Poly(N-isopropylacrylamide)-Coated Superparamagnetic Iron Oxide Nanoparticles: Relaxometric and Fluorescence Behavior Correlate to Temperature-Dependent Aggregation

Abstract

Magnetic nanoparticles coated with polymers have existing and further potential for applications in medicine, including magnetic resonance imaging (MRI) imaging for diagnostics and assessing biodistribution, and their capacity to remotely generate heat in response to alternating current magnetic fields to elicit biological responses. Advances in such domains rely on developing better understanding of how such materials respond to magnetic fields. This paper reports thermosensitive properties of poly(N-isopropylacrylamide-co-Nile Red)-coated magnetic nanostructures upon passing through the lower critical solution temperature (LCST) of the polymer brush, and correlation of this behavior with formation of aggregates. Discrete magnetite nanoparticles coated with brush layers comprised of terminally attached poly(N-isopropylacrylamide-co-Nile Red) afforded highly water-dispersible nanoparticles (intensity average diameter of 38 nm) with good colloidal stability in phosphate buffers. The nanoparticles displayed enhanced transverse (T 2 ) NMR relaxometric behavior as the temperature was increased through the LCST. Moreover, incorporation of the environmentally sensitive Nile Red dye into the copolymer leads to significant changes in fluorescence emission intensity upon aggregation that present new possibilities for the remote fluorescence detection of aggregated structures.

Stimuli-responsive self-assembly of nanoparticles

“…Davis and co-workers studied the behavior of B8 nm magnetite NPs coated with a poly(N-isopropylacrylamide-co-Nile Red) copolymer. 50 At room temperature, the polymer chains were hydrated and the NPs were stable in solution, even in the presence of a magnet (Fig. 8d, left).…”

“…10a, right). 50 As a result, the particles lose their colloidal stability and spontaneously assemble into aggregates comprising thousands to millions of individual NPs (e.g., Fig. 10b).…”

“…10c). 50 These films are based on an organogel -syndiotactic poly(methyl methacrylate) -soaked with Au or Ag NPs decorated with different amounts of thiolated azobenzene. Fig.…”

Amino covalent binding approach on iron oxide nanoparticle surface: Toward biological applications

“…Amongst other applications upon their potential biomedical applications [1][2][3][4][5][6] , many are used as carriers for the cellular delivery of various drugs 7,8 . However, to meet the requirements for cellular delivery, iron oxide nanoparticles (IONPs) have to be subjected to chemical modification, such as strong affinity between the carriers and biomolecules, as well as a good biocompatibility, amongst others, for example to allow for targeting or to enhance circulation times.…”

On the motion of superparamagnetic particles in magnetic drug targeting

“…The specific clusters modeled in this paper are chemically characterized in [16][17][18][19][20] and are composed of nanoparticles with a mean diameter of as low as 3 to 4 nm coated with oleic acid, a biocompatible polymer. The synthesis of stable clusters with controlled diameters ranging from 10 to 200 nm and containing a specified number of nanoparticles is described in [21].…”