In this study, a
facile one-pot solid-state synthesis
method is
developed to shed light on the metal-enhanced fluorescence (MEF) effect
in carbon quantum dots (CQDs) and gold nanoparticles (AuNPs) hybrid
materials. This is one of the few studies on the solid-state synthesis
of N-doped CQDs/gold hybrid nanomaterials. We have conducted various
sets of experiments to reveal the role of individual reagents during
the nucleation and growth of nanoparticles. We have demonstrated that
the addition of a small amount of gold salt illustrates a paramount
effect (103-fold) in photoluminescence intensity. This
effect is ascribed to MEF, which is caused due to interactions between
the excited-state fluorophores and the free surface electrons of metal
nanoparticles. It is interesting to note that a further increase of
gold yields fluorescence quenching due to a large number of formed
AuNPs causing fluorescence resonance energy transfer. By adjusting
the volume ratio of gold salt and CD precursors, it is possible to
obtain the CQDs–AuNPs hybrid with the highest fluorescence,
which produces extensive visible light under 460 nm excitation. Synthesized
materials have been successfully used for imaging human dermal fibroblasts
and A549 lung epithelial cells. The dose-dependent cytotoxicity studies
reveal that the hybrid structures do not have cytotoxicity.