This material is based upon work supported by a start-up fund at the University of Minnesota, Twin Cities and an NSF CAREER Award (CMMI-1454293). Parts of this work were carried out in the Characterization Facility at the University of Minnesota, a member of the NSF-funded Materials Research Facilities Network (via the MRSEC program. Portions of this work were conducted in the Minnesota Nano Center, which is supported by the National Science Foundation through the National Nano Coordinated Infrastructure Network (NNCI) under Award Number ECCS-1542202. C. D. acknowledges support from the 3M Science and Technology Fellowship.

CAUTION: Several of the chemicals used in these syntheses are toxic and may cause irritation and severe organ damage when touched or inhaled. Please use appropriate safety equipment and wear personal protective equipment when handling the chemicals.
1. Preparation of Aluminum Oxide and Chromium Protection Layers on a Copper Sacrificial Layer
<ol>
	<li>Using an electron-beam evaporator, deposit 10 nm thick chromium (Cr) and 300 nm thick copper (Cu) layers (sacrificial layer) on the silicon (Si) substrate (Figure 2a).</li>
	<li>Spin-coat a photoresist (PR)-1 at 2500 rpm followed by baking at 115 &#176;C for 60 s.</li>
	<li>Expose the designed 2D net areas to ultraviolet (UV) light on a contact mask aligner for 15 s and develop for 60 s in developer-1 solution. Rinse the sample with deionized (DI) water and blow-dry with an air gun.</li>
	<li>Deposit 10 nm thick Cr layer and lift-off of the remaining PR-1in acetone. Rinse the sample with DI water and blow-dry with an air gun (Figure 2b).</li>
	<li>To pattern 2D nets with six square Al2O3/Cr protection layers on the 2D net, spin-coat a PR-1 at 2500 rpm followed by baking at 115 &#176;C for 60 s.</li>
	<li>Expose the designed six square protection layers to UV light on a contact mask aligner for 15 s and develop for 60 s in developer-1 solution. Rinse the sample with DI water and blow-dry with an air gun.</li>
	<li>Deposit a 100 nm thick Al2O3 layer and 10 nm thick Cr layer. Remove remaining PR-1in acetone. Rinse the sample with DI water and blow-dry with an air gun (Figure 2c).</li>
</ol>
2. Preparation of Graphene and Graphene Oxide Membranes
Note: In this study, two types of graphene-based materials are used: (i) chemical vapor deposition (CVD) grown graphene and (ii) graphene oxide (GO).
<ol>
	<li>Preparation of multilayer CVD graphene membranes 
	Note: To obtain multilayer graphene membranes, single-layer graphene is transferred three separate times using multiple polymethyl methacrylate (PMMA) coating/removal steps.
	<ol>
		<li>Starting with a ~15 mm square piece of graphene adhered on Cu foil, spin-coat a thin PMMA layer at 3000 rpm on the surface of the graphene. Bake at 180 &#176;C for 10 min.</li>
		<li>Place the PMMA/graphene/Cu foil-layered sheet floating Cu-side down in Cu etchant for 24 h to etch away the Cu foil.</li>
		<li>After the Cu foil is completely dissolved (leaving PMMA/graphene), transfer the floating PMMA-coated graphene onto the surface of a pool of DI water using a microscope slide glass to remove any Cu etchant residue. Repeat the transfer of the PMMA-coated graphene onto new DI water pools several times to adequately rinse.</li>
		<li>Transfer the floating PMMA-coated graphene onto another piece of graphene adhered on Cu foil (graphene/Cu) to obtain a bi-layer graphene membrane (forming a PMMA/graphene/graphene/Cu foil structure).</li>
		<li>Thermally treat the double-layer graphene on the Cu foil on a hot plate at 100 &#176;C for 10 min.</li>
		<li>Remove the PMMA on top of the double-layer graphene on the Cu foil in an acetone bath (leaving a graphene/graphene/Cu foil layer stack), followed by transferring to DI water.</li>
		<li>Repeat the graphene transfer (2.1.1 - 2.1.5) one more time to get three stacked layers of graphene membranes. When step 2.1.4 is reached during the repeat process, instead of transferring the new PMMA-coated graphene sheet onto another piece of graphene/Cu, transfer the new PMMA-coated graphene onto the previously fabricated graphene double-layer from step 2.1.6 to form a PMMA/graphene/graphene/graphene/Cu foil layer combination. Then, repeat step 2.1.5 without modification.</li>
		<li>Place the PMMA/graphene/graphene/graphene/Cu foil-layered sheet floating Cu-side down in Cu etchant for 24 h to etch away the Cu foil.</li>
		<li>Transfer the PMMA-coated three-layers of graphene membranes (PMMA/graphene/graphene/graphene) onto the pre-fabricated Al2O3/Cr protection layers from section 1.</li>
