Limits...
Synthesis and Magneto-Thermal Actuation of Iron Oxide Core-PNIPAM Shell Nanoparticles.

Kurzhals S, Zirbs R, Reimhult E - ACS Appl Mater Interfaces (2015)

Bottom Line: Superparamagnetic nanoparticles have been proposed for many applications in biotechnology and medicine.Thereafter, it is shown that local heating by magnetic fields as well as global thermal heating can be used to efficiently and reversibly aggregate, magnetically extract nanoparticles from solution and spontaneously redisperse them.The coupling of magnetic and thermally responsive properties points to novel uses as smart materials, for example, in integrated devices for molecular separation and extraction.

View Article: PubMed Central - PubMed

Affiliation: Institute for Biologically Inspired Materials, Department of Nanobiotechnology, University of Natural Resources and Life Sciences, Vienna , Muthgasse 11, A-1190 Vienna, Austria.

ABSTRACT
Superparamagnetic nanoparticles have been proposed for many applications in biotechnology and medicine. In this paper, it is demonstrated how the excellent colloidal stability and magnetic properties of monodisperse and individually densely grafted iron oxide nanoparticles can be used to manipulate reversibly the solubility of nanoparticles with a poly(N-isopropylacrylamide)nitrodopamine shell. "Grafting-to" and "grafting-from" methods for synthesis of an irreversibly anchored brush shell to monodisperse, oleic acid coated iron oxide cores are compared. Thereafter, it is shown that local heating by magnetic fields as well as global thermal heating can be used to efficiently and reversibly aggregate, magnetically extract nanoparticles from solution and spontaneously redisperse them. The coupling of magnetic and thermally responsive properties points to novel uses as smart materials, for example, in integrated devices for molecular separation and extraction.

No MeSH data available.


Magnetic actuation of iron oxide PNIPAM nanoparticles(grafting-to, core 10.7 nm/PNIPAM 20 kDa), dissolved in water (5 mg/mL),(A) clear dispersion before magnetic actuation, solution temperature24 °C, (B) aggregation and turbidity after 5 min actuation, solutiontemperature 32.4 °C, (C) precipitation after 10 min actuation,solution temperature 35.7 °C, (D) redispersion of aggregatedparticles after cooling down to below the LCST.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4559841&req=5

fig5: Magnetic actuation of iron oxide PNIPAM nanoparticles(grafting-to, core 10.7 nm/PNIPAM 20 kDa), dissolved in water (5 mg/mL),(A) clear dispersion before magnetic actuation, solution temperature24 °C, (B) aggregation and turbidity after 5 min actuation, solutiontemperature 32.4 °C, (C) precipitation after 10 min actuation,solution temperature 35.7 °C, (D) redispersion of aggregatedparticles after cooling down to below the LCST.

Mentions: Superparamagnetic nanoparticles interactwith an externally applied oscillating magnetic field of the rightfrequency to produce heat by Néel relaxation.4 Large ferromagnetic particles coated by random block copolymerwith PNIPAM blocks have been shown to not pass a size exclusion columnduring the application of an alternating magnetic field that raisedthe bulk temperature of the solution above the LCST.58 It is conceivable that desolvation of the shell leadingto aggregation of the nanoparticles could be achieved exclusivelythrough the application of an alternating magnetic field, becausethe heat produced by magnetic heating is locally produced in the centerof the PNIPAM polymer brush grafted to the nanoparticle core surface.That magnetic heating changes the solvation of the shell without changein the bulk temperature above the LCST is suggested by results byRinaldi and co-workers on iron oxide nanoparticles with a PNIPAM shellincorporating fluorophores.18 To investigatethis hypothesis applied to magnetic separation, we exposed the largestnanoparticle (10.7 nm core/20 kDa PNIPAM) at a concentration of 5mg/mL in water to a magnetic field at 228 kHz using an Ambrell magneticheater. The largest cores are expected to lead to the most efficientmagnetic heating response. After 5 min actuation, the initially clearbrown solution (Figure 5A) turned turbid (Figure 5B). The bulk solution temperature at this point was 32.4 °C,which equals the LCST of the PNIPAM in the shell. A brown precipitatewas visible after actuation for additionally 5 min (Figure 5C), at which point the bulksolution temperature had increased to 35.7 °C. After coolingdown, the precipitate easily redispersed by gentle shaking (Figure 5D), proving the reversibilityof the magnetic heating cycle just as for the purely thermally actuatedparticles. Analogous experiments with the same sample at a concentrationof 1 mg/mL did not show turbidity or aggregation after prolonged magneticactuation for 20 min (bulk solution temperature: 37.2 °C), althoughparticle aggregation was clearly shown for purely thermal heatingat this concentration by DLS.


