Bipolar electrochemical sensor with perylene diimide-based cathodic luminophore for dopamine detection and imaging

Bipolar electrochemical microscopy (BEM), which visualizes the concentration distribution of molecular species in biological systems by electrochemiluminescence (ECL), is expected to be applied to the high-spatiotemporal-resolution imaging of biomolecules, enabling the analysis of cellular functions. In the past, the molecular species that could be imaged by BEM were generally restricted to oxidized molecules due to the limitation derived from the ECL mechanism of the luminophore. Recently, the imaging of dopamine (DA), a reduced molecule, was achieved using Ru (bpy)₃²⁺/glutathione disulfide (GSSG) as a cathodic luminophore. However, a large driving voltage was required for ECL generation, resulting in a low S/N ratio. In this study, we employed N,N'-dimethyl-3,4,9,10-perylenetetracarboxylic diimide (PDI-CH₃)/potassium peroxodisulfate (K₂S₂O₈), which is a cathodic luminophore that can be reduced at a nobler potential to produce ECL than [Ru(bpy)₃]²⁺/GSSG. First, the ECL mechanism of PDI-CH₃/K₂S₂O₈ was elucidated by using a PDI-CH₃ drop-cast glassy carbon electrode (GCE) immersed in K₂S₂O₈ solution as the working electrode in a 3-electrode system. The PDI-CH₃ drop-casted GCE, a single closed bipolar electrode (c-BPE), was used as the cathode in the successful quantification of 50-500 μmol L^-1 DA in a sample chamber in which a c-BPE anode was immersed, resulting in a high S/N. The selective detection of DA in the presence of ascorbic acid was achieved by modifying the anode with Nafion. Finally, DA imaging was demonstrated using a commercially available anisotropic conducting film with PDI-CH₃ coating on the cathode surface as a c-BPE array. The change in the concentration distribution in the inflow of DA was successfully imaged based on the change in the ECL intensity at the c-BPE cathode. This BEM system is expected to be useful for DA imaging of the brain.