		<li>After transfer of the graphene, remove the PMMA with acetone. Then, dip the sample in DI water and dry in air.</li>
		<li>Thermally treat the multi-layer graphene on the substrate on a hot plate at 100 &#176;C for 1 h.</li>
		<li>Spin-coat PR-1 at 2500 rpm and bake at 115 &#730;C for 60 s.</li>
		<li>UV expose the regions of PR-1 directly above the square protection layer areas using a contact mask aligner for 15 s and develop for 60 s in developer-1 solution.</li>
		<li>Remove the newly uncovered, unwanted graphene areas via an oxygen plasma treatment for 15 s.</li>
		<li>Remove the leftover PR-1 in acetone.</li>
		<li>Rinse the sample with DI water and dry in air (Figure 2d).</li>
	</ol>
	</li>
	<li>Preparation of graphene oxide membranes 
	Note: Traditional photolithography followed by a lift-off process via flood exposure is used to pattern the GO membranes.
	<ol>
		<li>Spin-coat PR-2 at 1700 rpm for 60 s on top of the previously fabricated Al2O3/Cr protection layers to obtain a 10 &#181;m thick layer. Bake the PR-2 at 115 &#176;C for 60 s and then wait for 3 h.</li>
		<li>With the same mask used for patterning the Al2O3/Cr protection layer, UV expose the sample on a contact mask aligner for 80 s and develop for 90 s in developer-2 solution. Rinse the sample with DI water and blow-dry with an air gun.</li>
		<li>Perform a UV flood exposure of the entire sample without a mask for 80 s.</li>
		<li>Spin-coat the prepared GO and water mixture (15 mg of GO powder in 15 mL of DI water) on the sample at 1000 rpm for 60 s. Perform the spin-coating a total of 3 times.</li>
		<li>Dip the sample in developer-2 solution to allow lift-off of unwanted GO.</li>
		<li>Rinse the sample with DI water and carefully blow-dry the sample with an air gun.</li>
		<li>Thermally treat the sample on a hot plate at 100 &#176;C for 1 h (Figure 2h).</li>
	</ol>
	</li>
</ol>
3. Metal Surface Patterning on Graphene-Based Membranes
Note: A common photolithography process was conducted to achieve the surface patterning using a UV contact mask aligner and electron-beam evaporator (see 1.2 - 1.4).
<ol>
	<li>Create 20 nm thick titanium (Ti) patterns on top of the patterned graphene-based membranes.</li>
	<li>Thermally treat the sample on a hot plate at 100 &#176;C for 1 h (Figure 2e for graphene and Figure 2i for GO).</li>
</ol>
4. Fabrication of Polymer Frames and Hinges
<ol>
	<li>On top of graphene-based membranes with Ti surface patterns, spin-coat PR-3 at 2500 rpm for 60 s to form a 5 &#181;m thick layer and bake at 90 &#176;C for 2 min.</li>
	<li>UV expose the samples for 20 s, bake at 90 &#176;C for 3 min, and develop for 90 s in developer-3 solution.</li>
	<li>Rinse the sample with DI water and isopropyl alcohol (IPA) and carefully blow-dry the sample with an air gun.</li>
	<li>Post-bake the samples at 200 &#176;C for 15 min to enhance the mechanical stiffness of the (PR-3) frames (Figure 2f for graphene and Figure 2j for GO).</li>
	<li>To make the hinge pattern, spin-coat PR-2 at 1000 rpm for 60 s to form a 10 &#181;m thick film on top of the prefabricated substrate. Bake at 115 &#730;C for 60 s and wait for 3 h.</li>
	<li>UV expose the sample on a contact mask aligner for 80 s and develop for 90 s in developer-2 solution.</li>
	<li>Rinse the sample with DI water and carefully blow-dry the sample with an air gun (Figure 2g for graphene and Figure 2k for GO).</li>
</ol>
5. Self-Folding in DI Water
Note: When the PR-2 hinges are melted (or reflow), a surface tension force is generated; hence, the 2D structures transform into 3D structures (a self-folding process).
<ol>
	<li>To release the 2D structure, dissolve the Cu sacrificial layer under the 2D nets in a Cu etchant (Figure 2l).</li>
	<li>Carefully transfer the released structure into a DI water bath by using a pipet and rinse a few times to remove the residual Cu etchant.</li>
	<li>Place the 2D structure in DI water heated above the melting point of the polymer (PR-2) hinges (Figure 2m).</li>
	<li>Monitor the self-folding in real-time via optical microscopy and remove from the heat source on successful assembly into closed cubes.</li>
</ol>
6. Removal of the Protection Layers
<ol>
	<li>After self-folding, remove the Al2O3/Cr protection layers with Cr etchant (Figure 2n).</li>
	<li>Gently transfer the cubes into a DI water bath and carefully rinse.</li>
</ol>

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The authors have nothing to disclose.

