Barbiturate squaraine dyes as fluorescent probes for serum albumins detection

•Three squaraine cyanine dyes possessing in their structures moieties derived from barbituric acid was synthesized and fully characterized.•The potential as probes for HSA and BSA detection of the three squaraine cyanine dyes was studied.•The binding constants showed that the dyes have a strong interaction and high affinity for both proteins.•The zeta potential values revealed that the dyes are quite stable in aqueous media. Three indolenine-based barbiturate squaraine dyes were synthesized, characterized and subjected to photophysical studies, including their affinity with human serum albumin and bovine serum albumin as protein models in phosphate buffer solution. All dyes successfully interact with both proteins with high affinity binding constants. It was found that dyes with hydrophobic substituents had superior binding constants with both proteins. The fluorescence intensity of all dyes increased in the presence of both proteins which allowed the determination of detection and quantifications limits in the tens of nanomolar, using a protein concentration of 0–3.5 μM. Concerning to the study on the binding sites of the synthesized dyes using the warfarin and ibuprofen markers, the results of this study suggest that, one dye binds to both BSA binding sites while the two others dyes binds only to site I, and that all three dyes bind to both HSA binding sites.