A low-cost sensor made from semiconducting plastic which has a “far simpler design” than existing sensors, has been developed by a team led by the University of Cambridge and King Abdullah University of Science and Technology (KAUST).

The hope is that this sensor could be used to diagnose or monitor a wide range of health conditions, such as surgical complications or neurodegenerative diseases.

According to the team, the sensor can measure the number of critical metabolites, such as lactate or glucose, present in sweat, tears, saliva or blood, and, when incorporated into a diagnostic device, could allow health conditions to be monitored quickly, cheaply and accurately.

"In our work, we've overcome many of the limitations of conventional electrochemical biosensors that incorporate enzymes as the sensing material," says lead author, Dr Anna-Maria Pappa of the University of Cambridge. "In conventional biosensors, the communication between the sensor's electrode and the sensing material is not very efficient, so it's been necessary to add molecular wires to facilitate and 'boost' the signal."

To build their sensor, Dr Pappa and her colleagues used a newly-synthesised polymer developed at Imperial College that acts as a molecular wire, directly accepting the electrons produced during electrochemical reactions. When the material comes into contact with a liquid such as sweat, tears or blood, it absorbs ions and swells, becoming merged with the liquid. This is said to lead to higher sensitivity than traditional sensors made of metal electrodes.

When the sensors are incorporated into more complex circuits, such as transistors, the signal can be amplified and respond to tiny fluctuations in metabolite concentration, despite the tiny size of the devices, the team adds.

According to the researchers, the sensor can be easily modified to detect a range of metabolites, such as glucose or cholesterol, by incorporating the appropriate enzyme, and the concentration range that the sensor can detect can be adjusted by changing the device's geometry.

"This is the first time that it's been possible to use an electron accepting polymer that can be tailored to improve communication with the enzymes, which allows for the direct detection of a metabolite: this hasn't been straightforward until now," explains Dr Pappa. "It opens up new directions in biosensing, where materials can be designed to interact with a specific metabolite, resulting in far more sensitive and selective sensors."

Since the sensor does not consist of metals such as gold or platinum, the team adds, it can be manufactured at a lower cost and can be easily incorporated in flexible and stretchable substrates, enabling their implementation in wearable or implantable sensing applications.

"An implantable device could allow us to monitor the metabolic activity of the brain in real time under stress conditions, such as during or immediately before a seizure and could be used to predict seizures or to assess treatment," continues Dr Pappa.

The researchers now plan to develop the sensor to monitor metabolic activity of human cells in real time outside the body. The Bioelectronic Systems and Technologies group where Dr Pappa is based is focused on developing models that can closely mimic our organs, along with technologies that can accurately assess them in real-time. The hope is that the developed sensor technology could be used with these models to test the potency or toxicity of drugs.