For the cubes fabricated with CVD graphene, because each face of a given cube is designed with an outer frame surrounding a ~160 &#215; 160 &#181;m2 area of free-standing graphene, a single sheet of monolayer graphene does not have the necessary strength to permit parallel processing of the cubes. For this reason, graphene membranes consisting of three layers of CVD graphene monolayer sheets are produced via three separate graphene transfers using multiple PMMA coating/removal steps. On the other hand...

Two-dimensional (2D) graphene sheets possess extraordinary optical, electronic, and mechanical properties, making them model systems for the observation of novel quantum phenomena for next-generation electronic, optoelectronic, electrochemical, electromechanical, and biomedical applications1,2,3,4,5,6. Apart from the as-produced 2D layered structure of graphene, recently, various modification approaches have been investigated to observe new functionalities of graphene and seek new application opportunities. For example, modulating (or tuning) its physical properties (i.e.,&#160;doping level and/or band gap) by tailoring the shapes or patterning of the 2D structure to a one-dimensional (1D) or zero-dimensional (0D) structure (e.g., graphene nanoribbon or graphene quantum dots) has been studied to obtain new physical phenomena including quantum confinement effects, localized plasmonic modes, localized electron distribution, and spin-polarized edge states7,8,9,10,11,12. In addition, varying the texture of 2D graphene by crumpling (often called kirigami), delamination, buckling, twisting, or stacking of multiple layers, or changing the graphene surface shape by transferring 2D graphene on top of a 3D feature (substrate) has been shown to change the graphene&#39;s wettability, mechanical characteristics, and optical properties13,14.
Beyond changing the surface morphology and layered structure of 2D graphene, assembly of 2D graphene into functionalized, well-defined, three-dimensional (3D) polyhedrons has been of great interest recently in the graphene community to obtain new physical and chemical phenomena15. In theory, the elastic, electrostatic, and van der Waals energies of 2D graphene-based structures can be leveraged to transform the 2D graphene into various 3D graphene-origami configurations16,17. Based on this concept, theoretical modeling studies have investigated 3D graphene structure designs, formed from nanoscale 2D graphene membranes, with possible uses in drug delivery and general molecular storage16,17.&#160;Yet, the experimental progress of this approach is still far from realizing these applications. On the other hand, a number of chemical synthetic methods have been developed to achieve 3D structures via template-assisted assembly, flow-directed assembly, leavening assembly, and conformal growth methods18,19,20,21,22. However, these methods are currently limited in that they cannot produce a 3D, hollow, enclosed structure without losing the intrinsic properties of the graphene sheets.
Here, a strategy for building 3D, hollow, graphene-based microcubes (overall dimension of ~200 &#181;m) by using origami-like self-folding is outlined; overcoming the foremost challenges in the construction of free-standing, hollow, 3D, polyhedral, graphene-based materials. In origami-like, hands-free self-folding techniques, 2D lithographically patterned planar features (i.e.,&#160;graphene-based membranes) are connected with hinges (i.e.,&#160;thermal-sensitive polymer, photoresist) at various joints, thereby forming 2D nets which fold up when the hinges are heated to melting temperature23,24,25,26. The graphene-based cubes are realized with window membrane components composed of a few layers of chemical vapor deposition (CVD) grown graphene or graphene oxide (GO) membranes; both with the use of polymer frames and hinges. The fabrication of the 3D graphene-based cubes involves: (i) preparation of protection layers, (ii) graphene-membrane transfer and patterning, (iii) metal surface patterning on graphene-membranes, (iv) frame and hinges patterning and deposition, (v) self-folding, and (vi) removal of the protection layers (Figure 1). This article focuses mostly on the self-folding aspects of the 3D graphene-based cubes fabrication. Details on physical and optical properties of the 3D graphene-based cubes can be found in our other recent publications27,28.

