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[[Vol. 22]Holes in gold enhance molecular sensing _ WPI-MANA.pdf](https://mdr.nims.go.jp/filesets/ff068000-4b31-43f0-91f2-1db98515c0e5/download)

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International Center for Materials Nanoarchitectonics (WPI-MANA)

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[[Research Highlights Vol.22] Holes in gold enhance molecular sensing](https://mdr.nims.go.jp/datasets/256260eb-45c1-40e1-8e74-a9aa30e2e84e)

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2022/04/04 10:19 Holes in gold enhance molecular sensing | MANAhttps://www.nims.go.jp/mana/research/highlights/vol22.html 1/2Previous  Index  NextResearch Highlights[Vol. 22]Holes in gold enhance molecular sensing19 May, 2015Electrochemical techniques produce tuneable porous gold films, where theempty spaces enhance light scattering and sensing signals.Figure: Electromagnetic-field distributions on mesoporous Au films. Scanningelectron microscope images (left) and the corresponding Electric-fielddistributions on mesoporous Au films under 532nm wavelength excitation. Theelectric-field distribution is taken from 10 nm in depth in the films, in whichmoderate electric-field amplitude is clearly observed inside or at the perimeter ofthe mesopores, as shown in dotted-line squares.Non-metallic mesoporous structures have already demonstrated potential for applications in gasstorage, separation, catalysis, ion-exchange, sensing, polymerization and drug delivery. Metalmesoporous films could have fascinating and useful optical properties as they are effectively theinverse of nanoparticle arrays. Now for the first time a collaboration of researchers in Japan,Turkey, Korea and Sweden demonstrate a simple approach for producing metal films with regulartuneable mesopores, and show their potential for high-sensitivity optical detection.When light is incident on nanostructures of noble metals such as gold, the electrons oscillatecollectively – a so-called plasmon – and this greatly enhances the electromagnetic field close by.According to Babinet’s principle in optics, the inverse structure – a mesoporous film – should leadto similar local electromagnetic field enhancements, but as Yamauchi and his colleagues point outin their report, controlling gold crystal growth well enough to produce mesoporous films has so farbeen difficult.The success of their approach relies on electrochemistry and micelle self-assembly. They dissolvehydrogen gold chloride (or chloroauric acid, HAuCl4) and polystyrene-block-poly (oxyethylene) in asolution of tetrahydrofuran, which leads to the formation of micelles with a polystyrene core andpolyoxyethylene shell. The micelles reduce the AuCl4- ions so that gold deposits on the micelles.The result is highly regular gold mesopores with a size that can be tuned by varying theconcentrations of the HAuCl4 and polystyrene-block-poly (oxyethylene).https://www.nims.go.jp/mana/research/highlights/vol21.htmlhttps://www.nims.go.jp/mana/research/highlights/index.htmlhttps://www.nims.go.jp/mana/research/highlights/vol23.html2022/04/04 10:19 Holes in gold enhance molecular sensing | MANAhttps://www.nims.go.jp/mana/research/highlights/vol22.html 2/2Calculations showed that hotspots of high electric field enhancement indeed exist in the pores ofthe structure, and the plasmon resonances can be tuned by changing the pore size. Furtherexperiments confirmed the surface enhancement of protein spectral signatures, known as surfaceenhanced Raman scattering. The researchers conclude, “The electrochemical approach is widelyapplicable to embed uniform mesopores in other metal and alloy systems, which are generallydifficult to be synthesized.”Reference"Electrochemical synthesis of mesoporous gold films toward mesospace-stimulated opticalproperties"Cuiling Li, Ömer Dag, Thang Duy Dao, Tadaaki Nagao, Yasuhiro Sakamoto, Tatsuo Kimura, OsamuTerasaki and Yusuke YamauchiJournal : Nature Communications 6, 6608 (2015).DOI : 10.1038/ncomms7608AffiliationsInternational Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for MaterialsScience (NIMS), Namiki 1-1, Tsukuba, Ibaraki 305-0044, JapanContact informationInternational Center for Materials Nanoarchitectonics(WPI-MANA)National Institute for Materials Science1-1 Namiki, Tsukuba, Ibaraki 305-0044 JapanPhone: +81-29-860-4710E-mail: mana-pr[AT]ml.nims.go.jphttps://samurai.nims.go.jp/profiles/nagao_tadaaki?locale=enhttps://samurai.nims.go.jp/profiles/yamauchi_yusuke?locale=enhttps://www.nature.com/articles/ncomms7608