## 5 Biosensor Application of Electrodeposited Composite Nanostructures
### Composite Electrodes Containing Carbon Nanomaterials
Then, the surface was modified with 3-mercaptoethanol acid, and an anti-TNF-\(\alpha\) antibody was covalently linked by amide bonds that were formed using EDC/NHSchemistry. The binding of TNF-\(\alpha\) was followed using Faradaic impedance spectroscopy with the Fe(CN)\({}_{6}\)\({}^{3-/4-}\) redox probe and using the change in resistance at one Hz as the reponse, a detection limit for TNF-\(\alpha\) of 0.43 pg mL\({}^{-1}\) was obtained, which was below the 10 to 30 pg mL\({}^{-1}\) that is expected in human serum. An electrochemical sensor for H\({}_{2}\)O\({}_{2}\) was constructed by electrodeposition bimetallic nanoparticles of gold and platinum onto reduced graphene sheets that had been drop cast onto a GCE surface and then dried under an infrared lamp [113]. The film of nanoparticles was electrodeposited by cyclic voltammetry in a solution of two mM of H\({}_{2}\)PtCl\({}_{6}\) and one mM of HAuCl\({}_{4}\) also containing the surfactant Brij 58 at 1.0 wt%. The potential was scanned from 0.4 V to -0.5 V at 100 mV sec\({}^{-1}\) for five cycles. If electrodeposition was carried out only from HAuCl\({}_{4}\) in solution, aggregated nanoparticles formed, and if carried out from H\({}_{2}\)PtCl\({}_{6}\) solution, only very few particles formed. However, when carried out from the mixed solution, more uniformly dispersed nanoparticles were seen in SEM (Sirion 200, FEI Inc., Eindhoven, Netherlands). The current response to H\({}_{2}\)O\({}_{2}\) was maximal when the ratio of Au/Pt was 1:2, and for this, composition was maximal for five cycles conducted at 100 mV sec\({}^{-1}\). Under these conditions, the nanoparticles were dispersed, and the surface area was maximized. Response to H\({}_{2}\)O\({}_{2}\) at zero V gave a limit of detection of 0.31 mM, and a linear range from one to 1.78 mM, and another linear range of a lower slope from 1.78 to 16.8 mM. The sensor was used to measure H\({}_{2}\)O\({}_{2}\) released from rat pheochromocytoma cells (PC 12) cancer cells. The electrodeposition of gold nanoparticles onto a GCE covered by a drop-cast layer of multiwall carbon nanotubes followed by adsorption of glucose oxidase was used to create a modified electrode useful both as a glucose biosensor and as a bioanode in a glucose fuel cell [114]. The multiwalled carbon nanotubes were modified with -NH\({}_{2}\) groups and were 13 to 18 nm in diameter and one to 12-\(\upmu\)m long. Gold nanoparticles were electrodeposited from KAuCl\({}_{4}\) solution and were 10 to 25 nm in size, and were seen by SEM (S-4700, Hitachi, Tokyo, Japan) to decorate the nanotubes. Adsorbed glucose oxidase resulted in a highly sensitive glucose biosensor with a detection limit of 0.5 mM and a linear range from one to 24 mM. The modified GCE was used as a bioanode, with the GCE modified by carbon nanotubes and gold nanoparticles giving the best performance as the bioachode. Acetylcholinesteraseterase and choline oxidase were immobilized in a composite film and used to create a sensor for acetylcholinesterasecholine chloride based on electrochemiluminescencecence [115]. Electrodeposition onto a GCE was carried out from a dispersion of graphene oxide sheets with dissolved HAuCl4 and chitosan by conducting 10 cycles between \(-\)1.6 V and 0.6 V (versus Ag/AgCl) at 50 mV sec\({}^{-1}\). SEM images showed sheet-like structures with dispersed nanoparticles. A dispersion of Fe\({}_{3}\)O\({}_{4}\) nanoparticles decorated by smaller TiO\({}_{2}\) nanoparticles was prepared and then surface modified with aminopropyltrimethoxysilane. Subsequently, the enzymes acetylcholinesterasecholineiser and choline oxidase were immobilized onto these composite nanoparticles by cross-linking with glutaraldehyde. The dispersion was then drop cast onto the modified electrode to complete the composite film. SEM confirmed the structure of aggregates of larger Fe\({}_{3}\)O\({}_{4}\) nanoparticles surrounded by TiO\({}_{2}\) nanoparticles.