A novel Lu3+ fluorescent nano-chemosensor using new functionalized mesoporous structures

Analytica Chimica Acta 771 (2013) 95–101

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A novel Lu3+ fluorescent nano-chemosensor using new functionalized mesoporous structures Morteza Hosseini a,∗ , Mohammad Reza Ganjali b , Zahra Rafiei-Sarmazdeh b , Farnoush Faridbod b , Hassan Goldooz c , Alireza Badiei c , Parviz Nourozi b , Ghodsi Mohammadi Ziarani d a

Department of Life Science Engineering, Faculty of New Sciences & Technologies, University of Tehran, Tehran, Iran Center of Excellence in Electrochemistry, Faculty of Chemistry, University of Tehran, Tehran, Iran c School of Chemistry, University College of Science, University of Tehran, Tehran, Iran d Department of Chemistry, Faculty of Science, Alzahra University, Tehran, Iran b

h i g h l i g h t s

g r a p h i c a l

 8-Hydroxyquinoline functionalized mesoporous silica is introduced as a selective fluorescent probe for lutetium ions.  Fluorescent intensity of the chemical probe enhances upon binding to lutetium ions.  Fluorescence measurements were done in a suspension of mesoporous silica in aqueous solution.

A novel Lu3+ sensitive fluorescent chemosensor is constructed through the preparation of 8hydroxyquinoline functionalized mesoporous silica with ordered hexagonal array structure (LUS-SPS-Q). Fluorescence measurements revealed that the emission intensity of the Lu3+ -bound mesoporous material increases significantly upon addition of various concentrations of Lu3+ , while the mono-, di-, trivalent cations result in either unchanged or weakened intensities.

a r t i c l e

a b s t r a c t

i n f o

Article history: Received 3 September 2012 Received in revised form 27 January 2013 Accepted 30 January 2013 Available online 11 February 2013 Keywords: Lutetium Fluorescent Mesoporous Enhancing Nano-chemosensor

a b s t r a c t

A new Lu3+ sensitive fluorescent chemosensor is designed using 8-hydroxyquinoline functionalized mesoporous silica with highly ordered structure (LUS-SPS-Q). The characterization of LUS-SPS-Q showed that the organized structure has been preserved after the post grafting procedure. The synthesized material showed a selective interaction with Lu3+ ion, most probably due to the presence of the fluorophore moiety at its surface. The emission intensity of the Lu3+ -bound mesoporous material increases with an increase in concentrations of Lu3+ ion. Addition of other mono-, di-, trivalent ions resulted in insignificant change in the fluorescent intensity. The enhancement of fluorescence is attributed to the strong covalent binding of Lu3+ ion. The linear response range of Lu3+ chemo-sensor was from 1.6 × 10−7 to 1.0 × 10−5 mol L−1 . The Limit of detection obtained was 8.2 × 10−8 mol L−1 and the pH range which the proposed chemo-sensor can be applied was 3.3–8.3. © 2013 Elsevier B.V. All rights reserved.

1. Introduction

∗ Corresponding author. Tel.: +98 21 61112788; fax: +98 21 66495291. E-mail address: [email protected] (M. Hosseini). 0003-2670/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.aca.2013.01.064

Mesoporous silicas, which exhibit ordered pore systems and uniform pore diameters, have shown great potential for sensing applications in recent years. Morphological control grants them versatility in the method of deployment whether as bulk powders,

