We have proposed a Fenton-like reaction-mediated etching of gold nanorods and applied
it to the sensitive visual detection of Co(2+) ions. With the presence of bicarbonate
(HCO3(-)) and hydrogen peroxide(H2O2), Co(2+) ions trigger a Fenton-like reaction,
resulting in the generation of superoxide radical (O2(•-)). As a result, the gold
nanorods are gradually etched by O2(•-) in the presence of SCN(-), accompanied by
an obvious color change from green to red. The gold nanorods etching process preferentially
occurs along the longitudinal direction, which is observed by transmission electron
microscope. The etching mechanism is carefully proved by investigating the effects
of different radical scavengers (e.g., dimethyl sulfoxide). The auto-oxidation of
hydroxylamine assay further confirms the mechanism. Then, the main factors, including
reactants concentrations, temperature, and incubation time, are specifically investigated.
Under optimized conditions, we get an excellent sensing performance for Co(2+) with
a lower detection limit of 1.0 nM via a spectrophotometer and a visual detection limit
of 40 nM. In addition, this principle may provide a new concept of "intermediate-mediated
etching of nanoparticles" for sensing.