ZnSe Quantum Dots Research Articles

Antioxidant, gene expression and metabolomics fingerprint analysis of Arabidopsis thaliana treated by foliar spraying of ZnSe quantum dots and their growth inhibition of Agrobacterium tumefaciens.

Nanotechnology, new fascinating field of science, is bringing many application's options. However, it is necessary to understand their potential environmental risk and toxicity. Zinc selenide quantum dots (ZnSe QDs) are getting valuable due to wide industrial usage, mainly as cadmium free diodes or stabilizing ligand. Thanks to unique properties, they could also open the possibilities of application in the agriculture. Their effects on living organisms, including plants, are still unknown. Therefore, the attention of this work was given to antioxidant response of Arabidopsis thaliana to 100 and 250 μM ZnSe QDs foliar feeding. ZnSe QDs treatment had no statistically significant differences in morphology but led to increased antioxidant response in the leaves at the level of gene expression and production secondary antioxidant metabolites. Concurrently, analysis of growth properties of Agrobacterium tumefaciens was done. 250 μM ZnSe solution inhibited the Agrobacterium tumefaciens viability by 60%. This is the first mention about effect ZnSe QDs on the plants. Although QDs induced oxidative stress, the apply treatment dose of ZnSe QDs did not have significant toxic effect on the plants and even no morphological changes were observed. However, the same amount of ZnSe QD induced an inhibitory effect on Agrobacterium tumefaciens.

Mechanistic Insights and Controlled Synthesis of Radioluminescent ZnSe Quantum Dots Using a Microfluidic Reactor

We describe the controlled colloidal synthesis and characterization of ZnSe quantum dots using a continuous-flow microfluidic reactor. A systematic investigation of the synthetic route reveals a po...

STUDY OF THE INFLUENCE OF TEMPERATURE AND pН LEVEL ON PROPETIES OF COLLOIDAL SOLUTIONS OF ZnSe AND CdSe QUANTUM DOTS IN THE SHELL OF CHITOSAN

In this paper, we present a technique for the synthesis of colloidal quantum dots ZnSe and CdSe in an aqueous medium stabilized with a solution of chitosan at different pH values, and also studies of the properties of the resulting solutions as a function of temperature and acidity of the medium. It has been established that as the pH is increased in the region of 4.50−5.45, the amount of light transmission of colloidal solutions of quantum dots in the shell of chitosan increases, both in the case of zinc selenide and in the case of cadmium selenide. The effect of the medium acidity on the kinematic viscosity of the colloidal obtained solutions was studied. It has been established that the kinematic viscosity of colloidal solutions of ZnSe and CdSe quantum dots decreases with increasing pH of the medium in the region of 4.50−5.45: in both cases, there is a sharp drop in the kinematic viscosity in the region of 4.50–4.75 and a smoother decrease in the range of 4.75–5.25. It is shown that the stabilizing effect of chitosan in colloidal solutions of semiconductor nanoparticles depends on the temperature. The most stable in time are colloidal solutions prepared at a temperature of 35, 40 and 45 °C, in which the decrease in the light transmission in time was the smallest. Solutions synthesized at temperature 25 °С, as well as at higher temperatures (35, 40, 45 и 70 °С), did not show strong aggregative stability.

Influence of surface and polarization effects on electronic excitation energy transfer in colloidal solutions and films of ZnSe quantum dots

Optical absorption spectra of colloidal solutions and films based on ZnSe quantum dots (QD) stabilized with thioglycerol or thioglycolic acid and precipitated on spherical nanoparticles of silicon dioxide are presented and studied. In addition to the usual quantum-size effect, two contributions to the energy of excitons in QD were found. The first (surface effect) occurs in colloidal solutions of QD stabilized by thioglycerol due to the absorption of the thiol –SH group by Zn and Se atoms. The second (polarization effect) is additional and is formed in the solid films of both colloids due to the dielectric mismatch between QD materials and the surrounding matrix. It was shown for the first time that the electronic excitation energy transfer on a spherical surface in dense ZnSe QD array occurs due to the mechanism of strong interaction (hybridization of orbitals) between neighboring QD, which is satisfactorily described by the proposed theoretical model.