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monoliths, thin films, or embedded in coatings. High surface areas and pore sizes greater than 2 nm make them as an effective adsorbent for humidity sensors [1]. The pore networks also provide the potential for immobilization of enzymes within the materials. Functionalization of mesoporous materials by silane grafting or through co-condensation of silicate precursors can be used to provide fluorescent mesoporous probes. Also surface properties aid in selective detection of specific analytes [1]. Versatile silylation reagents can be used to enhance the rigidity of the silicon wall through the linkage with oxygen of the hydroxyl groups. Reactive sites such as amino group or halogens are grafted to the silicon walls in order to link some chromophore or fluorescent functional molecules and make fluorescent mesoporous sensing materials. The rigidity of siliceous wall and the spatial restriction of the mesopore also strictly affect the photics property of the encapsulated molecules. Moreover, using siliceous hosts as solid binding units has some advantages including favorable biocompatibility, optical transparency in the visible region and especially its satisfactory anti-swelling property in the solution, which enables the resulting materials to be promising sensor substrates [2–4]. Since the early part of the twentieth century, because of finding the similarity of the lanthanide ions to calcium, the biological properties of lanthanide ions, as well as lutetium have been the bases form any clinical researches. Lanthanide ions have similar ionic radii to calcium, but they have a higher charge density. Hence, they have a high affinity for Ca2+ sites on biological molecules, and a stronger binding to water molecules [5–7]. Lutetium can be found in houses and equipments such as color televisions, fluorescent lamps energy-saving lamps and glasses and resulting from its growing use and it is being increasingly dumped in the environment mainly from petrol-producing industries or when household appliances are improperly disposed. Lutetium may accumulate gradually in soil and then water, or maybe leading to increased concentrations in human and animal bodies. This can specially be a threat to the liver when it accumulates in the human body and as far as water animals are concerned, in which case lutetium causes cell membrane damage, creating several negative effects on the reproduction and on the nervous system functions [8]. The conventional methods for the determination of lutetium ions are neutron activation analyses [9], spectrophotometric determination [10], X-ray crystal structure determination [11] and inductively coupled plasma optical emission spectrometry [12]. Furthermore, a number of potentiometric ion-selective electrodes for Lu3+ ion have been recently reported [13,14]. However, most of them present high limit of detection, narrow working concentration range, and serious interferences from various cations. Meanwhile, the development of a chemo-sensor for the determination of metal ions has become a rapidly expanding area of analytical chemistry in the past decade, most probably because they offer certain advantages like simple preparation, reasonable selectivity, improved sensitivity and no need for separate reference devices [15–17]. As continuing of our previous experiences in the development of a number of chemosensors and optical sensors for ions such as Zn2+ [18], Hg2+ [19], P2 O7 4− [20], Tb3+ [21–23], Er3+ [24] and regarding the effective coordinating ability of 8-hydroxyquinoline with specific cations [25–27] and the excellent structure properties of mesoporous silica (LUS-1), the fluorescent functionalized mesoporous material was used as a new sensing material. 8Hydroxyquinoline has been grafted covalently to the surface of LUS-1 via formation of a sulfonamide bond between sulfonyl chloride derivative of 8-hydroxyquinoline and amine functionalized LUS-1 (designated as LUS-SPS-Q). Preliminary experiments revealed that LUS-SPS-Q can interact selectively and sensitively

with Lu3+ ion respect to the other tested cations. Thus, it may be used as a suitable sensing element in construction of nano-sensor. To the best of our knowledge, there is no report on the assembly of a Lu3+ selective chemosensor based on mesoporous material LUS-1 by using fluorescence spectroscopy. 2. Experimental 2.1. Materials and reagents Nitrate and chloride salts of the all used cations with the highest purity available were purchased from Merck Co. (Germany). They were used as received without any further purification except for vacuum drying over P2 O5 . Hexadecyltrimethylammonium ptoluenesulfonate (CTATos), 3-aminopropyltriethoxysilane (APTES), 8-hydroxyquinoline (8-HQ), 8-hydroxyquinoline-5-sulfonic acid (8-HQS) and chlorosulfonic acid were also purchased from Merck Co. (Germany). Ludox HS-40 (40% SiO2 ) was from Aldrich (China). All solvents were of analytical reagent grade from Merck (Germany) and used as received. Doubled deionized distilled water was used through the experiments. 2.2. Synthesis of mesoporous silica LUS-1 LUS-1 type mesoporous silica was prepared according to the literature [28]. 2.3. Aminopropyl functionalization of LUS-1 (LUS-NH2 ) The aminopropyl functionalization of LUS-1 was carried out by using APTES. A1.0-g amount of LUS-1 was added to 100 mL of dry toluene in a 250 mL flask and then 2 mmol APTES was added and refluxed for 4 h. The obtained solid was filtered, washed with toluene and ethanol, and dried in air. 2.4. Synthesis of LUS-SPS-Q The synthesis route of LUS-SPS-Q is depicted in Scheme 1. 8-Hydroxyquinoline was attached to the surface of aminopropyl functionalized LUS-1 via formation of a sulfonamide bond between 8-hydroxyquinoline-5-sulfonyl chloride and surface amine groups of functionalized LUS-1 [29]. In a typical synthesis, 1 g of LUS-NH2 was dispersed in 60 mL of dichloromethane, and then an excess amount of 8-HQ-SO2 Cl and triethylamine were added to the above dispersion. The reaction mixture was refluxed for 3 h. Then, it was filtered and washed with dichloromethane and ethanol several times. The final product was obtained as a light yellow powder and designated as LUS-SPS-Q. 2.5. Instruments and spectroscopic measurements Low-angle X-ray diffraction (XRD) patterns were recorded with a Philips X Pert MPD diffractometer (Netherlands) using Cu K␣ radiation (40 kV, 40 mA) at a step width of 0.02. N2 adsorption–desorption isotherms were measured using a BELSORP mini-II. FT-IR spectra were recorded within a 4000–400 cm−1 region on a Bruker Vector 22 infrared spectrophotometer (Germany). SEM analysis was performed on a Philips XL-30 fieldemission scanning electron microscope operated at 16 kV. Elemental analyses of the silicates containing organic material were carried out in a Rapid elemental analyzer (Germany). The emission spectra were obtained on a Perkin-Elmer LS50 luminescence spectrometer. Fluorescence measurements were done in a 1 cm quartz cuvette containing amagnetic-stirred suspension of grafted mesoporous silica (0.08 g L−1 ) in 3 mL of aqueous solution.

