The detection of biological materials during a blood test, such as biomarkers or pathogens, is of great importance for our healthcare system. Current detection methods are based on stationary laboratory instruments and can only be carried out by qualified personnel. An example of a widely-used method to determine concentrations of biological materials in an analyte is the ELISA test (enzyme-linked immunosorbent assay). This includes several chemical steps, followed by a final photometric measurement of the marker molecules introduced. Biosensors are currently developed based on immobilised biological receptors, which enable a highly-selective measurement of biological, biomedical or chemical substances, while also enabling much more compact, mobile equipment.

One of the most important properties of biosensors is their potential for marker-free detection. The sensor surface itself assumes the role of the marker, and allows for direct detection of biological material. This facilitates faster, easier and more physiological measurement. Another characteristic of biosensors is their possible use for molecular binding kinetics experiments in real time, which answer important questions for drug development.

We research biosensors which use a periodic nanostructured sensor surface (photonic crystal). Quasi guided modes in these structures enable contact-free and sensitive measurement. We have demonstrated that by combining light source, polarising filters and photonic crystal, a simple intensity measurement allows real-time determination of concentration. In a series of experiments, we were able to determine the binding kinetics of a 2.5 nmol biotin-streptavidin solution with a compact prototype (Fig.1).