In situ growth of silver nanoparticles on alkali-treated cotton swabs as a cheap and highly sensitive SERS substrate for rapid detection of food additives

Surface-enhanced Raman scattering (SERS) technique has become a powerful and useful tool for detecting chemical substances in the field of food safety detection. However, the development of a highly sensitive, reliable, inexpensive and portable SERS substrate is still a great challenge. Herein, we developed a cheap, reliable and portable SERS sensor through in-situ growth of silver nanoparticles (AgNPs) on alkali-treated cotton swabs (CS) without using any expensive materials and complicated synthesis methods. The morphological analysis demonstrates that silver nanoparticles were highly homogeneous and controllably grown on the surface of cotton fibers. The effect of AgNPs content on the SERS performance of AgNPs@CS substrate is systematically investigated. The optimal AgNPs@CS SERS sensor not only achieves high detection sensitivity of 1.0 × 10^-9 M for toxic malachite green but also exhibits high enhancement factor up to 3.2 × 10⁶ and excellent signal homogeneity (relative standard deviation, RSD = 9.3 %). In addition, the SERS performance of the sensor toward food additive of indigo exhibits good linear correlation during the range of 1.0 × 10^-5 to 1.0 × 10^-9 M. Attributed to the good mechanical properties, flexibility and portability of the cotton swabs, a rapid and direct identification of indigo residues on the surface of edible amaranth using AgNP@CS SERS sensor was realized through a feasible and effective wipe-and-read route. The inexpensive, accessible and portable AgNP@CS SERS substrates demonstrate great potential in the identification of toxic and hazardous substances in the field food safety detection.