The shift of excitation spectra at blue edge of emission (BEEmS) as a new methodology to probe heterogeneity

Abstract

Many current methods for detecting molecular-level heterogeneity are complex and require stringent data analysis, limiting their widespread use. Herein, we propose a novel edge effect, i.e., the shift of excitation spectra at the blue edge of emission (which we termed as Blue Edge Emission Shift, BEEmS), to perceive the structural heterogeneity. This method is simple and can be easily implemented with commonly available fluorimeter. Red edge excitation shift (REES), a related technique, is already in use, but like most other known techniques, its usefulness is constrained by its dependence on environmental rigidity. Our method does not suffer from this drawback significantly. We showed the generality of the proposed method taking various chemically and biologically heterogenous systems including molecular liquid, deep eutectic solvents, organic cavitand, micelle and protein. BEEmS certainly comes out as a more effective sensor of heterogeneity than REES in certain cases (like denatured protein, hydrophobic deep eutectic solvent and SDS micelle) where solvation time is not sufficiently slow to be detected by REES, but can be measured though BEEmS. Furthermore, unlike most existing techniques, domain-specific heterogeneity of a model multi-domain protein is successfully measured.