oninthe situation. The electroactive species of 2.2.2. Effect of Scan and Effect theabove Basic Glucose Solution the Ni(OH)2 /NiOOH, redox couple generated on the modified HCNiO/GC electrode was tested with Figure 3 shows the effect of glucose addition on the above situation. The electroactive species of (peakthe X Ni(OH) in Figure 3a”) and without (peak Y in Figure 3a”) 1 mM glucose in 0.05 M NaOH solution. 2/NiOOH, redox couple generated on the modified HCNiO/GC electrode was tested with It can(peak be seen that an3a”) increased Ipa from „78 (blank to „114 NaOH X in Figure and without (peak Y inµA Figure 3a”)NaOH) 1 mM glucose inµA 0.05(glucose-mixed M NaOH solution. ´1 . This excellent electrocatalytic ability is due solution) were produced at the scan rate of 50 mV¨ s It can be seen that an increased Ipa from ~78 µA (blank NaOH) to ~114 µA (glucose-mixed NaOH −1. This to thesolution) rich production of NiOOH therate HCNiO material by virtue of the enhanced surface area were produced at the in scan of 50 mV·s excellent electrocatalytic ability is due to and themorphological rich productionnature of NiOOH in the HCNiOglassy material by virtue of the (GCE) enhanced surface special on the substrate, carbon electrode [42]. Here,area the and cathodic morphological nature on 50 themV¨ substrate, glassyrate carbon (GCE) [42]. the cathodic peak special (Ipc ) decreased at higher than s´1 sweep but electrode the enhancement ofHere, the glucose oxidation peak (I pc) decreased at higher than 50 mV·s−1 sweep rate but the enhancement of the glucose peak (Ipa ) was found (Figure 3a”) and there was no reduction peak at the lower than 15 mV¨ s´1 sweep oxidation peak (Ipa) was found (Figure 3a”) and there was no reduction peak at the lower than rate. This is due to the change in the Ni2+ /Ni3+ concentration ratio. The redox reaction occurring on 15 mV·s−1 sweep rate. This is due to the change in the Ni2+/Ni3+ concentration ratio. The redox 2+ 3+ the electrode surface (Ni ØNi ) is restricted due to the limited OH´ diffusion rate with the presence reaction occurring on the electrode surface (Ni2+↔Ni3+) is restricted due to the limited OH− diffusion of glucose ions, inofturn limits the production of Ni(OH) from the 2 from NiOOH, rate with the which presence glucose ions, which in turn limits the production of Ni(OH)2resulting from NiOOH, directresulting electrocatalytic oxidation of glucose to gluconolactone, as showed in Equation (4). The from the direct electrocatalytic oxidation of glucose to gluconolactone, as showedsimplest in proposed reaction its rate reaction constantmechanism for the above are shown theabove following Equation (4). mechanism The simplestand proposed andprocesses its rate constant forinthe Scheme 2 and are Equation [42,45]: processes shown (4) in the following Scheme 2 and Equation (4) [42,45]:
Scheme 2. Glucose oxidation reaction mechanism under basic conditions on Ni(OH)2/NiOOH system.
Scheme 2. Glucose oxidation reaction mechanism under basic conditions on Ni(OH)2 /NiOOH system.
By simply,
By simply, k ,k k , RDS Ni ( II ) − e− ←⎯⎯ → Ni(II) and Ni(III) + Glucose ⎯⎯⎯ → Ni(II) + Gluconolactone k 2
1
3
-1
k ,RDS
∝
k ,k(
∝)
2 3 1 = pIIq °expand [ Ni] pIIIq (oxd)`; Glucose k–1 = °exp [Ñ Ni pIIq ] (red) k1 Ni Ni pIIq ´ e´ ÐÝ ÝÝÑ ÝÝ Ý ` Gluconolactone
k´1
(4)
(4)
nFηconstants k1 (forward-anodic) p1´9qnFη ´r 9 ˝ ands k −1 (reverse-cathodic) are In the above expressions rate predq k1 “ k˝ expthe RT s poxdq ; k –1 “ k expr RT obviously potential-dependent for the redox reaction, ° is a standard-rate constant, η is the overpotential, other parameters of their usual meaning. The peak potentials (Epa) shifted In the above and expressions the rateareconstants k1 (forward-anodic) and k´1 (reverse-cathodic) ˝ towards the positive direction (higher E pa), which indicated that the diffusion limitation of glucose are obviously potential-dependent for the redox reaction, k is a standard-rate constant, η is the in the catalytic process (Figure 3a). The result might show glucose diffusion from the bulk solution overpotential, and other parameters are of their usual meaning. The peak potentials (E pa ) shifted phase to the surface of modified electrode in which NiOOH (Ni3+ active sites) formation and glucose towards the positive direction (higher Epa ), which indicated that the diffusion limitation of glucose oxidation simultaneously occurred. Adsorption of glucose is more competitive than OH− on the in the catalytic process (Figure 3a). The result might show glucose diffusion from the bulk solution surface of the electrode when the presence of glucose and OH− ions diffused from the solution. 3+ active sites) formation and glucose phaseHence, to thethe surface of modified electrode in which NiOOH (Ni 3+ higher potential was required to form more Ni sites from already-covered Ni2+ sites on oxidation simultaneously occurred. Adsorption of glucose is more competitive than OH´the on the the surface for the presence of glucose at the higher scan rates [45–47]. This demonstrated ´ surface of the of electrode when the presence glucose OH there ions diffused from theeffect solution. Hence, certainty electrocatalytic oxidation of of glucose. In and addition, was no poisoning on the surfacepotential by the consistent CV run to on form this system. scan already-covered rates was almost similar for the the higher was required more The Ni3+effect sitesoffrom Ni2+ sites on the absence andpresence the presence of 1 mMatglucose in 0.05 M NaOH system (Figures 2 and 3). The potential surface for the of glucose the higher scan rates [45–47]. This demonstrated the certainty sweep rates between the ranges of 50 to 3500 mV/s were used for the presence of glucose as in by of electrocatalytic oxidation of glucose. In addition, there was no poisoning effect on the surface Figure 3. It can be seen in Figures 2a and 3a, the potential shifting (both Epa and Epc) occurs upon the consistent CV run on this system. The effect of scan rates was almost similar for the absence and increasing sweep rates in both the cases. However, the oxidation peak (Epa) broadening started in the the presence of 1 mM glucose in 0.05 M NaOH system (Figures 2 and 3). The potential sweep rates case of glucose solution (Figure 3a). Eventually, at higher than 800 mV/s scan rates, a wider between the ranges of 50 to 3500 mV/s were used for the presence of glucose as in Figure 3. It can broadening arose that indicated the limitation was due to the charge transfer kinetics and which is
be seen in Figures 2a and 3a, the potential shifting (both Epa and Epc ) occurs upon increasing sweep rates in both the cases. However, the oxidation peak (Epa ) broadening started in the case of glucose
Int. J. Mol. Sci. 2016, 17, 1104
6 of 16
Int. J. Mol. Sci. 2016, 17, 1104 of 16 solution (Figure 3a). Eventually, at higher than 800 mV/s scan rates, a wider broadening arose6 that indicated the limitation was due to the charge transfer kinetics and which is also associated with alsocharge associated with the in charge propagation the surface A very slowine−the transfer occurs in the the propagation the surface film. Ainvery slow e´film. transfer occurs complex situation − 3+ 2+ 3+ when abrupt increasing complex situation of the film through Glu , Ni , Ni , and regenerated Ni ´ 3+ 2+ 3+ of the film through Glu , Ni , Ni , and regenerated Ni when abrupt increasing the sweep rate. the sweep This barrier for diffusion of ions and e-s.involve It couldthe alsochemical involve This couldrate. barrier forcould the diffusion ofthe ions and migration of e-migration s. It couldof also − − the chemical reactions thesolution ions in the solution (OH , Glu and the nickel active sitessurface on the ´ , Glu´ reactions between the between ions in the (OH ) and the )nickel active sites on the surface (i.e., EC’ mechanism). In addition, the polarizability of the ions might interfere for (i.e., EC’ mechanism). In addition, the polarizability of the ions might interfere for free movementfree (in movement (in and out) through the film. This similar diffusion process and the rate of the reaction and out) through the film. This similar diffusion process and the rate of the reaction have been already have been reported for other nickel-modified electrodes Figurerelationships 3b–c show the reported foralready other nickel-modified electrodes [43,44,48]. Figure 3b–c[43,44,48]. show the linear for linear relationships for adsorption controlled and diffusion controlled processes their 2 adsorption controlled and diffusion controlled processes with their regression (R > 0.99)with and slope regression (R2 >than 0.99) greater 0.5 (Ipa ~ 0.55 ~ 0.81), respectively values greater 0.5and (Ipaslope ~0.55values and Ipc ~0.81),than respectively [49]. and ThisIpcsame range of values [49]. was This same range of values was obtained in the case of the absence of the glucose obtained in the case of the absence of the glucose experiment (Figure 2). This diffusionexperiment process is (Figure 2). This diffusion is the the total rate-determining step ofwhen the total process on the the rate-determining stepprocess (RDS) of redox process on (RDS) the film theredox presence of glucose, − + film´when the counter presence ions and counterofNa charge The neutralization of the OH ions and Naof+ glucose, ions (for OH charge neutralization theions film)(for [41,43,49]. surface coverage film) [41,43,49]. The surface coverage concentration (Г) of HCNiO/GC was evaluated from the concentration (Г) of HCNiO/GC was evaluated from the following Equation (5) following Equation (5) Q Γ Г“= (5) (5) nFA
where A is the area of the GCE (0.071 cm2), n is the number of electrons involved in the where A is the area of the GCE (0.071 cm2 ), n is the number of electrons involved in the redox redox reaction, Q is the charge obtained by integrating the anodic peak area of CV at low scan rate reaction, Q is the charge obtained by integrating the anodic peak area of CV at low scan rate (ν = 10 mV/s) for HCNiO/GC, and F is the Faraday constant (96,500 C/mole). It is assumed that all of (ν = 10 mV/s) for HCNiO/GC, and F is the Faraday constant (96,500 C/mole). It is assumed that all of the immobilized redox centers are electro-active species on the voltammetry time scale. The values the immobilized redox centers are electro-active species on the voltammetry time scale. The values of surface coverage for 2 µL and 10 µL coated HCNiO/GC electrodes were 1.45 × 10−10 mol/cm2 and of surface coverage for 2 µL and 10 µL coated HCNiO/GC electrodes were 1.45 ˆ 10´10 mol/cm2 1.25 × 10−9 mol/cm2, respectively, which correspond to the presence of a monolayer of effective and 1.25 ˆ 10´9 mol/cm2 , respectively, which correspond to the presence of a monolayer of effective surface species. surface species.
