Cadmium Selenide Quantum Dots Research Articles

Investigation on Surface Properties of Mn-Doped CdSe Quantum Dots Studied by X-ray Photoelectron Spectroscopy

In this work, we report on the effects of incorporating manganese (Mn) dopant into different sizes of cadmium selenide (CdSe) quantum dots (QDs), which improves the electronic and optical properties of the QDs for multiple applications such as light-emitting diodes, lasers, and biological labels. Furthermore, the greener inverse Micelle method was implemented using organic ligand, which is oleic acid. This binding of the surface enhanced the QDs’ surface trap passivation of Mn-doped CdSe, which then increased the quantity of the output. In addition, the inverse Micelle technique was used successfully to dope Mn into CdSe QDs without the risk of Mn dopants being self-purified as experienced by wurtzite CdSe QDs. Also, we report the X-ray photoelectron spectroscopy (XPS) results and analysis of zinc blended manganese-doped cadmium selenide quantum dots (Mn-doped CdSe QDs), which were synthesized with physical sizes that varied from 3 to 14 nm using the inverse Micelle method. The XPS scans traced the existence of the Se 3d and Cd 3d band of CdSe crystals with a 54.1 and 404.5 eV binding energy. The traced 640.7 eV XPS peak is proof that Mn was integrated into the lattice of CdSe QDs. The binding energy of the QDs was related to the increase in the size of the QDs.

Cleaning Matters!

Translation of a manual process to high throughput for research and development requires special consideration. One important and often unreported aspect is the establishment of an efficient cleaning routine. This becomes significant, as precious time and, in particular, material would be lost, that is, when low-quality high-throughput experimentation is involved. We present a fully automated cleaning routine of the challenging synthesis of cadmium selenide quantum dots. Manual, semiautomated, and fully automated cleaning protocols were executed and compared in terms of spectral similarities of the synthesized colloids. Only the fully automated protocol enabled true 24/7 operation.

High Sensitivity Detection of Copper Ions in Oysters Based on the Fluorescence Property of Cadmium Selenide Quantum Dots

Cadmium selenide (CdSe) quantum dots (QDs) were synthesized by water phase synthesis method using 3-mercaptopropionic acid (3-MPA) as a stabilizer, and they were applied to the detection of copper ions (Cu2+). The results showed that CdSe QDs have excellent selectivity and sensitivity toward Cu2+. The fluorescence intensity of CdSe QDs decreased with the increase of Cu2+ concentration. The linear range was from 30 nM to 3 μM, and the detection limit was 30 nM. Furthermore, CdSe QDs were used for detecting the concentration of Cu2+ in oysters. The content of Cu2+ was 40.91 mg/kg, which was close to the one measured via flame atomic absorption spectrometry (FAAS), and the relative error was 1.81%. Therefore, CdSe QDs have a wide application prospect in the rapid detection of copper ions in food.

Lattice Strain Analysis of a Mn-Doped CdSe QD System Using Crystallography Techniques

In this work, we report on the different sizes of manganese-doped cadmium selenide quantum dots (Mn-doped CdSe QDs) synthesized for 0 to 90 min using a reverse micelle organic solvent method and surfactant having a zinc blende structure, with physical size varying from 3 to 14 nm and crystallite size from 2.46 to 5.46 nm and with a narrow size distribution. At similar reaction times, Mn-doped CdSe QDs displayed the growth of larger QDs compared with the pure CdSe QDs. Due to the implementation of lattice strain owing to the inclusion of Mn atoms in the CdSe QD lattice, the lattice parameter was compressed as the QD size increased. Strain was induced by the particle size reduction, as observed from X-ray diffractometer (XRD) analysis. The analyses of the strain effect on the QD reduction are discussed relative to each of the XRD characteristics.

Formation of laterally-oriented monolayers of plasmonic silver nanoplats and their ensembles with cadmium selenide quantum dots on the sur face of thin polymeric film

We present here a novel method for formation of laterally-oriented monolayers of plasmonic silver nanoplates and their electrostatic ensembles with semiconductor quantum dots. Monolayers were electrostatically deposited on the surface of thin polymeric film containing different amount of tertiary amino groups. This method allows simultaneously investigate optical properties and morphology of silver nanoplates using transmittance electron microscopy. The optical density of films and surface concentration of silver nanoplates is proportional to the percentage of tertiary amino groups in the polymeric film. A surface ligand exchange was used for functionalization of the surface of silver nanoplates toward formation of electrostatic ensembles with colloidal quantum dots. We observed a straight correlation between the red shift of surface plasmon resonances in silver nanoplates and alkyl chain length of ligand molecules.

