ABSTRACT We report a label‐free impedimetric immunosensor electrode for prostate‐specific antigen (PSA) detection, using laser‐induced graphene (LIG) coated with ZnO nanorods via pulsed electrodeposition. Two immobilization methods for anti‐PSA antibodies were evaluated: covalent bonding and direct adsorption. Only adsorption enabled clinically relevant detection within 0.1–10 ng/mL in PBS buffer, achieving a detection limit of 81 pg/mL and strong specificity against non‐target glycoproteins. Hence, this work demonstrates the potential of LIG/ZnO composites for low‐cost, scalable sensors suitable for decentralized diagnostics, particularly in low‐resource settings. Unlike conventional impedimetric immunosensors, the LIG/ZnO/adsorbed anti‐PSA sensor exhibited a “signaling‐off” behavior, with charge transfer resistance decreasing upon PSA binding—attributed to antibody conformational changes or desorption (as suggested by XPS measurements), possibly coupled to ZnO surface charge effects. This counterintuitive behavior challenges conventional models of impedimetric immunosensing, highlighting the need to reconsider design assumptions and to account for the unique properties of the transducing material and its biofunctionalization.
Soares et al. (Sun,) studied this question.