The worlds of biological systems and electronics have collided, giving rise to a new class of technology that is an inspiring game-changing innovation. Today, bioelectronic devices are already making waves in applications from brain-inspired computing to ultrasensitive diagnostics.
Organic electrochemical transistors (OECTs) are a prime example. These thin-film transistors are semiconductors that act as amplifiers to detect trace amounts of biomarkers such as ions, metabolites and DNA. According to experts, OECTs be the stepping stones into a future of personalised medicine; one with compact wearable devices to track health, diagnose diseases and administer medication.
Dexter Tam, a Scientist from A*STAR’s Institute of Sustainability for Chemicals, Energy and Environment (ISCE2), said that the challenge lies in making OECTs more flexible and multifunctional to facilitate their adoption in different medical devices.
“Like any other transistor-based devices, both p- and n-type semiconductors are needed for high device performance. A dream material would be ambipolar as it will greatly simplify the device architecture and thus lowering cost," Tam explained.
However, ambipolar semiconductors are hard to come by as they must fulfil certain conditions: they must have suitable highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels, as well as high charge carrier mobilities.
While in graduate school, Tam worked on bulk heterojunction (BHJ) organic solar cells where both p- and n-type semiconductors are mixed to form a blend film that is ambipolar. “It occurred to me that the same idea can be applied in OECTs to achieve ambipolarity since the new ladder-type conjugated polymers (LCPs) I am working on form nanoporous fibrillar networks, which could be an important ingredient in forming ambipolar BHJ OECTs,” he added.
An organic electrochemical transistor (OECT) device with a bulk heterojunction (BHJ) made from a blended ambipolar polymer.
In collaboration with colleagues from A*STAR’s Institute of Materials Research and Engineering (IMRE); Nanyang Technological University, Singapore; the National University of Singapore; and Princeton University in the US, Tam put his LCP idea to the test by fabricating the first BHJ-based OECTs.
Results from their study disproved some common misconceptions in the field, including that glycolated side chains are necessary for effective ion transport. Instead, nanostructures in the LCPs serve a similar function, which the team validated in a real-world medical application. They also integrated their OECT into a device that measures minute changes in voltage during eye movements.
“Overall, the BHJ complementary inverter shows outstanding performance in tracking eye movement, highlighting its great potential as a signal amplifier in wearable integrated systems,” Tam said.
The team’s BHJ OECTs possess a suite of favourable properties—they are highly sensitive, stable, easy-to-manufacture and non-toxic, to name a few. “This could usher in affordable and durable point-of-care diagnostics, making advanced healthcare more accessible to the general population,” said Tam, whose team is currently laying the foundations to commercialise the technology.
“I am also keen to develop more novel LCPs to be used in electrocatalysis, energy harvesting and storage applications,” Tam added.
The A*STAR-affiliated researchers contributing to this research are from the Institute of Sustainability for Chemicals, Energy and Environment (ISCE2) and the Institute of Materials Research and Engineering (IMRE).
