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.