Modification of zeolites for biosensor applications

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2018

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Ozansoy Kasap, Berna

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In the field of biosensor, zeolites are promising materials due to their large surface areas, mechanical and chemical stabilities, ion exchange capacities and controllable hydrophilicity/hydrophobicity. The powder form of zeolites was the only obstacle of their utilization for biosensor fabrication. In this study, drop-coating and polyethylenimine (PEI) coating methods were developed for improving and optimizing the zeolite usage in immobilization of enzymes. These methods were applied for fabrication of conductometric, amperometric and ion sensitive field effect transistor (ISFET) based biosensors. The conductometric biosensors developed by drop coating method with silicalite were compared with biosensors produced by the frequently used glutaraldehyde (GA) cross-linking method which uses toxic reagent and partially denatures the enzyme. The usage of zeolite increased sensitivity by one-thirds and decreased relative standard deviation (RSD) values for inter-reproducibility by approximately half. The produced biosensors were applied for urea detection in real serum samples and a satisfactory correlation was found when compared with diacetyl monoxime vi reaction. It is therefore asserted that this method is useful for application in real samples. Application of drop-coating method in amperometric biosensors for glucose determination resulted in a prolonged response time due to thick zeolite layers, which were thinned by the PEI method and the response time decreased by a factor of ten. The sensitivity of GA based biosensor increased by 88% using nano beta (nano BEA) and by 34% using silicalite. Furthermore, RSD of reproducibility decreased by half and RSD of inter-reproducibility decreased significantly by a factor of three using zeolite. Consequently, the method developed in this thesis was found to be promising in the development of amperometric biosensors without using toxic compounds. PEI coating method was also applied to ion-sensitive field-effect transistors for urea determination. The obtained results showed that enzyme adsorption on PEI coating of zeolites can promote a wider linear range of biosensors and cause a decrease in the error of signal reproducibility and inter-reproducibility with enhanced sensitivity without using any toxic compounds. This thesis is the first to study the incorporation of zeolite and gold nanoparticles for adsorption of creatinine deiminase on ISFET based biosensors. The effect of different types of zeolite frameworks, particle size variation and the presence of gold on zeolites (BEA-Gold) were investigated to improve the analytical characteristics of drop-coated zeolite modified ISFET based biosensors. The sensitivity of BEA-Gold based biosensor increased three fold compared to GA based biosensors which showed that gold nanoparticles can be used with zeolite to improve the characteristics of ISFET based biosensors.

Subject Keywords

Biosensors, Zeolites.

URI

http://etd.lib.metu.edu.tr/upload/12621764/index.pdf
https://hdl.handle.net/11511/27108

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Graduate School of Natural and Applied Sciences, Thesis

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Citation Formats

B. Ozansoy Kasap, “Modification of zeolites for biosensor applications,” Ph.D. - Doctoral Program, Middle East Technical University, 2018.