Enhancing terahertz circular dichroism spectrum of amino acid chiral enantiomers by all-dielectric metasurface

Abstract

The detection and identification of chiral substances have a wide range of applications, recently, using THz chiral spectroscopy to identify chiral biomolecules has attracted much attention. However, since the weak response, the difference between chiral enantiomers is not obvious only by THz chiral spectroscopy. To solve this problem, we combined THz time-domain polarization spectroscopy and all-dielectric metasurface to enhance the chiral spectroscopy of amino acids. The circular dichroism (CD) spectra of three pairs of amino acid chiral enantiomers were detected and compared by this method. Our results show that CD spectra of the amino acids are enhanced by the metasurface. L-Arg achieves a maximum chirality enhancement factor of 97.15 around 1 THz. For the recognition between L- and D- enantiomers, Cysteine has a maximum CD difference degree of 34.22°, which is 11.4 times higher than that without metasurface. Moreover, we also investigated the effect of amino acid concentration on chirality, founding that THz chirality was suppressed by high concentrations. Therefore, this metasurface sensor with the chiral sensing method has great potential in improving the THz chirality response of amino acids and distinguishing their chiral enantiomers with high sensitivity, which will provide new understanding and development in THz biophysics and biochemistry.