Ultrasensitive and selective detection of alkaline-earth metal ions using ion-imprinted Au NPs composites and surface plasmon resonance spectroscopy

Au nanoparticles (NPs) functionalized with electropolymerizable thioaniline units and with dithiothreitol ligands were synthesized. The NPs were electropolymerized onto Au-coated glass surfaces in the presence of the alkaline-earth metal ions Mg²⁺, Ca²⁺, Sr²⁺ or Ba²⁺, to yield the respective ion-imprinted bis-aniline-bridged Au NPs composites on the Au surfaces. After elimination of the ions from the crosslinked matrices, specific imprinted ion recognition sites were generated in the composites. Selective association of the respective ions to the imprinted sites consisting of the dithiothreitol ligands is demonstrated. The high affinities of the metal ions to the respective imprinted sites lead to impressive sensitivities (fM range). The association of the ions to the imprinted sites is monitored by surface plasmon resonance spectroscopy, and the coupling between the localized plasmon of the NPs and the surface plasmon wave is used as an amplification mechanism.