A label-free three potential ratiometric electrochemiluminescence immunosensor for cardiac troponin I based on N-(4-aminobutyl)-N-ethylisoluminol functionalized graphene quantum dots

•An ECL nanoluminophore with three potential-resolved emissions was synthesized.•A label-free three potential ratiometric immunosensor was built.•A low detection limit of 0.35 fg/mL was obtained for cardiac troponin I.•The developed strategy can effectively eliminate errors caused by environmental changes. In this work, we synthesized a novel ECL nanoluminophore N-(4-aminobutyl)-N-ethylisoluminol functionalized graphene quantum dots (ABEI@GQDs), which exhibited three completely potential-resolved dual-color ECL emissions with coreactant K2S2O8 in an aqueous solution. Blue color ECL-1, orange red color ECL-2 and blue color ECL-3 were observed at peak potential of -0.58, -1.85 and 1.20 V, respectively. On this basis, a label-free three potential ratiometric ECL immunosensor was developed for detecting cardiac troponin I (cTnI) by layer-by-layer assembly of ABEI@GQDs and antibody on a chitosan modified fluorine doped tin oxide electrode. In the presence of cTnI, ECL-2 increased, whereas ECL-1 and ECL-3 changed slightly and synchronously. It was found that ECL-1/ECL-3 ratio almost unchanged with increasing the concentration of cTnI, which laid the foundation for self-correction analysis. Accordingly, three potential ratiometric strategy based on the ratio of three ECL peaks was established for the determination of cTnI with a linear dynamic range from 1.0 fg/mL to 5.0 pg/mL and a detection limit of 0.35 fg/mL, which was superior to most reported ECL methods. Moreover, the developed three potential ratiometric ECL immunosensor can effectively eliminate systematic errors caused by environmental changes and thus offers more precise detection results than two potential ratiometric ECL immonosensors.