Chiral identification of lactic acid enantiomers by an achiral terahertz metasurface sensor

Lactic acid (LA) plays an essential role as a biochemical indicator in life, the detection and identification of chiral LAs have a wide range of applications. A method to detect chiral LA enantiomers (D-LA and L-LA) by using an achiral terahertz (THz) electromagnetically induced transparency (EIT) metasurface sensor is proposed. The chiral enantiomers of LA samples are measured, and the chiral parameters are extracted from the circular polarization transmission coefficients, theoretical analysis and experiment are combined to verify the principle of the achiral sensor to recognize the chiral LAs. The quantitative and qualitative recognition of LA enantiomers can be realized by the significant difference in the transmission spectrum at the characteristic frequency. The limit of detection reaches 0.01 μg/mL, and the sensing sensitivity of L-LA, D-LA, and DL-LA (achiral, racemate) is 0.28 THz/(mg/mL), 0.07 THz/(mg/mL) and 0.13 THz/(mg/mL), respectively. The proposed method can be further extended to a wide range of chiral bio-samples, showing a great potential in biomedical applications, food safety inspection, and environmental monitoring.