Unique optical properties of silver cluster-biochromophore hybrids: Comparison with copper and gold

We show that silver cluster-biochromophore hybrids exhibit markedly different optical properties than analogue copper and gold hybrids. This is reflected in a localized resonance at ≈320 nm enhancing strongly the absorption of biomolecules. In contrast, copper and gold hybrid systems exhibit very different behavior due to a small s-d energy gap leading to a high density of states with low intensities spread in a broad energy interval. Our results provide insight into the factors governing the proper choice of metallic labels for bioanalytical applications based on localized enhancement of absorption and fluorescence.