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Fig. 1. XRD patterns for (a) LUS-1; (b) LUS-NH2 ; (c) LUS-SPS-Q [29,31].

materials. However, in the case of functionalized LUS-1 materials the peaks intensity decreases after immobilizations due to the difference in the scattering contrast of the pores and the walls. The nitrogen adsorption–desorption isotherms of the prepared samples show characteristic type IV isotherms that indicates the presence of cylindrical mesoscale pores (Fig. 2). The textural parameters, specific surface areas (BET method), pore diameters (BJH method) and total pore volumes are given in Table 1, which shows a

Scheme 1. Synthesis route of LUS-SPS-Q.

This solution was titrated with a standardized Lu3+ ion solution and the fluorescence intensity of the system was measured after each addition. The emission intensity, at an excitation wavelength of 330 nm was measured. Spectral bandwidths of monochromators for excitation and emission were fixed at 5 nm. The fluorescence quantum yield was obtained by comparison of the integrated area of the emission spectrum and absorbance of the samples with the reference under the same excited wavelength. The concentration of the reference quinine sulfate ( = 0.54) in an aqueous solution was adjusted to match the absorbance of the test sample. The quantum efficiency of a metal-bound sample was measured by using a suspension solution of 0.08 g L−1 LUS-SPS-Q and 1.0 × 10−6 mol L−1 Lu3+ . Emission for Lu-LUS-SPS-Q was integrated from 340 to 540 nm with excitation at 310 nm, where as for LUSSPS-Q, the emission area was integrated from 340 to 540 nm. The quantum yields were then calculated by Eq. (1).

 emissionsample Areferences sample = reference  emissionsample Asample

(1)

3. Results and discussion The low angle XRD patterns of LUS-1 and its functionalized derivatives are depicted in Fig. 1. All the samples showed a typical mesoporous structure with three sharp peaks corresponding to (1 0 0), (1 1 0) and (2 0 0) reflections, which are associated with hexagonal array of the channels in the prepared mesoporous

Fig. 2. N2 adsorption–desorption isotherms of (a) LUS-1; (b) LUS-SPS-Q [29,31].

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Table 1 Textural parameters of prepared compounds.a Sample

SBET (m2 g−1 )

V (cm3 g−1 )

DBJH (nm)

LUS-1 LUS-SPS-Q

675 243

0.946 0.453

2.4 2.2

a SBET is the BET surface area; V is the total pore volume; DBJH is the average pore diameter calculated using BJH method.

Fig. 4. Fluorescence emission spectra of LUS-SPS-Q (3 mL 0.08 g L−1 ) suspended in aqueous solution in the presence of different metal ions (1.0 × 10−4 mol L−1 ). Excitation was performed at 310 nm.

Fig. 3. SEM image of LUS-1.

