Synthesis Of Symmetrical Bis-quaternary Ammonium Cationic Substituted Tetraphenylethene Fluorescent Probe And Its Research In Protein Detection

With the deep understanding of AIE mechanism,numerous AIE luminogens(AIEgens)have been exploited and the applications are extensively expanded in various research areas.Specially,tetraphenylethene(TPE)group is used as the representative building core of AIE molecule,which is characterized by simple structure and easy modification,and widely utilized to the design of sensing probes and photosensitizers.However,the water solubility of TPE group is very poor,which greatly limits the development and application in the field of biomedical science.Therefore,the development of highly soluble AIE fluorescent probe with tetraphenylethene-core is of significance to expand its application.When applying TPE AIEgens into fluorescence analysis,the detection sensitivity toward analyte is partially related to their structure.The cis configuration of disubstituted TPE derivate shows higher detection sensitivity than trans form in sensing application.In this study,a tetraphenylethene-cored,symmetrical and bis-quaternary ammonium substituted fluorescent probe(o-TPEDTA)with high water solubility was synthesized for the detection of casein with high sensitivity,and the mechanism of casein inducing o-TPEDTA fluorescence enhancement was investigated.The main research content of the paper is as follows:1)A symmetrical and bis-quaternary ammonium substituted AIE molecule with tetraphenylethene-core was designed and synthesized:o-TPEDTA.Through the study on the optical properties of increasing the proportion of poor solvents and changing the temperature and viscosity of the solution,o-TPEDTA was proved to have good AIE fluorescence characteristics and water soluble.The addition of protein into o-TPEDTA solution caused fluorescence increment,especially casein can produce more efficient and sensitive fluorescence.In order to explore the structural performance of o-TPEDTA,its fluorescence response to the protein was tested,and it was found that strong fluorescence could be detected when combined with casein,indicating that o-TPEDTA and casein have a strong interaction and have the potential to detect casein in aqueous solution.2)The fluorescence enhancement mechanism of casein inducing o-TPEDTA fluorescence enhancement was systematically studied and apply o-TPEDTA as a fluorescent probe to detect casein.Through dynamic light scattering,zeta potential and fluorescence spectrum tests,it was proved that the main reason for the fluorescence enhancement was not the self-aggregation of o-TPEDTA,and the effect of electrostatic attraction interaction was also excluded.By exploring the effect of casein micelle structure changes on o-TPEDTA luminescence,it was proved that the adsorption of o-TPEDTA into the cavity of casein micelle and the restriction of intramolecular motions(RIM)effect,leading to enhanced fluorescence.Through testing the fluorescence response of o-TPEDTA to casein concentration,solution pH and interferences,it is confirmed that o-TPEDTA has high sensitivity and high selectivity in detecting casein.Finally,o-TPEDTA was applied to evaluate casein in milk samples to verify the practicality of the probe.