Surfactant embedded carbon nanotube composite electrodes for antifouling electrochemical detection of serotonin in the bowel

Measuring serotonin (5-HT) in the bowel presents a major analytical challenge due to extensive chemical and biological fouling of electrochemical sensors. Although various carbon-based electrodes have previously been used for bowel measurements, they still lack the stability required for reliable 5-HT detection. Antifouling strategies, particularly those involving surfactants, have shown considerable promise for improving electrode performance. In this study, we systematically investigated the effect of incorporating different surfactants into multi-wall carbon nanotube (MWCNT) composite electrodes. The electrodes were evaluated for their resistance to fouling by 5-HT oxidation by-products and mucin, both individually and in combination, as well as within incubation media containing colonic tissue. Electrodes containing cetyltrimethylammonium bromide (CTAB) exhibited enhanced current responses for an inner-sphere redox probe compared with those containing Triton X-100 (TX) or sodium dodecyl sulfate (SDS). Although SDS and TX modified MWCNT electrodes offered some improvement over unmodified MWCNT composites, CTAB modified MWCNT electrodes demonstrated the best overall antifouling performance. MWCNT electrodes containing 5% CTAB showed markedly reduced fouling in the presence of 5-HT, mucin, and colonic tissue incubation media. Contact angle measurements confirmed increased hydrophilicity; CTAB's superior performance indicates antifouling is primarily driven by electrostatic effects rather than wettability. Overall, our findings highlight the incorporation of surfactants, especially CTAB, as a powerful strategy for producing antifouling carbon composite electrodes capable of stable and reliable electrochemical measurements in harsh biological environments.