Utilizing mixed-ligand shell gold nanoparticles for optimized Barium detection

Offer Zeiri, NRCN, Beer Sheva, Israel (offerzeiri@yahoo.com)
Nadav Lerner, Idf, Beer Sheva, Israel

Barium is an alkaline earth metal, with a variety of industrial uses. Soluble barium compounds are toxic to humans, with low concentrations of barium ions acting as muscle stimulant, and high concentrations effecting the nervous system and damaging other organs. Gold nanoparticles (GNPs) have found many applications as colorimetric sensors. Nanoparticle sensing usually involves binding of the stabilizing ligands in the nanoparticle shell to the analyte, with several particles binding to each analyte. The resulting change in the interparticle distance effects the surface plasmon resonance of the particles, leading to a change in color. Typically, the GNPs are stabilized by a single ligand, however, it has been shown that combining several ligands and forming a mixed-ligand shell can effect properties of GNP sensors. This usually involves combining reactive and passive ligands to improve the steric freedom of the reactive ligands or increase the stability of the ligand shell. We studied mono-ligand shell GNPs, stabilized by 11-mercaptoundecanoic acid (MUA) or 2-Sulfanylethanesulfonate (MSA) ligands, and found both capable of sensing barium but possessing different sensitivity, linear range, and selectivity. We then produced mixed ligand shell particles combining both ligands. The properties of the mixed ligand GNPs as barium sensors were examined. It was found that while the particles sensitivity remained as low as for the MSA stabilized particles (2 microM limit of detection), their linear range greatly increased. The particles selectivity for barium was also greatly improved. When one of the ligands is replaced by a ligand with no reactivity towards barium, sensing properties are diminished, indicating a cooperative effect between the MSA and MUA. These results demonstrate the high potential mixed-ligand shell GNPs have for optimizing GNP sensors.