Defective cuprous oxide as a selective surface-enhanced Raman scattering sensor of dye adulteration in Chinese herbal medicines

Chinese herbal medicine is an ancient part of humanity's heritage. However, the quality of commercial Chinese herbal remedies is currently compromised by illegal dyeing and adulteration. A rapid screening method of suspected dyeing compounds based on surface-enhanced Raman scattering (SERS) has proven difficult to develop due to the extreme complexity of the extraction of traditional Chinese medicinal products, as well as the lack of selective signal enhancement for target adulterants on commercially available Ag or Au substrates. Defective Cu2O nanostructures provide specific anchoring sites for dye adulterants such as Sudan red dyes on the basis of coordination between hydroxyl/azo groups and exposed Cu sites. This coordination facilitates an effective analyte-substrate charge-transfer, resulting in a prominent Raman signal enhancement for the analyte. Based on the mechanism of selective signal enhancement on Cu2O, this study shows that the adulterant Sudan red III in the extractions of various herbal medicines can be detected directly even at an extremely low concentration of 0.3 mg/kg. The findings suggest the advantages of semiconducting materials as promising SERS substrates for practical applications.

Automated summary

Chinese herbal medicine is facing challenges with illegal dyeing and adulteration. A study has shown that defective Cu2O nanostructures can provide specific anchoring sites for dye adulterants, allowing for direct detection of Sudan red III in herbal medicines even at extremely low concentrations. Advantages of semiconducting materials as promising SERS substrates for practical applications were also highlighted.