Perylene diimide and g-C3N4 nanosheet as potential-resolved cathode luminophores for ultrasensitive ratiometric electrochemiluminescence immunosensor

In electrochemiluminescence(ECL) field, the shortage of potential-resolved luminophores severiously limited the development of biosensors for accurate assay such as ratiometric biosensors. In this work, N,N′-dimethyl-3,4,9,10-perylenedicarboximide(PDI-CH3) and graphite-like carbon nitride(g-C3N4) nanosheet was firstly reported to produce potential-resolved ECL with coreactant K2S2O8 between 0 and − 1.2 V. And there was good overlap between the ECL spectrum of g-C3N4 and the absorption spectra of PDI-CH3. Moreover, PDI-CH3 and g-C3N4 were used to construct ECL ratiometric system for sandwiched immunosensors to detect tumor marker carcinoembryonic antigen (CEA), in which g-C3N4 was used as ECL platform and PDI-CH3 was used as ECL label of secondary antibody(Ab2). Increasing the CEA concentration, the loading of PDI-CH3 on the electrode stepwisely increased, which leaded to gradual increase of ECLPDI-CH3 at − 0.5 V and significant decrease of ECLg-C3N4 at − 1.2 V due to the high quenching effects of PDI-CH3 to g-C3N4 through dual-quenching mechanism: competitive consumption of coreactant and ECL resonance energy transfer. And the ECLPDI-CH3/ECLg-C3N4 showed ultrasensitive linear response for CEA between 0.1 fg mL−1 and 1 ng mL−1 with detection limit 0.052 fg mL−1 according to IUPAC criterion. In addition, the proposed ratiometric biosensor exhibited good recovery in human serum samples.