Ultrathin organic-inorganic device shows promise for wireless biomarker monitoring

In recent years, electronic engineers have developed a wide range of wearable and implantable devices that can detect and record biological signals. These devices can help track various physiological processes, such as heart rate, arterial pulse, sleep patterns, or calories burned during the day, which can be useful for sports and healthcare applications.

Organic electrochemical transistors (OECTs), electronic components based on flexible organic materials that can amplify biological signals, have shown promise for developing wearable technologies to monitor more subtle health-related signals. For example, these flexible transistors could collect information on glucose, lactate, cortisol, and pH levels, as well as neurotransmitters and metabolites, which could prove very useful for diagnosing or monitoring specific medical conditions.

Despite the advantages of OECTs, the data they collect must then be transmitted to external devices, which requires the use of wireless communication circuits. These circuits are typically based on inorganic and rigid materials, which can increase the size and thickness of the devices, while reducing their mechanical flexibility.

Researchers at the Korea Institute of Science and Technology (KIST) have recently developed a new wireless device that can monitor various biomarkers, including glucose, lactate, and pH levels. The device, presented in a paper published in Natural electronicseffectively integrates components based on organic and inorganic materials, resulting in good performance and excellent mechanical stability, with an overall thickness of 4 μm.

“We present an ultrathin organic-inorganic device for wireless optical monitoring of biomarkers, such as glucose in sweat and glucose, lactate, and pH in phosphate-buffered saline,” Kyung Yeun Kim, Joohyuk Kang, and colleagues wrote in their paper. “The conformable system integrates an organic electrochemical transistor and an inorganic near-infrared micro-light-emitting diode on a thin parylene substrate.”

The device developed by Kim, Kang, and their colleagues consists of OECT biochemical sensors integrated with inorganic micro-light-emitting diodes (μLEDs). The team fabricated the OECT sensors by patterning gold electrodes and a polymer blend of two ionomers (PEDOT:PSS) onto an ultrathin parylene substrate.

The sensor was then connected to the inorganic-based μLEDs. OECTs can detect specific biomarkers because the current flowing through them changes depending on the concentration of these biomarkers in the sensor environment. The changes in the OECT channel current in turn modulate the light radiating from the μLED, allowing the wearable device to monitor the biomarkers.

“The channel current of the transistor changes depending on the biomarker concentration, which changes the irradiance of the light-emitting diode to enable biomarker monitoring,” Kim, Kang, and colleagues wrote. “We combine the device with an elastomeric battery circuit to create a wearable patch. We also show that the system can be used for near-infrared image analysis.”

In initial tests, the 4 μm thick device for biomarker monitoring has achieved very promising results, exhibiting high transconductance (g_m) of 15 mS and excellent mechanical stability. The team found that the device could also be used to analyze near-infrared images and to predict glucose, lactate and pH concentrations from these images.

In the future, the new device could be tested and improved, which could contribute to the development of new medical technologies. The device could also be adapted to be powered by flexible batteries or solar cells, resulting in a completely chipless detection system.

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