Surveying colloid sedimentation by coplanar waveguides

By using coplanar waveguides, direct access to the dielectric properties of aqueous solutions of polystyrene beads with different diameters from 330 nm to 10 μm is provided. The relative variation of the transmission parameter with respect to water is monitored, ranging from [Formula: see text] obtained for a 9.5% solution with 330 nm diameter beads to ∼22% for 10 μm diameter particles at the same concentration. To highlight its applicability in biosensing, the technique was further employed to survey the clustering between biotin and streptavidin-coated beads. The transmission parameter displays a ∼50% increase for mixtures containing nine volumes of biotin and one volume of streptavidin-modified beads (4.5 ng μl(-1) of streptavidin) and reaches ∼400% higher values when equal volumes of biotin and streptavidin-coated beads (22.5 ng μl(-1) of streptavidin) were mixed.