Rapid and Label‐Free Detection of Protoberberine Alkaloids Using Raman Spectroscopy

ABSTRACT Protoberberine alkaloids are an important class of isoquinoline alkaloids with diverse potent pharmacological activities. The rapid, label‐free, and sensitive detection of these chemical compounds is of great significance for quality control, pharmacological research, and clinic medical assays. However, common detection methods such as high‐performance liquid chromatography have the shortcomings of time‐consuming and strict operation. Here, a rapid and label‐free method was developed for sensitive detection of protoberberine alkaloids. Raman spectra of four protoberberine alkaloids were recorded. Three of them exhibited strong fluorescence backgrounds, and the results revealed that the near‐infrared laser could effectively reduce the fluorescence signals. The four protoberberine alkaloids showed distinct Raman peaks and intensity ratios, which could be used to identify them. Furthermore, a plasmonic sensor was prepared for detection of berberine with 0.1‐mM sensitivity. The relative standard deviations of the SERS intensity were small, indicating the favorable spectral reproducibility. Besides, the SERS intensities measured in the first and seventh week were comparable, demonstrating the excellent stability of the plasmonic sensor, which may be attributed to the stable gold nanoparticles and film used. This rapid, fingerprint, and sensitive method provides a powerful new tool for protoberberine alkaloids detection.