A digital multimeter-based portable photoelectrochemical immunoassay for the detection of cardiac troponin I with enzymatic biocatalytic precipitation

Abstract

Early diagnosis of acute myocardial infarction (AMI) can significantly reduce mortality, which can be achieved by the highly sensitive detection of AMI-specific cardiac troponin I (cTnI) biomarkers. Herein a highly sensitive and portable photoelectrochemical (PEC) immunoassay for the detection of cTnI was innovatively fabricated based on an efficient photocurrent response of Cu₂O coupling with a split-type enzymatic biocatalytic precipitation reaction with a digital multimeter readout. Initially, Cu₂O cubic nanomaterials with a good photocurrent response were obtained by facile green room temperature synthesis and dropped on fluorine-doped tin oxide (FTO) plates as photoactive materials (Cu₂O/FTO). In the presence of target cTnI, horseradish peroxidase (HRP) on the detection antibody catalyzes the substrate 4-chloro1-naphthol (4-CN) to produce insoluble precipitates of benzo-4-chlorohexadienone (4-CD) on Cu₂O/FTO with the assistance of H₂O₂, resulting in a decrease in the photocurrent of the Cu₂O/FTO electrode. To make the whole inspection process more concise and efficient, we used a flashlight and a digital multimeter as the excitation light source and reading device for the PEC sensing system, respectively. Under the optimal conditions of immunoreaction time, pH, and loading, the photocurrent of Cu₂O/FTO decreased with increasing target cTnI concentration with a limit of detection (LOD) of 4.7 pg mL⁻¹ in the operating range of 0.01–10 ng mL⁻¹. It is of interest that the developed portable PEC immunoassay is also capable of detecting cTnI in human serum samples with acceptable accuracy compared to the reference cTnI enzyme-linked immunosorbent assay (ELISA) method while maintaining portability and sensitivity.