Terahertz Metamaterial Sensor With Embedded Microfluidic Channels for Real-Time Liquid Analytes Sensing

The vibrational and rotational energy levels of numerous biological macromolecules fall within the terahertz (THz) range, making THz spectroscopy a viable method for identifying biological samples. However, most biomolecular activities can only be observed in a liquid environment. Being a polar substance, water exhibits strong absorption characteristics toward THz waves. In this study, we proposed a novel THz metamaterial sensor with embedded microfluidic channels fabricated in the PDMS substrate that operates in reflective modes. This approach not only enables the reduction of THz wave absorptions by water by decreasing the volume of the liquid sample but also realizes the real-time detection of liquid samples. Simulated results reveal that the double splits ring resonators (DSRRs) metal structure exhibits two resonant dips below 1 THz, with a maximum figure of merit of 0.77 RIU<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup>. Meanwhile, the sensors show significant resonant frequencies red-shifts as the refractive index for the analytes varies in the microchannels. Moreover, the split ring resonators with two gaps (SRRsTG) and DSRRs sensors were fabricated and demonstrated using a THz time-domain spectroscopy system. It has been found that the experimental results are in good agreement with the simulation results when the microchannels are empty (air). The sensors are capable of distinguishing various liquid analytes (e.g., water, acetone, and alcohol) by observing the shifts and amplitude variations for two resonant frequencies under different electric field polarizations. In addition, the DSRRs sensors show higher sensitivities in comparison to those of SRRsTG sensors, giving frequency shifts up to 92.1 GHz in TE mode and 192.3 GHz in TM mode for alcohol (99.7%) detections. The presented approach has been easily realized by standard lithography methods and could be applied to other metamaterial structures, as well as for biological sample detections.