Diamond nanoparticles can be made to exhibit an anomalously strong positive zeta potential across the entire pH range (see nanodiamond). We have shown by electrostatically assembling these particles onto conventional filter membranes, we are able to reverse the filter zeta potential from negative to positive charge across a wide pH range. The graph left shows that quartz membranes are negatively charged from pH 3 to 10. By exposing the filter to increasing concentrations (from 0.15 to to 2.4 mg/mL) of diamond nanoparticles in solution, the zeta potential becomes increasingly positive until it exhibits a strong positive zeta potential across the entire pH range. The grey area represents the pH range within the body.
The nanodiamond modified filters have a strong affinity for viruses. For example, the bacteriophage MS2 was used to test the efficacy of the filter (see histograms right). An untreated filter (blue bars) has almost no capability to remove viruses, which is not surprising given that the pores are several micron (see electron micrograph below) and the MS2 virus <30nm. The treated filter removes log6 (>99.9999%) of the MS2 virus, with a slight reduction in efficacy at pH 9. This is due to the weaker zeta potential at this pH even though it is significantly stronger than commercially available positive charged membranes.
Recently, we have benchmarked our electropositive filter technology against commercially available electropositive filters. The graph right shows the variation of zeta potential with pH for the various filters. It is clear that the diamond nanoparticle enhanced filters exhibit a higher positive zeta potential across a wider pH range than those available commercially. A more complete discussion is available here: