Fluorescent Nanosensor from Amphiphilic Block Copolymers Functionalized with 1,8-Naphthalimide for Acidic...

An amphiphilic block copolymer, poly(ethylene glycol)-b-poly(N-vinyl carbazole) (PEG-b-PVK), containing 1,8-naphthalimide has been synthesized via reversible addition-fragmentation chain transfer polymerization. The block copolymer demonstrates a low polydispersity index and self-assembles into uniform nanoparticles in aqueous media, which can serve as a fluorescent sensor for detecting hydrogen ion in acidic medium. The average quantity ratio of 1,8-naphthalimide to carbazole moieties in the block copolymer is ~ 1/13 according to nuclear magnetic resonance spectra. The emission from the PVK block almost disappear, whereas the 1,8-naphthalimide moiety exhibits significantly enhanced fluorescence at 505 nm due to Förster resonance energy transfer from PVK to 1,8-naphthalimide in the polymer nanoparticles. The photoluminescence intensity at 505 nm displays a good linear correlation with decreasing pH values in the range of 3.0-6.5 for the polymer nanoparticles in acidic medium, highlighting the block copolymer's potential for quantitative pH sensing in acidic environments. In the polymer nanosensors, the PEG shell protects the PVK cores from damage in complex organisms, indicating its potential applications in living organisms.