Science

Sunday, March 18, 2012

Nanowire-based single-cell endoscopy

Nature Nanotechnology

191–196

(2012)

doi:10.1038/nnano.2011.226

Received: 30 August 2011
Accepted: 18 November 2011
Published online: 18 December 2011

One-dimensional smart probes based on nanowires and nanotubes that can safely penetrate the plasma membrane and enter biological cells are potentially useful in high-resolution and high-throughput gene and drug delivery, biosensing^6, 9 and single-cell electrophysiology^6, 10. However, using such probes for optical communication across the cellular membrane at the subwavelength level remains limited. Here, we show that a nanowire waveguide attached to the tapered tip of an optical fibre can guide visible light into intracellular compartments of a living mammalian cell, and can also detect optical signals from subcellular regions with high spatial resolution. Furthermore, we show that through light-activated mechanisms the endoscope can deliver payloads into cells with spatial and temporal specificity. Moreover, insertion of the endoscope into cells and illumination of the guided laser did not induce any significant toxicity in the cells.

High Aspect Subdiffraction-Limit Photolithography via a Silver Superlens

Hong Liu†, Bing Wang†, Lin Ke†, Jie Deng†, Chan Choy Chum†, Siew Lang Teo†, Lu Shen†, Stefan A. Maier*‡, and Jinghua Teng*†

^† Institute of Materials Research and Engineering,Agency for Science, Technology and Research (A*STAR), 3 Research Link, Singapore 117602

^‡ Department of Physics, Imperial College London, London SW7 2AZ, United Kingdom

Nano Lett., 2012, 12 (3), pp 1549–1554

DOI: 10.1021/nl2044088

Publication Date (Web): February 29, 2012

Photolithography is the technology of choice for mass patterning in semiconductor and data storage industries. Superlenses have demonstrated the capability of subdiffraction-limit imaging and been envisioned as a promising technology for potential nanophotolithography. Unfortunately, subdiffraction-limit patterns generated by current superlenses exhibited poor profile depth far below the requirement for photolithography. Here, we report an experimental demonstration of sub-50 nm resolution nanophotolithography via a smooth silver superlens with a high aspect profile of

45 nm, as well as grayscale subdiffraction-limit three-dimensional nanopatterning. Theoretical analysis and simulation show that smooth interfaces play a critical role. Superlens-based lithography can be integrated with conventional UV photolithography systems to endow them with the capability of nanophotolithography, which could provide a cost-effective approach for large scale and rapid nanopatterning.

Sunday, March 4, 2012

Highly Effective Separation of Semiconducting Carbon Nanotubes verified via Short-Channel Devices Fabricated Using Dip-Pen Nanolithography

Steve Park†, Hang Woo Lee‡, Huiliang Wang†, Selvapraba Selvarasah§, Mehmet R. Dokmeci§, Young Jun Park

, Seung Nam Cha

, Jong Min Kim

*, and Zhenan Bao‡*

^†Department of Materials Science & Engineering and^‡Department of Chemical Engineering, Stanford University, Stanford, California 94305, United States

^§ Department of Electrical & Computer Engineering,Northeastern University, Boston, Massachusetts 02115, United States

Frontier Research Lab, Samsung Advanced Institute of Technology, Korea

ACS Nano, Article ASAP

DOI: 10.1021/nn204875a

Publication Date (Web): February 21, 2012

We have verified a highly effective separation of semiconducting single-walled carbon nanotubes (sc-SWNTs) via statistical analysis of short-channel devices fabricated using multipen dip-pen nanolithography. Our SWNT separation technique utilizes a polymer (rr-P3DDT) that selectively interacts with and disperses sc-SWNTs. Our devices had channel lengths on the order of 300–500 nm, with an average of about 3 SWNTs that directly connected the source–drain electrodes. A total of 140 SWNTs were characterized, through which we have observed that all of the SWNTs exhibited semiconducting behavior with an average on/off current ratio of

10⁶. Additionally, we have characterized 50 SWNTs after the removal of rr-P3DDT, through which we have again observed semiconducting behavior for all of the SWNTs with similar electrical characteristics. The relatively low average on-conductance of 0.0796 μS was attributed to the distribution of small diameter SWNTs in our system and due to the non-ohmic Au contacts on SWNTs. The largely positive threshold voltages were shifted toward zero after vacuum annealing, indicating that the SWNTs were doped in air. To the best of our knowledge, this is the first time numerous SWNTs were electrically characterized using short-channel devices, through which all of the measured SWNTs were determined to be semiconducting. Hence, our semiconducting single-walled carbon nanotube sorting system holds a great deal of promise in bringing forth a variety of practical applications in SWNT electronics.

Harvesting Energy from Water Flow over Graphene?

