SYTO-9

Operating Instructions (The following is a recommended experimental protocol for guidance only and should be adjusted according to specific requirements)

1. Working Solution Preparation
1.1 Diluent: Phosphate-buffered saline (PBS) or HBSS is optional.
1.2 Working concentration: 0.5-5 µM for single staining; 33.4 µM for co-staining with propidium iodide (PI).
1.3 Notes: The concentration of the working solution can be adjusted as needed, and it must be prepared and used immediately.

2. Staining Procedures
2.1 Suspended bacterial samples^[1][2][3]:
2.1.1 Sample preparation: Adjust the bacterial suspension to a concentration of approximately 10⁵-10⁸ CFU/mL in the selected diluent; if removal of culture medium or fixative (if applicable) is required, centrifuge at 4000-8000 × g for 2-10 min before resuspension; centrifugation is not required for direct staining of live or formaldehyde-fixed aquatic bacteria.
2.1.2 Incubation conditions: Use a working concentration of 0.5-33.4 µM; incubate at room temperature in the dark for 5-45 min; for pure bacterial cultures, perform staining in amber tubes to avoid light exposure. For PI co-staining, use a combined system of 33.4 µM SYTO-9 and 0.4 mM PI, and incubate at room temperature in the dark for 15 min.
2.2 Adherent bacterial biofilms^[4]:
2.2.1 Sample preparation: Use biofilms grown on silicon wafers, coverslips or glass-bottom dishes; trypsin digestion is not required.
2.2.2 Washing before staining: Wash the samples 3 times with PBS.
2.2.3 Incubation conditions: Direct co-staining with SYTO-9-PI: Use the prepared co-staining working solution and incubate at room temperature for 15 min. Sequential staining: First incubate with SYTO-9 working solution at room temperature for 15 min, then directly add PI and image immediately; or after staining with DAPI and PI, directly add SYTO-9 and image immediately.
2.2.4 Washing after staining: Wash the samples 3 times with PBS to remove excess dye.

3. Control Setup
3.1 Bacterial samples without dye.
3.2 Blank control containing only peptone water.
3.3 Peptone water solution containing 0.5 µM SYTO-9.
3.4 Peptone water solution containing 1.0 µM SYTO-9.
3.5 Untreated Staphylococcus aureus biofilm control.
3.6 Staphylococcus aureus biofilm samples treated with 70% EtOH.

4. Detection and Analysis
5.1 Instrument types: Flow cytometer, fluorescence microscope, etc.
4.2 Excitation/emission wavelengths: RNA: Ex/Em = 486/501 nm; DNA: Ex/Em = 485/498 nm.
4.3 Result analysis:
After SYTO-9 binds to bacterial nucleic acids, the fluorescence intensity increases significantly, and the intensity varies with bacterial species, cell concentration, and the state of live/fixed bacteria.
4.3.1 Suspended bacteria: Staining duration (5-45 min) has minimal effect on fluorescence intensity, but gram-negative bacteria may show low signals at 5 min; the fluorescence intensity of live bacteria may be higher than that of fixed bacteria; double staining with PI allows differentiation between live and dead bacteria via intensity ratio or spectral analysis.
4.3.2 Biofilms: SYTO-9 can stain intracellular nucleic acids (intact cells appear solid green) or substances around cells (damaged cells appear hollow green); co-staining with PI shows overlapping green and magenta fluorescence, and SYTO 9 signals often distribute around PI signals; fluorescence intensity has no direct correlation with cell size.

MedChemExpress (MCE) has not independently confirmed the accuracy of these methods. They are for reference only.