Biopolymer Decorated Pencil Graphite Electrode for the In-situ Quantification of L-Tryptophan in Dietary Supplements

A simplistic and novel electrochemical sensor for selectively detecting the essential amino acid tryptophan in dietary supplements was fabricated on a pencil graphite electrode modified with a tryptophan-based dipeptide. The dipeptide was synthesized using common synthetic strategy for amino acid couplings. The modified electrode was characterized by scanning electron microscopy, impedance spectroscopy, cyclic voltammetry, and infrared spectroscopy. Differential pulse voltammetry was used to study the electrochemical response of the fabricated electrode to tryptophan in dietary supplements. Under the optimized experimental conditions, a distinct oxidation peak at + 0.671 V corresponding to tryptophan was noticed in differential pulse voltammetry, which indicated the detection of tryptophan by the fabricated electrode. The oxidation peak current for tryptophan was found to be linear within a concentration range of 10–350 µM with a lower detection limit of 1.2 µM, and the sensitivity of the fabricated electrode was 6.9 µA/µM/cm². Excellent selectivity, permissible reproducibility, and good stability of the sensor make it undoubtedly suitable for determining tryptophan in dietary supplements.