Selective Detection of Dopamine against Ascorbic Acid Interference Using 3D Carbon Interdigitated Electrode Arrays

3D carbon interdigitated electrode arrays (IDEAs) were fabricated using inexpensive conventional UV photolithography of SU8 with modified exposure and post exposure bake settings. SU8 patterns were pyrolyzed in an inert environment to obtain three-dimensional (3D) carbon IDEAs. In SU8 an IDEA with a digit width of 3µm, digit height of 6µm (aspect ratio of 2) and gap spacing of 0.8µm was achieved. The carbon sensor performance was investigated as a function of IDEA digit width/gap ratio and digit height under no flow and flow conditions. We demonstrated a gradual increase in redox amplification with an increase in IDEA digit width/gap ratio in the lower ratio range. At higher width/gap ratios, from 1.5 onwards, the amplification factor showed a much steeper increase. The highest amplification of 37 we obtained for a width/gap ratio of 2.45 for an electrode height of 0.95µm. Redox amplification increases significantly with increase in IDEA height. Redox amplification increased from a factor of 9 at 0.09µm digit height to a factor of 37 at 0.95µm height. The effect of potential sweep rate on redox amplification was also investigated. As the sweep rate was decreased from 50mV/s to 5mV/s, the collection efficiency increased from 0.92 to 0.97 whereas the amplification increased from 7 to 25. Under flow condition, the amplification decreases substantially as the recycling of the redox species is impeded by convection resulting in a drop in collection efficiency. The highest amplification of 37 dropped to 4 for the same electrode for a flow rate of 500nL/s.