Point-of-care analyses for diagnostics require rapid and automatic results from micro-litre volumes of patient samples. In the case of protein analyses, very different concentration ranges are relevant for different disease markers. For effective commercial product manufacturing it is advantageous that the sensor element and the corresponding read out device are identical for all tests, while the surface functionalization is adapted to the specific marker. This requires a sensor with the potential for high sensitivity combined with a wide dynamic detection range. A new optical sensor principle, based on a photonic crystal, provides sensitivity down to one single molecule as well as detection of higher concentrations. The sensor is suitable for integration in different types of disposable chips, utilizing microfluidic flows for rapid analyses. The corresponding instrument is simple, and the optical alignment of the disposable chip is not critical.