ER-Lite(TM) Blue-White DPX *Cell-Permeable*

ER-Lite(TM) Blue-White DPX is a highly photostable, environment-sensitive fluorescent probe designed for selective imaging of the endoplasmic reticulum (ER) in live cells. As a member of the Dapoxyl(TM) (DPX) dye family, it exhibits a large Stokes shift, high extinction coefficient, and exceptional quantum yield, making it an optimal tool for fluorescence microscopy. With an excitation maximum at approximately 374 nm, ER-Lite(TM) Blue-White DPX emits across a broad spectral range (430-640 nm), facilitating visualization using standard DAPI or UV long-pass optical filters. This probe demonstrates superior selectivity for the ER, with minimal off-target labeling of mitochondria, unlike conventional ER stains such as DiOC6(3). Its cell-permeant nature enables efficient intracellular uptake, and it remains non-cytotoxic at low working concentrations. The fluorescence properties of ER-Lite(TM) Blue-White DPX are highly environment-sensitive, shifting to longer emission wavelengths as solvent polarity increases while exhibiting a concomitant decrease in quantum yield. These characteristics allow for the study of ER organization and dynamics under various physiological conditions. ER-Lite(TM) Blue-White DPX is also compatible with two-photon microscopy, expanding its applicability for high-resolution, deep-tissue imaging. While aldehyde fixation partially retains staining patterns, significant fluorescence signal loss should be anticipated. When used according to the optimized staining protocol, ER-Lite(TM) Blue-White DPX enables high-contrast, high-fidelity visualization of the ER, making it a valuable tool for investigating ER structure, function, and its involvement in cellular homeostasis and stress responses.