FITC (Fluorescein 5-isothiocyanate) is a derivative of fluorescein for the labeling of amines.

I. Amine labeling
1. Binding: Dilute FITC in an appropriate solvent (usually dimethylsulfonamide DMSO) and mix it with the target biomolecule solution. The reaction is usually carried out under slightly alkaline conditions (pH 8.0-9.0) to ensure effective binding of FITC.
2. Incubation: Incubate the mixture at room temperature or 4°C for 1-2 hours. Since FITC is light-sensitive, it needs to be protected from light.
3. Purification: After the reaction is completed, excess FITC is removed by purification techniques such as dialysis and gel filtration to obtain labeled biomolecules.
II. Cell imaging
1. Cell staining: Apply FITC-labeled antibodies or proteins to cells or tissues and incubate for a certain period of time (usually 30 minutes to 1 hour) at room temperature or 4°C.
2. Fluorescence microscopy: After washing away unbound antibodies, use a fluorescence microscope to observe cells or tissues. FITC can be excited at a wavelength of about 495 nm and emit at a wavelength of 519 nm.
III. pH and Cu2+ sensitivity
1. pH sensitivity: When FITC-labeled molecules are placed in solutions of different pH values, the fluorescence intensity will change with the change of pH and can be quantitatively measured.
2. Cu2+ detection: The fluorescence of FITC is also affected by Cu2+, so it can be used to determine the concentration of Cu2+ in the sample by observing the change of fluorescence intensity.