Fluorescent dendritic nanoprobes: a new class of fluorescent probes for biological applications.

The microscopist’s utopia is filled with small, bright, photostable fluorescent probes. The contemporary toolbox of fluorescent probes—organic dyes, fluorescent proteins, and quantum dots—provides a range of sizes and photophysical properties, but we still await the perfect fluorescent probe. In a recent Biophysical Journal, Kim et al. (1) at the University of Illinois at Urbana-Champaign describe the synthesis, photophysical characterization, and use of a new class of fluorescent probes that they have named fluorescent dendritic nanoprobes (FDNs). FDNs consist of generation-5 and generation-6 polyaminoamine (PAMAM) dendrimers, with diameters of ~5 nm, used as scaffolds for the conjugation of multiple Cy5 or Cy3 fluorophores as well as functional groups such as biotin and dibenzocyclooctyne. The size of the FDNs places them on the same scale as fluorescent proteins: larger than single fluorescent dyes and smaller than quantum dots (2). The conjugation of multiple Cy5 fluorophores to the PAMAM dendrimers provides FDNs with a 6–10