A simulation study on the influence of energy migration and relative interaction strengths of homo- and hetero-FRET on the net FRET efficiency

Förster resonance energy transfer (FRET) is a powerful method for probing biomolecular conformations and dynamics in bulk as well as at a single-molecule level. FRET utilizes non-radiative mechanisms to transfer energy between fluorophores, donor and acceptor when placed in close proximity. The FRET efficiency has a strong distance dependence and serves as a direct read-out for molecular interaction. In case of a significant overlap of donor emission and absorption spectra, the excited state energy can be exchanged between the identical donors in close proximity, which eventually migrates back and forth until it gets dissipated. This form of energy transfer is called energy migration or homo-FRET. Here, we have simulated FRET efficiency by considering the donor-donor interaction strength (ξ_DD) and donor-acceptor interaction strength (ξ_DA) under conditions of non-uniform distribution of molecules. Our earlier studies indicate that energy migration modulate the FRET efficiency for various values of ξ_DD and ξ_DA. We, therefore, determined the limiting values of acceptor concentration (C_LA) that will allow the determination of FRET efficiency in the absence and presence of energy migration. Taken together, our study optimizes the conditions for meaningful FRET efficiency for a given FRET pair for better reporting of molecular interactions.