SEEDING to Enable Sensitive Electrochemical Detection of Biomarkers in Undiluted Biological Samples

Electrochemical biosensors have shown great potential for simple, fast, and cost-effective point-of-care diagnostic tools. However, direct analysis of complex biological fluids such as plasma has been limited by the loss of sensitivity caused by biofouling. By increasing the surface area, the nanostructured electrode can improve detection sensitivity. However, like a double-edged sword, a large surface area increases the nonspecific adsorption of contaminating proteins. The use of nanoporous structures may prevent fouling proteins. However, there is no straightforward approach for creating nanostructured and nanoporous surfaces compatible with microfabricated thin-film electrodes. Herein, the preferential etching of chloride and surfactant-assisted anisotropic gold reduction to create homogeneous, nanostructured, and nanoporous gold electrodes is demonstrated, yielding a 190 ± 20 times larger surface area within a minute without using templates. This process, "surfactant-based electrochemical etch-deposit interplay for nanostructure/nanopore growth" (SEEDING), on electrodes enhances the sensitivity and antibiofouling capabilities of amperometric biosensors, enabling direct analysis of tumor-derived extracellular vesicles (tEVs) in complex biofluids with a limit of detection of 300 tEVs µL^-1  from undiluted plasma and good discrimination between patients with prostate cancer from healthy ones with an area under the curve of 0.91 in urine and 0.90 in plasma samples.