Functionalized Filters for Nucleic Acid Capture

Whatman Fusion 5 (Cytiva, Marlborough, MA) was functionalized with chitosan (Sigma-Aldrich, Munich, Germany) using a protocol described by Rosenbohm et al.,^{33 (link)} and stored in a foil zipper lock bag at 4 °C until use. Capture efficiency of functionalized filters was tested using two random short DNA oligos (DNA oligo 1 and DNA oligo 2 in Figure S2d) or yeast tRNA (Sigma-Aldrich, Munich, Germany) by diluting the samples in 1X PBS (pH 5.0–5.4, unless stated otherwise). Functionalized Fusion 5 was inserted into modified Slide-A-Lyzer^™ MINI Dialysis Units (Thermofisher Scientific, Waltham, MA) and the diluted DNA or yeast tRNA was centrifuged through the filter units at 1300 × g or 4000 × g. Differences in the centrifugation speed did not impact capture results. Before and after filtration measurements of the eluate were taken using a NanoDrop^™ Lite Spectrophotometer (Thermofisher Scientific, Waltham, MA). A decrease in nucleic acid concentration in filtered eluate was used to indicated nucleic acid capture (Figure S2 and Table S2).