Smart Microfluidic Analogue of Wheatstone-Bridge for Real-Time Continuous Detection with Ultrasensitivity and Wide Dynamic Range

Abstract Real-time continuous detection of analytes such as environmental toxins is of great significance for myriad applications, ranging from environmental protection to warfare analysis. Efficient signal conversion and amplification are crucial for achieving real-time continuous detection with ultrasensitivity and wide dynamic range. Inspired by the electrical Wheatstone-bridge, a smart microfluidic analogue of Wheatstone-bridge (SMAW) with stimuli-responsive microgel as a variable flow-resistor is developed for such high-performance detection. Similar as current in Wheatstone-bridge, microflows in the SMAW microchip with well-designed microchannel sizes enables new mechanisms to efficiently convert and amplify minute volume changes of microgel induced by trace analytes, into significant width changes of indicating flow as easily measurable output. The typical use of SMAW microchip is highlighted by real-time continuous detection of Pb2+ using a simple optical microscope, with wide dynamic range (10-7 M∼10-14 M) and ultra-low detection limit (10-14 M, the lowest one reported to date). This Pb2+-detection also enables fast response, high selectivity, low sample volume, and easy-to-use protocol. The extraordinary SMAW microchip is general and can be extended to detect myriad analytes due to the wide choices of stimuli-responsive hydrogels, thus opening brand-new areas for developing high-performance microfluidic detectors.