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Magnetic nanoparticles turn up the heat on tumors
440 enabling improved specificity and the ability to deliver increased drug concentrations. ‘‘I think that the utilization of a ‘distributed’ system for drug delivery that uses communication between specialized types of nanoparticles is really exciting,’’ he told Nano Today. ‘‘These capabilities could enable the site-specific delivery of very potent and, on the
C. Sealy level of the whole organism, potentially dangerous agents.’’ E-mail address: [email protected] 1748-0132/$ — see front matter doi: 10.1016/j.nantod.2011.08.007
Magnetic nanoparticles turn up the heat on tumors Cordelia Sealy Using nanoparticles to convert electromagnetic radiation into heat — or hyperthermia — is attracting attention as a drug-free, non-invasive anti-cancer treatment, but poor conversion efficiencies have limited the approach. Now, however, a team from Yonsei University in Korea report a significant increase in efficiency using metal oxide nanoparticles [J.-H. Lee et al., Nat. Nano. 6 (2011) 418]. Jinwoo Cheon and his colleagues use the exchange coupling between the magnetically hard core of a nanoparticle and a magnetically soft shell to tune the magnetic properties, producing a system with typical specific loss power values an order of magnitude larger than conventional iron oxide nanoparticles (Fig. 1). The redesigned nanoparticles interact much more strongly with an externally applied magnetic field to produce up to ∼30 times more heat. ‘‘The heat emission property, measured as specific loss power (SLP), of magnetic nanoparticles is dominated by the several factors including particle size, magnetization value, and magnetocrystalline anisotropy constant,’’ explains coauthor Jae-Hyun Lee. ‘‘What we have achieved is the successful tuning of all these variables by taking advantage of exchange coupling in the core—shell, maximizing the SLP.’’ The researchers experimented with a range of nanoparticle combinations, including a 9 nm diameter core of CoFe2 O4 with a 3 nm thick MnFe2 O4 shell, CoFe2 O4 @Fe3 O4 , MnFe2 O4 @ CoFe2 O4 and Fe3 O4 @ CoFe2 O4 . The efficacy of the CoFe2 O4 @MnFe2 O4 core—shell nanoparticle as an anti-tumor hyperthermia therapy was demonstrated in mice implanted with human brain cancer cells. The mice were injected with the nanoparticles in a saline solution at the site of the tumor and then exposed to an ac magnetic field for 10 min. The magnetic field excites the nanoparticles, which generate heat that destroys the tumor tissue while surrounding tissue is unaffected. The tumor was completely destroyed in the mice treated with the nanoparticle and hyperthermia treatment, while untreated tumors increased over nine-fold in size. The nanoparticle and hyperthermia treatment was also more effective than conventional chemotherapy drug doxorubicin or hyperthermia treatment with a standard contrast agent.
Figure 1 Schematic of a core—shell structured magnetic nanoparticle showing the exchange-coupled magnetic property. (Credit: Jinwoo Cheon.)
Communicating nanoparticles improve tumor targeting ‘‘The significance of this research is that the enhancement in magnetic induction could provide an effective means for tumor therapy with relatively smaller dosage than known chemical drugs or conventional magnetic nanoparticles,’’ says Lee. ‘‘The treatment also is non-invasive and does not require a surgical operation.’’
441 E-mail address: [email protected] 1748-0132/$ — see front matter doi: 10.1016/j.nantod.2011.08.011
Nanoscale carpet makes objects invisible Cordelia Sealy Researchers have developed a nanoscale ‘carpet’ cloaking device that can hide objects in visible light [M. Gharghi et al., Nano Lett. 11 (2011) 2825]. The results are a significant step forward in invisibility cloaking, where specially designed materials route light or electromagnetic waves around an object without disturbing the propagation of the waves. Invisibility cloaking is still in its infancy and although promising results have been achieved in the microwave and infrared range, devising devices that can work in visible light has proven tricky. But Xiang Zhang and colleagues from the University of California, Berkeley, Lawrence Berkeley National Laboratory, Vanderbilt University and the University of Paderborn in Germany have found a possible solution to the problem. The team use a silicon nitride (SiN) waveguide deposited onto a specially designed low index, nanoporous silicon oxide substrate with a very low refractive index (n < 1.25) to create a carpet cloak device that works in visible light (Fig. 1).
‘‘The carpet cloak device is based on a metamaterial structure, in which the speed of light can be locallycontrolled, enabling light to be rerouted around an object under the carpet,’’ explains co-author Majid Gharghi. The SiN layer is etched with a pattern of varying nanosized holes that tune the refractive index locally, rerouting light around the cloaked object underneath to render it ‘invisible’. At the corners of the ‘bump’ in the SiN layer created by the object, larger holes of up to 65 nm are drilled using electron beam lithography, while directly above the bump the holes are at their smallest (20 nm). The holes modulate the refractive index, bending the light waves away from the object and reconstructing them so that the cloak appears flat and smooth like a mirror. Zhang and his team used the carpet cloak device to hide only a very small object, but the findings could indicate a route to hiding other objects. ‘‘The carpet cloak is one example of the exciting things one can do with non-resonant metamaterials, and how one can control the flow of light,’’ says Gharghi. ‘‘We are looking
Figure 1 (a) Cross sectional schematic of the cloak device fabricated from a SiN waveguide on a low index nanoporous silicon oxide substrate. The layers are 300 nm and 5—10 m thick, respectively. The holes, which vary in size from 20 nm to 65 nm, modulate the index. Inset shows a scanning electron micrograph of the silicon oxide substrate. (b) Atomic force micrograph of the hole pattern. (c) Scanning electron micrograph of the device. [Reprinted with permission from M. Gharghi et al., Nano Lett. 11 (2011) 2825. Copyright 2011 American Chemical Society.]
