Multidentate catechol-based polyethylene glycol oligomers provide enhanced stability and biocompatibility to iron oxide nanoparticles.

We have designed, prepared, and tested a new set of multidentate catechol- and polyethylene glycol (PEG)-derivatized oligomers, OligoPEG-Dopa, as ligands that exhibit strong affinity to iron oxide nanocrystals. The ligands consist of a short poly(acrylic acid) backbone laterally appended with several catechol anchoring groups and several terminally functionalized PEG moieties to promote affinity to aqueous media and to allow further coupling to target molecules (bio and others). These multicoordinating PEGylated oligomers were prepared using a relatively simple chemical strategy based on N,N'-dicyclohexylcarbodiimide (DCC) and N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) condensation. The ability of these catechol-functionalized oligomers to impart long-term colloidal stability to the nanoparticles is compared to other control ligands, namely, oligomers presenting several carboxyl groups and monodentate ligands presenting either one catechol or one carboxyl group. We found that the OligoPEG-Dopa ligands provide rapid ligand exchange, and the resulting nanoparticles exhibit greatly enhanced colloidal stability over a broad pH range and in the presence of excess electrolytes; stability is notably improved compared to non-catechol presenting molecular or oligomer ligands. By inserting controllable fractions of azide-terminated PEG moieties, the nanoparticles (NPs) become reactive to complementary functionalities via azide-alkyne cycloaddition (Click), which opens up the possibility of biological targeting of such stable NPs. In particular, we tested the Click coupling of azide-functionalized nanoparticles to an alkyne-modified dye. We also measured the MRI T(2) contrast of the OligoPEG-capped Fe(3)O(4) nanoparticles and applied MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay to test the potential cytotoxicity of these NPs to live cells; we found no measurable toxicity to live cells.

Tracking metastatic tumor cell extravasation with quantum dot nanocrystals and fluorescence emission-scanning microscopy.

Metastasis is an impediment to the development of effective cancer therapies. Our understanding of metastasis is limited by our inability to follow this process in vivo. Fluorescence microscopy offers the potential to follow cells at high resolution in living animals. Semiconductor nanocrystals, quantum dots (QDs), offer considerable advantages over organic fluorophores for this purpose. We used QDs and emission spectrum scanning multiphoton microscopy to develop a means to study extravasation in vivo. Although QD labeling shows no deleterious effects on cultured cells, concern over their potential toxicity in vivo has caused resistance toward their application to such studies. To test if effects of QD labeling emerge in vivo, tumor cells labeled with QDs were intravenously injected into mice and followed as they extravasated into lung tissue. The behavior of QD-labeled tumor cells in vivo was indistinguishable from that of unlabeled cells. QDs and spectral imaging allowed the simultaneous identification of five different populations of cells using multiphoton laser excitation. Besides establishing the safety of QDs for in vivo studies, our approach permits the study of multicellular interactions in vivo.

Multiplexed toxin analysis using four colors of quantum dot fluororeagents.

Quantum dots (QDs) have the potential to simplify the performance of multiplexed analysis. In this work, we prepared bioinorganic conjugates made with highly luminescent semiconductor nanocrystals (CdSe-ZnS core-shell QDs) and antibodies to perform multiplexed fluoroimmunoassays. Sandwich immunoassays for the detection of cholera toxin, ricin, shiga-like toxin 1, and staphylococcal enterotoxin B were performed simultaneously in single wells of a microtiter plate. Initially the assay performance for the detection of each toxin was examined. We then demonstrated the simultaneous detection of the four toxins from a single sample probed with a mixture of all four QD-antibody reagents. Using a simple linear equation-based algorithm, it was possible to deconvolute the signal from mixed toxin samples, which allowed quantitation of all four toxins simultaneously.