Hydrothermal synthesis of highly luminescent blue-emitting ZnSe(S) quantum dots exhibiting low toxicity

Reaction-dependent optical behavior and theoretical perspectives of colloidal ZnSe quantum dots

Colloidal quantum dots (QDs) are attracting research interest because of their unique optical properties that result from the quantum confinement effect. ZnSe QDs, which are II-VI semiconductors, offer a wide direct bandgap (2.7 eV), making them promising for applications such as light-emitting diodes, photodetectors, and biomedical labeling. In the present work, colloidal ZnSe (QDs) were synthesized by the hot-injection method with a Zn:Se ratio of 1:1. The optical properties of ZnSe QDs obtained at different reaction times were investigated by spectrophotometric UV-vis absorption and emission measurements. The as-synthesized ZnSe QDs exhibit blue excitonic emission, and no defect emission was detected. Transmission electron micrographs indicated that the QDs have a spherical morphology with dimensions ranging from 3.69 to 4.53 nm. In particular, the Brus model was applied to demonstrate a correlation between the QD sizes and the optical bandgaps obtained from Tauc plots.

An "off-on" fluorescent nanosensor for the detection of cadmium ions based on APDC-etched CdTe/CdS/SiO2 quantum dots

In this study, we have developed a novel fluorescent "OFF-ON" quantum dots (QDs) sensor based on CdTe/CdS/SiO2 cores. Ammonium pyrrolidine dithiocarbamate (APDC), ethylenediamine tetraacetic acid (EDTA), and 1,10-phenanthroline (Phen) served as potential chemical etchants. Among these three etchants, APDC exhibited the most pronounced quenching effect (94.06%). The APDC-etched CdTe/CdS/SiO2 QDs demonstrated excellent optical properties: the fluorescence of the APDC-etched CdTe/CdS/SiO2 QDs system (excitation wavelength: 365 nm and emission wavelength: 622 nm) was significantly and selectively restored upon the addition of cadmium ions (Cd2+) (89.22%), compared to 15 other metal ions. The linear response of the APDC-etched CdTe/CdS/SiO2 QDs was observed within the cadmium ion (Cd2+) concentration ranges of 0-20 μmol L-1 and 20-160 μmol L-1 under optimized conditions (APDC: 300 μmol L-1, pH: 7.0, reaction time: 10 min). The detection limit (LOD) of the APDC-etched CdTe/CdS/SiO2 QDs for Cd2+ was 0.3451 μmol L-1 in the range of 0-20 μmol L-1. The LOD achieved by the QDs in this study surpasses that of the majority of previously reported nanomaterials. The feasibility of using APDC-etched CdTe/CdS/SiO2 QDs for Cd2+ detection in seawater, freshwater, and milk samples was verified, with average recoveries of 95.27%-110.68%, 92%-106.47%, and 90.73%-111.60%, respectively, demonstrating satisfactory analytical precision (RSD ≤ 8.26).

UV Light as an Efficient Tool for Reducing Surface Defects of ZnSe-MSA Quantum Dots

Defects in ZnSe quantum dots are responsible for increasing the trap states, which can lead to the drastic reduction of their fluorescence output, being one of the major drawbacks of these materials. As surface atoms become more relevant in these nanoscale structures, energy traps due to surface vacancies, play a very definite role in the final emission quantum yield. In the present study, we report the use of photoactivation procedures to decrease surface defects of ZnSe QDs stabilized with mercaptosuccinic acid (MSA), in order to improve the radiative pathways. We applied the colloidal precipitation procedure in a hydrophilic medium and evaluated the role of Zn/Se molar ratios as well as the Zn2+ precursors (nitrate and chloride salts) on their optical properties. Best results (i.e. increment of 400% of the final fluorescence intensity) were obtained for nitrate precursor and a Zn/Se = 1.2 ratio. Thus, we suggest that the chloride ions may compete more efficiently than nitrate ions with MSA molecules decreasing the passivation capability of this molecule. The improvement in ZnSe QDs fluorescence can potentialize their use for biomedical applications.

Graphene oxide mediated CdSe quantum dots fluorescent aptasensor for high sensitivity detection of fluoroquinolones

In view of the urgent need for fluoroquinolones contamination detection in the fields of food safety, a novel aptasensor based on the fluorescence quenching property of graphene oxide (GO) and the fluorescence characteristic of cadmium selenide quantum dots (CdSe QDs) was developed for fluoroquinolones highly sensitive detection in this work. The CdSe QDs with carboxyl-rich surface were synthesized successfully and fluoresced at 525 nm under the optimal excitation light of 366 nm. Based on the hydrophobic and π-π stacking between GO and aptamer, aptamer labeled by CdSe QDs fluorescence (CdSe QDs-apt) were adsorbed by GO and the fluorescence of CdSe QDs was quenched. After the aptamer combined specifically with fluoroquinolones, greater specific force lead to the desorption of CdSe QDs-apt from GO and fluorescence recovery. Represented by Ciprofloxacin (CIP), a member of fluoroquinolones, the fluorescence emission increased with the increasing of CIP concentrations from 8 nM to 500 nM, and the detection limit was 0.42 nM. The spiked recoveries in real samples of honey and milk were 91.5-96.9 % and 90.3-95.2 %, respectively, indicating that the aptasensor was reliable. Moreover, the fluorescence responses of multiple members of fluoroquinolones were found to be consistent, denoting that the fluorescence aptasensor can be used to detect the total amount of multiple members of fluoroquinolones. These results showed that the aptasensor can be used as a promising platform for fluoroquinolones detection.

