Archive for the ‘Hot Article’ Category

HOT article: Nanostructured conducting polymer hydrogels for energy storage applications

Future energy storage solutions require a combination of high energy density, high reliability and low manufacturing cost. Conducting polymer hydrogels (CPHs) have emerged in recent years as a viable alternative for energy storage applications, as a Feature article by Shi et al. reports.

CPHs exhibit highly advantageous properties such as a large surface area, tunable mechanical properties and high conductivity compared to other polymers. These materials combine a conductive π–conjugated backbone with a porous structure.

Two synthesis routes are presented: template-guided synthesis (e.g. polymerization of monomers in a non-conductive hydrogel matrix) and direct formation using phytic acid as a gelator and dopant of the polymer.

Independent of synthesis route, CPHs were successfully demonstrated as bulk materials for electrochemical capacitors (also termed “supercaps”), as well as functional binders within Li-ion batteries. By careful modification of the polymer properties, a stable material able to withstand over 10000 charge-discharge cycles was demonstrated. Finally, the current hurdles for mass-market adoption, such as limited mechanical strength, lower conductivity than currently utilized material combinations and a lower capacity are explained, and paths to overcome these are discussed.

Nanostructured conducting polymer hydrogels for energy storage applications
Ye Shi, Lele Peng and Guihua Yu
Nanoscale, 2015, 7, 12796-12806. DOI: 10.1039/C5NR03403E

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.

Nanoscale, 2015,7, 12796-12806
DOI: 10.1039/C5NR03403E

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HOT article: Bridging the transport pathway of charge carriers in a Ta3N5 nanotube array photoanode for solar water splitting

Besides the wide field of photovoltaics research, additional technologies, such as the direct conversion of H2 via solar water splitting, are currently being researched. A recent article by Zhang et al. presents their findings on improved manufacturing routes for these cells.

For the time being, Ta3N5 is the material of choice as the band gap and structure are both well suited for light absorption. To form a large interfacial area for efficient light conversion within the cells, arrays of hollow nanorods are employed. As the authors describe in their article, earlier attempts of a one-step synthesis route, also evaluated by other researchers, led to weak adhesion of the brittle nanorod film on the substrate. Their new approach utilizes a two-step synthesis route: first, a nanorod layer of Ta2O5 is formed via anodization in a solution with a lower HF concentration compared to that employed by other groups. Next, this weakly adhering layer is removed by sonication and a second layer is formed. The formation of the second layer also employs a low reaction temperature to limit the reaction rate. Finally, this second nanorod layer is nitridated, forming Ta3N5 from the Ta2O5 layer.

(a) Schematic illustration of the synthetic process, (b) top-view SEM image and (c) cross-sectional SEM image of Ta3N5 NTAs.

The resulting layer was found to adhere well on the substrate surface and to exhibit only a few cracks. By further optimization of processing times and the additive material used during nitridation, a maximum current density of 11 mA/cm² at 1.6 V was demonstrated by the authors.

Bridging the transport pathway of charge carriers in a Ta3N5 nanotube array photoanode for solar water splitting
Peng Zhang, Tuo Wang, Jijie Zhang, Xiaoxia Chang and Jinlong Gong
Nanoscale, 2015, Advance Article. DOI: 10.1039/C5NR03013G

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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HOT article: Reversible control of pore size and surface chemistry of mesoporous silica through dynamic covalent chemistry: philicity mediated catalysis

Reversible engineering of the pore size and philicity of mesoporous SBA via dynamic covalent chemistry triggered by changes in pH.

Control of surface chemistry is important for utilisation of mesoporous silicas in many applications such as catalysis, drug delivery and separation sciences. Due to the mostly irreversible nature of covalent functionalisations and lack of rigidity in supramolecular approaches, in this study, dynamic covalent chemistry was used to reversibly alter the chemical coating on the surface of amine functional mesoporous silica SBA-15. This was achieved through the condensation reaction of the primary amine on SBA-15 with 4-decyloxybenzaldehyde (4-DB) to form an imine containing a hydrophobic decyl chain. This step both reduced the pore size and hydrophilicity of the pore surface, however, could be reversed by cleaving the imine at low pH in an ethanol/water mixture.

