Rapid and simultaneous detection of several infectious pathogens or their biomarkers in clinical or food samples is essential from the public health viewpoint. Conventional techniques for pathogen detection include cell culture, Enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR). While cell culture technique is considered the gold standard for pathogen detection, PCR techniques are widely adopted due to rapid detection within 4- 5 hours as opposed to several hours to days required for cell culture. PCR demands highly skilled personnel, infrastructure and expensive consumables, besides involving laborious protocols. As a quick alternative, ELISA can be performed to detect relevant biomarkers of pathogens of interest; however, limited by analysis time, cross-contamination between different wells and a laborious process. Fiber optic biosensors have been shown as a viable alternative, where it demonstrated rapid and label-free detection of pathogens based on their intrinsic optical absorption at 280 nm. The U-bent fiber optic sensor (U-FOS) probes have been shown to be a potential tool for analyte detection in attomolar concentrations. The remarkably high evanescent wave absorbance (EWA) sensitivity of the sensor with an ergonomic design and low-cost instrumentation could be advantageous for multiplexed analysis towards biomolecular interaction and biosensing studies.

This thesis aims to establish a multichannel fiber optic biosensor system based on U-FOS probes for the sensitive, specific, rapid and simultaneous detection of multiple pathogens or protein biomarkers at a time from a given sample or multiple samples. An eight-channel Array Fiber optic Absorbance Biosensor (ArFAB) was designed and developed as a proof-of-concept for the multiplexed sensing of proteins and pathogens, exploiting their optical absorption properties at 280 nm wavelength. The architecture of the ArFAB includes UV-LED and a CMOS linear detector coupled to a sensor probe module through a fan-out (1-to-8) and parallel (8 nos) fiber bundles, respectively. The multiplexed sensing by ArFAB was established for human IgG as a model protein analyte in both label-free, and gold nanoparticle labeled immunoassay formats and label-free detection of bacteria (E. coli). The ArFAB simultaneously detected various concentrations of IgG in label-free and labeled format with a limit of detection (LoD) of 0.1 µg/mL and 0.1 ng/mL, respectively.

Further, the ArFAB is utilized to demonstrate a new phenomenon called Surface enhanced UltraViolet Absorption (SeUVA), with gold nanoparticles coated U-FOS probes for label-free detection of IgG and E. coli cells with a 3-orders of enhancement in LoDs.

The ArFAB developed as part of this thesis has a great potential for multiplexed detection of biomarkers and pathogens, either different analytes in a single sample or the single analyte in multiple samples. For example, ArFAB promises early diagnosis of cancer based on multiple biomarkers, various heavy metals contamination etc.
Publications:
1. 1. J Kuzhandai Shamlee, VVL Swamy, Allwyn S Rajamani, Soumyo Mukherji, Jitendra Satija, Vani Janakiraman, VVR Sai, “A U-bent fiberoptic absorbance biosensor array (ArFAB) for multiplexed analyte detection” Biosensors and Bioelectronics: X, Volume 12, 2022, 100271, ISSN 2590-1370.