Nanobiotechnology is a discipline wherein tools from nanotechnology are applied to study biological phenomena. In application to biosensor development, the technically designed nanomaterial serves the purpose of signal amplification when the binding event takes place. In recent years, the use of metal-based nanomaterials has expanded in various biomedical applications due to the scope of facile synthesis and functionalization, high surface area, and extensive stability. Among the noble metal candidates, gold nanoparticles have been employed in the field of biosensor studies.

Nanoporous gold is one of the most extensively investigated materials owing to its unique properties which are highly dependent on its microstructure and feature size. In an effort, to improve the current design, nanoporous gold was electrochemically engineered to incorporate two distinguishable scales of ligament and pore sizes giving rise to a hierarchical nanoporous gold (hNPG) structure. We have chosen to take advantage of the surface architectures of hNPG due to the presence of a large specific surface area for functionalization and rapid transport pathways for faster response. Here small-sized pores are exploited for immobilization and a network of larger pores helps in transport. We present here the fabrication of hNPG using a procedure involving electrochemical dealloying-annealing-chemical dealloying to yield a structure of larger pores of several hundred nanometers and smaller pores below 100 nm in size. Different compositions of alloys were used as precursors to generate the desired material of interest. We have used several analytical techniques to characterize the fabricated electrode such as scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, cyclic voltammetry (CV), and thermogravimetric analysis (TGA). SEM-EDX colored images show the atomic percentage of silver left after each dealloying step. The essential role of two-step dealloying and annealing can be seen in cyclic voltammograms. The area under the gold oxide reduction peak was integrated to evaluate the electrochemically active surface area (ECSA) which is significantly higher for the hNPG. Surface coverage of self-assembled monolayers on hNPG was compared with NPG using TGA and reductive desorption. The loading performance of the electrodes was evaluated based on the solution depletion technique which was used to quantify the molecules of interest from the solution into hNPG and NPG. The enhanced catalytic response was seen through the technique of chronoamperometry. Chronoamperometric response of hNPG and NPG was recorded at an applied potential upon successive additions of glucose. Glucose sensing properties of hNPG were largely improved when compared with NPG.

The electrochemical detection of the glycoproteins using electrochemical assays based on lectin binding interactions is a current interest for use of this material. hNPG is a material of great promise for biosensor development as it enhances the scaling relations between volume and accessible surface area.