All pH measurements were taken with an Orion Star A111 pH meter using an Orion PerpHecT ROSS Combination pH Micro Electrode capable of measurements in a 96-well plate. All measurements were taken after the probe was freshly calibrated using 4.01, 7.00, and 10.01 standards. pH measurements were taken of pH-adjusted 10 ppm (GT)6-SWCNT prior to aliquoting into plate wells. This measurement had to remain unchanged (± 0.05 pH units) for 1 h to ensure equilibrium had been reached prior to aliquoting.