Compact Biocompatible Quantum Dots Functionalized for Cellular Imaging

Abstract

We present a family of water-soluble quantum dots (QDs) that exhibit low nonspecific binding to cells, small hydrodynamic diameter, tunable surface charge, high quantum yield, and good solution stability across a wide pH range. These QDs are amenable to covalent modification via simple carbodiimide coupling chemistry, which is achieved by functionalizing the surface of QDs with a new class of heterobifunctional ligands incorporating dihydrolipoic acid, a short poly(ethylene glycol) (PEG) spacer, and an amine or carboxylate terminus. The covalent attachment of molecules is demonstrated by appending a rhodamine dye to form a QD-dye conjugate exhibiting fluorescence resonance energy transfer (FRET). High-affinity labeling is demonstrated by covalent attachment of streptavidin, thus enabling the tracking of biotinylated epidermal growth factor (EGF) bound to EGF receptor on live cells. In addition, QDs solubilized with the heterobifunctional ligands retain their metal-affinity driven conjugation chemistry with polyhistidine-tagged proteins. This dual functionality is demonstrated by simultaneous covalent attachment of a rhodamine FRET acceptor and binding of polyhistidine-tagged streptavidin on the same nanocrystal to create a targeted QD, which exhibits dual-wavelength emission. Such emission properties could serve as the basis for ratiometric sensing of the cellular receptor's local chemical environment.

Functionalized Au22 Clusters: Synthesis, Characterization, and Patterning

“…Tsukuda et al synthesized a series of GSH-protected clusters and determined their chemical composition by ESI-MS (36). These clusters are Au 10 (SG) 10 , Au 15 (SG) 13 , Au 18 (SG) 14 , Au 22 (SG) 16 , Au 22 (SG) 17 , Au 25 (SG) 18 , Au 29 (SG) 20 , Au 33 (SG) 22 , and Au 39 (SG) 24 . All of these nine clusters have good stability.…”

Surface modification, functionalization and bioconjugation of colloidal inorganic nanoparticles

“…in an increased half-life in the blood stream. PEG-modified nanoparticles are more stable at high salt concentrations and in biological environments; they show less non-specific binding to proteins and cells (Gref et al 2000;Ballou et al 2004;Liu et al 2007bLiu et al , 2008van Vlerken et al 2007;Daou et al 2009). …”

“…with a methoxy group at the free end, yield basically more stable and inert particles (Hirsch et al 2003;Niidome et al 2006), bifunctional PEG molecules can be used to introduce new functional groups on the surface, like with bifunctional crosslinkers in conjugation chemistry (Jayagopal et al 2007). In particular, mixed PEG layers of mono-and bifunctional molecules can be useful because they stabilize the particles sterically by PEG molecules without free functional end and provide a number of new functional groups by the bifunctional PEG molecules (Sperling et al 2006;Pierrat et al 2007;Liu et al 2008). Again, the conjugation chemistry used for PEGylation and the further modification does not depend any more on the material of the particle cores and applies in the same way for other particle species (Butterworth et al 2001;Zillies et al 2007).…”

Quantum dots–DNA bioconjugates: synthesis to applications

“…The QDs are first coated with ligands that bear carboxylic acid functional groups. These ligands are either small molecules such as MAA (mercapto acetic acid), MPA, MHA and DHLA [35,42,80,81] or derived polymeric scaffolds terminating in carboxylic acid [82,86]. To all of these QDs 'terminating' in solvent-exposed carboxylic acid functional groups, conjugation of amine-functionalized DNA is carried out in the presence of EDC and NHS.…”