Synthesis and Magneto-Thermal Actuation of Iron Oxide Core-PNIPAM Shell Nanoparticles.

Kurzhals S, Zirbs R, Reimhult E - ACS Appl Mater Interfaces (2015)

Magnetic actuation of iron oxide PNIPAM nanoparticles(grafting-to, core 10.7 nm/PNIPAM 20 kDa), dissolved in water (5 mg/mL),(A) clear dispersion before magnetic actuation, solution temperature24 °C, (B) aggregation and turbidity after 5 min actuation, solutiontemperature 32.4 °C, (C) precipitation after 10 min actuation,solution temperature 35.7 °C, (D) redispersion of aggregatedparticles after cooling down to below the LCST.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4559841&req=5

fig5: Magnetic actuation of iron oxide PNIPAM nanoparticles(grafting-to, core 10.7 nm/PNIPAM 20 kDa), dissolved in water (5 mg/mL),(A) clear dispersion before magnetic actuation, solution temperature24 °C, (B) aggregation and turbidity after 5 min actuation, solutiontemperature 32.4 °C, (C) precipitation after 10 min actuation,solution temperature 35.7 °C, (D) redispersion of aggregatedparticles after cooling down to below the LCST.
Mentions: Superparamagnetic nanoparticles interactwith an externally applied oscillating magnetic field of the rightfrequency to produce heat by Néel relaxation.4 Large ferromagnetic particles coated by random block copolymerwith PNIPAM blocks have been shown to not pass a size exclusion columnduring the application of an alternating magnetic field that raisedthe bulk temperature of the solution above the LCST.58 It is conceivable that desolvation of the shell leadingto aggregation of the nanoparticles could be achieved exclusivelythrough the application of an alternating magnetic field, becausethe heat produced by magnetic heating is locally produced in the centerof the PNIPAM polymer brush grafted to the nanoparticle core surface.That magnetic heating changes the solvation of the shell without changein the bulk temperature above the LCST is suggested by results byRinaldi and co-workers on iron oxide nanoparticles with a PNIPAM shellincorporating fluorophores.18 To investigatethis hypothesis applied to magnetic separation, we exposed the largestnanoparticle (10.7 nm core/20 kDa PNIPAM) at a concentration of 5mg/mL in water to a magnetic field at 228 kHz using an Ambrell magneticheater. The largest cores are expected to lead to the most efficientmagnetic heating response. After 5 min actuation, the initially clearbrown solution (Figure 5A) turned turbid (Figure 5B). The bulk solution temperature at this point was 32.4 °C,which equals the LCST of the PNIPAM in the shell. A brown precipitatewas visible after actuation for additionally 5 min (Figure 5C), at which point the bulksolution temperature had increased to 35.7 °C. After coolingdown, the precipitate easily redispersed by gentle shaking (Figure 5D), proving the reversibilityof the magnetic heating cycle just as for the purely thermally actuatedparticles. Analogous experiments with the same sample at a concentrationof 1 mg/mL did not show turbidity or aggregation after prolonged magneticactuation for 20 min (bulk solution temperature: 37.2 °C), althoughparticle aggregation was clearly shown for purely thermal heatingat this concentration by DLS.

Bottom Line: Superparamagnetic nanoparticles have been proposed for many applications in biotechnology and medicine.Thereafter, it is shown that local heating by magnetic fields as well as global thermal heating can be used to efficiently and reversibly aggregate, magnetically extract nanoparticles from solution and spontaneously redisperse them.The coupling of magnetic and thermally responsive properties points to novel uses as smart materials, for example, in integrated devices for molecular separation and extraction.

View Article: PubMed Central - PubMed

Affiliation: Institute for Biologically Inspired Materials, Department of Nanobiotechnology, University of Natural Resources and Life Sciences, Vienna , Muthgasse 11, A-1190 Vienna, Austria.

ABSTRACT
Superparamagnetic nanoparticles have been proposed for many applications in biotechnology and medicine. In this paper, it is demonstrated how the excellent colloidal stability and magnetic properties of monodisperse and individually densely grafted iron oxide nanoparticles can be used to manipulate reversibly the solubility of nanoparticles with a poly(N-isopropylacrylamide)nitrodopamine shell. "Grafting-to" and "grafting-from" methods for synthesis of an irreversibly anchored brush shell to monodisperse, oleic acid coated iron oxide cores are compared. Thereafter, it is shown that local heating by magnetic fields as well as global thermal heating can be used to efficiently and reversibly aggregate, magnetically extract nanoparticles from solution and spontaneously redisperse them. The coupling of magnetic and thermally responsive properties points to novel uses as smart materials, for example, in integrated devices for molecular separation and extraction.

No MeSH data available.