Enhanced and broadened fluorescence of ZnSe quantum dots enabled by the fluorescence energy transfer system of ZnSe quantum dots and gold nanoparticles.

The enhanced and broadened fluorescence of ZnSe quantum dots (QDs) were studied by using a fluorescence energy transfer system (FETS) of ZnSe QDs and gold nanoparticles (NPs). The FETS were prepared via uniformly dispersing the gold nanoparticles into ZnSe QD solution in the condition of magnetic stirring. Enhanced and broadened fluorescence was observed on the film of the FETS due to the transfer of photo-generated carriers between the ZnSe QDs and the gold NPs, instead of the surface plasma resonance effect. The excitonic and enhanced fluorescence on the FETS film depended on the competition of electron-hole recombination and electron transfer from the ZnSe QDs to the gold NPs. In addition, because of the excitonic fluorescence of the ZnSe QDs absorbed by the gold NPs, the electrons of the s-p band of the gold NPs were further increased to facilitate its energy level shift toward the conduction band of the ZnSe QDs in order to create a blueshift in the enhanced fluorescence. This enhanced and broadened fluorescence method can be applied for controlling fluorescence in photoelectric detection, photodiodes, lightshows, and sensor devices.

Enriching Mn-Doped ZnSe Quantum Dots onto Mesoporous Silica Nanoparticles for Enhanced Fluorescence/Magnetic Resonance Imaging Dual-Modal Bio-Imaging.

Multimodal imaging is more suitable for disease diagnosis because of its ability to provide more complementary and accurate information over single-mode imaging. Mn-doped quantum dots (QDs), especially Mn-doped ZnS (ZnSe) QDs, possess unique fluorescent and magnetic properties and are thus attractive for fluorescence/magnetic resonance imaging (MRI) dual-mode imaging. However, the optimal dopant (Mn2+) concentration for maximizing the fluorescence of QDs is relatively low for the MRI imaging. Herein, based on the large Stokes shift of Mn-doped ZnSe QDs, an enrichment strategy with mesoporous silica (MSN) loading was explored for constructing a highly luminescent/paramagnetism Mn-doped ZnSe QDs assembly (MSN@QDs) for improved MRI/optical dual-model imaging. After assembly, the loading density of QDs in MSNs was estimated to be 152 ± 12. Upon loading, the fluorescence of the MSN@QDs assembly was enriched along with QDs (enrichment factor of ∼143). Because of the large Stokes shift (∼200 nm), no appreciable concentration quenching was observed. Meanwhile, the T1 MR contrast was also increased both in vitro and in vivo through improved local Mn2+ concentration, realizing MRI signal enrichment. In fluorescence imaging investigations, MSN@QDs showed better performance over both single QDs and equivalent numbers of MSN-free single QD. Therefore, this enrichment strategy allowed simultaneous signal enhancement of the two imaging modes of Mn-doped ZnSe QDs.

Adverse Interactions of Luminescent Semiconductor Quantum Dots with Liposomes and Shewanella oneidensis.

