Dual-mode droplet rolling strategy: mimicking Earth's rotation and revolution for dual-cycle synergy in the efficient capture and controlled release of trace targets

Abstract

Current microchips functionalized with antibodies or aptamers primarily enhance the capture and detection efficiency of single targets in microfluidics by refining microchannel designs or developing functional enhancement materials. However, strategies to extend the interaction path for efficiency optimization remain underexplored, as they may cause elevated hydraulic pressure and fluid shear forces within the microchannels, and the potential for path extension is inherently limited. This study introduces a novel dual-mode droplet rolling strategy, mimicking Earth's rotation and revolution, which employs a closed-loop patterned superwetting chip to achieve efficient capture of trace biological targets in gravity-driven droplets. Specifically, the external cyclic motion in the “revolution” mode greatly extends the interaction path between the droplet-contained targets and the active interface. Meanwhile, the internal cyclic vortex flow in the “rotation” mode markedly increases the contact frequency between droplet-contained targets and the active substrate. Consequently, the dual-cycle synergistic amplification significantly enhances the effective contact opportunities between the targets and the functionalized closed-loop track, thereby markedly improving target capture efficiency. As a proof of concept, we demonstrate the specific and efficient capture of both micron-sized polystyrene microspheres (6 μm and 15 μm) and nanoscale AuNPs (50 nm) through multilayer modification of the superslippery track, highlighting the platform's versatility for targets of varying sizes. We achieved 91.3% capture efficiency for circulating tumor cells (MCF-7 cells, ∼20 μm), underscoring the chip's high efficiency in specific target capture. Furthermore, we showcase the strategy's applicability throughout the entire workflow, encompassing efficient capture, controlled release, immediate recovery, and downstream cultivation using pathogenic bacteria (E. coli, ∼1 μm). This strategy holds significant promise for detecting tumor markers and pathogens in body fluid samples, offering an innovative approach to capture-based diagnostics.