Graphene Quantum Dots as Fluorescence Probes for Turn-off Sensing of Melamine in the Presence of Hg²⁺

Abstract

A rapid and sensitive fluorescence sensing system for melamine based on charge transfer quenching of the fluorescence of graphene quantum dots (GQDs) in the presence of Hg(2+) is proposed. The synthesized GQDs were strongly luminescent with predominantly aromatic sp(2) domains. Melamine could coordinate with mercury through nitrogen atoms in both its amine and triazine groups and bring more Hg(2+) to the surface of GQDs through π-π stacking, thus leading to quenching of the GQDs' fluorescence. The quenching mechanism was investigated in detail and ascribed to charge transfer from the GQDs to Hg(2+) with melamine acting as the linkage agent. The melamine demonstrated a linear range 0.15-20 μM and a detection limit of 0.12 μM, which was far below the regulatory level, suggesting the promising practical usage of this sensing system. This sensing system also possessed high selectivity for melamine in the presence of possible interferences. Finally, this novel sensor was successfully applied for melamine detection in raw milk and satisfactory recovery was achieved.

A unique turn-off fluorescent strategy for sensing dopamine based on formed polydopamine (pDA) using graphene quantum dots (GQDs) as fluorescent probe

“…The formed pDA films on GQDs induce FRET and fluorescence quenching (the inset of Fig. 1C), which is like an Hg-melamine system in the GQD solution [36]. The zeta-potential of GQDs decreased from −1.62 mV to −10.82 mV and −18.37 mV when 20 M and 100 M DA were added into GQDs solution, respectively.…”

“…GQDs prepared from pyrolysis of citric acid are surfacepassivated and have good fluorescence activity [34,35]. The change in the surface of GQDs, such as assembling a thin layer, can induce FRET and quench fluorescence intensity to fabricated signal-off sensor [36]. Although some proposed sensors for dopamine detection are based on fluorescent route [21,23], the mechanism of DA detection based on the selective polymerization of dopamine on the surface of fluorescent nanomaterials with high sensitivity and anti-interference ability in complex system remains blank.…”

Preparation of graphene quantum dots based core-satellite hybrid spheres and their use as the ratiometric fluorescence probe for visual determination of mercury(II) ions

“…1D), assigned to the pÀp* transition of aromatic sp 2 domains [49]. Note that the GQDs dispersion has optimal maximum excitation and emission wavelengths at 378 nm and 465 nm, respectively.…”

One-step fabrication of high quantum yield sulfur- and nitrogen-doped carbon dots for sensitive and selective detection of Cr(vi)

“…The broad absorption peak around 272 nm was ascribed to the p-p* transition of aromatic sp 2 domains, and the absorption peak centered at 340 nm indicated the presence of carbonyl or conjugated carbonyl groups. 33 At the same time, the excitation and emission peaks appeared at 350 nm and 430 nm, respectively. As illustrated in Fig.…”