Parafilm m

To analyze the samples using SERS, the 200 μL output of the sample preparation process was transferred to a sterile 1.5 mL microcentrifuge tube, rinsed with 200 μL of TSB and spun down. The supernatant was aspirated, and 1 mL of fresh TSB was added. The tubes were left open, but covered with Parafilm M (VWR), and incubated for 5 h at 37 °C on an orbital shaker at 160 rpm. Once the incubation time was complete, the Parafilm was removed and the samples were spun down at 4500 × g for 3 min. The supernatant was removed and 1 mL of 1 mM sodium diphosphate buffer (pH 6; Sigma-Aldrich) was used to resuspend the pellets. Sodium diphosphate buffer was found to generate the SERS signal faster for certain species than washing with water.^{61 (link)} The samples were spun down and the rinsing process was repeated 3×. Upon completion of the third centrifugation step, the supernatant was removed to leave approximately 10 μL of sample for SERS analysis. For samples directly from culture, the log-phase microorganisms were pelleted, washed 4× with deionized Millipore water, and then resuspended in 250 μL of deionized Millipore water.