Synthesis and characterization of colloidal fluorescent silver nanoclusters.

Ultrasmall water-soluble silver nanoclusters are synthesized, and their properties are investigated. The silver nanoclusters have high colloidal stability and show fluorescence in the red. This demonstrates that like gold nanoclusters also silver nanoclusters can be fluorescent.

Nanotubular J-aggregates and quantum dots coupled for efficient resonance excitation energy transfer.

Resonant coupling between distinct excitons in organic supramolecular assemblies and inorganic semiconductors is supposed to offer an approach to optoelectronic devices. Here, we report on colloidal nanohybrids consisting of self-assembled tubular J-aggregates decorated with semiconductor quantum dots (QDs) via electrostatic self-assembly. The role of QDs in the energy transfer process can be switched from a donor to an acceptor by tuning its size and thereby the excitonic transition energy while keeping the chemistry unaltered. QDs are located within a close distance (<4 nm) to the J-aggregate surface, without harming the tubular structures and optical properties of J-aggregates. The close proximity of J-aggregates and QDs allows the strong excitation energy transfer coupling, which is around 92% in the case of energy transfer from the QD donor to the J-aggregate acceptor and approximately 20% in the reverse case. This system provides a model of an organic-inorganic light-harvesting complex using methods of self-assembly in aqueous solution, and it highlights a route toward hierarchical synthesis of structurally well-defined supramolecular objects with advanced functionality.

How colloidal nanoparticles could facilitate multiplexed measurements of different analytes with analyte-sensitive organic fluorophores.

Multiplexed measurements of several analytes in parallel using analyte-sensitive organic fluorophores can be hampered by spectral overlap of the different fluorophores. The authors discuss how nanoparticles can help to overcome this problem. First, different organic fluorophores can be separated spatially by confining them to separate containers, each bearing a nanoparticle-based barcode. Second, by coupling different fluorophores to nanoparticles with different fluorescence lifetimes that serve as donors for excitation transfer, the effective fluorescence lifetime of the organic fluorophores as acceptors can be tuned by fluorescence resonance energy transfer (FRET). Thus, the fluorophores can be distinguished by their effective lifetimes. This is an example of how the modification of classical functional materials has already yielded improved and even new functionalities by the integration of nanoparticles with hybrid materials. We outline future opportunities in this area.