C. Sealy level of the whole organism, potentially dangerous agents.’’ E-mail address: [email protected] 1748-0132/$ — see front matter doi: 10.1016/j.nantod.2011.08.007
Magnetic nanoparticles turn up the heat on tumors Cordelia Sealy Using nanoparticles to convert electromagnetic radiation into heat — or hyperthermia — is attracting attention as a drug-free, non-invasive anti-cancer treatment, but poor conversion efficiencies have limited the approach. Now, however, a team from Yonsei University in Korea report a significant increase in efficiency using metal oxide nanoparticles [J.-H. Lee et al., Nat. Nano. 6 (2011) 418]. Jinwoo Cheon and his colleagues use the exchange coupling between the magnetically hard core of a nanoparticle and a magnetically soft shell to tune the magnetic properties, producing a system with typical specific loss power values an order of magnitude larger than conventional iron oxide nanoparticles (Fig. 1). The redesigned nanoparticles interact much more strongly with an externally applied magnetic field to produce up to ∼30 times more heat. ‘‘The heat emission property, measured as specific loss power (SLP), of magnetic nanoparticles is dominated by the several factors including particle size, magnetization value, and magnetocrystalline anisotropy constant,’’ explains coauthor Jae-Hyun Lee. ‘‘What we have achieved is the successful tuning of all these variables by taking advantage of exchange coupling in the core—shell, maximizing the SLP.’’ The researchers experimented with a range of nanoparticle combinations, including a 9 nm diameter core of CoFe2 O4 with a 3 nm thick MnFe2 O4 shell, CoFe2 O4 @Fe3 O4 , MnFe2 O4 @ CoFe2 O4 and Fe3 O4 @ CoFe2 O4 . The efficacy of the CoFe2 O4 @MnFe2 O4 core—shell nanoparticle as an anti-tumor hyperthermia therapy was demonstrated in mice implanted with human brain cancer cells. The mice were injected with the nanoparticles in a saline solution at the site of the tumor and then exposed to an ac magnetic field for 10 min. The magnetic field excites the nanoparticles, which generate heat that destroys the tumor tissue while surrounding tissue is unaffected. The tumor was completely destroyed in the mice treated with the nanoparticle and hyperthermia treatment, while untreated tumors increased over nine-fold in size. The nanoparticle and hyperthermia treatment was also more effective than conventional chemotherapy drug doxorubicin or hyperthermia treatment with a standard contrast agent.
Figure 1 Schematic of a core—shell structured magnetic nanoparticle showing the exchange-coupled magnetic property. (Credit: Jinwoo Cheon.)
Communicating nanoparticles improve tumor targeting ‘‘The significance of this research is that the enhancement in magnetic induction could provide an effective means for tumor therapy with relatively smaller dosage than known chemical drugs or conventional magnetic nanoparticles,’’ says Lee. ‘‘The treatment also is non-invasive and does not require a surgical operation.’’
441 E-mail address: [email protected] 1748-0132/$ — see front matter doi: 10.1016/j.nantod.2011.08.011
Nanoscale carpet makes objects invisible Cordelia Sealy Researchers have developed a nanoscale ‘carpet’ cloaking device that can hide objects in visible light [M. Gharghi et al., Nano Lett. 11 (2011) 2825]. The results are a significant step forward in invisibility cloaking, where specially designed materials route light or electromagnetic waves around an object without disturbing the propagation of the waves. Invisibility cloaking is still in its infancy and although promising results have been achieved in the microwave and infrared range, devising devices that can work in visible light has proven tricky. But Xiang Zhang and colleagues from the University of California, Berkeley, Lawrence Berkeley National Laboratory, Vanderbilt University and the University of Paderborn in Germany have found a possible solution to the problem. The team use a silicon nitride (SiN) waveguide deposited onto a specially designed low index, nanoporous silicon oxide substrate with a very low refractive index (n < 1.25) to create a carpet cloak device that works in visible light (Fig. 1).
‘‘The carpet cloak device is based on a metamaterial structure, in which the speed of light can be locallycontrolled, enabling light to be rerouted around an object under the carpet,’’ explains co-author Majid Gharghi. The SiN layer is etched with a pattern of varying nanosized holes that tune the refractive index locally, rerouting light around the cloaked object underneath to render it ‘invisible’. At the corners of the ‘bump’ in the SiN layer created by the object, larger holes of up to 65 nm are drilled using electron beam lithography, while directly above the bump the holes are at their smallest (20 nm). The holes modulate the refractive index, bending the light waves away from the object and reconstructing them so that the cloak appears flat and smooth like a mirror. Zhang and his team used the carpet cloak device to hide only a very small object, but the findings could indicate a route to hiding other objects. ‘‘The carpet cloak is one example of the exciting things one can do with non-resonant metamaterials, and how one can control the flow of light,’’ says Gharghi. ‘‘We are looking
Figure 1 (a) Cross sectional schematic of the cloak device fabricated from a SiN waveguide on a low index nanoporous silicon oxide substrate. The layers are 300 nm and 5—10 m thick, respectively. The holes, which vary in size from 20 nm to 65 nm, modulate the index. Inset shows a scanning electron micrograph of the silicon oxide substrate. (b) Atomic force micrograph of the hole pattern. (c) Scanning electron micrograph of the device. [Reprinted with permission from M. Gharghi et al., Nano Lett. 11 (2011) 2825. Copyright 2011 American Chemical Society.]