On-chip analysis of particles and fractionation of particle mixtures using light-controlled electrokinetic assembly of particles near surfaces

A method of determining the zeta potential of particles suspended in an electrolyte solution and/or the mobility of ions or molecules within a region adjacent to said particles, the method comprising:

• providing a plurality of particles having a characteristic relaxation frequency suspended at an interface between an electrolyte solution which resides in a gap between a first electrode and a light-sensitive electrode;
• illuminating the interface with a predetermined light pattern;
• generating an electric field at the interface by application of an AC voltage, said electric field having a frequency, and adjusting the frequency of said electric field to produce formation of a planar array of substantially one layer of particles in a designated area on the electrode defined by the pattern of illumination, wherein said interface exhibits impedance gradients when subjected to the electric field and the illumination;
• determining the relaxation frequency of said particles;
• determining maximal velocity (vmax) of said particles;
• and
• converting the maximal velocity and the relaxation frequency to either the zeta potential or the surface conductivity of said particles, or to both the zeta potential and the surface conductivity.

A method of determining the zeta potential of particles suspended within an electrolyte solution and/or the mobility of ions or molecules within a region adjacent to said particles, the method comprising:

• providing a first electrode positioned in the first plane and a second electrode positioned in a second plane different from the first plane, an electrolyte solution located therebetween and a plurality of particles of one or more types, each type having a characteristic relaxation frequency, said particles being suspended at an interface between the electrolyte solution and the second electrode, wherein the second electrode comprises a planar electrode having a surface and an interior, the surface or the interior having been patterned to modify the spatial distribution of the interfacial electric field;
• generating an electric field between the first and the second electrode by applying an AC voltage between the two electrodes, said electric field having a frequency;
• adjusting the frequency of said electric field to produce particle transport into a designated area of the electrode defined by said patterning of the electrode;
• determining relaxation frequencies of said one or more types of particles;
• determining maximal velocity (vmax) of transport of said particles through image analysis and particle tracking;
• and
• converting said relaxation frequency and said maximal velocity to either the zeta potential of said particles or the mobility of ions or molecules within a region adjacent to said particles, or to both the zeta potential and said mobility.