Rapid prototyping of noncontact microwave microfluidic devices for sensing applications

Microfluidics is an innovative technological platform with a vast potential to streamline processes in biology, chemistry, and biomedical fields. Microfluidic integrated biosensors attract much attention due to extreme miniaturization, low sample consumption, and increased homogeneity in mixing conditions, leading to enhanced sensitivity. Nowadays, many researchers focus on inexpensive and flexible laser production of polymer-based microfluidic devices for sensing applications due to their ease of production and rapid processing benefits. In this article, we present some key factors for the simple and rapid production of microfluidic components of the microwave sensor by using the CO₂ laser ablation technique. The technique does not require any cleanroom or complex laboratory setups and provides short fabrication times for prototyping. It is observed that, at high laser power (30 W) and low scan speed (125 cm s⁻¹), both the channel depth and the surface roughness increase greatly as opposed to channel waviness. It is also demonstrated that heat treatment is a viable method to reduce the channel roughness with a trade of channel depth. In the second section, prepared channels are bonded onto the split ring resonators (SRRs) fabricated using polymethyl methacrylate as a substrate. Power reflection measurements from SRR are performed using a continuous flow system that injects 100 mM glucose solutions into the channels. Change of dielectric constant due to glucose loading generates a meaningful resonance frequency shift, showing a possible use scenario of the device as a biosensor. (technical note)