Liquid metal-based terahertz metamaterial sensors with integrated microfluidic channels for sensitive biosensing applications

In this paper, we designed, fabricated, and experimentally validated liquid metal (LM)-based terahertz (THz) metamaterial (MM) sensors in the THz frequency range. The sensor consists of two layers of embedded microfluidic channels filled with liquid metal (LM) and liquid analyte, respectively, where the LM layer functions as the MM resonators. By designing different resonant structures (MM-1 and MM-2), different desired sensing effects can be obtained theoretically and experimentally. The finite integral method (FIT) was used to verify the resonant characteristics of the sensors, where the simulated results show that MM-1 gives a sensitivity of 46 GHz/RIU and a figure of merit (FOM) of 0.98, while MM-2 exhibits a quality factor (<i>Q</i>) of 14.11. The sensors were fabricated by traditional lithography and characterized by a THz time-domain spectroscopy system (THz-TDS) for bovine serum albumin (BSA) and glucose solution detections. The experimental results reveal that the resonant frequencies show significant redshifts when the concentrations of BSA and glucose solution increase. For the MM-1 sensor, the limit of detections (LODs) for BSA and glucose solutions are 0.13 mg/mL and 1.31 mmol/L, respectively. For the MM-2 sensor, the frequency shift reaches 80.2 GHz when the concentration of BSA is as high as 10 mg/mL, and the LODs for BSA and glucose solutions are 0.19 mg/mL and 2.37 mmol/L, respectively. The sensors exhibit the merits of small size, easy operation, and fast detection speed, and show the potential for rapid concentration measurement, biomolecular detection, and disease diagnosis in the biomedical field.