Electrocatalytical Chemical Sensor for Hydrogen Peroxide

The fast and selective determination of hydrogen peroxide (H₂O₂) is of importance not only because of strong interest to this widely applied analyte but also because of the development of enzymatic biosensors for glucose or other metabolites where the sensor for H₂O₂ can be used as the transducer. We report here electrocatalytical amperometric sensor for detection of H₂O₂. The sensor consists of a gold electrode covered by self-assembled monolayer (SAM) with immobilized p-benzoquinone. To provide highly stable immobilization of p-benzoquinone at the distance of effective electron tunneling, a new anchor compound - 1,3-dimercaptopropan-2-ol – was synthesized and used for the preparation of the SAM. Due to two thiol groups binding gold surface this compound provides a high stability of the SAM. The surface concentration of p-benzoquinone obtained from cyclic voltammetry is 2.5 ± 0.2 × 10⁻¹⁰ mol·cm⁻². Cyclic voltammetry and chronoamperometry experiments proved that the immobilized benzoquinone exhibited high electrocatalytic activity towards the decomposition of H₂O₂. Depending on the used potential range, different sensing modes can be realized. For example, one can measure electrochemical response due to the oxidation of H₂O₂ at anodic potentials or due to the reduction of oxygen formed during oxidative decomposition of H₂O₂. Also amperometric response at fixed potential of +0.4 V vs. Ag/AgCl corresponding to the oxidation of benzoquinone to hydroquinone was studied. The sensor exhibited a linear response over a concentration range of 0.1–2 mM with a low detection limit of 4.24 µM. The reproducibility of three different electrodes prepared was examined at the H₂O₂ concentration range from 0.1 till 3 mM, which resulted in a relative standard deviation below 4.2%.