In this work, coumarin derivatives
(C) are used to enhance the
fluorescence of graphene quantum dots (GQDs) by covalently linking
the carboxyl groups on the edge of the GQD sheet. The as-synthesized
coumarin-modified graphene quantum dots (C-GQDs) have a uniform particle
size with an average diameter of 3.6 nm. Simultaneously, the C-GQDs
have strong fluorescence emission, excellent photostability, and high
fluorescence quantum yield. C-GQDs and CN– can form
a C-GQDs+CN– system due to deprotonation and/or
intermolecular interactions. The introduced hydroquinone (HQ) is oxidized
to benzoquinone (BQ), and the interaction between BQ and the C-GQDs+CN– system could lead to fluorescence enhancement of C-GQDs.
Meanwhile, the redox reaction between BQ and ascorbic acid (AA) can
be used for quantitative detection of AA with CN– and HQ being used as substrates. Based on the above mechanism, C-GQDs
are developed as a multicomponent detection and sensing platform,
and the detection limits for CN–, HQ, and AA were
4.7, 2.2, and 2.2 nM, respectively. More importantly, satisfactory
results were obtained when the platform was used to detect CN–, HQ, and AA in living cells and fresh fruits.