Composition-Tunable Optical Properties of Zn x Cd(1 − x)S Quantum Dot–Carboxymethylcellulose Conjugates: Towards One-Pot Green Synthesis of Multifunctional Nanoplatforms for Biomedical and Environmental Applications

Abstract

Quantum dots (QDs) are colloidal semiconductor nanocrystals with unique properties that can be engineered by controlling the nanoparticle size and chemical composition by doping and alloying strategies. However, due to their potential toxicity, augmenting their biocompatibility is yet a challenge for expanding to several biomedical and environmentally friendly applications. Thus, the main goal of this study was to develop composition-tunable and biocompatible ZnxCd1 − xS QDs using carboxymethylcellulose polysaccharide as direct capping ligand via green colloidal aqueous route at neutral pH and at room temperature for potential biomedical and environmental applications. The ternary alloyed QDs were extensively characterized using UV–vis spectroscopy, photoluminescence spectroscopy (PL), transmission electron microscopy (TEM), X-ray diffraction (XRD), electron energy loss spectroscopy (EELS), and X-ray photoelectrons spectroscopy (XPS). The results indicated that ZnxCd(1 − x)S QDs were surface stabilized by carboxymethylcellulose biopolymer with spherical morphology for all composition of alloys and narrow sizes distributions ranging from 4 to 5 nm. The XRD results indicated that monophasic ternary alloyed ZnxCd1 − xS nanocrystals were produced with homogenous composition of the core as evidenced by EELS and XPS analyses. In addition, the absorption and emission optical properties of ZnxCd1 − xS QDs were red shifted with increasing the amount of Cd2+ in the alloyed nanocrystals, which have also increased the quantum yield compared to pure CdS and ZnS nanoparticles. These properties of alloyed nanomaterials were interpreted based on empirical model of Vegard’s law and chemical bond model (CBM). As a proof of concept, these alloyed-QD conjugates were tested for biomedical and environmental applications. The results demonstrated that they were non-toxic and effective fluorophores for bioimaging live HEK293T cells (human embryonic kidney cells) using confocal laser scanning fluorescence microscopy. Moreover, these conjugates presented photocatalytic activity for photodegradation of methylene blue used as model organic industrial pollutant in water. Hence, composition-tunable optical properties of ternary ZnxCd1 − xS (x = 0–1) fluorescent alloyed QDs was achieved using a facile eco-friendly aqueous processing route, which can offer promising alternatives for developing innovative nanomaterials for applications in nanomedicine and environmental science and technology.

Recent Developments of Carboxymethyl Cellulose

“…For instance, [327] synthesized a novel quantum dot/CMC nano-conjugate material that showed its high potentialities for use as a fluorescent nanoprobe for in vitro bio-imaging of living cells (Figure 7c). In the same year, the authors developed a multifunctional, compositiontuneable semiconductor nanocrystal of a Zn x Cd (1-x) S quantum dot/CMC composite that exhibited its effectivity as a fluorophore for the bioimaging of living cells (HEK293T cells were used for the bioimaging test) [328]. Aswathy et al (2012) [329] synthesized a multifunctional biocompatible nanoparticle based on CMC for specific recognition of cancer cells (Figure 7e-h).…”

A novel fabrication strategy for alloyed Cd–Zn–S quantum dots–embedded glass with efficient red emission

“…Nevertheless, moderate light scattering is favorable for improving the color uniformity and the light extraction of high‐power WLED, especially when laser diodes are used as the excitation source 48,49 . The room‐temperature PLE and PL spectra in Figure 4C exhibit the characteristic shoulder peak of Cd x Zn 1− x S QDs and defect emission due to the large Stokes shift, respectively, consisting in the previous results 50,51 . What is more, both of the PLE and PL spectra continuously redshift, especially the emission peaks shift from 537 to 614 nm, along with the increase of the x value in Cd x Zn 1− x S QDEG samples, which reflects the reduction of effective bandgap energies of QDs through expanding the Cd/Zn ratio 52 .…”

“…48,49 The roomtemperature PLE and PL spectra in Figure 4C exhibit the characteristic shoulder peak of Cd x Zn 1−x S QDs and defect emission due to the large Stokes shift, respectively, consisting in the previous results. 50,51 What is more, both of the PLE and PL spectra continuously redshift, especially the emission peaks shift from 537 to 614 nm, along with the increase of the x value in Cd x Zn 1−x S QDEG samples, which reflects the reduction of effective bandgap energies of QDs through expanding the Cd/Zn ratio. 52 PLE and PL spectra of Cd 0.6 Zn 0.4 S QDEG sample have been shown in Figure S6, whose emission is located at 656 nm and too weak to be negligible for further discussion.…”

Enhanced Photoluminescence in CdxZn1–xS Solid Solution by Suppressing Non-Radiative Recombination for White Light-Emitting Diodes

“…x Zn 1−x S Solid Solution. Cd x Zn 1−x S solid solution (x = 0, 0.3, 0.5, 0.7, 1) has been synthesized via a simple coprecipitation method with some modifications, 34 followed with a vacuum-assisted heat treatment. The detailed procedures are as follows:…”