3.2. UV–vis measurements trend of decreasing in surface area, pore volume and pore diameter due functionalization inside the channels of LUS-1. Fig. 3 illustrates the SEM image of LUS-1 that shows the long rod-shaped material. FT-IR spectra confirm the incorporation of 8-hydroxyquinoline (8-HQ) in the LUS-1 framework. The peaks at 1610, 1580, 1500, 1471 and 1387 cm−1 are related to the C N and C C ring skeletal vibrations of the grafted 8-HQ ligand and the band appearing at 1334 cm−1 can be ascribed to asymmetric vibration of O S O group of sulfonamide bond that linked the 8-HQ moiety to the surface of functionalized LUS-1. The specific peak belonging to the symmetric vibration of O S O was not observed in the spectrum because of the broad peak at 1100 and 800 cm−1 due to the stretching vibration of Si O Si [30]. The chemical compositions of the grafted organic groups in functionalized mesoporous silica were determined by elemental analyses (Table 2). From elemental analyses data it can be concluded that the reaction yield of LUS-NH2 with HQ-SO2 Cl is about 50% [31].

The cations binding properties of the ionophore were also investigated by UV–vis absorption. The experiments were carried out in aqueous solution by adding aliquots of Lu3+ form a Lu(NO3 )3 solution. As shown in Fig. 5, LUS-SPS-Q revealed to possess three intensive absorption bands centered at 239, 253 and 362 nm which can be contributed to ␲→␲* and n→␲* transition. As seen in Fig. 5, after the addition of Lu3+ to the solution of LUS-SPS-Q, the absorption band at 239 and 362 nm decreased and the intensity of the peak at 253 nm gradually increased. Notably, titration of LUS-SPS-Q with Lu3+ led to a red–shifted shoulder in the UV spectra (max = 17 nm shift) with two well define disosbestic points at 249 nm and 266 nm respectively, indicating that the stable complex between the receptor LUS-SPS-Q and Lu3+ was formed.

3.1. Preliminary studies In order to evaluate the applicability of LUS-SPS-Q as a selective fluorescent ionophore in a chemosensor for Lu3+ ion, in preliminary experiments the interaction of LUS-SPS-Q with a number of metal ions was spectrofluorometrically investigated in an aqueous solution at 25.0 ± 0.1 ◦ C. A solution of 0.08 g L−1 of LUS-SPS-Q in an aqueous solution was spectrofluorometrically titrated with microliter amounts of 1.0 × 10−4 mol L−1 solutions of metal ions. Fluorescence measurements were recorded at an excitation wavelength of 310 nm. As it is shown in Fig. 4, as LUS-SPS-Q is titrated by Lu3+ solution, a significant enhancement in the fluorescence intensity was observed. There is no significant fluorescence changes in the case of other lanthanides and metal ions tested. Table 2 Elemental analysis data of prepared compounds. Sample

C (%)

N (%)

S (%)

SBA-NH2 LUS-SPS-Q

4.6 11

1.8 2.7

– 1.9

Fig. 5. UV-vis spectra change of LUS-SPS-Q (3 mL 0.1 g L−1 ) upon addition of Lu3+ (1.0 × 10−3 mol L−1 ) in aqueous solution.

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Fig. 6. Emission spectra of the proposed chemosensor in the presence of varying concentration of Lu3+ ions: (1) 0, (2) 1.6 × 10−7 mol L−1 , (3) 3.3 × 10−7 mol L−1 , (4) 6.6 × 10−7 mol L−1 , (5) 1.0 × 10−6 mol L−1 , (6) 1.3 × 10−6 mol L−1 (7) (8) 2.0 × 10−6 mol L−1 , (9) 2.3 × 10−6 mol L−1 , (10) 1.6 × 10−6 mol L−1 , 2.6 × 10−6 mol L−1 , (11) 3.0 × 10−6 mol L−1 , (12) 3.3 × 10−6 mol L−1 , (13) 4.0 × 10−6 mol L−1 , (14) 4.6 × 10−6 mol L−1 , (15) 5.0 × 10−6 mol L−1 , (16) 6.0 × 10−6 mol L−1 , (17) 6.6 × 10−6 mol L−1 , (18) 8.3 × 10−6 mol L−1 , (19) 1.0 × 10−5 mol L−1 , (20) 1.3 × 10−5 mol L−1 ; ex = 310 nm. Visual fluorescence changes of sensor LUS-SPS-Q (0.08 g L−1 ) in the absence (B) and excess presence of Lu3+ ions (A) (1.0 × 10−2 mol L−1 ). The photo was taken under a handheld UV (365 nm) lamp.

