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Tuberculosis (TB) is the second deadliest infectious disease claiming the lives of 1.6 million individuals annually. One of the significant challenges in controlling the spread of TB is the lack of affordable, user-friendly, and rapid TB diagnostic facilities. Currently, the conventional method for diagnosing TB involves a sputum culture test. Although highly accurate, this approach necessitates specialists, expensive laboratory facilities, and weeks to generate results. A more efficient and non-invasive approach involves targeting TB biomarkers in urine samples. A TB patient's urine contains an additional glycolipid called lipoarabinomannan (LAM) that acts as a TB biomarker. Here, we demonstrate a rapid and portable optical sensor that utilizes a functionalized tapered fiber and phase shift-cavity ringdown spectroscopy (PS-CRDS) to detect LAM in an aqueous solution. We employ motorized stages and a flame to fabricate tapered fibers from single-mode fibers, thereby reducing their diameter from 125 μm to 10-15 μm, enabling them to interact with the surrounding analyte effectively. To specifically target LAM in a solution, we develop a functionalization process that involves a silanization step followed by anchoring an aldehyde-bearing monolayer onto the fiber's surface. The surface aldehyde groups facilitate the covalent attachment of CS-35 LAM antibodies, which only target LAM in a urine sample. The functionalized tapered fiber is the sensing head in the proposed sensing modality. We perform experiments to detect LAM concentrations in aqueous solutions using PS-CRDS. The sensor offers a minimum detection limit of 2 pg/ml and a sensitivity of 2.74 o/mgl−1. The proposed sensor is a step toward a rapid, specialist-free, and non-invasive TB diagnostics platform.
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