Plasmonics: the Aluminium Rush

news & views on the slow kinetics of silica polymerization 50 nm) have been derived after the removal complex specimens for biomedical research adds to the structural diversity currently of the self-assembled organic templates. These and bioengineering applications. In organ available from the natural biomineralizing materials are of great interest as catalysts and transplant research, there has been substantial microorganisms. advanced functional materials. interest in using decellurized organs as a Another interesting aspect of the silica In the future, the use of the silica host for seeding stem cells from patients10. replica of the cell is that when amphiphilic replicas of the mammalian cells to create The inverted biomaterial replicas of tissues, lipid bilayers in the form of liposomes were biomaterials for cell culture and tissue organoids and organs may potentially act as a added to the replicas, they localized only on engineering applications could be possible. structural support and offer an environment the outer surfaces of the replicas, suggesting For example, the replica can act as a mould for controlled differentiation of stem cells. ❐ that the membrane lipids could potentially for the polymerization of different types of be reconstituted. Furthermore, when treated biomaterials. Following the removal of silica Jackie Y. Ying is in the Institute of Bioengineering with high-temperature pyrolysis (900 °C (for example, by etching in a basic solution), and Nanotechnology, 31 Biopolis Way, The Nanos, in nitrogen) followed by dissolution of the a porous biomaterial that is an inverted copy Singapore 138669, Singapore. silica with basic solutions, the replicas were of the silica replica can be obtained. The e-mail: [email protected] converted to carbonized systems. These unique microstructure of the inverted copy porous carbon replicas, which possessed and the surface chemistry of the biomaterial References greater conductivity than the silica ones, may facilitate the expansion of stem cells 1. Fratzl, P. & Weiner, S. Adv. Mater. 22, 4547–4550 (2010). could potentially be used as absorbents or in and primary cells. They may also induce the 2. Khripin, C. Y., Pristinski, D., Dunphy, D. R., Brinker, C. J. & 3 Kaehr, B. ACS Nano 5, 1401–1409 (2011). sensing applications . selective differentiation of stem cells towards 3. Kaehr, B. et al. Proc. Natl Acad. Sci. USA 109, 17336–17341 (2012). Both the silica and carbon replicas of the desired cell type when the inverted 4. Huo, Q. S. et al. Nature 368, 317‒321 (1994). mammalian cells add to the diversity of biomaterial replica of the desired cells is 5. Sun, T. & Ying, J. Y. Nature 389, 704–706 (1997). porous materials that have been created employed as a cell-culture substrate. 6. Zhao, D. et al. Science 279, 548‒552 (1998). 7. Kresge, C. T., Leonowicz, M. E., Roth, W. J., Vartuli, J. C. & through the use of organic templates such Furthermore, it would be of interest to Beck, J. S. Nature 359, 710–712 (1992). as surfactants4, short-chain molecules5 and examine if the present approach with cells can 8. Tanev, P. T. & Pinnavaia, T. J. Science 267, 865–867 (1995). block copolymers6. For example, silica7, be extended to obtain silica replicas of tissues, 9. Antonelli, D. M. & Ying, J. Y. Angew. Chem. Int. Ed. Engl. 8 9 34, 2014–2017 (1995). alumina and transition metal oxides with organoids and organs. Such replicas would 10. Gilbert, T. W., Sellaro, T. L. & Badylak, S. F. Biomaterials well-defined porosities (in the range of ~1– present an interesting way of preserving 27, 3675–3683 (2006). PLASMONICS The aluminium rush An electromagnetic field may promote with minimal loss of energy. However, a concerted oscillation of electrons on for some applications propagation a metal surface, allowing light to be distance can be compromised, and the concentrated in spaces that are smaller 50 40 nm focus therefore shifted to the ability of than its wavelength. To visualize these nanorods to confine plasmons in tighter waves (or plasmonic modes), researchers spaces. Here, aluminium outperforms use cathodoluminescence, where a both silver and gold. A particularly highly focused electron beam excites the 100 40 nm relevant application of this type involves surface electrons, which then emit light on the coupling between the semiconductor recombination. technology used in computers and the In Nano Letters (http://doi.org/jrw; plasmonic modes of a nanorod. Aluminium 2012), Naomi Halas at Rice University 150 40 nm is already compatible with fabrication (USA) and co-workers report the plasmonic technology for complementary metal- modes of an aluminium nanorod with oxide semiconductors, and optimization spatial resolution of about 20 nm. The of its optical properties at the nanoscale nanorod functions as an optical antenna 200 40 nm could lead to the integration of plasmonics concentrating light in specific regions. and semiconductor electronics. Therefore, Transitions from circular emission (top row the spatially resolved characterization in the figure), where the modes from the of the plasmonic properties of the longitudinal and transverse directions are 250 40 nm aluminium nanoantenna reported by degenerate, to dipolar and even quadrupolar Halas and co-workers is an essential emission, which arise from the longitudinal step in this direction. Add to the mix the confinement, are clearly visible as the rod fact that aluminium is the third most length increases. The modes remain intense abundant element in the Earth’s crust, 300 40 nm 2012 ACS throughout the investigated regions and can © and the potential for an aluminium rush be tuned from the ultraviolet to the visible practical applications of plasmonics. Gold in plasmonic science and technology is range by changing the nanorod length. and silver have been the main players since easily envisaged. It is only recently that aluminium has the inception of the field because they allow been regarded as a serious contender for long-distance propagation of plasmons ALBERTO MOSCATELLI 778 NATURE NANOTECHNOLOGY | VOL 7 | DECEMBER 2012 | www.nature.com/naturenanotechnology © 2012 Macmillan Publishers Limited. All rights reserved.

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