Low-cost label-free SERS detection of E. coli and S. aureus using dendritic Ag@Cu substrates in contaminated drinking water

Abstract

Street food and beverages are popular in Indonesian culinary. However, concerns over its safety persist, due to cross contamination between the food and water used during food processing, by pathogenic bacteria such as Escherichia coli and Staphylococcus aureus. In this study, we developed a low-cost bacterial detection using Surface Enhanced Raman Spectroscopy (SERS) with hybrid Ag@Cu substrate. The substrate was fabricated by electroless deposition of silver, to form dendritic structures. Two label-free SERS detection techniques, ex-situ and in-situ, were compared to evaluate their sensitivity for detecting E. coli and S. aureus in drinking water. The concentration of 100 mM AgNO₃ promotes the formation of AgNPs, facilitating signal amplification and enhancing the detection of bacterial molecular fingerprints. The results demonstrate that the in-situ method, which promotes bacterial trapping within dendritic Ag cavities, results in significantly enhanced Raman signal compared to the ex-situ method. The SERS response of S. aureus and E. coli, shows opposite trends due to differences in their surface charge. This study confirms that the in-situ label-free SERS technique can detect bacteria in real water samples, although its sensitivity is influenced by matrix interference. These findings offer a practical approach for bacterial detection, particularly for water monitoring and safety.