Κατασκευή και εφαρμογές μικροαισθητήρων για χημική ανάλυση

Abstract

Stripping voltammetry (SV) has proved a powerful technique for the determination of trace metals in samples of environmental, clinical and industrial origin, due to its high sensitivity, low cost, rapidity and the potential for multi-element determinations. Mercury film electrodes (MFEs) and the hanging mercury drop electrode (HMDE) have been traditionally used in SV. However, the metallic mercury in the HMDE and the mercury salts used to generate MFEs are toxic and are considered undesirable. Βismuth-film electrodes (BiFEs) - consisting of a thin bismuth film deposited on a conductive substrate - has been proposed as a new type of electrode that could potentially substitute the toxic mercury electrodes. Numerous studies over the last decade have demonstrated that BiFEs possess analytical performance similar to mercury electrodes in SV. By far the most widely used method for the preparation of BiFEs is electroplating, which is usually carried out potentiostatically (in situ or ex situ). In this work, a novel method for the fabrication of BiFEs is proposed based on standard microelectronics thin-film technology. The sensors were fabricated by sputtering of a thin film of bismuth on the surface of an oxidized silicon wafer while the geometry of the devices was defined by photolithography.This alternative approach for the generation of the bismuth film has some distinct advantages compared to electroplating: i) the use of Bi(III) ions is avoided and, therefore, the experimental procedure is simplified; ii) a conductive substrate is not necessary, because the sputtered bismuth coating serves as both the sensor and the transducer of the signal (current); iii) the fabrication parameters (such as electrode geometry and bismuth film thickness) can be easily controlled; iv) the use of standard thin-film technology offers increased scope of massproduction of inexpensive and disposable devices. The sputtered bismuth film electrodes were characterized by optical methods (scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD)) as well as by cyclic voltammetry. The determination of Cd(II) and Pb(II) in aqueous samples was carried out by square wave anodic stripping voltammetry (SWASV), using sensors which were fabricated by sputteringlithography. For the determination of Ni(II) and Co(II) by square wave adsorptive stripping voltammetry (SWdASV), three-electrode cells featuring a Ag reference electrode, a Pt counter electrode and a Bi working electrode were fabricated by sputtering- lithography. For the determination of Tl(I) by SWASV, the sensors were fabricated by lithography – double sputtering. In order to alleviate the interferences from surface-active compounds in ASV, Nafion modified sensors were fabricated and they were applied for the determination of Cd(II) and Pb(II). Finally, cyclic microelectrodes arrays of different geometries and dimensions were fabricated by lithography – double sputtering, for the determination of Pb(II), Cd(II), Νi(II) and Cο(II) in aqueous samples. Various…