3.3. Fluorescence properties The fluorescence spectrum of the LUS-SPS-Q suspended in aqueous medium (0.08 g L−1 ) and excited at 310 nm exhibited an emission maximum at 486 nm at 298 K. The emission spectra of LUS-SPS-Q in the presence of various concentrations of Lu3+ (10−4 mol L−1 ) were recorded (Fig. 6). It can be seen in Fig. 6 that the fluorescent intensity of the LUS-SPS-Q is sensitive to Lu3+ , in the presence of various concentration of Lu3+ ion significant fluorescence enhancement of fluorescence probe was observed. This can be termed as a Lu3+ ion selective chelating enhanced fluorescence. The new peak emission band (486 nm) of the complex LUS-SPS-Q compared to that at 405 nm of the free ligand is quite unexpected (Fig. 6). One observes a red shift of about 81 nm for the emission spectrum peak of LUS-SPS-Q from its uncomplexed state (zero Lu3+ concentration) to complexed form. The red shift in the emission of LUS-SPS-Q after Lu3+ coordination can be explained in terms of the photoinduced charge transfer (PCT) mechanism. When a fluorophore contains an electrondonating group conjugated to an electron-withdrawing group, it undergoes intramolecular charge transfer (ICT) from the donor to the acceptor upon excitation by light. The consequent change of the dipole moment leads to a larger Stokes shift, which is influenced by the micro environment of the fluorophore. Therefore, when a cation such as Lu3+ interacts with the acceptor group, the excited state is more stabilized by the cation than is the ground state and this leads to a red shift of the absorption and emission spectra [32,33]. The binding constant value has been determined from the emission intensity data following the modified Benesi–Hildebrand equation [34]: 1 1 = + F Fmax

 1  K[C]

1 Fmax



where F = Fx − F0 and Fmax = F∞ − F0 , and where F0 , Fx and F∞ are the emission intensities of LUS-SPS-Q considered in the absence of

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Fig. 7. Effect of pH of the test solution on the fluorescence response of LUS-SPS-Q (0.08 g L−1 ). (A) LUS-SPS-Q (0.08 g L−1 ) in the presence of Lu3+ 1.0 × 10−5 mol L−1 ; (B) ex = 310 nm.

Lu3+ , at an intermediate Lu3+ concentration, and at a concentration of complete interaction, respectively. K is the binding constant for the interaction and [C] is the Lu3+ concentration. From the plot of (F∞ − F0 )/(Fx − F0 ) against [C]−1 for LUS-SPS-Q, the value of K extracted from the slope is 5 × 106 M−1 . In the presence of various concentrations of Lu3+ ions, ranging from 1.6 × 10−7 to 1.0 × 10−5 mol L−1 , significant fluorescence enhancement of the fluorescent probe was observed (Fig. 6). Limit of detection (LOD), corresponding to three times the standard deviation of the blank (3 criterion), was determined to be 8.2 × 10−8 mol L−1 for the Lu3+ ion The regression equation was F (RSD:2.1%) = 3 × 107 C + 65.77 (R2 = 0.992) and the relative standard deviation (RSD) was 2.1% by 10 replicate determination of 0.6 × 10−7 mol L−1 Lu3+ . A comparison between this work and other previous reported methods for Lu3+ ion is listed in Table 3. In comparison with these methods, the nano-chemosensor has a wider linear range than potentiometric and spectrophotometric methods. The detection limit of the nano-chemosensors 8.2 × 10−8 mol L−1 which is lower than those of the activation analyses, spectrophotometric, ICP-OEC and ion-selective electrodes methods It can be seen that the nanochemosensor displays more favorable linear range and detection limit than most of the reported methods [9,10,12–14]. 3.4. Effect of pH Fig. 7 shows the influence of pH of the test solution on the fluorescence response of the proposed chemo-sensor. The fluorescence intensity measurements were made for a 1.0 × 10−5 mol L−1 Lu3+ solution at different pH values. As it is seen (Fig. 7), in the presence of Lu3+ response of the chemosensor is independent on the pH of the test solution in a range of 3.3–8.3. Thus, LUS-SPS-Q can detect Lu3+ in a wide pH range from 3.3 to 8.3. The pH solution was adjusted by either HCl or NaOH. 3.5. Selectivity To further explore the availability of LUS-SPS-Q as a highly selective probe for Lu3+ , fluorescent responses of LUS-SPS-Q spectra to the other metal ions that probably affect the fluorescence intensity were acquired. Changes in the fluorescence properties of LUS-SPSQ in aqueous solution caused by other metal ions, including all mono, bivalent metal ions and trivalent lanthanide ions were also measured. The results are shown in Fig. 8, revealed that among

