Membraneless, self-powered immunosensing of a cardiac biomarker by exploiting a PEC platform based on CaBi₂Ta₂O₉ combined with bismuth oxyiodides

This work describes the development of a membraneless, self-powered immunosensor exploiting a photoelectrochemical system based on two photoelectrodes for cardiac troponin I (cTn). An electrode based on CaBi2Ta2O9 combined with bismuth oxyiodides (BiOI/Bi4O5I2/Bi5O7I) was modified with the cTnI antibody (anti-cTnI) and applied in a photoelectrochemical cell as a photoanode. To perform the cTnI detection exploiting a self-powered photoelectrochemical setup, the immunosensor (anti-cTnI/BiOI/Bi4O5I2/Bi5O7I/CaBi2Ta2O9/FTO) was coupled to a photoelectrochemical cell containing a photocathode based on CuBi2O4 (CBO/FTO) for zero-biased photoelectrochemical immunosensing of cardiac troponin I (cTnI) biomarker. For comparison purposes, the photoanode was applied for cTnI detection in a three-electrode electrochemical cell. The spectroscopic, structural, and morphological characteristics of the photoelectrochemical (PEC) materials were evaluated using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). Electrochemical impedance spectroscopy (EIS) measurements were performed in the presence and absence of light to investigate the effects of photons on the charge transfer resistance of the photoanode. The influence of the cTnI biomarker on the photoelectrochemical response of the anti-cTnI antibody-modified photoelectrochemical platform (anti-cTnI/BiOI/Bi4O5I2/Bi5O7I/CaBi2Ta2O9/FTO) was evaluated by measuring the photocurrent of the system. The immunosensor presented a linear response ranging from 1 pg mL(-1) to 200 ng mL(-1) as well as a mean recovery percentage between 95.7% and 108.0% in real human serum samples for the cTnI biomarker.