Y
80
400 60
200
I / μA
40 20
1500
R 2=
0 -20
0
0.3
0.4
0.5
0.6
I / μA
0.2
500
0.3
0.4
0.5
0.6
0.7
3500 mV/s I pa
0
800 mV/s
Epc shifting
-500 0.1
0.2
0.3
0.4
0.5
0.6
0.7
− 0.0 087
0.8
E / V vs. Ag/AgCl/NaCl (3 M)
0.9
1.0
3.0
=
.2 20
2.5 3.0 log (ν / mVs-1)
5 52
3.5
15
2.0
-1.5 -2.0
41 1/ 2 ν
900
.99 2 =0 R
25
35
-3.0
1200
92
R 2= Ip = 0.997 c -12. 8 0204 1/2 ν + 93 .5797 5
2.5
-2.5
(c) ν = 50-3500 mVs-1 366 .2
0.8
E / V vs. Ag/AgCl/NaCl (3 M)
logν
0.983 5
2.0
Epa shifting
-200
logI pc = -0. 8104
0.7
E / V vs. Ag/AgCl/NaCl (3 M)
1000
-1
23 2 0.9993 + 1.12 logν R = 7 0 55 = 0. l ogI pa
(a)
100
log (Ip / µA)
2000
X
45
ν1/2 / (mV/s)1/2
600
Ip / µA
(a') ν = 50-750 mVs
(b) ν = 50-3500 mVs
120
(a'')
-1
I pa / μA
2500
300 0 -300 -600
55
Figure 3. 3. CVs CVs of of the the conditioned conditioned HCNiO/GC HCNiO/GC electrode mM glucose glucose at at Figure electrode in in 0.05 0.05 M M NaOH NaOH containing containing 11 mM different scan rates of inset (a’) 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, and different scan rates of inset (a’) 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, and −1 (current response from lower to ´1and 3.5 V V ss´1 0.75 V¨ V·ss−1 0.75 and(a) (a)0.8, 0.8,0.85, 0.85,0.9, 0.9,0.95, 0.95,1,1,1.25, 1.25, 1.5, 1.5, 2, 2, 2.5, 2.5, 3, 3, and and 3.5 (current response from lower to 1/2. Inset (a”) modified electrode vs.log logν;ν;and and(c) (c)plot plotofofIpIpvs. vs.νν1/2 higher, respectively); respectively);(b) (b)Plot plotofoflog logIpIpvs. higher, . Inset (a”) modified electrode with 11 mM mM glucose glucose (X), (X), and and without without glucose glucose (Y), (Y), in in 0.05 0.05 M M NaOH NaOH at at the the scan scan rate rateof of50 50mV/s. mV/s. with
Int. J. Mol. Sci. 2016, 17, 1104
7 of 16
2.2.3. Kinetic Studies of HCNiO/GC Electrode in the Basic Glucose Solution Moreover, the adsorption process confirmed by the plot of the scan rate normalized current function (I/ν1/2 ) vs. scan rate (ν). Current function increased with scan rate, as shown in Figure 4a. It is expected for catalytically-coupled adsorption of an electrochemical-chemical (EC’) process. Steady linearity was found at higher ν in both the presence and absence of glucose cases, which indicates that the current function is independent of ν. This consistent fact revealed that the Ni(OH)2 /NiOOH transition is the quasi-reversible process in the NaOH/glucose solution [44,50]. In order to obtain information on the rate determining step (RDS), the Tafel slope “b”, was determined from the Figure 4b, plot of Ep vs. log ν, using the following Tafel equation (Equation (6)), valid for a totally irreversible diffusion-controlled process: η “ a ` b log i (6) or E p “ 2b log ν ` constant ´2.3RT , respectively; and i and i are current where “a” and “b” are Tafel constants 2.3RT o αF log io and αF B E , equal to and exchange current, respectively [51]. The partial derivative of E vs. log ν plot is B log ν the Tafel slope b/2. Slope b/2 obtained for this work is 0.0573 V/decade, so, b = 0.1146 V/decade. This slope indicates that a one electron transfer process is the RDS (slow) with the electronic transfer coefficient (α = 0.52) for glucose solution. This one electron transfer (rate-limiting step) process was also confirmed by the another type of Tafel plot (Epa vs. log I), which were drawn using the data from the rising part of the steady-state current–voltage (I–E) curve for electrocatalytic oxidation of glucose recorded after 30 s of polarization at the desired potential at a scan rate of 5 mV/s in 0.05 M NaOH. A slope of 0.114 V/decade (i.e., 8.77 (V/decade)´1 ) is obtained as in Figure 4c, indicating the one electron transfer process to be the rate-limiting step with the transfer coefficient of α = 0.52 [52]. The value of diffusion coefficient (D, cm2 /s) were obtained by the Randles-Sevcik equation (Equation (7)) for irreversible systems using the slope of scan rates study (Ip vs. ν1/2 ) with 1 mM glucose solution in 0.05 M NaOH [53]: Ip “ p2.99 ˆ 105 q α1/2 A C˚ D1/2 ν1/2 (7)
where C* is the bulk concentration of glucose in 0.05 M NaOH in terms of molar (mol/cm3 ) solution. In this study the obtained D value is 1.75 ˆ 10´6 cm2 /s from the slope value of Figure 3c, which is correlated with the reported literature; A is the electrode surface area (cm2 ) and ν is the scan rate (V¨ s´1 ). The rate constant of the heterogeneous electron transfer (ks ) reaction between basic glucose solution and electro-generated Ni(II)/Ni(III) couple on the solid surface can be calculated by the CV technique [50]. Here, this system involved a second-order rate constant ks (M´1 ¨ s´1 ) because OH´ and Glu´ ions are necessary for the oxidation. It may be affected by specific adsorption, surface solvent layer, nature of the electrode material itself (GCE), and the film on the electrode surface. There is no bond formation and bond dissociation in this case [53,54]. The rate constant (ks ) was calculated using the following Nicholson and Shain’s interpreted equation (Equation (8)) [50]: Icat “ Ipa
ˆ
1 0.447
˙ˆ
RT nF
˙1{2 ˆ
ks C ν
˙1{2 (8)
where Icat is the catalytic oxidation peak current with known glucose concentration (C) and Ipa is the diffusion current of oxidation peak without glucose in 0.05 M NaOH. The linearity plot of (Icat /Ipa ) vs. (1/ν)1/2 arrived with the different potential scan rates of 25 to 900 mV/s CV run in the basic glucose and basic solutions separately. The rate constant values 40.52, 63.15, 67.04, and 59.92 M´1 ¨ s´1 were obtained for different glucose concentrations 0.5, 1, 1.5, and 2 mM in 0.05 M NaOH solution as shown in Figure 5a–d, respectively. When increasing the concentration of glucose from 0.5 to 1.5 mM, the rate constant also increased gradually, and then decreased, starting at 2 mM glucose, as shown in the Figure 5d. This implied that the limitation of the rate constant occurred which could be attributed to the saturation of the active sites by the passive layer of the basic glucose molecules on the surface
Int. J. Mol. Sci. 2016, 17, 1104
8 of 16
Int. J. Mol. Sci. 2016, 17, 1104 Int. J. Mol. Sci. 2016, 17, 1104
