Fig. 2

Concentration gradient change of the L-hydroxyproline spectrum. a THz absorption spectra of L-hydroxyproline samples at different concentrations measured experimentally. b Absorbance at 0.73 THz (square), 1.13 THz (circle) and 1.78 THz (pentagram) for different concentrations of L-hydroxyproline samples. c The area under the absorption peaks of all L-hydroxyproline samples; error bars have been labelled on each data point