shows the electrochemical characterisation of AuNPs/Cht-Au IDE in 5 mM Fe -4 /Fe 3-redox couple at different scan rates (10 mV-200 mV). As expected, the peak currents increased with an increased scan rate, suggesting that the redox reaction is diffusion-controlled . The inset shows linear relationships of the anodic and cathodic peak currents as a function of the square root of scan rate which indicates that the diffusional profiles of individual micro bands overlap and the electrode behaves like a larger microelectrode. Following electrode optimisation as described above, an optical and electron microscopy characterisation study was undertaken in Figure . and Figure . Figure shows an optical image of a sensor following modification of one IDE (dark bands) with AuNPs. It can be seen that the modification only occurred at a sensor IDE while the accumulator IDE remained unmodified. Figure . (B) shows an SEM image of the AuNPs modified sensor IDE and an inset at higher magnification. Two different nanostructure morphologies were observed, round nanoparticles on the length of the electrode and bigger clusters at the electrode edges. The size of the round NPs varied between ~30 nm and ~90 nm (see Figure . (A)) while larger dendritic particles, ~500 nm, were observed at the band edges. These larger particles arose from the high electric fields, present at the boundary discontinuities occurring at the interface between the top surface and sidewalls of the bands, enhancing gold deposition. Figure . (C) shows an optical image of a microelectrode, with a sensor IDE following AuNPs/CHI-Au modification. A defined green coloured layer can be seen around each band in the sensor IDE, compared to the electrode modified with just AuNPs only (Figure . (A)). This green layer is attributed to the chitosan and suggests that the polymer was deposited on top of the IDE. The SEM image in Figure . (D) shows the gold nanostructures of the AuNP modification. At higher magnification (inset) a thin layer can be seen around the Au nanostructures, indicated by the arrows, which can be attributed to the chitosan. This suggests that using 50 ppm Au in a chitosan solution did not cause additional deposition of AuNPs, but facilitated polymer deposition. Optical and SEM images for an IDE modified with Cht-Au only (i.e., with the AuNP layer suppressed) are presented in Figure . (B). The optical image shows a green coloured layer, indicative of chitosan, around the bands in the sensor IDE while under high-resolution SEM, a thin layer, similar to the inset of Figure . (D), at the electrode edges, can be observed. EDX analysis of IDEs electrodes modified with AuNPs and AuNPs/Cht-Au modified was undertaken as it is well known that chitosan is rich in amine functional groups. Consequently, EDX can be used to confirm the presence of nitrogen on the surface of a modified electrode. Nitrogen was not present on the electrode modified with AuNPs only (negative values in the table; inset), Figure . (E), while it was present on the electrode modified with AuNPs/CHI-Au, (positive 3.43% in the table, inset), Figure . (F).