Minimal microfluidic metamaterial sensor for concentration detection

The design of high sensitivity and minimal size sensors for liquid concentration detection has significant importance in biomedical and chemical engineering. In this paper, we present a microfluidic liquid sensor for concentration detection based on metamaterial, with a minimal size of 20 x 16 mm2. The sensor consists of a modified square split-ring resonator (SRR) and a microstrip transmission line (MTL), integrated with a microfluidic device. The operating frequency of the sensor is 4.38 GHz. Experimental results demonstrate that the resonant frequency of the water-ethanol mixture with concentrations ranging from 0 to 100 % has a linear shift of 290 MHz. A mathematical model is established by examining the relationship between the transmission parameters and the complex dielectric constant, the maximum deviation between the ethanol solution concentration predicted by this model and the actual concentration is 0.5 %. The sensor exhibits a sensitivity of 2.14 x 10<^>-3 dB/(mg/dL) to aqueous glucose solutions with 0---400 mg/dL. A fitting formula is derived from the transmission parameters to predict unknown concentrations of aqueous glucose solutions, could detect the change of 1 mg/dL glucose solution accurately with a maximum error of 0.7 %.