Amplified fluorescence quenching of lucigenin self-assembled inside silica/chitosan nanoparticles by Cl⁻

Fluorescence sensing of an analyte based on the fluorophore collective effect is a reliable, sensitive sensing approach. Many ultralow targets can be detected on the basis of the high sensitivity and signal amplification of the fluorescence sensing system. However, the complicated synthesis procedures, harsh conditions required to design and control the fluorescence molecular probes and conjugated chain length, and the higher cost of synthesis are still challenges. To address these issues, we developed a simple, rapid, and sensitive collective effect based fluorescence sensing platform. In this sensing platform, the fluorophore unit was self-assembled on the wall of the nanopores of the porous structural silica/chitosan nanoparticles (SCNPs) on the basis of the electrostatic interaction and supermolecular interaction between the fluorophores and SiO(-) groups and chitosan. Since these self-assembled fluorophores are close enough to communicate with each other on the basis of the space confinement effect of the pore size, many fluorophore units could interact with a single analyte and produce an amplified fluorescence sensing ability. Chloride ion, an important anion in biological fluids, and lucigenin, a typical fluorescent dye, were used as a model to confirm the proof-of-concept strategy. Our results showed that, compared to free-state lucigenin in solution, the assembled-state lucigenin in SCNPs presented an about 10-fold increase in its Stern-Volmer constant when the concentration of Cl(-) was lower than 10 mM, and this fluorescence nanosensor was also successfully used to sense the chloride ion in living cells.