Femtosecond Laser Direct Writing of Plasmonic Ag/Pd Alloy Nanostructures Enables Flexible Integration of Robust SERS Substrates

This paper demonstrates femtosecond laser direct writing mediated flexible integration of plasmonic Ag/Pd alloy nanostructures that can be potentially used as a robust surface-enhanced Raman spectroscopy substrate inside the microfluidic chip. Silver–palladium alloy with controllable composition ratio can be patterned into plasmonic nanostructures due to two-photon absorption induced coreduction of silver/palladium double metal ions. Since the alloy structures can effectively protect the silver from oxidation, thus they can facilitate the stable on-chip detection devices with long lifetime. The as-fabricated silver–palladium alloy substrate with 18% content of palladium maintains a relatively high enhancement factor of about 2.62 × 108 while at the same time demonstrating the best stability against aerobic oxidation, as it is stable for up to 20 d under ambient aerobic conditions, exhibiting a significant improvement compared to those unprotected silver substrates which have a limited lifetime of only 3 or 4 d.