Attenuated total reflection infrared studies of oleate and trioctylphosphine oxide ligand adsorption and exchange reactions on CdS quantum dot films.

Departments of Chemistry, and Anatomy and Structural Biology, University of Otago, Dunedin, New Zealand.
Langmuir (Impact Factor: 4.38). 05/2008; 24(8):3841-9. DOI: 10.1021/la703655v
Source: PubMed

ABSTRACT Ligand exchange reactions at the surface of oleate- and trioctylphosphine oxide (TOPO)-capped CdS quantum dots have been studied with attenuated total reflection infrared (ATR-IR) spectroscopy, using thin films deposited from organic solvent suspensions. The oleate and trioctylphosphine capping ligands were found to form highly ordered and densely packed monolayers on the CdS surface. Adsorbed oleate is coordinated to CdS in a chelating bidentate manner through the carboxylate functional group, while adsorbed trioctylphosphine oxide is coordinated though the P=O functional group and appears to have numerous adsorption environments on the CdS surface. Exposure of such films to aqueous solution was found to cause partial delamination of the films from the ATR prism interface which was reversible upon redrying. Ligand exchange reactions on the oleate- and trioctylphosphine-capped CdS films were studied in situ at room temperature by allowing the films to be exposed to dilute aqueous solutions of thiol-containing ligands. Oleate and trioctylphosphine oxide are both strongly adsorbed to the CdS surface, and ligand exchange with monothiol-containing ligands has been found to be highly dependent upon experimental conditions, in particular pH, where exchange is only observed at solution pH where the exchanging ligand is uncharged. This is attributed to the inability of a charged ligand to penetrate the hydrophobic polymethylene layer on the CdS surface.

  • [Show abstract] [Hide abstract]
    ABSTRACT: Near infrared (NIR) CdHgTe/CdS quantum dots (QDs) were successfully prepared by a green synthetic route. The characteristics such as morphology, size, spectra, stability and toxicity were investigated in detail. The fluorescence wavelength of CdHgTe/CdS QDs could be adjusted to the NIR range (812nm), which made the in vivo NIR imaging possible. The in vivo dynamic biodistribution of CdHgTe/CdS QDs in a mouse model was monitored by an NIR imaging system. Results indicated that CdHgTe/CdS QDs with a diameter of about 5.8nm targeted to spinal column effectively. Further imaging of the dissected spine disclosed that QDs targeted to vertebra rather than spinal cord. The high fluorescence intensity together with targeting effect makes CdHgTe/CdS QDs particular candidates for imaging purposes in experimental animal models of vertebral injury.
    Photochemistry and Photobiology 10/2010; 87(1):72-81. · 2.29 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Given the importance of nanoparticle surface composition in nanotoxicology, analytical tools that can probe nanoparticle surfaces in aqueous media are crucial but remain limited. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy is a technique capable of in situ characterization of the liquid-solid interface to probe surface adsorption on nanoparticle surfaces in environmentally and biologically relevant media. Furthermore, given that the interfacial region in these media is dynamic, ATR-FTIR spectroscopy facilitates monitoring these dynamics by interrogating a layer of immobilized nanoparticles coated on the ATR element while changing the overlying aqueous phase. The molecular information acquired from this technique allows for the determination of the adsorption mode, including conformational and structural changes of the coordinating ligand, and can directly measure ligand displacement reactions. Furthermore, in some cases, ATR-FTIR spectroscopy can be used as a quantitative surface analytical tool. In this article, we briefly review the fundamentals of the technique and then provide several examples of using ATR-FTIR spectroscopy to probe nanoparticle surfaces in general with respect to: (i) the adsorption of different environmentally and biologically relevant coordinating ligands; (ii) competitive ligand adsorption and; (iii) the determination of kinetic and thermodynamic parameters. We have also investigated surface adsorption of TiO2 nanoparticles in different biological media typically used for toxicity studies and show that the surface composition of TiO2 nanoparticles depends to a large extent on the composition of the medium due to surface adsorption. This result has important implications for the interpretation of toxicity data as well as inter-comparisons between toxicity studies.
    The Analyst 12/2013; · 4.23 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We describe a new class of ligands for semiconductor nanoparticles (quantum dots = QDs), which bind well and allow for their facile dissolution in aqueous solution. As a proof of principle, we have designed and synthesized a novel bis(phosphine)-modified peptide (BPMP) and shown that it has the ability to solubilize quantum dots in aqueous media. We further showed that the corresponding phosphine oxide derivatives of these new ligands are less good at solubilizing the quantum dots. These new bis(phosphine)-modified peptide ligands are easy to prepare and may well replace thiol-containing binding sequences in functionalized peptides for quantum dot coating, potentially resulting in quantum dots with higher quantum yields.
    Synthesis 09/2013; 45(17):2426-2430. · 2.50 Impact Factor