Cadmium-containing luminescent quantum dots (QD) are increasingly used in display, bioimaging, and energy technologies; however, significant concerns have been raised about their potentially adverse impact on human health and the environment. This study makes use of a broad toolkit of analytical methods to investigate and increase our understanding of the interactions of luminescent cadmium-containing (CdSe) and cadmium-free (ZnSe) QD, with and without a passivating higher bandgap energy ZnS shell, with phospholipid vesicles (liposomes), which model bacterial membranes, and with Shewanella oneidensis MR-1, an environmentally relevant bacteria. A unique feature of this study is that all QD types have the same surface chemistry, being capped with uncharged poly(ethylene glycol) ligands. This enables focusing the study on the impact of the QD core on liposomes and bacterial cells. The study reveals that QD association with liposome and bacterial cell membranes is imperative for their adverse impact on liposomes and bacterial cells. The QD' concentration-dependent association with liposomes and bacterial cells destabilizes the membranes mechanically, which leads to membrane disruption and lysis in liposomes and to bacterial cell death. The study also shows that cadmium-containing QD exhibit a higher level of membrane disruption in bacterial cells than cadmium-free QD. ZnSe QD have low membrane impact, and coating them with a ZnS shell decreases their membrane disruption activity. In contrast, CdSe QD exhibit a high level of membrane impact, and coating them with a ZnS shell does not decrease, but in fact further increases, their membrane disruption activity. This behavior might be attributed to higher affinity and association of CdSe/ZnS QD with liposomes and bacterial cells and to a contribution of dissolved zinc ions from the ZnS shell to increased membrane disruption activity.

Enhanced photocatalytic activity of ZnSe QDs/g-C3N4 composite for Ceftriaxone sodium degradation under visible light

A ZnSe quantum dot (QDs)/g-C3N4 composite with an excellent photocatalytic activity was synthesized to degrade Ceftriaxone sodium in an aquatic environment under visible light irradiation. The enhanced photocatalytic activity of the composite during antibiotic degradation could be attributed to the expanding light-harvesting scope and the efficient separation of photogenerated electron-hole pairs. Experiments involving reactive species trapping revealed that the reactive species OH and h+ played major roles in Ceftriaxone sodium degradation. Recycling experiments showed that the ZnSe QDs/g-C3N4 composite was highly stable and reusable. This work provided new insights into the construction of a novel photocatalyst that removes antibiotics in aquatic environments.

Facile and green synthesis of core–shell ZnSe/ZnS quantum dots in aqueous solution

In this work, core–shell ZnSe/ZnS quantum dots (QDs) with excellent blue light emission were successfully synthesized in aqueous solution using thioglycolic acid as a stabilizer, thiourea as a sulphur source, and zinc acetate dihydrate as a Zn source. The crystal structure and optical properties of the as-synthesized ZnSe/ZnS QDs were characterized using X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, photoluminescence (PL) and UV–Visible spectroscopy. The ZnSe/ZnS QDs had a cubic zinc blende crystalline structure with an average particle size of approximately 4.6 nm. The excitonic emission slightly shifted to a longer wavelength and the PL intensity increased considerably with the growth of the ZnS shells. Meanwhile, the PL quantum yield of the ZnSe/ZnS QDs increased to 58.5%, which was much higher than that of ZnSe QDs. The exciton radiative lifetimes were approximately 46.3 and 23.1 ns for the core–shell ZnSe/ZnS QDs and ZnSe QDs, respectively.

Photocatalytic activity enhanced by synergistic effects of nano-silver and ZnSe quantum dots co-loaded with bulk g-C3N4 for Ceftriaxone sodium degradation in aquatic environment

The development of novel semiconductor with highly efficient photocatalytic activity for completely degrading organic pollutants in the aquatic environment is a dominating goal of modern chemistry. Herein, a novel composite with excellent photocatalytic activity was firstly synthesized by loading small size of ZnSe quantum dot (QDs) and nano-Ag onto the surface of the bulk g-C3N4 (CN). The novel composite (ZnSe-Ag/CN) was used to degrade Ceftriaxone sodium in the aquatic environment at low concentrations under visible light irradiation, and the 7%-ZnSe-Ag/CN composite displayed superior photocatalytic activity, approximately 89.24% of Ceftriaxone sodium has been degraded under visible light irradiation for 90 min, which was approximately 10.14-folds, 2.72-folds, 2.09-folds and 1.39-folds higher than pure ZnSe QDs, CN, 7%-Ag/CN and 5%-ZnSe/CN sample, respectively. Based on the adsorption test, the UV–vis diffuse reflectance spectra (DRS), the N2 adsorption–desorption isotherm, the photoluminescence spectra, the transient photocurrent response and the electrochemical impedance spectroscopy (EIS) measurements, the enhanced photocatalytic activity of the ZnSe-Ag/CN composite could be attributed to the excellent adsorbability, expansion of the light-harvesting scope, as well as the efficient separation of photogenerated electron-hole pairs. Meanwhile, the ZnSe-Ag/CN composite could produce a large amount of the hydroxyl radicals (OH) during the photocatalytic degradation process. Furthermore, a possible pathway of Ceftriaxone sodium degradation was proposed according to the detailed analyses of the produced intermediates to better understand the reaction process. Therefore, this work offers a new strategy for designing novel photocatalyst with excellent photocatalytic activity to remediation of water contamination.

