The Development of an Optofluidic Biosensing Platform for Multi-Functional Biomolecular Analysis

Abstract

Biosensors are devices or systems that can be used to detect, quantify, and analyze targets with biological activities and functions. As one of the largest subsets of biosensors, biomolecular sensors are specifically developed and programmed to detect, quantify and analyze biomolecules in liquid samples. Wide-ranging applications have made immunoassays increasingly popular for biomolecular detection and quantification. Among these, enzyme-linked immunosorbent assays (ELISAs) are of particular interest due to high specificity and reproducibility. To some extent, ELISAs have been regarded as a “gold standard” for quantifying analytes (especially protein analytes) in both clinical diagnostics and fundamental biological research. However, traditional (96-well plate-based) ELISA still suffers from several notable drawbacks, such as long assay time (4–6 hours), lengthy procedures, and large sample/reagent consumption (∼100 μL). These inherent disadvantages still significantly limit the applicability of traditional ELISA in areas such as rapid clinical diagnosis of acute diseases (e.g., viral pneumonia, acute organ rejection), and biological research that requires accurate measurements with precious or low abundance samples (e.g., tail vein serum from a mouse). Thus, a bimolecular sensing technology that has a high sensitivity, short assay time, and small sample/reagent consumption is still strongly desired. In this dissertation, we introduce the development of a multifunctional and automated optofluidic immunoassay platform that can resolve the aforementioned problems. In contrast to conventional plate-based ELISA, our optofluidic ELISA platform utilizes mass-producible polystyrene microfluidic channels with a high surface-to-volume ratio as the immunoassay reactors, which greatly shortens the total assay time. We also developed a low-noise signal amplification protocol and an optical signal quantification system that was optimized for the optofluidic ELISA platform. Our optofluidic ELISA platform provides several attractive features such as small sample/reagent consumption (< 8 µL), short total assay time (30-45 min), high sensitivity (~1 pg/mL for most markers), and broad dynamic ranges (3-4 orders of magnitude). Using these features, we successfully quantified mouse FSH (follicle stimulating hormone) concentration from a single drop of tail vein serum. We also successfully monitored bladder cancer progression in orthotopic xenografted mice with only < 50 µL of mouse urine. More excitingly, we achieved highly sensitive exosome quantification and multiplexed immuno-profiling with < 40 ng/mL of total input protein (per assay). These remarkable milestones could not be achieved with conventional plate-based ELISA but were enabled by our unique optofluidic ELISA. As an emerging member of the biomolecular sensor family, our optofluidic ELISA platform provides a high-performance and cost-effective tool for a plethora of applications, including endocrinology, oncology, cellular biology, and even forensic science research. In the future, this technology platform can also be adopted for clinical applications such as personalized cancer diagnosis/prognosis and rapid point-of-care diagnostics for infectious diseases.