Ultra-sensitive electrochemical sensors for simultaneous determination of dopamine and serotonin based on titanium oxide-gold nanoparticles-poly Nile blue (in deep eutectic solvent)

•Screen-printed carbon electrodes were modified with TiO2NP, PNBDES, and AuNP.•TiO2NP, PNBDES, and AuNP were characterized by FE-SEM-EDX, FTIR, and XRD.•Electrochemical characterizations of the modified electrode were performed by CV and DPV.•Disposable sensors were developed for the simultaneous determination of DA and SE.•DA and SE levels in blood serum were simultaneously measured by the developed sensor. Determining blood serum levels of dopamine (DA) and serotonin (SE), which are important neurotransmitters, is of great importance in diagnosing and treating many diseases. In this work, a new disposable sensor was developed for the simultaneous determination of DA and SE. First, titanium oxide nanoparticles (TiO2NP) were modified on the screen-printed carbon electrodes (SPCE) by physical adsorption. Then, AuNP was coated on SPCE/TiO2NP by cyclic voltammetry (CV). Finally, a deep eutectic solvent (DES) appropriate for green chemistry, ethylene glycol/choline chloride, was used to electro-polymerize Nile blue (NB) on SPCE/TiO2NP/AuNP. The materials of TiO2NP, AuNP, and PNBDES were characterized by FE-SEM-EDX, XRD, and FTIR. The effects of TiO2NP, AuNP, and PNBDES modification order on the electrode surface on the separation of differential pulse voltammetry (DPV) peaks of DA and SE were investigated. DPV analysis conditions (deposition time and potential) and pH effect were examined. Analytical parameters of the prepared sensor were determined for both individual and simultaneous determination of DA and SE. The detection limits (3 σ/m) for simultaneous detection are 1.39 nM and 2.47 nM for DA and SE, respectively. The sensor's repeatability, reproducibility, and reusability were examined for the simultaneous determination of DA and SE. Application stability of the developed sensor was determined as 20 days and storage stability as 4 weeks. The selectivity of the DA and SE sensor in the presence of ascorbic acid, uric acid, glucose, and citric acid was investigated, and it was observed that the selectivity of the sensor was satisfactory. The disposable sensor simultaneously determined DA and SE in blood serum samples, and high recoveries were acquired. A new disposable sensor with great repeatability and reproducibility was created for the quick, practical, selective, and simultaneous analysis of DA and SE at low concentrations. [Display omitted]