SERS-based sensor for high sensitivity melamine detection

In this work, we present a sensor for the detection of melamine, a nitrogen-rich compound that has been illegally used to enhance the apparent protein content in dairy products. Due to its toxicity, strict regulatory limits have been established: 1 ppm in infant formula and 2.5 ppm in other food products. Hence, the development of reliable, rapid, and highly sensitive detection methods is essential. Conventional analytical techniques used for melamine detection are High-performance liquid chromatography (HPLC), Gas chromatography (GS), and Enzyme-linked immunosorbent assay (ELISA) [1-3]. Despite their good reliability, these methods suffer from high costs and long turnaround time. Surface-Enhanced Raman Scattering (SERS) has overcome these disadvantages, being a simpler, quicker, and cheaper tool for detecting trace amounts of toxic molecules across multiple fields, namely in food safety. In our work, we used a highly efficient and easily fabricated SERS substrate based on a cold-plasma-assisted silver film. This approach allows us to achieve signal amplification factors of the order of 10⁷, while maintaining excellent reproducibility. To evaluate the performance of our biosensor, we calibrated the system using melamine dissolved in water. Then, we extended our study to detect melamine in a milk matrix. Unlike many previously reported methods that require chemical treatments or extensive sample processing, we adopted a straightforward approach undergoing the milk samples to a simple centrifugation step. This effectively removed macromolecules such as fats and proteins, which could otherwise interfere with detection. Our results are particularly promising, as we achieved a detection limit of 200 ppb, well below the regulatory limits for melamine in food. This demonstrates the strong potential of our SERS-based sensor as a rapid, cost-effective, and highly sensitive tool for food safety monitoring.