ABSTRACT
A fluorescent sensing system based on a conjugated polyelectrolyte was constructed to detect dopamine (DA) in complex samples. The conjugated polymer PFPE-PBA with poly[fluorenyl-alt-p-phenyleneethynylene] (PFPE) as the backbone and carrying four pendant phenylboronic acid (PBA) groups in each repeat unit was synthesized. PFPE-PBA was found to have good solubility in polar solvents. After optimization, glycine-NaOH at pH 10 was selected as the buffer, and the solvent composition of the system was set to methanol/water (9/1 by volume). Titration experiments showed that DA could effectively quench the fluorescence of the polymer solution with a response time within 60 s and a limit of detection of 23 nM. Polyols, cations, and other possible interfering substances do not significantly affect the fluorescence of the polymer, thereby allowing for the highly selective detection of DA. Furthermore, quantitative determination of DA in spiked serum and artificial urine samples was successfully demonstrated, with recoveries ranging from 96.7 to 104%. Preliminary mechanism studies suggest that the pedant PBAs capture DA via reaction with the catechol group, and the fluorescence quenching is most likely due to the photoinduced electron transfer between the aromatic part of DA and the conjugated backbone. This study provides a general strategy for the future design of conjugated polyelectrolyte-based sensing systems.
ABSTRACT
Developing a new anti-counterfeiting strategy is of great significance to combating the global counterfeiting problem. Here we report the construction of a dynamic fluorescence response system for anti-counterfeiting by combining the photochromism induced by the ring-opening of spiropyran (SP) to merocyanine (MC) with the fluorescence resonance energy transfer (FRET) between the conjugated polymer and MC. After elucidating the design principle, a new conjugated polymer, PPETE-SP, consisting of a poly[p-(phenylene ethynylene)-alt-(thienylene-ethynylene)] (PPETE) backbone with pendant SP, was synthesized and characterized. With poly(methyl methacrylate) (PMMA) as the matrix, the PPETE-SP/PMMA fibrous membrane was prepared via electrospinning. Under the irradiation of UV light, the fluorescent color of the membrane dynamically changed from green to light green, then light pink, and finally pink, and this process was reversible under visible light. The fluorescence emission switch was examined for 10 cycles and proved to have good repeatability, indicating that the membrane can be directly used as an anti-counterfeiting label for multiple verifications. The FRET efficiency was found to be about 61% based on the FRET study with confocal laser scanning microscopy. The covalent bonding between PPETE backbone and SP, the confinement of PPETE-SP chains in the fibrous membrane, as well as employing PMMA as the matrix were demonstrated to be crucial in realizing the photochromism and the FRET. Different anti-counterfeiting modes were proposed, providing rich selections for operation of verification. Such facile-to-operate and hard-to-imitate dynamic fluorescent responsive materials are very promising for use in practical anti-counterfeiting applications.
