Research on polarization-chiral sensing of arginine based on S-shaped and X-shaped terahertz metamaterials

As fundamental building blocks of living organisms, amino acids impose stringent demands on the sensitivity and specificity of biosensing technologies owing to their low physiological concentrations and similar molecular structures. In this work, two THz metamaterials are designed and fabricated. The "S-shaped" resonator exhibits a resonance peak at 1.01 THz via electric dipole resonance, which closely matches the absorption peak of arginine (Arg) at 0.99 THz. The "X-shaped" resonator operates at 0.51 THz through a parallel magnetic dipole resonance. We performed chiral discrimination and concentration detection of Arg solutions using a terahertz time-domain polarization spectroscopy (THz-TDPS) system. Through the analysis of orthogonal polarization components and the calculation of chiral optical parameters, we achieved multi-dimensional sensing characterization that encompasses both polarization and chiral parameters. Experimental results demonstrate three key findings: (1) Across all parameter characterizations, the S-shaped sensor exhibits consistently higher sensitivity than its X-shaped counterpart for both D-Arg and L-Arg. (2) The sensitivity derived from the characterization of both polarization and chiral parameters is superior to that from frequency-shift. (3) Superior sensitivity is observed for chiral parameters over polarization parameters. Moreover, chiral characterization shows a pronounced response to enantiomeric differences. In contrast, frequency shift and amplitude parameters show no significant ability to discriminate between D- and L-Arg, and both sensors achieve a limit of detection (LOD) of 10^-5 mg/μL for the enantiomers. This study offers a reliable approach for chiral recognition and quantitative analysis of amino acids, which is vital for early biomedical screening and reliable quality control in the pharmaceutical industry.