Time controlled growth of CdSe QDs for applications in white light emitting diodes

Semiconductor nanophosphors have the exceptional resources to demonstrate the quantum phenomenon due to their tailored-size dependent photoluminescence (PL). The work here is focused on the synthesis of highly luminescent Cadmium Selenide (CdSe) Quantum Dots (QDs) by a simple technique. This is a time dependent process where change in the size of CdSe QDs was observed at a reaction temperature of 100 °C without any inert atmosphere. The CdSe QDs were synthesised by using 3-Mercapto propionic acid (MPA) rather than using the typically utilized capping agent. All the samples were characterised for their optical properties. The size of QDs was calculated in a range up to 3 nm by UV–Vis Spectroscopy and confirmed by High Resolution Transmission Electron Microscopy (HRTEM). It was clear from the UV studies that QDs exhibit size dependent tunable optical absorption. The broad Photoluminescence (PL) emission spectra depicts the presence of surface defects produced along with band edge spectrum. The absorbance and emission spectra were shifted to the red region due to the quantum confinement effect occurred in QDs. The water soluble QDs were economical and easy to fabricate has applications in Light Emitting Diodes (LEDs).

Isolating the Escherichia coli Transcriptomic Response to Superoxide Generation from Cadmium Chalcogenide Quantum Dots.

Nanomaterials have been extensively used in the biomedical field and have recently garnered attention as potential antimicrobial agents. Cadmium telluride quantum dots (QDs) with a bandgap of 2.4 eV (CdTe-2.4) were previously shown to inhibit multidrug-resistant clinical isolates of bacterial pathogens via light-activated superoxide generation. Here we investigate the transcriptomic response of Escherichia coli to phototherapeutic CdTe-2.4 QDs both with and without illumination, as well as in comparison with the non-superoxide-generating cadmium selenide QDs (CdSe-2.4) as a negative control. Our analysis sought to separate the transcriptomic response of E. coli to the generation of superoxide by the CdTe-2.4 QDs from the presence of cadmium chalcogenide nanoparticles alone. We used comparisons between illuminated CdTe-2.4 conditions and all others to establish the superoxide generation response and used comparisons between all QD conditions and the no treatment condition to establish the cadmium chalcogenide QD response. In our analysis of the gene expression experiments, we found eight genes to be consistently differentially expressed as a response to superoxide generation, and these genes demonstrate a consistent association with the DNA damage response and deactivation of iron-sulfur clusters. Each of these responses is characteristic of a bacterial superoxide response. We found 18 genes associated with the presence of cadmium chalcogenide QDs but not the generation of superoxide by CdTe-2.4, including several that implicated metabolism of amino acids in the E. coli response. To explore each of these gene sets further, we performed both gene knockout and amino acid supplementation experiments. We identified the importance of leucyl-tRNA downregulation as a cadmium chalcogenide QD response and reinforced the relationship between CdTe-2.4 stress and iron-sulfur clusters through examination of the gene tusA. This study demonstrates the transcriptomic response of E. coli to CdTe-2.4 and CdSe-2.4 QDs and parses the different effects of superoxide versus material effects on the bacteria. Our findings may provide useful information toward the development of QD-based antibacterial therapy in the future.

Energetics at the Surface: Direct Optical Mapping of Core and Surface Electronic Structure in CdSe Quantum Dots Using Broadband Electronic Sum Frequency Generation Microspectroscopy

Understanding and controlling the electronic structure of nanomaterials is the key to tailoring their use in a wide range of practical applications. Despite this need, many important electronic states are invisible to conventional optical measurements and are typically identified indirectly based on their inferred impact on luminescence properties. This is especially common and important in the study of nanomaterial surfaces and their associated defects. Surface trap states play a crucial role in photophysical processes yet remain remarkably poorly understood. Here we demonstrate for the first time that broadband electronic sum frequency generation (eSFG) microspectroscopy can directly map the optically bright and dark states of nanoparticles, including the elusive below gap states. This new approach is applied to model cadmium selenide (CdSe) quantum dots (QDs), where the energies of surface trap states have eluded direct optical characterization for decades. Our eSFG measurements show clear signatures of electronic transitions both above the band gap, which we assign to previously reported one- and two-photon transitions associated with the CdSe core, as well as broad spectral signatures below the band gap that are attributed to surface states. In addition to the core states, this analysis reveals two distinct distributions of below gap states, providing the first direct optical measurement of both shallow and deep surface states on this system. Finally, chemical modification of the surfaces via oxidation results in the relative increase in the signals originating from the surface states. Overall, our eSFG experiments provide an avenue to directly map the entirety of the QD core and surface electronic structure, which is expected to open up opportunities to study how these materials are grown in situ and how surface states can be controlled to tune functionality.