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Table 3 Comparison of the linear range and detection limit (LOD) of several different methods for determination of Lu3+ . Method

Linear range (mol L−1 )

LOD (mol L−1 )

Reference

Activation analyses Spectrophotometric ICP-OEC Ion-selective electrodes Ion-selective electrodes Fluorescent nano-chemosensor

– 1.6 × 10−6 – 1.0 × 10−6 1.0 × 10−6 1.6 × 10−7

1.4 × 10−5 2.5 × 10−7 5.4 × 10−3 8.0 × 10−7 6.0 × 10−7 8.2 × 10−8

[9] [10] [12] [13] [14] This work

to 6.8 × 10−4 to 1.0 × 10−2 to 1.0 × 10−1 to 1.3 × 10−5

Table 4 Recovery of the Lu3+ ions concentration in various binary and ternary mixtures. Lu3+ (mol L−1 ) −6

2 × 10 2 × 10−6 2 × 10−6 2 × 10−6 2 × 10−6 2 × 10−6 2 × 10−6 2 × 10−6 2 × 10−6 2 × 10−6 2 × 10−6 2 × 10−6 2 × 10−6 a

Fig. 8. Fluorescence responses of LUS-SPS-Q (0.08 g L−1 ) upon addition of cations (5.0 × 10−4 mol L−1 ) (ex : 330 nm). Fluorescence responses of LUS-SPS-Q (0.08 g L−1 ) containing 30 ␮M Lu3+ and the background cations (120 ␮M) (ex : 330 nm).

the metal ions studied; only Lu3+ ion has a significant effect on the fluorescence intensity of LUS-SPS-Q (0.08 g L−1 ). No fluorescence enhancement of LUS-SPS-Q was observed upon the addition of excess (5 × 10−4 mol L−1 ) of Na+ , K+ or various other metal ions Cu2+ , Zn2+ , Cd2+ , Hg2+ and other lanthanide ions La3+ , Ce3+ , Dy3+ , Yb3+ , Sm3+ , Gd3+ , Pr3+ . It is likely that poor complexation happens between metals ions with the chelator within the channel LUS-SPSQ. To explore practical applicability of LUS-SPS-Q (0.08 g L−1 ) as a Lu-selective fluorescent chemosensor, competition experiments were also performed in the presence of Lu3+ at 30 ␮M mixed with 120 ␮M background metal cations such as Co2+ , Ni2+ , Zn2+ , K+ , Ag+ and other lanthanide ions. The fluorescence intensity ratios (I486 /I405 ) of solutions containing both background other cations and Lu3+ shown in Fig. 8. As can been seen, other background metal ions had small or no obvious interference with the detection of Lu3+ . All these results indicated that L could be used as a potential candidate of fluorescent chemosensor for Lu3+ ion with very high selectivity. Due to the considerable selectivity of the proposed chemosensor, this sensor was additionally used for determination of Lu3+ ions in presence of other cations (in some binary and ternary mixtures). To a 2 × 10−6 mol L−1 of lutetium solution some other cations were added and the mixed solutions as shown in Table 4 were prepared. Then the lutetium contents of these solutions were measured by the calibration method using the proposed method as mentioned in Section 2.5. The corresponding results are summarized in Table 4. Table 4 illustrates that Lu3+ ion recovery, in the presence of the added cations with higher concentration than Lu3+ ion, is acceptable in the range of 98.6–103.1%. 3.6. Analytical application The proposed chemosensor was used in low level monitoring of the lutetium ion concentrations in spiked water samples. 10.0 mL

Added cation (mol L−1 )

Recovery (%)

Ce3+ (1 × 10−4 ) Tb3+ (1 × 10−4 ) Sm3+ (1 × 10−4 ) La3+ + Ho3+ (1 × 10−4 ) Er3+ (1 × 10−4 ) Eu3+ + Pr3+ (1 × 10−4 ) Co2+ (1 × 10−3 ) Zn2+ (1 × 10−4 ) Cu2+ (1 × 10−3 ) Mg2+ (1 × 10−3 ) Ca2+ (1 × 10−2 ) Li+ (1 × 10−2 ) Na+ (1 × 10−2 )

100.2a 99.6 98.9 102.3 99.5 100.7 102.4 103.1 99.3 98.6 101.5 101.7 101.8

± ± ± ± ± ± ± ± ± ± ± ± ±

0.5 0.3 0.4 0.6 0.7 0.5 0.3 0.5 0.6 0.6 0.5 0.3 0.7

Results are based on three measurements.

