Synthesis and characterization of luminescent cadmium selenide/zinc selenide/zinc sulfide cholinomimetic quantum dots

Abstract

Luminescent quantum dots conjugated with highly selective molecular recognition ligands are widely used for targeting and imaging biological structures. In this paper, water soluble cholinomimetic cadmium selenide (core), zinc selenide/zinc sulfide (shell) quantum dots were synthesized for targeting cholinergic sites. Cholinomimetic specificity was incorporated by conjugation of the quantum dots to an aminated analogue of hemicholinium-15, a well known competitive inhibitor of the high affinity choline uptake transporter. Detailed evaluation of the nanocrystal synthesis and characterization of the final product was conducted by (1)H and (31)P NMR, absorption and emission spectroscopy, as well as transmission electron microscopy.

Synthesis, Optical Characterization, and Size Distribution Determination by Curve Resolution Methods of Water-Soluble CdSe Quantum Dots

“…11,20,21 Because the large absorption and emission bands of water-soluble CdSe nanocrystals remain poorly understood, there is little information about their size distribution. Exchange of the short-chain surface ligand for a long-chain ligand renders water-soluble CdSe QDs easily soluble in organic solvents, 22 as shown by Gégout et al 23 Obtaining nanocrystals that are compatible with organic solvents is vital for applications in optoelectronic devices. All these advantages have motivated research into watersoluble QDs in an attempt to increase the photoluminescence quantum yield (ɸ f ) of materials synthesized in aqueous medium and to promote surface modifications that will ensure desirable optical and electronic properties as well as good chemical stability.…”

“…On average, [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] emission spectra were collected for each CdSe QDs dispersion obtained at different synthesis time of reaction by varying the excitation wavelength by 5 nm. To include all the geometric characteristics of the emission spectrum, for each sample, the initial excitation wavelength was defined in such a way that recording of the emission spectra began between 50 and 60 nm before the emission increased sharply.…”

Synthesis and characterization of water soluble choline labeled cadmium selenide/zinc selenide/zinc sulfide luminescent quantum dots

“…Peaks in the 31 P NMR spectra for the core-shell QDs were consistent with a TOPO and TOP coated surface. [16] Upon reaction with Ch-SH the characteristic TOPO and TOP peaks disappeared providing further evidence that ligand exchange occurred. Figure 3 shows the comparison of the UV-visible spectra for the CdSe/ZnSe/ZnS core-shell QDs in CHCl 3 to the Ch-S-QDs in 0.1 M PBS pH 7.3.…”

“…[15] To target and investigate cholinergic sites, we reported the first example of water-soluble CdSe/ZnSe/ZnS QDs with an aminated analogue of hemicholium-15 (HC-15), a well-known inhibitor of CHT, attached to the surface of the QDs. [16] In this manuscript a new bioconjugate with a thiolated Ch analogue (Figure 1b) was synthesized and coupled to QDs to mimic the natural Ch substrate for CHT. The thiolated Ch derivative was designed with the important recognition elements for CHT, the quaternary ammonium and hydroxyl groups, and a terminal thiol to function as the tether to anchor the recognition label to the outer ZnS layer of the QDs.…”

“…The choline-labeled QDs were prepared by first synthesizing the CdSe/ZnSe/ZnS core-shell QD [16] followed by ligand exchange of TOPO coated QDs with Ch-SH. Ch-SH was dissolved in ethanol and filtered through a cotton filled pipette.…”