In situ deposition of gold nanoparticles on polydopamine functionalized silica nanosphere for ultrasensitive nonenzymatic electrochemical immunoassay

• We develop a novel ultrasensitive nonenzymatic electrochemical immunoassay method.
• The in situ deposition method provides a simple way to prepare gold nanoprobe.
• The high loading ability of the nanoprobe greatly amplifies the detection signal.
• The electrode modification of carbon nanotubes can enhance the stripping current.
• The positive stripping potential range avoids the interference of dissolved oxygen.

A novel gold nanoprobe was prepared for the signal tracing of ultrasensitive nonenzymatic electrochemical immunoassay at a carbon nanotubes (CNTs)-based disposable immunosensor. The gold nanoprobe was prepared via in situ deposition of gold nanoparticles (Au NPs) on the polydopamine functionalized silica nanosphere followed by the labeling of signal antibodies. The immunosensor was prepared through the covalent immobilization of capturing antibodies on the CNTs modified screen-printed carbon electrode. After a sandwich-type immunoreaction on the immunosensor surface, the gold nanoprobes were captured onto the electrode surface to form immunocomplex. The multiple Au NPs on the attached nanoprobe composites were then measured by electrochemical stripping analysis to obtain signal response. This method provided a simple and controllable way to prepare a novel gold nanoprobe which greatly amplified the signal response of every single immuno-recognition event. The modification of electrode surface with CNTs also facilitated the stripping current enhancement of Au NPs resulting in the ultrahigh sensitivity of this immunoassay method. Using human IgG as a model analyte, the proposed method showed a wide linear range over three orders of magnitude with the detection limit down to 6.9 pg/mL. Besides, this method showed excellent analytical performance with low cost, good portability, and acceptable reproducibility, stability and accuracy, thus providing great potentials for clinical applications.