Continuous Flow Assisted Synthesis of SnO₂–CdS Nano‐Heterostructures with Enhanced Oxygen and Sulfur Vacancies for Hypersensitive Electrochemical Determination of Metronidazole

Aquatic pollution from pharmaceutical residues, particularly non‐steroidal anti‐inflammatory drugs (NSAIDs), poses serious ecological risks. Real‐time monitoring of these pollutants is crucial for environmental sustainability. This study presents a highly sensitive electrochemical sensor based on ultrasmall SnO₂–CdS heterostructured semiconductor nanocomposite for detecting the antibiotic metronidazole (MNZ), a NSAID. The sensor was developed via a simple and efficient continuous flow microreactor technology at a realistically low reaction temperature and exceptionally short period. Compared to individual SnO₂ and CdS, the heterostructure demonstrated superior electrocatalytic performance, attributed to the formation of oxygen and sulfur vacancies at the junction, enhancing diffusion and electro‐reduction of the analyte. The outstanding performance of the sensor might also be related to the formation of a heterojunction between SnO₂ and CdS semiconductors, which led to improved electron conduction efficiency through the hybrid electronic structure. The sensor exhibited high sensitivity (0.7044 µA µM⁻¹ cm⁻²), excellent selectivity, a low detection limit (0.0008 µM), a wide linear range (0.01‐1500 µM), and strong long‐term stability. Its practical potential was confirmed through successful detection of MNZ in real samples like lake water and human urine.