Application of iridium(III) complex in label-free and non-enzymatic electrochemical detection of hydrogen peroxide based on a novel 'on-off-on' switch platform

We herein report a label-free and non-enzymatic electrochemical sensor for the highly sensitive detection of hydrogen peroxide (H₂O₂) based on a novel "on-off-on" switch system. In our design, MB was used as an electron mediator to accelerate the electron transfer while AuNPs was used to amplify the electrochemical signal due to its excellent biocompatibility and good conductivity. The "switch-off" state was achieved by introducing the guanine-rich capture probe (CP) and an iridium complex onto the electrode surface to form a hydrophobic layer, which then hinders electron transfer. Upon addition of H₂O₂, fenton reaction occurs and produces OHin the presence of Fe²⁺. The OHcleaves the CP into DNA fragments, thus resulting in the release of CP and iridium complex from the sensing interface, recovering the electrochemical signal to generate a "switch-on" state. Based on this novel switch system, a detection limit as low as 3.2 pM can be achieved for H₂O₂ detection. Moreover, satisfactory results were obtained by using this method for the detection of H₂O₂ in sterilized milk. To the best of our knowledge, this is the first G-quadruplex-based electrochemical sensor using an iridium(III) complex.