Fluorescent cadmium telluride quantum dots embedded chitosan nanoparticles: a stable, biocompatible preparation for bio-imaging

Abstract

Fluorescent cadmium telluride quantum dots (CdTe QDs) are an optically attractive option for bioimaging, but are known to display high cytotoxicity. Nanoparticles synthesized from chitosan, a natural biopolymer of β 1-4 linked glucosamine, display good biocompatibility and cellular uptake. A facile, green synthetic strategy has been developed to embed green fluorescent cadmium telluride quantum dots (CdTe QDs) in biocompatible CNPs to obtain a safer preparation than 'as is' QDs. High-resolution transmission electron microscopy showed the crystal lattice corresponding to CdTe QDs embedded in CNPs while thermogravimetry confirmed their polymeric composition. Electrostatic interactions between thiol-capped QDs (4 nm, -57 mV) and CNPs (~300 nm, +38 mV) generated CdTe QDs-embedded CNPs that were stable up to three months. Further, viability of NIH3T3 mouse fibroblast cells in vitro increased in presence of QDs-embedded CNPs as compared to bare QDs. At the highest concentration (10 μg/ml), the former shows 34 and 39% increase in viability at 24 and 48 h, respectively, as compared to the latter. This shows that chitosan nanoparticles do not release the QDs up to 48 h and do not cause extended toxicity. Furthermore, hydrolytic enzymes such as lysozyme and chitinase did not degrade chitosan nanoparticles. Moreover, QDs-embedded CNPs show enhanced internalization in NIH3T3 cells as compared to bare QDs. This method offers ease of synthesis and handling of stable, luminescent, biocompatible CdTe QDs-embedded CNPs with a favorable toxicity profile and better cellular uptake with potential for bioimaging and targeted detection of cellular components.

Shining Light on Chitosan: A Review on the Usage of Chitosan for Photonics and Nanomaterials Research

“…Fluorescence-based bioimaging techniques have been greatly encouraged due to several advantages, such as high sensitivity, high selectivity, diversity of use, and non-destructive nature of the imaging agent [ 57 ]. Current fluorescent dyes used for imaging and detection undergo a degradation process known as photobleaching that is irreversible and is known to severely hinder the imaging ability of the dyes [ 58 ]. Fluorescent quantum dots (QDs) (1–10 nm) are an attractive alternative for biological labelling because of their unique size-tunable fluorescence properties and excellent photostability [ 58 , 59 ].…”

“…Current fluorescent dyes used for imaging and detection undergo a degradation process known as photobleaching that is irreversible and is known to severely hinder the imaging ability of the dyes [ 58 ]. Fluorescent quantum dots (QDs) (1–10 nm) are an attractive alternative for biological labelling because of their unique size-tunable fluorescence properties and excellent photostability [ 58 , 59 ]. The interesting optical properties of QDs are due to quantum confinement of electron motion.…”

“…The quantization of energy levels resulting from quantum confinement of electrons results in emission, which is dependent upon the size of the QDs. QDs have robust fluorescence intensity with the advantage of a narrow emission and broad excitation wavelengths [ 58 , 59 ]. However, the main concern with QDs for biological imaging is their toxicity, since they are typically made from combinations of zinc(II), cadmium(II), selenide, and sulfide [ 58 , 60 ].…”

“…QDs have robust fluorescence intensity with the advantage of a narrow emission and broad excitation wavelengths [ 58 , 59 ]. However, the main concern with QDs for biological imaging is their toxicity, since they are typically made from combinations of zinc(II), cadmium(II), selenide, and sulfide [ 58 , 60 ]. Biocompatible polymers like CS were introduced with the toxic QDs to improve hydrophilicity, stability, functionalization, and biocompatibility, making these CS coated QDs useful for biological imaging and sensing applications [ 58 ].…”

“…However, the main concern with QDs for biological imaging is their toxicity, since they are typically made from combinations of zinc(II), cadmium(II), selenide, and sulfide [ 58 , 60 ]. Biocompatible polymers like CS were introduced with the toxic QDs to improve hydrophilicity, stability, functionalization, and biocompatibility, making these CS coated QDs useful for biological imaging and sensing applications [ 58 ]. Incorporation or entrapment of QDs within a biocompatible polymer also enhances colloidal stability of QDs, and allows the possibility of loading other materials such as drugs for multitudinal applications [ 58 ].…”