Detection of dopamine in the presence of excess ascorbic acid at physiological concentrations through redox cycling at an unmodified microelectrode array

• Published in: Analytical and bioanalytical chemistry 2013-04, Vol.405 (11), p.3859-3869
• Main Authors: Aggarwal, Anupama, Hu, Mengjia, Fritsch, Ingrid
• Format: Article
• Language: English
• Subjects: Accumulators; Acids; Analytical Chemistry; Arrays; Ascorbic acid; Ascorbic Acid - chemistry; Biochemistry; Biosensing Techniques - instrumentation; Buffers; Catecholamines; Characterization and Evaluation of Materials; Chemical properties; Chemistry; Chemistry and Materials Science; Collectors; Cycles; Dopamine; Dopamine - analysis; Dopamine - cerebrospinal fluid; Electrochemical analysis; Electrochemical Techniques - instrumentation; Electrochemistry; Electrodes; Electrons; Equipment Design; Food Science; Identification and classification; Laboratory Medicine; Limit of Detection; Methods; Microarray Analysis - instrumentation; Microelectrodes; Microorganisms; Monitoring/Environmental Analysis; Original Paper; Oxidation; Oxidation-Reduction; Oxidation-reduction reaction; Physiology; Vitamin C; Voltammetry
• ISSN: 1618-2642; 1618-2650
• DOI: 10.1007/s00216-013-6738-z

The electrochemical behavior of dopamine was examined under redox cycling conditions in the presence and absence of a high concentration of the interferent ascorbic acid at a coplanar, microelectrode array where the area of the generator electrodes was larger than that of the collector electrodes. Redox cycling converts a redox species between its oxidized and reduced forms by application of suitable potentials on a set of closely located generator and collector electrodes. It allows signal amplification and discrimination between species that undergo reversible and irreversible electron transfer. Microfabrication was used to produce 18 individually addressable, 4-μm-wide gold band electrodes, 2 mm long, contained in an array having an interelectrode spacing of 4 μm. Because the array electrodes are individually addressable, each can be selectively biased to produce an overall optimal electrochemical response. Four adjacent microbands were shorted together to serve as the collector, and were flanked on each side by seven microbands shorted as the generator (a ratio of 1:3.5 of electroactive area, respectively). This configuration achieved a detection limit of 0.454 ± 0.026 μM dopamine at the collector in the presence of 100 μM ascorbic acid in artificial cerebrospinal fluid buffer, concentrations that are consistent with physiological levels. Enhancement by surface modification of the microelectrode array to achieve this detection limit was unnecessary. The results suggest that the redox cycling method may be suitable for in vivo quantification of transients and basal levels of dopamine in the brain without background subtraction. Figure 1 Microelectrode array chip design and assignment of electrodes used for determination of dopamine (DA) in the presence of large excess of ascorbic acid (AA) by redox cycling. Analytes (DA and AA) are oxidized at the generator electrodes to form dopamine-o-quinone (DAQ) and dehydroascorbic acid (AAo) which diffuse to the nearest collector electrodes. DA is selectively detected at the collector electrodes, because DAQ can be reduced there, but AAo hydrolyzes to a nonelectroactive form prior to arrival