A Silicon Resonator Sensing Platform with Integrated Microfluidic Concentrator for Label-Free Detection of Biomarkers at High Speed and Sensitivity

In this study, we report a highly sensitive label-free biosensing platform combining an electrokinetic concentrator with a silicon microring resonator in a microfluidic chip. Electrokinetic concentration of biomolecules increases the concentration of charged biomolecules locally on the microring resonator inside a microfluidic channel and enhances the detection speed and sensitivity. Based on this unique combination of electrokinetics and silicon photonics, we have built an ultrasensitive label-free sensing platform in a multiplexed format for a direct and rapid analysis of various biomarkers such as DNA and RNA molecules that are becoming increasingly important in liquid biopsy. In our electrokinetic concentration scheme, two reservoirs are connected by both a conductive polymer membrane, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), directly printed on top of a polydimethylsiloxane (PDMS) microfluidic channel. For integration, the microfluidic concentrator chip is aligned and reversibly sealed with a silicon substrate containing an array of microrings. We demonstrated the performance of this hybrid optofluidic-electrokinetic sensing platform for DNA from an initial concentration of C₀ = 100 nM and its enhanced hybridization result on MO (“Morpholinos”, a class of uncharged DNA mimics) capture probes. Our result validated the effectiveness of electrokinetic concentration for MO-based detection of DNA, leading to significantly faster DNA hybridization to MO capture probes even in the sub-nanomolar target concentration regimes that usually require extensive incubation times or simply remain undetectable. Once fully developed, our multiplexed concentrator-enhanced micro resonators could become an indispensable tool to detect genes expressed at even very low levels more rapidly and reproducibly.