Electrodeposition of Gold Nanoparticles for a Highly Sensitive Immunosensor for White Spot Syndrome Virus (WSSV) Envelope Protein VP28 Detection Based on Electrochemical Impedance Spectroscopy Technique

Lacking effective treatment, white spot syndrome virus (WSSV) causes mass mortality in farmed shrimp, significantly damaging the shrimp industry worldwide. To enable early detection and diagnosis of this disease, we have demonstrated an electrochemical immunosensor to detect the VP28 antigen, a key envelope protein of this virus. First, gold nanoparticles (AuNPs) were electrodeposited on the sensor’s carbon surface to enhance both its sensitivity and its capability to form a self-assembled monolayer (SAM). Subsequently, an SAM using 11-Mercaptoundecanoic acid was coated as an intermediary layer for immobilizing VP28 antibodies. The specific interaction of VP28 antigen-antibody, confirmed by Western Blot, impeded electrons transfer, leading to an increase in charge transfer resistance. Cyclic voltammetry (CV) was utilized to deposit AuNPs and combined with electrochemical impedance spectroscopy (EIS) to characterize the modification of the sensor’s electrode surface through changes in electric current and impedance. The scanning electron microscope (SEM) results showed that nanosized gold particles were uniformly dispersed on the carbon electrode surface. Electric measurement results showed that the change in charge transfer resistance ( $\Delta {R}_{\text {CT}}$ ) correlates linearly with the VP28 protein concentration range from 0 to 60 ng/mL, with an ${R}^{\,{2}}$ coefficient of 0.98945 and a low limit of detection (LOD) of 2.38 ng/mL. Additionally, the anode peak current decreased from 15.150 to $7.725~\mu $ A with increasing antigen concentration. Control experiments with various proteins demonstrated the specificity of the proposed immunosensor for detecting VP28. This sensor offers an accessible electrochemical sensing tool, enabling convenient, direct, and immediate diagnosis of WSSV on shrimp farms.