Tunable High-Quality Nanoporous Gold Electrodes for Bioelectronic Applications

The nanoporous gold (np-Au) electrode, created through the oxidative dissolution of less noble elements in gold alloys, features a network of nanometer-sized metallic struts and interconnected pores. This structure enhances electrode surface area, making it highly suitable for various bioelectronic applications. Controlling pore morphology allows for a broad investigation of mechanical and surface properties, laying the groundwork for the development of diverse biosensing and stimulation interfaces. However, precise control over np-Au electrode morphology is challenging due to the rapid dealloying process and the lack of robust characterization tools to monitor the evolution of the material's matrix.<br/>Here, we investigated the impact of different fabrication techniques and key process parameters on np-Au electrode morphology, then leveraged the findings to devise a simple method for fabricating high-quality np-Au electrodes with tunable features. In our approach, the master alloy matrix was initially formed through gold/silver sputtering at a 1:2 ratio. The dealloying process was conducted via either electrochemical or direct acid treatment, monitored by electrochemical quartz crystal microbalance (EQCM) and analyzed post-dealloying using Scanning Electron Microscopy (SEM). The speed of dealloying significantly influenced morphology, with electrochemical dealloying proving more controllable and programmable through various applied voltage profiles, resulting in a high-quality np-Au surface.<br/>To demonstrate the practicality of these high-quality electrodes, they were further functionalized with a thiol-based aptamer probe for electrochemical sensing. The sensors exhibited enhanced antifouling capabilities and an improved signal-to-noise ratio (SNR) due to the optimized controlled dealloying process. The resultant concave features acted as physical sieves to enhance antifouling properties. Additionally, the high catalytic activity of the gold surface was confirmed through oxygen reduction reaction cyclic voltammetry, indicating the superior quality of the dealloyed electrode surface.<br/>To evaluate the robustness of the electrode interfaces for in vivo applications, the fabricated sensor was implanted in a rat model for antibiotic monitoring. The sensor delivered high-SNR in vivo drug concentration data within hours of operation and exhibited a significant reduction in signal drift compared to other reported nanostructured in vivo electrochemical sensors. This confirmed the suitability of the np-Au electrodes for in-vivo biosensing applications. The scalability and adaptability of this fabrication process make it ideal for creating high-quality np-Au interfaces on various substrates for diverse bioelectronic device-level integrations.