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Tuberculosis (TB) is one of the world’s largest infectious diseases. It causes high mortality in humans and leads to about three million deaths worldwide annually, hence early detection is crucial, especially in a point-of-care (POC) setting to prevent the spreading of the pathogen by undiagnosed individuals. In the current work, a photonic crystal (PhC)-based optical biosensor chip was developed for diagnosing TB using mycolic acid TB antigen as a biorecognition element to capture anti-mycobacterium tuberculosis antibodies. Mycolic acid was successfully immobilized on the PhC biosensor chip to react with anti- mycobacterium tuberculosis antibody, and the white light-based transmission setup was used for optical biosensing to monitor biomolecular interactions between the antigen and antibody. Gold nanoparticles (AuNPs) before and after bioconjugation with goat anti-rabbit IgG H&L secondary antibody were characterised using ultravioletvisible (UV-vis) spectroscopy. Bioconjugated AuNPs were subsequently bound to the biosensing surface to enhance the detection signal of biomolecular binding events. The biosensing surface was further characterised using atomic force microscopy (AFM). Analysis of biomolecular binding events on the biosensing surface was achieved using a custom-built PhC optical biosensing setup which successfully distinguished between experiment and control samples. From our findings, it was realised for the first time that mycolic acid antigen could be immobilised on a biosensing surface to capture anti-mycobacterium tuberculosis antibodies. From this result, it was concluded that the PhC optical biosensing technique was successful in detecting small refractive index changes on the biosensing surface for the diagnosis of TB. These results pave the way for the development of a photonics-based POC diagnostic device for TB.
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