Effect of Preparation Parameters on Deep-Blue Light-Emitting Diodes Based on Nanostructured ZnSe/ZnS Multilayer Films

Compared to colloidal quantum dots, nanostructured multilayer films may also be a promising emission layer in future light-emitting diodes, due to their excellent photoluminescence (PL), narrow full width at half-maximum (FWHM), and wide color gamut. In this paper, multilayer-structured deep-blue light-emitting diodes (LEDs) were prepared, where nanostructured ZnSe/ZnS multilayer films act as the light-emitting layer. The device showed good blue electroluminescence (EL) spectrum locating at 448 nm with an FWHM of 31 nm. To improve the performance of the device, the effect of preparation parameters of different layers was investigated in detail. The results demonstrated that the preparation parameters of each layer affected the performance in different ways, and choosing the most suitable preparation parameters can achieve optimal performance. Furthermore, this multilayer-structured device based on nanostructured films as emission layer can also be applied in green and red LEDs or all-inorganic QLEDs.

Extracellular biosynthesis of biocompatible CdSe quantum dots

An extracellular biosynthesis method has been developed to prepare cadmium selenide (CdSe) quantum dots (QDs) with strong fluorescence emission by incubating cheap Cd and Se inorganic salts with Escherichia coli (E.coli) bacteria. Ultraviolet-visible absorption spectra, photoluminescence (PL) spectra, and high-resolution transmission electron microscopy analysis showed that the biosynthesised CdSe QDs have an average size of 3.1 nm, the excellent optical properties with fluorescence emission around 494 nm, and the good crystallinity. It was found that addition of 80 mg of mercaptosuccinic acid resulted in the formation of CdSe QDs with highest PL intensity. Furthermore, Fourier-transform infrared spectra of as-synthesised CdSe QDs confirmed the presence of a surface protein capping layer. The biosynthesised CdSe QDs were incorporated into the yeast cells as illustrated by laser confocal scanning microscopy images, showing a great potential in bio-imaging and bio-labelling application.

Ligand-assisted synthesis and cytotoxicity of ZnSe quantum dots stabilized by N-(2-carboxyethyl)chitosans

Here we report a green synthesis of ZnSe quantum dots (QDs) in aqueous solution of polyampholyte chitosan derivative - N-(2-carboxyethyl)chitosan (CEC) with substitution degrees (DS) from 0.7 to 1.3 and molecular weight (MW) of 40 kDa and 150 kDa. We have shown that the maximum intensity of photoluminescence (PL) is exhibited by ZnSe QDs synthesized in solutions of CEC with DS 1 at Se:Zn molar ratio 1:2.5. The defect-related band was predominant in the PL spectra of ZnSe QDs obtained at room temperature; however, hydrothermal treatment at 80-150 °C during 1-2 h significantly increased contribution of exciton emission to the spectra. Cytotoxicity of ZnSe QDs was investigated by MTT assay using cancer cell lines SKOV-3; SkBr-3; PANC-1; Colon-26 and human embryonic kidney cell line HEK293. Cytotoxicity of ZnSe QDs did not depend on MW or DS of CEC but significantly depended on the cell line, being the lowest for normal human cells HEK293 and breast cancer cell line SKOV-3. The hydrothermally treated ZnSe QDs showed higher toxicity toward both normal and cancer cell lines. Since ZnSe QDs were toxic for most of the investigated cancer cell lines, they cannot be used as inert tracers for bioimaging, but can be promising for further investigation for anticancer therapy.

Nanoparticles for Bioapplications: Study of the Cytotoxicity of Water Dispersible CdSe(S) and CdSe(S)/ZnO Quantum Dots

Semiconductor nanocrystals or quantum dots (QDs) have unique optical and physical properties that make them potential imaging tools in biological and medical applications. However, concerns over the aqueous dispersivity, toxicity to cells, and stability in biological environments may limit the use of QDs in such applications. Here, we report an investigation into the cytotoxicity of aqueously dispersed CdSe(S) and CdSe(S)/ZnO core/shell QDs in the presence of human colorectal carcinoma cells (HCT-116) and a human skin fibroblast cell line (WS1). The cytotoxicity of the precursor solutions used in the synthesis of the CdSe(S) QDs was also determined in the presence of HCT-116 cells. CdSe(S) QDs were found to have a low toxicity at concentrations up to 100 µg/mL, with a decreased cell viability at higher concentrations, indicating a highly dose-dependent response. Meanwhile, CdSe(S)/ZnO core/shell QDs exhibited lower toxicity than uncoated QDs at higher concentrations. Confocal microscopy images of HCT-116 cells after incubation with CdSe(S) and CdSe(S)/ZnO QDs showed that the cells were stable in aqueous concentrations of 100 µg of QDs per mL, with no sign of cell necrosis, confirming the cytotoxicity data.

