Science: August 2012

Sunday, August 26, 2012

3D Nanofabrication of Fluidic Components by Corner Lithograph

Erwin J. W. Berenschot¹,

Narges Burouni¹,

Bart Schurink²,

Joost W. van Honschoten¹,

Remco G. P. Sanders¹,

Roman Truckenmuller²,

Henri V. Jansen¹,

Miko C. Elwenspoek¹,

Aart A. van Apeldoorn²,

Niels R. Tas^1,*

Article first published online: 21 AUG 2012

DOI: 10.1002/smll.201201446

A reproducible wafer-scale method to obtain 3D nanostructures is investigated. This method, called corner lithography, explores the conformal deposition and the subsequent timed isotropic etching of a thin film in a 3D shaped silicon template. The technique leaves a residue of the thin film in sharp concave corners which can be used as structural material or as an inversion mask in subsequent steps. The potential of corner lithography is studied by fabrication of functional 3D microfluidic components, in particular i) novel tips containing nano-apertures at or near the apex for AFM-based liquid deposition devices, and ii) a novel particle or cell trapping device using an array of nanowire frames. The use of these arrays of nanowire cages for capturing single primary bovine chondrocytes by a droplet seeding method is successfully demonstrated, and changes in phenotype are observed over time, while retaining them in a well-defined pattern and 3D microenvironment in a flat array.

Reusable Nanostencils for Creating Multiple Biofunctional Molecular Nanopatterns on Polymer Substrate

Min Huang †, Betty C. Galarreta †, Alp Artar †, Ronen Adato †, Serap Aksu ‡, and Hatice Altug *†‡

^†Electrical and Computer Engineering and ^‡Materials Science and Engineering, Photonics Center, Boston University, Boston, Massachusetts 02215, United States

Nano Lett., Article ASAP

DOI: 10.1021/nl302266u

Publication Date (Web): July 27, 2012

In this paper, we demonstrate a novel method for high throughput patterning of bioprobes with nanoscale features on biocompatible polymer substrate. Our technique, based on nanostencil lithography, employs high resolution and robust masks integrated with array of reservoirs. We show that the smallest pattern size can reach down to 100 nm. We also show that different types of biomolecules can be patterned on the same substrate simultaneously. Furthermore, the stencil can be reused multiple times to generate a series of identical patterns at low cost. Finally, we demonstrate that biomolecules can be covalently patterned on the surface while retaining their biofunctionalities. By offering the flexibility on the nanopattern design and enabling the reusability of the stencil, our approach significantly simplifies the bionanopatterning process and therefore could have profound implications in diverse biological and medical applications.

Shedding Light on Helical Microtubules: Real-Time Observations of Microtubule Self-Assembly by Light Microscopy

Hee-Young Lee , Hyuntaek Oh , Jae-Ho Lee , andSrinivasa R. Raghavan *

Department of Chemical and Biomolecular Engineering,University of Maryland, College Park, Maryland 20742-2111, United States

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja3031856

Publication Date (Web): August 21, 2012

Helical tubules are a fascinating and an intriguing class of self-assemblies. They occur frequently in biology and are believed to be intermediates in formation of gallstones. The pathway by which amphiphiles transform from an initial state of vesicles or micelles into such tubules has puzzled soft matter physicists, and it has raised important questions about the interplay between molecular chirality and self-assembly. Here, for the first time, we demonstrate direct, real-time observations by light microscopy of the pathway to helical microtubules from an initial solution of nanoscale vesicles. The tubules are formed in aqueous mixtures of the single-tailed diacetylenic surfactant, 10,12-pentacosadiynoic acid (PCDA), and a short-chain alcohol. The stepwise process involves nucleation of thin helical microribbons from the vesicle solution. These ribbons then thicken, rearrange, and fold into closed tubules. Subsequently, most tubules further rearrange into plate-like structures, and once again, we are able to visualize this process in real time. A notable aspect of the above system is that the precursors are achiral; yet, the tubules are formed from helical ribbons. Our study provides new insights into tubule formation that will be valuable in clarifying and refining theoretical models for these fascinating structures.