Fluorescent Biomolecules Capped ZnSe Quantum Dots and Their Photocatalytic Activities

The preparation of semiconductor Quantum Dots (QDs) with controllable size, shape and doping remains a biggest challenge, especially the size below 10 nm. To date, only scarce attempts have been made on the synthesis of ZnSe QDs using biomolecule-assisted hydrothermal approach. Hence the current research work examines the influence of some amino acids namely L-cysteine, methionine and tyrosine as stabilizing agents in the synthesis of ZnSe nanocrystals. The ZnSe QDs exhibited strong absorption and photoluminescence properties in the region from 200-600 nm. Spectroscopic and structural properties of the as-synthesized biomolecule-capped ZnSe QDs were characterized by UV-vis absorption spectrophotometer, FT-IR, fluorescence spectrophotometer, X-ray diffractometer, Scanning Electron Microscope and EDX analysis. The stabilizing agents have played a crucial role in preparing ZnSe QDs and in determining the photoluminescence properties. The luminescence intensity was enhanced significantly when amino-acid-capped ZnSe QDs were illuminated by UV light compared to visible light. The as-synthesised ZnSe QDs were capable of effectively degrading an organic azo dye Azophlexin, under direct sunlight irradiation and exhibited good stability during photocatalytic experiments which can be attributed to the small size of amino acid capped ZnSe. The degradation mechanism is discussed. The absorbance and FT-IR measurements confirmed the biocompatibility and water-solubility of the pure ZnSe and capped ZnSe QDs.

Relaxation Kinetics of Excitonic States in ZnSe Quantum Dots: A Femtosecond Laser Spectroscopy Study

Relaxation processes in ZnSe quantum dots upon excitation by a 30-fs pulse at a wavelength of 360 nm have been studied by broadband femtosecond absorption spectroscopy. The diameter of ZnSe nanoparticles was 3.7 ± 0.6 nm. A colloidal solution of ZnSe in cyclohexane was used. In the differential spectra, a bleaching band at the edge of the excitonic absorption band of ZnSe, an absorption band of the biexcitonic transition with a peak at about 420 nm, and a broad structureless absorption band in the region from 440 to 750 nm have been revealed. From the analysis of the absorption and luminescence spectra, the shift of the excitonic luminescence band δXX = 127 meV has been measured. From the femtosecond photolysis data, an estimate of the biexcitonic interaction ΔXX ≈ 75 meV has been obtained. It has been shown that the relaxation kinetics of the differential spectra is described by three-exponential dependences with time constants and corresponding amplitude contributions of 1 ps (42%), 13 ps (22%), and 91 ps (17%). The kinetic component of 1 ps (42%) is presumably due to hole transport to surface traps. The kinetic components of 13 ps (22%) and 91 ps (17%) apparently describe the processes of electron transport to shallow and deep traps.

Aqueous manganese-doped ZnSe quantum dots with fluorescence and paramagnetism as dual-modality imaging probes

Aqueous manganese-doped ZnSe quantum dots with fluorescence and paramagnetism as dual-modality imaging probes

Affinity Binding-Induced Hg2+ Release and Quantum Dot Doping for General, Label-Free, and Homogenous Fluorescence Protein Assay.

