Archive for the ‘Hot Article’ Category

HOT article: The support effect on the size and catalytic activity of thiolated Au25 nanoclusters as precatalysts

TEM images and size distribution (inset) of various Au25 (1 wt%)/support samples before and after 300 °C calcination.

The use of nanogold (Au NP) catalysts has been widely established for various applications including pharmaceuticals and perfumes.  However, their usage has been limited due to the conventional protocols employed for Au NP synthesis producing polydisperse size ranges, which have proven problematic for identifying catalytic active sites. Recently, this issue has been circumvented through instead using Au nanoclusters (Au NCs), which produce defined cluster sizes with well-defined physiochemical properties. As a direct consequence of being able to exert such control, there have been a number of applications established using such catalysts for processes including CO oxidation, and the oxidation of styrene and cyclohexane. However, whilst the role of the solid support is well established for Au NP catalysis, there currently exists a lack of knowledge on what effect/role the support plays in Au NCs catalysis.

In this study, Fang and co-workers report a systematic assessment of thiolated Au NCs on five different solid supports through examination of the size and electronic structure evolution of the Au NCs during heat treatment, and their catalytic performance when applied to the hydrogenation of nitrobenzene and oxidation of styrene.  The solid supports investigated include hydroxy-apatite (HAP), TiO2 (P25), activated carbon (AC), pyrolyzed grapheme oxide (PGO) and fumed SiO2.

The key findings of these studies establish that AuNCs on HAP and P25 supports presented enhanced activities over the other considered supports. This was found to be due to a number of factors, including reduced NC growth during calcination (heat treatment) following the removal of the thiolated ligands from the nanocluster surface. Further to this, the catalytic activity established during the hydrogenation of nitrobenzene and oxidation of styrene overwhelmingly showed that AuNC-HAP had a greater activity than any of the other supported catalysts. This was found to be due to both the reduced NC growth following heat treatment, and a change in the electronic structure of bound Au, resulting in strengthened metal support interactions.

Although this study has shown HAP to be a superior support in comparison to the others investigated, it should be noted that during heat treatment, an increase in the size of the nanoclusters was still observed.  As a consequence of this, the authors have objectively established improvements which should be made for future studies, including pursuing different support methods and improving the conditions under which the thiolated ligands can be removed from the Au NCs.

The support effect on the size and catalytic activity of thiolated Au25 nanoclusters as precatalysts
Jun Fang, Jingguo Li, Bin Zhang, Xun Yuan, Hiroyuki Asakura, Tsunehiro Tanaka, Kentaro Teramura, Jianping Xie and Ning Yan
Nanoscale, 2015, 7, 6325-6333. DOI: 10.1039/C5NR00549C

Dr Derek Craig is a guest web writer for the Nanoscale blog. He is a Post Doctoral Research Fellow at the University of St. Andrews based in the fields of Biophotonics and Materials Science. With a background in chemistry, his work mainly focuses on the synthesis of nano to meso materials and the use of imaging techniques to study biological samples.

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HOT article: Radiolabelled magnetic particles for imaging

Radiolabelling of core–shell and dumbbell-like nanoparticles

Bi-modal imaging agents are becoming more popular as they can be used to overcome limitations of single imaging modalities. In this work, radiolabelling of gold containing magnetic nanoparticles (Fe3O4-Au) with a nuclear isomer of technetium (99mTc), a commonly used radionuclide for clinical photon emission computed tomography (SPECT), was assessed using two different methods.  In the first approach, Fe3O4-Au core-shell nanoparticles were coated with ligands containing thiol groups to bind to gold and chelator groups for [99mTc(CO)3]+. In the second approach, 99mTc containing ligands were first synthesised, then attached to gold on Fe3O4-Au dumbbell-like nanoparticles. Both synthetic routes were successful in providing a sufficient radiochemical yield on the surface of magnetic nanoparticles, and are ideal candidates as dual magnetic resonance imaging MRI/SPECT imaging agents. In future studies, the authors plan to use the radiolabelled magnetic particles for bimodal imaging of tumours, through attachment of cancer-specific targeting vectors.

99mTc radiolabelling of Fe3O4–Au core–shell and Au–Fe3O4 dumbbell-like nanoparticles
M. Felber and R. Alberto
Nanoscale, 2015, 7, 6653-6660. DOI: 10.1039/C5NR00269A

Dr Mike Barrow is a guest web writer for the Nanoscale blog. He currently works as a Postdoctoral Researcher at the University of Liverpool.

