Development and optimization of the Virus-Bioresistor: A potential Point-of-care diagnostic platform

Point of Care (PoC) diagnostics have made healthcare available for a large audience of non-specialists and patients with introduction of miniaturized, simple and user-friendly electronic devices. Electrochemical biosensors have emerged victorious candidates for PoC owing to the ease of transforming a biological interaction to simple electrical signal. This work is dedicated towards exploring a sensor architecture that connects the biological sensing element, virus, to an external circuitry at nanometer scale. Chapter 2 introduces the Virus-bioresistor in detail. It is demonstrated that M13 phage particles can be wired into an electrical circuit by embedding them in an electronically conductive polymer composed of poly(3,4-ethylenedioxythiophene) or PEDOT via electropolymerization. The signals transduced by impedance spectroscopy are recorded as an increased resistance of the virus-PEDOT material in the presence of the target protein and the amplitude of the resistance change allows its concentration in the contacting solution to be measured. This concept is demonstrated on a model system in which a dynamic range of 7.5 nM – 900 nM human serum albumin (HSA, 66kDa) is detected in phosphate buffer solution. The VBR overcomes the challenges of label-free, non-faradaic sensors pertaining to non-specific adsorption and lower sensitivity. Elemental problem of coupling of target binding from ionic conduction is solved as an equivalent circuit description for the data procured, establishes signal independence over solution conductivity. The next segment employs the VBR for detection of bladder cancer biomarker, DJ-1 (20 kDa), which is achieved by engineering the sensing layer that enables successful pico-molar detection of analyte without compromising on the speed and reproducibility of detection. A range of 10 pM – 300 nM DJ-1 protein is detected, which beautifully accommodates the established 100-1000 pM DJ-1 detected in bladder cancer patient’s urine. A possible signal transduction mechanism is uncovered with experiments based on quartz crystal microbalance (QCM) gravimetry. The last section exploits the potentiality of the VBR to be modified in a controlled fashion to enable large biomolecule (antibody) sensing. This is achieved by oxidizing the VBR channel using chronoamperometry. The morphological changes for VBRs have been tracked with microscopy techniques. Overall, this work establishes that VBRs can be associated with speed, specificity and reproducibility with coefficient of variation values <16%. The signal output can be tuned as per convenience to detect biomolecules with molecular weights that fall within an appreciable range of 20 kDa to 150 kDa