When you’re first exposed to nanotechnology, it can be difficult to grasp the immense difference in scale that nano-sized objects have. It’s helpful to think through the actual mechanics of how objects that size interact. For example, we use DNA linkers to bind DNP cubes together into useful structures. Just how strong are the bonds between DNA linkers? Imagine you’re playing a nano-sized version of the claw game, except instead of a mechanical claw, you’re going to lift objects with using DNA. It would look something like this:
How large of a DNP cube could you lift?
While there are many ways to bind nanoparticles together (e.g. covalent bonds, electrostatic attraction, hydrophilic/hydrophobic interactions, etc.), we typically use the stickiness of double stranded DNA. We do this by first painting single-stranded DNA on the cube's faces:
When two cubes get close, they will bind together to form double stranded DNA, if and only if they have complementary sequences:
At least a couple sources list the binding force of DNA as being in the piconewton (pN) range.1Let’s assume it takes a force F= 4 pN to break apart one of the short DNA strands holding the cubes together. If you have two DNA strands binding the cubes together, it should take 10 pN of force. If you have 3 DNA strands, it should take 15 pN. If 10 DNA strands, it should take 50 pN. The more DNA strands you have, the stronger the cubes will bind together.
How many DNA strands can you fit on the face of a cube? Clearly it depends on the size of the cube. Suppose you have cube of length L= 10 nanometer (nm). The area Acubeof a cube face with that length would be
Acube= L × L = 10 nm × 10 nm = 100 nm2
DNA is 2 nm wide, giving it an area of roughly2
ADNA= 2 nm × 2 nm = 4 nm2
Assuming you’re covering the surface of the cube completely, we should be able to fit roughly N = 25 DNA strands with a 4 nm2area onto a cube face with a 100 nm2area,
N= Acube/ ADNA= 100 nm2/ 4 nm2= 25 strands
Since DNA has a force of 4 pN per strand, the total force binding the cubes together will be
FDNA= F× N= (4 pN/strand) × (25 strands) = 100 pN
What if we make the cube larger? We can rearrange the equations above to get an equation for the DNA force that depends on the length of the cube,
FDNA= FL2/ ADNA
FDNAtells us the strength of the force that binds cubes together. In order to lift a cube, it needs to overcome it’s weight, i.e. the force of gravity. The force of gravity is given by the equations
Fgrav= m g,
where m is the mass and g= 9.8 m/s2is the acceleration of gravity. We can calculate the mass using the density of cube and its length.
m= ρ L3
We’ll assume the silver nanocube has the same density of silver, ρ= 10.5 g/cm3. Combining the two previous equations, we get
Fgrav= ρ g L3= (10.5 g/cm3) × (9.8 m/s2) × L3,
Notice that Fgrav~ L3, whereas FDNA~ L2. This means that as the cube grows in size, the force of gravity pulling the cube down grows faster than the force of the DNA binding pulling it up. Eventually, the weight of the cube will be too much, and the DNA strands will not be strong enough to lift it. We can see that on a plot of force versus cube length:
We see that the gravitational force acting on the cube (green) grows faster than the DNA binding force (orange). The forces intersect at a cube length L= 2.4 m. That’s an 8 foot long cube weighing 165 tons! Evidently, DNA molecules are very strong if you have enough of them.
I should point out that for a real silver cube, the largest size the DNA can lift is almost certainly smaller than the result computed here. Nanocube faces are very flat, whereas bulk silver is rough and bumpy. When you stack bumpy cubes on top of each other, the bumps that stick out will be in contact with the other cube, but the dimples won’t be in contact with the other cube. Since the bumps and dimples will be larger than the short DNA strands, the strands located in the dimples will never reach far enough to bind with the DNA on the other cube.
 The cross-sectional area of DNA is more accurately described as a circle, but for an order of magnitude estimation such as this, the difference between the area of a square and the area of a circle will not be significant.
A colleague recently asked "What can you build out of DNP cubes that you can't build out of spheres?" We've always had a difficult time answering this question succinctly. Rather than answer in words, we're going to actually show you...by running a nanotech design contest!
You: Hey! What do you mean by "nanotech design contest"?
DNP: We want you to design a solution to a real-world problem using nanotech. We'll see who can come up with the best solution to a given problem.
You: How will the contest work?