<table><tbody><tr><td>Acetone</td><td>Fisher Chemical</td><td>A18P-4</td><td>N/A</td></tr><tr><td>Aluminium oxide</td><td>Kurt J. Lesker Company</td><td>EVMALO-1-2.5</td><td>99.99% Pure</td></tr><tr><td>APS Copper Etchant 100</td><td>Transene Company, Inc.</td><td>N/A</td><td>N/A</td></tr><tr><td>Camera (for 3D image)</td><td>Nikon</td><td>D5100</td><td>1080p Full HD, Effective pixels: 16.2 million, Sensorsize: 23.6 mm x 15.6 mm</td></tr><tr><td>CE-5 M Chromium Mask Etchant</td><td>Transene Company, Inc.</td><td>N/A</td><td>N/A</td></tr><tr><td>Chemical deposition growth (CVD) system</td><td>Customized</td><td>N/A</td><td>Lindberg/Blue Tube Furnace</td></tr><tr><td>Chromium</td><td>Kurt J. Lesker Company</td><td>EVMCR35J</td><td>99.95% pure</td></tr><tr><td>Chromium Etchant 473</td><td>Transene Company, Inc.</td><td>N/A</td><td>N/A</td></tr><tr><td>Copper</td><td>Kurt J. Lesker Company</td><td>EVMCU40QXQJ</td><td>99.99% pure</td></tr><tr><td>Developer-1 (MF319 developer)</td><td>Microposit</td><td>10018042</td><td>N/A</td></tr><tr><td>Developer-2 (AZ developer)</td><td>Merck performance Materials Corp.</td><td>1005422496</td><td>N/A</td></tr><tr><td>Developer-3 (SU-8 developer)</td><td>MicroChem</td><td>NC9901158</td><td>N/A</td></tr><tr><td>Digital Hot Plate</td><td>Thermo Scientific</td><td>HP131725</td><td>Super-Nuvoa series, maximum temperature: 370 &amp;deg;C</td></tr><tr><td>E-Beam Evaporator System</td><td>Rocky Mountain Vacuum Tech.</td><td>N/A</td><td>RME-2000</td></tr><tr><td>Graphene oxide</td><td>Goographene</td><td>N/A</td><td>Purity: ~ 99%; Single layer ratio: ~99%;&amp;nbsp; 0.7-1.2 nm in thickness.</td></tr><tr><td>Isopropyl Alcohol</td><td>Fisher Chemical</td><td>A416-4</td><td>N/A</td></tr><tr><td>Mask Aligner</td><td>Midas</td><td>MDA-400LJ</td><td>N/A</td></tr><tr><td>Microscope</td><td>Omax</td><td>NJF-120A</td><td>N/A</td></tr><tr><td>multiple polymethyl methacrylate (PMMA)</td><td>MicroChem</td><td>950 PMMA A9</td><td>N/A</td></tr><tr><td>Oxygen plasma&amp;nbsp;</td><td>Technics Inc.</td><td>SERIES 800</td><td>Microscale reactive ion etching (RIE)</td></tr><tr><td>Photoresist-1 (S1813 Photoresist)</td><td>Microposit</td><td>10018348</td><td>N/A</td></tr><tr><td>Photoresist-2 (SPR220 Photoresist)</td><td>MicroChem</td><td>SPR00220-7G</td><td>N/A</td></tr><tr><td>Photoresist-3 (SU-8 Photoresist)</td><td>MicroChem</td><td>SU-8-2010</td><td>N/A</td></tr><tr><td>Profilometer</td><td>Tencor Instruments</td><td>N/A</td><td>Alpha-Step 200</td></tr><tr><td>Raman</td><td>WITec Instruments Corp.</td><td>Alpha300R</td><td>Confocal Raman Microscope</td></tr><tr><td>Silicon Wafer</td><td>Siltronic AG</td><td>N/A</td><td>100mm diameter, N-type, one-side polish, resitivity: 560-840 &amp;Omega;&amp;bull;cm</td></tr><tr><td>Spinner</td><td>Best Tools</td><td>S0114031123</td><td>SMART COATER 100</td></tr><tr><td>Titanium</td><td>Kurt J. Lesker Company</td><td>EVMTI45QXQA</td><td>99.99% Pure</td></tr><tr><td>Ultrasonic Cleaner</td><td>Crest Ultrasonics</td><td>N/A</td><td>Powersonic series</td></tr></tbody></table>

fabrication of three-dimensional graphene-based polyhedrons via origami-like self-folding

The assembly of two-dimensional (2D) graphene into three-dimensional (3D) polyhedral structures while preserving the graphene's excellent inherent properties has been of great interest for the development of novel device applications. Here, fabrication of 3D, microscale, hollow polyhedrons (cubes) consisting of a few layers of 2D graphene or graphene oxide sheets via an origami-like self-folding process is described. This method involves the use of polymer frames and hinges, and aluminum oxide/chromium protection layers that reduce tensile, spatial, and surface tension stresses on the graphene-based membranes when the 2D nets are transformed into 3D cubes. The process offers control of the size and shape of the structures as well as parallel production. In addition, this approach allows the creation of surface modifications by metal patterning on each face of the 3D cubes. Raman spectroscopy studies show the method allows the preservation of the intrinsic properties of the graphene-based membranes, demonstrating the robustness of our method.

