Nanozyme-integrated CuS@f-CB composite based electrochemical sensor for ultrasensitive detection of L-tryptophan in biological and food matrices.

Abstract

Nanozyme-based composites, a promising novel class of materials that mimic natural enzymes while offering greater stability, more catalytic activity, and cost-effectiveness, making them ideal for developing next-generation sensors. This work presents the synthesis and testing of a redox-active CuS@f-CB composite, synthesized by a combined hydrothermal-ultrasonication method, as a nanozyme-based electrocatalyst for label-free detection of L-tryptophan (L-TRP). This nanozyme-based composite combines the oxidase-like catalytic activity of copper sulfide with the high surface area, conductivity, and defect-rich structure of acid-treated carbon black. The partnership promotes fast charge transfer, surface catalysis, and, most importantly, the selectivity mimicking the behaviour of natural oxidases. The characterization, performed using various techniques, demonstrates that the CuS nanoparticles are evenly dispersed in the carbon matrix and strongly bonded at their interface. Modified electrodes give strong electrochemical signals for L-TRP, spanning a wide linear range (10-1800 μM via SWV and 50-1050 μM via DPV), a low detection limit (0.56 μM), excellent repeatability (RSD <2 %), and steady long-term output. Tests in real samples-milk, chicken, egg, human blood and urine-show the sensor is accurate and resistant to common interferents. The work shows that CuS@f-CB can serve as a powerful nanozyme blend in biosensors, bridging advanced nanomaterial design with real-world tools for bioanalysis.