A cardiac troponin I photoelectrochemical immunosensor: nitrogen-doped carbon quantum dots-bismuth oxyiodide-flower-like SnO₂

A novel photoelectrochemical (PEC) immunosensor for the determination of cardiac troponin I (cTnI) was constructed. The flower-like stannic oxide (SnO₂) with large specific surface area was prepared by hydrothermal synthesis. Nitrogen-doped carbon quantum dots (NCQDs) with excellent surface property were used as a sensitizer for SnO₂. Bismuth oxyiodide (BiOI) is a narrow band gap (1.83 eV) nanomaterial, which was firstly modified on NCQDs-sensitized SnO₂ through in situ growth method. After NCQDs with small size and BiOI nanoparticles are successively combined with SnO₂, the SnO₂/NCQDs/BiOI microflower was obtained, which possessed good photochemical properties. Using visible light as excitation source and ascorbic acid (AA) as electron donor, the ultrasensitive and quantitative determination of cTnI was realized by detecting the changes of photocurrent under different concentrations of cTnI. The PEC immunosensor showed a large-scaled response (0.001-100 ng mL^-1) and a low detection limit (0.3 pg mL^-1) under optimised experimental conditions. The sensor has potential clinical value in the prediction and diagnosis of cardiovascular diseases in elderly patients with diabetes. Graphical abstract.