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Synthesis of polymer nanocapsules simplified
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Figure 1 A mass-selected cluster of Cu-ZnO nanoparticles visualized by atomic-resolution TEM in an H2 atmosphere (1 mbar, 300 ◦ C). Adapted from J. Phys. Chem. C 119 (5) (2015) 2804—2812, http://dx.doi.org/10.1021/jp510015v.
encapsulation-decapsulation process has not been observed before and is likely to be the result of volume expansion of Cu as it oxidizes. In another surprising finding, the
C. Sealy researchers observed the presence of small amounts of metallic Zn after reduction. ‘‘[This] is interesting,’’ says Helveg, ‘‘because Zn atoms in the Cu surface have been considered as promoters of methanol synthesis.’’ The observations could reveal the origin of the relationship between Cu and ZnO that has been known for decades but not understood. The approach is also likely to be applicable to other alloys, Martin Muhler of RuhrUniversität Bochum in Germany told Nano Today. Exploring other nanoparticle combinations in this way could reveal new catalytic functionalities. Christian Kisielowski of Lawrence Berkeley National Laboratory agrees that the results point to a model catalyst system, which can be well understood. ‘‘Industrial catalysts exhibit a great structural complexity that largely prohibits improved understanding and stimulates vivid discussion that cannot be concluded. This paper changes that,’’ he says. The researchers’ use of electron microscopy reveals the atomic structure of real catalysts and promises an exciting way forward for analyzing their behavior during operation. E-mail address: [email protected] 1748-0132/$ — see front matter http://dx.doi.org/10.1016/j.nantod.2015.02.004
Synthesis of polymer nanocapsules simplified Cordelia Sealy
Tiny reactors for carrying out chemical reactions, novel carriers for drugs or efficient sensors could, in the future, be based on polymer nanocapsules. But current synthesis routes for such capsules require UV light or relatively high polymerization temperatures of 60—70 ◦ C, which can damage the delicate cargo of proteins, biological or lightsensitive molecules. To get around the problem, researchers from the University of Connecticut have devised a new synthesis strategy for polymer nanocapsules that does not need UV light and can be carried out at near physiological conditions [M.D. Kim, et al., Langmuir 31 (2015) 2561, http://dx.doi.org/10.1021/la5046095]. ‘‘We [have] found a way to prepare hollow polymer nanocapsules under mild conditions that does not damage the molecules we want to incorporate into capsules,’’ explains Eugene Pinkhassik. ‘‘For example, if we incorporate enzymes into nanocapsules, we can make highly efficient nanoreactors.’’
The method relies on vesicles, which form spontaneously when surfactants or lipids are mixed with water. Monomers — the building blocks for the polymer nanocapsules — are loaded into the interior layers of vesicles and then an initiator chemical is added to thermally kick-start polymerization. The monomers form a crosslinked network that, after the surfactant scaffold is removed, yield free-standing nanocapsules. The entire process takes place in neutral pH and mild temperatures of 35—40 ◦ C. The 50—400 nm diameter capsules have an outer skin just a single nanometer thick, which means they can carry more cargo than other similarly sized structures. The capsule walls are also porous, with tunable pore sizes of 0.5—2 nm, so permeability can be predetermined (Fig. 1). ‘‘Because of the single-nanometer shell thickness, transport of molecules or ions through the pores happens very quickly,’’ says Pinkhassik. ‘‘Molecules larger than the pore size do not pass through the shell, while
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123 The pores can also be decorated with chemical groups like carboxylics, which can capture and release other molecules. The researchers are now exploring this behavior as a means for delivering drugs and imaging agents. ‘‘These capsules can be used as smart containers for the catch and release of drugs and imaging agents, fastacting sensors, and nanoreactors, to name a few immediate applications,’’ says Pinkhassik. In Su Lee of POSTECH in Korea agrees that the approach should be useful for applications. ‘‘What is most attractive is that their strategy can generate hollow nanocapsules in near physiological conditions and enable the in situ or in vivo encapsulation of a range of biologically relevant molecules,’’ he told Nano Today. ‘‘[This could contribute to] the expansion of the use of hollow nanocapsules in biological and medical applications.’’
Figure 1 Illustration of a hollow porous nanocapsule with programmed uniform nanopores and the utility of capsules in industrial and biomedical applications, enabling the creation of nanoreactors, nanosensors, and devices for the delivery of drugs and imaging agents. Credit: Mariya D. Kim, University of Connecticut.
molecules smaller than the pore size pass through the shells rapidly.’’ The researchers demonstrate this permeability by introducing pH-sensitive dye molecules during synthesis. The larger dye molecules became trapped inside the nanocapsules, while the smaller ones escaped through the capsules’ pores. ‘‘We describe these capsules as having ‘invisible’ walls because capsules with entrapped pH-sensitive dyes showed the same color or fluorescence change as free (nonencapsulated) dyes,’’ explains Pinkhassik.
Cordelia Sealy has many years’ experience as a scientific journalist and editor in areas spanning nanotechnology, materials science and engineering, physics and chemistry. She has served as Editor of Materials Today and Nano Today, and more latterly as Managing Editor of both titles. She has also worked in academic publishing as a books acquisitions editor and in business-to-business publishing as a journalist on European Semiconductor. She has a First in Physical Sciences (BSc) from University College London and a DPhil in materials science from the University of Oxford, and is a Member of the Institute of Physics. Cordelia is currently a freelance science writer for her own company, Oxford Science Writing, and News and Opinions Editor for Nano Today.
