Laterally-Resolved Force Microscopy of Biological MicrospheresOocysts of Cryptosporidium Parvum

Abstract

An atomic force microscope (AFM) has been used to measure the force of interaction between individual biological microspheres (oocysts of Cryptosporidium parvum) and an amorphous silica surface (hydrolyzed AFM tip). One of the main barriers to oocyst contamination of drinking waters is provided by sand-bed filtration. The AFM tip has been functionalized to silica in order to investigate the interaction between oocysts and model sand (siliceous) particles at the most fundamental level. The AFM force curves have been compared and contrasted with the ζ-potentials of silica particles and oocysts obtained from electrophoretic mobility measurements. It has been concluded that there is a steric interaction between the silica surface and the oocyst material, in addition to electrical double-layer and van der Waals interaction. The proteinaceous materials on the surface of the oocysts are considered to be responsible for the steric interaction. The magnitude of the steric interaction is little changed by varying t...