Gold Coplanar Waveguide Resonator Integrated With a Microfluidic Channel for Aqueous Dielectric Detection

Abstract

This work presents the development of a coplanar waveguide based split ring resonator, integrated with a microfluidic channel suitable for liquid sensing applications. The sensor was fabricated via photolithography on a 0.5 mm borosilicate glass substrate with patterned gold. The microfluidic channel was aligned with the sensing area and bonded to the substrate to ensure consistent liquid volume ( $0.784~\mu \text{L}$ ) over the sensing region. The microwave sensor was $1.5\times 3$ cm2 and had a resonant frequency between 19.3 and 19.4 GHz, offering the advantage of measuring extremely small sample volumes. The performance of the sensor was validated through simulations and a series of experiments using a $\vert \text{Z}\vert $ -probe station. The sensor demonstrated a resonant amplitude sensitivity of -0.085 dB/vol.% for isopropyl alcohol in water (0-100 vol.%), 0.00023 dB/[mg/dL] for various glucose concentrations (50-1200 mg/dL), and 0.00056 dB/[mg/dL] for NaCl in water (50-1200 mg/dL, with equivalent Na+ 9 - 226 mEq/L solutions); measured under room ambient conditions (24 ± 1°C and RH: 36 ± 1 %).