8 of 16 8 of 16
of the electrode [55]. It resulted that there may not be sufficient active sites for the adsorption of on the surface of the electrode [55]. It resulted that there may not be sufficient active sites for the higheron concentrations of glucose. addition, some other chemical suchsites as the the surface of the electrodeIn[55]. It resulted that there may notcomplications, be sufficient active for glucose the adsorption of higher concentrations of glucose. In addition, some other chemical complications, intermediate occurring, could be a barrieroftoglucose. reach the of thechemical electrode for the diffusion adsorption of higher concentrations In catalytic addition,surface some other complications, such as the glucose intermediate occurring, could´be a barrier to reach the catalytic surface of the such as the glucoseAintermediate occurring,ofcould a barrier to reach the surface of of glucose molecules. high concentration OH bemight be required forcatalytic the oxidation ofthe a high electrode for the diffusion of glucose molecules. A high concentration of OH− might be required for electrode for the diffusion of glucose molecules. A highprogress concentration of with OH− might be required for The concentration glucose, and this part of work is under along this study [50,52]. the oxidation of a high concentration glucose, and this part of work is under progress along with this thevalue oxidation of arate high concentration glucose, and this range part ofof work under along with this was average of the constant forofthe 0.5 is mM torange 2progress mMofglucose study [50,52]. The average value theconcentration rate constant for the concentration 0.5 mMsolution to 2 mM study [50,52]. The average value of the rate constant for the concentration range of 0.5 mM to 2 mM ´ 1 ´ 1 57.65 M ¨ s solution , whichwas is in agreement with isthe [47,50]. literature [47,50]. glucose 57.65 M−1·s−1, which in reported agreementliterature with the reported
star - with glucose star - with glucose
19.1 17.1 17.1 15.1
square - no glucose square - no glucose
15.1 13.1 13.1 11.1
Scan rate ν / (mV/s) Scan rate ν / (mV/s)
11.1 9.1 9.1
E pa / V/ vs. Ag/AgCl/NaCl (3 (3 M)M) E pa V vs. Ag/AgCl/NaCl
(a) current function vs. ν (a) current function vs. ν
21.1 21.1 19.1
515 515 510 510
0
500 1000 1500 2000 2500 3000 3500 4000 4500 5000
0
500 1000 1500 2000 2500 3000 3500 4000 4500 5000
(b) Tafel plot (E vs. log ν ) (b) Tafel plot (E vs. log ν )
2 R2 = 0.9944 R = 0.9944 Epa = 57.2736 log ν + 272.36 Epa = 57.2736 log ν + 272.36
500 500 495 495 490 490
1.70 1.70
log (ν / mV/s) log (ν / mV/s) 1.80 1.80
(c) Tafel plot (E vs. log I ) (c) Tafel plot (E vs. log I )
Epa = 0.1136 log I + 1.14 Epa = 0.1136 log I + 1.14 2 R = 0.9917 0.52 2 R = 0.9917 0.52 alpha,α = 0.52 alpha,α = 0.52
0.50 0.50
alpha, α = 0.52 alpha, α = 0.52
505 505
0.54 0.54
Ag/AgCl/NaCl (3 M E pa / V/ vs. Ag/AgCl/NaCl (3)M ) E pa V vs.
1/21/2 (I /(Iν /1/2 ) / )(µA/(mV/s) ) ) / (µA/(mV/s) ν 1/2
glucose solution was 57.65 M−1·s−1, which is in agreement with the reported literature [47,50].
1.90 1.90
0.48 0.48 -5.80 -5.80
-5.70 -5.70
-5.60 -5.60
-5.50 -5.50
-5.40 -5.40
log (I / μA) log (I / μA)
-5.30 -5.30
2.00 2.00
Figure 4.Variations (a) Variations of the peak current function (I/ν1/2) )vs. for thethe oxidation of glucose; FigureFigure 4. (a)4. of the peak current function vs.νν ν oxidation of glucose; (a) Variations of the peak current function(I/ν (I/ν1/2) vs. forfor the oxidation of glucose; (b) dependence of the peak potential, Epa on log ν; and (c) Tafel plot derived from the (b) Dependence of the peak potential, E on log ν; and (c) Tafel plot derived from the potentiodynamic pa (b) dependence of the peak potential, Epa on log ν; and (c) Tafel plot derived from the potentiodynamic polarization curve (I–E) at 5 mV/s for a HCNiO/GC electrode in 0.05 M NaOH in polarization curve (I–E) at 5 mV/s for (I–E) a HCNiO/GC electrode in 0.05 M NaOH in the presence potentiodynamic polarization curve at 5 mV/s for a HCNiO/GC electrode in 0.05 M NaOH in of the presence of 1 mM glucose. 1 mMthe glucose. presence of 1 mM glucose. 1/2
1.60
(a) 0.5 mM glucose (a) 0.5 mM glucose -1 -1 ks = 40.52 M-1 s-1 ks = 40.52 M s
1.50 1.50 1.40
1.50
1.30
1.50
1.20 1.20
2 R2 = 0.9925 R = 0.9925
1/2 Icat / Ipa = 1.6137 / ν1/2 + 0.9402 Icat / Ipa = 1.6137 / ν + 0.9402
0.05 0.05
0.10
0.15
0.10 0.15 1/ν1/2 / (mV/s)-1/2 1/ν1/20.10 / (mV/s)-1/2 0.15 0.10
(c) 1.5 mM glucose (c) 1.5 mM glucose -1 -1 ks = 67.04 M-1 s-1 ks = 67.04 M s
0.15
(b) 1 mM glucose (b) 1 mM glucose -1 -1
ks = 63.15 M s ks = 63.15 M-1s-1
2 R2 = 0.9950 R = 0.9950
1.40 1.40
1.00 1.00
1.30
0.90
1.30
1/2 Icat / Ipa = 2.8488 / ν1/2 + 1.1384 Icat / Ipa = 2.8488 / ν + 1.1384
0.90
0.20
0.04
0.06
0.20
0.04
0.06
0.20
2.00
0.20
2.00
2.40 2.40
1.80 2.20 2.20
2 R2 = 0.9923 R = 0.9923
2.00 2.00
1.80
Icat / Ipa Icat / Ipa
0.05
1.10 1.10
Icat / Ipa Icat / Ipa
1.40 1.30
0.05
1.60
1.60 1.60
0.05 0.05
0.08
0.10
0.12
0.14
0.08 0.10 0.12 0.14 1/ν1/2 / (mV/s)-1/2 -1/2 1/2 1/ν 0.10 / (mV/s) 0.15 0.20 0.10
(d) 2 mM glucose (d) 2 mM glucose -1 -1 ks = 59.92 M-1 s-1 ks = 59.92 M s
0.15
0.16 0.16
0.20
2 R2 = 0.9918 R = 0.9918
1.40
1/2 Icat / Ipa = 3.5951 / ν1/2 + 1.6187 Icat / Ipa = 3.5951 / ν + 1.6187
1.80
1.40
1.80 1.20
1/2 Icat / Ipa = 3.9244 / ν1/2 + 1.1144 Icat / Ipa = 3.9244 / ν + 1.1144
1.20
Figure 5. Plot of Icat/Ipa vs. 1/ν1/2 for rate constant studies on a HCNiO/GC electrode in different 1/2 for rate constant studies on a HCNiO/GC electrode in different 1/2 5. of Plot Ipa cat/I pa vs. 1/ν FigureFigure 5. Plot Icatof /Iglucose vs. 1/ν forNaOH rate constant studies on mV/s) a HCNiO/GC in1different concentrations of in 0.05 M at different ν (25–900 (a) 0.5 mMelectrode glucose; (b) mM concentrations of glucose in 0.05 M NaOH atdifferent differentνν(25–900 (25–900 mV/s) (a)(a) 0.50.5 mM glucose; (b) 1(b) mM concentrations of glucose in 0.05 M NaOH at mV/s) mM glucose; 1 mM glucose; (c) 1.5 mM glucose; and (d) 2 mM glucose. glucose; (c) 1.5 mM glucose; and (d) 2 mM glucose.
glucose; (c) 1.5 mM glucose; and (d) 2 mM glucose.
