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 nano- particles supported on a Si/SiO 2 structure are presented. Oxygen plasma etching at moderate power (<200 W) provides a convenient and efficient way to remove organic capping agents from the gold nanoparticles without significant damage. Higher power intensities destroy the linkage between the SiO 2 and the gold nanoparticles, and some of the gold nanoparticles are removed from the surface. The flat-band potential shift, i.e. the pH depen- dence of the gold-coated EIS sensors is similar (33 mV/ pH) to the uncoated EIS pH-sensor. Lead, penicillin and glucose sensors were prepared by immobilization of β- cyclodextrin, penicillinase and glucose oxidase by various immobilization techniques. Keywords Field-effect device . Gold nanoparticles . Functionalization . EIS sensor . Penicillin . Glucose . Lead Introduction Since they were first introduced to the sensor arena by Brust et al. [1] functionalized gold and precious metal nanoparticles have been increasingly used to enhance electrochemical and photometric sensing applications [2]. Their high surface area, easy functionalization, high electric conductivity, high stability and corrosion resistance, and their pronounced plasmon resonance band in the visible range as well as sensitivity to aggregation are amongst their most attractive features. However, despite the popularity of gold nanoparticles in electrochemical and photoelectro- chemical sensing there are only a few articles describing the use of metal nanoparticle-based field-effect sensors. A notable exception is the work of Willner’ s laboratory [3, 4] to detect neurotransmitters and DNA by modified gold nanoparticle-coated alumina gate field-effect transistors (FET). Willner ’ s FET sensors utilize gold nanoparticles embedded in a polymeric film (polyethyleneimine), which hinders the accessibility of analytes to the functionalized surface of the nanoparticles. Presumably, the capping agent used to prevent aggregation of the nanoparticles in the solution phase also limits the amount of the selective recognition elements that can be bound on the gold nanoparticles. This drawback deters to some extent researchers from utilizing nanoparticles as a vector for incorporation of desirable functionalities in FET sensors. In this article, we demonstrate a strategy to remove the protective capping agent moieties by oxygen plasma treatment. Oxygen plasma ashing involves RF (radio frequency) excitation of pure oxygen gas under an electric field to give active oxygen species that effectively oxidize (ash) carbonaceous materials. The ash and residues are removed by mechanical vacuum pumping. The process is routinely used in electronic industries either under low Microchim Acta (2009) 164:395–404 DOI 10.1007/s00604-008-0073-7 J. Gun : D. Rizkov : O. Lev (*) Institute of Chemistry, The Hebrew University of Jerusalem, Givat Ram, Jerusalem IL-91904, Israel e-mail: ovadia@vms.huji.ac.il J. Gun Institute of Nano- and Biotechnologies (INB), Aachen University of Applied Sciences, Campus Jülich, Ginsterweg 1, DE-52428 Jülich, Germany M. H. Abouzar : A. Poghossian : M. J. Schöning (*) Research Centre Jülich, Institute of Bio- and Nanosystems (IBN2), DE-52425 Jülich, Germany e-mail: m.j.schoening@fz-juelich.de