Terahertz sensing of L-Valine and L- Phenylalanine solutions

Abstract An asymmetric folded double-open ring of metasurface sensor based on the Fano resonance has been designed, with its resonant frequency matching the absorption peak of L-Valine at 1.7 THz. A mixture of water and glycerol in a volume ratio of 2:8 was proposed as a solvent to reduce the absorption of terahertz waves by water. A sample chamber with a controlled liquid thickness of (15 μm) was fabricated. A vertical incidence of terahertz time-domain spectrometer (THz-TDS) was constructed to allow solutions to be placed horizontally, and two different concentrations of amino acid solutions were subsequently measured. As the concentration of L-Valine solution varied from 0 to 20mM, the resonance peak of sensor shifted from 1.39 THz to 1.58 THz, demonstrating a concentration sensitivity of 9.98GHz/mM. The resonance peak shift in the L-Phenylalanine solution was not pronounced. It is speculated that the coupling enhancement between the solute absorption peak and the sensor resonance peak in the solution leads to an increased frequency shift, highlighting the distinctive sensing detection.