Homemade Filament Incorporating an Organic Modifier (Coumarin-Benzothiazole) for the Fabrication of High-Performance Voltammetric Sensors for Serotonin Determination.

3D printing enables low-cost, high-performance electrochemical sensors for bioanalytical and clinical use. Herein, we report, for the first time, a graphite/polylactic acid (G/PLA) conductive composite modified with a coumarin-benzothiazole derivative for 3D-printed electrodes targeting enhanced serotonin detection. The optimized composition (G/coumarin-benzothiazole/PLA, 35:5:60 wt %) was processed with a 3D pen to produce conductive electrodes without electrochemical activation. Electrochemical impedance spectroscopy showed an ≈74% decrease in charge-transfer resistance for the modified material, while cyclic voltammetry revealed an ≈137% increase in serotonin oxidation current and a distinct oxidation peak at +0.375 V vs Ag|AgCl|KCl(sat.). Optimized differential pulse voltammetry (modulation amplitude 70 mV; scan rate 30 mV s-1; step potential 8 mV) provided a linear range of 0.1-6.0 μmol L-1 (R 2 = 0.997), LOD = 0.075 μmol L-1, LOQ = 0.10 μmol L-1, and precision RSD < 5%. The sensor exhibited selectivity against common interferents (glucose, urea, uric acid, tyrosine, epinephrine, and dopamine), delivered near-quantitative recoveries in fortified human serum and cerebrospinal fluid, and interelectrode reproducibility RSD < 3%. To our knowledge, this G/coumarin-benzothiazole/PLA composite is the first 3D-printable, organic-modified conductive material demonstrating superior electrochemical performance, offering a robust, scalable platform for portable serotonin monitoring in bioanalytical and clinical applications.