Int. J. Mol. Sci. 2016, 17, 1104 Int. J. Mol. Sci. 2016, 17, 1104
9 of 16 9 of 16
2.3. Electrocatalytic of Glucose Glucose by by aa HCNiO/GC HCNiO/GC Electrode Electrode 2.3. Electrocatalytic Determination Determination of (CV) Method Method for for the the Detection Detection of of Glucose Glucose 2.3.1. Cyclic Voltammetric (CV) ´10 −10mol/cm shows the theCVs CVsofofthe the2 2µL µLHCNiO HCNiO = 1.45 mol/cm22)-coated Figure 6a shows (Г(Г = 1.45 ˆ ×1010 )-coated GC electrode recorded in indifferent differentglucose glucose concentrations (0.10 to 2 in mM) M solution NaOH solution at a recorded concentrations (0.10 mMmM to 2 mM) 0.05in M0.05 NaOH at a 50 mV/s 2 = 0.99 50 mV/s sweep The plot linearity plot obtained for theversus current versus concentration sweep rate. Therate. linearity obtained for the current concentration with R2 =with 0.99 R from the fromdata theisCV data in is shown in(Figure the inset (Figure 6a’). Thecurrent catalytic of a HCNiO/GC electrode CV shown the inset 6a’). The catalytic of current a HCNiO/GC electrode increased increasedthe towards theoxidation glucose oxidation and the enhancement of the peak anodic peak current attributed towards glucose and the enhancement of the anodic current attributed to the to the profound conductivity and large active surface area of the material coated on the electrode. profound conductivity and large active surface area of the material coated on the electrode. 80
(a) CV plot
70
(h) 2.0 mΜ
(a') Linear Plot 60
60
Ipa / µA
2 R = 0.9939
I / μA
40
Ipa = 21.0535 C + 25.4784
20 0.00
0.50
1.00
1.50
2.00
50
(a ) 0.0 μΜ
40
30
20
h g f e d c b a
Conc. (mM) 0
0.2
0.3
0.4
0.5
0.6
E / V vs. Ag/AgCl/NaCl (3 M) Figure 6. 6. (a) different Figure (a) CVs CVs of of the the conditioned conditioned HCNiO/GC HCNiO/GC electrode electrode in in 0.05 0.05 M M NaOH NaOH with with different concentrations of glucose, (a) 0.0 mM; (b) 0.1 mM; (c) 0.2 mM; (d) 0.4 mM; (e) 0.6 mM; (f) concentrations of glucose, (a) 0.0 mM; (b) 0.1 mM; (c) 0.2 mM; (d) 0.4 mM; (e) 0.6 mM; (f) 0.8 0.8 mM; mM; (g) 1.0 mM; and (h) 2.0 mM at ν = 50 mV/s; and inset (a’) linearity plot of current vs. concentraion of (g) 1.0 mM; and (h) 2.0 mM at ν = 50 mV/s; and inset (a’) linearity plot of current vs. concentraion the CV data. The mean peak current (n = 3) at the relevant concentration is shown with error bars of the CV data. The mean peak current (n = 3) at the relevant concentration is shown with error bars equal to to three three standard standard deviation deviation (3σ). (3σ). equal
2.3.2. Amperometric of Glucose Glucose 2.3.2. Amperometric i–t i–t Detection Detection of The lower lower quantity quantity of of glucose glucoseoxidation oxidationcan canbe beachieved achievedusing usingi–ti–tmethod, method, which potential The inin which potential at at 0.52 V was selected. Figure 7a,b show the amperometric sensing of glucose by successive addition 0.52 V was selected. Figure 7a,b show the amperometric sensing of glucose by successive addition of a of a range low range of glucose concentration of 10 0.2µM to in 10 aµM in a continuously-stirred 0.05 Msolution. NaOH low of glucose concentration of 0.2 to continuously-stirred 0.05 M NaOH solution. Figure 7c shows its two different calibration plot. Moreover, Figure 8a showed the current Figure 7c shows its two different calibration plot. Moreover, Figure 8a showed the current response response forconcentration a higher concentration range ofµM 0.5 glucose, to 500 µM glucose, which increment the currentwas increment for a higher range of 0.5 to 500 in which theincurrent limited wastolimited to current 250 µM.response The current response decreased after 250 µM concentration, up 250 µM.upThe decreased gradually aftergradually 250 µM concentration, which may be which may be due to the diffusion dominance and adsorption difficulties of glucose ions onto the due to the diffusion dominance and adsorption difficulties of glucose ions onto the small volume small volume of the active sites when compared to the high glucose concentration. Figure 8a’ is the of the active sites when compared to the high glucose concentration. Figure 8a’ is the linearity plot linearity plot of 0.5 to 250 µM. The fast steady-state current achieved (95% of all within 3 s) of 0.5 to 250 µM. The fast steady-state current achieved (95% of all within 3 s) and stable response and stable response upon the successive additions of 10 µM glucose with the reliable RSD value upon the successive additions of 10 µM glucose with the reliable RSD value (1.14% ˘ 4.32%) for (1.14% ± 4.32%) for the 13 additions is shown in Figure 8a”. The limit of detection (LOD) was 0.9 µM the 13 additions is shown in Figure 8a”. The limit of detection (LOD) was 0.9 µM measured by the measured by the standard deviation of the blank run in 0.05 M NaOH by the i–t technique (n = 10) standard deviation of the blank run in 0.05 M NaOH by the i–t technique (n = 10) and its signal was and its signal was also observed by this method. The HCNiO/GC sensor exhibits much higher also observed by this method. The HCNiO/GC sensor exhibits much higher sensitivities of 3978.9 and sensitivities of 3978.9 and 1232.4 µA mM−1 cm−2 for the linear ranges 0.2 to 3.5 µM and 0.5 to 250 µM, 1232.4 µA mM´1 cm´2 for the linear ranges 0.2 to 3.5 µM and 0.5 to 250 µM, respectively, compared to respectively, compared to other nickel-based GCEs reported in the literature [23]. The analytical other nickel-based GCEs reported in the literature [23]. The analytical parameters are listed in Table 1 parameters are listed in Table 1 for a comparison study. The stability and reproducibility of the for a comparison study. The stability and reproducibility of the sensor checked by tests every week, sensor checked by tests every week, and a number of experiments on the same day, indicated that and a number of experiments on the same day, indicated that there was almost no change in current there was almost no change in current density for more than two weeks’ time and up to 25 tests on density for more than two weeks’ time and up to 25 tests on the same day. the same day.
Int. J. Mol. Sci. 2016, 17, 1104
10 of 16
Int. J. Mol. Sci. 2016, 17, 1104 Int. J. Mol. Sci. 2016, 17, 1104
10 of 16 10 of 16 1.2
1.2 1.0 1.0
3.0 μΜ 3.0 μΜ
(a) i-t Plot (a) i-t Plot (0.2 μM - 3.0 μM) (0.2 μM - 3.0 μM)
I /IµA / µA
0.2 μΜ 0.2 μΜ
0.6
0.6
10 μΜ
2.5 μΜ 2.5 μΜ
9.5 μΜ 9.09.5μΜμΜ 9.0μμΜΜ 8.5 8.5μΜμΜ 8.0 1.5 μΜ 7.58.0 μΜμΜ 1.0 μΜ 0.5 μΜ 7.0 7.5μΜ μΜ 1.0 μΜ 0.5 μΜ 6.5 7.0μΜ μΜ 300 400 500 600 6.0 6.5μΜ μΜ 300 (s) 400 500 600 Time 3.0 μΜ 5.5 μΜ 6.0 μΜ Time (s) 5.5μΜ μΜ 2.0 μ3.0 Μ μΜ 5.0 1.0 μ2.0 Μ 4.5 μΜ μΜ 5.0 μΜ 4.04.5 μΜ 0.2 μΜ 1.0 μΜ μΜ 3.5 4.0μΜ μΜ 0.2 μΜ 2.5 μ3.5 Μ μΜ (b) i-t Plot (0.2 μM - 10 μM) 1.5 μ2.5 Μ μΜ (b) i-t Plot (0.2 μM - 10 μM) 1.5 μΜ
0.4
0.4 μΜ 0.4 μΜ
2.0 μΜ μΜ 1.5 μ2.0 Μ
I /IµA / µA
0.4 0.2 0.2
6 6
10 μΜ
0.8
0.8
200 200
205 205
405 405
605 805 605Time 805 (s)
1005 1005
1205 1205
5 5 4 4 3 3 2 2 1 1
0 1405 0 1405
Time (s)
6.0
(c) Linear Plot (0.2 μM - 10 μM) (c) Linear Plot (0.2 μM - 10 μM)
6.0 5.0
I = 0.7320 C - 1.3859 I = 0.7320 C - 1.3859
5.0
I / IμΑ / μΑ
4.0
2
4.0
R2 = 0.9982 R = 0.9982
3.0
3.0 2.0 2.0
2
R2 = 0.9701 R = 0.9701 I = 0.2825 C + 0.3236 I = 0.2825 C + 0.3236
1.0 1.0 0.0
0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.510.0
Conc. ( μM ) Conc. ( μM )
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.510.0
Figure 7. Amperometry i–t curve of a HCNiO/GC electrode in different concentrations of glucose in
Figure 7. Amperometry i–ti–t curve ofofaaHCNiO/GC electrodeinindifferent different concentrations of glucose Figure Amperometry curve HCNiO/GC concentrations glucose in in 0.05 M7.NaOH at E = 0.52 V; (a) i–t plot of 0.2 to 3electrode µM glucose; (b) i–t plot of 0.2 to 10of µM glucose; 0.050.05 M NaOH at Eat=E0.52 V; (a) i–t i–t plot of of 0.20.2 to to 3 µM glucose; (b) µM glucose; and = 0.52 V; µM (a) 3 µM glucose; (b)i–t i–tplot plotofof0.2 0.2=toto3)10 10 and M (c)NaOH lnearity plot of 0.2 to plot 10 µM glucose. The mean peak current (n at µM the glucose; relevant (c) lnearity plot of 0.2 µMofto0.2 10µM µM to glucose. The meanThe peak current (ncurrent = 3) at the relevant concentration and (c) lnearity plot 10 µM glucose. mean peak (n = 3) at the relevant concentration is shown with error bars equal to three standard deviation (3σ). is shown with error bars equal to three deviation (3σ). concentration is shown with error barsstandard equal to three standard deviation (3σ).
