Determination of serotonin by using a thin film containing graphite, nanodiamonds and gold nanoparticles anchored in casein

[Display omitted] •The CSN formatted a stable nanomaterials biofilm.•Gold and diamond nanoparticles increase the sensitivity of 5-HT determination.•The NDs-AuNPs-Gr-CSN/GCE presented low-cost, high sensitivity and good accuracy.•The present sensor may be useful in 5-HT monitoring as disease marker in urine. The determination of serotonin has become relevant in biological fluid analysis since some neurological disorders may be related to abnormal amounts of this neurotransmitter in human beings. In this work, it is proposed the construction of a low-cost electrode sensitive to the quantification of serotonin by a biofilm of graphite, nanodiamonds and gold nanoparticles anchored in casein. The casein biofilm was used to anchor the conductive nanomaterials on the GCE. Measurements were performed by differential pulse voltammetry in which showed a linear response with LDR of 0.3 to 3.0 μmol L−1, LOD of 0.1 μmol L−1 and a sensitivity of 0.18 µA L mol−1. The sensor was applied for the serotonin quantification in synthetic urine samples enriched with good recovery (91.4 to 103%). Therefore, the proposed electrode improved the conductivity and the electronic transfer capacity of the pristine electrode by low-cost biofilm, which could be applied in electrochemical biosensing.