Abstract
Semiconductor quantum dots (QDs) offer tremendous scope to be used in the field of energy, imaging, sensors and optoelectronic devices. However, several issues regarding their hydrophilicity, stability and cytotoxicity remain unresolved. One of the methods to render CdTe QDs water-soluble is to functionalize the surface with carboxylate groups by the use of heterobifunctional ligands such as 3-mercaptopropionic acid (MPA). Following this motif, we report the synthesis of CdTe QDs using the non-aqueous organometallic route, ligand exchange with MPA was performed to replace the initial surface passivation ligands trioctylphosphine oxide (TOPO) and hexadecylamine, and finally, the prepared MPA-CdTe QDs were encapsulated into the biocompatible polyethylene glycol. Our results show that pegylation of CdTe QDs provided minimal cytotoxicity against baby hamster kidney (BHK 21) cells even at high levels. The IC50 values of pegylated CdTe QDs were higher than the non-pegylated ones with a % viability ranges from 89:90% at a concentration range of 0.01:0.03 nM. Currently, available ligand exchange procedures lead to significant loss of quantum yields. In our study, the photoluminescence (PL) emission of the MPA capped CdTe QDs decreased gradually as the pH increased from 4 to 10 while after pegylation the prepared QDs exhibited significantly enhanced PL efficiency and storage stability.
Highlights
Quantum dots (QDs) have attracted attention in recent years due to their potential applications [1]
The stability of the CdTe quantum dots (QDs) prepared in non-aqueous phase has been conducted by comparing the newborn CdTe QDs with the CdTe QDs that has been stored for 1 year in a solid form using HRTEM images as indicated in Figs. 3c and 2d; the size of the CdTe QDs increased during the 1-year shelf life monitoring from 4–5.5 nm to 6–7.5 nm
The results show that the polyethylene glycol (PEG) encapsulated mercaptopropionic acid (MPA)-CdTe QDs remained stable with a slight decrease in the PL intensity from 450 a.u. to 100 a.u. when compared with the PL intensity of the freshly prepared QDs
Summary
Quantum dots (QDs) have attracted attention in recent years due to their potential applications [1]. The most successful method to prepare highly luminescent CdTe QDs is the organometallic synthetic route, which uses TOPO and HDA as surface ligands. These methods require high temperatures, and the resulting QDs are insoluble in water, which makes the final product incompatible with the biological systems. QDs have been prepared in aqueous medium in a simpler route generating less toxic water-soluble biologically compatible nanocrystals [10, 11]. Researchers have investigated the influence of hydrophilic surface ligands exchange method so as to enhance hydrophilicity and improve the optical properties to be used in biological applications [14]
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