Confirmation of sensor functionality using fluorescence Following EDX confirmation of the presence of nitrogen at an AuNPs/Cht-Au modified sensor IDE surface, Atto565 NHS ester (a fluorescent dye modified to bind to primary amine groups) was used to confirm the presence of amine groups on the AuNPs/Cht-Au modified IDE and visualise their distribution along the electrode; similar to Wu, Yi . Subsequently, Atto565 modified DNA complementary and non-complementary strands were used to visualise DNA binding to probe ssDNA. Figure . (A) presents a fluorescent image of AuNPs/Cht-Au IDE following 30 min incubation with Atto565 NHS ester. The observed uniform fluorescent signal strongly suggests that the amine groups are equally distributed along the whole length of the modified sensor IDE. In addition, the high intensity suggests the amine groups are quite dense. By contrast, the lack of fluorescence from the unmodified accumulator IDE confirms the selective deposition of the polymer matrix at the sensor IDE only. By contrast, a uniform fluorescent signal was observed for the Cht-Au modified electrode, see Figure . (B), however, the signal intensity was significantly reduced compared to electrodes with an underlying AuNPs layer presented in Figure . (A). This suggests that the underlying AuNPs layer, below the Cht-Au layer, is essential not only to increase the conductivity of the chitosan film but also to increase the concentration of amine groups. Subsequently, ssDNA was immobilised at AuNPs/Cht-Au IDEs using 0.2% glutaraldehyde as a linker molecule. Atto565 modified target (10 nM) DNA was introduced onto an electrode and incubated for 30 minutes. Following hybridisation, unattached DNA was washed away and fluorescent microscopy was used to confirm specific hybridisation of the complementary DNA occurred.