Photoelectrochemical Sensor with a Z-Scheme Fe 2 O 3 /CdS Heterostructure for Sensitive Detection of Mercury Ions.

Mercury (Hg 2+ ) is a highly toxic element and can seriously affect human health. This work proposed a photoelectrochemical (PEC) sensor with a Z-scheme Fe 2 O 3 /CdS heterostructure and two thymine-rich DNA strands (DNA-1 and Au@DNA-2) for sensitive detection of Hg 2+ . The light excitation of the Fe 2 O 3 /CdS composite accelerated the electron transfer among Fe 2 O 3 , CdS, and the electrode to produce a stable photocurrent response. Upon the recognition of Hg 2+ to thymine bases (T) in two DNA strands to form a stable T-Hg 2+ -T biomimetic structure, the photocurrent response increased with the increasing concentration of Hg 2+ due to the opening of electronic transmission channels from Au nanoparticles to Fe 2 O 3 /CdS nanocomposite. Under the optimal conditions screened by the Box-Behnken experiments, the proposed PEC sensor showed excellent analytical performance for Hg 2+ detection with high sensitivity, a detection limit of 0.20 pM at a signal-to-noise ratio of 3, high selectivity, a detectable concentration range of 1 pM-100 nM, and acceptable stability. The good recovery and low relative standard deviation for the analysis of Hg 2+ in lake and tap water samples demonstrated the potential application of the designed Z-scheme Fe 2 O 3 /CdS heterostructure in the PEC detection of heavy metal ions.