Transparent and Flexible Graphene Charge-Trap Memory

Sung Min Kim †, Emil B. Song †, Sejoon Lee †‡*,Jinfeng Zhu †, David H. Seo §, Matthew Mecklenburg

, Sunae Seo ¶, and Kang L. Wang †

^† Electrical Engineering Department, University of California, Los Angeles, California 90095, United States

^‡ Quantum-Functional Semiconductor Research Center,Dongguk University-Seoul, Seoul 100-715, Korea

^§ Samsung Advanced Institute of Technology, Yongin, 446-711, Korea

Microelectronics Technology Department, The Aerospace Corporation, Los Angeles, California 90009, United States

^¶ Department of Physics, Sejong University, Seoul 143-747, Korea

ACS Nano, Article ASAP

DOI: 10.1021/nn302193q

Publication Date (Web): August 13, 2012

A transparent and flexible graphene charge-trap memory (GCTM) composed of a single-layer graphene channel and a 3-dimensional gate stack was fabricated on a polyethylene naphtalate substrate below eutectic temperatures (

110 °C). The GCTM exhibits memory functionality of

8.6 V memory window and 30% data retention per 10 years, while maintaining

80% of transparency in the visible wavelength. Under both tensile and compressive stress, the GCTM shows minimal effect on the program/erase states and the on-state current. This can be utilized for transparent and flexible electronics that require integration of logic, memory, and display on a single substrate with high transparency and endurance under flex.

Sunday, August 19, 2012

Water-Driven Micromotors

Wei Gao , Allen Pei , and Joseph Wang *

Department of Nanoengineering, University of California, San Diego, La Jolla, California 92093, United States

ACS Nano, Article ASAP

DOI: 10.1021/nn303309z

Publication Date (Web): August 14, 2012

*Address correspondence to josephwang@ucsd.edu.

We demonstrate the first example of a water-driven bubble-propelled micromotor that eliminates the requirement for the common hydrogen peroxide fuel. The new water-driven Janus micromotor is composed of a partially coated Al–Ga binary alloy microsphere preparedvia microcontact mixing of aluminum microparticles and liquid gallium. The ejection of hydrogen bubbles from the exposed Al–Ga alloy hemisphere side, upon its contact with water, provides a powerful directional propulsion thrust. Such spontaneous generation of hydrogen bubbles reflects the rapid reaction between the aluminum alloy and water. The resulting water-driven spherical motors can move at remarkable speeds of 3 mm s^–1 (i.e., 150 body length s^–1), while exerting large forces exceeding 500 pN. Factors influencing the efficiency of the aluminum–water reaction and the resulting propulsion behavior and motor lifetime, including the ionic strength and environmental pH, are investigated. The resulting water-propelled Al–Ga/Ti motors move efficiently in different biological media (e.g., human serum) and hold considerable promise for diverse biomedical or industrial applications.

Quantitative Thermopower Profiling across a Silicon p–n Junction with Nanometer Resolution

Byeonghee Lee †, Kyeongtae Kim ‡, Seungkoo Lee §,Jong Hoon Kim §, Dae Soon Lim §, Ohmyoung Kwon*‡, and Joon Sik Lee †

^† School of Mechanical and Aerospace Engineering,Seoul National University, Seoul 151-744, Korea

^‡ Department of Mechanical Engineering, Korea University, Seoul 136-701, Korea

^§ Department of Materials Science and Engineering,Korea University, Seoul 136-701, Korea

Nano Lett., Article ASAP

DOI: 10.1021/nl301359c

Publication Date (Web): August 13, 2012

*E-mail: omkwon@korea.ac.kr.

Thermopower (S) profiling with nanometer resolution is essential for enhancing the thermoelectric figure of merit, ZT, through the nanostructuring of materials and for carrier density profiling in nanoelectronic devices. However, only qualitative and impractical methods or techniques with low resolutions have been reported thus far. Herein, we develop a quantitative S profiling method with nanometer resolution, scanning Seebeck microscopy (SSM), and batch-fabricate diamond thermocouple probes to apply SSM to silicon, which requires a contact stress higher than 10 GPa for stable electrical contact. The distance between the positive and negative peaks of the S profile across the silicon p–n junction measured by SSM is 4 nm, while the theoretical distance is 2 nm. Because of its extremely high spatial resolution, quantitative measurement, and ease of use, SSM could be a crucial tool not only for the characterization of nano-thermoelectric materials and nanoelectronic devices but also for the analysis of nanoscale thermal and electrical phenomena in general.

Writing on Superhydrophobic Nanopost Arrays: Topographic Design for Bottom-up Assembly

