An off-chip platform for on-demand, single-target encapsulation for ultrasensitive biomarker detection

Closed-channel microfluidic systems offer versatile on-chip capabilities for bioanalysis but often face complex fabrication and operational challenges. In contrast, free-boundary off-chip microfluidic platforms are relatively simple to fabricate and operate but lack the ability to perform complex tasks such as on-demand single-target sorting and encapsulation. To address these challenges, we develop an off-chip platform powered by a fluorescent-activated mechanical droplet sorting and production (FAM-DSP) system. The system integrates target detection, sorting, encapsulation, and on-demand droplet generation into a single compact platform, eliminating the need for microfabrication and minimizing the use of specialized fluidic control equipment. It achieves precise single-target encapsulation with a high efficiency of over 70%. Such a capability is applied for improving the performance of droplet digital enzyme-linked immunosorbent assay (ddELISA) by reducing the number of empty droplets and increasing the throughput, enabling precise quantification of target biomarkers with a low limit of detection. This versatile off-chip platform holds promise not only for biomarker detection but also for single-cell analysis and various applications in clinical diagnostics and biomedical research.