Kondüktometrik ve iyon seçici alan etkili transistör tipli biyosensör uygulamalarında kullanılmak üzere proteinlerin zeolit ve zeolit benzeri malzemeler üzerine immobilizasyonu.

Over the last decade, immobilization of proteins onto inorganic materials is becoming more crucial to extend a deep understanding of interaction between proteins and nanoparticles. With understanding of the real interaction lying under the protein-nanoparticle relations, it is possible to organize the conformation and orientation of surface and framework species of nanoparticles to generate ideal surfaces for potential biotechnological applications. Due to their unique properties such as large clean surface, tunable surface properties, adjustable surface charge, and dispersibility in aqueous solutions, zeolite and zeo-type materials are one of the remarkable classes of inorganic materials that are widely studied in the literature. These properties make zeolites promising alternative candidates for the immobilization of enzymes and incorporation into biosensing devices. In the current study, a new approach was developed for direct determination of urea, glucose, and butyrylcholine where zeolites were incorporated to the electrode surfaces of a conductometric biosensor and Ion Sensitive Field Effect Transistors were used to immobilize the enzymes. Biosensor responses, operational stabilities, and storage stabilities of the new approach were compared with results obtained from the standard membrane methods for the same measurements. For this purpose, different surface modification technique, which are simply named as Zeolite Modified Transducers (ZMTs) were compared with Standard Membrane Transducers (SMTs). During the conductometric measurements ZMT electrodes were used, which allowed the direct evaluation of the effect of zeolite morphology on the biosensor responses for the first time. It was seen that silicalite added electrodes lead to increased performances with respect to SMTs. As a result, the zeolite modified urea and glucose biosensors were successfully applied for detecting urea and glucose, which can offer improved possibilities to design biosensors. The results obtained show that zeolites could be used as alternatives for enzyme immobilization in conductometric biosensors development. Furthermore, the sensitivities of urease and butyrylcholinesterase biosensors, prepared by the incorporation of zeolite Beta crystals with varying acidity on the surface of pH-sensitive field-effect transistors (pH-FETs), have been studied and compared. In order to study exclusively the effect of zeolite acidity, highly crystalline pure zeolite Beta sample with Si/Al ratio of 17 was synthesized and subjected to different heat treatment protocols. In this way, the surface acidic OH groups were controllably altered, as confirmed by Fourier transform infrared (FTIR) spectroscopy without changing any other zeolitic properties, such as zeolite morphology and Si/Al ratio. Upon incorporation of zeolite Beta, the biosensors sensitivity towards urea and butyrylcholine increased 2 and 3 times, respectively. Operational stability and possibility to use the biosensors for inhibition analysis were also investigated. The combined ion-sensitive field-effect transistor (ISFET) and FTIR data provided evidence that urease and butyrylcholinesterase responded to changes in the nature of surface OH groups in zeolite Beta samples. Accordingly, it was found that the Brønsted acidity of zeolite Beta is important for the ultimate ISFET performance. Additionally, analytical characteristics of urease and butyrylcholinesterase based ISFET sensors were investigated by the incorporation of zeolite (70 nm zeolite beta crystals with varying Si/Al ratio, particle size, and surface charge) and zeo-type materials with varying pore diameter and surface charge for the first time. The results obtained by the zeolite modified ISFET transducers suggested that the Si/Al ratio, particle size and surface charge of the zeolite Beta crystals were strongly influenced the biosensor performances due to the electrostatic interactions between enzyme molecules, substrates, and zeolite surface as well as the nature of the enzymatic reaction.M.S. - Master of Scienc

An STM Study of Metal Nanoclusters and Molecular Fragments on Graphene/Cu(111)

