Investigation of the fluorescence quenching behavior of PEI-doped silica nanoparticles and its applications

Abstract

Although the primary amine groups on PEI-based materials were widely used to bind fluorophores for optical sensing, the fluorescence quenching behavior of the tertiary amine groups on the same PEI macromolecules toward fluorophores was always ignored. To address these issues, in this work, we developed a new strategy that could not only avoid the limitation of the fluorescence quenching effect of the tertiary amino groups of PEI, but also keep the high reactivity of the primary amine groups. This new strategy was based on supramolecular integration of PEI into a silica matrix to form porous PEI-doped silica nanoparticles (PEI/silica nanoparticles). Our results showed that the primary amine groups of PEI inside porous PEI/silica nanoparticles possess great space freedom to maintain their high reactivity, but the tertiary amine groups of PEI were effectively masked based on the stronger supramolecular interaction between SiO⁻ and the tertiary amino groups. Based on this finding, calcein/Co²⁺ fluorescence sensing systems were chosen as the model to demonstrate novel fluorescent properties of the porous PEI/silica nanoparticles. Our results showed that bright fluorescent porous calcein/PEI/silica nanoparticles (CPSNPs) could be easily prepared and further used to detect Co²⁺ based on the fluorescence quenching effect of Co²⁺ on calcein. A detection limit as low as 0.3 nM for Co²⁺ was achieved by these designed sensing nanomaterials.