Flexible Sensors for Health and Bioanalytics

There is an increasing need for health sensors that can conveniently collect data over extended periods of time. Acquisition of such data on or near living organisms imposes special challenges. The sensor must work reliably under complex and variable conditions. Most sensors used today are bulky and need complex connectivity to extract the sensor information.

In the future, such sensors will be wearable, flexible and compatible with the organic matter. To make the next steps towards flexible (Bio)sensors one has to solve a number of essential problems, which are interdisciplinary in nature. Therefore, expertise from materials science, materials processing, life science and technology is required to generate innovative solutions

Essential challenges of flexible sensors for health:

  • novel sensing materials (e.g. functionalized polymers, ceramics, etc.)
  • novel materials forms (e.g. processing)
  • highly structured sensing films (e.g. specific functional surface)
  • sensing surfaces (e.g. specific affinity chemistry)
  • sensing techniques (e.g. cheap, portable, reliable, etc.)
  • simple connectivity (e.g. electrical, optical, etc.)
  • long-term host compatibility (e.g. bio-compatibility)

Our approach:

  • we address these challenges by an interdisciplinary network with internal and external partners.
  • we are interested in both fundamental and applied research.
  • with this interdisciplinary knowledge we steer the functions of materials for the development of specific sensors.

Showcase of selected competences:

We develod physical and chemical sensors with polymer optical fibers, nanofiber meshes, or hydrogels as substrates. Modification of the substrate with sensitive moieties (e.g. fluorophores, chromophores), or the simple integration into textiles, allows detection of gases, liquids, biomolecules, body vital parameters, and microorganisms. Detection occurs by changes in light intensity, wavelength, and/or fluorescent intensity.

Image: Boesel, Luciano Luciano.Boesel@empa.ch

To study the adsorption of macromolecules on a surface, e.g. protein adsorbtion, we have developed an optical sensor that measures the increase of optical path when an adsorbate is formed. The principle is based on transmission of originally white light, which is modulated by the thin film interference. It is the so-called Transmission Interferometrical Adsorption Sensor (TInAS) (2007, Heuberger, Balmer). Recently, we started exploring the combination of open circuit potential (OCP) measurement and TInAS. The temporal correlation of the simultaneously measured adsorbed mass and surface potential change allows deeper insights into structural changes at the interface during the adsorption process.

Novel fluid cell design combining TInAS in transmission and open circuit potential measurement at up to 8 positions simultaneously. The thin film sensor can accommodate different electrode shape. In this example only 2 of 8 electrodes were contacted. Image: Heuberger, Manfred (Manfred.Heuberger@empa.ch) Heuberger, M. and T. Balmer (2007). "The Transmission Interferometric Adsorption Sensor." Journal of Physics D: Applied Physics 40: 7245-7254.

CMOS compatible silicon nanowires (SiNWs) operated as ion-sensitive field-effect transistors (ISFETs) can function as chemical and biochemical sensors. In these devices, the gate metal of the transistor is replaced by the solution carrying the analyte species. The reactions of charged analytes with ligand groups at the sensor surface cause a change of the electrical surface potential at the gate contact. This change in surface potential is detected as a shift in the transistor transfer function and can be quantitatively related to the number of adsorbed analytes.

Left: Chip carrier with 48 bonded Si nanowires. Right: Schematic of a binding cycle showing a typical sensor response. The association of proteins to the surface ligands occurs upon injection and dissociation upon switching to running buffer. Figures: Transport at Nanoscale Interfaces Laboratory. Wipf, M., Stoop, R.L., Navarra, G., Rabbani, S., Ernst, B., Bedner, K., Schönenberger, C., Calame, M. (2016). Label-Free FimH protein interaction analysis using silicon nanoribbon bioFETs. ACS Sensors 1 (6), 781-788. http://doi.org/10.1021/acssensors.6b00089