Highly sensitive detection of copper ions by densely grafting fluorescein inside polyethyleneimine core–silica shell nanoparticles

Abstract

In this work, polyethyleneimine (PEI) core–silica shell nanoparticles were synthesized and used for densely grafting fluorescent receptor units inside the core of these particles to result in multi-receptor units collectively sensing a target. Herein, copper ion quenching of the fluorescence intensity of a fluorescein isothiocyanate (FITC) system was selected as a model to confirm our proof-of-concept strategy. Our results showed that, compared to free FITC in solution, a 10-fold enhancement of the Stern–Volmer constant value for Cu²⁺ quenching of the fluorescence intensity of the grafted state of FITC in PEI core–silica shell nanoparticles was achieved. Furthermore, compared to a previous collective sensing scheme by densely grafting fluorescent receptor units on a silica nanoparticle surface, the proposed scheme, which grafted fluorescent receptor units inside a polymer nano-core, was simple, highly efficient and presented higher sensitivity.