80 80
20
(a) i-t Plot (a)μM i-t Plot (0.5 - 500 μM) (0.5 μM - 500 μM)
2018 1816 1614 1412 1210
(a'') i-t Plot - 10 μM (a'') i-t Plot= -1.14 10 μM RSD + 4.32% RSD = 1.14 + 4.32% I / μA I / μA
100 100
40 40
800
600
Time /1000 s
800
1000
1200 1200
(a') Linearity Plot (a') Linearity Plot (0.5 μM - 250 μM) (0.5 μM - 250 μM)
20.0 20.0 15.0 15.0 10.0 10.0
250 μM 250 μM
I = 0.0875 C + 0.5404 2 I = 0.0875 C + 0.5404 R = 0.9947 2 R = 0.9947
5.0
20 20
600
8
I / μA I / μA
I /IμA / μA
60 60
500 μM 500 μM 350 μM 350 μM 300 μM 300 μM
Time / s
10 8
5.0
Conc. ( μM )
0.0 0
0.0 0
25
50
25 50 0.5 μM 0.5 μM
200 200
75 75
400 400
Conc. ( μM 100 125 150) 100
125
150
600 600
175
200
225
250
200 μM 225 250 6.25 6.25 μM
175
800 800
100 μM 100 μM 1000 1000
Time / s Time / s
1200 1200
1400 1400
1600 1600
Figure 8. Amperometric i–t curve of a HCNiO/GC electrode in different concentrations of glucose in
Figure 8. Amperometric curve HCNiO/GC in different of glucose in 0.058.MAmperometric NaOH at E = 0.52 V; (a) i–t plot of 0.5 µM toelectrode 500 µM glucose; insetconcentrations (a’) linearity plot µM Figure i–ti–t curve ofof aaHCNiO/GC electrode in different concentrations of 0.5 glucose in 0.05 M NaOH at E = 0.52 V; (a) i–t plot of 0.5 µM to 500 µM glucose; inset (a’) linearity plot of 0.5 µM µM glucose; andV;inset (a”)plot i–t plot 10 µM glucose for Relative standard deviation 0.05 to M 250 NaOH at E = 0.52 (a) i–t of 0.5ofµM to 500 µM glucose; inset (a’) linearity plot(RSD). of 0.5 µM to to 250 µM glucose; and inset (a”) i–t plot of 10 µM glucose for Relative standard deviation (RSD). 250 µM glucose; and inset (a”) i–t plot of 10 µM glucose for Relative standard deviation (RSD).
Int. J. Mol. Sci. 2016, 17, 1104
11 of 16
Table 1. Comparison of non-enzymatic glucose sensors’ analytical parameters for different 11 of 16 nickel-based glassy carbon electrodes (GCEs).
Int. J. Mol. Sci. 2016, 17, 1104
Serial Modified GC Linear Range LOD Sensitivity Year Reference Table 1. Comparison of non-enzymatic (µM) glucose sensors’ analytical parameters for different nickel-based Number Electrodes (µM) glassy carbon electrodes (GCEs). 0.2–3.5 3978.9 µA·mM−1·cm−2 1 HCNiO/GC 0.9 2016 This work 1232.4 µA·mM−1·cm−2 0.5–250 Linear Range Modified GC Sensitivity Year Serial 2 Number Ni-rGO/GC 1.0–10 937 µA·mM−1·cm−2 LOD (µM) 2012 Reference [23] (µM) Electrodes ´1´2 3 NiO/MWCNT/GC 200–12,000 160 2010 [55] 3978.9 µA¨ mM ¨ cm 0.2–3.5 1 0.9 2016 HCNiO/GC This work ´1 0.5–250 −5¨ µA·M cm´2 −1 190 2014 [53] 4 NiOOH/MWCNT/GC 250–5600 1232.4 µA¨ 1.5 mM × 10 ´1 ´2 2 1.0–10 2012 Ni-rGO/GC [23] 937 µA¨ mM ¨ cm −1 5 3 GNS/NiO/DNA-GC 1–200 14.3 µA·mM ·cm−2 160 2.5 2010 2012 [56] 200–12,000 NiO/MWCNT/GC [55] 4
NiOOH/MWCNT/GC
´5
250–5600
´1
190
2014
[53]
1.5 ˆ 10 µA¨ M GC:5 glassy carbon; rGO: reduced graphene oxide; MWCNT: multi-walled2.5carbon 2012 nanotube; GNS: 1–200 GNS/NiO/DNA-GC [56] 14.3 µA¨ mM´1 ¨ cm´2 graphene nanosheet; DNA: deoxyribonucleic LOD:multi-walled limit of detection. GC: glassy carbon; rGO: reduced graphene oxide;acid; MWCNT: carbon nanotube; GNS: graphene
nanosheet; DNA: deoxyribonucleic acid; LOD: limit of detection.
The interference test was also done to check the selectivity. The main interferents and the same oxidation potential fortest glucose detection biological samples are dopamine (DA), The interference was also doneintoserum check or theother selectivity. The main interferents and the ascorbic acid (AA), and for uricglucose acid (UA). Figure 9a expressed selectivity by the of same oxidation potential detection in serum or otherthe biological samples arepresence dopamine interferences AA,(AA), UA, and anduric DAacid for glucose detection. This sensor shows a better to (DA), ascorbicofacid (UA). Figure 9a expressed the selectivity by the response presence of glucose than of other AA, DA, and UA, which demonstrated good selectivity. interferences AA, interferents UA, and DAincluding for glucose detection. This sensor shows a better response to glucose The good was obtained forAA, real DA, samples in 0.05 M NaOH, as shown in Figure 9b. This than otherresult interferents including and UA, which demonstrated good selectivity. Thesensor good could be used for the screening purposes without the invasion for the patients who suffer result was obtained for real samples in 0.05 M NaOH, as shown in Figure 9b. This sensor could be diabetes mellitus. used for the screening purposes without the invasion for the patients who suffer diabetes mellitus. 18.0
(a) i-t Plot (selectivity and sensitivity)
16.0 14.0
Glucose (Glu) 1 mΜ
Uric Acid (UA)
I / µA
12.0
Uric Acid (UA) 0.2 mΜ
0.1 mΜ
10.0 8.0
0.1 mΜ Ascorbic Acid (AA)
6.0
0.1 mΜ Dopamine (DA)
4.0
Time (s)
2.0 0.0 100
30.0
200
300
(b) i-t Plot (Glucose detected in Real Samples)
I / µA
Orange Juice 20.0
10.0
Human Urine
0.0 75
100
125
150
175
Time (s) Figure 9.9. Amperometric Amperometrici–t i–tcurve curveofof a HCNiO/GC electrode in 0.05 M NaOH at0.52 E =V0.52 V for Figure a HCNiO/GC electrode in 0.05 M NaOH at E = for (a) an (a) an interference test in 1 mM glucose, including interferents of 0.1 mM ascorbic acid (AA), 0.1 mM interference test in 1 mM glucose, including interferents of 0.1 mM ascorbic acid (AA), 0.1 mM uric acid uric acid (UA), 0.1 mM dopamine (DA), mM (b) real samples of human urinejuice. and (UA), 0.1 mM dopamine (DA), and 0.2 mMand UA0.2 and (b) UA real and samples of human urine and orange orange juice.