Figure 2&#160;displays optical images of the lithographic processes of the 2D graphene and GO net structures and subsequent self-folding process. The self-folding process is monitored in real-time via a high-resolution microscope. Both types of 3D graphene-based cubes are folded at ~80 &#176;C. Figure 3 lays out video captured sequences showing the self-folding of 3D graphene-based cubes in a parallel manner. Under an op...

Watch this Scientific Journal Video about Fabrication of Three-Dimensional Graphene-Based Polyhedrons via Origami-Like Self-Folding at JoVE.com

Fabrication of Three-Dimensional Graphene-Based Polyhedrons via Origami-Like Self-Folding

Here, we present a protocol for fabrication of 3D graphene-based polyhedrons via origami-like self-folding.

Fabrication of Three-Dimensional Graphene-Based Polyhedrons via Origami-Like Self-Folding

The assembly of two-dimensional (2D) graphene into three-dimensional (3D) polyhedral structures while preserving the graphene's excellent inherent ...

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8.9K Views.  University of Minnesota, Minneapolis, United States. Here, we present a protocol for fabrication of 3D graphene-based polyhedrons via origami-like self-folding.

Video: Fabrication of Three-Dimensional Graphene-Based Polyhedrons via Origami-Like Self-Folding

Fabrication, Densification, and Replica Molding of 3D Carbon Nanotube Microstructures

The introduction of new materials and processes to microfabrication has, in large part, enabled many important advances in microsystems, lab-on-a-chip devices, and their applications. In particular, capabilities for cost-effective fabrication of polymer microstructures were transformed by the advent of soft lithography and other micromolding techniques 1, 2, and this led a revolution in applications of microfabrication to biomedical engineering and biology. Nevertheless, it remains challenging to fabricate microstructures with well-defined nanoscale surface textures, and to fabricate arbitrary 3D shapes at the micro-scale. Robustness of master molds and maintenance of shape integrity is especially important to achieve high fidelity replication of complex structures and preserving their nanoscale surface texture. The combination of hierarchical textures, and heterogeneous shapes, is a profound challenge to existing microfabrication methods that largely rely upon top-down etching using fixed mask templates. On the other hand, the bottom-up synthesis of nanostructures such as nanotubes and nanowires can offer new capabilities to microfabrication, in particular by taking advantage of the collective self-organization of nanostructures, and local control of their growth behavior with respect to microfabricated patterns. 
Our goal is to introduce vertically aligned carbon nanotubes (CNTs), which we refer to as CNT "forests", as a new microfabrication material. We present details of a suite of related methods recently developed by our group: fabrication of CNT forest microstructures by thermal CVD from lithographically patterned catalyst thin films; self-directed elastocapillary densification of CNT microstructures; and replica molding of polymer microstructures using CNT composite master molds. In particular, our work shows that self-directed capillary densification ("capillary forming"), which is performed by condensation of a solvent onto the substrate with CNT microstructures, significantly increases the packing density of CNTs. This process enables directed transformation of vertical CNT microstructures into straight, inclined, and twisted shapes, which have robust mechanical properties exceeding those of typical microfabrication polymers. This in turn enables formation of nanocomposite CNT master molds by capillary-driven infiltration of polymers. The replica structures exhibit the anisotropic nanoscale texture of the aligned CNTs, and can have walls with sub-micron thickness and aspect ratios exceeding 50:1. Integration of CNT microstructures in fabrication offers further opportunity to exploit the electrical and thermal properties of CNTs, and diverse capabilities for chemical and biochemical functionalization 3.

We present methods for fabrication of patterned microstructures of vertically aligned carbon nanotubes (CNTs), and their use as master molds for production of polymer microstructures with organized nanoscale surface texture. The CNT forests are densified by condensation of solvent onto the substrate, which significantly increases their packing density and enables self-directed formation of 3D shapes.

The introduction of new materials and processes to microfabrication has, in large part, enabled many important advances in microsystems, lab-on-a-chip ...

Origami Inspired Self-assembly of Patterned and Reconfigurable Particles

There are numerous techniques such as photolithography, electron-beam lithography and soft-lithography that can be used to precisely pattern two dimensional (2D) structures. These technologies are mature, offer high precision and many of them can be implemented in a high-throughput manner. We leverage the advantages of planar lithography and combine them with self-folding methods1-20 wherein physical forces derived from surface tension or residual stress, are used to curve or fold planar structures into three dimensional (3D) structures. In doing so, we make it possible to mass produce precisely patterned static and reconfigurable particles that are challenging to synthesize.
In this paper, we detail visualized experimental protocols to create patterned particles, notably, (a) permanently bonded, hollow, polyhedra that self-assemble and self-seal due to the minimization of surface energy of liquefied hinges21-23 and (b) grippers that self-fold due to residual stress powered hinges24,25. The specific protocol described can be used to create particles with overall sizes ranging from the micrometer to the centimeter length scales. Further, arbitrary patterns can be defined on the surfaces of the particles of importance in colloidal science, electronics, optics and medicine. More generally, the concept of self-assembling mechanically rigid particles with self-sealing hinges is applicable, with some process modifications, to the creation of particles at even smaller, 100 nm length scales22, 26 and with a range of materials including metals21, semiconductors9 and polymers27. With respect to residual stress powered actuation of reconfigurable grasping devices, our specific protocol utilizes chromium hinges of relevance to devices with sizes ranging from 100 &mu;m to 2.5 mm. However, more generally, the concept of such tether-free residual stress powered actuation can be used with alternate high-stress materials such as heteroepitaxially deposited semiconductor films5,7 to possibly create even smaller nanoscale grasping devices.

