DNA is one of nature’s most amazing molecules, providing a means to carry the instructions needed to create almost any form of life on Earth in a microscopic package. Today, scientists are finding ways to push DNA even further, using it not only to store information, but also to create physical components in a range of biological machines.
Deoxyribonucleic acid or “DNA” carries the genetic information that we, and all living things, use to function. It usually comes in the form of the famous double helix form, which is made up of two single-stranded DNA molecules folded into a spiral. Each of them is made up of a series of four different types of molecular components: adenine (A), guanine (G), thymine (T) and cytosine (C).
Genes are made up of different sequences of these building blocks, and the order in which they appear in a strand of DNA is what encodes genetic information. But by precisely designing different A, G, T, and C sequences, scientists have recently been able to develop new ways to Folded DNA in different shapes of origami, beyond the conventional double helix.
This approach has opened up new possibilities for the use of DNA beyond its genetic and biological purpose, by transforming it into a Lego-like material for the construction of objects of a few billionths of a meter in diameter (at the nanoscale). DNA-based materials are now used for a variety of applications, ranging from models for electronic nano-devices to means of accurately transporting drugs to diseased cells.
Designing electronic devices of a few nanometers opens up all kinds of possible applications, but makes it more difficult to detect faults. To remedy this, researchers at the University of Montreal used DNA to create ultra-sensitive nanometric thermometers this could help find tiny hot spots in nanodevices (which would indicate a fault). They could also be used to monitor the temperature inside living cells.
Nanothermometers are made using loops of DNA that act like switches, folding or unfolding in response to changes in temperature. This movement can be detected by attaching optical probes to DNA. Researchers now want to build these nanothermometers into larger DNA devices that can work inside the human body.
Harvard Medical School researchers used DNA to design and build a nanoscale robot that acts as a drug delivery vehicle to target specific cells. The nanobot comes in the form of an open barrel made of DNA, the two halves of which are connected by a hinge held closed by special DNA handles. These handles can recognize specific protein combinations found on the surface of cells, including those associated with disease.
When the robot makes contact with the right cells, it opens the container and delivers its cargo. Applied to a mixture of healthy and cancerous human blood cells, these robots have shown the ability to target and kill half of cancer cells, while healthy cells have remained unharmed.
Bio-computers in living animals
Since DNA structures can act like switches, moving from one position to another and vice versa, they can be used to perform the logical operations that make computational calculations possible. Researchers at Harvard and Bar-Ilan University in Israel used this principle to build different nanoscale robots that can interact with each other, using their DNA switches to react and produce different signals.
In addition, scientists implanted the robots into a living animal, in this case a cockroach. This allowed them to develop a new type of biological computer capable of controlling the delivery of therapeutic molecules inside the cockroach by activating or deactivating elements of their structure. A trial of these DNA nanorobots is now planned for take place in humans.
Light harvesting antennas
In addition to creating tiny machines, DNA can provide us with a way to copy natural processes at the nanoscale. For example, nature can harness energy from the sun by using photosynthesis to convert light into chemical energy, which acts as fuel for plants and other organisms (and the animals that eat them). Researchers at Arizona State University and the University of British Columbia have now constructed a three-armed DNA structure that can capture and transfer light which mimics this process.
Photosynthesis occurs in living organisms using tiny antennae made up of large numbers of pigment molecules at specific orientations and distances from each other, capable of absorbing visible light. Artificial DNA-based structures act like similar antennae, controlling the position of specific dye molecules that absorb light energy and channel it to a reaction center where it is converted into chemical energy. This work could pave the way for devices that can more efficiently use the most abundant energy source available to us – sunlight.
So what’s the next step for DNA nanotechnology? It’s hard to know, but with DNA, nature has given us a very versatile tool. Now it’s up to us to make the best use of it.