Adsorption of Pt, Rh and Pd nanoclusters and molecular fragments on a graphene moiré pattern on Cu(111) was studied with ultrahigh vacuum scanning tunneling microscopy (UHV-STM). Isolated graphene islands with different periodicities were successfully grown on the Cu surface. As a result of weak coupling to the Cu substrate, different graphene rotational domains were observed including one with a periodicity of 4 nm that has not been previously reported. Our results have shown that Pt and Rh form dispersed nanoclusters on graphene/Cu(111) with Pt forming more regular structures mostly trapped at the hollow sites. This variation in growth behavior is mainly attributed to differences in Pt–carbon and Rh-carbon interaction energies. Moreover, the shape, organization and structural evolution of the Pd nanoclusters on graphene/Cu(111) were investigated using two different growth methods, continuous and stepwise. The size and shape of the formed nanoclusters were found to greatly depend on the growth technique used. The size and density of spherical Pd nanoclusters increased with increasing coverage during stepwise deposition as a result of coarsening of existing clusters and continued nucleation of new clusters. In contrast, continuous deposition gave rise to well-defined triangular Pd clusters as a result of anisotropic growth on the graphene surface. Exposure to ethylene caused a decrease in the size of the Pd clusters. This is attributed to the exothermic formation of ethylidyne on the cluster surfaces and an accompanying weakening of the Pd-Pd bonding. Additionally, single methoxy molecules and oxygen atoms were successfully adsorbed on graphene/Cu(111) at low temperatures. Motion of a single methoxy molecule was induced by means of STM/AS and IETS with the aim of understanding the coupling between molecular motions and electronic/vibrational excitations of the molecule. C-H stretching and frustrated rotation of methyl groups were found to be responsible for the observed motion. The motion of molecules adsorbed on graphene was found to be too fast compared to previous single molecule studies conducted on metal surfaces. Although too-fast motion results in an “averaging out of the numerous stable adsorption configurations of the molecule” on the graphene, AS and IETS provided important information about the nature of the motion. The interaction between single methoxy molecules and graphene was found to be stable and the hopping probability was found to be only 6%. The combined properties of imaging and triggering molecular motion on surfaces make STM the perfect tool for exploring molecular rotors and motors in more detail. A key existing challenge is to obtain full control over the rate and/or direction of molecular motion on the graphene surface

A novel urea conductometric biosensor based on zeolite immobilized urease

A new approach was developed for urea determination where a thin film of silicalite and zeolite Beta deposited onto gold electrodes of a conductometric biosensor was used to immobilize the enzyme. Biosensor responses, operational and storage stabilities were compared with results obtained from the standard membrane methods for the same measurements. For this purpose, different surface modification techniques, which are simply named as Zeolite Membrane Transducers (ZMTs) and Zeolite Coated Transducers (ZCTs) were compared with Standard Membrane Transducers (SMTs). Silicalite and zeolite Beta with Si/Al ratios 40, 50 and 60 were used to modify the conductometric electrodes and to study the biosensor responses as a function of changing zeolitic parameters. During the measurements using ZCT electrodes, there was no need for any cross-linker to immobilize urease, which allowed the direct evaluation of the effect of changing Si/Al ratio for the same type of zeolite on the biosensor responses for the first time. It was seen that silicalite and zeolite Beta added electrodes in all cases lead to increased responses with respect to SMTs. The responses obtained from ZCTs were always higher than ZMTs as well. The responses obtained from zeolite Beta modified ZMTs and ZCTs increased as a function of increasing Si/Al ratio, which might be due to the increased hydrophobicity and/or the acid strength of the medium

Direct evidence of advantage of using nanosized zeolite Beta for ISFET-based biosensor construction

