A newly identified selective interaction between As(iii) and luminol enhances the formation of excited 3-aminophthalate, thereby amplifying the ECL signals. The luminol/As(iii) ECL response was observed across all studied electrodes; however, Au/BDD was selected for its highest sensitivity, driven by the strong electrocatalytic activity of the immobilized gold nanoparticles. This journal is © The Royal Society of Chemistry, 2026