2.9. Cellular uptake by fluorescence microscopy

FITC was used as a fluorescent probe and was loaded into MSN-NH₂ with or without GC to evaluate the cellular uptake qualitatively by a fluorescence microscope. SW620 (containing the receptor of galectins) cells were seeded on 12-well plates (3 × 10⁴ cell/well) and incubated for 24 h. Then, the plates were washed twice with PBS. FITC@MSN-NH₂ and FITC@MSN-NH₂/GC (FITC: MSN-NH₂ or MSN-NH₂/GC = 1 : 50) were added to the culture medium for 4 h, with cells treated with free FITC in culture medium as a control. The cells were measured using a fluorescence microscope.

For competition assays, the cells were pre-treated with 2 mg ml⁻¹ of free galactose before incubation with FITC@MSN-NH₂/GC. After 30 min incubation, the medium with galactose was aspirated and FITC@MSN-NH₂/GC was added to the wells at a concentration of 50 µg ml⁻¹ for 4 h. The results were compared with FITC@MSN-NH₂/GC without the addition of galactose [27].