Tag Archives: circuit

Heat-free metallic print can form electronic circuits on soft surfaces (flowers, gelatin)

Martin Thuo of Iowa State University and the Ames Laboratory can show you several remarkable photos in his collection: a curled sheet of paper with a LED display or a rose with metal traces printed on a petal. This isn’t an artistic project — Thuo is working on a new technology which allows printing conductive metallic lines on all kinds of materials, from a wall to a leaf.

This could be a game changer.

Image credits: Martin Thuo.

The technology features liquid metal (alloys of bismuth, indium, and tin) and is remarkable for multiple reasons. For starters, it’s capable of producing extremely small particles, about 10 millionths of a meter across. The resulting print is also not hot, which means you can print it on anything you want — including living things.

The printed metal acts like a quickly-solidifying weld, creating conductive, metallic lines and traces which can be used for electronic circuits.

“This work reports heat-free, ambient fabrication of metallic conductive interconnects and traces on all types of substrates,” Thuo and colleagues write in a recent study.

Through the ‘printing’ process, the metal inside flows and solidifies, creating a heat-free weld or, in this case, printing conductive, metallic lines and traces on all kinds of materials — everything from a concrete wall to a leaf.

The technology could have numerous applications. It could be used to print sensors to measure the growth and state of crops (assessing whether everything is going smoothly, or if they require more water or are being attacked by pests). Similarly, the sensors could be used to monitor the structural integrity of a building. The technology has also been tested in this regard. The researchers used a paper-based setting as a base for the sensor, and the sensor read changes in electrical currents when the paper was curved. Researchers say that, ultimately, the approach could also be used for medical sensors or models for biological tissues (since it can also be printed on soft surfaces such as gelatin). All this is done without damaging the base, even when it’s a living biological system.

Printed electronic traces on gelatin. Image credits: Martin Thuo / Iowa State University.

Initially, this started as a teaching exercise. Thuo wanted to give his undergrad students something to work on that would be both useful and fun.

“I started this with undergraduate students,” he said. “I thought it would be fun to get students to make something like this. It’s a really beneficial teaching tool because you don’t need to solve 2 million equations to do sophisticated science.”

Now it’s grown spectacularly — the university has even sponsored Thuo’s lab with start-up funds to continue working on the technology.

“The students discovered ways of dealing with metal and that blossomed into a million ideas,” Thuo said. “And now we can’t stop.”

The study was published in the journal Advanced Functional Materials.

Scientists tested a DNA circuit capable of splitting and combining current, much like an adapter that can connect multiple appliances to a wall outlet. Credit: Limin Xiang.

Scientists build electrical circuit out of four-stranded DNA

Besides carrying the genetic blueprint for all living organisms, DNA is also a  versatile building block for practical affairs. Scientists are experimenting, for instance, with DNA as a storage device. One promising method can encode 215 petabytes of data — twice as much as Google and Facebook combined hold in their servers — on a single gram of DNA. Now, American researchers have found a way to use DNA in microelectronic circuits after they showed how to design, create, and use a DNA circuit capable of splitting and combining current. It works much like an adapter that can connect multiple appliances to a wall outlet.

Scientists tested a DNA circuit capable of splitting and combining current, much like an adapter that can connect multiple appliances to a wall outlet. Credit: Limin Xiang.

Scientists tested a DNA circuit capable of splitting and combining current, much like an adapter that can connect multiple appliances to a wall outlet. Credit: Limin Xiang.

DNA has remarkable self-assembly properties, which scientists previously exploited to great effect to assemble graphene transistors and to design new drugs. This works rather easily because the molecule’s four nucleotide bases (A, T, C, and G) can be programmed to self-assemble into the iconic double-helices, snapping together like matched puzzle pieces, A always bonding with T and C with G. Indeed, various 2-D and 3-D DNA structures have been synthetically designed by scientists in the past using this straightforward principle.

The double-helix molecule can also conduct electric charge over considerable distances. Combine this with self-assembly and you’ve got a very promising candidate for niche applications in electronics such as nanobots, photonic devices, or various tiny electronic circuits.

“The ability of DNA to transport electrical charge has been under investigation for some time,” said Nongjian “N.J.” Tao, a co-author of the new study researchers at Arizona State University. “Splitting and recombining current is a basic property of conventional electronic circuits. We’d like to mimic this ability in DNA, but until now, this has been quite challenging.”

There’s one problem though: In its most common duplex form, DNA poorly splits current into three or more terminals as the charge tends to dissipate at the splitting junctions or convergence points. This doesn’t bode well for electronics applications. However, scientists at Arizona State University, New York University, and Duke University, used a special form of DNA known as G-quadruplex (G4) DNA. As the name implies, G4-DNA is composed of four rather than two strands of DNA, which are rich in the nucleotide guanine (G).

