DNA Adsorption onto Glass Surfaces

Abstract

Streaming potential measurements were performed on microspheres of silica, soda lime silicate (SLS) and calcium aluminate (CA) glasses containing silica and iron oxide (CASi and CAFe). The silicate based glasses exhibited acidic surfaces with isoelectric points (IEP) around a pH of 3 while the calcium aluminates displayed more basic surfaces with IEP ranging from 8-9.5. The surface of the calcium aluminate microspheres containing silica reacted with the background electrolyte, altering the measured zeta potential values and inhibiting electrolyte flow past the sample at ~ pH 4 due to formation of a solid plug. DNA adsorption experiments were performed using the microspheres and a commercially available silicate based DNA isolation filter using a known quantity of DNA suspended in a chaotropic agent free 0.35 wt% Tris(hydroxymethyl)aminomethane (Tris) buffer solution. The microspheres and commercial filter were also used to isolate DNA from macrophage cells in the presence of chaotropic agents. UV absorbance at ~260 nm and gel electrophoresis were used to quantify the amount and size of the DNA strands that adsorbed to the microsphere surfaces. In both experiments, the 43-106 μm CAFe microspheres adsorbed the largest quantity of DNA. However, the 43-106 μm SLS microspheres isolated more DNA from the cells than the <43 μm CAFe microspheres, indicating that microsphere size contributes to isolation ability. The UV absorbance of DNA at ~260 nm was slightly altered due to the dissolution of the calcium aluminate glasses during the adsorption process. Inductively coupled plasma - optical emission spectroscopy (ICP-OES) determined that calcium and aluminum ions leached from the CA and CAFe microsphere surfaces during these experiments. Circular dichroism (CD) spectroscopy showed that the leached ions had no effect on the conformation of the DNA, and therefore would not be expected to interfere in downstream applications such as DNA replication. The 0.35 wt% Tris solution completely inhibited the formation of the hydrated crystalline layer that develops when the calcium aluminate glassess are incubated in deionized water. A Tris concentration of 0.24 wt% allowed for the formation of both hexagonal and cubic hydrates, however they were severely distorted and present in low amounts such that they were undectable by XRD.