Target-driven switch-on fluorescence aptasensor for trace aflatoxin B1 determination based on highly fluorescent ternary CdZnTe quantum dots

Development of sensitive methods for trace aflatoxin B1 (AFB1) determination is of great significance due to its high toxicity and carcinogenicity. Herein, 3-mercaptopropionic acid (MPA)-capped ternary CdZnTe quantum dots (QDs) have been prepared via a simple hydrothermal route. We found that they exhibited enhanced intensity when benchmarked against their binary counterpart CdTe QDs. On this basis, a target-driven switch-on fluorescence aptasensor for trace AFB1 determination has been developed by employing the fluorescence resonance energy transfer (FRET) between the CdZnTe QDs and Au nanoparticles (AuNPs) pair. In the detection diagram, amino group-functionalized aptamers against AFB1 were firstly labelled with the CdZnTe QDs donors coated on silica nanospheres while the AuNPs acceptors were bioconjugated with the thiol group-modified complementary DNA (cDNA) of aptamer. By taking advantage of the DNA hybridization of aptamer and cDNA, the CdZnTe QDs (energy donor) and AuNPs (energy acceptor) were brought into close proximity, thereby leading to the occurrence of FRET during the aptasensor fabrication. When the aptasensor was incubated with AFB1, the specific binding between aptamer and target resulted in the detachment of AuNPs acceptors. This behavior would disturb the FRET process and led to the subsequent fluorescence recovery of CdZnTe QDs. Such designed aptasensor showed an increased fluorescence recovery upon the increasing concentration of AFB1 over a broad range of 50 pg mL^-1 - 100 ng mL^-1 and succeeded in spiked peanut samples. The proposed aptasensor is separation-free and easy-to-use, which might open up new possibilities in aptasensor fabrication by employing the novel CdZnTe QDs-AuNPs pair.

Fabrication of luminescent TiO2:Eu3+ and ZrO2:Tb3+ encapsulated PLGA microparticles for bioimaging application with enhanced biocompatibility

Rare earth is of great interest because of their unique optical properties, especially the rich luminescent spectra. In this study, we developed a facile one-pot microwave-assisted synthesis of luminescent Eu³⁺ doped TiO₂ nanoparticles and Tb³⁺ doped ZrO₂ nanoparticles. As a result, the emitting centers (Eu³⁺ and Tb³⁺) were all well dispersed in the amorphous host oxide materials, leading to high luminescence. The obtained TiO₂:Eu³⁺ and ZrO₂:Tb³⁺ nanoparticles were then encapsulated into PLGA microparticles for bio-applications. These luminescent microparticles were then proven to be highly stable, biocompatible and of low cytotoxicity. We successfully demonstrated the bioimaging of live cells using the red-luminescent TiO₂:Eu³⁺ nanoparticles and green-luminescent ZrO₂:Tb³⁺ nanoparticles embedded PLGA microparticles. The microwave-assisted synthetic methodology can be further developed to be general method to prepare oxide nanoparticles.

Cytotoxicity study of Piper nigrum seed mediated synthesized SnO2 nanoparticles towards colorectal (HCT116) and lung cancer (A549) cell lines

Different sized tetragonal tin oxide nanoparticles (SnO₂ NPs) were synthesized using Piper nigrum seed extract at three different calcination temperatures (300, 500, 900°C) and these nanoparticles (NPs) were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), dynamic light scattering (DLS) and Fourier transform infrared spectrophotometry (FT-IR). The optical properties were studied using UV-Vis and photoluminescence (PL) spectrophotometers. The generation of reactive oxygen species (ROS) was monitored by using a fluorescence spectrophotometer and fluorescence microscope. The cytotoxicity of the synthesized SnO₂ NPs was checked against the colorectal (HCT116) and lung (A549) cancer cell lines and the study results show that SnO₂ NPs were toxic against cancer cell lines depending on their size and dose. IC₅₀ values of SnO₂ NPs having average particle sizes of 8.85±3.5, 12.76±3.9 and 29.29±10.9nm are 165, 174 and 208μgL^-1 against HCT116, while these values are 135, 157 and 187μgL^-1 against A549 carcinoma cell lines, respectively. The generated ROS were responsible for the cytotoxicity of SnO₂ NPs to the studied cancer cells and smaller size NPs generated more ROS and hence showed higher cytotoxicity over larger size NPs. The results of this study suggest that the synthesized stable nanoparticles could be a potent therapeutic agent towards cancerous cell lines.