For drug-release experiments, the amount of DOX and the amount
of Fe3O4-DGx nanoparticles were quantified on the basis of the loading
efficiency. In a typical drug-loading experiment, 500 μg of Fe3O4-DGx
(x = 3, 5, or 6) nanoparticles was incubated with 500 μg of the drug (1
mg/mL) in the dark for 3 h. The drug-loaded particles were collected
with a permanent magnet and were utilized for drug-release
experiments. For a typical drug-release study, DOX-loaded Fe3O4-
DGx nanoparticles were immersed in 5 mL of sodium acetate buffer
(pH 5) and put into a dialysis bag, which was then suspended in 200
mL of phosphate-buffered saline (PBS, pH 7.34) to form the reservoir
sink. Dialysis was performed under continuous stirring at 37 °C. At
different time intervals, 1 mL aliquots from the sink (PBS) were
withdrawn and replaced with equal amounts of fresh PBS to maintain
the sink conditions. The amount of drug released was determined by
the measurement of fluorescence (λexc = 490 nm and λemi = 560 nm)
from the aliquots against standard plots prepared under similar
conditions (R2 = 0.999).