FITC-Dextran (MW 10000) is a marker (10 kDa) formed by coupling FITC to dextran. FITC-Dextran is a labeled polysaccharide composed of branched glucose molecules of various lengths, enabling the determination of solute, ionic, and protein permeability of the blood-brain barrier depending on the size of the dextran used.

METHODS: FITC-dextran assay for RBL-2H3 mast cell line:
1. Mix 1 mg of FITC-dextran powder per 1 mL of medium. Use a cellulose acetate syringe filter with a pore size of 0.22 µm to filter the dissolved FITC-dextran.
2. Add 10 µL of cell suspension to a chamber coverslip pre-filled with fresh FITC-dextran supplemented medium.
3. Incubate RBL cells overnight at 37°C in a humidified environment with 5% CO2. Cells should be maintained at a subfusion level to ensure cell separation and that each cell can be easily identified individually under a microscope.
4. Wash the chamber coverslips three times by aspirating the medium from the chamber and refilling with 300 µL of Tyrode Buffer preheated to 37°C. The coverslips should be cleaned with the Tyrode Buffer. Finally, replenish the chamber with 300 µL of Tyrode Buffer preheated to 37°C.
5. Select the region of interest to be tracked by turning on the fluorescent light source and selecting an appropriate fluorescent filter, choose a filter with green fluorophores to view FITC-dextran. if using a laser-based microscope, turn on the 488 nm laser, the emission should be centered around 500-550 nm. [1]

METHODS: Intestinal permeability was determined by FITC-dextran:
1. FITC-dextran was dissolved in sterilized PBS at a concentration of 80 mg/mL.
2. Mice were fasted for 4 h prior to FITC-dextran injection, followed by oral administration of 100 µL of FITC-dextran.
3. After 4 h, mouse blood is collected and centrifuged at 4000 rpm for 15 min. Plasma samples are collected in clear EP tubes and placed at 4°C, protected from light.
4. Standard FITC-dextran samples were diluted to 0-100 µg/mL with PBS and transferred to a black 96-well plate.
5. Measure the fluorescence at 485 nm excitation wavelength and 528 nm emission wavelength using a microplate reader. [2]