Characterization of Nanoparticles Using Solid State Nanopores

Solid state nanopores are widely used in detection of highly charged biomolecules like DNA and proteins. In this study, we use a solid state nanopore based device to characterize spherical nanoparticles to estimate their size and electrical charge using the principle of resistive pulse technique. The principle of resistive pulse technique is the method of counting and sizing particles suspended in a fluid medium, which are electrophoretically driven through a channel and produce current blockage signals due to giving rise to a change in its initial current. This change in current is denoted as a current blockage or as a resistive pulse. The information from these current blockage signals in case of nanopore devices and spherical nanoparticles helps us to look at the properties of each individual nanoparticles such as size, electrical charge and electrophoretic mobility. In this thesis, two spherical nanoparticles of different sizes and different surface charge groups are used: Negatively charged 25 nm iron oxide nanoparticle with – COOH surface group and positively charged 53 nm polystyrene nanoparticle with – NH2 surface group. Nanopores used in these studies are about twice the nanoparticle size. These nanopores were fabricated by various fabrication techniques such as, Focused ion beam milling and ion beam sculpting method. The current blockage events produced by these two nanoparticles were measured as a function of applied voltage. The parameters extracted from the current blockage events, such as the current drop amplitudes and event duration are analyzed to estimate the size and electrical charge of the nanoparticles. Estimation of drift velocity of the nanoparticle and diffusion coefficient are also discussed. The estimated size is then compared to the nanoparticle size obtained from dynamic light scattering technique. Stable nanoparticles are widely used in biological and pharmacological studies and understanding the behavior of these nanoparticles in a nanopore environment would make a significant contribution to the studies at the nanoscale