We describe experimental details of the synthesis of patterned and reconfigurable particles from two dimensional (2D) precursors. This methodology can be used to create particles in a variety of shapes including polyhedra and grasping devices at length scales ranging from the micro to centimeter scale.

There are numerous techniques such as photolithography, electron-beam lithography and soft-lithography that can be used to precisely pattern two ...

Chemistry

Folding and Characterization of a Bio-responsive Robot from DNA Origami

The DNA nanorobot is a hollow hexagonal nanometric device, designed to open in response to specific stimuli and present cargo sequestered inside. Both stimuli and cargo can be tailored according to specific needs. Here we describe the DNA nanorobot fabrication protocol, with the use of the DNA origami technique. The procedure initiates by mixing short single-strand DNA staples into a stock mixture which is then added to a long, circular, single-strand DNA scaffold in presence of a folding buffer. A standard thermo cycler is programmed to gradually lower the mixing reaction temperature to facilitate the staples-to-scaffold annealing, which is the guiding force behind the folding of the nanorobot. Once the 60 hr folding reaction is complete, excess staples are discarded using a centrifugal filter, followed by visualization via agarose-gel electrophoresis (AGE). Finally, successful fabrication of the nanorobot is verified by transmission electron microscopy (TEM), with the use of uranyl-formate as negative stain.

DNA origami is a powerful method for fabricating precise nanoscale objects by programming the self-assembly of DNA molecules. Here we describe a protocol for the folding of a bio-responsive robot from DNA origami, its purification and negative staining for transmission electron microscopic imaging (TEM).

The DNA nanorobot is a hollow hexagonal nanometric device, designed to open in response to specific stimuli and present cargo sequestered inside. Both ...

Synthesis and Functionalization of 3D Nano-graphene Materials: Graphene Aerogels and Graphene Macro Assemblies

Efforts to assemble graphene into three-dimensional monolithic structures have been hampered by the high cost and poor processability of graphene. Additionally, most reported graphene assemblies are held together through physical interactions (e.g., van der Waals forces) rather than chemical bonds, which limit their mechanical strength and conductivity. This video method details recently developed strategies to fabricate mass-producible, graphene-based bulk materials derived from either polymer foams or single layer graphene oxide. These materials consist primarily of individual graphene sheets connected through covalently bound carbon linkers. They maintain the favorable properties of graphene such as high surface area and high electrical and thermal conductivity, combined with tunable pore morphology and exceptional mechanical strength and elasticity. This flexible synthetic method can be extended to the fabrication of polymer/carbon nanotube (CNT) and polymer/graphene oxide (GO) composite materials. Furthermore, additional post-synthetic functionalization with anthraquinone is described, which enables a dramatic increase in charge storage performance in supercapacitor applications.

This video method describes the synthesis of high surface area, monolithic 3D graphene-based materials derived from polymer precursors as well as single layer graphene oxide.

Efforts to assemble graphene into three-dimensional monolithic structures have been hampered by the high cost and poor processability of graphene. ...

Self-assembling Morphologies Obtained from Helical Polycarbodiimide Copolymers and Their Triazole Derivatives

A facile method for the preparation of polycarbodiimide-based secondary structures (e.g., nano-rings, &#34;craters,&#34; fibers, looped fibers, fibrous networks, ribbons, worm-like aggregates, toroidal structures, and spherical particles) is described. These aggregates are morphologically influenced by extensive hydrophobic side chain-side chain interactions of the singular polycarbodiimide strands, as inferred by atomic force microscopy (AFM) and scanning electron microscopy (SEM) techniques. Polycarbodiimide-g-polystyrene copolymers (PS-PCDs) were prepared by a combination of synthetic methods, including coordination-insertion polymerization, copper(I)-catalyzed azide alkyne cycloaddition (CuAAC) &#34;click&#34; chemistry, and atom transfer radical polymerization (ATRP). PS-PCDs were found to form specific toroidal architectures at low concentrations in CHCl3. To determine the influence of a more polar solvent medium (i.e., THF and THF/EtOH) on polymer aggregation behavior, a number of representative PS-PCD composites have been tested to show discrete concentration-dependent spherical particles. These fundamental studies are of practical interest to the development of experimental procedures for desirable architectures by directed self-assembly in thin film. These architectures may be exploited as drug carriers, whereas other morphological findings represent certain interest in the area of novel functional materials.

