Minimum Inhibitory Concentration (MIC) Assay with E. coli.

MIC assays were performed, as previously reported,³² in a MHB system (pH 7.3). In short, bacteria culture was inoculated overnight in 5 mL of MHB at 37 °C. After shaking overnight at 70 rpm, 500 μL of the bacteria suspension was transferred to an Eppendorf tube and centrifuged at 8000 rpm for 1.5 min. The supernatant was removed, and the bacterial pellet was resuspended in fresh MHB. These washed cells were diluted to a final OD₅₉₅ of 0.001 -corresponding to a bacterial concentration of about 10⁶ cells/mL- and then 190 μL was transferred to each appropriate well in 96 well plates. Next, 10 μL of polymer, QDs, polymer-QDs, and controls of stock concentrations were pipetted into well plates in duplicates (one duplicate = one biological replicate). The final well concentrations of free PONs and PONs-QDs samples ranged from 6.25 to 400 μg/mL PONs equivalents. The final well concentrations of MPA-QDs and PONs-QDs samples ranged from 0.001 to 1 μM QD equivalents. Plates were mixed well before placing in a 37 °C incubator. After incubating overnight, the OD₅₉₅ was evaluated to quantify bacteria cell viability. For exposures with irradiation, plates were rested directly on top of the neutral white light LED plate for 2 h at the beginning of the incubation in the 37 °C incubator. The 50% amine propyl PONs was used as a positive control in this assay. MES buffer and DMSO were tested with bacteria to ensure the solvents alone did not influence bacteria growth. MHB alone, and with DMSO and MES buffer addition were tested as a negative controls. Further details can be found in the SI.