Protein homeostasis (proteostasis) is the quality control mechanism cells use to maintain the function of the proteome. To study proteostasis in cells,a cysteine reactive solvatochromic maleimide dyes were designed and synthesized. The maleimide group enables targeting of the dyes to cysteine, which is usually buried in folded proteins but exposed when proteins unfold. In addition to target unfolded proteins, an electron donor-acceptor push-pull maleimide dye was found to be solvatochromic, making them of interest for probing cellular environments of proteins. NTPAN-MI was selected for detailed studies due to its compatible photophysical properties with excitation sources (405nm) in commonly used cell imaging instruments. The versatility of NTPAN-MI was demonstrated by the application to a wide range of experiments, including in-vitro study of protein kinetics studies and redox proteins with different cysteine reactivities, intracellular studies through confocal laser microscopy (CLSM) in combination with spectral phasor analysis for the observation of local environment polarity of bound proteins andr the quantification of unfolded protein load in cells.