Methods of detecting bacterial contamination in a platelet concentrate are performed using a dynamic light scattering (DLS) instrument and a sample holder. A sample of platelet concentrate can be held vertically or horizontally in a capillary in the sample holder. Alternatively, novel platelet storage bags modified to include an optically translucent window can be held within another variant of the sample holder. Still alternatively, platelet storage bags having one or more tubes detachably appended to the bag can be used. A sample is drawn off into an appended tube for placement directly into the sample holder. This method provides a number of related, non-invasive techniques for detecting whether bacteria has contaminated a platelet concentrate. Contamination indicators include a population of particles different from platelets, microparticles or proteins, bad-quality platelets, i.e. low DLS score, and very high or very low scattering intensity.
