Removable PDMS Films with Ultra‐Low AgNPs Content and Effective SERS Effect by N‐Octylamine Transfer and Immersion Deposition

Abstract The short alkyl chain of N‐octylamine was demonstrated to be able to transfer silver nanoparticles (AgNPs) from the aqueous to toluene phase with a narrow average size lower than 10 nm via ligand exchange between N‐octylamine and the sodium citrate used as a reducing and stabilizing agent during AgNPs synthesis. Surface plasmon analysis by UV‐visible spectroscopy showed that the N‐octylamine concentration significantly influences the concentration and stability of AgNPs transferred to the toluene phase and the time required for such transfer. Then, the transferred silver nanoparticles were deposited on a polydimethylsiloxane (PDMS) substrate by drop‐casting (PDMS‐T‐50‐D) or immersion (PDMS‐T‐50‐I). XPS analysis demonstrated that the AgNPs are deposited at lower than 0.02 % atomic percentages through both deposition methods. The Raman signal and the noise by fluorescence signal were shown to be significantly influenced by the AgNPs deposition method on PDMS film. The trace content of AgNPs on the flexible PDMS films on both PDMS‐T‐50‐D and PDMS‐T‐50‐I substrates can eliminate the fluorescence signal of the analyte; however, only the PDMS‐T‐50‐I substrate demonstrated a remarkable SERS‐enhanced signal. These results could significantly contribute to the design of new flexible and removable SERS substrates with ultra‐low contents of noble metal NPs.