Fabrication of a new fluorescent polymeric nanoparticle containing naphthalimide and investigation on its interaction with bovine serum albumin

A new fluorescent nanoparticle was synthesized by chemical crosslinking of polyacrylic acid using 4-aminoethanol-N-hydroxyethanyl-1,8-naphthalimide as the crosslinker. The particle possesses excellent characteristics, including low cytotoxicity, water solubility and good fluorescence properties. The interaction of the particle with bovine serum albumin was investigated by absorbance, fluorescence and circular dichroism spectroscopic methods. The interaction mechanisms, binding model and reciprocal effects on structure and fluorescence between nanoparticle and protein are discussed. The spectral data indicated that the nanoparticle could spontaneously form a reversible complex with bovine serum albumin in solution used mainly by hydrogen bonds and van der Waals forces. Fluorescence resonance energy transfer from tryptophan to naphthalimide in the complex was demonstrated and employed to determine their relative separation distance. During the interaction process, unfolding of polypeptide chains in the protein occurred but no adjustments of local polarities around the tryptophan and tyrosine residues were observed. In addition, it was found that the presence of protein induced a notable enhancement in nanoparticle fluorescence and a blue-shift in the emission maximum. These results will be useful for further applications of the developed nanoparticle in biomedical areas.