3. Materials and Methods 3. Materials and Methods 3.1. Reagents 3.1. Reagents NiCl2 ¨ 6H2 O, NaOH, urea, methanol, and ethanol were obtained from Choneye Pure Chemicals NiCl 2·6H2O, NaOH, urea, methanol, and ethanol were obtained from Choneye Pure Chemicals (Taipei, Taiwan), yeast from Becton Dickinson Biosciences (Taipei, Taiwan), ammonium sulfate, (Taipei, Taiwan), yeast from Becton Dickinson Biosciences (Taipei, Taiwan), ammonium sulfate, Tris–HCl were purchased from J.T. Baker (Chu-Bei, Taiwan), glucose from Sigma-Aldrich China ˝ Inc. (Shanghai, China), and Milli-Q (MQ-18.2 MΩ¨ cm at 25 C) water were used. All chemicals were
Int. J. Mol. Sci. 2016, 17, 1104
12 of 16
Tris–HCl were purchased from J.T. Baker (Chu-Bei, Taiwan), glucose from Sigma-Aldrich China Inc. (Shanghai, China), and Milli-Q (MQ-18.2 MΩ·cm at 25 °C) water were used. All chemicals were used Int. J. Mol. Sci. 2016, 17, 1104 12 of 16 without further purification, analytically pure, and all electrochemical experiments were carried out at ambient temperature unless otherwise stated anywhere in this paper. used without further purification, analytically pure, and all electrochemical experiments were carried 3.2.atElectrochemical Measurements out ambient temperature unless otherwise stated anywhere in this paper. Cyclic voltammetry studies were performed on a CHI627C Electrochemical Analyzer (CH 3.2. Electrochemical Measurements Instruments, Inc., Austin, TX, USA). The conventional three-electrode system was used throughout voltammetry studies consisted were performed onGCE a CHI627C Electrochemical (CH the Cyclic electrochemical experiments of a bare (geometric area 0.071 cm2Analyzer ) or a modified Instruments, Inc., Austin, TX, USA). The conventional three-electrode system was used throughout GCE as the working electrode, a platinum wire as the auxiliary electrode, and Ag/AgCl (3 M NaCl) the experiments a bare GCE (geometric 0.071 cm2 )For or asteady-state modified as electrochemical the reference electrode againstconsisted which allofpotentials were measuredarea in this paper. GCE as the working electrode, athe platinum wire as the auxiliary andthe Ag/AgCl M NaCl) amperometric measurements, working potential was set atelectrode, 0.52 V and solution(3was stirred asgently the reference electrode against which all pH potentials measured this paper. For steady-state with a magnetic stirrer. A digital meter were (SUNTEX TS-1,in Suntex Instruments Co., Ltd., amperometric measurements, the working and potential was setcomputer at 0.52 V and solution was stirred Xinbei, Taiwan) for pH measurements a personal weretheused for data storage gently with a magnetic stirrer. A digital pH meter (SUNTEX TS-1, Suntex Instruments Co., Ltd., Xinbei, and processing. Taiwan) for pH measurements and a personal computer were used for data storage and processing. 3.3. Preparation of Hollow Cylinder NiO Nanostructured Material 3.3. Preparation of Hollow Cylinder NiO Nanostructured Material The synthesis procedure followed the method developed by our group [57]. Briefly, a The synthesis procedure followed the byMQ ourwater, group1.0[57]. Briefly, a homogeneous mixture was prepared from 0.1method M NiCl2developed ·6H2O, 20 mL M urea solution, homogeneous mixturebroth was prepared from 0.1 MTeflon NiCl2 ¨tube. 6H2 O, 20 mL MQ water, M urea solution, and 40 mL bacterial in a screw-capped Bacterial culture of 1.0 Sporosarcina pasteurii and 40 mL bacterial broth in a screw-capped Teflon tube. Bacterial culture of Sporosarcina pasteurii was carried out using 20 g/L yeast extract, 10 g ammonium sulfate, and 20.48 g Tris–HCl (pH ofwas 8.5) carried using 20 g/L yeastThe extract, g ammonium sulfate, andin20.48 g Tris–HCl (pH of in 1The L in 1 L out sterilized MQ water. tube 10 was then kept for one day a mechanical shaker at 8.5) 35 °C. ˝ sterilized water. The tube was thenbykept for one day in mechanical at 35 C.the Theprecipitate obtained obtainedMQ precipitate was separated centrifugation at a3700 rpm forshaker 15 min. Then precipitate was separated by centrifugation at 3700 rpm for 15 min. Then the precipitate was was washed several times with water and, consecutively, with ethanol, dried in an air oven washed for 6 h at several with water and, consecutively, dried in an air oven forof6 bio-inorganic h at 50 ˝ C, followed 50 °C,times followed by calcination at 550 °Cwith forethanol, 6 h. The green precipitate nickel ˝ C for 6 h. The green precipitate of bio-inorganic nickel compound changed to by calcination at 550 compound changed to a black color. The hollow cylinder of microbacterial shape with nanocell awall-like black color. The hollow cylinder of microbacterial shape with nanocell wall-like structured NiO structured NiO (HCNiO) compound was confirmed with the help of transmission electron (HCNiO) compound wasscanning confirmed with the help of transmission microscopy (TEM) andof microscopy (TEM) and electron microscope (SEM) (seeelectron Figure 10 for TEM and SEM scanning electron microscope (SEM) (see Figure 10 for TEM and SEM of bacterial shaped HCNiO). bacterial shaped HCNiO).
(a) Figure10. 10.Cont. Cont. Figure
Int. J. Mol. Sci. 2016, 17, 1104
13 of 16
Int. J. Mol. Sci. 2016, 17, 1104
13 of 16
(b) Figure10. 10. (a) electron microscopy (TEM) of bacterial cell wall-like HCNiO; and (b) Figure (a)Transmission Transmission electron microscopy (TEM) of bacterial cell wall-like HCNiO; Scanning electron microscope (SEM)(SEM) of bacteria-templated HCNiO. and (b) Scanning electron microscope of bacteria-templated HCNiO.
3.4. HCNiO/GC Electrode Preparation and Its Activation by CV Cycle 3.4. HCNiO/GC Electrode Preparation and Its Activation by CV Cycle Prior to each experiment, the GCE was first polished with gamma alumina in water slurry using Prior to each experiment, the GCE was first polished with gamma alumina in water slurry using a polishing cloth and rinsed thoroughly with MQ water and ethanol. Then the required amount a polishing cloth and rinsed thoroughly with MQ water and ethanol. Then the required amount of of HCNiO material was ultrasonically dispersed in methanol:water (20:1) solution to achieve HCNiO material was ultrasonically dispersed in methanol:water (20:1) solution to achieve a 10 mg/mL a 10 mg/mL uniform ink. Finally, 2 µL of the ink was drop-casted onto the GCE and dried before uniform ink. Finally, 2 µL of the ink was drop-casted onto the GCE and dried before the electrochemical the electrochemical experiments to study the properties of HCNiO/GCE. Then the electrode experiments to study the properties of HCNiO/GCE. Then the electrode (HCNiO/GC) was conditioned (HCNiO/GC) was conditioned between +0.2 to +0.7 V in 0.05 M NaOH, to attain the stable, between +0.2 to +0.7 V in 0.05 M NaOH, to attain the stable, well-defined peaks of Ni(OH)2 /NiOOH well-defined peaks of Ni(OH)2/NiOOH film on the modified GCE by cyclic voltammetry, and the film on the modified GCE by cyclic voltammetry, and the optimum 54 cycles developed as in Figure 1; optimum 54 cycles developed as in Figure 1; its characteristic peak potentials were identified with its characteristic peak potentials were identified with the reported literature [10,55]. the reported literature [10,55]. 4. Conclusions 4. Conclusions A modified GCE with bacteria-template HCNiO was successfully employed for the enzymeless A modified GCE with bacteria-template HCNiO was successfully employedwere for the enzymeless detection of glucose in basic solutions. Electrochemical characteristic parameters obtained for detection of glucose in basic solutions. Electrochemical characteristic parameters were obtained for this well-developed redox couple on the HCNiO/GC by CV method. The detection of glucose was this well-developed couple oni–t thetechniques HCNiO/GC byLOD CV method. Theasdetection glucose was performed by CV andredox amperometric and was found 0.9 µM. of The excellent performed by CV and amperometric i–t techniques and LOD was found as 0.9 µM. The excellent electrocatalytic activity of HCNiO/GC sensor was stable, reproducible, and sensitive towards the electrocatalytic activity HCNiO/GC was was stable, reproducible, and sensitive towards the detection of glucose. It isof noticed that thesensor electrode stable for the wide range of potential scan detection of glucose. It is noticed that the electrode was stable for the wide range of potential scan rates up to 5 V/s with the linearity curves. Limitation of second order rate constant for the higher rates up to 5 of V/s with the linearity Limitation second order rate constant for the higher concentration glucose solution wascurves. observed. The lowofcost of the preparation and high catalytic concentration of glucose solution was observed. The of the preparation and high catalytic ability of the oxyhydroxide (NiOOH) were achieved forlow the cost electro-oxidation of glucose. ability of the oxyhydroxide (NiOOH) were achieved for the electro-oxidation of glucose. Acknowledgments: The authors are very grateful to the MOST (Ministry of Science and Technology) in Taiwan for funding this research Acknowledgments: Theproject. authors are very grateful to the MOST (Ministry of Science and Technology) in Taiwan for funding this research project. Author Contributions: Settu Vaidyanathan and Chien-Yen Chen conceived designed and performed the experiments; Settu Vaidyanathan and Jong-Yuh Cherng analyzed the data; An-Cheng Sun contributed Author Contributions: Settu Vaidyanathan and Chien-Yen Chen Chen conceived reagents/materials/analysis tools; Settu Vaidyanathan and Chien-Yen wrote designed the paper. and performed the experiments; Settu Vaidyanathan and Jong-Yuh Cherng analyzed the data; An-Cheng Sun contributed Conflicts of Interest: The authors no conflict of interest. reagents/materials/analysis tools;declare Settu Vaidyanathan and Chien-Yen Chen wrote the paper.
