10-02-2022 | By Robin Mitchell
Recently, researchers have developed a sensor using 3D transistors that can record signals sent between cells to further humanity's understanding of biological processes. What challenges do sensors face when recording the microverse, what did the researchers develop, and how could it be used to improve future medical science?
Any engineer worth their salt understands the multitude of challenges faced when measuring very small things. Voltage signals whose size is similar to the nominal voltage noise can be extremely tricky to isolate. Any signal that falls below the noise threshold cannot be determined reliably. The same applies to digital signals such as analogue-to-digital converters; the least significant bit can be unreliable, which is why most engineers will only take the top few bits (for example, a 12-bit ADC will often be used as an 8-bit ADC).
But it's not just the signals that can be challenging to measure; even physically small things can prove to be horrendously complex. For example, researchers can still not measure individual molecular reactions reliably due to the atomic size of molecules. The same applies to cellular activity; it is very easy to probe a mass of tissue and detect electrical signals, but trying to do so on individual cells is a difficult feat. Not only are the cells themselves microscopic, but the signals they produce are minuscule.
If researchers could measure activity from individual molecules or cells, it would allow them to properly document the behaviour of individual discrete parts instead of the behaviour of a group of parts, which allows for the correct understanding of how that part works. For example, seeing an individual oxygen molecule react with a glucose molecule can shed light on the physical process of bonding.
Recently, researchers from the University of California have developed a new sensor built from 3D transistor structures that can measure the electrical signals of individual cells. One of the researchers involved with the project, Dr Yue Gu, used a technique called "pop-up" architecture that he had developed during his postdoctoral studies. The method utilises conventional cleanroom microfabrication to create 3D structures that initially start out as 2D and then can be expanded into a 3D design.
The electrical potential changes on a cell membrane active the terminals of the 3D transistors. The increase in the electrical activity of a cell directly corresponded to an increase in current flow. The use of the transistor array allows for the measurement of different electrical potentials around the same cell, essentially providing a 3D detection grid on the surface of a cell.
Using this technique, arrays of 3D transistors were developed to measure electrical signals generated by cells. Furthermore, it can also measure signals sent across cells, allowing researchers to explore messaging between discrete cells.
By looking at how cardiovascular cells communicate, researchers can develop better treatments for cardiovascular diseases and design better equipment for maintaining regular cardiovascular activity (such as a smart pacemaker). Furthermore, understanding the electrical relationship between individual cells of a patient may also help to provide better dietary changes that can improve cardiovascular activity.
The promising results of the research have now led the team to explore cellular activity between other cells, including neurons in the brain. The team also plans to utilise their sensors directly in-vivo, hoping that they will be able to record activity in real-time in living tissue.
But what does this mean about future possibilities? It is hard to predict exactly how it can be used due to the complex nature of biology, but understanding how cells communicate could lead to the possibility of targeted cancer treatments and regenerative cell growth. In the case of cancer, sending and receiving signals throughout tissue may allow the body to target the destruction of cancer cells by either signalling the cell to die or signalling the body to attack the cancer cells.
In the case of regenerative cell growth, it has been documented that electrical current can stimulate cells to repair damage (such as in bones). Thus the sensor technology could be used to direct electrical signals into damaged areas.