Tailoring Amino-Functionalized Graphitic Carbon-Encapsulated Gold Core/Shell Nanostructures for the Sensitive and Selective Detection of Copper Ions

The effective transfer of strong electromagnetic field from the gold core through the coating shell represents the most significant challenge for the applications of plasmonic nanoparticles. This study applies a one-step arc discharge method to synthesize graphitic carbon-encapsulated gold nanoparticles (Au@G NPs) functionalized with amino groups uniformly via adding NH3 into He background gas. By tailoring the coating shell into few-layered graphene, a strong localized surface plasmon resonance (LSPR) absorption band is achieved. The NH3 introduces H radicals to strengthen the LSPR characteristic by etching the coating graphitic shell, as well as provides dissociated NH or NH2 species to functionalize the surfaces with amino groups. With an LSPR-based colorimetric method, it is demonstrated that trace Cu2+ ions can be detected rapidly with excellent sensitivity (as low as 10 x 10(-9) M linearly) and selectivity against other metal ions (Na+, K+, Mg2+, Ca2+, Co2+, Fe2+, Cd2+, Pb2+, and Hg2+ ions) by amino-functionalized Au@G NPs in water samples.