Electrochemical Synthesis of Nanostructured Noble Metal Films for Biosensing

Nanostructures of noble metals (Au and Ag) are of interest because of their important intrinsic properties. Noble metals by themselves are conductive, physically robust, chemically inert, and strongly bind to thiols. However, when the nanostructures are formed, they in addition possess high surface area and unique optical properties tunable by adjusting the shape and size. All of these properties make nanostructures of noble metals suitable candidates to be used as a transducer for biosensing. Individual nanostructures might be easier to prepare but difficult to handle to be used as a transducer. Therefore, we prepared and analyzed nanostructured films/coating of noble metals and used them as a transducer for optical and electrochemical biosensing. We have electrochemically prepared nanoporous gold (NPG) on gold wire by varying different dependable parameters to obtain optimal structure in term of stability, morphology, and surface area. NPG prepared using deposition potential of −1.0 V for 10 min from 30:70% 50 mM potassium dicyanoaurate(I) and 50 mM potassium dicyanoargentate(I) was used as an optimal surface for protein immobilization, and to perform square wave voltammetry (SWV) based enzyme-linked lectinsorbent assays. On flat gold surface, adjacent protein molecules sterically block their active sites due to high-density packing, which can be reduced using NPG as a substrate. Unlike flat gold surfaces, NPG can also show significant peak current in SWV experiments. All these make NPG a suitable substrate, electrode, and transducer to be used in electrochemical biosensing. We have also discovered facile electrochemical method to synthesize plasmonic noble metal nanostructured films (NFs). As- prepared NFs are very sensitive for detecting biomolecules using localized surface plasmon resonance (LSPR) spectroscopy, and are regenerable. We compare the sensitivity of three different types of NFs and discuss the advantages and disadvantages of the prepared structures. Finally, we report carbohydrate–lectin, lectin–protein, and layer-by-layer interactions of molecules using LSPR spectroscopy along with real-time interactions to find the equilibrium dissociation constant of the interactions. The results from these experiments could contribute to the development of cheap and sensitive biosensors that can be used for diagnostic purposes.