Recent developments of nanoenzyme-based colorimetric sensors for heavy metal detection and the interaction mechanism

Heavy metal contamination has posed a great threat to human survival and social development. For this, a series of nanoenzyme-based colorimetric sensors, e.g., metal nanoparticles, metal oxides, metal sulfides, graphene-based nanomaterials, G-quadruplex and so on, were developed for the rapid and efficient detection of toxic heavy metal ions, whose detection limit for heavy metal ions could be as low as the nmol L^-1 level. The recognition mechanism was based on the catalysis and signal amplification of nanozymes, a new type of nanomaterial possessing specific catalytic activity towards certain chemical reactions such as the oxidation of colorless TMB to blue oxTMB. In this work, we are trying to present readers with a better understanding of this important colorimetric sensing material by illustrating its application in the detection of heavy metal ions using metal nanoparticles, metal oxides, metal sulfides, graphene-based nanomaterials, G-quadruplex, etc. respectively.