"Off-on" fluorescence probe based on green emissive carbon dots for the determination of Cu ions and glyphosate and development of a smart sensing film for vegetable packaging.

An ultra-sensitive glyphosate nanosensor, based on carbon dots (CDs), was successfully developed with excellent long-wavelength emission (530 nm), a high quantum yield (41.3%), and an impressive detection limit (0.8 ng·mL). This is the lowest value for glyphosate detection achieved by CD-based fluorescence analysis. The sensor was derived from a separate precursor, 1,4-dihydroxyanthraquinone, and was based on the "off-on" fluorescence analysis, where Cu acts as a dynamic quencher and glyphosate as a fluorescence restorer (excitation wavelength 460 nm). Trace detection of glyphosate is possible with a wide detection range of 50-1300 ng·mL and spiked recoveries between 93.3 and 110.0%. Exploration in depth confirmed that (1) the fluorescence of CDs was derived from the carbon core, (2) the large sp conjugated domain consisting of graphitic carbon and nitrogen contributed to the long-wavelength emission, and (3) CDs had an impressive binding interaction with Cu, which endow high sensitivity to glyphosate detection. The nanosensor has also be used as a dual-mode visual sensor and a smart sensing membrane that can identify glyphosate on the surface of vegetables, thus showing good practical applicability. Synthetic methods of G-CDs and its detection mechanisms for glyphosate.