QSA is a group of water soluble alloy CdSSe/ZnS or CdSe/ZnS core/shell quantum dots with amphiphilic polymer and PEG coating. The reactive group is amine. The zeta potential of QSA is from -20mV to +10mV. The organic layers consist of a monolayer of oleic acid/octadecylamine, a monolayer of amphiphilic polymer and a monolayer of PEG. The thickness of the total organic layers is about 6 nm. The hydrodynamic size of the QDs is about 12-14 nm larger than their inorganic core size measured by TEM.
QSA is very stable in most buffer solutions in the pH range of 5-10 and can survive autoclaving process (121°C for 30 min). The amine density of QSA is low due to the long PEG chain.