Aim. To find out approaches for studying cellular functional state using new fluorescent squaraine probes. Methods. Dependence of fluorescence parameters of squaraine and polymethine dyes on the properties of their microenvironment in biomembranes was studied by microspectrofluorimetry. The quantitative microfluorimetry of single cells was applied for the evaluation of probes accumulation in cells and for investigation of dynamics of dyes photobleaching. Results. The data obtained evidence that a chromophoric part of the squaraine dyes molecules is mainly localized in a more polar microenvironment in biomembranes, as compared to the cationic polymethine probes. Conclusions. Chromophore of anionic squaraine probe in native membranes is located in the upper membrane layer in the region of polar phospholipids heads, while the cationic probes can penetrate deeper into the membrane. The anionic squaraine probe SqSC4 was determined as the most photostable dye among the investigated probes.

Keywords: emission spectra, squaraine probes, polymethine probes, biomembranes.