Abstract
As the improvement of medication, kinds of particles are studied and applied in biology and medication. For example, vesicles, viruses and endosomes are particles in nanoscale, currently under studied for the application of medication. For well use of these nanoparticle, we need to measure the size, concentration and surface properties to control the parameters systematically. Proper tools to measure these parameters for nanoscale particle are not perfect enough now, so the accuracy and precision need more improvement. Tunable resistive pulse sensing, based on the coulter counter, is a non-optical sensing technique to measure the size and concentration of nanoparticles. A voltage drop is applied on the both reservoirs connecting with a conical-shaped nanopores full of electrolytes. When a particle travels through the nanopore, a current decrease can be observed since the difference of the resistance between particle and electrolytes. The magnitude of current decrease is related to the volume of particle. Hence, this technique can measure the size of nanoparticle. In this thesis, we study the magnitude of current in the case of non-spherical particle traveling through the nanopore, and the parameters affecting positive peaks. The formation of positive peaks is related to the surface charge of the particle, so there is a potential for measuring the surface charge via positive peaks. In this thesis, we use finite element analysis to investigate paramters which can affect the magnitude of current drop when a particle travels through the nanopore, including path, tilt angle and the ratio of length and width of cylindrical particle. According to the simulation results, we find the magnitude of current change increases with the distance from particle and central line of nanopore increases. The more the tilt angle of the cylindrical particle is, the more the magnitude of current change increases. The more the ratio of length and width of cylindrical particles with same volume, the more the magnitude of current change increases. In the study of positive peaks, we simulated parameters which affect the magnitude of positive peak, including electric potential, pressure drop, concentration of electrolytes, size of particles, and surface charge density of particles. The major cause of the formation of positive peak is the phenomenon called ionic concentration polarization. The surface charges on the particles and nanopores induce the redistribution of ionic concentration near their surfaces which is related to the direction of voltage drop in the system and surface charges. In the case of positive peak, the ionic concentration in the nanopore is higher because the charged particles carry more ions into the nanpore. The magnitude of positive peaks are related to the surface charge on the particles.