No Time to Dye: Portable Surface Enhanced Raman Scattering for On-site Detection of Sudan IV Dye in Palm Oil

Abstract The widespread use of Sudan dyes as adulterants in palm oil poses significant public health risks. These non-food-grade dyes, linked to carcinogenic effects, have prompted a pressing need for efficient, rapid and reliable field-portable detection methods. This study investigates the application of handheld Surface-Enhanced Raman Scattering (SERS) technology for the rapid and sensitive detection of Sudan dyes in palm oil. By leveraging the enhanced sensitivity of SERS, we aim to provide a field-deployable solution that can be utilised in local markets and production sites, facilitating real-time monitoring and ensuring food safety. Using a univariate calibration approach, a predictive model was developed to quantify Sudan IV in palm oil, achieving a limit of detection (LOD) of 0.0065 mg/mL. In total, 64 palm oil samples obtained from markets in Cameroon and 9 palm oil samples purchased online were screened for Sudan IV using SERS, which identified four online samples as testing positive for this azo dye. To verify these findings, liquid chromatography - mass spectrometry (LC-MS) was subsequently performed on the samples bought online. LC-MS analysis confirmed the presence of Sudan IV in the four SERS-positive oils purchased online from UK markets and additionally detected the dye in a fifth oil from the same source.