Dilute but powerful biological markers, such as hormones in blood stream, are potent but difficult to detect quickly and accurately using current biosensor technologies. Nanoporous structures offer greatly increased surface area which can be functionalized for use as a biosensor, amplifying throughput and the enhancing the ability to detect small concentrations. With the option for diverse component materials and conformations, a sensor with prescribed properties could be easily incorporated into devices for clinical diagnosis or research applications. This study evaluates the suitability of a nanoporous gold (NPG) wire for use as a biosensing component as a proof of concept through the detailed characterization of the porosity, structural support, and electrical properties of the wires. The nanoporous gold wires were created using electrochemical etching equipment.
Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were used to image and evaluate the pores and effectiveness of the etching procedure. Pores were found to be 9.86 ± 4.92 µm in diameter with a density of 880 pores/µm2 and only 5% silver remained following etching procedures. The storage capacity of the nanoporous wire annealed to a gold support structure at 15.6 mF/cm, was found to be higher than that of unsupported wires at 10.6 mF/cm. Structurally supported NPG wires also demonstrated a lower resistance (4.2Ω compared to 13.4Ω) owing to the capacitance of the nonporous gold support structure at high frequencies.
Wires annealed to a gold support structure demonstrated greater mechanical stability and generally more consistent electrical properties. Samples were found highly susceptible to fracture and any coatings vulnerable to denaturing with extensive transport, handling, and testing. Some cross-contamination of samples was detected. Most contamination effects were minimal and confined to materials used in the manufacturing process.
Future investigation should include other support structure conformations, functionalizing samples, and performing biocompatibility testing. NPG wires demonstrate potential for environmental applications and as medical device component, but have not yet been evaluated for direct-contact in vivo applications. The brittleness of the material necessitates that it be used in conjunction with other support structures; however the material provides interesting electrical properties, a good base for the adhesion of biomolecules, and a thorough porosity.
