[en] This study reports the sensing of micro viscosity variation of Styryl 7(LDS 750) dye in different solvents and biological samples through thermal lens and fluorescence lifetime techniques. Fluorescence properties of Styryl 7 dye in different solvents and with DNA-CTMA (deoxyribonucleic acid attached with cetyltrimethyl-ammonium cationic surfactant molecules) were measured using fluorescence lifetime technique. Fluorescence lifetime of Styryl 7 in different solvents are found to increase with the viscosity of the samples. With increase in weight percentage of DNA-CTMA, the fluorescence lifetime increases from 0.17 ns to1.47 ns. Lifetime studies confirm that Styryl 7 dye is a good fluorescent probe for detecting the micro viscosity of the samples. Thermal lens technique, which is an efficient probe to measure non-radiative relaxation route were used to measure the thermal diffusivity of Styryl 7 in different solvents and with varying weight percentage of DNA-CTMA. Thermal diffusivity of the samples are found to decrease with increase in solvent viscosity and increased weight percentage of DNA-CTMA