Conflicts of Interest: The authors declare no conflict of interest. References 1.References Wild, S.; Roglic, G.; Green, A.; Sicree, R.; King, H. Global prevalence of diabetes: estimates for the year 2000 and projections for 2030. Diabetes Care 2004, 27, 1047–1053. [CrossRef] [PubMed] Wild,J.S.; Roglic, G.; Green, A.; biosensors. Sicree, R.; King, Global of diabetes: for the year 2.1. Wang, Electrochemical glucose Chem.H. Rev. 2008,prevalence 108, 814–825. [CrossRef]estimates [PubMed] 2000 and projections for 2030. Diabetes Care 2004, 27,1047–1053. 3. Narayanan, K.B.; Sakthivel, N. Biological synthesis of metal nanoparticles by microbes. Adv. Colloid Interface 2. Sci. Wang, Electrochemical glucose biosensors. Chem. Rev. 2008, 108, 814–825. 2010,J.156, 1–12. [CrossRef] [PubMed] 3. Narayanan, K.B.; Sakthivel, N. Biological synthesis of metal nanoparticles microbes. Adv. Colloid 4. Iravani, S. Green synthesis of metal nanoparticles using plants. Green Chem. 2011, by 13, 2638–2650. [CrossRef] Interface Sci. 2010, 156, 1–12. 4. Iravani, S. Green synthesis of metal nanoparticles using plants. Green Chem. 2011, 13, 2638–2650.
Int. J. Mol. Sci. 2016, 17, 1104
5. 6. 7. 8.
9. 10.
11. 12. 13.
14.
15. 16. 17.
18. 19.
20. 21.
22. 23.
24. 25.
26.
14 of 16
Deplanche, K.; Macaskie, L.E. Biorecovery of gold by Escherichia coli and Desulfovibrio desulfuricans. Biotechnol. Bioeng. 2008, 99, 1055–1064. [CrossRef] [PubMed] Nair, B.; Pradeep, T. Coalescence of Nanoclusters and Formation of Submicron Crystallites Assisted by Lactobacillus Strains. Cryst. Growth Des. 2002, 2, 293–298. [CrossRef] Haefeli, C.; Franklin, C.; Hardy, K. Plasmid-determined silver resistance in Pseudomonas stutzeri isolated from a silver mine. J. Bacteriol. 1984, 158, 389–392. [PubMed] Holmes, J.D.; Smith, P.R.; Gowing, R.E.; Richardson, D.J.; Russell, D.A.; Sodeau, J.R. Energy-dispersive X-ray analysis of the extracellular cadmium sulfide crystallites of Klebsiella aerogenes. Arch. Microbiol. 1995, 163, 143–147. [CrossRef] [PubMed] Philipse, A.P.; Maas, D. Magnetic colloids from magnetotactic bacteria: chain formation and colloidal stability. Langmuir 2002, 18, 9977–9984. [CrossRef] Casella, I.G.; Cataldi, T.R.I.; Salvi, A.M.; Desimoni, E. Electrocatalytic oxidation and liquid chromatographic detection of aliphatic alcohols at a nickel-based glassy carbon modified electrode. Anal. Chem. 1993, 65, 3143–3150. [CrossRef] Heller, A.; Feldman, B. Electrochemical glucose sensors and their applications in diabetes management. Chem. Rev. 2008, 108, 2482–2505. [CrossRef] [PubMed] Fang, L.; He, J. Nonenzymatic Glucose Sensors. Prog. Chem. 2015, 27, 585–593. Ahmad, R.; Vaseem, M.; Tripathy, N.; Hahn, Y.B. Wide linear-range detecting nonenzymatic glucose biosensor based on CuO nanoparticles inkjet-printed on electrodes. Anal. Chem. 2013, 85, 10448–10454. [CrossRef] [PubMed] Pandya, A.; Sutariya, P.G.; Menon, S.K. A non enzymatic glucose biosensor based on an ultrasensitive calix[4]arene functionalized boronic acid gold nanoprobe for sensing in human blood serum. Analyst 2013, 138, 2483–2490. [CrossRef] [PubMed] Pang, H.; Lu, Q.; Wang, J.; Li, Y.; Gao, F. Glucose-assisted synthesis of copper micropuzzles and their application as nonenzymatic glucose sensors. Chem. Commun. 2010, 46, 2010–2012. [CrossRef] [PubMed] Ibupoto, Z.H.; Khun, K.; Beni, V.; Willander, M. Non-Enzymatic Glucose Sensor Based on the Novel Flower Like Morphology of Nickel Oxide. Soft Nanosci. Lett. 2013, 3, 46–50. [CrossRef] Fang, B.; Gu, A.; Wang, G.; Wang, W.; Feng, Y.; Zhang, C.; Zhang, X. Silver Oxide Nanowalls Grown on Cu Substrate as an Enzymeless Glucose Sensor. ACS Appl. Mater. Interfaces 2009, 1, 2829–2834. [CrossRef] [PubMed] Wang, J.; Thomas, D.F.; Chen, A. Nonenzymatic Electrochemical Glucose Sensor Based on Nanoporous PtPb Networks. Anal. Chem. 2008, 80, 997–1004. [CrossRef] [PubMed] Jia-Hong, H.; Qiang, X.; Zhong-Rong, S.; Hai-Yan, K. Study on non-enzymatic glucose sensor based on a Ag2 O nanoparticles self-assembled Ag electrode. In Proceedings of the 2010 International Conference on Electrical and Control Engineering, Wuhan, China, 25–27 June 2010; pp. 2109–2111. Lei, J.; Liu, Y.; Wang, X.; Hua, P.; Peng, X. Au/CuO nanosheets composite for glucose sensor and CO oxidation. RSC Adv. 2015, 5, 9130–9137. [CrossRef] Thiagarajan, S.; Chen, S.M. Preparation and characterization of PtAu hybrid film modified electrodes and their use in simultaneous determination of dopamine, ascorbic acid and uric acid. Talanta 2007, 74, 212–222. [CrossRef] [PubMed] Feng, D.; Wang, F.; Chen, Z. Electrochemical glucose sensor based on one-step construction of gold nanoparticle–chitosan composite film. Sens. Actuators B 2009, 138, 539–544. [CrossRef] Wang, Z.; Hu, Y.; Yang, W.; Zhou, M.; Hu, X. Facile One-Step Microwave-Assisted Route towards Ni Nanospheres/Reduced Graphene Oxide Hybrids for Non-Enzymatic Glucose Sensing. Sensors 2012, 12, 4860–4869. [CrossRef] [PubMed] Liu, S.; Yu, B.; Zhang, T. A novel non-enzymatic glucose sensor based on NiO hollow spheres. Electrochim. Acta 2013, 102, 104–107. [CrossRef] Kumar, D.R.; Manoj, D.; Santhanalakshmi, J. Au–ZnO bullet-like heterodimer nanoparticles: synthesis and use for enhanced nonenzymatic electrochemical determination of glucose. RSC Adv. 2014, 4, 8943–8952. [CrossRef] Park, B.; Cairns, E.J. Electrochemical performance of TiO2 and NiO as fuel cell electrode additives. Electrochem. Commun. 2011, 13, 75–77. [CrossRef]
Int. J. Mol. Sci. 2016, 17, 1104
27. 28. 29. 30.
