Electrochemical determination of folic acid in triple-matrix biofluids: a PAni-DES and Au/Printex L6@Chitosan enhanced lab-made screen-printed sensor.

The development and application of a highly sensitive electrochemical screen-printed electrode (SPE) for the determination of folic acid (FA) is presented. The SPE was fabricated on a polyethylene substrate using customized graphite ink and modified with Printex L6 carbon (PL6C) dispersed in chitosan (Chi). Gold (Au) nanoparticles were electrodeposited onto the SPE surface, followed by electropolymerization of polyaniline (PAni) in a deep eutectic solvent (DES), enhancing the electrochemical performance. The modified PAni-DES/Au/PL6C@Chi/SPE was characterized using cyclic voltammetry and differential pulse voltammetry in 0.1 mol L⁻ Britton-Robinson buffer solution at pH 7.0. Compared to the bare SPE, the modified sensor showed a significantly enhanced current response for FA detection, with a linear dynamic range of 1.15 to 40.00 μmol L⁻ (R = 0.998) and a limit of detection (LOD) of 0.018 μmol L⁻. The sensor was successfully applied to real samples such as saliva, blood serum, and urine, exhibiting high sensitivity with recovery between 95.25% and 103.80%. It also demonstrated excellent selectivity against common interferents, and the fully lab-made platform offers competitive performance compared to conventional systems, highlighting its innovative design and potential for customization. The absence of a significant memory effect and minimal matrix interference further underscore the sensor's reliability for clinical diagnoses and quality control analyses. Additionally, the sensor is cost-effective and requires low reagent and sample consumption, making it a promising alternative for practical applications.