## 4 Biosensor Application of Ramified or Dendritic Electrodeposited Structures
### Dendritic-Like Nanostructures
Deposition time under these conditions was also examined, and denser dendrites were observed at 5400 s and 7200 s. The morphologies were deemed consistent with growth by diffusion limited aggregation. The conditions of electrodeposition from 10 mM of HAuCl\({}_{4}\), at \(-0.3\) V, and for 3600 s were deemed ideal for the electrocatalytic oxidation of glucose. An applied potential of 0.15 V was optimal for detection, balancing sensitivity and stability, and a detection limit of 0.05 mM and a linear range from 0.1 to 25 mM were found. Dendritic structures of CuNi were formed by electrodeposition onto copper foil and shown to be useful as a potential non-enzymatic glucose sensor [79]. Electrodeposition was carried out from solutions of 0.03 M of NiSO\({}_{4}\), 0.03 M of CuCl\({}_{2}\), and 0.1 M of Na\({}_{2}\)SO\({}_{4}\) at a series of potentials from \(-0.6\) V to \(-1.2\) V (versus SCE) for 3600 s. Dendritic structures were obtained. Energy dispersive spectroscopy (EDS) revealed that the Cu/Ni ration varied along the stem of the dendrites, increasing in the direction of dendrite stem growth. Cyclic voltammetry in 0.1 M of NaOH and one mM of glucose confirmed the electrocatalytic oxidation of glucose. Dendritic gold nanostructures formed on GCE were used as a support for an aptamer-based sandwich assay for thrombin [80]. Dendritic gold nanostructures were electrodeposited onto GCE at \(-0.6\) V (versus SCE) from 0.1 M of Na\({}_{2}\)SO\({}_{4}\) and 30 nM of HAuCl\({}_{4}\). Then, the surfaces were modified by a thiolated anti-thrombin aptamer and 6-mercapto-1-hexanol. Also, 150-nm mesoporous silica nanoparticles (MSN) were prepared, onto which eight-nm Au nanoparticles were formed, and these  
Figure 7: Scanning electron microscopy images of the DenAu/GC (dendritic gold/glassy carbon) electrodes with different electrodeposition times of 300 s (**A**), 500 s (**B**), and 700 s (**C**), and the energy dispersive spectroscopy (EDS) spectrum (**D**) of the DenAu/GC electrode of 700 s. Reproduced with permission from ref. [76], Copyright 2014, Elsevier. particles were loaded with thionine and also modified by the adsorption of an anti-thrombin aptamer. The binding of thrombin to the electrode surface was followed by binding of the aptamer-modified MSN, which allowed for thrombin detection using the detection of thionine using DPV. A detection limit of 0.5 ng mL\({}^{-1}\) for thrombin was achieved, as well as a log-linear range from 0.03 pM to 0.018 \(\upmu\)M thrombin. Dendritic gold micro/nanostructures grown on ITO-coated glass electrodes were demonstrated as useful for DNA detection [81]. Gold structures were electrodeposited from 12 mM of HAuCl\({}_{4}\) and 0.05 M of HClO\({}_{4}\) at potentials ranging from 0.3 V to \(-\)0.3 V (versus Ag/AgCl) and times from two to 15 min. A comparison of structures deposited at a constant amount of charge passed of 0.2 C showed a trend toward a more dendritic morphology as the deposition potential became more negative up until \(-\)0.1 V; then, at \(-\)0.3 V, the structures appeared more irregular and less branched. The gold surfaces were modified by a thiolated 18-mer complimentary DNA strand followed by treatment with 6-mercapto-1-hexanol. The binding of a target DNA, and subsequently a reported DNA bound to gold nanoparticles, were monitored by using the electrochemical response of a bound methylene blue redox indicator by square-wave voltammetry. The response has a log-linear range from 50 aM to one pM, and a detection limit of 12 aM. Dendritic silver structures formed on gold foil by electrodeposition were shown to have electrocatalytic activity for the reduction of H\({}_{2}\)O\({}_{2}\)[82]. The dendritic structures were formed by electrodeposition at \(-\)0.3 V (versus Ag/AgCl) at times of 10 s, 60 s, or 120 s. XRD confirmed that the Ag dendrites were of crystalline silver. The dendrites were about eight \(\upmu\)m long, with branches that were 70 to 80 nm in diameter.