Stable aqueous ZnS quantum dots obtained using (3-mercaptopropyl)trimethoxysilane as acapping molecule

Abstract

We have examined the synthesis and stability of ZnS quantum dots (QDs) using an all-aqueous routeat pH = 12 with (3-mercaptopropyl)trimethoxysilane (MPS) as the capping molecule. TheMPS-capped ZnS QDs obtained were well dispersed with a particle size around 5nm and a cubic zinc blende crystalline structure. The QDs exhibited optimalphotoluminescence (PL) emission when the MPS:Zn:S ratio was between and . Compared with the earlier obtained ZnS QDs capped with 3-mercaptopropionic acid(MPA), the MPS-capped ZnS QDs exhibited a similar, high quantum yield, 42% and 25%for MPS:Zn:S and , respectively, but much better photostability. With the MPS:Zn:S ratio of , we showed that at room temperature and under the normal laboratory lightingconditions, the MPS-capped QDs were able to maintain their PL intensity for more than 50days without degradation. We further showed that the MPS-capped QDs were stable notonly in their synthesis solution but also in deionized (DI) water and in phosphatebuffer saline (PBS) solution. The QDs with were able to stay at 50 °C for more than 20 h without degrading the PL intensity. They were also stable undercontinuous UV exposure for 3 h. With the high quantum yield and significantly improvedphotostability, the MPS-capped ZnS QDs could be good imaging tools for many biologicalapplications.