Benjamin D. Hatton * and Joanna Aizenberg

School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States

Nano Lett., Article ASAP

DOI: 10.1021/nl301775x

Publication Date (Web): August 9, 2012

A well-known property of superhydrophobic surfaces, such as an array of hydrophobic nanoposts, is to allow only limited surface contact of a liquid to the tips of the nanoposts. Herein we demonstrate that material deposition from solution, whether solid precipitation, surface adsorption or colloidal adhesion in static system, or dynamic “writing”, can be limited to these specific areas of the surface when in this nonwetting state. As an example of solid precipitation, we show that nucleation of CaCO₃ results in the growth of small, uniform, amorphous deposits (which can merge and recrystallize) instead of disordered, large crystals due to the abundance of identical, small heterogeneous nucleation sites. The growth of amorphous CaCO₃ can be used to trap molecules from solution, as a potential application for controlled drug release. To demonstrate the localized surface adsorption, we show that chemical functionalization of the post tips can make them “sticky” for specific attachment of species (such as colloidal particles) from solution. The electrostatic charge and relative size ratio of the particle/post diameters control the attachment of particles to the post tips with great specificity. Dynamic conditions have also been shown for writing using droplets translated across the nonwetting surface at controlled speeds during deposition. These methods offer unprecedented control over the heterogeneous nucleation and localized growth of crystals from solution and avoid nonspecific adsorption. There is selective control of colloidal or molecular attachment to the nanopost tips, whereby the contact area, time of contact, and tip surface chemistry for reaction are all independently tunable parameters.

Parallel Dip-Pen Nanolithography using Spore- and Colloid-Terminated Cantilevers

Marcus A. Kramer,

Albena Ivanisevic^*

Article first published online: 17 AUG 2012

DOI: 10.1002/smll.201200378

Parallel dip-pen nanolithography is used to generate micrometer-scale patterns with protein and lipid dyes on both a glass surface and spore layer. Spore- and colloid-based tips are used to facilitate parallel patterning.

Flexible Vertical Light Emitting Diodes

Rak-Hwan Kim⁴,

Stanley Kim⁴,

Young Min Song⁴,

Hyejin Jeong⁵,

Tae-il Kim⁴,

Jongho Lee³,

Xuling Li²,

Kent D. Choquette²,

John A. Rogers^1,*

Article first published online: 13 AUG 2012

DOI: 10.1002/smll.201201195

Strategies are presented to achieve ultrathin light-emitting diodes using the technique of epitaxial liftoff in ways that protect the materials from the etchants used for release and tether the devices to the underlying wafer for subsequent transfer printing onto substrates of interest. The results lead to an advanced interconnection scheme and vertical device layout that facilitate electrical contacts and system integration on flexible substrates.

Mechanical Chameleon

Science 17 August 2012:
Vol. 337 no. 6096 p. 775
DOI: 10.1126/science.337.6096.775-a

A wide range of animals can adapt their color patterns as a means of camouflage or otherwise changing their appearance. This is accomplished through changes in coloration, contrast, patterning, or shape. Morin et al. (p. 828) show at a basic level that some of these features can be added as microfluidic layers attached to mobile, flexible, soft machines. By pumping different fluids through the channels, the robots were able to change their coloration or overall contrast and could thus blend into the background of the surface they were lying upon. Conversely, by pumping through fluids of different temperature, the infrared profile of the robot could be changed without changing its visible coloration.

Sunday, August 12, 2012

Nanorods standing at attention!

Thibaut Thai^1,2,

Dr. Yuanhui Zheng^1,2,

Soon Hock Ng^1,2,

Dr. Stephen Mudie³,

Dr. Matteo Altissimo²,

Prof. Udo Bach^1,2,*

Article first published online: 29 JUL 2012

DOI: 10.1002/anie.201204609

A self-assembly technique based on convective and capillary forces was used for the direct fabrication of standing arrays of gold nanorods on lithographically predefined areas (see picture). The hexagonal close-packed structure of gold nanorods creates an ideal substrate for surface-enhanced Raman spectroscopy.

High-Resolution, Large-Area, Serial Fabrication of 3D Polymer Brush Structures by Parallel Dip-Pen Nanodisplacement Lithography

Xuechang Zhou^1,2,

Zhilu Liu^1,2,

Zhuang Xie^1,2,

Xuqing Liu^1,2,

Zijian Zheng^1,2,*

Article first published online: 8 AUG 2012

DOI: 10.1002/smll.201201544

Parallel dip-pen nanodisplacement lithography (p-DNL) is used for high resolution, serial fabrication of 3D structures of polymer brushes over millimeter length scales. With p-DNL, 2D initiator templates consisting of arrays of nanolines and nanodots with rationally designed lateral spacings are fabricated in parallel via a locally tip-induced nanodisplacement process, from which highly defined 3D polymer structures are grown via surface-initiated atom transfer radical polymerization.

