Figure 1 . QCL-GAP optical setup used for microorganism sample acquisition.
2.3 Sample Preparation
Aliquots of 20 µL of neat and mixtures of bacteria samples were deposited on the 2 X 2-in2(25.8-cm2) stainless-steel (SS) plates. Substrates were cleaned with isopropyl alcohol and left to dry in a chemical hood to avoid any sample contamination. Bacterial samples Sa, Se, andMl were used to create the following mixtures: Sa/Se ,Sa/Ml , and Se/Ml . A sample smearing technique using a micropipette tip (~1 mm diameter) was used to deposit the sample onto the substrate [20]. The smearing procedure accounts for minimal sample loss during handling. The solutions deposited on the substrate were left air-dry for 20 minutes until the solvent evaporated. Each bacterial sample acquired twenty (20) replicas by moving the optical stage in the QCL-GAP setup.