To obtain carbon dots-entrapped OSP–agarose gel film,
agarose powder (0.2 g), OSP (0.1 g) and carbon dots (1.2mL)
were mixed in 5mL of deionized water within 20-mL glass
vials. After following the above-outlined protocol,the thin film
was tested for water permeabilization and color detection of
Mn2+ and Fe3+ ions at 0.1, 1.0, and 10 ppm.