Fig. 3: Differentiating molecule-specific information from complex analytes.

a Graphical representation of a gradient metasurface. The in-plane dimensions of the super-metaatom decrease gradually from left to right. b A plot of relative spectral efficiency versus the operating frequency. Comparative works are marked with numbers: dual-gradient metasurfaces (ref. ¹⁵), pixelated sensors (refs. ^25,44), gradient dielectric metasurfaces (refs. ^14,45). Our work is highlighted with an asterisk (*), showcasing the multiband (ref. ⁴⁶) and the gradient metasurface, respectively. In addition, we summarize and compare the literature in the Table S2. c Spatial barcode of the mixture (L-Glu, GABA and Gln) absorption extracted from the measured data. d, e Normalized simulated transmission spectra of a bare metasurface (color-encoded) with varying δ illustrating the continuous spectral coverage with resonant peaks. Each spectral line is obtained from a metasurface composed of periodically arranged microbars of the same size. The resonance highlighted in blue corresponds to the area marked with the same color in (a). The operating range of the device is about from 1.2 to 2.1 THz. f, g Normalized simulated transmission spectra of a metasurface covered with mixture analyte. Intensity modulations are observed at the characteristic absorption frequencies of the mixture.