Oxygen plasma-treated gold nanoparticle-based field-effect devices as transducer structures for bio-chemical sensing

Microchim Acta (2009) 164:395–404 DOI 10.1007/s00604-008-0073-7

ORIGINAL PAPER

Oxygen plasma-treated gold nanoparticle-based field-effect devices as transducer structures for bio-chemical sensing Jenny Gun & Dan Rizkov & Ovadia Lev & Maryam H. Abouzar & Arshak Poghossian & Michael J. Schöning

Received: 2 April 2008 / Accepted: 30 May 2008 / Published online: 4 July 2008 # Springer-Verlag 2008

Abstract EIS (electrolyte-insulator-semiconductor) sensors based on the functionalization of uncoated gold nanoparticles supported on a Si/SiO2 structure are presented. Oxygen plasma etching at moderate power (100 W) to etch away undesirable polymeric films and photoresists. Here, we adopt the same setup to completely remove the capping agents off the gold nanoparticles, and to eliminate the thiol films that bind the gold nanoparticles to the surface. As far as we know such a process was never reported before in the context of sensing applications. The process was extensively used by Boyen and coworkers [5] for the removal of polymer coatings from gold nanoparticles at 50 W oxygen plasma. Raiber et al. [6] and Hesse and Creighton [7] recently demonstrated that selfassembled monolayers of alkanethiolates and other thiolates can be effectively etched off gold surfaces by either hydrogen or oxygen plasma etching. The authors showed that the treatment results in an Au2O3-covered surface. In our case, the residual gold oxide is removed by alcohol reduction, leaving an organic-free sensing element. Due to its compatibility with the electronic industry, for a future practical application of nanoparticle-based field-effect devices, this technique was preferred over other wellestablished wet chemistry processes (e.g., Pirahna, ozonation, electrochemical etching) for removal of gold thiolate moieties. Four different key experiments have been performed in order to exemplify the use of plasma-etched gold nanoparticle-coated EIS (electrolyte-insulator-semiconductor) devices: pH sensing by bare gold nanoparticle-modified surfaces, lead ion-sensing by methylamine β-cyclodextrinmodified gold nanoparticles, penicillin and glucose sensing by adsorbed and covalently bonded enzymes (glucose oxidase and penicillinase, respectively). Currently, the main advantage of using gold modified EIS stem from their convenient use, but in a forthcoming publication we shall demonstrate that the same approach can be used to enhance glucose electrosensing [8].

Experimental section Reagents and materials All chemicals were of reagent grade and were used as received. (3-mercaptopropyl)trimethoxysilane (MPTMOS), 95%, and hydrogen tetrachloroaurate were from Aldrich (http://www.sigmaaldrich.com), toluene and DMSO were from J.T. Baker (http://www.jtbaker.com), and sodium borohydride was from Merck (http://www.merck.com). Water was deionized (conductivity