Metal nano-cluster biosensors

Resonant enhancement of absorptive properties of metal clusters bound to a surface by biorecognitive interactions is an effective means to set up bio-optical devices. Resonant amplification of a four-layer system has been proposed and recently demonstrated with a metal mirror, a polymer distance layer, a biomolecule interaction layer and a sub-monolayer of biorecognitively bound metal nano-clusters. Calculations and corresponding experiments indicated a strong influence of cluster symmetry and cluster shell on the distinct reflection minimum induced by the resonant behavior. Here, we present the first biosensor which clearly shows a narrow reflection minima system in the red or infra-red and therefore far away from the limit exhibited by spherical gold colloids at around 600 nm. The asymmetry of the metal clusters (synthesized by thermal step reduction in a detergent system) as well as metal-dielectric shell clusters (synthesized by multiple shell deposition processes) enabled us to shift the readout of the device to a frequency range where blood is highly transparent. Disposable single step assays were established, employing lectin-sugar, antigen-antibody and protein-receptor interactions.