Self-regulating pen-needle-based micronozzle for printing array of nanoliter droplets under fluorinated liquid

Abstract

High-throughput evaluation of materials and cells is crucial for scientific progress. Creating arrays of nanoliter (nL) droplets via contact printing offers an effective method for such evaluations. However, precise calibration between the printing tip and substrate is typically required, which can be time-consuming and affect printing quality. To address this issue, we developed a self-regulating microneedle based on a spring and pen needle and created an automated droplet printer using a Cartesian robot. The self-regulation mechanism eliminated the need for precise tip-substrate calibration. Nanoliter droplets were printed onto a Petri dish beneath a layer of perfluorocarbon (PFC) to maintain shape and prevent evaporation. Droplet volume (V) increased linearly with flow rate (Q) as V = 8.8 Q − 5.4 (nL, µL/min). Droplet volume decreased hyperbolically with robot speed (w) as V = 1613 w −1 + 14.3 (nL, mm/s), while the number of droplets produced per minute (N) increased linearly with speed as N = 2.0 w + 28.5. The system achieved a production rate of 42 droplets/min at 10 mm/s, scaling up to 180 droplets/min at 80 mm/s. This versatile platform enables nL-scale assays for various applications.