What is a biosensor?
A biosensor is defined as an analytical device capable of performing qualitatively and semi-quantitatively analyte determination, employing the specific interaction between the analyte and the bioactive component used. Due to this interaction, the variation of a physical or chemical property of the bioactive element is converted into a measurable signal, through the appropriate signal transducer. The signal thus obtained, appropriately amplified and processed, will provide the analytical information required. The purpose of a biosensor is, therefore, to convert a chemical parameter (concentration of an analyte or group of analytes) into a digital signal.
A class of biosensors is based on the measurement of an electrochemical reaction directly or indirectly connected with the presence and the concentration of the target analyte. Much evolution in the detection system has happened in recent years, with one of the most important steps being the invention, development, and mass production of the so-called screen-printed electrodes (SPEs).
SPEs have soon become the center of research and industries attention, due to several reasons as their compact size which includes all the items necessary to perform electrochemical measurements -working electrode, reference electrode, and counter electrode-, low cost, high degree of personalization since different inks can be used to print each electrode composing the SPE resulting in different electrochemical properties, and ease of further functionalization, both with nanomaterials and biological components, such as enzymes, antibodies or DNA/RNA strands (Figure 1).
The most common model of SPE shows a concentric disposition of the three electrodes, with the working electrode at the center, with reference and counter electrode on the sides. The reference electrode is usually made of silver, while counter and working electrodes are commonly made using different carbon materials, produced from petroleum-derived precursors.
It can be then understood that, due to their large use both in research and everyday application, SPE use results in a significant consumption of materials coming from non-renewable, polluting sources. Indeed, it is estimated that the market for fully printed sensors will reach $4.5 billion by 2030 (Printed and Flexible Sensors 2020-2030: Technologies, Players, Forecasts; 2020).
Biosensors in EUCALIVA
Biosensor s.r.l. developed, within the frame of project EUCALIVA, a new electrode model, whose carbon inks come from a renewable resource, lignin, extracted from the wastes of Eucalyptus globulus tree processing in paper industries. The lignin, after appropriate treatment to make conductive nanocarbon materials, is used to produce inks and further screen-printer electrodes.
Biosensor has produced and patented (Basile, G.; Giardi, M.T.; Varani, G.; Zappi, D. Modello multiplo di sette disegni di elettrodi stretch per analisi elettrochimiche 2020) various designs for electrodes to be suitable for flexible and stretchable applications.
One example of such developed designs is inspired by the Eucalyptus globulus fruit (Figure 2).
A second developed design involves the use of curved contact traces to minimize the electrical noise upon stretching (Figure 3).
Such electrodes have proven their resistance to mechanical stress and thus can be used as wearable sensors, to monitor the health situation of clinical patients or significant parameters of athletes, both in real-time.
The electrodes have been printed on different plastic substrates, coming too from renewable resources, both flexible and stretchable, in both cases achieving electrochemical performances comparable to those obtained using electrodes produced using traditional inks.