Enhanced photoelectrochemical immunosensing of cardiac troponin I based on energy transfer between N-acetyl-L-cysteine capped CdAgTe quantum dots and dodecahedral Au nanoparticles

An immunosensor was fabricated with an immobilized antibody for cardiac troponin I (anti-cTnI) on a photoresponsive composite material consisting of N-acetyl-L-cysteine capped CdAgTe quantum dots (NAC-CdAgTe QDs) and dodecahedral gold nanoparticles (AuNPs) stabilized by 1-(10-bromodecyl)-3-methylimidazolium bromide ionic liquid. Synthesized materials were characterized by TEM, SEM, UV-Vis, XRD, XPS, EIS, fluorescence, and photoelectrochemical method to confirm their morphology, elemental composition, and properties. The sensing element, anti-cTnI, was then covalently bound to the composite material coated on a glassy carbon electrode to complete the immunosensor, abbreviated as anti-cTnI(BSA)/NAC-CdAgTe QDs/AuNPs/GCE. Photocurrent was measured when the sensor was excited by a 405 nm 100 mW laser light. Optimal operating conditions, stability, reversibility, and reproducibility of the sensor have been studied. Performance of the aforementioned sensor was monitored with the photocurrent and the relative photocurrent variation, which is expressed as the changes in photocurrent upon the formation of antibody-antigen complex relative to the initial current measured in the unbound state of antibody. The experiment showed the relative photocurrent variation is directly proportional to the logarithm of cTnI concentration between 5.0 pg mL−1 and 20.0 ng mL−1 with a detection limit of 1.756 pg mL−1 (S/N=3). Performance of the immunosensor in common interferents and clinical human serum samples was investigated, showing comparable to ELISA with good selectivity, accuracy, and precision.