Fig. 1: Concept of the THz plasmonic resonance-gradient metasurface.

Schematic diagram of the gradient metasurface formed by introducing variation of the geometrical parameters along the y-axes. The super-metaatom is an extension of the metaatom concept, constituting a composite unit structure composed of metaatoms with different functionalities (e.g., variable size). The electric field of the broadband excitation source is aligned with the varying long axis (x) of the microbars. The resonance frequencies are tuned over a continuous spectral range. Resonance frequency coverage enables continuous spectral mapping. Simultaneous enhancement and detection of changes in analyte absorption spectra are achieved by arbitrarily designing gradient microbars to promote broadband enhancement. The design enables overlap with the vibrations of the characteristic absorption bands of the L-glutamic acid(L-Glu), γ-aminobutyric acid (GABA) and glutamine (Gln). The platform works stably, allowing for real-time detection of dynamic changes in characteristic fingerprints and quantitative identification with the help of machine learning in multi-analyte systems. The machine learning process extracts multi-dimensional sensing information to identify molecules and distinguish the proportions of mixtures.