Highly sensitive technique for detection of adulterants in centella herbal samples using surface enhanced Raman spectroscopy (SERS)

The trace level detection of adulterants in food, nutritional supplements and medicinal herbs is highly challenging in the field of food processing and herbal industries. In addition, laborious sample processing procedures and well trained personnel are required to analyse the samples using conventional analytical equipments. In this study, a highly sensitive technique with minimal sampling processes and human intervention is proposed for the trace amount detection of pesticidal residues in centella powder. Herein, graphene oxide gold (GO-Au) nanocomposite coated parafilm is developed as substrate by simple dropcasting technique to facilitate dual surface enhanced Raman signal. The dual SERS enhancement involving chemical enhancement from graphene and electromagnetic signal enhancement from gold nanoparticles is utilized for detection of chlorpyrifos in the ppm level concentration. The flexible polymeric surfaces could be the better choice for SERS substrates due to their inherent properties such as flexibility, transparency, roughness and hydrophobicity. Among the various types of flexible substrates explored, GO-Au nanocomposites coated parafilm substrates showed better Raman signal enhancement. Parafilm coated with GO-Au nanocomposites is successful in achieving detection limits down to 0.1 ppm of chlorpyrifos in centella herbal powder sample. Thus, the fabricated parafilm based GO-Au SERS substrates could be used as a screening tool at quality control of herbal product manufacturing sectors for trace level detection of adulterants in herbal samples from their unique chemical and structural information.