On-Demand Nanoliter Delivering Platform via Electrical-Activated Microdroplet Assembling.

Precise delivery of nanoliter-scale reagents is essential for high-throughput biochemical assays, yet existing platforms often lack real-time control and selective content fusion. Conventional methods rely on passive encapsulation or stochastic pairing, limiting both throughput and biochemical specificity. Here, we introduce an on-demand nanoliter delivery platform that seamlessly integrates electrical sensing, triggered droplet merging, and passive sorting in a single continuous flow. Leveraging impedance-based content detection, the system selectively identifies target droplets and initiates electrocoalescence-based fusion only when specific biochemical criteria are met. Fused nanoliter droplets are then sorted via size-dependent hydrodynamic deflection, enabling energy-free enrichment. Applied to bacterial screening, the system accurately distinguishes metabolically active droplets and could achieve over 6000 events per minute with postfusion purity exceeding 92%. This platform provides a label-free, high-precision solution for programmable nanoliter delivery, offering broad potential for drug discovery, synthetic biology, and single-cell analysis applications.