A self assembled shell of 11-mercaptoundecanoic aminophenylboronic acids on gold nanoclusters

Sensors employing gold clusters coated with biomimetic compounds offer considerable advantages like long-term stability and simple sensor handling in comparison to sensors based on bioaffinity interactions. We took advantage of the unique properties of boronate molecules in binding hexose as well as their ability to form self assembled monolayers (SAMs) on 14 nm Gold nanoclusters. 11-Mercaptoundecanoic aminophenylboronic acid was synthesised in a one pot reaction step. The hydroxyl group of 11-mercaptoundecanoic acid was coupled with aminophenylboronic acid via activation by carbonyldiimidazole (CDI). Gold nanoclusters were covered with a monolayer of these boronate molecules by a self assembling process. At a pH of 9.5 thiols were found to bind irreversibly to the surface of gold nano-clusters, producing a particle exposing sugar binding sites to the solution; these clusters were stable against centrifugation, high salt and low pH. Such clusters were bound to the sensor surface at defined distance from a mirror layer. Thereby cluster-absorption was strongly enhanced. This phenomenon enables us to transduce affinity interactions highly amplifying changes in surface coverage of clusters. The optical properties of the sensors were found to be dependent on the size and number of the metal-clusters as well as their distance to the metal layer sputtered on the support surface.