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HOT article: Scalable and cost effective patterning of graphene layers

Visual image after EBL treatment, corresponding Raman spectroscopy map of a graphene flake and Raman spectra recorded at different spots on the sample.

Research articles on graphene have been numerously been presented throughout the last decade, indicating the promising future of this material. However, bridging the gap between laboratory research and industrial application remains difficult due to missing specialized large-scale production equipment.

A new article recently published by A. Caglinani et al. introduces an electron beam-based patterning technique using solely widely available clean-room equipment. Based on the findings of the paper, graphene structuring could become a more widespread processing technique.

The researchers developed a patterning process utilizing an industry-standard electron beam lithography system and a standard oven to achieve a resolution of 40 nm.

In the first step, a graphene layer is irradiated by the electron beam which locally generates defects within the crystal lattice. The damage was found by the researchers to be spatially confined to the exposed areas, thus allowing for arbitrary patterns.

The second step comprised etching the irradiated areas by means of hot air at atmospheric pressure. The high defect density (e.g. dangling bonds) induced by the electron beam lead to a large difference in the etch rate compared to the unmodified areas. By exposing the samples for 16 min at 435°C to air, the previously irradiated areas were selectively etched.

In conclusion, the presented process can be used to easily structure graphene layers for future application without the need for specialized equipment. According to the authors, future improvements could reduce the minimum feature size further.

Alberto Cagliani, Niclas Lindvall, Martin Benjamin Barbour Spanget Larsen, David M. A. Mackenzie, Bjarke Sørensen Jessen, Timothy J. Booth and Peter Bøggild
Nanoscale, 2015, 7, 6271-6277. DOI: 10.1039/C4NR07585D

Sebastian Axmann is a guest web-writer for the Nanoscale blog. His interests comprise manufacturing and metrology of nanostructures as well as their usage in current semiconductor devices. He also posts links to interesting research articles on Twitter: @SebastianAxmann.

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Viruses: Feeling the strain

Viruses are highly complex biological nanostructures.  This complexity has renewed an interest in viruses from the perspective of fundamental physics at the nanoscale. An understanding of the mechanical properties of virus particles at the molecular level can reveal information regarding stiffness, intrinsic elasticity, structural strength and resistance to mechanical fatigue.  This information can provide a basis for researchers to engineer virus-based nanoparticles as nanodevices/ nanocontainers for different biotechnological applications.

The MVM virion.

Castellanos and co-workers have endeavoured to understand the conformational stability and dynamics of the minute virus of mice (MVM), a small ~ 25 nm virus particle, which serves as a model system to understand some of the mechanical properties of viruses. To this end, the researchers have investigated the linkage between the DNA-mediated increase in mechanical stiffness and heat-induced structural changes, and a quantitative relationship between mechanical elasticity and conformational dynamics in MVM nanoparticles.

The researchers used a combination of transmission electron microscopy (TEM) and atomic force microscopy (AFM) for determining the thermal inactivation behaviour and the mechanical stiffness of the viruses, respectively.  By utilizing these techniques, the researchers have deduced that infectious MVM particles may have evolved architectural functions that increase their survival in thermally stressed environments.

This proof-of-principle study has demonstrated that nanoscale features of virus nanoparticles can be probed analytically using AFM and the elucidation of these features have future impact in the field of protein engineering.

Milagros Castellanos, Pablo J. P. Carrillo and Mauricio G. Mateu
Nanoscale, 2015, 7, 5654-5664. DOI: 10.1039/C4NR07046A

Dr Lee Barrett is a guest web writer for the Nanoscale blog. Lee is currently a postdoctoral researcher in the Centre for Molecular Nanometrology at the University of Strathclyde. His research is currently focused on the development of nanoparticle-based sensors and surface enhanced Raman scattering (SERS). Follow him on twitter @L_Bargie.

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HOT article: Unfolding the secrets of DNA origami nanostructures

DNA origami machine components

DNA origami is an emerging field of nanotechnology that exploits the unique base-pairing capabilities of the DNA bases to produce complex and mechanically stiff self-assembled nanoscale geometries. Recently, DNA origami has found uses in applications such as single molecule sensing, drug delivery and templating molecular components.

This review, by researchers from Ohio State University, sets out to explore the mechanical nature of DNA nanostructures in order to understand how these structures will respond to physical interactions. The review covers three major areas of progress, including measuring and designing mechanical properties of DNA nanostructures, designing complex nanostructures based on imposed mechanical stresses and, finally, designing and controlling structurally dynamic nanostructures.

