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The ability to conduct diagnostic functions on a single chip has long been of interest to the medical community. Decentralization of laboratories combined with reduced costs, increased speed and a higher throughput of potential assays are all driving forces for lab-on-a-chip technology. The small chip sizes facilitate low sample volumes, which in turn allow better control of the molecular interactions close to the sample surface. The design and quality of transducers, microfluidics and functionalization processes have all improved over recent years. Despite the growing interest for lab-on-a-chip components, several challenges remain. Combining all three disciplines into a high-quality well-functioning chip that is cheap to fabricate while providing reproducible results is challenging. A project attempting to address these challenges is presented. The main goal is to design and fabricate a labon-a-chip silicon photonic biosensor with multiple channels for detection of antigens with improved sensitivity and selectivity compared to state-of-the-art. As a proof-of-concept, the sensor is designed for simultaneous detection of three distinct antigens: C-reactive protein (CRP), lipocalin and tumor necrosis factor (TNF). The main challenge lies within their respective concentrations as well as the specificity for each analyte, where concentrations vary from the mg/ml to pg/ml regime. Multiplexing is achieved by using photonic crystal resonators, which function as drop-filters, allowing for single input/output while simultaneously probing select transducers that are functionalized for different chemistries. The individual resonator designs facilitate different limit-of-detections (LODs) and dynamic ranges for each analyte. Preliminary results from the first single channel prototype are presented, while work on the multiplexed sensor continues.
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