## 4 Biosensor Application of Ramified or Dendritic Electrodeposited Structures
### Dendritic-Like Nanostructures  
The electrodeposition of 'ice-like', dendritic gold nanostructures on a gold electrode was used to construct a DNA sensor for an _Enterococcus faecalis_ gene sequence [71]. Electrodeposition was carried out at 0.0 V (versus Ag/AgCl) for 300 s in a solution of 0.5 M of H\({}_{2}\)SO\({}_{4}\), 0.020 M of HAuCl\({}_{4}\), and 0.150 M of sorbitol. The fractal dimension of the nanostructures of 2.44 \(\pm\) 0.19 was obtained by analysis of the SEM (Mira 3-XMU, TSCAN, Brno-Kohoutovice, Czech Republic) images, and a roughness factor of 9.5 was found. Thiolated DNA was immobilized onto the Au nanostructures, and pinholes were filled using 6-mercapto-1-hexanol. The binding of the complimentary DNA strand, which was released from the bacteria, was detected using DPV scans with toluidine blue as the redox probe, and the higher binding affinity of redox probe for double-stranded DNA (dsDNA) over single-stranded DNA (ssDNA). A limit of detection for the complimentary DNA strand of 4.7 \(\times\) 10\({}^{-20}\) mol L\({}^{-1}\) that was 25 nucleotides long was found with a range of detection from 1.0 \(\times\) 10\({}^{-17}\) to 1.0 \(\times\) 10\({}^{-10}\) mol L\({}^{-1}\). The rapid and convenient preparation of dendritic gold nanostructures onto fluorine-doped tin oxide (FTO)-coated glass was achieved from a solution of HAuCl\({}_{4}\) containing 0.1 vol% of 3-aminopropylriethoxysilane (3-APTS) as a structure-directing agent [72]. Electrodeposition was carried out at \(-\)0.25 V (versus Ag/AgCl) for 300 s. 3-APTS forms a moderately strong bond to the Au surface, preferring the Au(111) plane, and induces anisotropic growth and the formation of dendrites that were not observed in its absence. The structures exhibited an electrocatalytic oxidation of glucose and of H\({}_{2}\)O\({}_{2}\). Hyperbranched pine-like gold nanostructures were prepared on the surface of a gold electrode by electrodeposition in a solution of 20 mM of HAuCl\({}_{4}\), 0.5 M of H\({}_{2}\)SO\({}_{4}\), and 150 mM of histidine, serving as a structure-directing agent [73]. Electrodeposition was at 0.0 V (versus Ag/AgCl) for 600 s. The hyperbranched pine-like and dendritic morphology appeared to be composed of nanoparticles that were 150 to 200 nm in size. Electrochemical determination of the real surface area using the [Fe(CN)\({}_{6}\)]\({}^{3-/4-}\) redox probe and the Randles-Sevcik equation gave a roughness factor of 8.2. The resulting electrode was found to be effective as a non-enzymatic sensor for glucose at a potential of 70 mV, and had a limit of detection of 3.39 uM, and a linear range from 0.020 mM to 0.240 mM. The sensor showed good selectivity against a range of interferents, including theophylline, lysine,methionine, histidine, xanthine, arginine, and ascorbic acid. The operating potential of 70 mV was lower than others that had been reported. Electrodeposited gold microstructures with nanoscale dendritic morphology were used as a sensor for a glycoprotein HRP based on the carbohydrate-boronic acid interaction [74]. Electrodeposition from 0.1 M of Na\({}_{2}\)SO\({}_{4}\) and 30 mM of HAuCl\({}_{4}\) at \(-\)0.6 V (versus Ag/AgCl) for 400 s onto a gold electrode produced dendritic forms that were microns in size, with dendritic morphology on the nanoscale. The gold surfaces were modified with 4-mercaptoethanol-polyboronic acid. The interaction of the boronic acid with cis-diols such as those found in the glycans on the glycoprotein resulted in the formation of cyclic esters, thus binding the glycoprotein to the surface. The glycoprotein binding reduced the current for gold oxidation near 1.2 V. A detection limit of 0.5 nM and a linear range from 2.5 nM to 25 mM was obtained using the reduction in the peak current for gold oxidation as the sensing response. Nickel hydroxide-covered copper dendrites were formed on a gold electrode surface and used as a non-enzymatic glucose sensor [75].