Metal ions-modulated near-infrared electrochemiluminescence from Au nanoclusters enhanced by 4-(2-Hydroxyethyl)-1-piperazineethanesulfonic acid at physiological pH

The enhancement of near IR ECL from Au nanoclusters by the commonly used good's buffer 4-(2-Hydroxyethyl)-1-Piperazineethanesulfonic Acid (HEPES) as coreactants is presented. Lipoic acid (LA) stabilized Au₂₂ nanocluster is used based on its high quantum efficiency of near IR photoluminescence, also in reference to the EDTA enhancement and metal ion responses previously reported. Metal ions are demonstrated to be effective in modulating ECL signal. Specifically, zinc ion is found to drastically enhance the AuNC-HEPES ECL while magnesium and calcium ions lower the ECL intensity. Differentiation of different metal ions or sensing specificity can be better achieved by both intensity and kinetics analysis. The enhancement in ECL by zinc ions is attributed to the direct coordinate interactions with ligand monolayer in the presence of HEPES and confirmed by similar enhancement in the near IR photoluminescence. The ECL profiles are sensitive to pH and display optimal responses at physiological pH which makes HEPES better suited over EDTA for the corresponding applications. The design is translational to other ions and other amine-based good's buffers.