Investigating the relationship between composite multiscale entropy and optical property of bovine serum albumin solutions using THz pulsed system

Abstract We investigated the relationship between composite multiscale entropy (CMSE) and absorption coefficient, refractive index within the terahertz (THz) region by using six concentrations (5000, 1000, 500, 50, 10, and 5 µg/ml) of bovine serum albumin (BSA) aqueous solutions. Variational mode decomposition (VMD) method served as a preprocessing tool was attempted to introduce to decompose THz signal into three mode functions. An exhaustive search optimization with the criteria of maximizing coefficient of determination and minimizing the error bars for linear fitting was conducted to select the parameter of controlling bandwidth in VMD. The results demonstrate a number of linear models can validate the linear relationship between the selected sample entropy and absorption coefficient, refractive index at specific frequency. Additionally, the nonlinear behavior between the selected sample entropy and concentration of BSA is similar to that between absorption coefficient and concentration. The bridge between THz optical properties of the material and CMSE is established preliminarily.