Dual signal amplification strategy of Au nanopaticles/ZnO nanorods hybridized reduced graphene nanosheet and multienzyme functionalized Au@ZnO composites for ultrasensitive electrochemical detection of tumor biomarker

Herein, a dual signal amplification strategy was employed in fabricating ultrasensitive electrochemical immunosensor for alpha fetoprotein (AFP) detection, which was realized by utilizing of ZnO nanorods/Au nanopaticles hybridized reduced graphene nanosheet (Au/ZnO/RGO) and horseradish-peroxidase (HRP) bioconjugated detection antibody (Ab2) functionalized Au@ZnO (Ab2/HRP-Au@ZnO). During the fabrication of the immunosensor, a new kind of multiple-head surfactants CxN3 with different alkyl chain length played important roles such as acting as the surfactants of Au/ZnO/RGO and the reductant agents of Au@ZnO composite. Due to the good adsorption property and large surface area of Au/ZnO/RGO, plenty of the capture antibodies (Ab1) were immobilized on the electrode surface, and trace AFP was sensitively monitored. Furthermore, Ab2/HRP-Au@ZnO exhibited high affinity interaction with AFP through “sandwich” immunoreactions, along with the peroxidase-like catalytic activity of Au@ZnO, leading to a further enhancement in the sensitivity of the proposed immunosensor. The successful synthesis of the nanomaterials was characterized through a serious of techniques including Raman, XRD, FT-IR, SEM and UV-vis. Under the optimal conditions, two linear ranges of 0.02-10,000 and 10,000-100,000 pg mL-1 AFP with a lower detection limit of 0.01  pg mL-1 (S/N=3) was obtained. Especially, the proposed AFP immunosensor can be applied to detect human serum samples with satisfactory results, indicating a potential application in clinical monitoring of tumor biomarkers.