SERS Detection of Hg²⁺ using Rhenium Carbonyl Labelled Nanoparticle Films

Modified silver nanoparticles with a self-assembled disulfide functionalized 2,2'-bipyridine (L1 and L2) monolayer, and the corresponding rhenium complex [Re(L2)(CO)3Br] are shown to provide a method to position the nanoparticles at a water/dichloromethane interface forming a lustrous metal-like-liquid film (MeLLF) with a unique SERS response. The film formed using L2 showed divergent behaviour in the presence of a range of metal ions whilst bound to the surface. [Re(L)(CO)3Br] (where L=2,2'-bipyridine, L1 and L2) in solution demonstrates a selective interaction with Hg2+, observed by UV-vis, emission and H-1 NMR spectroscopy, attributed to abstraction of the bromide. This interaction was demonstrated by subtle changes in the characteristic Raman Re-CO stretch at 510 cm(-1) both with the MeLLF, and when the film is immobilized in a PVA surface-exposed-nano-sheet (SENS). The work provides proof of concept that the organometallic complexes can be employed as "labels" to generate SERS-active nanoparticle films that possess detection capabilities.