Rapid Detection of Erythrosine (FD&C Red 3) in Candy Using a Paper-Based SERS Substrate and a Handheld Raman Spectrometer

• A paper SERS substrate was developed by suspending silver nanoparticles in acetone. • A 3D printed module facilitated data collection with a handheld Raman instrument. • This setup was used to detect Red 3 in candy with an analysis time of 5 minutes. Erythrosine (FD&C Red 3) is a synthetic colorant that was banned in food products by the Food and Drug Administration in January 2025. Monitoring Red 3 in food products is significant for the FDA to ensure that the food industry complies with its regulations. Traditional detection methods such as high-performance liquid chromatography requires expensive benchtop instrumentation and time-consuming sample preparation. Surface-enhanced Raman Spectroscopy (SERS) is a molecular spectroscopic technique that enables rapid and sensitive detection out of a lab setting with a portable instrument. However, portable SERS detection is challenging due to its poor focus control and low spectral resolution. In this study, we developed a simple, low-cost SERS substrate and compatible sample holder to overcome these limitations. The substrate enables three-dimensional distribution of silver nanoparticles, providing both enhanced signal intensity and focal depth buffering, which is critical for consistent performance with handheld Raman devices. The entire substrate can be fabricated in 30 seconds at a material cost of less than 0. 10. A custom-designed sample holder enables easy alignment with the spectrometer and allows for one-time use liquid sample application. Using this set-up, Red 3 was successfully detected at both 10% and 50% adulteration levels (5 mg/L and 25 mg/L) in solutions of Red 40, carmine, and red radish extract. Additionally, Red 3 was successfully identified in commercial sprinkles and peppermint candy products claimed to contain Red 3. The method enables specific, rapid detection of Red 3 within 5 minutes of sample preparation in a low resource setting, offering a significant improvement over existing techniques and supporting enforcement of recent FDA regulations.