A novel THz molecule-selective sensing strategy in aqueous environments: THz-ATR spectroscopy integrated with a smart hydrogel.

Terahertz (THz) spectroscopy, with fascinating advantages for biomedical applications, is still in its infancy in terms of the selective detection of aqueous biomolecules because the strong absorption of solvent water always obscures the THz spectroscopic features of biomolecules. Nevertheless, solvent water is not a passive spectator but a useful indicator, as this proposed strategy describes. This strategy utilizes THz attenuated total reflection (THz-ATR) spectroscopy to probe the glucose-induced hydration state changes of smart hydrogels for label-free and selective detection of aqueous glucose. A notable dramatic increase in both the THz absorption coefficient and hydration state (calculated by weighing) of the smart hydrogel was observed with increasing aqueous glucose concentration, which was further verified by a simple two-component model. For aqueous glucose sensing, this method surpasses individual THz-ATR devices and exhibits suitable sensitivity, ideal selectivity and excellent reusability. Moreover, the proposed strategy may provide an alternative option for the selective detection of various aqueous molecules by THz spectroscopy.