A wire-based capillary ratchet biosensor for microgravity applications

To address the challenges of health monitoring during long-duration space missions, this study develops a novel biosensor based on the capillary ratchet effect. The sensor features a tunable microchannel constructed from three wires, which generates a Laplace pressure difference by modulating the channel width, thereby driving droplets to advance unidirectionally. By recording the time required for droplets to traverse a unit distance, rapid analysis of the physicochemical properties of liquids can be achieved. Experimental results demonstrate that the sensor attains a resolution of 0.5 mPa s and a detection limit of 0.4445 mPa s for polyethylene glycol (PEG) solution viscosity measurement, enabling naked-eye readout. Using Ca2+ as a model target, rapid detection across the 0.1–10 mM concentration range was achieved with a sample volume of only 5 μL (3 min), yielding a detection limit as low as 0.07544 mM. By employing biomimetic microstructures, this design innovatively overcomes the challenges of fluid manipulation and bubble elimination under microgravity. Its miniaturized architecture (3) and pump-free operation provide a new paradigm for developing automated, low-power biochemical detection systems for use in orbit, holding strategic significance for life-support assurance in deep-space exploration.