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Hepatocytes exhibit a regulatory volume decrease (RVD) during hypotonic shock, which comprises loss of intracellular K+ and Cl- accompanied by hyperpolarization of transmembrane potential (Vm) due to an increase in membrane K+ conductance, (GK). To examine hepatocyte K+ homeostasis during RVD, double-barrel, K+-selective microelectrodes were used to measure changes in steady-state intracellular K+ activity (aKi) and Vm during hyposmotic stress. Cell water volume change was evaluated by measuring changes in intracellular tetramethylammonium (TMA+). Liver slices were superfused with modified Krebs physiological salt solution. Hyposmolality (0.8×300 mosm) was created by a 50 m m step-decrease of external sucrose concentration. Hepatocyte Vm hyperpolarized by 19 mV from -27 ± 1 to -46 ± 1 mV and aKidecreased by 14% from 91 ± 4 to 78 ± 4 m m when slices were exposed to hyposmotic stress for 4-5 min. Both Vm and aKireturned to control level after restoring isosmotic solution. In paired measurements, hypotonic stress induced similar changes in Vm and aKiboth control and added ouabain (1 m m) conditions, and these values returned to their control level after the osmotic stress. In another paired measurement, hypotonic shock first induced an 18-mV increase in Vm and a 15% decrease in aKiin control condition. After loading hepatocytes with TMA+, the same hypotonic shock induced a 14-mV increase in Vm and a 14% decrease in aTMAi. This accounted for a 17% increase of intracellular water volume, which was identical to the cell water volume change obtained when aKiwas used as the marker. Nonetheless, hyposmotic stress-induced changes in Vm and aKiwere blocked partly by Ba2+ (2 m m). We conclude that (i) hepatocyte Vm increases and aKidecreases during hypotonic shock; (ii) the changes in hepatocyte Vm and aKiduring and after hypotonic shock are independent of the Na+-K+ pump; (iii) the decrease in aKiduring hypotonic stress results principally from hepatocyte swelling.

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

In this dissertation I present results on our efforts to increase the sensitivity and selectivity of silicon nanowire ion-sensitive field-effect transistors for the detection of biomarkers, as well as a novel method for wireless power transfer based on metamaterial rectennas for their potential use as implantable sensors. The sensing scheme is based on changes in the conductance of the semiconducting nanowires upon binding of charged entities to the surface, which induces a field-effect. Monitoring the differential conductance thus provides information of the selective binding of biological molecules of interest to previously covalently linked counterparts on the nanowire surface. In order to improve on the performance of the nanowire sensing, we devised and fabricated a nanowire Wheatstone bridge, which allows canceling out of signal drift due to thermal fluctuations and dynamics of fluid flow. We showed that balancing the bridge significantly improves the signal-to-noise ratio. Further, we demonstrated the sensing of novel melanoma biomarker TROY at clinically relevant concentrations and distinguished it from nonspecific binding by comparing the reaction kinetics. For increased sensitivity, an amplification method was employed using an enzyme which catalyzes a signal-generating reaction by changing the redox potential of a redox pair. In addition, we investigated the electric double layer, which forms around charges in an electrolytic solution. It causes electrostatic screening of the proteins of interest, which puts a fundamental limitation on the biomarker detection in solutions with high salt concentrations, such as blood. We solved the coupled Nernst-Planck and Poisson equations for the electrolyte under influence of an oscillating electric field and discovered oscillations of the counterion concentration at a characteristic frequency. In addition to exploring different methods for improved sensing capabilities, we studied an innovative method to supply power to implantable biosensors wirelessly, eliminating the need for batteries. A metamaterial split ring resonator is integrated with a rectifying circuit for efficient conversion of microwave radiation to direct electrical power. We studied the near-field behavior of this rectenna with respect to distance, polarization, power, and frequency. Using a 100 mW microwave power source, we demonstrated operating a simple silicon nanowire pH sensor with light indicator.

Ion sensitive field effect transistors (ISFETs) are semiconductor sensors that have the capability to determine the selected concentration of a specific ion in a solution. Most modern ISFETs utilize their ion selective properties for glucose monitors for diabetics. However, in this thesis, the ISFET fabricated is for the selective detection of K+. The goals of this thesis are to develop a functioning ion-selective polymer membrane, manufacture a working FET device, and implement the two aspects together into a working bench-top K+ selective ISFET device. Properties of a polymer composed of 33 wt.% polyvinyl chloride (PVC) 66 wt.% dioctyl sebacate (DOS) and 1 wt.% valinomycin applied to an ion-sensitive electrode (ISE) were investigated. The membrane generated a sensitivity value of -9.864E-08 Ω/log10(CK). Though this data set was affected by both the maximum resolution of the I-V curve tracing device and the thin-membrane effect. Selectivity tests following the IUPAC two-solution method in the presence of Na+ as the interfering ion, provided selectivity values of 0.228 and 0.443 with higher ratios of primary ion to interfering ion resulting in higher selectivity coefficients. Additionally, utilizing an illumination test, dielectric constants of 17.71 and 10.88 were calculated dependent on the amount of solvent used during formulation. Fabrication of the FET device also resulted in developments in metal contact materials, nitride film processing, and physical vapor deposition (PVD) processes. With further improvements, it is possible to fabricate a biocompatible, wearable K+-selective monitor for continuously testing dialysis patients.