E-mail address: [email protected] 1748-0132/$ — see front matter http://dx.doi.org/10.1016/j.nantod.2015.02.005
Figure 1 A mass-selected cluster of Cu-ZnO nanoparticles visualized by atomic-resolution TEM in an H2 atmosphere (1 mbar, 300 ◦ C). Adapted from J. Phys. Chem. C 119 (5) (2015) 2804—2812, http://dx.doi.org/10.1021/jp510015v.
encapsulation-decapsulation process has not been observed before and is likely to be the result of volume expansion of Cu as it oxidizes. In another surprising finding, the
C. Sealy researchers observed the presence of small amounts of metallic Zn after reduction. ‘‘[This] is interesting,’’ says Helveg, ‘‘because Zn atoms in the Cu surface have been considered as promoters of methanol synthesis.’’ The observations could reveal the origin of the relationship between Cu and ZnO that has been known for decades but not understood. The approach is also likely to be applicable to other alloys, Martin Muhler of RuhrUniversität Bochum in Germany told Nano Today. Exploring other nanoparticle combinations in this way could reveal new catalytic functionalities. Christian Kisielowski of Lawrence Berkeley National Laboratory agrees that the results point to a model catalyst system, which can be well understood. ‘‘Industrial catalysts exhibit a great structural complexity that largely prohibits improved understanding and stimulates vivid discussion that cannot be concluded. This paper changes that,’’ he says. The researchers’ use of electron microscopy reveals the atomic structure of real catalysts and promises an exciting way forward for analyzing their behavior during operation. E-mail address: [email protected] 1748-0132/$ — see front matter http://dx.doi.org/10.1016/j.nantod.2015.02.004
Synthesis of polymer nanocapsules simplified Cordelia Sealy
Tiny reactors for carrying out chemical reactions, novel carriers for drugs or efficient sensors could, in the future, be based on polymer nanocapsules. But current synthesis routes for such capsules require UV light or relatively high polymerization temperatures of 60—70 ◦ C, which can damage the delicate cargo of proteins, biological or lightsensitive molecules. To get around the problem, researchers from the University of Connecticut have devised a new synthesis strategy for polymer nanocapsules that does not need UV light and can be carried out at near physiological conditions [M.D. Kim, et al., Langmuir 31 (2015) 2561, http://dx.doi.org/10.1021/la5046095]. ‘‘We [have] found a way to prepare hollow polymer nanocapsules under mild conditions that does not damage the molecules we want to incorporate into capsules,’’ explains Eugene Pinkhassik. ‘‘For example, if we incorporate enzymes into nanocapsules, we can make highly efficient nanoreactors.’’
The method relies on vesicles, which form spontaneously when surfactants or lipids are mixed with water. Monomers — the building blocks for the polymer nanocapsules — are loaded into the interior layers of vesicles and then an initiator chemical is added to thermally kick-start polymerization. The monomers form a crosslinked network that, after the surfactant scaffold is removed, yield free-standing nanocapsules. The entire process takes place in neutral pH and mild temperatures of 35—40 ◦ C. The 50—400 nm diameter capsules have an outer skin just a single nanometer thick, which means they can carry more cargo than other similarly sized structures. The capsule walls are also porous, with tunable pore sizes of 0.5—2 nm, so permeability can be predetermined (Fig. 1). ‘‘Because of the single-nanometer shell thickness, transport of molecules or ions through the pores happens very quickly,’’ says Pinkhassik. ‘‘Molecules larger than the pore size do not pass through the shell, while
News and opinions
123 The pores can also be decorated with chemical groups like carboxylics, which can capture and release other molecules. The researchers are now exploring this behavior as a means for delivering drugs and imaging agents. ‘‘These capsules can be used as smart containers for the catch and release of drugs and imaging agents, fastacting sensors, and nanoreactors, to name a few immediate applications,’’ says Pinkhassik. In Su Lee of POSTECH in Korea agrees that the approach should be useful for applications. ‘‘What is most attractive is that their strategy can generate hollow nanocapsules in near physiological conditions and enable the in situ or in vivo encapsulation of a range of biologically relevant molecules,’’ he told Nano Today. ‘‘[This could contribute to] the expansion of the use of hollow nanocapsules in biological and medical applications.’’
Figure 1 Illustration of a hollow porous nanocapsule with programmed uniform nanopores and the utility of capsules in industrial and biomedical applications, enabling the creation of nanoreactors, nanosensors, and devices for the delivery of drugs and imaging agents. Credit: Mariya D. Kim, University of Connecticut.
molecules smaller than the pore size pass through the shells rapidly.’’ The researchers demonstrate this permeability by introducing pH-sensitive dye molecules during synthesis. The larger dye molecules became trapped inside the nanocapsules, while the smaller ones escaped through the capsules’ pores. ‘‘We describe these capsules as having ‘invisible’ walls because capsules with entrapped pH-sensitive dyes showed the same color or fluorescence change as free (nonencapsulated) dyes,’’ explains Pinkhassik.
Cordelia Sealy has many years’ experience as a scientific journalist and editor in areas spanning nanotechnology, materials science and engineering, physics and chemistry. She has served as Editor of Materials Today and Nano Today, and more latterly as Managing Editor of both titles. She has also worked in academic publishing as a books acquisitions editor and in business-to-business publishing as a journalist on European Semiconductor. She has a First in Physical Sciences (BSc) from University College London and a DPhil in materials science from the University of Oxford, and is a Member of the Institute of Physics. Cordelia is currently a freelance science writer for her own company, Oxford Science Writing, and News and Opinions Editor for Nano Today.
E-mail address: [email protected] 1748-0132/$ — see front matter http://dx.doi.org/10.1016/j.nantod.2015.02.005