For researchers interested in the future possibilities of DNA origami, this review should provide an insightful first stop for discussing the mechanical design of DNA nanostructures.

Mechanical design of DNA nanostructures
Carlos E. Castro, Hai-Jun Su, Alexander E. Marras, Lifeng Zhou and Joshua Johnson
Nanoscale, 2015, Advance Article. DOI: 10.1039/C4NR07153K

Dr Lee Barrett is a guest web writer for the Nanoscale blog. Lee is currently a postdoctoral researcher in the Centre for Molecular Nanometrology at the University of Strathclyde. His research is currently focused on the development of nanoparticle-based sensors and surface enhanced Raman scattering (SERS). Follow him on twitter: @L_Bargie

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HOT article: Effects of morphology and chemical doping on electrochemical properties of metal hydroxides in pseudocapacitors

With a limited amount of fossil fuels in the ground, developing alterative strategies for energy production is of the utmost importance.  However, without a way to store that energy, these endeavors could be futile.

From the team of Gyeonghee Lee, Chakrapani V. Varansi, and Jie Liu (an Associate Editor here at Nanoscale), comes one of this month’s HOT papers, “Effects of morphology and chemical doping on electrochemical properties of metal hydroxides in pseudocapacitors.” In this paper, the team’s specific metal hydroxide of interest is Ni(OH)2.

image file: c4nr06997h-s1.tif

Schematic illustration of the proposed mechanism for the morphology modification of Ni(OH)2 by glucose in the solvothermal medium.

Lee et al. state “…that both morphology control and chemical doping positively affect the electrochemical performance of Ni(OH)2 when applied individually.”  In this paper, they set out to determine what happens to the electrochemical performance when morphology and doping are combined instead of applied individually.  In order to investigate the effects of both, they chose a solvothermal synthesis route for metal hydroxide flakes, creating both cobalt-doped (CoxNi1-x(OH)2) and undoped particles (Ni(OH)2) that have varying amounts of D-glucose added.  For both the doped and undoped particles, four sets of particles are created, where 0, 10, 20, and 50% of the urea normally used in the solvothermal process is replaced by the D-glucose.  All of the particles were characterized with x-ray diffraction (XRD) and scanning electron microscopy (SEM), with the SEM showing that increasing amounts of glucose decreased flake size.  XRD and thermogravimetric analysis also revealed that increasing D-glucose amounts created an increase in the amount of interlayer water, with XRD also indicating degree of crystallinity decreased with increasing D-glucose.

In order to understand how the glucose affects morphology, the authors ran the solvothermal synthesis without the metal precursor. XRD and nuclear magnetic resonanace (NMR) data indicates the presence of ethyl-substituted glucose (formed during the synthesis process) instead of D-glucose.   The authors conclude that “…ethyl glucoside molecules can hinder the precursor diffusion and thus inhibit the metal hydroxide growth during synthesis.”

The electrochemical performance of all of the types of particle is evaluated using cyclic voltammetry (CV), galvanostatic charge–discharge, and electrochemical impedance spectroscopy (EIS).  Increasing glucose levels on undoped particles increased specific capacitance and cobalt doping is also shown to improve specific capacitance.  Combining the two showed that specific capacitance increased up to 50% of Co doping, but was less effective above 50%.

Lee et al. find that “…the addition of glucose in the ethanol-mediated solvothermal synthesis effectively reduces the particle size of metal hydroxide flakes. The specific capacitance is improved as a result of the increased surface area and reduced particle size.”  In terms of specific capacitance, the higher interlayer water levels found for increasing glucose levels may make ion mobility easier in the materials, enhancing the specific capacitance of the doped-Ni(OH)2.  In the doped materials, the specific capacitance was increased with low doping and decreased with high doping.

In designing future iterations of Ni(OH)2 batteries, careful attention will need to be placed on both morphology and doping levels in order to find the best balance for electrochemical performance.

Effects of morphology and chemical doping on electrochemical properties of metal hydroxides in pseudocapacitors
Gyeonghee Lee, Chakrapani V. Varanasi and Jie Liu
Nanoscale, 2015, 7, 3181-3188. DOI: 10.1039/C4NR06997H

Stephanie E. Vasko is currently a Senior Research Assistant at The Rock Ethics Institute at the Pennsylvania State University in State College. Her research focuses on science communication, STEM education, and the intersections between art, craft, and science.  You can follow her on Twitter at @stephanievasko.

