(76a) Force Measurements between Cryptosporidium Parvum Oocysts and Positively and Negatively Charged Colloidal Particles | AIChE

(76a) Force Measurements between Cryptosporidium Parvum Oocysts and Positively and Negatively Charged Colloidal Particles

Authors 

Byrd, T. L. - Presenter, Yale University
Walz, J. Y. - Presenter, Virginia Tech


In our previous research we studied the interaction force profile between single Cryptosporidium parvum oocysts and silica particles by measuring the force in aqueous solutions using an atomic force microscope. The oocysts were immobilized during the measurements by entrapment in a Millipore polycarbonate membrane with 3 µm pore size. Experiments were performed in both NaCl and CaCl2 solutions at ionic strengths ranging from 1 to 100 to mM. We found that for both electrolytes, the decay length of the repulsive force profile, obtained via the slope of a plot of the logarithm of the interaction force versus oocyst/substrate separation, was found to be essentially independent of the ionic strength and always much larger than the expected Debye length of the system. In addition, we found the magnitude of the force was found to be essentially the same for both electrolytes, suggesting that the long-range repulsive forces are strictly steric in nature. Measurements made using positively-charged, silane-coated particles showed almost identical behavior. This finding supports the theory that the Cryptosporidium parvum oocysts are coated with a large layer of weakly-charged carbohydrates.