Fig. 6: Concentration testing of various solutions.

a Measured absorptance spectra for ethanol aqueous solutions with concentrations decreasing from 40 to 0.5% (each repeated for 60 times). The inset shows the test tubes containing the respective solutions. The red arrows denote the trend of absorptance variation with increasing solution concentration. b Predicted ethanol concentrations using our random forest model. The inset provides an enlarged view of the prediction results at low concentrations. c Measured absorptance spectra for solutions of ethylene glycol in isopropanol with concentrations decreasing from 40 to 0.5%. d Predicted concentrations using our random forest model. e Measured absorptance spectra for glucose aqueous solutions with concentrations decreasing from 40% down to 0.1%. f Predicted glucose concentrations using our random forest model.