Dynamic control of the pore properties was demonstrated using the catalytic reduction of p-nitrophenol in aqueous conditions by gold nanoparticles, which were imbedded into both amine and imine/decyl SBA-15 materials. The more porous/hydrophilic amine-based material completely reduced p-nitrophenol to p-aminophenol after 30 minutes, whereas the more hydrophobic imine-based surface exhibited no catalytic activity. The authors suggest that this methodology could be used to generate a host of new covalently functionalised materials with tuneable surface properties.

Reversible control of pore size and surface chemistry of mesoporous silica through dynamic covalent chemistry: philicity mediated catalysis
Dheeraj Kumar Singh, B. V. V. S. Pavan Kumar and M. Eswaramoorthy
Nanoscale, 2015, Advance Article. DOI: 10.1039/C5NR02959G

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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A SERS biosensor for detecting metal ions in saliva

A gold nanohole array based surface-enhanced Raman scattering biosensor for detection of silver(I) and mercury(II) in human saliva

Researchers from West Virginia University have developed a method for detecting heavy metal ions in human saliva. Silver (I) (Ag) and mercury (II) (Hg) ions form part of dental fillings so it is important to have non-invasive analytical methods to monitor the toxicity of these metal ions should they be accidentally released into saliva.

Here, the authors exploited the strong electromagnetic coupling between gold (Au) nanostars and a Au nanohole array to detect Ag (I) and Hg (II) using surface enhanced Raman scattering (SERS). The Au nanostars and nanohole array were functionalised with mismatched pairs of single-stranded (ssDNA) probes that hybridise to form stable duplexes in the presence of the corresponding metal ions. Hybridisation allows the Au nanostars to come into close proximity with the Au nanohole array, which results in a large amplification of the SERS signal.

In this way, the authors were able to detect Ag (I) and Hg (II) ions in human saliva with limits of detection (LODs) of 0.17 nM and 2.3 pM for Ag (I) and Hg (II), respectively. This demonstrates the applicability of the SERS-based detection platform for on-site, non-invasive detection of analytes in body fluids.

A gold nanohole array based surface-enhanced Raman scattering biosensor for detection of silver(I) and mercury(II) in human saliva
Peng Zheng, Ming Li, Richard Jurevic, Scott K. Cushing, Yuxin Liu and Nianqiang Wu
Nanoscale, 2015, 7, 11005-11012. DOI: 10.1039/C5NR02142A

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: One-step direct synthesis of layered double hydroxide single-layer nanosheets

Single-layer nanosheets as layered double hydroxides (LDH) are of widespread interest both in research and application as they offer unique advantages for electronic devices. A recent communication in Nanoscale by Yu et al. reports on a new approach to simplify the overall manufacturing process.

Direct growth of single-layer nanosheets with the assistance of layer growth inhibitors

Common techniques yielding LDH nanosheets are based on exfoliation of synthesized multi-layer stacks. Due to the high binding forces in between the single layers, obtaining single layers requires aggressive chemicals and long processing times.

The approach presented by the authors comprises the utilization of formamide during the material growth process to suppress vertical growth for MgAl. Thus, only in-plane layer formation continues, leading to large single-layer LDH nanosheets. The authors demonstrate that only LDH single-layer nanosheets are obtained by means of TEM, XRD and AFM measurement techniques to compare this new method with the standard synthesis procedure.

The underlying mechanism is believed to be based on the weakened layer interaction by formamide. In addition, the same approach was also successfully applied to LDH nanosheets based on Co and Al.