Analytical characteristics of urease- and butyrylcholinesterase (BuChE)-based ion sensitive field-effect transistor (ISFET) biosensors were investigated by the incorporation of zeolite Beta nanoparticles with varying Si/Al ratios. The results obtained by the zeolite-modified ISFET transducers suggested that the Si/Al ratio strongly influenced the biosensor performances due to the electrostatic interactions among enzyme, substrate, and zeolite surface as well as the nature of the enzymatic reaction. Using relatively small nanoparticles (62.7 +/- 10, 76.2 +/- 10, and 77.1 +/- 10 nm) rather than larger particles, that are widely used in the literature, allow us to produce more homogenous products which will give more control over the quantity of materials used on the electrode surface and ability to change solely Si/Al ratio without changing other parameters such as particle size, pore volume, and surface area. This should enable the investigation of the individual effect of changing acidic and electronic nature of this material on the biosensor characteristics. According to our results, high biosensor sensitivity is evident on nanosize and submicron size particles, with the former resulting in higher performance. The sensitivity of biosensors modified by zeolite particles is higher than that to the protein for both types of biosensors. Most significantly, our results show that the performance of constructed ISFET-type biosensors strongly depends on Si/Al ratio of employed zeolite Beta nanoparticles as well as the type of enzymatic reaction employed. All fabricated biosensors demonstrated high signal reproducibility and stability for both BuChE and urease

Investigation of characteristics of urea and butyrylcholine chloride biosensors based on ion-selective field-effect transistors modified by the incorporation of heat-treated zeolite Beta crystals

Urea and butyrylcholine chloride (BuChCl) biosensors were prepared by adsorption of urease and butyrylcholinesterase (BuChE) on heat-treated zeolite Beta crystals, which were incorporated into membranes deposited on ion-selective field-effect transistor (ISFET) surfaces. The responses, stabilities, and use for inhibition analysis of these biosensors were investigated. Different heat treatment procedures changed the amount of Bronsted acid sites without affecting the size, morphology, overall Si/Al ratio, external specific surface area, and the amount of terminal silanol groups in zeolite crystals. Upon zeolite incorporation the enzymatic responses of biosensors towards urea and BuChCl increased up to similar to 2 and similar to 5 times, respectively; and correlated with the amount of Bronsted acid sites. All biosensors demonstrated high signal reproducibility and stability for both urease and BuChE. The inhibition characteristics of urease and BuChE were also related to the Bronsted acidity. The pore volume and pore size increases measured for the heat-treated samples are very unlikely causes for the improvements observed in biosensors' performance, because urease and BuChE are approximately one order of magnitude larger than the resulting zeolite Beta pores. Overall, these results suggest that the zeolites incorporated into the biologically active membrane with enhanced Bronsted acidity can improve the performance of ISFET-based biosensors

NANOSIZED ZEOLITES AS A PERSPECTIVE MATERIAL FOR DEVELOPMENT OF ELECTROCHEMICAL ENZYME BIOSENSORS

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°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

The cost of care of rheumatoid arthritis and ankylosing spondylitis patients in tertiary care rheumatology units in Turkey

Objectives: To determine the direct and indirect costs due to rheumatoid arthritis (RA) and ankylosing spondylitis (AS) patients in Turkey. Methods: An expert panel was convened to estimate the direct and indirect costs of care of patients with RA and AS in Turkey. The panel was composed of 22 experts chosen from all national tertiary care rheumatology units (n=53). To calculate direct costs, the medical management of RA and AS patients was estimated using "cost-of-illness" methodology. To measure indirect costs, the number of days of sick leave, the extent of disability, and the levels of early retirement and early death were also evaluated. Lost productivity costs were calculated using the "human capital approach", based on the minimum wage. Results: The total annual direct costs were 2,917.03 Euros per RA patient and 3,565.9 Euros for each AS patient. The direct costs were thus substantial, but the indirect costs were much higher because of extensive morbidity and mortality rates. The total annual indirect costs were 7,058.99 Euros per RA patient and 6,989.81 for each AS patient. Thus, the total cost for each RA patient was 9,976.01 Euros and that for an AS patient 10,555.72 Euros, in Turkey. Conclusion: From the societal perspective, both RA and AS have become burden in Turkey. The cost of lost productivity is higher than the medical cost. Another important conclusion is that indirect costs constitute 70% and 66% of total costs in patients with RA and AS, respectively.Abbott Compan