The opinions and views expressed in this piece are those of the author and do not represent or reflect the opinion, views, or policy of the Pennsylvania State University, the Rock Ethics Institute, or the National Science Foundation.

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HOT article: A tunable submicro-optofluidic polymer filter based on guided-mode resonance

image file: c4nr07233b-f3.tif

SEM images of the polymer submicro-channels and photographs of the fabricated submicro-optofluidic PGMR filter with empty channels and with water filled channels, respectively.

Optical filters are routinely included in devices used for communications, displays and bio-sensing. One such class of optical filters, which have been frequently used, are guided-mode resonance (GMR) filters. Inherent errors with common GMR filters are assigned to fabrication difficulties and as a result, new classes of reconfigurable GMR filters have been created.

In this HOT article, Jin and co-workers have proposed and devised a novel polymer-based GMR (PGMR) which can be incorporated into lab on a chip devices and become tuned by the optical properties of the fluidic mixture present. The simple and low cost PGMR filter was fabricated in three stages, using two-beam interference lithography, floating nanofilm transfer, and finally, thermal bonding technology.

The tunability of this class of PGMR was tested by filling the fluidic channels with a range of liquid mixtures of differing refractive indices. The resulting PGMR exhibited high reflection efficiency in the visible wavelength region, a narrow band tuning range and a high tuning efficiency. The successful incorporation of the PGMR in an optofluidic device operating in the visible wavelength region opens up the possibility of the inclusion of such PGMR devices in future lab on a chip devices.

A tunable submicro-optofluidic polymer filter based on guided-mode resonance
Guohui Xiao, Qiangzhong Zhu, Yang Shen, Kezheng Li, Mingkai Liu, Qiandong Zhuang and Chongjun Jin
Nanoscale, 2015, 7, 3429-3434. DOI: 10.1039/C4NR07233B.

Dr Derek Craig is a guest web writer for the Nanoscale blog. He is a Post Doctoral Research Fellow at the University of St. Andrews based in the fields of Biophotonics and Materials Science. With a background in chemistry, his work mainly focuses on the synthesis of nano to meso materials and the use of imaging techniques to study biological samples.
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HOT article: Glance into the nanoparticle-imprinted mirror antenna (NIMA)

An ultrahigh-sensitivity plasmonic antenna (NIMA)

Researchers using surface enhanced Raman scattering (SERS) are always on the look out for new substrates that take advantage of coupled metallic nanoparticles to improve sensitivity.  In this HOT article, researchers from Taiwan have introduced NIMAs (nanoparticle (NP)-imprinted mirror antennas) for exactly this purpose.

The researchers deposited Ag on a polycarbonate substrate and used Si molds to create 2D periodic nanostructures, which were then used to create NIMAs by self-assembling Ag nanoparticles onto the Ag mirrors.  The formation of 2D nanoclusters on the mirror results in more intense Raman signals as a result of electromagnetic coupling between the NPs in the clusters. NIMAs have several advantages over other SERS-active substrates. For example, NIMAs gain broadband enhancement from single structures, rather than from various substrates with different morphologies. Also, using a deeper, more consistent structure and tuning the surface plasmon resonance (SPR) modes can drastically improve the SERS enhancement observed from NIMAs.

The researchers have produced a SERS-active substrate that is compatible in the visible to near-infrared regime and is capable of detecting rhodamine 6G at a concentration as low as 10-15 M.  These attractive advantages should be enough for any SERS researcher to reflect on the possibility of adopting NIMAs as a sensing platform in the future.

Chen-Chieh Yu, Yi-Chuan Tseng, Pao-Yun Su, Keng-Te Lin, Chang-Ching Shao, Sin-Yi Chou, Yu-Ting Yen and Hsuen-Li Chen
Nanoscale, 2015, Advance Article. DOI: 10.1039/C4NR05902F.

Dr Lee Barrett is a guest web writer for the Nanoscale blog. Lee is currently a postdoctoral researcher in the Centre for Molecular Nanometrology at the University of Strathclyde. His research is currently focused on the development of nanoparticle-based sensors and surface enhanced Raman scattering (SERS).

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HOT article: A facile synthesis of highly luminescent nitrogen-doped graphene quantum dots for the detection of 2,4,6-trinitrophenol in aqueous solution

The last decade observed immense growth in applications of graphene, a carbon allotrope with applications in diverse areas of science, including fluorescent nanoparticles like quantum dots. However, the applications of graphene-based nanodevices in biological contexts have still been a bit slow. This is primarily due to the metal-free nature of graphene nanoparticles, leading to poor fluorescence abilities, and their lack of sensing abilities for various analytes.

