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Immobilization of zeolite crystals on solid substrates for biosensor aplications

Öztürk, Seçkin
Electrochemical biosensors are cost effective, fast and portable devices, which can determine the existence and amounts of chemicals in a specific medium. These devices have many potential applications in many fields such as determination of diseases, process and product control, environmental monitoring, and drug research. To realize these potentials of the devices, many studies are being carried out to increase their sensitivity, selectivity and long term stabilities. Surface modification studies with various types of particles (metal nano particles, carbon nano tubes etc.) can be count among these studies. Although zeolites and zeo-type materials are investigated for many years, they still hold interest on them due to their capabilities. By means of their chemical resistances, large surface areas, tailorable surface properties, and porous structures they can be applied in many applicational fields. In some recent studies, these properties are intended to be used in the field of biosensors. The purpose of the current study was to investigate the effect of zeolite nanoparticles on electrochemical biosensor performances. Firstly, several different procedures were investigated in order to find the best and optimum methodology to attach previously synthesized zeolites on Si wafer substrates for the first time. For this purpose, the ultrasonication, spin coating and direct attachment methods were used and their efficiencies were compared. Perfectly oriented, fully covering, zeolite monolayers are produced by direct attachment method. Successively produced zeolite thin films were then patterned with the help of Electron Beam Lithography technique to show the compatibility of coating methods to the CMOS technology. Combination of Direct Attachment and EBL techniques resulted well controlled zeolite monolayer patterns. Then zeolite modified electrochemical biosensors were tested for their performances. With these experiments it was intended to improve the selectivity, sensitivity and storage stabilities of standard electrochemical biosensors. Experiments, conducted with different types of zeolites, showed that zeolites have various effects on the performances of electrochemical biosensors. Amperometric biosensor response magnitudes have been doubled with the addition of Silicalites. Faster conductometric electrode responses were achieved with enzyme immobilization on zeolite film technique. Also it is seen that Beta type zeolites modified through different ion exchange procedures, resulted different responses in IS-FET measurements.