A researcher at the University of Nebraska-Lincoln is one step closer to developing a new type of transistor chip that uses the biological response of organisms to drive electrical current through the device, revealing cell activity with unprecedented sensitivity. Ultimately, this "living" chip can enable faster and simpler sepsis diagnosis, clarify the understanding of antibiotic resistance, and promote efforts to develop neuromorphic devices that mimic the human brain.

In a recent article published in ACS Applied Nano Materials, Ravi Saraf detailed the micro-network of self-assembled necklaces made of gold particles developed by his team. Each network spans about 25 microns, which is about a quarter of the diameter of a human hair. Once connected, these networks act as current conduits, which can regulate current to form transistors.

The structural complexity of the network makes the transistor's response to external stimuli approximately 1,000 times higher than today's state-of-the-art metal devices.

The research marked the first use of a gold necklace structure in a transistor, and this method allowed Saraf's team to overcome long-standing obstacles in the physical field of the device. So far, scientists have relied on the so-called Coulomb blockade effect (a method of controlling current by charging certain nanoparticles with a single electron) to develop small, highly sensitive metal transistors with low power requirements. But this process can only work at an extremely low temperature of approximately minus 325 degrees Fahrenheit, which limits its application.

The necklace-like form circumvents this problem by introducing a complicated network that determines the channel through which the current can pass. Saraf likens this setting to the thousands of interstate highways, highways, streets, and dirt roads that connect the east and west coasts of the United States. Under the traditional Coulomb blockade method, the "traffic flow" or current is adjusted by setting small roadblocks in the form of single electron charges on most major channels. But at room temperature, the obstacle is overcome, eliminating the impact.

Saraf's innovation achieved a more effective method of traffic flow control: opening and closing some network transmission channels.

"The roads are always there, but what we are doing is regulating the flow of traffic by controlling the roads that are being used," said Saraf, Lowell E. and Betty Anderson Distinguished Professors of Chemical and Biomolecular Engineering. "Now it’s a whole set of additional road participation, and the current has increased a lot. By opening up more roads, you can make a device with the same current transmission characteristics as the low-temperature all-metal transistor with Coulomb blocking, but it works at room temperature and the current The adjustment can be more than 1,000 times higher."

Saraf says that the architecture of the network can be customized to introduce additional properties, such as electroluminescence or magnetism, through a process called nano-bonding. This gives the necklaces memory, allowing them to function in increasingly complex neuromorphic devices. These tools simulate the brain and enhance artificial intelligence capabilities.

He said that one of the most exciting findings of this research is the key phenomenon of controlling transistors. Unlike Coulomb block devices, the tipping potential of the turn-on current in the Saraf transistor does not change during gate control. His team showed that with the opening and closing of the channel, the network topology is unchanged. This universal behavior, together with the memory induced by nano-cement, may one day lead to devices with multiple terminals that can act as analogs to human neuronal networks.

The function at room temperature opened the door for the Saraf team to deploy another new concept: put living cells that require water and cannot survive extremely low temperatures on the chip, and use their biological response to drive current through the device.

"When you give living cells something, such as drugs, nutrients, or antibiotics, it causes biochemical activities, and these reactions change the surface potential of the cells," Saraf said. "This is the same as applying an external voltage to control the current."

One way of using the device is as a building block for a chip, which consists of 10 to 12 transistors, each of which is connected to a single cell through a micro-hole. When a cell colony is placed on the chip and then stimulated, the cells in the well will control the current. Scientists can analyze electrical currents to find out what is happening in the population, including key information about communication between cells.

The chip can pave the way for a more detailed understanding of antibiotic resistance, which occurs when bacteria and fungi work together as a team and learn to avoid drugs that should kill them. By observing the electric current patterns triggered when cells are exposed to different antibiotics, scientists can learn more about how cells evade treatment-potentially reducing the $55 billion that the United States spends on antimicrobial resistance each year.

Saraf said he believes that the chip may have a profound impact on the fight against sepsis, which is a dangerous extreme response to infection. A timely decision on the best combination of antibiotics to treat this disease may have a life-and-death impact. Today, this determination requires cell culture, which takes several days. In the future, Saraf's technology can shorten this time frame to a few hours: the bacteria in the blood will be placed on the chip and exposed to a set of antibiotics. By evaluating the current output, the doctor can determine the ideal treatment plan.

Another potential application is machine learning. Scientists can use the chip as an "artificial nose", linking the cumulative response of cell populations to toxic chemicals and physical conditions in a complex environment.

The work of the team is funded by the Army Research Laboratory of the US Army Combat Capability Development Command, which focuses on the biological applications of transistors.

Saraf is affiliated with the Nebraska Center for Materials and Nanoscience, where his team made some of the chips. Husker students Abhijeet Prasad and Aashish Subedi contributed to this work.

Certain parts of this website work best with JavaScript enabled.