Voltammetric monitoring of prostasome aggregation and self-fusion

Abstract

We have demonstrated the applicability of cyclic voltammetry and rotating disk electrode techniques to study adsorption, aggregation, and self-fusion of prostasomes, nanoparticles present in human semen. Prior to the electrochemical experiments, we have characterized prostasomes through nanoparticle tracking analysis, dynamic light scattering, and zeta potential measurements at various pH. One of our main findings in this work has been the prostasome concentration in human semen, determined to be 4.8×1011cm−3, which is 20000 times higher than the sperm cell concentration. We have found the hydrodynamic diameter of the prostasome to range from 35 to 475nm, with the mean value of 151nm, in agreement with the literature. Then, we have adsorbed a monolayer of prostasomes at the surface of gold rotating disk electrode and studied its effect on the limiting diffusion current at the electrode. We have conducted our measurements in a standard three-electrode cell. We have described the monolayer effect in terms of the equivalent layer thickness of stagnant solution layer. Next, we have added a small amount of prostasomes to the three-electrode cell and decreased pH to 4.0 to allow their aggregation at the surface of rotating disk electrode. We have used the chronoamperometry method to monitor multilayer adsorption of the prostasome for 180min. Then, we have again characterized the adsorbed layer of prostasomes in terms of the equivalent layer thickness. Through a comparison of the equivalent layer thickness determined for the mono- and multilayer, we have found the amount of prostasomes adsorbed during chronoamperometry. We have also compared the number of prostasomes adsorbed at pH 4.0 with the number of prostasomes transported to the rotating disk electrode during this experiment. From that comparison, we have estimated the two-prostasome aggregation probability and the surface area fractions corresponding to the positive and negative surface charges of the prostasome. We believe that our results can be useful for better understanding of prostasome surface properties and, consequently, processes such as prostasome-sperm cell fusion or prostasome-bacterium interactions.