Design And Synthesis Of Organic Molecule Based Fluorescent Probes And Their Biomedical Applications

With the introduction of laser technique and nanomaterials,fluorescence analysis has been rapidly developed and widely used in biomedical science.As an indispensable tool of fluorescence analysis,appropriate fluorescent probes are vital for the improvement of the selectivity and sensitivity of fluorescence analysis and its applications in bioanalysis.Small organic molecule-based fluorescent probes have advantages including easy to synthesis,low cost and easy to operate,etc.However,organic fluorescent probes used in bioanalysis usually suffer from the complex biological environment,which influences their sensitivity and selectivity greatly.As a result,it is essential to synthesize organic fluorescent probes with high sensitivity,high selectivity and good photophysical properties which can be further used in biomedical science.In order to overcome the poor selectivity,sensitivity and photostability of some current fluorescent probes,we have designed and synthesized some new organic fluorescent probes for bioanalysis.Details are as follows:1.We have synthesized a ratiometric fluorescent probe R1 by Miyaura borylation,which has a naphthalene-benzoxazole fluorophore as the reporter and an arylboronate group as the recognition unit.Conventional arylboronate probes are usually highly selective to H2O2.Surprisingly,different from conventional arylboronate probes,R1 is highly selective to CIO-.Detailed mechanistic studies reveal that R1 reacts with CIO-through an oxidation to chlorination mechanism.After the oxidation reaction,boronate moiety is removed and the fluorescence color shows no obvious changes.The chlorination reaction further results in an apparent red shift of fluorescence of R1.In contrast,R1 can only react with H2O2 through an oxidation mechanism,which will not change the fluorescence.Other ROS cannot react with Rl,indicating high selectivity of Rl to ClO-.Besides,Rl is highly sensitive to CIO-,and the detection limit is determined to be 6.4 nM.Arylboronate not only plays the role as a reporter,but also acts as a "lock" to eliminate the influences of pH fluctuations.Although Rl reacts with CIO-through a multistep reaction mechanism,it reacts with ClO-very fast(only about 2 min).In addition to its merits,such as high sensitivity,selectivity,pH tolerance and fast response speed for CIO-detection,Rl is also highly photostable.These results indicate that Rl is a promising fluorescent probe for bioanalysis.2.Fluorescence emissions from conventional fluorescent probes are often quenched at high concentrations,which is known as aggregation caused quenching(ACQ).Photophysical properties of these fluorescent probes are easily affected by their concentrations.They often show strong background fluorescence and poor photostability.All of these limit the applications of fluorescent probes in biomedical science.Herein,we have synthesized a pH-sensitive AIE(aggregation-induced emission)fluorescent probe TPE-Leu,which has a tetraphenylethene(TPE)fluorophore as the reporter and an amine moiety as the site for acid-base reactions.Different from conventional fluorescent probes,TPE-Leu is non-emissive when molecularly dissolved but highly emissive when aggregated,which eliminates the influence of background fluorescence and is favorable for its applications in bioanalysis.TPE-Leu has an aliphatic amine and an aromatic amine.It is insoluble under alkaline condition and shows strong fluorescence.Under acidic condition,the aliphatic amine is protonated since the aliphatic amine is more alkaline than the aromatic amine,which makes TPE-Leu more soluble and decreases its fluorescence intensity.In addition,TPE-Leu shows highly selective response to the pH values over other potentially competing species like metal ions and biomolecules coexisting in the sample.TPE-Leu has also been used for selective detection of enzymes like AChE and Urease.