Hybridizing Energy Conversion and Storage in a Mechanical-to-Electrochemical Process for Self-Charging Power Cell

Xinyu Xue †, Sihong Wang †, Wenxi Guo †, Yan Zhang†, and Zhong Lin Wang *†‡

^† School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0245, United States

^‡ Beijing Institute of Nanoenergy and Nanosystems,Chinese Academy of Sciences, Beijing, China

Nano Lett., Article ASAP

DOI: 10.1021/nl302879t

Publication Date (Web): August 9, 2012

Energy generation and energy storage are two distinct processes that are usually accomplished using two separated units designed on the basis of different physical principles, such as piezoelectric nanogenerator and Li-ion battery; the former converts mechanical energy into electricity, and the latter stores electric energy as chemical energy. Here, we introduce a fundamental mechanism that directly hybridizes the two processes into one, in which the mechanical energy is directly converted and simultaneously stored as chemical energy without going through the intermediate step of first converting into electricity. By replacing the polyethylene (PE) separator as for conventional Li battery with a piezoelectric poly(vinylidene fluoride) (PVDF) film, the piezoelectric potential from the PVDF film as created by mechanical straining acts as a charge pump to drive Li ions to migrate from the cathode to the anode accompanying charging reactions at electrodes. This new approach can be applied to fabricating a self-charging power cell (SCPC) for sustainable driving micro/nanosystems and personal electronics.

Programmable Release of Multiple Protein Drugs from Aptamer-Functionalized Hydrogels via Nucleic Acid Hybridization

Mark R. Battig , Boonchoy Soontornworajit , andYong Wang *

Department of Chemical, Materials, and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut 06269, United States

J. Am. Chem. Soc., 2012, 134 (30), pp 12410–12413

DOI: 10.1021/ja305238a

Publication Date (Web): July 23, 2012

Polymeric delivery systems have been extensively studied to achieve localized and controlled release of protein drugs. However, it is still challenging to control the release of multiple protein drugs in distinct stages according to the progress of disease or treatment. This study successfully demonstrates that multiple protein drugs can be released from aptamer-functionalized hydrogels with adjustable release rates at predetermined time points using complementary sequences (CSs) as biomolecular triggers. Because both aptamer–protein interactions and aptamer–CS hybridization are sequence-specific, aptamer-functionalized hydrogels constitute a promising polymeric delivery system for the programmable release of multiple protein drugs to treat complex human diseases.

Photodegradable Macromers and Hydrogels for Live Cell Encapsulation and Release

Donald R. Griffin and Andrea M. Kasko *

Department of Bioengineering, University of California, Los Angeles, 410 Westwood Plaza, 5121 Eng V, Los Angeles, California 90095, United States

J. Am. Chem. Soc., 2012, 134 (31), pp 13103–13107

DOI: 10.1021/ja305280w

Publication Date (Web): July 5, 2012

Hydrogel scaffolds are commonly used as 3D carriers for cells because their properties can be tailored to match natural extracellular matrix. Hydrogels may be used in tissue engineering and regenerative medicine to deliver therapeutic cells to injured or diseased tissue through controlled degradation. Hydrolysis and enzymolysis are the two most common mechanisms employed for hydrogel degradation, but neither allows sequential or staged release of cells. In contrast, photodegradation allows external real-time spatial and temporal control over hydrogel degradation, and allows for staged and sequential release of cells. We synthesized and characterized a series of macromers incorporating photodegradbale ortho-nitrobenzyl (o-NB) groups in the macromer backbone. We formed hydrogels from these macromers via redox polymerization and quantified the apparent rate constants of degradation (k_app) of each via photorheology at 370 nm, 10 mW/cm². Decreasing the number of aryl ethers on the o-NB group increases k_app, and changing the functionality from primary to seconday at the benzylic site dramatically increases k_app. Human mesenchymal stem cells (hMSCs) survive encapsulation in the hydrogels (90% viability postencapsulation). By exploiting the differences in reactivity of two different o-NB linkers, we quantitatively demonstrate the biased release of one stem cell population (green-fluoroescent protein expressing hMSCs) over another (red-fluorescent protein expressing hMSCs).

Monday, August 6, 2012

CdS–Polymer Nanocomposites and Light-Emitting Fibers by In Situ Electron-Beam Synthesis and Lithography

Luana Persano^1,2,*,
Andrea Camposeo^1,2,
Francesca Di Benedetto¹,
Ripalta Stabile¹,
Anna M. Laera⁴,
Emanuela Piscopiello⁴,
Leander Tapfer⁴,
Dario Pisignano^1,2,3

Article first published online: 26 JUL 2012

DOI: 10.1002/adma.201202440

A straightforward, electron-beam induced synthesis and patterning approach to the in situ generation of CdS nanocrystals in nanocomposite films and light-emitting electrospun nanofibers is used. Smartly combining room-temperature nanoimprinting, electrospinning, and electron-beam decomposition of nanocrystal precursors and subsequent nucleation of nanoparticles in a polymer matrix allows exploitation of the most favorable flow conditions of organics to produce various nanocomposite nanostructures.