The effects of QD stabilizer structures on pH dependence, fluorescence characteristics, and QD sizes

Abstract

CdTe quantum dots (QDs) were prepared in aqueous solution using various mercaptocarboxylic acids such as mercaptopropionic acid (MPA), mercaptoethylamine (MEA), and L-cysteine (L-Cys) as stabilizing agents. The pH control of QD suspensions is essential when using fluorescent QDs in biological systems. The pH-dependent photoluminescence (PL) of MPA-and L-Cys-stabilized CdTe QDs was systematically investigated. Experimental results showed that CdTe-L-Cys is effective within a wider pH range than CdTe-MPA and CdTe-MEA, although it is ineffective in the vicinity of the isoelectric point, which makes CdTe-L-Cys quantum dots potentially suitable as a biological labeling probe under physiological conditions. Meanwhile, the effect of stabilizer structure on QD size was studied by comparing CdTe-MPA and CdTe-L-Cys QDs using x-ray diffraction, x-ray photoelectron spectroscopy and transmission electron microscopy. The results indicated that the coordination of amines with cadmium reduced the activity of Cd precursors, and the coordination of S with the CdTe QDs affected their crystal structure, resulting in the formation of relatively large CdTe-L-Cys quantum dots.

Сolloidal synthesis and characterization of hydrophilic CdTe quantum dots for medical diagnostics

“…The value of zeta potential of the QDs obtained in the paper is twice as much as that described in the literature [21,34] although the nature of the dependence is the same. The difference in charges may be due to the fact that there are more functional groups of a stabilizer on the surface of the QDs.…”

“…water. In ACS, heavy metals precursors (for example, CdCl 2 , Cd(NO 3 ) 2 and Cd(CH 3 COO) 2 ) readily dissolve in water and are coordinated by hydrophilic agents such as TGA [16,17], mercaptopropionic acid (MPA) [18], L-cys, [19], glutathione (GSH) [20], MEA [21], mercaptosuccinic acid (MSA) [22]. Chalcogen precursors can be NaHE (E = Se, Te) which are freshly prepared in an aqueous medium and obtained by chemical reduction of selenium (Se) or tellurium (Te) in the presence of boron sodium hydride (NaBH 4 ).…”

“…The pH of a medium has a major effect on the optical properties of QDs [21]. The QDs coated with ligands with carboxyl functional groups are stable in the pH range of 10-5.…”

“…The QDs coated with ligands with carboxyl functional groups are stable in the pH range of 10-5. A decrease in the pH of the medium leads to a sharp decrease in the intensity of fluorescence, which is caused by a decrease in the negative surface charge and the formation of aggregated microparticles [21,31].…”