Screen-printed electrodes for biosensors are revolutionising point-of-care applications

By Dr. Erika Rebrosova, Electronic Materials Technology Manager at Sun Chemical Corp

Biosensor applications

The end applications for electrochemical (EC) biosensors are shown in Figure 1. In medical diagnostics and health monitoring, printed EC biosensors are used to monitor glucose levels in diabetic patients, detect pathogens, and identify biomarkers for diseases such as cancer and cardiovascular conditions. They enable immediate analysis of biological samples, such as blood or saliva, allowing for quick decision-making and timely medical interventions. In the pharmaceutical industry, they are employed for drug development and monitoring therapeutic drug levels in patients. In environmental monitoring, these biosensors help detect pollutants, heavy metals, and pesticides in water and soil, ensuring environmental safety and compliance with regulations. The food and agriculture industry benefits from screen-printed biosensors by using them to detect contaminants, pathogens, and allergens, thereby ensuring food safety and quality. Portability and ease of use make them ideal for on-field testing, providing quick and reliable results without the need for complex and large laboratory equipment.

Figure 1. Example end-applications of electrochemical biosensors

Printing in manufacturing of biosensors

Among printing processes, screen printing is the dominant process in electronics manufacturing, including manufacturing of electrodes for biosensors, where it has been used for many years. Biosensors with screen-printed electrodes (SPEs) have a wide range of applications due to their versatility and cost-effectiveness. Screen printing is ideally suited for mass production, which is essential for meeting the high demand for medical and environmental biosensors. Screen printing has proven its value due to easy scalability during the recent pandemic and the ensuing increase in demand for biosensors for rapid Covid-19 testing. Screen printing is an additive printing process offering high precision, accuracy, and consistency; all of which are important for reliability of an analytical device.

SPEs are most often used in the electrochemical (EC) type of biosensors, where high sensitivity and selectivity is needed for accurate detection of various analytes even at low concentrations. There are special considerations for designing and processing materials for EC sensing. The electrode surface is the place of interaction between an analyte and sensor cell. Materials for sensing electrodes are required to induce an electrical response due to chemical and biological reactions on the electrode surface. Therefore, the surface quality, functionality, and high consistency of printed electrodes is of critical importance. The electrical response can be, for example, in the form of voltage potential difference, electrical current levels, or conductivity/impedance changes. EC performance requirements also need to coincide with the process requirements for screen printing, like having suitable rheology, curing dynamics, processing stability, reliability, and biocompatibility.

The single-use blood-glucose test strip is the best-known example of an electrochemical biosensor device. While the “finger-prick” technology may appear out-of-fashion compared to the newer devices such as insulin pumps or continuous glucose monitors (CGMs), the test strips are often used alongside higher-tech monitors and are therefore still an essential part of diabetes management. SPEs are used for both single-use glucose test strips and CGM sensors.

Screen-printed EC biosensors are revolutionising the point-of-care (POC) industry by offering accessible, cost-effective, and efficient healthcare solutions. This technology not only reduces the dependency on centralised laboratories but also enhances and accelerates patient care by delivering results in real time. They are designed to be portable and user-friendly, making them ideal for use in clinics, homes, and even remote locations. Additionally, using EC biosensor devices for biomedical analysis is considered less invasive and less stressful for the patient/user.

In addition, recent advances in screen printing technologies, for example high-resolution capable emulsions, high open area stainless steel meshes, and fine-line printable functional inks, enable miniaturisation of sensor electrodes for more advanced sensor designs. Smaller footprint and thinner sensors are ideal for integration into wearable devices. Higher electrode density is needed for multiplex biomarker detection on a single transducer for POC biosensor applications.

SunSens materials solutions from Sun Chemical

Sun Chemical is a leading manufacturer of inks, coatings, and pigments, supplying a diverse range of products to numerous industries. In electronics applications, Sun Chemical’s materials are used, for example, in the manufacturing of printed circuit boards, advanced solar cells, flexible switches and displays for human-machine interface, and a variety of printed biosensors used for medical diagnostics, health monitoring, environmental monitoring, and food safety.

The SunSens product range, designed for EC biosensor applications, includes a wide range of conductive inks for screen-printed electrodes (SPEs), such as working, counter, and reference electrodes. Other materials on offer are dielectric or insulator pastes, which are used in the EC sensor construction to precisely define sensing areas and insulate and protect the sensor’s circuitry. When selecting materials for SPE-based electrochemical sensors, it is important to find the best balance between optimum sensitivity, signal response, processability, reliability, and cost.

The key functional materials for EC biosensors are conductive pastes for working electrodes, as this is the primary detection surface. Figure 2 shows a variety of SPE designs printed with SunSens pastes.

Figure 2. screen-printed electrodes

SunSens carbon conductive pastes and mediated carbon pastes are suitable for working electrodes used in multiple electrochemical techniques and detection methods. The pastes based on precious metals, such as gold and platinum, are used for immuno-electrochemical assays or applications where high conductivity, inertness, and oxidation resistance are important. For reference electrodes, Silver/Silver Chloride (Ag/AgCl) pastes with different ratios of Ag-to-AgCl are available to accommodate the requirements of various EC sensors designs and detection methods.