Lin et al., in the current work, intelligently overcome these two problems by doping graphene quantum dots with nitrogen-containing species like amines, which not only make the dots much brighter, but also sensitive to various analytes. They show the detection of trinitrophenol, one of the most explosive materials in aqueous solutions, with good sensitivity and a detection limit of 300 nM. The stability of these doped dots to various acidic and alkaline conditions make them suitable for sensing applications in different samples and solutions, especially with biological samples, since the conditions are extremely diverse in these samples. The sensitive detection of trinitrophenol in solutions using simple fluorescence based assays can actually be explored for commercial low cost detectors.

Although much remains to be done to make these dots universally applicable, like doping with different molecules to sense specific analytes, the initial platform technology makes these nanoparticles suitable for applications in biosensing to detect materials like toxins, poisons or even explosives.

Dr Dhiraj Bhatia

A facile synthesis of highly luminescent nitrogen-doped graphene quantum dots for the detection of 2,4,6-trinitrophenol in aqueous solution
Liping Lin, Mingcong Rong, Sisi Lu, Xinhong Song, Yunxin Zhong, Jiawei Yan, Yiru Wang and Xi Chen
Nanoscale, 2015, 7, 1872-1878. DOI: 10.1039/C4NR06365A

Dr Dhiraj Bhatia is a guest web writer for the Nanoscale blog. He is a chemist by training and received his PhD in Chemical Biology of Nucleic Acids from the National Center for Biological Sciences, TIFR India with an outstanding thesis award in 2013. He joined the Chemical Biology department at the Curie Institute, Paris, as an HFSP long term Postdoctoral Fellow and is currently investigating the mechanisms of endocytois using various chemical biology tools.

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HOT article: On the mechanical and electronic properties of thiolated gold nanocrystals

Whilst undertaking my PhD I was repeatedly warned that the synthesis of nanoparticles was a ‘dark art’ i.e. luck. When, in fact, synthesising these particles actually turned out to be the easy part, whilst the most difficult parts were attempting to achieve stable nanoparticle systems and understanding their resulting properties.

Gold nanocrystals: description and experimental setup.

Even as the field of nanotechnology has undergone considerable expansion there still remain many unanswered fundamental questions. One such question is whether the mechanical and electrical properties of gold nanoparticles are representative of those of the bulk material and how these properties become modified in the presence of an organic coating layer.

Smaali and co-workers have tackled this issue by performing quantitative analysis on the mechanical and electrical properties of thiolated gold nanocrystals. Utilising a recently published procedure, single nanoparticles were grown in a silicon bed with an alkyl-thiol coating on one side and an ohmic contact on the other. To investigate the properties of these nanoparticles, a conducting atomic force microscope (AFM) tip was used, primarily as it offered the ability to interact with the nanocrystals using a variable loaded force with high precision, but also, due to the presence of an ohmic contact, the electrical properties of the nanocrystals and the alkyl-thiol coating could be tested.

Employing AFM measurements and finite elemental analysis (FEA) simulations, the Youngs Modulus of the embedded single nanocrystals was estimated to be 4 times smaller than those of free standing single nanocrystals. The molecular junctions formed between the thiol SAM coating and the individual nanoparticles provided an interesting insight into electronic properties of these materials, with a significant decrease in the tunnel current decay factor and potential barrier height being measured when forces even in the low nN range were applied. These results have been substantiated through FEA and DFT calculations to be a result of strain-induced molecular deformation, which causes a significant impact on the interfacial dipole, resulting in a change in the HOMO position with respect to the Au Fermi energy.

The authors of this study predict that this research could be used as a base model for other studies of functional molecular junctions and mechanical switches, with even small changes in van der Waals forces of a few nN thought to be sufficient to change the electron properties of nanoparticle-based molecular electronic devices.

On the mechanical and electronic properties of thiolated gold nanocrystals
K. Smaali, S. Desbief, G. Foti, T. Frederiksen, D. Sanchez-Portal, A. Arnau, J. P. Nys, P. Leclère, D. Vuillaume and N. Clément
Nanoscale, 2015, 7, 1809-1819. DOI: 10.1039/C4NR06180B

Dr Derek Craig is a guest web writer for the Nanoscale blog. He is a Post Doctoral Research Fellow at the University of St. Andrews based in the fields of Biophotonics and Materials Science. With a background in chemistry, his work mainly focuses on the synthesis of nano to meso materials and the use of imaging techniques to study biological samples.

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