Complementary Split-Ring Resonator for Microwave Heating of µL Volumes in Microwells in Continuous Microfluidics

This work presents the design and evaluation of a planar device for microwave heating of liquids in continuous microfluidics (CMF) made in polydimethylsiloxane (PDMS). It deals with volumes in the µL range, which are of high interest and relevance to biologists and chemists. The planar heater in this work is conceived around a complementary split-ring resonator (CSRR) topology that offers a desired electric field direction to—and interaction with—liquids in a microwell. The designed device on a 0.25 mm thick Rogers RO4350B substrate operates at around 2.5 GHz, while a CMF channel and a 2.45 µL microwell are manufactured in PDMS using the casting process. The evaluation of the performance of the designed heater is conducted using a fluorescent dye, Rhodamine B, dissolved in deionized water. Heating measurements are carried out using 1 W of power and the designed device achieves a temperature of 47 °C on a sample volume of 2.45 µL after 20 s of heating. Based on the achieved results, the CSRR topology has a large potential in microwave heating, in addition to the already demonstrated potential in microwave dielectric sensing, all proving the multifunctionality and reusability of single planar microwave-microfluidic devices.