Fluorescence Behavior and Mechanisms of Poly(ethylene glycol) and Their Applications in Fe<sup>3+</sup> and Cr<sup>6+</sup> Detections, Data Encryption, and Cell Imaging
Chunqi Sun, Xubao Jiang, Bin Li, Shusheng Li, Xiang Zheng Kong
Abstract
In contrast to conventional fluorescent polymers featured by large conjugation structures, a new class of fluorescent polymers without any conjugations is gaining great interest in immerging applications beyond the possibility to achieve by the conjugated polymers. Poly(ethylene glycol) (PEG), widely used in biomedical fields for a long time owing to its nontoxicity and nonimmunogenicity, is found to be fluorescence emissive in the solid state and in aqueous solution, though deemed as not fluorescent in numerous reports. Through systematic study under different conditions, the emission is ascribed to the cluster formation of its chains; thereby the blue-shift of the emission with the excitation wavelength was interpreted through the Förster resonance energy transfer. The clusterization was ascertained through size measurements, Fourier transform infrared spectroscopy, NMR analyses, and the dependence on temperature, pH, and nonsolvent presence. Tested in the presence of competitive metal ions, selective emission quenching by Fe3+ and Cr6+ was observed. PEG was used as a sensor for the detection of Cr6+, Fe3+, and H2O2, outperforming most of the reported sensors alike. Its uses for data encryption and cell imaging were also presented. This work provides therefore a novel face of PEG with great potential in a variety of emerging applications, in particular, as sensors in the biomedical area.