Here, we present a protocol to prepare and visualize secondary structures (e.g., fibers, toroidal architectures, and nano-spheres) derived from helical polycarbodiimides. The morphology characterized by both atomic force microscopy (AFM) and scanning electron microscopy (SEM) was shown to depend on molecular structure, concentration, and the solvent of choice.

A facile method for the preparation of polycarbodiimide-based secondary structures (e.g., nano-rings, &#34;craters,&#34; fibers, looped fibers, fibrous ...

Assembly of Gold Nanorods into Chiral Plasmonic Metamolecules Using DNA Origami Templates

The inherent addressability of DNA origami structures makes them ideal templates for the arrangement of metal nanoparticles into complex plasmonic nanostructures. The high spatial precision of a DNA origami-templated assembly allows controlling the coupling between plasmonic resonances of individual particles and enables tailoring optical properties of the constructed nanostructures. Recently, chiral plasmonic systems attracted a lot of attention due to the strong correlation between the spatial configuration of plasmonic assemblies and their optical responses (e.g., circular dichroism [CD]). In this protocol, we describe the whole workflow for the generation of DNA origami-based chiral assemblies of gold nanorods (AuNRs). The protocol includes a detailed description of the design principles and experimental procedures for the fabrication of DNA origami templates, the synthesis of AuNRs, and the assembly of origami-AuNR structures. In addition, the characterization of structures using transmission electron microscopy (TEM) and CD spectroscopy is included. The described protocol is not limited to chiral configurations and can be adapted for the construction of various plasmonic architectures.

We describe the detailed protocol for the DNA origami-based assembly of gold nanorods into chiral plasmonic metamolecules with strong chiroptical responses. The protocol is not limited to chiral configurations and can be easily adapted for the fabrication of various plasmonic architectures.

The inherent addressability of DNA origami structures makes them ideal templates for the arrangement of metal nanoparticles into complex plasmonic ...

Fabricating van der Waals Heterostructures with Precise Rotational Alignment

In this work we describe a technique for creating new crystals (van der Waals heterostructures) by stacking distinct ultrathin layered 2D materials. We demonstrate not only lateral control but, importantly, also control over the angular alignment of adjacent layers. The core of the technique is represented by a home-built transfer setup which allows the user to control the position of the individual crystals involved in the transfer. This is achieved with sub-micrometer (translational) and sub-degree (angular) precision. Prior to stacking them together, the isolated crystals are individually manipulated by custom-designed moving stages that are controlled by a programmed software interface. Moreover, since the entire transfer setup is computer controlled, the user can remotely create precise heterostructures without coming into direct contact with the transfer setup, labeling this technique as &#8220;hands-free&#8221;. In addition to presenting the transfer set-up, we also describe two techniques for preparing the crystals that are subsequently stacked.

In this work we describe a technique that is used to create new crystals (van der Waals heterostructures) by stacking ultrathin layered 2D materials with precise control over position and relative orientation.

In this work we describe a technique for creating new crystals (van der Waals heterostructures) by stacking distinct ultrathin layered 2D materials. We ...

DNA Origami-Mediated Substrate Nanopatterning of Inorganic Structures for Sensing Applications

Structural DNA nanotechnology provides a viable route for building from the bottom-up using DNA as construction material. The most common DNA nanofabrication technique is called DNA origami, and it allows high-throughput synthesis of accurate and highly versatile structures with nanometer-level precision. Here, it is shown how the spatial information of DNA origami can be transferred to metallic nanostructures by combining the bottom-up DNA origami with the conventionally used top-down lithography approaches. This allows fabrication of billions of tiny nanostructures in one step onto selected substrates. The method is demonstrated using bowtie DNA origami to create metallic bowtie-shaped antenna structures on silicon nitride or sapphire substrates. The method relies on the selective growth of a silicon oxide layer on top of the origami deposition substrate, thus resulting in a patterning mask for following lithographic steps. These nanostructure-equipped surfaces can be further used as molecular sensors (e.g., surface-enhanced Raman spectroscopy (SERS)) and in various other optical applications at the visible wavelength range owing to the small feature sizes (sub-10 nm). The technique can be extended to other materials through methodological modifications; therefore, the resulting optically active surfaces may find use in development of metamaterials and metasurfaces.

Here, we describe a protocol to create discrete and accurate inorganic nanostructures on substrates using DNA origami shapes as guiding templates. The method is demonstrated by creating plasmonic gold bowtie-shaped antennas on a transparent substrate (sapphire).

