Size-dependent conductivity dispersion of gold nanoparticle colloids in a microchip: contactless measurements

We performed admittance measurements to investigate the particle size dependence of the conductivity of gold nanoparticle (Diameters: 6–100 nm) colloids in electrophoresis microchip in the frequency range of 0.03–1.00 MHz. The admittance was measured with two electrodes capacitively coupled to the colloid contained in a microchip capillary channel. The imaginary and real components of the admittance showed low-frequency dispersion associated with the polarization of the nanoparticles induced by the AC electric field. This was evident from the linear dependence of the process relaxation time as a function of the square of the radius of the nanoparticle.