One-step synthesis of conductive hydrogel for selective electrochemical detection of H2O2 via a dissolved oxygen-assisted ECE/DISP mechanism

Hydrogen peroxide (H 2 O 2 ), a common reactive oxygen species, not only plays an important role in biological systems but is also widely used in industry. Its concentration varies across biological and environmental samples, and elevated levels can be highly hazardous and toxic. In aquaculture and lake water environments, H 2 O 2 may even reach the millimolar level. In this work, a highly conductive hydrogel (HG) was synthesized using a one-pot method from 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), methacrylamide (MAM), and 2-hydroxyethyl methacrylate (HEMA) as raw materials. This conductive HG was coated on a glassy carbon electrode (GCE) surface. The resulting HG-GCE shows amplified cathodic current response toward H 2 O 2 in the presence of dissolved oxygen (DO) in electrolyte at neutral and acidic condition. Interestingly, the reduction current toward H 2 O 2 was markedly higher than in deoxygenated (N 2 -saturated) buffer, where the HG–GCE exhibited almost no response. This indicates that dissolved oxygen (molecular O 2 ) is essential for the H 2 O 2 sensing process of the HG–GCE, which we attribute to an O 2 -assisted electrochemical–chemical–electrochemical (ECE) mechanism. First, the HG may provide suitable microenvironment for the electrochemical reduction of the dissolved oxygen, producing O 2 ·− radical. Then, the produced O 2 ·− reacts with H 2 O 2 , which might /produce electrochemically active intermediates (HO 2 · radicals and HO 2 − ). These intermediates are further reduced at the GCE surface, generating measurable cathodic currents at −0.5 to −0.8 V vs. Ag/AgCl. Furthermore, in addition to the above ECE reaction process, we speculate two kinds of disproportionation (DISP) reactions within the HG-layer, which regenerate the O 2 and the H 2 O 2 , leading to the repeated ECE process (i.e., DO-assised amplified-H 2 O 2 response at the HG-GCE). Based on this ECE/DISP mechanism, the resulting HG/GCE-based H 2 O 2 sensor exhibits a good linear range for detecting H 2 O 2 from 1-35 mM, with low detection limit of 100 μM and sensitivity of 35.99 μA mM cm −2 , in air-saturated electrolyte buffer (at pH 3). The sensor demonstrated excellent stability, maintaining efficient detection for up to 45 days. This study also provides a new direction for the detection of H 2 O 2 using hydrogel materials.