Polyethyleneimine-based fluorescent polymeric nanoparticles: synthesis and application in fluorescence sensing of pH and para-nitrophenol

Abstract

The use of metal-free fluorescent polymeric nanoparticles is gaining wide interest in the field of sensing and biosensing. Herein, water-soluble polyethyleneimine-based fluorescent polymeric nanoparticles, PEIFPL NPs, were synthesized, characterized and employed for the fluorescence sensing of pH and nitroaromatic compounds. The branched polyethyleneimine (b-PEI) was cross-linked with formaldehyde (FA), followed by reaction with pyridoxal to obtain the cyan-blue emitting PEIFPL NPs. The HR-TEM analysis supported the formation of near-spherical NPs with an average diameter of 7 ± 1 nm. The fluorescence emission of the PEIFPL NPs (λ_ex = 320 nm) at 388 nm between pH 4.0 and 8.0 was blue-shifted to 365 nm at basic pH between 9.0 and 12.0. In acidic pH, the fluorescence intensity of the PEIFPL NPs declined, and the emission maximum red-shifted to 430 nm. The change in fluorescence emission at 388 nm of the PEIFPL NPs was monitored in the presence of nitroaromatics, metal ions and amino acids. The fluorescence emission of the PEIFPL NPs was selectively quenched by para-nitrophenol (p-NP). The fluorescence lifetime study revealed that the fluorescence quenching of the PEIFPL NPs by p-NP was static in nature. Without any interference, the PEIFPL NPs can be employed to detect p-NP down to 0.42 μM. The analytical utility of the PEIFPL NPs was explored by quantifying the p-NP concentration in a river water sample.