One-step direct synthesis of layered double hydroxide single-layer nanosheets
Jingfang Yu, Benjamin R. Martin, Abraham Clearfield, Zhiping Luo and Luyi Sun
Nanoscale, 2015, 7, 9448-9451. DOI: 10.1039/C5NR01077B

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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HOT article: Design and assembly of supramolecular dual-modality nanoprobes

Self-assembled supramolecular nanoprobes

The synthesis of nanoprobes for application in more than one imaging technology is becoming more popular. So-called “bi-modal” probes can reduce limitations of single imaging modalities such as sensitivity or penetration depth. In this Hot article, the synthesis of two amphiphilic, dual-modality, optical imaging/MRI nanoprobes is reported. Each probe, containing both a fluorophore and a gadolinium complex, was specifically engineered using hydrophobic and hydrophilic components so they would self-assemble above the critical micelle concentration (CMC), which in turn would improve the MRI performance. The materials could offer potential advantages compared to conventional, unimolecular probes. Flow cytometry was used to confirm that both negatively charged assemblies were efficient at labelling KB-3-1 (human cervical cancer) cells at different labelling concentrations and incubation periods, through measurement of cell fluorescence. Cells viability was not compromised for each condition. The authors are now looking to further improve performance of self-assembled cell tracking agents through synthetic manipulation of construct size and surface charge.

Design and assembly of supramolecular dual-modality nanoprobes
Shuang Liu, Pengcheng Zhang, Sangeeta Ray Banerjee, Jiadi Xu, Martin G. Pomper and Honggang Cui
Nanoscale, 2015, 7, 9462-9466. DOI: 10.1039/C5NR01518A

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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Ready. Set. GO!

Graphene oxide (GO) is a versatile material with applications ranging from electronics to energy storage and biosensors. As a biosensing substrate, GO has many favorable attributes such as low cost, high signal-to-noise ratio, and the ability to efficiently quench fluorescence.

Scheme for the GO-aptamer based sensor for detection of thrombin.

This ability to quench fluorescence has inspired a range of biosensors using GO and Förster resonance energy transfer (FRET) for the sensitive detection of proteins using labelled probes, such as aptamers. However, the target proteins in such assays can non-specifically adsorb onto the surface of GO, thereby reducing the sensitivity.

To address this, Gao and co-workers implemented the use of polyethylene glycol (PEG) to prevent the non-specific adsorption of thrombin onto GO while implementing an aptamer-binding assay.  The authors report that the detection limit could be improved by optimizing the GO:PEG concentration. This manuscript helps to establish GO as promising tool in the biomedical and biotechnology fields.

Highly sensitive detection for proteins using graphene oxide-aptamer based sensors
Li Gao, Qin Li, Raoqi Li, Lirong Yan, Yang Zhou, Keping Chen and Haixia Shi
Nanoscale, 2015, Advance Article. DOI: 10.1039/C5NR01187F

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: Two-dimensional materials and their prospects in transistor electronics

Recently, the 50th anniversary of Moore’s law has been celebrated by the semiconductor industry. Although the current ITRS (International Technology Roadmap for Semiconductors) continues to propose “traditional” transistor materials such as Si and GaAs, attractive, two-dimensional alternatives have become visible on the horizon.

Schwierz et al. have recently published a Feature article in Nanoscale compiling the current knowledge on 2D materials. Their article focuses on the application of these as the channel material in field effect transistors.

According to the authors, two large trends can currently be observed: More Moore and More than Moore. The former utilizes well known semiconductors and improves performance by sophisticated manufacturing and scaling techniques. In contrast, the latter one employs compound semiconductors and novel alloys as 2D materials with a wide range of new properties.

Two-dimensional materials and their prospects in transistor electronics

The main material classes researched to date are explained further, covering X-anes, Fluoro-X-enes, TMDs (transition metal–chalcogen combinations), SMCs (semimetal–chalcogen combinations), MX-enes and (currently theoretical) group IV-IV and III-V 2D materials.

To assess the viability of the materials for applications within electronic circuits, Schwierz et al. also describe a wish list of ideal properties of next generation channel materials: bandgap, carrier mobility, heat conductivity, contact resistance and scale length. Based on experiences from established semiconductors, they also derive practical values needed for high performance FET.

