Flexible Surface-enhanced Raman Scattering Strips Using Colloidal Ink of Gold-silver Alloyed Nanoparticles

Surface-enhanced Raman scattering (SERS) has been used for trace detection at the single-molecule level. The low-cost preparation of high-performance test strips has enabled the development of SERS techniques. In this study, oil-dispersible metal or alloy nanoparticles prepared by the Brust-Schiffrin method were used as "inks" in a ballpoint pen to handwrite SERS test strips on polytetrafluoroethylene (PTFE) membranes. Because of the good PTFE lipophilicity, the flexible substrates had good uniformity. The large laser damage threshold of the PTFE membrane also enabled increased laser powers for SERS testing. The Au and Ag alloy nanoparticle inks exhibited increased performance with larger proportions of Ag. The Au₁Ag₈ nanoparticles had the best properties, and those strips could detect 10^-11-M Rhodamine 6G dyes in a 10-μL volume with an enhancement factor of 5.4×10⁸. The SERS strips were used to demonstrate detection of malachite green, the use of which is prohibited in aquaculture and fish tanks.