Nanoelectrode ensembles NEEs

In order to explore the effects of small electrode size, we have used the template method to prepare ensembles of disk-shaped nanoelectrodes with diameters as small as 10 nm. We have shown that these nanoelectrode ensembles (NEEs) demonstrate dramatically lower electroanalytical detection limits compared to analogous macroelectrodes. The experimental methods used to prepare these ensembles and some recent results are reviewed below. 

The first part of this section focuses on the main characteristics and fabrication techniques used for obtaining templating membranes and depositing metal nanostructures by suitable electroless and elecuochemical procedures. Methods such as sol-gel (10-12) or chemical vapor deposition (10, 13), which have been used primarily for the template deposition of carbon, oxides, or semiconducting-based materials, will not be considered here in detail. The second part of the section focuses on the electrochemical properties of the fabricated nanomaterials with emphasis on the characteristics and applications of nanoelectrode ensembles (NEEs). 

Nanoelectrode ensembles (NEEs) (see also Chapter 10 of this handbook) are nanotech-based electroanalytical tools which find application in a variety of fields ranging from electroanalysis to sensors (86) and electronics (7). They are fabricated by growing metal nanowires in the pores of a template, typically a PC nanoporous manbrane. The density of the pores in the template determines the number of Au-disk nanoelectrode elanents per cm of NEE surface and, correspondingly, the average distance between the nanoelectrode elements. Such electrode systems proved to be valuable tools for trace determinations and kinetics studies by simply using cyclic voltammetry (CV) (5, 69, 86, 97). 

Nanoelectrodes have been widely used in the form of nanoelectrode arrays (NEAs) or nanoelectrode ensembles (NEEs) where individual nanoelectrodes are isolated from one another by various... 

We have demonstrated a new method for preparing electrodes with nano-scopic dimensions. We have used this method to prepare nanoelectrode ensembles with individual electrode element diameters as small as 10 nm. This method is simple, inexpensive, and highly reproducible. The reproducibility of this approach for preparing nanoelectrodes is illustrated by the fact that NEEs given to other groups yielded the same general electrochemical results as obtained in our laboratory [84]. These NEEs display cyclic voltammetric detection limits that are as much as 3 orders of magnitude lower than the detection limits achievable at a conventional macroelectrode. 

FIGURE 6.16 Fabrication of a glucose biosensor based on CNT nanoelectrode ensembles (a) Electrochemical treatment of the CNT-NEE for functionalization, (b) Coupling of the enzyme (GOx) to the functionalized CNT-NEE. (Adapted with permission from Y. Lin et al., Nano Lett. 4, 191. Copyright 2004, American Chemical Society.)... 

Because the fractional electrode area at the lONEE is lower than at the 30NEE (Table 1), the transition to quasireversible behavior would be expected to occur at even lower scan rates at the lONEE. Voltammograms for RuCNHs) at a lONEE are shown in Eig. 8B. At the lONEE it is impossible to obtain the reversible case, even at a scan rate as low as 5 mV s . The effect of quasireversible electrochemistry is clearly seen in the larger AEp values and in the diminution of the voltammetric peak currents at the lONEE (relative to the 30NEE Fig. 8). This diminution in peak current is characteristic of the quasireversible case at an ensemble of nanoelectrodes [78,81]. These preliminary studies indicate that the response characteristics of the NEEs are in qualitative agreement with theoretical predictions [78,81]. 

FIGURE 9.41 SEM images of the NEA, (a) distribution of nanoelectrodes, (b) growth of SiOj islands on B-NCD layer, (c) growth of i-NCD around the SiOj island for the B-NCD, and (d) final recessed nanoelectrode after removal of the SiOj islands NEE, (A) distribution of nanoelectrodes, (B) SiOj spheres after growth of i-NCD, (C) final recessed nanoelectrode after removal of SiOj spheres, and (D) schematic of the cross section for the B-NCD NEAs and NEEs. (Reprinted with permission from Hees, J., Hoffmann, R., Kriele, A. et al.. Nanocrystalline diamond nanoelectrode arrays and ensembles, ACS Nano, 5, 3339-3346. Copyright 2011, American Chemical Society.)... 

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