Supramolecular Complexation of BeRST for Live-Cell Voltage Imaging

Voltage-sensitive fluorescent dyes enable optical measurements of transmembrane potential but can be limited by poor aqueous solubility, aggregation, and incomplete cellular membrane loading. Here, we evaluated supramolecular complexation as an approach to improve the imaging performance of the voltage-sensitive fluorophore Berkeley Red Sensor of Transmembrane potential (BeRST). BeRST was complexed with bovine serum albumin (BSA) and structurally distinct cyclodextrins (CDs), and its solution-phase photophysical properties and live-cell fluorescence intensity were assessed. Both host identity and concentration influenced the local environment of the BeRST chromophore, producing spectral changes consistent with reduced aggregation. In HEK 293T cells, the effects of complexation on mean cellular fluorescence intensity were likewise host- and concentration-dependent, with all hosts evaluated significantly enhancing mean cellular fluorescence intensity under at least one condition. The voltage sensitivity of complexed BeRST in live cells remains unchanged from noncomplexed BeRST, as determined by voltage imaging. Together, these findings show that CD complexation can tune the photophysical and cellular imaging properties of BeRST while preserving its voltage sensitivity, supporting supramolecular complexation as a strategy to improve the delivery and cellular brightness of lipophilic voltage-sensitive fluorescent dyes.