Fabrication and characterization of vertically aligned carbon nanofiber electrodes for biosensing applications

We describe recent experiments aimed at using carbon nanofibers for biosensing applications. Vertically aligned carbon nanofibers are grown on molybdenum electrodes to provide electrical contact to the nanofibers. Upon exposure to electrolyte solutions, we find that short nanofibers of < 1 μm length can be wet and dried without significant mechanical disruption. However, longer fibers are prone to clumping due to meniscus forces. Deposition of SiO2 adds mechanical strength and electrically insulates the nanofiber sidewalls, which can be further augmented by additional deposition of epoxy-based photoresist. Reactive-ion etching re-exposes the carbon core, localizing the electrical response to the nanofiber ends and leading to electrically active electrodes of ∼ 40 nm radius. Measurements of the diffusion-limited current from ensembles of nanofibers are solutions containing redox agents are in excellent agreement with classical electrochemical theory. We also briefly describe the use of chemical and electrochemical methods to functionalize carbon nanofibers.