Single-celled architects inspire newnanotechnology16 July 2018

Base-pairing properties of DNA were used to constructtiny structures that accumulated a silica outer skeletonsimilar to shell-building organisms known as diatoms.Credit: Yan Lab.

Diatoms are tiny, unicellular creatures, inhabitingoceans, lakes, rivers, and soils. Through theirrespiration, they produce close to a quarter of theoxygen on earth, nearly as much as the world'stropical forests. In addition to their ecologicalsuccess across the planet, they have a number ofremarkable properties. Diatoms live in glasslikehomes of their own design, visible undermagnification in an astonishing and aestheticallybeautiful range of forms.

Researchers have found inspiration in thesemicroscopic, jewel-like products of nature sincetheir discovery in the late 18th century. In a newstudy, Arizona State University (ASU) scientists ledby Professor Hao Yan, in collaboration withresearchers from the Shanghai Institute of AppliedPhysics of the Chinese Academy of Sciences andShanghai Jiaotong University led by Prof. ChunhaiFan, have designed a range of diatom-likenanostructures.

To achieve this, they borrow techniques used bynaturally-occurring diatoms to deposit layers ofsilica—the primary constituent in glass—in order togrow their intricate shells. Using a technique knownas DNA origami, the group designed nanoscaleplatforms of various shapes to which particles ofsilica, drawn by electrical charge, could stick.

The new research demonstrates that silicadeposition can be effectively applied to synthetic,DNA-based architectures, improving their elasticityand durability. The work could ultimately have far-reaching applications in new optical systems,semiconductor nanolithography, nano-electronics,nano-robotics and medical applications, includingdrug delivery.

Yan is the Milton D. Glick Distinguished Professorof Chemistry and Biochemistry and directs theBiodesign Center for Molecular Design andBiomimetics. The group's findings are reported inthe advanced online of the journal Nature.

Researchers like Yan and Fan create sophisticatednanoarchitectures in 2- and 3-dimensions, usingDNA as a building material. The method, known asDNA origami, relies on the base-pairing propertiesof DNA's four nucleotides, whose names areabbreviated A,T,C and G.

The ladder-like structure of the DNA double-helix isformed when complementary strands of nucleotidesbond with each other—the C nucleotides always

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pairing with Gs and the As always pairing with Ts.This predictable behavior can be exploited in orderto produce a virtually limitless variety of engineeredshapes, which can be designed in advance. Thenanostructures then self-assemble in a test tube.

A selection of nanostructures built using DNA origami,alongside naturally-occurring diatoms -- single-celledorganisms that come in many beautiful and elaborateforms. They are ubiquitous inhabitants of the world'slakes, rivers, and oceans. A scale shows the sizes of thenanostructures and diatoms. Credit: Shireen Dooling

In the new study, researchers wanted to see ifarchitectures designed with DNA, each measuringjust billionths of a meter in diameter, could be usedas structural frameworks on which diatom-likeexoskeletons composed of silica could grow in aprecise and controllable manner. Their successfulresults show the power of this hybrid marriage ofnature and nanoengineering, which the authors callDNA Origami Silicification (DOS).

"Here, we demonstrated that the right chemistrycan be developed to produce DNA-silica hybridmaterials that faithfully replicate the complexgeometric information of a wide range of differentDNA origami scaffolds. Our findings established ageneral method for creating biomimetic silicananostructures," said Yan.

Among the geometric DNA frameworks designedand constructed in the experiments were 2-D

crosses, squares, triangles and DOS-diatomhoneycomb shapes as well as 3-D cubes,tetrahedrons, hemispheres, toroid and ellipsoidforms, occurring as single units or lattices.

Once the DNA frameworks were complete, clustersof silica particles carrying a positive charge weredrawn electrostatically to the surfaces of theelectrically negative DNA shapes, accreting over aperiod of several days, like fine paint applied to aneggshell. A series of transmission- and scanningelectron micrographs were made of the resultingDOS forms, revealing accurate and efficient diatom-like silicification.

The method proved effective for silicification offramelike, curved and porous nanostructuresranging in size from 10-1000 nanometers, (thelargest structures are roughly the size of bacteria).Precise control over silica shell thickness isachieved simply by regulating the duration ofgrowth.

The hybrid DOS-diatom nanostructures wereinitially characterized using a pair of powerful toolscapable of unveiling their tiny forms, TransmissionElectron Microscopy (TEM) and Atomic ForceMicroscopy (AFM). The resulting images revealmuch clearer outlines for the nanostructures afterthe deposition of silica.

The method of nanofabrication is so precise,researchers were able to produce triangles,squares and hexagons with uniform poresmeasuring less than 10 nm in diameter—by far thesmallest achieved to date, using DNA origamilithography. Further, the technique outlined in thenew study equips researchers with more accuratecontrol over the construction of 3-D nanostructuresin arbitrary forms that are often challenging toproduce through existing methods.

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3D cube made using DNA Origami Silicification (DOS),which deposits a fine layer of silica onto the DNA origamiframework. Credit: Yan Lab

One property of natural diatoms of great interests tonanoengineers like Yan and Fan is the specificstrength of their silica shells. Specific strengthrefers to a material's resistance to breakage relativeto its density. Scientists have found that the silicaarchitectures of diatoms are not only inspiringlyelegant but exceptionally tough. Indeed, the silicaexoskeletons enveloping diatoms have the highestspecific strength of any biologically producedmaterial, including bone, antlers, and teeth.

In the current study, researchers used AFM tomeasure the resistance to breakage of their silica-augmented DNA nanostructures. Like their naturalcounterparts, these forms showed far greaterstrength and resilience, displaying a 10-foldincrease in the forces they could withstand,compared with the unsilicated designs, whilenevertheless retaining considerable flexibility.

The study also shows that the enhanced rigidity ofDOS nanostructures increases with their growthtime. As the authors note, these results are inagreement with the characteristic mechanical

properties of biominerals produced by nature,coupling impressive durability with flexibility.

A final experiment involved the design of a new 3-Dtetrahedral nanostructure using gold nanorods assupportive struts for a DOS fabricated device. Thisnovel structure was able to faithfully retain its shapecompared with a similar structure lacking silicationthat deformed and collapsed.

The research opens a pathway for nature-inspiredinnovations in nanotechnology in which DNAarchitectures act as templates that may be coatedwith silica or perhaps other inorganic materials,including calcium phosphate, calcium carbonate,ferric oxide or other metal oxides, yielding uniqueproperties.

"We are interested in developing methods to createhigher order hybrid nanostructures. For example,multi-layered/multi-component hybrid materials maybe achieved by a stepwise deposition of differentmaterials to further expand the biomimeticdiversity," said Fan.

Such capabilities will open up new opportunities toengineer highly programmable solid-statenanopores with hierarchical features, new porousmaterials with designed structural periodicity, cavityand functionality, plasmonic and meta-materials.The bio-inspired and biomimetic approachdemonstrated in this paper represents a generalframework for use with inorganic devicenanofabrication that has arbitrary 3-D shapes andfunctions and offers diverse potential applications infields such as nano-electronics, nano-photonics,and nano-robotics.

More information: Xiaoguo Liu et al, Complexsilica composite nanomaterials templated with DNAorigami, Nature (2018). DOI:10.1038/s41586-018-0332-7

Provided by Arizona State University

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APA citation: Single-celled architects inspire new nanotechnology (2018, July 16) retrieved 9 January2022 from https://phys.org/news/2018-07-single-celled-architects-nanotechnology.html

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