Pen-on-Paper Label-Free Surface-Enhanced Raman Scattering (SERS) Detection of Tetracycline in Milk

Monitoring food quality requires the development of low-cost and sensitive analytical tools with label-free and point-of-site detection capabilities. Surface-enhanced Raman scattering (SERS) is a powerful analytical technique that combines fingerprint detection capabilities with high sensitivity. In this paper, we present the pen-on-paper fabrication of SERS substrates, whereby plasmonic nanoinks were written on a paper substrate and used for the detection of food contaminant residues. To construct sensitive and robust SERS sensors, four different nanoinks with different plasmonic properties were synthesized and tested on eight papers of different weights, textures, and hydrophilicities. The combination of silver nanoink and Bristol printing paper resulted in the strongest SERS substrate, which was used for crystal violet (CV) and tetracycline detection. Concentrations as low as 10^-12 M were obtained for CV and 2.5 ppm of tetracycline in milk, showing the application potential of these paper-based SERS sensors for label-free detection of residuals in complex food matrices.