Targeted sensing of L-tryptophan in human urine using imprinted polypyrrole-based screen-printed electrodes.

L-tryptophan (L-Trp) is an essential aromatic amino acid involved in key physiological pathways. Altered L-Trp levels in biological fluids, particularly serum, have been associated with metabolic and neurological disorders. Given its narrow physiological range, developing rapid, accurate, and cost-effective analytical methods for L-Trp determination is clinically relevant. In this work, a voltammetric sensor for L-Trp determination is presented; it is based on screen-printed electrodes (SPEs) modified with an electrosynthesized molecularly imprinted polymer (eMIP). In particular, a polypyrrole-based eMIP was electropolymerized on the carbon-ink working electrode via cyclic voltammetry, using L-Trp as the template molecule. Electropolymerization conditions were optimized through a Design of Experiments approach. Differential pulse voltammetry (DPV) was used for the analyte quantification, exploiting the well-defined irreversible oxidation peak at +0.86 V. The eMIP-modified SPE demonstrated enhanced sensitivity, selectivity, and reproducibility compared to bare and non-imprinted electrodes. Applications to simulated and real biological fluid samples yielded results in good agreement with those obtained by HPLC, confirming the reliability and practical applicability of the proposed method.