Review Potentiometric Studies and Various Applications of Solid State Electrodes Based on Silicon and Epoxy Glass Structures – an Overview P. Ciosek,* Michał Chudy , Łukasz Go ´ rski, Ilona Grabowska, Ewa Grygołowicz-Pawlak, Elz ˙bieta Malinowska, W. Wro ´ blewski Warsaw University of Technology, Faculty of Chemistry, Noakowskiego 3, 00-664 Warsaw, Poland *e-mail: pciosek@ch.pw.edu.pl Received: December 12, 2008 Accepted: February 7, 2009 Abstract Potentiometric microelectrodes are attractive sensor tools for the determination of ionic components in liquids, in wide area of applications, from environmental monitoring to medical diagnostics. Appropriate design of miniaturized transducers based on solid-state technology and the fabrication of dedicated flow multiparameter systems allow the reduction of sample volume and reagents loss. In this overview various examples of the design, performance, and applications of solid-state potentiometric microelectrodes based on back-side contact transducers for flow-cell analysis are presented. The presented results summarize the research works on that field that were conduced in CSRG/Warsaw University of Technology. Keywords: Microelectrodes, Back-side contact transducers, ISE, Silicon, Sensors, Monolayers DOI: 10.1002/elan.200804612 Presented at the International Conference on Electrochemical Sensors Ma ´trafüred 2008 1. Introduction The miniaturization of the potentiometric sensors provides integrated analytical systems which can result in significant reduction of manufacturing costs and quantity of consumed reagents. Nowadays, most of the used microelectrodes are fabricated on solid substrates (Solid State Electrodes, SSEs) [1]. However, the development of miniaturized potentio- metric systems faces several challenges, including the construction of an appropriate solid-state transducer, the replacement of the internal electrolyte solution by an intermediate layer and deposition of ion-sensitive layer of appropriate composition ensuring high sensor durability. Moreover, the development of a reliable solid-state refer- ence microelectrode remains still a serious problem [2, 3]. However, this approach is very advantageous, since solid- state microelectrodes can be easily mounted and applied in channels in microsystems, dedicated to flow analysis. The development of analytical flow systems based on solid-state microelectrodes was driven by the advantages of miniatur- ized sensor arrays. Their application results in the decrease of the volume of the sample solution needed to perform the measurement, the decrease of the volume of chemical and waste solutions required, and leads to a reduction in the overall cost of the analysis. The flow mode of measurement causes a decrease in the single analysis time and makes the calibration procedure faster. In this paper we present the results of our group work, devoted to the development of robust, versatile flow systems based on back-side contact (BSC) solid-state transducers. First, the transducer fabrication will be presented, and then flow-through cell designed for such sensors. Some problems considering sensor durability, response stability, which were improved by the application of various polymer layers as well as redox-active intermediate layer, are discussed. Finally, applications of the designed solid-state microelectr- odes for multicomponent analysis and sensor array meas- urements are presented. 2. Transducers Design The introduction of the all-solid-state potentiometric sen- sors in miniaturized flow systems requires the design of specialized planar transducers. A simple method to obtain such transducers suitable for flow-cell analysis, i.e., planar Au or Ag/AgCl microelectrodes on epoxy-glass laminate substrate has been proposed in our laboratory [4]. The transducer structure (squares 5 by 5 mm, 0.5 mm in thick- ness) was produced from a double-sided layer printed circuit board (PCB), where back-side contact was achieved by the metallization of a hole. After etching of useless copper area, the structure was electrochemically covered with a silver or gold layer. In the case of Ag/AgCl transducers, silver 1895  2009 WILEY-VCH Verlag GmbH&Co. KGaA, Weinheim Electroanalysis 2009, 21, No. 17-18, 1895 – 1905