One-step synthesis of fluorescent organic nanoparticles: The application to label-free ratiometric fluorescent pH sensor

摘要

In this work, we develop a facile one-step synthesis method of poly(3,4-dihydroxyphenylalanine) (poly(DOPA)) fluorescent organic nanoparticles (FONPs) by polymerization of DOPA in alkaline alcohol solution under ultrasonic radiation. The morphology and size of poly(DOPA)-FONPs are dependent on the synthesis conditions, such as solvent and alkali concentration. Under the optimized condition, the prepared poly(DOPA)-FONPs possess not only uniform size and morphology, but also strong green fluorescence, good solubility in water and organic solvents. Under excitation of single wavelength, two emission peaks can be clearly observed, which are pH-sensitive. Moreover, the intensity ratio of two emission peaks is linear against pH values from 4.0 to 8.0 in buffer solution. In addition, the pH-sensitive response of the poly(DOPA)-FONPs be free from the influence of various metal ions and biomolecules, indicating the excellent specificity to pH. Further, due to the excellent biocompatibility, the poly(DOPA)-FONPs might also be applied on biological imaging for monitoring intracellular pH. The as-prepared poly(DOPA)-FONPs would be promising to be applied on the low-cost, low-toxic and label-free ratiometric pH sensor.