Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 109, Issue 51, Pages 20826-20831Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1213291110
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Funding
- Nano/Bio Interface Center through National Science Foundation Nanoscale Science and Engineering Centers [DMR08-32802]
- Penn Medicine Neuroscience Center
- Office of Naval Research Multidisciplinary University Research Initiative on Optical Metamaterials [N00014-10-1-0942]
- American Heart Association [11SDG7600037]
- National Institutes of Health [S10-RR022428]
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We report a group of optical imaging probes, comprising upconverting lanthanide nanoparticles (UCNPs) and polyanionic dendrimers. Dendrimers with rigid cores and multiple carboxylate groups at the periphery are able to tightly bind to surfaces of UCNPs pretreated with NOBF4, yielding stable, water-soluble, biocompatible nanomaterials. Unlike conventional linear polymers, dendrimers adhere to UCNPs by donating only a fraction of their peripheral groups to the UCNP-surface interactions. The remaining termini make up an interface between the nanoparticle and the aqueous phase, enhancing solubility and offering multiple possibilities for subsequent modification. Using optical probes as dendrimer cores makes it possible to couple the UCNPs signal to analyte-sensitive detection via UCNP-to-chromophore excitation energy transfer (EET). As an example, we demonstrate that UCNPs modified with porphyrin-dendrimers can operate as upconverting ratiometric pH nanosensors. Dendritic UCNPs possess excellent photostability, solubility, and biocompatibility, which make them directly suitable for in vivo imaging. Polyglutamic dendritic UCNPs injected in the blood of a mouse allowed mapping of the cortical vasculature down to 400 mu m under the tissue surface, thus demonstrating feasibility of in vivo high-resolution two-photon microscopy with continuous wave (CW) excitation sources. Dendrimerization as a method of solubilization of UCNPs opens up numerous possibilities for use of these unique agents in biological imaging and sensing.
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