Streptavidin is covalently attached to the quantum dot or through electrostatic interactions, which allows them to bind to biotinylated targeting agents.
Green N.M. // Methods Enzymol. 1990. V. 184. P. 51–67
The following link may be useful https://www.researchgate.net/figure/Schematic-of-conjugation-of-Carbon-dots-to-Streptavidin-through-Glutaraldehyde_fig5_304631206