Development of a Highly-Sensitive and Selective Electrochemical Sensor for Cr³⁺ Detection Using an Ag@Co₃O₄-Polythiophene Nanocomposite-Modified Glassy Carbon Electrode

Environmental monitoring requires sensitive, reliable techniques for detecting trace amounts of heavy metals, particularly Cr³⁺ ions, due to their toxicity and widespread use. Herein, an electrochemical sensor for Cr³⁺ detection was developed by modifying a glassy carbon electrode (GCE) with a silver-cobalt oxide-polythiophene (Ag@Co₃O₄-PTh) nanocomposite, fabricated via wet-chemical synthesis, oxidative polymerization, sonication, and photo-reduction methods. Comprehensive characterizations confirmed the successful synthesis of the Ag@Co₃O₄-PTh nanocomposite and its superior electrochemical properties. The sensor exhibited a high sensitivity of 2.617 µAµM⁻¹cm⁻², a wide linear dynamic range of 1–112 µM, and low detection limit of 0.067 µM in neutral phosphate-buffered solution. The sensor demonstrated excellent operational stability, retaining 90% of its performance after 28 days, and strong repeatability and reproducibility, with relative standard deviation values of 4.35% and 3.11%, respectively. Selectivity studies showed negligible interference (<3%) from common interfering ions such as Sn2+, Cd²⁺, Co²⁺, Pb²⁺, Hg²⁺, or Cl⁻, confirming its capability for accurate Cr³⁺ detection. Practical use of the Cr3+ sensor was validated using the standard addition method in real environmental samples, with reliable and precise Cr³⁺ ion recovery tests. These findings make the Ag@Co₃O₄-PTh nanocomposite-modified GCE a highly sensitive, selective, and stable platform for Cr³⁺ detection, with promising applications.