Table 5 Determination of lutetium ion in tap water and river samples with the proposed chemosensor. Sample

Lu3+ added (mg L−1 )

Found by nano-chemosensora (mg L−1 )

Relative error (%)

Tap water

1 0.5

0.92a ± 0.11 0.53 ± 0.15

8.0 6

River water

1 0.5

1.07 ± 0.11 0.52 ± 0.17

a

7 4

Results are based on three measurements.

of each water sample (tap and river water samples, Tehran, Iran) was taken and diluted with distilled water in a 25.0 mL volumetric flask. The different amounts of lutetium ions (0.5, 1 mg L−1 ) as shown in Table 5 were added to the water samples. The lutetium concentration of the water samples was measured by the proposed chemosensor using the calibration method as described in Section 2.5. The results obtained with the sensor are summarized in Table 5. It was found that the accuracy of lutetium detection in different solution samples is almost quantitative. To find accuracy of the proposed chemosensor, the proposed chemosensor was used to the Lu3+ ion determination in a Table 6 Results from the Coal And Fuel Ash analysis (FFA 1 Fly Ash). Certified values for (mg kg−1 ) Al As Ba Ce Co Ca Cs Cu Dy Er Eu F Fe Gd

14.87 53.6 835 120 39.8 156 48.2 158 9.09 4.52 2.39 198 4.89 10.0

Hf La Li Lu Mn Na Nd Ni P Pb Rb Sb Sc Si

6.09 60.7 128 0.658 1066 2.19 56.8 99.0 725 369 185 17.6 24.2 22.48

Sm Sr Ta Tb Th Tm U V W Y Yb Zn

10.9 250 2.11 1.38 29.4 0.705 15.1 260 10.5 45 4.24 569

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certified reference material (CRM), called Coal and Fuel Ash (FFA 1 Fly Ash). According to Table 6, where the CRM analysis was summarized, the lutetium content is 0.658 mg kg−1 . Using the proposed chemosensor and the calibration method, lutetium content of 0.672 ± 0.4 mg kg−1 was obtained. The results of t-test on the 95% confidence limit for 5 replicate measurements (ttable = 2.132) was 0.035. The experimental data revealed that the proposed method can determine lutetium in the presence of other elements accurately. 4. Conclusions In summary, we design and prepare a novel Lu3+ ion selective fluorescent chemosensor that is designed by preparation of 8-hydroxyquinoline functionalized mesoporous silica with highly ordered structure. A remarkable enhancement in the fluorescence intensity of LUS-SPS-Q upon the addition of Lu3+ ion is attributes to the formation of a coordinate complex of a large rigid conjugate system to Lu3+ ions. In competition of other ions tested, this chemosensor exhibits a high selectivity and sensitivity for detecting Lu3+ ion in aqueous solution. Acknowledgements The Financial support of this work by Iran National Science Foundation (INSF 90005872) and Tehran University Research Council is gratefully acknowledged. References [1] B.J. Melde, B.J. Johnson, P.T. Charles, Sensors 8 (2008) 5202–5228. [2] C. Beck, W. Hartl, R. Hempelmann, Angew. Chem. Int. Ed. 38 (1999) 1297–1300. [3] A.B. Descalzo, K. Rurack, H. Weisshoff, R. Manez, M. Dolores, P. Amoros, K. Hoffmann, J. Sato, J. Am. Chem. Soc. 127 (2005) 184–200. [4] J. Wang, L. Huang, M. Xue, L. Liu, Y. Wang, L. Gao, J. Zhu, Z. Zou, Appl. Surf. Sci. 254 (2008) 5329–5335. [5] S.P. Fricker, Chem. Soc. Rev. 35 (2006) 524–533. [6] K. Wang, Y. Cheng, X. Yang, R. Li, Met. Ions Biol. Syst. 40 (2003) 707–751. [7] C.H. Evans, Trends Biochem. Sci. 8 (1983) 445–449.

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