Non-traditional intrinsic luminescence from non-conjugated polymer dots: designing a hybrid biomaterial

Abstract

Herein, an eco-friendly and facile synthesis of nitrogen-containing non-conjugated polymer dots (NCPD) with optimal blue emission is reported from the biopolymer β-glucan with a peptide–polysaccharide linkage (namely NH₂-β-glucan). The crosslink-enhanced emission effect was proposed to explain the strong luminescence of the NCPDs possessing either non-emissive or weakly emissive sub-luminophores. The water-soluble NCPDs were synthesized via a feasible and facile route to produce a fluorescent material by dehydration/crosslinking reactions without additional matrix compositing. The nanocomposite's photoluminescence spectra unveiled the red-shifted emission from 420 to 515 nm as the excitation wavelengths vary from 300 to 450 nm, showing a maximum blue emission at 430 nm for the 340 nm excitation wavelength. Here, luminescent NCPDs with carboxyl, amino, and hydroxyl groups were comprehensively characterized, in which acidic/alkaline conditions were varied to probe the influence of surface charge on their fluorescence emission. The study also demonstrates that SERS (Surface Enhanced Raman Spectroscopy) is an excellent technique for exploring the chemical structures using Ag and Au nanoparticles. In closing, we have presented a consistent study using Raman and IR spectroscopy to lead to an undoubted identification of promising fluorescent non-conjugated polymer dots.