Dynamic Light Scattering (DLS) is a widely used tool for the measurement of Zeta Potential, taking benefit of automated detection to achieve fast measurements. However, the mathematical criteria on which the calculations in DLS devices are based, assume a very narrow set of conditions. One of them is a perfect spherical shape, since a hard sphere model is assumed for calculating scattering patterns and therefore the analysis of different shapes could result in significant deviations. One frequent example where the determination of the surface charge in rod shaped colloids is required is the characterization of bacterial surface charges, which is complicated by complex surface properties. To test whether the commercial device gives a reasonable approximation, we constructed a homemade optical device and tested inorganic spherical and rod-shape SiO2 particles and compared them to a model bacterium. A different case is the determination of surface potentials of light sensitive materials under illumination. Commercial devices often do not allow the additional implementation of light sources other than the laser, but our setup flexibly enables us to plug in different illuminations.
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