Metal-metal-interaction-facilitated coordination polymer as a sensing ensemble: a case study for cysteine sensing.

A detailed investigation of the absorption and CD signals of Ag(I)-cysteine (Cys) aqueous solutions at buffered or varying pH has allowed us to suggest that coordination polymers are formed upon mixing Ag(I) and Cys bearing a Ag(I)-Cys repeat unit. The formation of the coordination polymers are shown to be facilitated by both the Ag(I)···Ag(I) interaction and the interaction between the side chains in the polymeric backbone. The former allows for an immediate spectral sensing of Cys with enantiomeric discrimination capacity with both high sensitivity and selectivity, and the contribution of the side-chain/side-chain interaction serves to guide extended sensing applications by means of modulating this interaction. With our preliminary data on the corresponding Cu(I)-Cys and Au(I)-Cys systems that exhibited similar spectral signals, we conclude that the M(I)-SR coordination polymers (M = Cu, Ag, or Au) could in general function as spectral sensing ensembles for extended applications. This sensing ensemble involves the formation of coordination polymers with practically no spectral background, thus affording high sensing sensitivity and selectivity.