Ultrasensitive detection of diclofenac based on electrochemiluminescent immunosensor with multiple signal amplification strategy of palladium attached graphene oxide as bioprobes and ceria doped zinc oxide as substrates

Herein, Pd nanoparticles (PdNPs) and CdSe@CdS QDs decorated poly(etherimide) (PEI)-graphene oxide (GO) (PdNPs/PEI-GO-QDs) and ceria-zinc oxide were prepared and severally applied as probe and substrate to assemble an electrochemiluminescence (ECL) immunosensor for detecting diclofenac (DCF). The carboxyl groups (−COOH) covered Ce:ZnO and PEI-GO were creatively applied in this sensor not only load more CdSe@CdS QDs and accelerate electron conduction to obtain sensitive ECL signal, but also provide large surface for coating antigen and antibody loading. Furthermore, it is worth noting that the rapid Ce 4+  ↔ Ce 3+ reaction in this Ce:ZnO and PdNPs/PEI-GO can increase the rate of electron transfer to achieve multiple signal amplification. A competitive immunoassay strategy was used for determining DCF, where DCF in the sample would compete with the coating antigen for the limited antibodies. The proposed ECL immunoassay had exhibited high sensitivity for DCF detection with a wide linear range from 0.001 to 1000 ng mL −1 and an ultralow detection limit of 0.3 pg mL −1 . This ECL immunosensor had good stability, acceptable fabrication reproducibility and accuracy for detecting DCF in environmental samples, and provided an approach for determining other important small molecules.