Flexible wearable biosensors based on graphene and conductive polymer will be reusable, low cost, and easy to manufacture. A high sensitivity to various chemical compounds will ensure the accuracy of the measurements.
Work on the creation of sensors is carried out on the basis of the SB RAS Institute of Semiconductor Physics named after A. V. Rzhanov under the guidance of a leading researcher at the Institute, Professor of the Department of Semiconductor Devices and Microelectronics at NSTU-NETI, Doctor of Physico-Mathematical Sciences, Professor Irina Antonova. Detailed results of the work have been published in the journals "Physical Chemistry", "Chemical Physics", "Russian Nanotechnologies", and "Successes of Physical Sciences". A patent has been obtained for the invention.
As Anna Buzmakova, a 2-year undergraduate student at the Faculty of Radio Engineering and Electronics at NSTU-NETI, an engineer at the Institute of Physics and Technology of the Siberian Branch of the Russian Academy of Sciences, notes, there are a huge number of different methods for diagnosing glucose that can be divided into two groups: methods that require the use of special equipment, and methods of personalized medicine for home use. Currently, there is considerable interest in flexible wearable sensors that can be used as miniature analytical devices. Special attention is being paid to the development of non—invasive biosensors, whose work is based on the use of a liquid other than blood, in particular, devices that analyze human sweat.
However, such sensors usually have a complex multilayer structure, which makes it difficult for sweat to penetrate to the sensor element and leads to a decrease in signal amplitude. In addition, sweat consists of 98% water, the remaining 2% includes about 250 chemical compounds that can interfere with the accurate detection of glucose. An additional limitation is the high cost of materials.
"The goal was to create flexible wearable biosensors for personalized medicine and to investigate the response of ultrathin layers when analyzing human sweat. The developed graphene/polymer composite PEDOT:PSS has become the basis for the production of inks that can print ultrathin conductive layers. The ink was applied to a flexible substrate using a 2D inkjet printer. Office paper was used as a substrate. This manufacturing method is a good alternative to expensive sensor manufacturing methods. The printed structures were being tested for use as wearable glucose sensors. The liquid under study was sweat secreted on the skin," said Anna Buzmakova, author of the thesis "Research and development of biosensors made of composite layers based on graphene and the conductive polymer PEDOT:PSS."
According to her words, the use of these sensors is promising in devices that read the signal and transmit it to the phone. Therefore, a reader for continuous data recording has also been developed. For testing, the sample was attached to the wrist, and the signal from the sensor was transmitted directly to the smartphone. Since the sensor is of a resistive type, its principle of operation was to change the electrical resistance when reactants interact with a sensitive element. When the sensor came into contact with the skin, sweat released onto the surface of the printed layers, adsorption of its components, chemical reaction of glucose decomposition and transfer of charge carriers (electrons) occurred, which increased the conductivity of the sensor. Thus, the dependence of the response of sensory structures on the current and concentration of glucose in human blood was observed.
The scientific novelty of the work lies in the fact that the creation of a conductive composite with a unique structure based on graphene and the PEDOT:PSS polymer opens up opportunities for the development of biosensors that are ultra-sensitive to various chemical compounds. The thickness of the sensitive layer, which does not exceed several tens of nanometers, allows you to see the signal using microscopic droplets of sweat released, for example, on the wrist. Sensitivity is important because it determines the absolute magnitude of the useful signal, the rate of its appearance after the start of testing, and, most importantly, the range of changes in the signal: the wider it is, the smaller the fluctuations in glucose can be measured.
The result of the work were sensors with high sensitivity made of a conductive graphene/polymer composite PEDOT:PSS. They are characterized by low cost and ease of manufacture. Their stability and the possibility of reusable use have been demonstrated. In addition, an application has been developed for transmitting a signal to a smartphone wirelessly.
Future plans include testing sensory structures in everyday conditions, establishing the specifics of their operation and range of applications. It is also an important task to calibrate the device at the beginning of its use and monitor the parameters during long-term wear.