In one aspect, the disclosure relates to methods of label-free surface-enhanced Raman spectroscopy (SERS) comprising plasmonically enhanced electronic Raman scattering (ERS) signals from metal nanostructures as an internal calibration standard to improve multivariate analysis of living biological systems, and the uses of the methods therein. This abstract is intended as a scanning tool for purposes of searching in the particular art and is not intended to be limiting of the present disclosure.