Preparation Of Water-soluble Chemosensor Systems And Their Application In Fluorescent Detection

Many ions and biomolecules play important roles in environmental and biological fields, design and synthesis of fluorescent sensors for these substances’ detection is of great significance. Without the use of any organic solvents, water-soluble fluorescent sensor systems can avoid the interference of solvents and reduce biological toxicity, so they display better application potential.In this paper, we prepare three kinds of water-soluble fluorescent sensor systems by using electroneutral hydrophilic polymer, zwitterionic compound and polyelectrolyte respectively, and successfully realize quantitative detection for some important ions and biomolecules.First, we demonstrate a robust fluorescent turn-on sensor for detecting fluoride ion in totally aqueous solution. In this study, a biocompatible hydrophilic polymer poly(ethylene glycol)(PEG) is incorporated into the sensing system to ensure water solubility and to enhance biocompatibility. Then, tert-butyldiphenylsilyl(TBDPS) groups were covalently introduced onto fluorescein moiety, which effectively quenched the fluorescence of the sensor. Upon addition of fluoride ion, the selective fluoride-mediated cleavage of Si-O bond leads to the recovery of the fluorescein moiety, resulting in a dramatic increase in fluorescence intensity under visible light excitation. The sensor is fast-responding and highly selective for fluoride anion over other common anions; it also exhibits a very low detection limit of 19 ppb. In addition, this sensor is operative in some real samples like running water, urine and serum, and it can accurately detect fluoride ions in these samples. The cytotoxicity of the sensor was determined to be Grade-I toxicity according to United States Pharmacopoeia and ISO 10993-5, suggesting the very low cytotoxicity of the sensor. Moreover, it was found that the senor could be readily internalized by both He La and L929 cells and the sensor could be utilized to track fluoride level change inside the cells.Second, we synthesize a water-soluble, low-cytotoxic and sensitive fluorescent sensor for detecting sulfide anion. In this probe, the strong electron-withdrawing dinitrobenzenesulfonate ester group is incorporated onto fluorescein fluorophore, and correspondingly the fluorescence of fluorescein is efficiently quenched; while when the dinitrobenzenesulfonate ester is cleaved by the nucleophilic sulfide anion, the substantial fluorescence enhancement can be observed. The probe is capable of permeating the cell membrane and realizing sulfide anion monitoring and imaging in live cells and real sample.Third, we report the first betaine-based sulfide anion fluorescent sensor, which features excellent water solubility, low cytotoxicity and short response time. This sensor is based on the chelator/Cu(II) approach so as to achieve fast sensing, in which tris(2- aminoethyl)amine is selected as the Cu(II) chelator since this tripodal chelator can strongly bind with Cu2+. Two sulfobetaine groups, which are utilized to achieve water solubility and biocompatibility, are incorporated onto the sensor. The fluorophore-chelator-Cu(II) complex functions as the sulfide sensor which exhibits very low fluorescence, and sulfide anion can extract Cu2+ from the sensor since sulfide anion can form very stable Cu S with Cu(II), resulting in fluorescence enhancement. With two betaine groups and a tripodal chelator in its structure, the sensor exhibits excellent water solubility and low cytotoxicity, and is capable of permeating the cell membrane and realizing sulfide anion imaging in live cells. The sensor displays high selectivity and low detection limit of 1.1 mM, and can be used for sulfide monitoring in such real sample as running water.Finally, the first ratiometric fluorescent sensing system for ALP was designed. This sensing system consists of two components: the betaine-modified and positively-charged polyethyleneimine(PEI) and the negatively-charged pyrene derivative containing one ALP-responsive phosphate group(Py-P, an aliphatic phosphate ester). In the absence of ALP, the two-component sensing system shows the excimer’s emission of Py-P, since Py-P molecules complex with the positively-charged polyelectrolyte via electrostatic interactions, leading to the formation of pyrene excimers. While in the presence of ALP, the phosphate moieties are cleaved from Py-P molecules due to the enzymatic reaction, thereby destroying the electrostatic interactions; as a result, the system displays the monomer emission of Py-P. This assay system is operable in aqueous media with a very low detection limit of 0.1 U/m L. The system is capable of detecting ALP in such biological fluid as serum, and this strategy may provide a new and effective approach for designing ratiometric sensing systems for detecting other biomolecules.