Abstract: The invention provides a method of detecting the redispersion of particles into a solution by means of FTIR or other optical detection methods comprising the following steps: providing a sensor surface with dry particles; illuminating the sensor surface with light along a first optical path and detecting the light reflected by the sensor surface; providing a liquid to a volume in contact with the sensor surface; and detecting the reflected light while the dryparticles redisperse into the liquid. Therein, the angle between first optical path and sensor surface fulfils the condition of total internal reflection. The present invention also provides an FTIR cartridge for use in said method comprising a sensor surface accessible for FTIR detection, said sensor surface comprising at least one binding area, wherein label particles are situated on said surface.