DNP: It will run like a hackathon, except instead of programming, you'll be designing nanotech devices. We'll start at 9a EST on a Monday, November 11, 2019 and run through 11:59p EST the following Sunday, November 17, 2019. Prior to 9a on Monday, we'll email you a packet of materials including a description of a real-world problem that should be solvable with nanotech. Then you get to (1) design a nanotech solution on paper, (2) describe your solution in three pages or less, and (3) enter your three-page write-up for a chance to win.
You: Have you done anything like this before?
DNP: Not formally. However, while presenting our work at the University of Michigan, we did have the audience design "some cool nanotech device" using DNP cubes. In only 5 minutes, they were able to come up with a wide variety of protein detectors, drug delivery schemes, and other cool nano devices:
Fig. Sample nanotech designs created by audience members.
You: Who can enter?
DNP: Any team of 2-5 people. We're recruiting teachers and students, but anyone is welcome to enter.
You: Why should I enter?
DNP: Because it’ll be fun, and you want to solve big problems that will change the world!
You: Great! Where do I sign up?
DNP: There's an entry form below. To enter, gather 2-5 friends and form a team. Designate someone as the primary contact. (The primary contact is responsible for sending/receiving info for the contest.) Enter the primary contact's name, the email address where you'd like us to send contest info, and the names of all additional team members.
You: Anything else I should know?
DNP: To help you prepare, I'll make a few posts on this blog explaining the physics behind different nanotechnologies. This should help you prepare for the contest.
Interested in designing nanotech devices? Sign up today!
Check out Derek Lyons presenting on DNP123 spinout ExpresSeed at 1 Million Cups.
Consider the figure above. If you wish to synthesize any of the shapes shown on the left (Fig. A), you will find a variety of methods that suit your needs. Researchers have grown adept at synthesizing nanospheres, nanocubes, nanoprisms, nanotubes, lattices of nanoparticles, and a multitude of other highly symmetric monodisperse systems of nearly identical particles. However, if you instead wish to synthesize the object on the right (Fig. B), you will find currently available synthesis techniques extremely lacking.
In the time since Richard Feynman first predicted the coming age of nanotechnology, popular science writers have promoted future advances with images of remote-controlled nanobots piloted through our blood streams, lancing our cancer cells, and keeping us healthy well into old age. Today, nanobots (and many other useful devices) can be conceived and designed theoretically, but they simply cannot be manufactured using tools currently available. While we have lathes, 3D printers, and a variety of other shape molding methods to create complex shapes at macroscale, there is presently no all-purpose “3D printer” equivalent manufacturing tool that can create a complete set of all shapes at nanoscale. Until we develop such a tool, the nanobot dream scenario will be relegated to the realm of science fiction.
At DNP123, we are bridging the gap between design and assembly. This is possible because our patent-pending core IP—patched nanocubes that can be programmed to assemble any designable shape—affords a simple, standardized method of creating any structure at nanoscale. This assembly method permits the modular connection of device components, allowing complex products to be programmatically designed and assembled simply, quickly, and easily.
What’s new in your approach? Why is it advantageous? At its core, our innovation is simply the ability to connect blocks. Its strength lies in simplicity and customizability: assembling complex new structures is just like building with LEGOs. Using DNA-patches on each face, we are able to program how nanocube blocks will bind to each other. The ability to connect blocks provides a general method for scaling up to complex three-dimensional structures in any desired shape, regardless how anisotropic or complex the target structure may be. Furthermore, the blocks self-assemble. This makes automating manufacturing particularly easy, since one need not use complicated robotic machinery in the assembly process.
What impact will it make? From drug delivery containers to chemical sensors that detect bioterrorism, there is broad societal need for a standardized manufacturing platform that can assemble nanoscale products. A fast, inexpensive method of rapidly prototyping nanoscale products will extend nano- and biotech innovation beyond high priced research labs into early stage startups and college dorm rooms. The simplicity of our design-and-connect methodology makes it so that anyone with an imagination and the desire to invent can manufacture the next world changing nanotech device. Makers building with our technology can generate an explosion of products and innovation that one company alone could never hope to produce.
What will it take to succeed? To be successful, DNP123 technologies needs an active base of dedicated users looking to build the next generation of nanoscale technologies. Are you an academic, governmental, or industrial researcher with a nanotech problem you’ve been unable to solve by conventional means? Are you a tinkerer looking for a new medium to play in? If so, we want to hear from you. Visit our Contact page and introduce yourself. We’ll work with you to get you up and running.
The future is in your hands. What will you build?