## 4 Biosensor Application of Ramified or Dendritic Electrodeposited Structures
### Nanostructures Described as 'Flower-Like', Irregular, of Unusual Morphology
Cyclic voltammetry of the three nanostructures showed differing contributions of oxidation peaks at +1.1 V due to Au(200) or Au(220) crystal facets and at +1.4 V due to Au(111) facets. For immobilized hemoglobin, which was analyzed using the Laviron analysis of the cyclic voltammetry data, resulted in different electron transfer rates of 0.34 sec\({}^{-1}\), 0.16 sec\({}^{-1}\), and 0.13 sec\({}^{-1}\) on flower-like, spherical, and convex nanoparticles, respectively. Platinum nanopetal structures were formed by electrodeposition onto either Pt screen-printed electrodes or platinum electrodes, and used to make a glucose sensor based on the detection of H2O2 produced by the enzyme glucose oxidase [88]. Electrodeposition parameters regarding concentration, potential, and time were systematically varied for electrodeposition from solutions of H2 PtCl6 in H2 SO4 or for K2 PtCl4 in H2 SO4. Electrodeposition at -1.0 V (versus Ag pseudoreference) from 25 mM of H2 PtCl6 and 50 mM of H2 SO4 gave nanopetals with a size of 68 \(\pm\) 20 nm. Electrodeposition from 25 mM of K2 PtCl4 and 50 mM of H2 SO4 at \(-\)0.2 V resulted in regular nanospheres with a size of 52 \(\pm\) 18 nm. Lowering the potential to \(-\)2.0 V resulted in the formation of nanopetals from the K2 PtCl4 solution. Hybrid structures made by electrodeposition nanopetals over the nanospheres were found to be the most sensitive for the non-enzymatic amperometric detection of glucose. Glucose oxidase immobilized by casting from a solution containing glutaraldehyde resulted in a first-generation (H2O2 detection) glucose sensor operating at +0.7 V (versus Ag/AgCl). The Pt nanopetals were covered by a K\({}^{+}\) sensitive polyvinyl chloride membrane, and used as an ion-selective electrode to detect K\({}^{+}\) released by cells undergoing osmotic shock [89]. Flower-shaped gold nanostructures were formed by electrodeposition onto silanized ITO-coated glass electrodes, and found to be sensitive substrates for the detection of dopamine by surface-enhanced Raman spectroscopy [90]. The ITO-coated glass was first silanized with a monolayer of aminopropyltrimethoxysilane followed by electrodeposition using a two-second nucleation step at 0.7 V (versus SCE) followed by 600 s at \(-\)0.4 V from 0.5 to 1.0 mM of HAuCl4. The result was gold 'nanoflower' shapes with a size of 300 to 600 nm. Hierarchical gold nanostructures were formed by electrodeposition in which the pH of the solution and the temperature were used to control the morphology [91]. From 5 mM of HAuCl4, deposition at 0.5 V (versus SCE) onto GCE for 10 min at pH 2-3 gave popcorn-like morphologies that were aggregates of nanocrystals. At pH 4, deposition produced waxberry nanostructures that were 600 nm in size and made of 30 nm nanocrystals. Deposition at 40 \({}^{\circ}\)C gave waxberry nanostructures of 1 \(\upmu\)m size with some nanoparticles linking in between. At pH 6, irregular structures were formed. The change in pH favored different Au complexes in solution with different redox potentials and growth rates, with AuCl4\({}^{-}\) dominant at lower pH and Au(OH)4\({}^{-}\) at higher pH. The structures formed at pH 4 and 40 \({}^{\circ}\)C were very active for the electrocatalytic oxidation of glucose, with detection at 0.36 V giving a linear range from two to 38 mM and a detection limit of 4 \(\upmu\)M.  
Anisotropic Au nanoparticles were formed by electrodeposition and used as a support for a DNA sensor for _Trichomonas Vaginalis_[92]. The nanoparticles were formed by electrodeposition from 0.5 M of H2 SO4 with 20 mM of HAuCl4 and 150 mM of phenobarbital at 0.0 V (versus Ag/AgCl) for 300 s. The modification of the surface with the anisotropic Au nanoparticles resulted in a roughness factor of 6.0. The gold surfaces were modified with a thiolated probe oligonucleotide and mercaptohexanol.