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Šio darbo tikslas, buvo pagaminti stabilų elektrodą naudojant džiovintas ir „gyvas“ mielių ląsteles. Tyrimo metu buvo naudojama trijų elektrodų celė: darbinis anglies elektrodas, pagalbinis platinos elektrodas ir Ag/AgCl elektrodas. Visos potencialų vertės tiesiogiai nurodytos palyginamojo elektrodo atžvilgiu. Tyrimo metu ištyrėme biologinių jutiklių oksidacinių srovių stiprio priklausomybę nuo L-pieno rūgšties koncentracijos naudojant įvairius koncentracijų mediatorius. Nustatėme, kad didėjant mediatoriaus koncentracijai nuo 0,5-1,0-1,5 mM elektrodo stabilumas ir pasikartojamumas didėja. Be to, ištyrėme oksidacinių srovių priklausomybę nuo L-pieno rūgšties naudojant įvairių modifikacijų biologinius jutiklius. Nustatėme, kad stabilus elektrodas gaunamas tik tuo atveju jeigu, naudojame modifikuotas džiovintas mieles ant elektrodo paviršiaus. Taipogi iš gautų kreivių nustatėme, potencialo įtaka oksidacinių srovių stipriui. Visais atvejais prie visų potencialų stebima L-pieno rūgšties oksidaciją bet vis dėl to, skiriasi oksidacinių srovių skaitinės reikšmės. Darbo tikslas įvykdytas nes, pavyko gauti stabilu elektrodą, kurio jautrumą L-pieno rūgščiai patikrinome kefyro ir jogurto pagalba. / The purpose of this research paper, was to create a stable electrode using dry and „alive“ cells of yeast. During the research we used cell of three electrodes: working carbon electrode, supportive platin electrode and Ag/AgCl electrode. All potential values are directly shown in relation to comparison electrode. During the research we have tested the dependence of biosensors oxidical streams strength upon L-milk acid concentration using various concentration mediators. We have established, that increasing mediators concentration from 0.5-1.0-1.5 mM stability and recurrence of electrode is increasing. Furthermore, we have tested the dependence of oxidical streams upon L-milk acid using various modification biosensors. We have established that it is possible to get stable electrode only if using modificated dry yeast on electrode surface. Also from curves we have found, we established the influence of potential on strength of oxidical streams. In all cases, we could notice oxidation of L-milk acid with every potential, however there is difference in oxidical streams numerical values. The research was succesful, as we succeeded in getting stable electrode, the sensitivity of which we have checked with use of sour milk and yogurt.

Designing a biosensor capable of continuously monitoring blood glucose concentration in people with diabetes has been a major challenge for over three decades. In this work we attempt to develop a novel microspike based minimally invasive biosensor for this purpose. Also, as a part of an ongoing study, we attempt to improve the current design of coil-type implantable biosensors. Microspikes, which are able to painlessly penetrate the skin layer, were fabricated using lithographic techniques and sputtered with gold to serve as an electrode. The biosensor design is based on thiomalic acid self-assembled monolayer (SAM) on which glucose oxidase was immobilised by a simple coupling technique together with a tetrathiafulvalene mediator entrapped in an epoxy-polyurethane permselective membrane. Functional testing revealed that such modified sensors are capable of detecting glucose concentration within the clinically relevant range. This was followed by studying the microspike based biosensors incorporated into the microfluidics platform mimicking the sensor behaviour in interstitial fluid. Data from these experiments revealed that the sensor response is mainly dependent on enzyme kinetics rather than membrane permeability to glucose. In contrast, an attempt to address the reproducibility issues of coil-type biosensors is presented. The hypothesis for this study was that a crosslinked hydrogel would have a sufficiently uniform porosity and hydrophilicity to address the variability in sensor sensitivity. The hydrogel was prepared by crosslinking di-hydroxyethyl methacrylate, hydroxyethyl methacrylate and N-vinyl pyrrolidone with 2.5 mol% ethylene glycol dimethacrylate using the water soluble initiators – ammonium persulphate and sodium metabisulfite under a nitrogen atmosphere. The hydrogel was applied to the sensor by dip coating during polymerisation. Electrochemical measurements revealed that the response characteristics of sensors coated with this membrane are highly consistent. Scanning Electrochemical Microscopy (SECM) was used to spatially resolve glucose diffusion through the membrane by measuring the consequent hydrogen peroxide release and compared with an epoxy- polyurethane membrane.

Advanced healthcare requires novel technologies capable of real-time sensing to long-term health monitoring. One example includes biomarker detection for disease diagnosis and deciding treatment options. But several limitations exist with current technologies; however, the COVID pandemic brought these limitations to a global presence as the authorities struggled to quickly authorize a facile test for the early detection of SARS-CoV-2. An important next step is to research alternate strategies, utilize the current infrastructure available, and build sensors that meet standards the current technologies fail to. One of the strategies involves identifying novel sensing parts. To this end, we turned our attention to bacteria as they provide a plethora of novel sensing parts. Bacteria respond to stimuli using a wide range of biomolecules that include enzymes and transcription factors. Our group reported an optical progesterone biosensor based on a novel progesterone responsive allosteric transcription factor (aTF). Firstly, the electrochemical transduction of the binding affinity between this aTF and its cognate DNA sequence is discussed. The binding and unbinding of aTF-DNA results in an impedance change and is directly proportional to progesterone concentration. The limit of detection is comparable to the optical progesterone sensor and relevant to the physiological ranges of progesterone present in bodily fluids. Secondly, to convert the sensor into a point of care system, the expression of the aTF-enzyme fusion protein that undergoes the binding-unbinding event is discussed. The enzyme in presence of its excess substrate acts as a signal amplifier to track the binding changes. The signal depends on the proximity of the fusion protein to the electrode surface and correlates to the progesterone concentration. As we recover from the deadly COVID pandemic, we realize that early diagnosis is a key pillar of disease containment, in addition to other approaches such as contact tracing, distancing, and personal protective equipment. A truly transformative technology in the fight against future viruses is a rapid and quantitative point-of-care (POC) test with a low limit of detection and a high specificity. To that end, an inverted glucometer technology for the detection of infectious diseases is presented. As a model system, SARS-CoV-2 antigens – nucleocapsid protein, antibodies against it, and an inflammatory biomarker are detected. Antigen of interest is sandwiched between capture and detection reagents with biotin and glucose oxidase tags respectively. Glucose oxidase, a widely used enzyme in glucometers, amplifies the output signal in presence of excess glucose. The following chapters encompass designs, different immobilization techniques, characterization, and optimization methods to develop biosensors that meet requirement standards. This research serves as a platform for development of state of the art technologies for diagnostics applications. / 2025-01-16T00:00:00Z

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