Thioflavine S (Direct Yellow 7) is a fluorescent histochemical marker.

Instructions
I. Solution preparation
1. Stock solution: Prepare Thioflavine S into a 0.05–0.1% (w/v) solution. The solvent can be deionized water or PBS. If necessary, filter the solution to remove particles.
2. Working solution: Dilute the stock solution to the working concentration according to the experimental needs, usually 0.01–0.1% (w/v). The specific concentration depends on the experimental requirements.
II. Operation steps
1. Tissue preparation: Tissue samples should be fixed with formalin or paraformaldehyde before paraffin embedding or frozen sectioning.
2. Staining: Add the working solution to the tissue sections and incubate at room temperature for 10–30 minutes. The specific time depends on the tissue type and the required staining intensity.
3. Washing: Wash the sections with PBS to remove excess dye and avoid background fluorescence.
4. Sealing: Use an appropriate sealing solution (such as glycerol or fluorescent sealing solution) to seal the stained sections.
5. Fluorescence detection:
1) Microscopic observation: Observe the stained sections using a fluorescence microscope. Thioflavine S is excited at a wavelength of about 450 nm and emits at a wavelength of about 485 nm.
2) Observation results: Amyloid plaques bound to Thioflavine S will appear bright green or yellow-green under appropriate fluorescence conditions.
6. Calibration and control:
1) Control group: Use samples known to contain amyloid deposits as positive controls, and set unstained or undyed sections as negative controls.
2) Standard curve: A standard curve between fluorescence intensity and amyloid load can be established by using tissue samples known to contain amyloid plaques.
Notes:
1) Photosensitivity: Thioflavine S is light-sensitive and should be avoided from exposure to strong light during staining and storage.
2) Storage conditions: Thioflavine S solution should be stored in a cool, dark place, ideally at 4°C. Avoid repeated freezing and thawing.