Coexistence of Dopamine (DA), Ascorbic Acid (AA), Uric Acid (UA) and Serotonin (5-HT) in a biological environment (e.g. cerebral spinal fluid) and their relative closely spaced redox potential makes it challenging to be detected using electrochemical sensing. In this study, we propose a highly selective electrochemical sensor for the detection of Dopamine, Ascorbic Acid, Uric Acid and Serotonin using a single chip implemented on a paper substrate. Working electrodes made of four different types of materials, graphitic carbon, carbon nanotube, reduced graphene oxide and platinum nanowires are fabricated on paper. Microfabricated carbon and silver / silver chloride serve as counter and reference electrode respectively. Overpotential which is defined as additional potential needed to drive a reaction, depends on the electrode material and the reactive species. We used this principle achieve a fingerprint response out of voltammetric analysis for all the mentioned species.
The paper-based sensors employed in the system were fabricated on standard parchment paper. Commonly available adhesive tape was patterned as a mask through laser engraving with a laser cutter and affixed to parchment paper. The paper was then spin coated with Ag/AgCl ink and allowed to cure. At this point six Ag/AgCl electrodes were formed. Carbon ink was subsequently screen printed on all of these electrodes except one and the patterned tape was peeled off leaving a Ag/AgCl RE, a carbon CE and four carbon WE. Dielectric ink was then painted on top of the device to protect all of non-sensing areas and pads. Mentioned nanomaterials were subsequently drop casted on top of the working electrodes and covered by Nafion polymer with drop casting and drying.
The platform chip testing was performed using different concentration of one of the species in the mixture and its cross sensitivity was examined with other interfering species. It was repeated individually for each of the DA, AA, UA and 5-HT. Our initial results show excellent sensitivity and selectivity of the designed chip for the detection of DA, AA, UA and 5-HT in presence of other co-existing spices.