## 6 Comparison of the Advantages and Performance of Different Nanostructures  
The research reported to date involves many kinds of nanostructures, which were prepared under a variety of conditions on different sizes and types of electrodes, and addressing different analytical targets using different methods of measurement. Some of the studies concern the same or similar analytical target measured using the same technique. It is important to consider the question of which structures appear to be providing the most promising limits of detection (generally reported for S/N = three) and linear range, amongst other analytical parameters such as the stability of the response over time. Across all of the studies, analytical parameters are not necessarily reported in the same format. However, it is possible to make some comparisons for analytes, which have been the subject of multiple studies, such as sensors using glucose oxidase with direct electrochemical detection, sensors for non-enzymatic glucose detection, the detection of glucose-based on the detection of H\({}_{2}\)O\({}_{2}\) generated by the action of glucose oxidase, and DNA hybridization sensors. For the case of DNA hybridization, oligonucleotide length is a complicating factor, as is the use of different detection methods. Other studies may concern an analyte that has only been studied once or a few times using an electrochemically-deposited nanostructure, and are thus not able to be used in comparisons. A significant fraction of studies concern the detection of H\({}_{2}\)O\({}_{2}\), which is usually because it is produced by the action of the enzyme glucose oxidase in an effort to make a first-generation glucose sensor. Almost all of these studies report the performance of the sensor in terms of the response to glucose. One study did report both the response to H\({}_{2}\)O\({}_{2}\) concentration and the response to glucose concentration [123], finding them to be slightly different (detection limit of 0.9 uM for H\({}_{2}\)O\({}_{2}\) alone versus a detection limit of 0.5 uM for glucose). A desirable outcome would clearly be both a low limit of detection and a wide linear range. Many of the reports cite detection limits for glucose, as detected by the H\({}_{2}\)O\({}_{2}\) resulting from glucose oxidase action, in the low micromolar range. The most promising results in this case appear to have been found for some of the composite nanostructured films, providing some motivation for the appeal of developing these more complex electrodeposited structures in which different components may act together synergistically. The limit of detection of 0.02 uM and linear range from 2 uM to 5.5 mM that was reported for the composite structure that was previously described [103] is impressive. The result of a limit of detection of 0.21 uM and two linear ranges extending up to 16.8 mM [105] is also noteworthy, although it is not clear why two distinct linear ranges occur. Some studies have reported the detection of H\({}_{2}\)O\({}_{2}\) by direct electron transfer between immobilized HRP and the electrode surface [13; 21; 25], and the results for HRP physisorbed on gold nanoparticles on ITO glass seem most attractive, offering both a low limit of detection of two uM and an extended linear range of up to 30 mM. As has been proposed [1], sensors working on direct electron transfer require minimizing the distance between enzyme active sites and the gold nanoparticle or nanostructure surface. The electrochemical response to glucose alone without enzymes on the nanostructured electrode is the aim of 'non-enzymatic' glucose sensing, of which some examples have been described above. Of the reported studies, the result of a limit of detection of 2.1 uM and an extended linear range from five uM to 16.4 mM on gold nanotube arrays is outstanding, and suggests that the access of glucose in solution to these regularly ordered structures of high surface area can be a promising principle for this and related sensors [48].