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D4.03 - Optofluidic ELISA Laser for Biomolecular Detection 
December 1, 2014   4:15pm - 4:30pm

Enzyme-linked immunosorbent assay (ELISA) is a powerful method for biomolecular analysis. It has been widely used for medical diagnostics and quantification of biomarkers in complex mixtures. However, current traditional ELISA technology employing light intensity (i.e., absorption, fluorescence, and chemiluminescence) as a sensing signal often encounters a few notable drawbacks such as inadequate detection limit, limited dynamic detection range, and large sample and reagent consumption. Those drawbacks have prevented ELISA from being employed in many applications such as early diagnosis and monitoring of diseases, where the analyte concentration is extremely low and may vary orders of magnitude, depending on the physiological condition of a patient. Here we develop a new ELISA detection paradigm- optofluidic laser based ELISA, where ELISA takes place in a microfluidic channel, which also forms an optical microcavity that provides the optical feedback for lasing. The fluorescent product resulting from the enzyme-substrate reaction is used as the laser gain medium, whose concentration increases over time. The laser emission starts to emerge when the product reaches a threshold concentration. Instead of fluorescence intensity, the laser onset time is used as the sensing signal, which is inversely proportional to the number of the enzymes (hence the analytes) in the detection volume. First, we will present the principle of the optofluidic laser based ELISA, and characterization of the optofluidic laser performance. Then, we will present side by side comparison of traditional fluorescence based and optofluidic laser based ELISA using the same commercial ELISA kits of human interleukin-6 (IL-6). Our results of dual-mode detection of IL-6, where the sensing signals are simultaneously obtained by the traditional and the optofluidic laser based ELISA, exhibited a detection limit of 1 fg/mL (38 aM) and a dynamic range of 6 orders of magnitude. Those correspond to 100-1000 times better sensitivity and dynamic range than currently available traditional ELISA assays in the market. We will also demonstrate recent finding of IL-6 biomarker detection in serum using the optofluidic laser.

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