Nanostructured Geometries Strongly Affect Fouling of Carbon Electrodes

Electrode fouling is a major factor that compro-mises the performance of biosensors inin vivousage. It can beroughly classified into (i) electrochemical fouling, caused by theanalyte and its reaction products, and (ii) biofouling, caused byproteins and other species in the measurement environment. Here,we examined the effect of electrochemical fouling [in phosphatebuffer saline (PBS)], biofouling [in cell-culture media (F12-K)with and without proteins], and their combination on the redoxreactions occurring on carbon-based electrodes possessing distinctmorphologies and surface chemistry. The effect of biofouling onthe electrochemistry of an outer sphere redox probe, [Ru-(NH3)6]3+, was negligible. On the other hand, fouling had amarked effect on the electrochemistry of an inner sphere redox probe, dopamine (DA). We observed that the surface geometryplayed a major role in the extent of fouling. The effect of biofouling on DA electrochemistry was the worst on planar pyrolyticcarbon, whereas the multiwalled carbon nanotube/tetrahedral amorphous carbon (MWCNT/ta-C), possessing spaghetti-likemorphology, and carbon nanofiber (CNF/ta-C) electrodes were much less seriously affected. The blockage of the adsorption sitesfor DA by proteins and other components of biological media and electrochemical fouling components (byproducts of DAoxidation) caused rapid surface poisoning. PBS washing for 10 consecutive cycles at 50 mV/s did not improve the electrodeperformance, except for CNF/ta-C, which performed better after PBS washing. Overall, this study emphasizes the combined effect ofbiological and electrochemical fouling to be critical for the evaluation of the functionality of a sensor. Thus, electrodes possessingcomposite nanostructures showed less surface fouling in comparison to those possessing planar geometry.