Development of a quantifiable optical reader for lateral flow immunoassay

An optimized optical reader was developed for quantitative fluorescence detection of lateral flow immunoassay in point-of-care test (POCT). Different from existing readers for qualitative test, the developed reader is able to perform quantitative test with a line-shaped excitation beam to obtain the distribution of fluorescence signal intensity along the lateral flow strip. To reduce system complexity, a custom Y-shaped optical fiber, instead of one set of optical lenses, was adopted to couple the excitation and emission channels. A high power Light Emitting Diode (LED) with a specific wavelength interfaced with one of the two split ends of the optical fiber for excitation, while a highly sensitive photodiode with the other split end for detection. A linear stage with high resolution, which was driven by a step motor, was incorporated to facilitate strip scanning. Considering the inhomogeneous nature of lateral flow immunoassay, an optimized global searching algorithm was developed to identify test and control peaks and their boundaries, which further improves reader's sensitivity and specificity. Finally, a calibration model was built into the reader to report the concentration of the test sample. As an example, quantitative CRP (C — reactive protein) test was performed on this reader achieving a reasonable clinical diagnostics range from 1 μg/mL to 200 μg/mL. With its machine reading function, simplicity and relatively low cost, the optical reader could play an important role in POCT.