Simple Melatonin Determination Using Disposable and Low-Cost Lab-Made Screen-Printed Carbon Electrode.

This work describes the preparation and application of a screen-printed electrode (SPE) for direct melatonin (MT) determination in samples of saliva and urine. The low-cost SPE was obtained using a simple and feasible 2D printing methodology and a lab-made conductive ink based on graphite powder and colorless nail polish. The proposed electrode showed similar electrochemical performance compared to a commercial SPE towards melatonin oxidation. Based on electrooxidation of melatonin recorded at +0.62 V an electroanalytical method was developed using the lab-made SPE under square wave voltammetric conditions. Repeatability and reproducibility studies showed that the relative peak current values did not show significant differences between them. Under optimized parameters inherent to the methodology and voltammetric technique, the proposed SPE presented a linear dynamic range (LDR) between 0.25 to 75.0 µmol L-1 (R2 = 0.99), and calculated limit of detection (LOD) and limit of quantification (LOQ) of 25.8 and 83.3 nmol L-1, respectively, were obtained. The effect of other biologically relevant compounds such as glucose, urea, and estradiol was investigated, and non-significative signal interference was observed. The method proposed was successfully applied to MT determination in spiked samples providing good recovery values between 95.6 to 104%. [ABSTRACT FROM AUTHOR]