Preparation of Ag@SiO2@NH2 core-shell nanocomposites for the fluorescence enhancement of carbon quantum dots

In this paper, the fluorescence enhancement phenomenon of carbon quantum dots (C-QDs) via metal fluorescence effect has been investigated. Firstly, uniform Ag nanoparticles was prepared, which theoretically can supply a strong enhancement effect with a diameter as small as 20 nm. Then SiO2 shell was utilized to control the distance between Ag core and C-QDs while surface charge of as-synthesized Ag@SiO2 was further modified to bond C-QDs via electrostatic effect. Four different kinds of SiO2 shell, with thickness 12 nm, 15 nm, 20 nm, and 27 nm, were synthesized to study the enhancement effect of distance. With the increase of SiO2 shell, the fluorescence of Ag@SiO2@NH2-C-QDs nanocomposites rise first but then fall while the sample with the 20-nm shell obtained the best enhancement effect as high as 3.92-fold. Surface charge vibration of metal particles was used to explain this phenomenon.