Engineering of nano-bio interfaces towards the development of portable biosensors
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The rapid development in bio-nanotechnology coupled with advancements in microelectronics and computing power has given rise to an enormous potential for the development of point-of-care diagnostic devices and portable biosensors. The application area encompasses human disease detection, analyzing bio-hazardous molecules and toxins and other inorganic materials. Amongst the plethora of receptors in such biosensors, aptamers, which are oligonucleotides with high affinity for target analytes, have demonstrated considerably improved performance over traditional receptors like antibodies. The hallmark of a portable biosensor is high throughput in response to analyte characterized by appreciable signal/noise ratio, dynamic range and low limit of detection. However, these characteristics are difficult to achieve in practical scenarios due to a variety of factors and thus the success is mostly limited to lab based developments. Particularly, the poor commercial success of portable biosensors directed towards human disease detection is noticeable.
In this study, effort has been made to address some of the issues like external control over target binding to receptor, low signal/noise ratio and detection in presence of interfering molecules, challenging the practical deployment of a portable aptamer-based biosensor by focusing on engineering of the nano-bio interface of the transducer in such devices. The investigation is carried out in three directions:
1. Electrical actuation of receptor-target complex
2. Impedance characterization of nanoporous transducer
3. Engineering of the receptor arrangement on the transducer
The goal of the present research is to provide improved understanding of such processes which can lead to the design and creation of a point-of-care diagnostic device with the ability to detect human disease markers like:
(i) Ebola virus protein sGP/GP1-GP2 as a biomarker for Ebola virus infection
(ii) NGAL protein related to Acute Kidney Injury
Through the research described in this thesis, the following have been understood:
(a) The actuation of aptamer-protein complex, where the protein may be dissociated from the aptamer immobilized on the electrode surface due to externally applied electric field depends on the length of the aptamer nucleotide sequence, charge of protein and the surface grafting density of aptamer.
(b) Four-electrode electrochemical sensors, utilizing nanoporous alumina membrane with aptamer immobilized on one surface can be used as a biosensor in which membrane impedance depends on target concentration and greater sensitivity is observed with serum albumin in the sample to be tested. Also, there exists an optimal frequency for aptamer-protein complexes which can help in reducing the time of operation of such a biosensor by eliminating the need for long range of frequency scans to get system impedance.
(c) Competition mode of sensing, using a receptor weakly attached to the surface via a linker, and having higher propensity to bind with target analyte in the solution compared to remaining surface bound, may be used as a technique to increase signal/noise ratio by increasing sensitivity to low concentration analyte in presence of interfering molecules.