## 5 Biosensor Application of Electrodeposited Composite Nanostructures
### Composite Electrodes Containing Organic Polymers  
Molecular imprinting combined with electrochemical deposition based on electrostatic interaction has been employed in the construction of a composite nanostructured electrode for electrochemical detection of glucose [124]. An amphiphilic random copolymer was used as a template for the molecular imprinting of glucose in organic solvent with the formation of polymer particles with an average diameter 100 nm, which was induced by the addition of water. Then, gold nanoparticles were formed by the direct reduction of AuCl4- by the pendant amino groups of the polymer. The imprinted polymer particles/Au nanoparticles composite was electrostatically immobilized on the surface of an Au electrode by the application of a \(-2.0\) V potential for two minutes. The glucose templates were extracted using acetic acid/methanol over a period of five days. The resulting modified electrode, with the use of [Fe(CN)6]3-4- as a probe, was found to be highly selective for glucose versus other sugars, as measured by the extent of current reduction in the presence of sugar. A three-component layer of gold nanoparticles, nickel oxide nanoparticles, and conducting polymer was used for the covalent immobilization of tyrosinase to make an impedimetric sensor for dopamine [125]. Gold nanoparticles were first electrodeposited onto an ITO-coated glass electrode by applying 20 cycles between 0.1 V and \(-0.9\) V (versus Ag/AgCl) at 50 mV sec-1 in a one-mM solution of HAuCl4 with the resulting nanoparticles noted as having an average size of 74.49 nm. Next, nickel oxide nanoparticles were electrodeposited by applying 20 cycles between \(-1.2\) V and zero V at 50 mV sec-1 in a solution of 10 mM of Ni(NO3)2. The resulting NiO nanoparticles were on top of the gold nanoparticles, and were described as having an average diameter of 357.96 nm. Finally, on top of the dual nanoparticle layer, a conducting polymer layer was formed by the electropolymerization of pyrrole propionic acid. The change in charge transfer resistance gave the sensor a linear range of 80 uM to 0.20 mM with a detection limit of 5.46 uM. A composite film of gold nanoparticles and carboxymethyl-\(\beta\)-cyclodextrintrins (CMCDs) was prepared by co-electrodeposition onto a GCE and used as a non-enzymatic glucose sensor [126]. Cyclic voltammetry scans were applied from \(-\)1.4 to 0.6 V (versus Ag/AgCl) at 100 mV sec\({}^{-1}\) for two cycles in a solution of HAuCl\({}_{4}\) and CMCD in pH 8.04 phosphate buffer. Cycling of the potential between -1.0 V and 1.0 V at 100 mV sec\({}^{-1}\) was used to polymerize CMCDs. The presence of CMCDs resulted in a higher density of smaller gold nanoparticles on the GCE surface. The electrode showed electrocatalytic activity against a range of analytes, including dopamine, tyrosine, ascorbic acid, chloramphenicol, guanine, uric acid, thymine, and glucose. The performance as a non-enzymatic glucose sensor was evaluated by chronoamperometry at a potential of 0.07 V, and the response was 3.7 times greater for the composite-modified electrodes than for GCE modified with gold nanoparticles alone. The composite-modified electrode also had an extended linear range from 0.001 to 110 mM and a detection limit of 0.99 uM. The electropolymerization of aniline from a solution containing dispersed gold nanoparticles capped by polyvinylpyrrolidone resulted in a composite nanostructured film that was used as a support for glucose oxidase to make a glucose biosensor [127]. TEM images (Tecnai-12, Phillips, Eindhoven, Netherlands) showed that the PVP-capped gold nanoparticles were better dispersed than those that were uncapped. The film was electropolymerized onto a GCE by cycling the potential between \(-\)0.2 and 0.75 V (versus SCE) at 100 mV sec\({}^{-1}\). Glucose oxidase (eight mg mL\({}^{-1}\)) was drop cast onto the composite film, and then, a layer of Nafion was applied from a 0.5% solution. SEM (S-4800, Hitachi, Tokyo, Japan) images showed that the composite film had distinct flower-like structures.