Innovative solutions for printed electronics and biocompatible electrodes in medical diagnostics and sensors

Our research in printed electronics and biocompatible electrodes is opening up exciting opportunities in medical diagnostics and sensing. Using innovative printing technologies, we can produce tailor-made electrodes for biosensors and cell model characterisation in microfluidics, among other applications. The direct printing approach offers significant advantages:

• Cost and time savings: The printing processes used, such as inkjet, aerosol jet and screen printing, avoid complex thin film processes (including masks, etching steps, ...) and are material saving.
• Flexibility and rapid prototyping: By using printing processes, prototypes and test versions of printed electrodes can be produced quickly and improved iteratively (rapid prototyping).
• Customisation through digital printing: Inkjet printing in particular allows electrode geometries and sizes to be easily adapted via software to meet the requirements of different biosensors.
• Scalability: The technological approach offers high scalability, i.e. large quantities of electrodes can be produced cost-effectively and in a short time (roll-to-roll production).

Fraunhofer IKTS has developed special inks and pastes that can also be printed on flexible substrates such as plastic or paper, enabling integration into wearable or flexible biosensor platforms. Our solutions for printable materials cover a broad spectrum:

• Gold, Platinum, Palladium for Electrodes and Sensitive Layers Our gold and platinum inks in the form of printed electrodes have been successfully tested several times for biocompatibility according to DIN EN ISO 10993-5 / -12 (Biological evaluation of medical devices - Part 5: Tests for in vitro cytotoxicity and Part 12: Sample preparation and reference materials).
• Carbon and silicon as cost-effective and alternative electrode materials.
• Other metals such as silver and copper for electrical wires and contacts.
• Marking inks for permanent marking and digital traceability of metallic or ceramic components using data matrix codes when other marking solutions such as laser marking or engraving are not an option.
• We also develop special formulations on customer request, e.g. composites with glass.
• The properties of all materials are tailored to the specific printing process and customer requirements.

We use modern, high-quality methods and processes for our research and development. These include:

• High-precision analysis to determine key material properties such as rheology and viscosity, surface tension and substrate wetting, particle size and sedimentation stability.
• Advanced inkjet (Dimatix DMP, Pixdro LP50, Ceradrop F-Series) with printheads from 2.4 pL to 80 pL, aerosol jet (Optomec M3D) and screen printing (Ekra E5, X5, HX2).
• Innovative sintering processes for the functionalisation of printed conductors using continuous line laser treatment (HDPL) and flash lamp processes (FLA).

Thanks to these benefits, printed electronics for biosensing enables efficient, flexible and cost-effective production of electrodes that enable precise and reliable detection of biochemical signals. In this way, we contribute to the research and development of innovative medical diagnostic procedures.

Since 2010, we have been supporting numerous research groups and industry with our inks and pastes. Our materials have been tested for the following applications:

• In microfluidics, printed gold electrodes were used as electrochemical sensors for dissolved oxygen and reactive oxygen species to monitor hypoxia of cultured intestinal bilayers in a microfluidic platform. In another application, a liver microphysiology system with embedded sensors has been developed to enable real-time monitoring of fibrosis development or zonation of liver function.
• Micro heating plates (150x150 µm²) on polymeric film for portable gas and chemical sensors, temperature measurement, thermal actuators and microfluidics. Printed gold electrodes result in very low power consumption (heating at approx. 12 °C/mW and a constant operating temperature of 250 °C with only 22 mW).
• Heart muscle models printed with gold electrodes underneath allow direct electrical measurement of heart muscle cell groups for drug testing. Until now, only light microscopy was available to evaluate the beating effects of such cell models.
• Aptamer functionalisation of printed gold electrodes on low-cost polymer films. Depending on the type of aptamer, it is possible to detect a variety of different bioanalytes such as proteins, peptides, antibodies or nucleic acids. For example, we have detected the enzyme alpha-thrombin electrochemically using a gold electrode functionalised with an aptamer and methylene blue.
• Smart catheters with improved sensitivity of miniaturised tip electrodes by printing thin layers of our platinum ink. Orders of magnitude reduction in electrical contact resistance for electrochemical measurements compared to standard electrodes.
• Environmental sensors for measuring temperature and humidity by printing interdigital or resistance electrodes with silver ink.
• Highly sensitive pH sensors based on polymer-functionalised gold electrodes (PANI, PSS, PPy) or IrOx-coated platinum electrodes on flexible substrates showed linear super-Nernst behaviour and highest sensitivity values.
• Ozone sensor for oxygen-ozone injection therapy based on printed amperometric and impedimetric sensors with gold electrodes. Special attention has been paid to the assessment of biocompatibility according to the international standard ISO 10993.
• Fast, sensitive and cost-effective detection of bacteria using organic electrochemical transistors printed on flexible polymer films. The integrated gold electrodes have been successfully biochemically functionalised with antibodies to detect Escherichia coli (E. coli).
• Sensors based on surface-enhanced Raman spectroscopy (SERS), with printed gold electrodes in polymer- or glass-based microfluidics, enabling applications such as drug detection or bioanalysis.
• Low-cost gas sensors for portable applications using a catalytic platinum electrode as the sensing element to detect ethanol/acetone gas mixtures. Printed platinum layers showed sensitivity almost twice that of conventional magnetron sputtered electrodes. Electrochemical-amperometric gas sensors for the detection of ethylene gas based on aerosol-printed gold electrodes with unique electrochemical activity were also demonstrated.
• Metal oxide gas sensors for CO and NO₂ detection with very low power consumption (250 °C operating temperature at 78 mW) thanks to printed heater and gold ink electrodes.

An overview of published work using our inks and pastes can be found here.