Portable microfluidic platform employing Young–Laplace pumping enabling flowrate controlled applications

Abstract

Facile, customizable platforms are important for a variety of microfluidic applications. This work presents a platform that utilizes surface tension induced pumping based on Young–Laplace pressure. The approach allows modifiable transport of fluids across surfaces without external pumping modules. The Laplace-chip is based on a superhydrophobic coating (NeverWet™) that is patterned by laser micromachining. For fast and consistent deposition of specific liquid volumes/droplets onto the “Laplace-chip” without the need for conventional fluid dispensing tools (e.g. pipette), a multiplexed droplet factory (MDF) was developed. The MDF is placed above the Laplace-chip and consists of cylindrial reservoirs that are filled by a “pour and swipe” approach. It enables the formation of hundreds of droplets (10–140 µL, 7.3% deviation) with both position and volume control as well as the simultaneous initiation of Young–Laplace induced pumping on the Laplace-chip. Furthermore, the flowrate of Young–Laplace induced pumping is adjustable through different pattern designs and dispensed droplet volumes. The Laplace-chip and MDF is used to carry out silver nanoparticle and nanocluster synthesis, where the reagent introduction rate is critical to material properties, to demonstrate flowrate controlled application possibilities. A Laplace-chip employing different channel length is employed to carry out the reduction of Ag⁺ to Ag⁰, using NaBH₄. Low reducing agent concentrations and long pumping times (40–60 min) resulted in molecule-like silver cluster (AgNC) synthesis, while high reducing agent concentrations and short pumping times (5–20 min) led to the synthesis of silver nanoparticles (AgNPs).