Colloidal nanoparticles are used for a wide range of applications, for example catalysis, electronics, optoelectronics, plasmonics, information storage, optical sensing, bio-imaging and biomedicine. The small size of nanoparticles gives rise to unique catalytic, optical, electronic, and magnetic properties not observable in the bulk. These properties can be altered by modifying the nanoparticle size, composition, crystal structure, and morphology. Consequently, structural control provides an effective approach to tune the properties of colloidal nanoparticles.
The structural properties of nanoparticle can be altered by manipulating the kinetics and thermodynamics of the growth conditions. This is typically achieved by using capping ligands to modify growth and varying the synthesis parameters such as temperature, concentration, precursor etc. At MCAG we synthesise a range of nanoparticles include transition metals, noble metals, oxides and bimetallic nanoparticles. Analysis of nanoparticle includes a variety of techniques including XRD, SEM, EDX and ATR-IR. At MCAG, microscopy analysis by transmission electron spectroscopy is a central technique to evaluating the structural properties of nanoparticles at the atomic scale. Colloidal characteristics including size, shape, monodispersity and crystallinity can be assessed in detail.
Surface Analysis of Nanoparticles
The properties of nanoparticles are strongly dependent on the surface characteristics due to the large surface area to volume ratio of nanoparticles. Furthermore, colloidal nanoparticles are stabilised by capping ligands, usually small organic molecules or polymer coatings. Therefore, the nature of the capping ligand can impact on the nanoparticle physical and chemical properties such as solubility, stability and catalytic activity. At MCAG we focus on investigating both the structural properties of nanoparticles through high resolution transmission microscopy (HRTEM) and the chemical properties through X-ray photoelectron spectroscopy (XPS). XPS can be used to probe the chemical environment at the nanoparticle surface providing valuable information such as the binding mode of capping ligands or the oxidation state of nanoparticle, which is essential to many applications such as catalysis.
Applications of Nanoparticles
Colloidal nanoparticles are advantageous for studying morphology and composition dependent catalytic properties due to the variety of controllable synthesis strategies available. At MCAG we are interested in correlating structure-property in nanoparticle catalysed reactions. Altering the morphology of catalyst nanoparticles exposes distinct surface facets which have different atomic arrangements at the surface and consequently can influence catalytic stability and activity.
Size controlled Au NPs capped with polyethylene glycol (PEG)
The high ionic strength of many biological fluids and the non-specific interaction of nanoparticles with biomolecules, such as proteins or DNA often leads to nanoparticle aggregation and so coating the nanoparticles with organic ligands is needed. Furthermore, colloidal nanoparticle for use in bio-applications must not be cytotoxic (toxic to cells). In MCAG we tailor make surface functionalities with bio-compatibility through click chemistry.
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Santos-Martinez, M. J.; Rahme, K.; Corbalan, J. J.; Faulkner, C.; Holmes, J. D.; Tajber, L.; Medina, C.; Radomski, M. W. ‘Pegylation increases platelet biocompatibility of gold nanoparticles’ J. Biomed. Nanotech. 2014, 10 (6), 1004-1015.
Rahme, K.; Hobbs, R. G.; Chen, L.; Morris, M. A.; O’Driscoll, C.; Holmes, J. D. ‘PEGylated gold nanoparticles: polymer quantification as a function of PEG lengths and nanoparticle dimensions’ RSC Advances 2013, 3, 6085-6094.