Biyosensör uygulamaları için zeolitlerin madifikasyonu.

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.  Ph.D. - Doctoral Progra

Design of Zeolite Modified Electrodes and Their Influence on Biosensor Performance

Enzyme-based biosensors have been of intense investigation and field-effect transistor (FET)-based sensors are one of the widely produced, miniaturized silicon-based semiconductor devices used to quantify ion concentrations in the analyte solution. Overall, current research has focused on enhancement of the sensitivity, detection limit, selectivity and the storage stability of these electrochemical biosensors. For this purpose, variety of modification methods on electrochemical biosensor surfaces is proposed. At present, use of new nanosized materials in biosensor design is a promising approach to improve analytical characteristics of the devices. Zeolites are perspective nanomaterials for biosensor modification. They are inorganic compounds, the structure of which is a crystal lattice consisting of alumina and silica tetrahedra bound by oxygen atoms. This framework forms a lot of pores and channels which considerably increases the zeolite surface. In the current study, a review on precise control over structural and chemical properties of zeolites and their consequent effect on electro-chemical biosensors will be given. All results suggest that the methodology of surface immobilization and zeolitic properties such as Si/Al ratio, surface roughness, particle size, hydrophilicity and the ability to create gold nanoparticles within the nanopores effect and ultimately enhance the biosensor sensitivity and stability. Considering the important biological role of urea as a diagnostic indicator of kidney failure and major uremic toxin, its determination was needed in medical diagnostics. It was shown that distinction of healthy people from people with renal dysfunction became easier by zeolite modified biosensors. Our results show that the performance of constructed ISFET-type biosensors strongly depends on Si/Al ratio of employed zeolite nanoparticles as well as the type of enzymatic reaction employed. All fabricated biosensors demonstrated high signal reproducibility and stability. The obtained results were used for the development and design for an experimental prototype of novel nanobiosensor located implant

Biosensors Based on Nano-Gold/Zeolite-Modified Ion Selective Field-Effect Transistors for Creatinine Detection

The combination of advantages of using zeolites and gold nanoparticles were aimed to be used for the first time to improve the characteristic properties of ion selective field-effect transistor (ISFET)-based creatinine biosensors. The biosensors with covalently cross-linked creatinine deiminase using glutaraldehyde (GA) were used as a control group, and the effect of different types of zeolites on biosensor responses was investigated in detail by using silicalite, zeolite beta (BEA), nano-sized zeolite beta (Nano BEA) and zeolite BEA including gold nanoparticle (BEA-Gold). The presence of gold nanoparticles was investigated by ICP, STEM-EDX and XPS analysis. The chosen zeolite types allowed investigating the effect of aluminium in the zeolite framework, particle size and the presence of gold nanoparticles in the zeolitic framework

Creatinine Deiminase Adsorption onto Silicalite-Modified pH-FET for Creation of New Creatinine-Sensitive Biosensor

In the work, silicalite particles were used for the surface modification of pH-sensitive field-effect transistors (pH-FETs) with the purpose of developing new creatinine-sensitive biosensor. Creatinine deiminase (CD) adsorbed on the surface of silicalite-coated pH-FET served as a bioselective membrane. The biosensor based on CD immobilized in glutaraldehycie vapor (GA) was taken as control. The creatinine-sensitive biosensor obtained by adsorption on silicalite was shown to have better analytical characteristics (two-to threefold increased sensitivity to creatinine, three-to fourfold lesser response and recovery times, a decrease of the detection limit of creatinine determination to 5 mu m, etc.)

Application of silicalite-modified electrode for the development of sucrose biosensor with improved characteristics

The application of silicalite for improvement of working characteristics of conductometric enzyme biosensors for determination of sucrose was studied in this research. Biosensors based on different types of silicalite-modified electrodes were studied and compared according to their analytical characteristics. Polyethylenimine/glutaraldehyde/silicalite-modified biosensors showed higher sensitivity compared with others type of biosensors. Moreover, the polyethylenimine/glutaraldehyde/silicalite sucrose biosensors were characterized by high selectivity and signal reproducibility (relative standard deviation (RSD) = 2.78% for glucose measurements and RSD = 3.2% for sucrose measurements). Proposed biosensors were used for determination of sucrose in different samples of beverages. The obtained results had good correlation with results obtained by HPLC. Thus, polyethylenimine/glutaraldehyde/ silicalite-modified biosensors have shown perspective characteristics for the development of effective conductometric enzyme biosensors

Nanosized zeolites as a perspective material for conductometric biosensors creation

In this work, the method of enzyme adsorption on different zeolites and mesoporous silica spheres (MSS) was investigated for the creation of conductometric biosensors. The conductometric transducers consisted of gold interdigitated electrodes were placed on the ceramic support. The transducers were modified with zeolites and MSS, and then the enzymes were adsorbed on the transducer surface. Different methods of zeolite attachment to the transducer surface were used; drop coating with heating to 200 degrees C turned out to be the best one. Nanozeolites beta and L, zeolite L, MSS, and silicalite-1 (80 to 450 nm) were tested as the adsorbents for enzyme urease. The biosensors with all tested particles except zeolite L had good analytical characteristics. Silicalite-1 (450 nm) was also used for adsorption of glucose oxidase, acetylcholinesterase, and butyrylcholinesterase. The glucose and acetylcholine biosensors were successfully created, whereas butyrylcholinesterase was not adsorbed on silicalite-1. The enzyme adsorption on zeolites and MSS is simple, quick, well reproducible, does not require use of toxic compounds, and therefore can be recommended for the development of biosensors when these advantages are especially important

Nano- and microsized zeolites as a perspective material for potentiometric biosensors creation

A number of potentiometric biosensors based on coimmobilization of enzymes with different types of zeolite on pH-ion-sensitive field-effect transistor (ISFET) have been developed. Their working characteristics have been determined and compared