Jun Yin, Zhuhua Zhang, Xuemei Li, Jianxin Zhou, and Wanlin Guo*

State Key Laboratory of Mechanics and Control of Mechanical Structures, Key Laboratory for Intelligent Nano Materials and Devices of the Ministry of Education, and Institute of Nanoscience, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

Nano Lett., Article ASAP

DOI: 10.1021/nl300636g

Publication Date (Web): March 1, 2012

It is reported excitingly in a previous letter (Nano Lett.2011, 11, 3123) that a small piece of graphene sheet about 30 × 16 μm² immersed in flowing water with 0.6 M hydrochloric acid can produce voltage

20 mV. Here we find that no measurable voltage can be induced by the flow over mono-, bi- and trilayered graphene samples of

1 × 1.5 cm² in size in the same solution once the electrodes on graphene are isolated from interacting with the solution, mainly because the H₃O⁺ cations in the water adsorb onto graphene by strong covalent bonds as revealed by our first-principles calculations. When both the graphene and its metal electrodes are exposed to the solution as in the previous work, water flow over the graphene-electrode system can induce voltages from a few to over a hundred millivolts. In this situation, the graphene mainly behaves as a load connecting between the electrodes. Therefore, the harvested energy is not from the immersed carbon nanomaterials themselves in ionic water flow but dominated by the exposed electrodes.

Absorption Enhancement in Ultrathin Crystalline Silicon Solar Cells with Antireflection and Light-Trapping Nanocone Gratings

Ken Xingze Wang†, Zongfu Yu‡, Victor Liu‡, Yi Cui§

, and Shanhui Fan*‡

^†Department of Applied Physics, ^‡Department of Electrical Engineering, and ^§Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States

Stanford Institute for Materials and Energy Sciences,SLAC National Accelerator Laboratory, Menlo Park, California 94205, United States

Nano Lett., Article ASAP

DOI: 10.1021/nl204550q

Publication Date (Web): February 22, 2012

Enhancing the light absorption in ultrathin-film silicon solar cells is important for improving efficiency and reducing cost. We introduce a double-sided grating design, where the front and back surfaces of the cell are separately optimized for antireflection and light trapping, respectively. The optimized structure yields a photocurrent of 34.6 mA/cm2 at an equivalent thickness of 2 μm, close to the Yablonovitch limit. This approach is applicable to various thicknesses and is robust against metallic loss in the back reflector.

Painting with Biomolecules at the Nanoscale: Biofunctionalization with Tunable Surface Densities

Robert Schlapak†, Jürgen Danzberger‡, Thomas Haselgrübler†, Peter Hinterdorfer†§, Friedrich Schäffler‡, and Stefan Howorka*†

^† Center for Advanced Bioanalysis GmbH, 4020 Linz, Austria

^‡Institute for Semiconductor and Solid State Physics,^§Institute for Biophysics, Johannes Kepler University, 4040 Linz, Austria

Department of Chemistry, Institute of Structural and Molecular Biology, University College London, London, England

Nano Lett., Article ASAP

DOI: 10.1021/nl2045414

Publication Date (Web): February 29, 2012

We present a generic and flexible method to nanopattern biomolecules on surfaces. Carbon-containing nanofeatures are written at variable diameter and spacing by a focused electron beam on a poly(ethylene glycol) (PEG)-coated glass substrate. Proteins physisorb to the nanofeatures with remarkably high contrast factors of more than 1000 compared to the surrounding PEG surfaces. The biological activity of model proteins can be retained as shown by decorating avidin spots with biotinylated DNA, thereby underscoring the universality of the nano-biofunctionalized platform for the binding of other biotinylated ligands. In addition, biomolecule densities can be tuned over several orders of magnitude within the same array, as demonstrated by painting a microscale image with nanoscale pixels. We expect that these unique advantages open up entirely new ways to design biophysical experiments, for instance, on cells that respond to the nanoscale densities of activating molecules.

Controlled Synthesis of 3D Multi-Compartmental Particles with Centrifuge-Based Microdroplet Formation from a Multi-Barrelled Capillary

Kazuki Maeda¹,

Hiroaki Onoe^1,2,

Masahiro Takinoue^1,†,

Shoji Takeuchi^1,2,*

Article first published online: 6 FEB 2012

DOI: 10.1002/adma.201102560

Controlled synthesis of micro multi-compartmental particles using a centrifuge droplet shooting device (CDSD) is reported. Sodium alginate solutions introduced in a multi-barreled capillary form droplets at the capillary orifice under ultrahigh gravity and gelify in a CaCl₂solution. The size, shape, and compartmentalization of the particles are controlled. Co-encapsulation of Jurkat cells and magnetic colloids into Janus particles is demonstrated. The Janus particles present sensitive reaction toward magnetic fields, while the viability of the encapsulated cells is 91%.