Herein, a general protein conversion and analysis strategy was developed for homogeneous, label-free, and sensitive protein detection, on the basis of the affinity binding-induced Hg2+ release for protein conversion, and the succeeding Hg2+ doping-induced ZnSe quantum dot (QD) photoluminescence for signal readout. Two DNA motifs were designed, each of which was conjugated with a protein-specific recognition ligand. The mercury ions were initially introduced into one DNA motif by T-Hg2+-T interaction. The Hg2+ releasing was then accomplished after protein recognition-initiated strand exchange reaction between two DNA motifs. Then, the simultaneous incorporation of the released Hg2+ into ZnSe QD resulted in a doping-dependent fluorescence emission at 560 nm correlated with protein analysis. The protein assay is outperformed only by a simple one-step mixing operation but no separation or washing steps. Also, the use of doped QD as a fluorogenic reporter can avoid the fluorophore and/or quencher labeling, and eliminate complex DNA manipulation procedures for signal readout or amplification involved in most existing nucleic acid-based protein conversion and analysis methods. The versatile and sensitive detection toward multivalent proteins was verified with the detection limits achieved at 0.034 nM for anti-Dig antibody, 0.012 nM for streptavidin, and 0.025 nM for thrombin. Thus, it shows great promise for protein analysis to accommodate the applications in disease diagnosis, biomarker screening, and clinical medicine.

Controlling wide-spectrum fluorescence on Au/ZnSe multi-heterojunction

We present a wide-spectrum photoluminescence (PL) enhancement effect on the multi-heterojunction of ZnSe quantum dots and gold nanoparticles (NPs). The Au/ZnSe heterojunction is fabricated using Langmuir–Blodgett assembling method. The photoluminescence is measured using a 150 nm aperture ultraviolet laser beam spot of a scanning near-field optical microscope. The enhancement of band-gap emission and defect PL, the quenching of the fluorescence are, respectively, observed, which depend on the distance of gold NPs and ZnSe quantum dots. The enhancement of the band-gap emission is ascribed to the local field enhancement induced by the resonant coupling between the excitons of ZnSe and the surface plasmons of gold NPs. The enhancement of the defect PL is a result of the electron trapped by the defect states in the process of transporting electrons from ZnSe QDs to gold NPs due to the increase of the built-in electric field to hinder the electron transfer to gold nanoparticles. In addition, the quenching of the fluorescence is due to the electron transfer from ZnSe quantum dots to gold NPs. Our result opens the possibility of applications in forming uniform optoelectronic heterojunction and in controlling fluorescent efficiency of PL devices.

Optical properties of Cu ions‐doped ZnSe quantum dots in silicate glasses

AbstractIn order to alleviate the effect of the surface defects on the emission properties of quantum dots, copper ions‐doped ZnSe quantum dots (QDs) in the glasses are prepared using melt‐quenching and subsequent thermal annealing methods. For glasses without copper doping, tunable band‐edge emission from ZnSe QDs is achieved. For glasses with copper doping, efficient energy transfer from ZnSe QDs to copper ions is observed, and efficient broad band emission from copper ions is realized at the expense of the band‐edge emission of ZnSe QDs. Absorption spectra, size‐dependent broad‐band emission spectra and electron spin resonance spectra show the cupric ions are doped into the ZnSe QDs. Results reported here shows that doping of transition‐metal ions into semiconductor QDs in glasses is promising for development of high efficient luminescent glasses.

Magnetic field insensitive photoluminescence decay of ZnSe/CdS core/shell type-II colloidal quantum dots

We have synthesized ZnSe/CdS core/shell type-II colloidal quantum dots, where an electron and a hole are separated in the CdS shell and the ZnSe core, respectively. Our theoretical model has revealed that absorbance spectrum of bare ZnSe quantum dots in 2 nm radius becomes broadened with a large redshift (∼1.15 eV) when the electron in ZnSe core is separated by 3.2 nm CdS shell. Also, we found that our type-II QDs are insensitive to an external magnetic field up to 5 T in terms of central emission energy, degree of polarization, and photoluminescence decay time. This can be attributed to the electron–hole charge separation in a type-II structure, whereby the suppressed exchange interaction gives rise to a magnetic insensitivity with a small energy difference between the bright and dark exciton states.

