Fluorescence lifetime of pyrene butyric acid as a versatile sensing tool for monitoring self-assembled systems and microenvironment

Abstract

Sensing applicability of the fluorescence lifetime of pyrene butyric acid (PBA) to understand the aggregation behaviour and microheterogeneity of different charged self-assembled surfactants i.e., anionic (sodium dodecyl sulfate, ∼ 8.5 mM), cationic (Cetyltrimethylammonium bromide, ∼ 0.95 mM), and non-ionic (Triton X100, ∼ 0.27 mM) in aqueous solution is explored in this study. Time domain fluorescence decay of PBA is introduced for the first time as a sensitive tool for characterizing the molecular microenvironment and for predicting the aggregation behaviour of surfactants, including the monitoring low to higher-order aggregates. A non-extensive distribution analysis on the fluorescence decay profiles yields the fluorescence lifetime and Full Width at Half Maxima (FWHM), with the latter serving as an indicator of the heterogeneity of the molecular microenvironment of the 'fluoroprobe'.The analytical strength of the fluorescence lifetime of PBA as a sensing tool has been validated using biosurfactants sodium cholate (NaC) and sodium deoxycholate (NaDC) with high fidelity. Careful analysis of the non-extensive distribution of the lifetime of PBA displays a substantial sensitivity towards microheterogeneity in its immediate vicinity and hence monitors the higher-order aggregation behaviour of bile salts in aqueous medium.