“DNA is capable of conducting charge, but to be useful for nanoelectronics, it must be able to direct charge along more than one path by splitting or combining it. We have solved this problem by using the guanine quadruplex (G4) in which a charge can arrive on a duplex on one side of this unit and go out either of two duplexes on the other side” says Peng Zhang, an assistant research professor of chemistry at Duke University and a co-author of the new study.

“This is the first step needed to transport charge through a branching structure made exclusively of DNA. It is likely that further steps will result in successful DNA-based nanoelectronics that include transistor-like devices in self-assembling ‘pre-programmed’ materials,” Zhang says.

Guanine-rich quadruplex DNA occurs naturally, a configuration that can be found in telomeres — the ends of linear chromosomes, which play a key role in aging. Some research is targeting G4 quadruplexes with drugs for therapeutic reasons. Previously, research showed that DNA quadruplexes in telomeres decrease the activity of an enzyme responsible for telomere length and which is involved in 85 percent of all cancers.

Among other things, G4 DNA — stacked guanine bases that form hydrogen bonds with their immediate neighbors — have improved charge transport properties. This allowed the researchers to used G4 DNA and double-stranded wires to form the terminals for either splitting or merging electrical current flow. Previously, scientists who tried to make Y-shaped electrical junctions with conventional double-helix DNA failed because of the inherent poor charge transport properties.

The conductance of charge of the G4-DNA nanostructure was measured with a scanning tunneling microscope (STM), whose tip came in and out of contact with the molecule, breaking and reforming the junction while the current through each terminal is recorded. This “break junction” method allowed the researchers to fine-tune all sorts of prototype circuits to achieve maximal charge transport.

Besides opening the doors for innovative G4-based electronics, the paper published in Nature Nanotechnology sheds new light on the way nature maintains genetic integrity within cells, and could also teach us how various diseases break down DNA error-correcting mechanisms.

Duke scientists Song and Reif made an analog DNA circuit inside a test-tube. Credit: John Joyner

Scientists make DNA analog circuit that can add and substract

Duke scientists Song and Reif made an analog DNA circuit inside a test-tube. Credit:  John Joyner

Duke scientists Song and Reif made an analog DNA circuit inside a test-tube. Credit: John Joyner

The blueprint molecule that codes every living thing on the planet was exploited by researchers to make something far less glamorous, but still very exciting: a simple calculator. The Duke University researchers toyed around with DNA and managed to make an analog circuit out of it that can do basic mathematical operations like addition and subtraction.

Previously, scientists made DNA computers that could do things like calculate square roots or even play tic-tac-toe. These projects were digital-only, though. The DNA circuit made at Duke University is all analog, meaning it doesn’t need an additional hardware that converts the signal into 1s and 0s.

An analog computer is a form of computer that uses the continuously changeable aspects of physical phenomena such as electrical, mechanical, or hydraulic quantities to model the problem being solved. In our case, instead of measuring changes in voltage as most analog computers and devices do, the DNA circuit reads the concentrations of various DNA strands as signals.

DNA has this natural ability to zip and unzip, as its nucleotide bases can pair up and bind in predictable ways. This makes it an excellent material for logic gates.

First, Duke graduate student Tianqi Song and computer science professor John Reif synthesized short pieces of DNA, which were either single-stranded or double-stranded with single-stranded ends, then mixed them together. What happens next is a single DNA strand will perfectly bind to the end of a partially double-stranded DNA. In the process, the previous bond strand detaches — like someone cutting in on a dancing couple.

The now orphaned strand can now pair up with other complementary molecules in the same circuit, creating a domino effect.

acs_synthetic_biology

Credit: ACS Synthetic Biology

As the reaction reaches equilibrium, the researchers measure concentrations of outgoing strands to solve math problems, based on input concentrations and the predictable nature of locking DNA. And if this sounds like it takes a lot of time, you’re right. Unlike a silicon-based computer which can perform a simple math operation in an instant, the DNA circuit takes hours.

So why are scientists even working on this? Well, it’s not just for the sake of experimentation, although this too is well worth it sometimes. I mean, a computer made from DNA? That just sounds very exciting to try, besides the practical applications which we might uncover by working in such an obscure field.

The other thing that makes this sort of research novel is that unlike previous attempts, the circuit is analog. The test-tube DNA circuit can also operate in wet environments and can very tiny, unlike a conventional digital computer. Theoretically, analog DNA circuits can be used to make some very sophisticated operations such as logarithms and exponentials — this is next on the list, for the Duke team. There’s also hope that at some point these circuits could be embedded in bodies and release DNA and RNA when a specific blood marker value lies outside a given range.

Findings appeared in the journal ACS Synthetic Biology.