Evaluation of ZnSe(S) Quantum Dots on the Cell Viability of Prostate Cancer Cell (PC3)

Nanomedicine is described as the process of diagnosing, treating, and preventing disease using nanostructured materials to improve human health. Quantum dots (QDs) host suitable optical properties for light-driven therapies, e.g., photo-dynamic therapy (PDT), for cancer treatment. The efficacy of QDs-assisted PDT relies on the capability of QDs to generate reactive oxygen species, which can be enhanced by inducing structural defects at the atomic level. Furthermore, data concerning the applicability of QDs-PDT in medicine is scarce, particularly for prostate cancer cells (PC3). On this basis, and as a first step in this research, the present report focused on the direct aqueous-synthesis of water-stable ZnSe(S) QDs via a microwave-assisted synthesis approach in the presence of thioglycolic acid (TGA) and mercaptopropionic acid (MPA). XRD analysis confirmed the face centered cubic structure in host ZnS; the average crystallite size was estimated at 10 nm. The photoluminescence of MPA-capped ZnSe(S) showed a strong main emission peak around 363 nm and a trap emission, attributed to structural defects, centered on 450 nm. The photoluminescence spectrum for TGA-capped ZnSe(S) QDs exhibited only the band gap peak around 390 nm, suggesting the absence of major structural defects. In turn, cell viability assays TGA-capped ZnSe(S) were not toxic at concentrations up to 100 ppm, whereas MPA-capped ZnSe(S) evidenced cytotoxicity at a concentration of 10 ppm. The lethal dose (LD50) for the MPA-capped ZnSe(S) in the PC3 cell line was 36 ppm and 35 ppm for 24 h and 48 h, respectively.

Highly fluorescent positively charged ZnSe quantum dots for bioimaging

Quantum Dots (QDs) are fluorescent semiconductor nanocrystals with unique optical properties, which are being highly applied in opto-electronic devices and biological sciences. Aiming at biological applications we developed highly blue fluorescent Cysteamine coated ZnSe QDs. They were prepared in aqueous medium at near physiological pH by a fast precipitation process followed by hydrothermal growth. The characteristic excitonic emission output was enhanced by decreasing their surface defects via an UV photoactivation procedure. We tested their in vitro cytotoxicity towards macrophage cells and probed their functionality by labeling two different cell types: Candida albicans and red blood cells by electrostatic interaction with the negative cell membranes. The overall results show that these positively charged QDs can be applied as new low toxic and promising platforms for biolabeling purposes.

Based on ZnSe quantum dots labeling and single particle mode ICP-MS coupled with sandwich magnetic immunoassay for the detection of carcinoembryonic antigen in human serum

A highly sensitive sandwich-type magnetic immunoassay based on inductively coupled plasma mass spectrometry detection in single particle mode, with ZnSe Quantum dots (QDs) serving as model tags, was proposed. The transient signals induced by the flash of ions (64Zn+) in the plasma torch from the ionization of nanoparticles tagged on antibody were recorded in a single particle mode. The frequency of transient signals is directly related to the concentration of nanoparticle tags, and the concentration of nanoparticle tagged antibodies can be quantified by the frequency of transient signals. Amino-modified magnetic nanoparticles (AMNPs) were synthesized and conjugated with primary carcinoembryonic antigen (CEA) antibody to extract the target biomarker. ZnSe QDs were synthesized as a probe to determine CEA by ICP-MS. A detection limit of 0.006 ng mL−1 was obtained for CEA after immunoreactions, and a wide linear range of 0.02–100 ng mL−1 with the relative standard deviation (RSD) was 4.4%. The method was successfully applied to human serum samples.