Untersuchungen zur Entwicklung einer feldeffektbasierten Biosensoranordnung mit integriertem Referenzsystem

One topic of the present work was the development of miniaturised reference electrodes. Different techniques like evaporation, electrochemical methods, pulsed laser deposition and thick-film technique were used for the fabrication of reference electrodes without inner electrolyte (so called quasi-reference electrodes). The stability of these electrodes was investigated in 3 M KCl solution. The best results were obtained with quasi-reference electrodes prepared by means of thick-film technique. The fluctuations of the potential were less than 5 mV over 1000 hours. Thick-film based reference electrodes were covered with KCl-containing pHEMA or agar as inner electrolyte. The agar membrane of some reference electrodes was additionally covered with different protective layers to reduce the leaching of chloride ions out of the membrane. As protective coatings Nafion, cellulose nitrate, PVC or a double layer with PCV and Nafion, or PVC and cellulose nitrate were used. The leaching of chloride ions out of the pHEMA took 10 times longer than it took in the case of agar. By covering the agar membrane with protective coatings the leaching of the chloride ions was significantly reduced. A second topic of the work was the optimisation of porous pH and penicillin sensors with an electrolyte-insulator-substrate (EIS)-structure. Porous silicon was used to improve the adhesion of the enzyme penicillinase in the pores of the substrate. For realising the insulating layer the surface of Si was thermal oxidised to SiO2 and Si3N4 as pH sensitive layer was deposited on top of the SiO2 by means of LPCVD. Compared with pH-sensors from previous works where SiO2 and Si3N4 were deposited by means of PECVD the pH-sensors in this work clearly showed improved long time stability. A third topic was the combination of the developed reference electrode with the optimised sensor. For this purpose, a "one chip" sensor including planar pH sensor and a thick-film reference electrode was developed. The chip with the integrated reference electrode and ...