Rapid Detection of Mercury Ions Based on Nitrogen-Doped Graphene Quantum Dots Accelerating Formation of Manganese Porphyrin

Mercuric ion (HgII) is a stable form of mercury pollution with high toxicity and bioaccumulation ability, and its sensitive and visible determination is of great importance. Herein, a simple method to significantly improve the complexation reaction rate between porphyrin and manganous ions (MnII) has been implemented by using the synergistic effect of trace nitrogen-doped graphene quantum dots (NGQDs) and Hg(II). A mechanism is proposed in accordance with a substitution reaction in which the deformed porphyrin nucleus by relatively larger Hg(II) ions is favorable for attacking small divalent metal ions carried by NGQDs from the back. Meanwhile, the formation of metalloporphyrin is accompanied by the absorption red-shift and fluorescence quenching of porphyrins; simultaneously, the fluorescence of NGQDs is gradually enhanced because of the inner filter effect between porphyrins and NGQDs. Thus, the ratiometric fluorescence and colorimetric methods for trace HgII sensing have been proposed on the basis of the distinct absorption/fluorescence spectral changes, which have potential application in complex environmental and biological conditions.