Synthesis of Compact Multidentate Ligands to Prepare Stable Hydrophilic Quantum Dot Fluorophores

Abstract

We describe a simple and versatile scheme to prepare an array of heterofunctional multidentate ligands that permit strong and stable interactions with colloidal semiconductor nanocrystals (quantum dots, QDs) and render them soluble in aqueous environments. These ligands were synthesized by reacting various chain length poly(ethylene glycols) with thioctic acid, followed by ring opening of the dithiolane moiety, creating a bidentate thiol motif with enhanced affinity for CdSe-ZnS core-shell QDs. Functionalization with these ligands permits processability of the nanocrystals not only in aqueous but also in many other polar solvents. These ligands provide a straightforward means of preparing QDs that exhibit greater resistance to environmental changes, making them more amenable for use in live cell imaging and other biotechnological applications.

Improved peptidyl linkers for self-assembly of semiconductor quantum dot bioconjugates

“…The combination of the remaining 6-carbon linker that joins the thiol group to the DNA, along with the modifi ed T-nucleotide and the extended diamino/6-carbon spacer linking the TAMRA dye to this T-base more than account for the remaining 14 15 Å of lateral peptide-DNA length even when not fully extended (energy minimized) or when accounting for some heterogeneity in conformation. Similar results were obtained when self-assembling the same peptide-DNA conjugates with polyethylene glycol (PEG)-modifi ed QDs (data not shown) [25,26].…”

Aqueous-phase hydrogenation and hydroformylation reactions catalyzed by a new water-soluble [rhodium]–thioligand complex

“…Dihydrothioctic acid (DHTA) was prepared as described [25]. Thioctic acid (510 mg, 2.5 mmol) was dissolved in a solution of 210 mg (2.5 mmol) of Na 2 CO 3 in 12 mL of H 2 O and cooled to 0 • C in an ice bath.…”

Bioconjugation of quantum dots: Review & impact on future application

“…Coupling of CdSe/ZnS core-shell nanocrystals covered with bidentate surface ligands composed of DHLA or TGA was not reproducible and resulted in macroscopic aggregates when a simple EDC conjugation strategy was used. To avoid this problem introduction of PEG or a combination of DHLA and PEG can be used for the hydrophilization of QDs [74]. These limitations underscore the need for the development of new approaches for surface functionalization of QDs to improve their stability and broaden their resistance to environmental changes.…”

“…Therefore, QDs can be embedded in a siloxane shell and functionalized with thiol and/or amine groups and phosphonate groups [8,76] or with PEG [91] and thiol-terminated biolinkers. This will result in stable QDs, while the thiol groups serve as anchor group for bioconjugation [7,74]. These QDs are potentially useful for a number of applications in biolabeling and imaging [90].…”

“…QDs capped with DHLA-PEG-OH [74] or DTT [96]). Surface modification of QDs with hydroxyl groups leads to solubility properties very similar to those of QDs-COOH.…”