31. 32.
33. 34. 35. 36. 37. 38.
39. 40. 41.
42. 43. 44. 45.
46. 47. 48.
49.
15 of 16
Needham, S.A.; Wang, G.X.; Liu, H.K. Synthesis of NiO nanotubes for use as negative electrodes in lithium ion batteries. J. Power Sources 2006, 159, 254–257. [CrossRef] Pang, H.; Lu, Q.; Zhang, Y.; Li, Y.; Gao, F. Selective synthesis of nickel oxide nanowires and length effect on their electrochemical properties. Nanoscale 2010, 2, 920–922. [CrossRef] [PubMed] Ichiyanagi, Y.; Wakabayashi, N.; Yamazaki, J.; Yamada, S.; Kimishima, Y.; Komatsu, E.; Tajima, H. Magnetic properties of NiO nanoparticles. Phys. B 2003, 329, 862–863. [CrossRef] Ren, S.; Yang, C.; Sun, C.; Hui, Y.; Dong, Z.; Wang, J.; Su, X. Novel NiO nanodisks and hollow nanodisks derived from Ni(OH)2 nanostructures and their catalytic performance in epoxidation of styrene. Mater. Lett. 2012, 80, 23–25. [CrossRef] Fernando, L.M.; Merca, F.E.; Paterno, E.S. Biogenic synthesis of gold nanoparticles by plant-growth-promoting bacteria isolated from philippine soils. Philipp. Agric. Sci. 2013, 96, 129–136. Millo, C.; Ader, M.; Dupraz, S.; Guyot, F.; Thaler, C.; Foy, E.; Ménez, B. Carbon isotope fractionation during calcium carbonate precipitation induced by ureolytic bacteria. Geochim. Cosmochim. Acta 2012, 98, 107–124. [CrossRef] Chahal, N.; Rajor, A.; Siddique, R. Calcium carbonate precipitation by different bacterial strains. Afr. J. Biotechnol. 2011, 10, 8359–8372. Xing, W.; Li, F.; Yan, Z.F.; Lu, G.Q. Synthesis and electrochemical properties of mesoporous nickel oxide. J. Power Sources 2004, 134, 324–330. [CrossRef] Lyons, M.; Brandon, M. The Oxygen Evolution Reaction on Passive Oxide Covered Transition Metal Electrodes in Aqueous Alkaline Solution. Part 1-Nickel. Int. J. Electrochem. Sci. 2008, 3, 1386–1424. Kuroda, Y.; Hamano, H.; Mori, T.; Yoshikawa, Y.; Nagao, M. Specific Adsorption Behavior of Water on a Y2 O3 Surface. Langmuir 2000, 16, 6937–6947. [CrossRef] Kumary, V.A.; Nancy, T.E.M.; Divya, J.; Sreevalsan, K. Nonenzymatic Glucose Sensor: Glassy Carbon Electrode Modified with Graphene-Nickel/Nickel Oxide Composite. Int. J. Electrochem. Sci. 2013, 8, 2220–2228. Mu, Y.; Jia, D.; He, Y.; Miao, Y.; Wu, H.L. Nano nickel oxide modified non- enzymatic glucose sensors with enhanced sensitivity through an electrochemical process strategy at high potential. Biosens. Bioelectron. 2011, 26, 2948–2952. [CrossRef] [PubMed] Wu, M.S.; Yang, C.H.; Wan, M.J. Morphological and structural studies of nanoporous nickel oxide films fabricated by anodic electrochemical deposition Techniques. Electrochim. Acta 2008, 54, 155–161. [CrossRef] Wang, C.; Yin, L.; Zhang, L.; Gao, R. Ti/TiO2 Nanotube Array/Ni Composite Electrodes for Nonenzymatic Amperometric Glucose Sensing. J. Phys. Chem. C 2010, 114, 4408–4413. [CrossRef] Salimi, A.; Abdi, K.; Khayatiyan, R. Preparation and electrocatalytic oxidation properties of a nickel pentacyanonitrosylferrate modified carbon composite electrode by two-step sol–gel technique: improvement of the catalytic activity. Electrochim. Acta 2004, 49, 413–422. [CrossRef] Hamdan, M.S.; Nordin, N.; Amir, S.F.M.; Riyanto; Othman, M.R. Electrochemical Behaviour of Ni and Ni-PVC Electrodes for the Electroxidation of Ethanol. Sains Malays. 2011, 40, 1421–1427. Kibria, A.K.M.F.; Tarafdar, S.A. Electrochemical studies of a nickel–copper electrode for the oxygen evolution reaction (OER). Int. J. Hydrog. Energy 2002, 27, 879–884. [CrossRef] Ender, B.; Pakize, C. Electrochemical behaviuor of the antibiotic drug Novobiocin sodium on a mercury electrode. Croat. Chem. Acta 2009, 82, 573–582. Danaee, I.; Jafarian, M.; Forouzandeh, F.; Gobal, F.; Mahjani, M.G. Impedance spectroscopy analysis of glucose electro-oxidation on Ni-modified glassy carbon electrode. Electrochim. Acta 2008, 53, 6602–6609. [CrossRef] Zhao, C.; Shao, C.; Li, M.; Jiao, K. Flow-injection analysis of glucose without enzyme based on electrocatalytic oxidation of glucose at a nickel electrode. Talanta 2007, 71, 1769–1773. [CrossRef] [PubMed] Ojani, R.; Raoof, J.B.; Afagh, P.S. Electrocatalytic oxidation of some carbohydrates by poly(1-naphthylamine)/nickel modified carbon paste electrode. J. Electroanal. Chem. 2004, 571, 1–8. [CrossRef] Jafarian, M.; Mahjani, M.G.; Heli, H.; Gobal, F.; Heydarpoor, M. Electrocatalytic oxidation of methane at nickel hydroxide modified nickel electrode in alkaline solution. Electrochem. Commun. 2003, 5, 184–188. [CrossRef] Elahi, M.Y.; Heli, H.; Bathaie, S.Z.; Mousavi, M.F. Electrocatalytic oxidation of glucose at a Ni-curcumin modified glassy carbon electrode. J. Solid State Electrochem. 2007, 11, 273–282. [CrossRef]
Int. J. Mol. Sci. 2016, 17, 1104
50. 51. 52. 53. 54. 55.
56. 57.
16 of 16
Muthuraman, G.; Pillai, K.C. Electrocatalysis in micellar media: Indirect reduction of allylchloride in cationic surfactant cetrimide containing aqueous solution. Bull. Electrochem. 1999, 15, 448–451. Bard, A.J.; Faulkner, L.R. Electrochemical methods, Fundamentals and Applications, 2nd ed.; John Wiley: New York, NY, USA, 2001; pp. 96–108. Golabi, S.M.; Zare, H.R. Electrocatalytic oxidation of hydrazine at a chlorogenic acid (CGA) modified glassy carbon electrode. J. Electroanal. Chem. 1999, 465, 168–176. [CrossRef] Acelino, C.S.; Leonardo, L.P.; Nelson, R.S. Sugars Electrooxidation at Glassy Carbon Electrode Decorate with Multi-Walled Carbon Nanotubes with Nickel OxyHydroxide. Int. J. Electrochem. Sci. 2014, 9, 7746–7762. Noel, M.; Vasu, K.I. Cyclic Voltammetry and the Frontiers of Electrochemistry; Oxford and IBH publishing Co. Pvt. Ltd.: New Delhi, India, 1990; pp. 272–304. Shamsipur, M.; Najafi, M.; Hosseini, M.R.M. Highly improved electrooxidation of glucose at a nickel(II) oxide/multi-walled carbon nanotube modified glassy carbon electrode. Bioelectrochemistry 2010, 77, 120–124. [CrossRef] [PubMed] Wei, L.; Feng, M.J.; Quangui, G.; Quan, H.Y.; Feiyu, K. DNA dispersed graphene/NiO hybrid materials for highly sensitive non-enzymatic glucose sensor. Electrochim. Acta 2012, 73, 129–135. Atla, S.B.; Chen, C.Y.; Fu, C.W.; Chien, T.C.; Sun, A.C.; Huang, C.F.; Lo, C.J. Microbial induced synthesis of hollow cylinder and helical NiO micro/nanostructure. MRS Commun. 2014, 4, 121–127. [CrossRef] © 2016 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC-BY) license (http://creativecommons.org/licenses/by/4.0/).
