Researchers Develop New Transistor Technology to Improve Biochemical Sensing Outside the Lab

Recently, researchers have made significant strides in the field of biochemical sensing by developing a new transistor technology that can work in conjunction with biomolecule sensors to amplify signals by up to 1000 times, which could pave the way for biosensors with higher selectivity and sensitivity, while also allowing for portable biosensors and wearable technology that could be used for early detection and intervention in medical care, wound monitoring, and addressing the rise of antibiotic resistance. 

This technology is particularly noteworthy as it could help overcome some of the significant challenges faced by traditional sensing technologies, such as spectroscopy and PCR tests, which often require laboratory conditions, as well as provide greater opportunities for the integration of aptamers and organic electrochemical transistors (OECT) to improve the accuracy and efficiency of electrochemical signal detection. What challenges does biochemical sensing introduce, what did the researchers develop, and how could this technology be used to improve medical care?

What challenges does biochemical sensing introduce?

Over the years, researchers have developed methods for detecting trace amounts of compounds. Some of these methods involve advanced spectroscopy utilising extremely sensitive photoreceptors, while others have taken advantage of exponential replication (such as PCR tests, where a single strand of target DNA is rapidly copied to make it easier to detect in a sample). 

However, most of these methods have involved laboratory conditions which require strict environmental controls. Trying to achieve the same level of sensitivity on a wearable device far away from a lab is highly challenging, to say the least. Portable biosensors have been developed, but these typically require chemical concentrations several orders of magnitude more than what a lab would require, meaning that their use is limited. 

Another challenge that biochemical sensing can face is selectivity. While numerous sensing technologies have been developed, only those that can bind to a specific molecule (such as enzymes and DNA) can detect specific biomolecules. Thus, sensors that operate on pH, electrical charge, or other more generic testing methods cannot distinguish between different molecules if present in a sample. This problem becomes more complex when considering that even the simplest organisms on earth have complex biology consisting of thousands of different biomolecules. 

When considering these challenges, it quickly becomes clear why researchers continue to struggle with creating advanced sensors capable of measuring specific biochemical reactions outside of the lab. 

Researchers develop a transistor capable of amplifying weak biochemical signals

Recognising the challenges faced with biosensing, researchers from Northwestern University have recently developed a new transistor technology that can work in conjunction with biomolecule sensors to amplify signals by up to 1000 times. 

To create their sensor, the researchers first turned to aptamers in order to obtain a high degree of selectivity in their sensors. An aptamer is a single strand of DNA that is able to bind to specific molecules and, upon binding, generate electrochemical signals. The advantage of using a DNA-based sensor doesn’t just lie in a high degree of selectivity but also that DNA can readily be programmed by researchers. 

Fig. 1: Design concept of ref-OECT-based E-AB sensor.

a) The ref-OECT-based E-AB sensor is depicted in a schematic image. b) A testing scheme for the ref-OECT-based E-AB sensor is provided, where the output of the channel current in OECT can be monitored during the operation of the E-AB sensor in the 3-electrode setup. c) The sensing mechanism of the ref-OECT-based E-AB sensor for TGF-β1 involves a conformational change in the aptamer, causing the methylene blue (MB) redox reporter to move away from the gate electrode surface, resulting in a decrease in gate current (IG) and smaller channel current modulation (IDS). Conversely, without the presence of TGF-β1, the MB redox reporter is closer to the gate electrode surface, leading to a high gate current and a larger channel current modulation.

However, aptamers alone cannot be used reliably for detecting trace amounts of a biomolecule as the resulting electrochemical signal is extremely weak. These signals can be detected in a lab, but only under controlled conditions. To solve this challenge, the researchers have developed a new transistor technology that is able to amplify the signal from electrodes designed to detect the electrochemical signature from aptamers by around 1000 times. The type of transistor used by the researchers is called an Organic Electrochemical Transistor (OECT), and these types of transistors have the ability to convert ion flow into an electron flow, which is why researchers often turn to these types of transistors in biochemical detection applications. In the case of the researchers, their development involved the integration of electrodes and aptamers into the OECT while also incorporating them to help improve sensitivity.

To learn more about how the transistor developed by the researchers works, you can read the full Nature article here (Open Access).

How could this technology be used to improve medical care?

While the ability to detect small traces of biomolecules has numerous applications, one application that has the researchers of the new sensor excited is medical care, specifically, healing. When injured, the human body undergoes thousands of biomolecular interactions, whether it is signalling cells to multiply, ordering white blood cells to fight off infection, or diverting more resources to the area to quicken healing. 

However, if a wound becomes infected, it is possible for the wound to become septic, and this can lead to blood and tissue poisoning. From there, necrosis can set in, with flesh turning black as it dies, and this often requires amputation. Worse, the injection can spread around the body, infecting other areas, and with the rise of antibiotic-resistant bacteria, this can quickly become a death sentence. 

If the sensor developed by the researchers can be miniaturised and made portable, it is possible for such sensors to be integrated into dressings for wounds that can actively monitor the smallest biochemical signals. Thus, a wound that becomes infected would be able to alert medical professionals at an extremely early stage, allowing for medical intervention to prevent further deterioration.

Overall, what the researchers have developed here is truly exciting, having an extremely wide range of applications. The next step for the researchers would be to integrate this new technology into a wearable capable of monitoring an injury or wound.