A diamond paste-based stochastic sensor modified with protoporphyrin IX was optimized and used for the assay of tumor necrosis factor-alpha (TNF-alpha) when a potential of 125 mV vs Ag/AgCl was applied. Its high selectivity versus acethylcholine (ACh), glutamate, and gamma-aminobutyric acid (GABA) made possible the accurate assay of TNF-alpha at 125 mV vs Ag/AgCl as well as of the above neurotransmitters at 50 mV vs Ag/AgCl. The sensor was reliable used for screening tests of children's cerebrospinal fluids, recoveries higher than 98.00% with low RSD (%) (lower than 1.0%) being recorded. The limit of determination obtained for the proposed sensor for the assay of TNF-alpha was 10 pg/mL, which is lower than the one reported for ELISA (16 pg/mL). (C) 2015 The Electrochemical Society. All rights reserved.