## 3 Biosensor Application of Nanostructures Electrodeposited onto a Template
### Electrodeposition onto Regularly Packed Thin Films of Colloidal or Nanoscale Spheres
The Raman intensity for adsorbed rhodamine 6G measured at 1362 cm\({}^{-1}\) was high for structures prepared by electrodeposition for five-fifteen hours, but significantly lower on those prepared for either 30 h or two hours. The approach taken in this study allowed for comparison of the produced template versus non-templated structures, and showed superior signal intensity for the structures produced on the template, which was further improved by optimizing the electrodeposition time. The electrodeposition of Au nanoparticles onto a template of three-dimensional close-packed silica spheres of 320-nm diameter was used to create an ordered macroporous structure of connected Au nanoparticles [44]. Producing such a structure was noted as having the advantage of providing both a high surface area and a high conductivity. The silica spheres were deposited on gold-coated glass slides by a vertical dipping method. Au nanoparticles were electrodeposited from 5.0 mM of HAuCl\({}_{4}\) by first allowing one hour of immersion, and then applying 0.5 V (versus SCE) until a desired amount of 1000 nm was used. Figure 3: Scanning electron microscopy (SEM) images of representative samples for each type of Pt-OP (platinum ordered porous) electrode: (**a**) sample type one-third (inset, viewed at a 45\({}^{\circ}\) tilt); (**b**) sample type three-fourths (inset, viewed at a 45\({}^{\circ}\) tilt); and (**c**) sample type one and three-fourths (inset, cross section viewed at a 60\({}^{\circ}\) tilt). (**d**) Optical micrograph of a typical Pt-OP electrode with a length of one cm indicated by the arrow on the grid. Reproduced with permission from ref. [42], Copyright 2013, Elsevier. of charge was passed, such as 0.1 C. The silica spheres were removed using aqueous hydrofluoric acid (HF). The remaining structure resulted from the deposition of gold nanoparticles that were found to have an average size of 4.09 nm in the interstices between the silica spheres, and was macroporous and interconnected as a framework. Hemoglobin was adsorbed onto the structure over times up to three hours. Using electrochemical impedance spectroscopy with the [Fe(CN)\({}_{6}\)]\({}^{3-/4-}\) redox probe, a coverage of 88% was determined for the protein. Coverage of the gold surface by protein significantly reduced the capacitance and also decreased the charge transfer rate constant of the redox probe. Direct electron transfer between the Au nanoparticles of the framework and hemoglobin was observed, and using the Laviron analysis [45], an electron transfer rate constant of 0.95 sec\({}^{-1}\) was obtained. Nanorings and split nanorings of a range of metals were formed by electrodeposition onto a special template using a process referred to as lithographically-patterned nanoscale electrodeposition [46]. Gold nanorings produced by nanosphere lithography using vapor deposition were found to have a superior refractive index response of 350 nm RIU\({}^{-1}\) with a high figure of merit of 3.1, and were found to give excellent performance as real-time sensors for DNA hybridization [47]. Hence, there is a significant value to producing nanorings by the more straightforward approach of electrodeposition. Split nanorings exhibit independently addressable plasmonic resonances, depending upon the polarization of the incident light, and thus have attracted interest for use in multiplexed DNA sensing [48]. A monolayer of polystyrene beads was first spin-coated onto hydrophilic glass slides, and then etched in oxygen plasma to reduce their size. Then, a 70-nm layer of silver was thermally evaporated over the beads, and the beads were removed by sonication in toluene and then in acetone. Positive photoresist was spin-coated over this nanohole array. To ultimately make nanorings, the photoresist was backside exposed at normal incidence, or backside exposed at a variable angle to produce split nanorings.