Fluorescence characterisation To confirm a uniform electrodeposited chitosan layer, modified electrodes were immersed in a fluorescently labelled succinimidyl ester (Atto565-NHS ester) which is known to bind to the primary amine groups. First, 0.5 mg Atto565-NHS ester was reconstituted in 500 uL DMF. Then, 50 µL of this solution was diluted in 30 mL of PBS buffer. Chips with chitosan modified electrodes were immersed in this mixture and incubated for 30 minutes at room temperature. After this time, chips were removed, washed with DI water to remove the unattached dye and dried in a stream of nitrogen. Fluorescent microscopy was then used to confirm that the target DNA hybridised with the probe DNA and that no unspecific binding took place. Two different DNA strands, target and non-target, tagged with Atto565 were employed. AuNPs/CHI-Au/ssDNA modified sensor IDEs were incubated for 30 minutes with either 10 nM target DNA or non-target DNA both DNA strands were tagged with Atto565. Afterwards, chips were washed with DI water, dried under nitrogen. and characterised using fluorescent microscopy.