Herrera-Barros, Adriana P.

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    Synthesis and agglomeration of gold nanoparticles in reverse micelles
    (2005) Herrera-Barros, Adriana P.; Rinaldi, Carlos; College of Engineering; Briano, Julio G.; Castro, Miguel; Department of Chemical Engineering
    Reverse micelles prepared in the system water, sodium bis-(2-ethylhexyl) sulfoccinate (AOT), and isooctane were investigated as a templating system for the production of gold nanoparticles from the reduction of Au (III) by sulfite ions. A coreshell Mie model was used to describe the optical properties of gold nanoparticles synthesized inside the reverse micelles. Dynamic light scattering measurements of gold colloids in aqueous media and in reverse micelle solution indicated agglomeration of micelles containing particles. This agglomeration was verified theoretically by estimating the total interaction energy between pairs of particles as a function of particle size. The analysis indicated that particles larger than about 8 nm diameter should reversibly flocculate. Transmission Electron Microscopy measurements of gold nanoparticles produced inside reverse micelles showed diameters of 8 to 10 nm. Evidence of cluster formation was also observed. Time correlated UV-Vis absorption measurements showed a red shift for the peak wavelength. This was interpreted as the result of multiple scattering and plasmon interaction between particles due to agglomeration of micelles with particles larger than 8 nm.
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    Synthesis of multifunctional magnetic nanoparticles for biomedical applications
    (2009) Herrera-Barros, Adriana P.; Rinaldi, Carlos; College of Engineering; Coutin, Sandra; García, Eduardo Juan; Torres-Lugo, Madeline; Department of Chemical Engineering; Vega, Carmen
    Magnetite nanoparticles are attractive for biomedical applications such as magnetic fluid hyperthermia (MFH), a novel cancer treatment, due to their ability to induce heating through energy dissipation in an oscillating magnetic field. This application requires suitable nanoparticle surface modification which provides colloidal stability in biological fluids and improves the nanoparticle’s transport and retention in specific areas of the human body. We studied the synthesis of multifunctional magnetic nanoparticles coated with silane-functional molecules, which allow the expression of amine or acrylate end groups on the nanoparticle surface. These functional end groups were used to graft attractive materials such as carboxymethyl dextran (CMDx) or a thermo-responsible polymer such as poly(N-isopropyl acrylamide) (NIPAM). Highly stable suspensions of CMDx coated magnetic nanoparticles were obtained over a broad range of pH and ionic strength. The effect of these nanoparticles on viability of human colon (CaCo-2) and mammary (MCF-7) cancer cells was study in vitro, as well as the distribution/transport of particles in these cells. The energy dissipation of CMDx coated magnetic nanoparticles was determined upon the application of an oscillating magnetic field at 233 kHz and 6.6 kA/m. Surface modification of magnetic nanoparticles with a fluorescent thermo-responsive polymer such as poly(NIPAM-co-FMA) can be used to visualize temperature profiles during MFH application. Furthermore, we present an approach to using AC susceptibility measurements in studying changes in the state of a colloidal suspension, from which we demonstrate how temperature-dependent measurements of the AC susceptibility of a sample at fixed field frequency can be used to identify and interpret transitions in suspensions of magnetic nanoparticles coated with thermo-responsive polymers.