The final part of the review examines the current status of the material classes. Notable performance records of well researched materials (e.g. 100 GHz graphene FET) as well as first demonstrators (e.g. first X-ane based FET) are given here. Finally, some arguments for a revival of silicon as a promising material for future applications are also given.

Two-dimensional materials and their prospects in transistor electronics
F. Schwierz, J. Pezoldt and R. Granzner
Nanoscale, 2015, 7, 8261-8283. DOI: 10.1039/C5NR01052G

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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HOT article: Photo-fluorescent and magnetic properties of iron oxide nanoparticles for biomedical applications

As cancer treatments evolve, focus has shifted to techniques and tools, which provide tumor-targeting capabilities and are uncoupled from common detrimental side effects.  The efficient delivery of new therapeutics has been a common area of interest, with studies focused on nanoparticle delivery systems being an eminent research area.

(a) TEM image of PS/Fe3O4 microspheres showing the amorphous coating entrapping multiple Fe3O4 nuclei. (b) TEM image of PAA/Fe3O4 and (c) cumulant size distribution of PAA/Fe3O4.

In this review article, Shi and co-workers draw attention to the properties of magnetite nanoparticles (Fe3O4), which can be utilised as customized therapeutics.  This review provides an overview of the synthesis of magnetite nanoparticles with an in-depth discussion related to their synthesis, functionalization and applications in a biological environment.

A highlight of this review includes an exploration into the recently discovered photo-luminescence properties of magnetite nanoparticles through studies of the electronic band structures to explain the emission mechanisms occurring.  The implications of thermal and magnetic induced hypothermia treatments utilizing these nanoparticles are also discussed relative to the patients being treated by such techniques.

From this review it can be determined that a new theragnostic platform has emerged with multi-functional capabilities both in terms of imaging and drug delivery.

Photo-fluorescent and magnetic properties of iron oxide nanoparticles for biomedical applications
Donglu Shi, M. E. Sadat, Andrew W. Dunn and David B. Mast
Nanoscale, 2015, 7, 8209-8232. DOI: 10.1039/C5NR01538C

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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Single-walled carbon nanotubes: Catching some rays

Precision printing and optical modeling of ultrathin SWCNT/C60 heterojunction solar cells

Inexpensive photovoltaics (PV) are an attractive avenue of research in the field of solar cells. In particular, semi-conducting single-walled carbon nanotubes  (s-SWCNTs) are a promising photo-absorbing material due to their strong near-infrared (near-IR) absorption and high carrier mobility. However, most current production methods for SWCNT PVs suffer from high surface roughness and lack nanometer-scale deposition precision, thereby hampering the reproducibility of ultrathin PV devices.

To this end, the authors have utilized ultrasonic spraying in order to tune the thickness of s-SWCNT layers with nanometer-scale precision. The researchers have used a combination of atomic force microscopy (AFM) and optical profilometry to show that their ultrasonic spraying method produces smooth, uniform films with an average roughness of about 5 nm.  The advantage of this low roughness enables fabrication of s-SWCT/C60 bilayer devices with significantly thinner C60 layers than previously reported.

The results reported by the authors help to advance the production of low-cost PV devices by improving the performance and scalability of ultra-thin SWCNT-based solar cells. Ultra-thin SWCNTs reported here could find potential use in other emerging technologies such as vertical field effect transistors and light-emitting diodes incorporating s-SWCNT injection layers.

Precision printing and optical modeling of ultrathin SWCNT/C60 heterojunction solar cells
Sarah L. Guillot, Kevin S. Mistry, Azure D. Avery, Jonah Richard, Anne-Marie Dowgiallo, Paul F. Ndione, Jao van de Lagemaat, Matthew O. Reese and Jeffrey L. Blackburn
Nanoscale, 2015, 7, 6556-6566. DOI: 10.1039/C5NR00205B

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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