Enhancing the quantum yield and Cu2+ sensing sensitivity of carbon dots based on the nano-space confinement effect of silica matrix

Although the analytical applications of the fluorescent carbon dots (CDs) were widely explored, the development of effective fluorescence signal amplification scheme based on the CDs was challengeable. In this work, we firstly found that, after CDs and polyethyleneimine (PEI) were together doped into silica nanoparticles via a reverse microemulsion route, the CDs inside as-prepared CDs/PEI/silica nanoparticles (CDs/PEI/SiO2 NPs) presented the higher fluorescence quantum yield and stronger signal amplification ability than that of free-state CDs. Here, the possible fluorescence enhancing mechanism of CDs inside CDs/PEI/SiO2 NPs was investigated by UV-vis absorption spectra, fluorescence spectra, IR spectra, transmission electron microscope and zeta potential technique and the possible mechanism was also proposed. In addition, the Cu2+ was selected as the model to investigate the signal amplification feature of the CDs/PEI/SiO2 NPs. Our results showed that, encapsulation of CDs and PEI into silica NPs lead to a fluorescence enhancement of CDs, the fluorescence quantum yield of CDs increased from 13.7% to 38.6%. The as-prepared CDs/PEI/SiO2 NPs exhibited 100-times sensitivity increasing for sensing Cu2+ compared with free-state CDs sensing scheme reported by the previous literature.