Home / Science / The Caltech team manages to "paint" the smaller Mona Lisa using DNA

The Caltech team manages to "paint" the smaller Mona Lisa using DNA



Paul Rothemund (BS & # 39; 94) from Caltech -currently professor of bioengineering, computer and mathematical sciences research, and computation and neural systems – developed a technique for folding a long chain of DNA in a prescribed way back in 2006. The method, labeled as origami DNA, allowed researchers to develop self-assembling DNA structures that could adopt any specific pattern, such as a smiling face 1

00 nanometers wide. [19659004] The fractal assembly process, using wooden puzzle pieces. (Credit: Caltech)

DNA origami transformed the field of nanotechnology, paving the way for the construction of tiny molecular devices or "intelligent" programmable materials. However, some of these applications require much larger DNA origami structures.

Now, researchers in the laboratory of Lulú Qian, assistant professor of bioengineering at Caltech, have developed an economic technique whereby origami DNA is self-assembled into large matrices with fully customizable patterns, forming a kind of canvas that can exhibit any picture. To prove it, the team created the world's smallest recreation of DNA that uses Mona Lisa by Leonardo da Vinci.

The study is described in an article published in the December 7 edition of the journal Nature.

known for coding the genetic information of living beings, the molecule is also an exceptional chemical component. A single-stranded DNA molecule is made up of smaller molecules known as nucleotides, abbreviated A, T, C and G, organized in a chain or sequence. The nucleotides in a single-stranded DNA molecule can be linked with those of another single strand to create double-stranded DNA, but nucleotides bind only in very particular ways: a C nucleotide with a G nucleotide or an A with a T. These strict " rules of base pairing make it possible to design DNA origami.

To create a single DNA origami square, only a single long DNA strand and numerous shorter individual strands, known as staples, are required to be designed to join several designated places on the long strand. When the short staples and the long strand are joined in a test tube, the staples drag the regions of the long strand together, causing it to bend over the anticipated shape. A large DNA canvas is made up of many smaller square mosaics of origami, like putting together a puzzle. The molecules can be selectively bound to the staples to create an elevated pattern that can be seen by atomic force microscopy.

The Caltech team created software that can use an image like the Mona Lisa, divide it into small square sections. , and establish the DNA sequences required to form those squares. Then, his test consisted of making those sections self-assemble into a superstructure that recreates the Mona Lisa.

We could make each tile have unique edge staples so that they can only join certain other tiles and self-assemble in a single position in the superstructure, but we would have to have hundreds of unique edges, which would not only be very difficult to design, but also extremely expensive to synthesize. We wanted to use only a small number of different edge clamps, but still get all the tiles in the right places.

Grigory Tikhomirov, senior postdoctoral scholar and senior author of the document

The strategic part in achieving this was to assemble the chips into stages, like putting together small regions of a puzzle and then assembling them to create larger regions before joining the regions larger to form the finished puzzle. Each small puzzle uses the same four edges, but because these puzzles are assembled independently, there is no risk, for example, that a corner meets at the wrong corner. The team has called the technique "fractal assembly" because the same set of assembly rules is applied at different scales.

Once we have synthesized each individual tile, we put each one in its own test tube for a total of 64 tubes, w We know exactly what mosaics are in which tubes, so we know how to combine them to assemble the Final product. First, we combine the contents of four particular tubes together to get 16 squares two by two. Then those combine in a certain way to get four tubes each with a square of four by four. And then the final four tubes combine to create a large eight by eight square consisting of 64 tiles. We design the edges of each tile so we know exactly how they will be combined.

Philip Petersen, graduate student, co-first author of the article.

The final structure of the Qian team was 64 times larger than the innovative DNA origami structure created by Rothemund in 2006. Extraordinarily, due to the recycling of the same edge interactions, the number of different DNA strands required for assembly of this DNA superstructure was approximately the same as for the original origami of Rothemund. This should make the new technique equally economical, according to Qian.

The hierarchical nature of our approach allows us to use only a small and constant set of unique building blocks, in this case DNA strands with unique sequences, to build structures with increasing sizes. and, in principle, an unlimited number of different paintings, t its economic approach of building more with less is similar to how our bodies are constructed. All of our cells have the same genome and are constructed using the same set of building blocks, such as amino acids, carbohydrates and lipids. However, through variable gene expression, each cell uses the same blocks to build different machinery, for example, muscle cells and cells in the retina.

Grigory Tikhomirov, senior postdoctoral scholar and lead author of the article

The team also developed software to allow scientists around the world to produce DNA nanostructures using fractal assembly.

"In order to make our technique easily accessible to other researchers interested in exploring applications using flat DNA nanostructures on a micrometric scale, we developed an online software tool that converts the user's desired image into DNA chains. and wet laboratory protocols, " says Qian. "The protocol can be read directly by a liquid handling robot to automatically mix the DNA strands.The DNA nanostructure can be assembled effortlessly."

Using this online software tool and automatic liquid handling methods, several other patterns were designed and assembled using strands of DNA, including a portrait of a rooster the size of a bacterium and a portrait of a life-size bacteria.

Other researchers have previously worked to link various molecules such as polymers, proteins, and nanoparticles to much smaller DNA canvases for the purpose of building electronic circuits with small features, making advanced materials, or studying the interactions between chemicals or biomolecules, or their work gives them an even bigger canvas to take advantage of.

Philip Petersen, graduate student, first author on paper.

The research paper is entitled "Fractal set of origami matrices of DNA at micrometric scale arbitrary patterns". The study was funded by the Burroughs Wellcome Fund, the National Institutes of Health's National Research Service Award and the National Science Foundation.


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