Structural DNA nanotechnology provides a viable route for building from the bottom-up using DNA as construction material. The most common DNA ...

Microscopic Visualization of Porous Nanographenes Synthesized through a Combination of Solution and On-Surface Chemistry

On-surface synthesis has recently been regarded as a promising approach for the generation of new molecular structures. It has been particularly successful in the synthesis of graphene nanoribbons, nanographenes and intrinsically reactive and instable, yet attractive species. It is based on the combination of solution chemistry aimed at preparation of appropriate molecular precursors for further ultra-high vacuum surface assisted transformations. This approach also owes its success to an incredible development of characterization techniques, such as scanning tunneling/atomic force microscopy and related methods, which allow detailed, local characterization at atomic scale. While the surface-assisted synthesis can provide molecular nanostructures with outstanding precision, down to single atoms, it suffers from basing on metallic surfaces and often limited yield. Therefore, the extension of the approach away from metals and the struggle to increase productivity seem to be significant challenges toward wider applications. Herein, we demonstrate the on-surface synthesis approach for generation of non-planar nanographenes, which are synthesized through a combination of solution chemistry and sequential surface-assisted processes, together with the detailed characterization by scanning probe microscopy methods.

A combination of solution and surface assisted synthesis opens new directions in the atomically precise synthesis of nanostructures. Scanning tunneling microscopy (STM) supplemented by non-contact atomic force microscopy (nc-AFM) enables detailed characterization of newly designed and generated carbon-based nano-objects.

On-surface synthesis has recently been regarded as a promising approach for the generation of new molecular structures. It has been particularly ...

Self-Assembly of Polymer-Grafted Metal Organic Framework Monolayers

Synthesis and Characterization of Self-Assembled Metal-Organic Framework Monolayers Using Polymer-Coated Particles

Metal-organic frameworks (MOFs) are materials with potential applications in fields such as gas adsorption and separation, catalysis, and biomedicine. Attempts to enhance the utility of MOFs have involved the preparation of various composites, including polymer-grafted MOFs. By directly grafting polymers to the external surface of MOFs, issues of incompatibility between polymers and MOFs can be overcome. Polymer brushes grafted from the surface of MOFs can serve to stabilize the MOF while enabling particle assembly into self-assembled metal-organic framework monolayers (SAMMs) via polymer-polymer interactions.
Control over the chemical composition and molecular weight of the grafted polymer can allow for tuning of the SAMM characteristics. In this work, instructions are provided on how to immobilize a chain transfer agent (CTA) onto the surface of the MOF UiO-66 (UiO = Universitetet i Oslo). The CTA&#160;serves as initiation sites for the growth of polymers. Once polymer chains are grown from the MOF surface, the formation of SAMMs is achieved through self-assembly at an air-water interface. The resulting SAMMs are characterized and shown to be freestanding by scanning electron microscopy imaging. The methods presented in this paper are expected to make the preparation of SAMMs more accessible to the research community and thereby expand their potential use as a&#160;MOF-polymer composite.

Author Spotlight: Exploring Self-Assembled MOF-Polymer Composites

A protocol for the synthesis and characterization of self-assembled metal-organic framework monolayers is provided using polymer-grafted, metal-organic framework (MOF) crystals. The procedure shows that polymer-grafted MOF particles can be self-assembled at an air-water interface resulting in well-formed, free-standing, monolayer structures as evidenced by scanning electron microscopy imaging.

Metal-organic frameworks (MOFs) are materials with potential applications in fields such as gas adsorption and separation, catalysis, and biomedicine. ...

Fabrication of Three-Dimensional Graphene-Based Polyhedrons via Origami-Like Self-Folding

Summary

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Fabrication, Densification, and Replica Molding of 3D Carbon Nanotube Microstructures

Origami Inspired Self-assembly of Patterned and Reconfigurable Particles

Folding and Characterization of a Bio-responsive Robot from DNA Origami

Synthesis and Functionalization of 3D Nano-graphene Materials: Graphene Aerogels and Graphene Macro Assemblies

Self-assembling Morphologies Obtained from Helical Polycarbodiimide Copolymers and Their Triazole Derivatives

Assembly of Gold Nanorods into Chiral Plasmonic Metamolecules Using DNA Origami Templates

Fabricating van der Waals Heterostructures with Precise Rotational Alignment

DNA Origami-Mediated Substrate Nanopatterning of Inorganic Structures for Sensing Applications

Microscopic Visualization of Porous Nanographenes Synthesized through a Combination of Solution and On-Surface Chemistry

Synthesis and Characterization of Self-Assembled Metal-Organic Framework Monolayers Using Polymer-Coated Particles