A microwave resonator integrated on a polymer microfluidic chip

[Display omitted] •A novel stacked split-ring type MW resonator integrated into a microfluidic chip is proposed.•Precise positioning and handling of volume-limited samples for EPR experiments at X-band frequencies.•The resonator is characterised by FEM simulations and RF measurements as well as spatial EM mode mapping.•Spin sensitivity of the resonator has been evaluated on MTSL spin label dissolved in DMSO.•Application to time-resolved EPR spectroscopy on light-induced triplet states in pentacene. We describe a novel stacked split-ring type microwave (MW) resonator that is integrated into a 10mm by 10mm sized microfluidic chip. A straightforward and scalable batch fabrication process renders the chip suitable for single-use applications. The resonator volume can be conveniently loaded with liquid sample via microfluidic channels patterned into the mid layer of the chip. The proposed MW resonator offers an alternative solution for compact in-field measurements, such as low-field magnetic resonance (MR) experiments requiring convenient sample exchange. A microstrip line was used to inductively couple MWs into the resonator. We characterised the proposed resonator topology by electromagnetic (EM) field simulations, a field perturbation method, as well as by return loss measurements. Electron paramagnetic resonance (EPR) spectra at X-band frequencies were recorded, revealing an electron-spin sensitivity of 3.7·1011spins·Hz-1/2G-1 for a single EPR transition. Preliminary time-resolved EPR experiments on light-induced triplet states in pentacene were performed to estimate the MW conversion efficiency of the resonator.