Evaluation of amplitude difference referencing technique with terahertz metasurfaces for sub-micron analytes sensing

Terahertz metasurfaces with subradiant modes that allow excitation of a high-quality factor are potential candidates for label-free sensing of thin-film biomolecules. Nevertheless, sensing sub-micron analytes are rather difficult due to the normalization method that has been used so far. Here, we evaluate an amplitude difference referencing technique that exploits the response of the uncoated metasurface structure as a reference. Amplitude difference percentage has been calculated by subtracting the frequency response of coated metasurface from the frequency response of the uncoated metasurface for different analyte thicknesses. To our surprise, we observe significantly large values of the amplitude difference that can be easily measured using conventional terahertz time-domain spectrometers. In future, this technique can be utilized to detect analytes with sub-micron thickness and could be exploited across the electromagnetic spectrum.