Transparent SU-8 Micronozzle Array with Minimal Dead Volume for Parallel Liquid-to-Liquid Sample Ejection

High-throughput biological and chemical assays increasingly require parallel sample manipulation using arrays of micronozzle apertures. Liquid-to-liquid ejection avoids air–liquid interfaces, thereby reducing sample evaporation and mechanical stress while simplifying device operation. However, existing microfluidic platforms for parallel handling suffer from high dead volume, limited optical access, and poor scalability due to thick structural layers. Here, we present a transparent three-layer 4 × 4 micronozzle array with 40 μm diameter openings and a photolithographically fabricated SU-8 membrane. Our sacrificial layer process yields a 30 µm SU-8 membrane—approximately a 70% reduction in thickness—thereby lowering vertical channel dead volume and eliminating the need for costly glass etching. The resulting architecture enables parallel particle and nanoliter liquid manipulation with real-time optical clarity and enables water-to-water ejection, avoiding air–liquid interfaces. This work demonstrates the water-to-water ejection of 0.5–10 µm microparticles using a transparent, low-dead volume SU-8/PDMS micronozzle array and provides a basis for future studies on substrate deposition and cell handling workflows.