Intensified Stiffness and Photodynamic Provocation in a Collagen-Based Composite Hydrogel Drive Chondrogenesis.

Directed differentiation of bone‐marrow‐derived stem cells (BMSCs) toward chondrogenesis has served as a predominant method for cartilage repair but suffers from poor oriented differentiation tendency and low differentiation efficiency. To overcome these two obstacles, an injectable composite hydrogel that consists of collagen hydrogels serving as the scaffold support to accommodate BMSCs and cadmium selenide (CdSe) quantum dots (QDs) is constructed. The introduction of CdSe QDs considerably strengthens the stiffness of the collagen hydrogels via mutual crosslinking using a natural crosslinker (i.e., genipin), which simultaneously triggers photodynamic provocation (PDP) to produce reactive oxygen species (ROS). Experimental results demonstrate that the intensified stiffness and augmented ROS production can synergistically promote the proliferation of BMSCs, induce cartilage‐specific gene expression and increase secretion of glycosaminoglycan. As a result, this approach can facilitate the directed differentiation of BMSCs toward chondrogenesis and accelerate cartilage regeneration in cartilage defect repair, which routes through activation of the TGF‐β/SMAD and mTOR signaling pathways, respectively. Thus, this synergistic strategy based on increased stiffness and PDP‐mediated ROS production provides a general and instructive approach for developing alternative materials applicable for cartilage repair.

Enhancement in the Microelectronic Properties of a PFB–CdSe Quantum Dots Nanocomposite Based Schottky Barrier Diode

This paper reports on the electronic and interfacial properties of a Schottky barrier diode (SBD) prepared from a blend consisting of a matrix semiconductor, poly(9,9-fluorufluorene) (PFB), and a dopant, cadmium selenide (CdSe) quantum dots (QDs) having size less than 5 nm. A uniform blend of PFB and CdSe QDs is prepared in chloroform 1:1 by volume and from a 0.5 wt.% of CdSe QDs and 20 mg/mL of PFB. The Schottky device ITO/PEDOT:PSS/PFB–CdSe/LiF/Ag is fabricated by spin coating the PFB–CdSe QDs blend on a pre-deposited PEDOT:PSS/ITO layer. Lithium fluoride (LiF) and silver (Ag) are thermally deposited via vacuum thermal evaporator as buffer layer and ohmic contact, respectively. The fabricated SBD is studied by current–voltage (I–V) characteristics under dark conditions at 300 K. The device exhibits rectifying behavior with rectification ratio of 301.28 at ± 2.5 V. The interface properties of the device such as series resistance (Rs), barrier height (ϕB), ideality factor (n) and reverse saturation current (I0) are measured to be 58.6 kΩ, 0.99 eV, 1.7 and 2.01 × 10−11 A, respectively. Charge carrier conduction mechanisms across the device such as Richardson–Schottky and Poole–Frenkel effects are studied where Schottky emission was identified at lower voltages while at higher voltages Poole–Frenkel effects were observed.

Water-Soluble Cadmium Selenide Quantum Dots with Controlled Surface Charge

By chemical modification of poly(maleic anhydride-alt-1-tetradecene) with different negatively and positively charged groups, we demonstrate how magnitude of zeta potential of encapsulated CdSe quantum dots and their sensitivity to pH can be tuned by varying type and proportion of the negatively and positively charged groups on the surface of quantum dots.

Impact of size and shape on trap state controlled luminescence properties of trioctylphosphine-capped cadmium selenide quantum dots

Color tunability using different synthesis approaches and to intentionally change the shape of cadmium selenide (CdSe) quantum dots (QDs) using different synthesis processes have been widely investigated. Even in a single synthesis procedure, there is a probability of shape change with QD growth time. In this work, we have analyzed the size- and shape-dependent effects on the quantum yield (QY) and average lifetime with the growth of trioctylphosphine (TOP)-capped CdSe nanoparticles synthesized using a standard synthesis approach. The decrease in the average fluorescence lifetime and QY with the increase in particle size of the QDs has been reported. Transmission electron microscopy (TEM) analysis shows that as the size of QDs increases, the shape changes from spherical to approximately ovoid; thus, the surface area increases at a higher rate. From x-ray photoelectron spectroscopy, we have found that selenium content is increasing at a higher rate with shape change, and TOP has the capability of capping cationic facets; hence, there is an increase in the weakly bonded anionic facets per unit area, and there are atomic dislocations during the fabrication process. So, these two factors create a large number of trap states, resulting in the increment of nonradiative recombination centers. Effects of these trap states on radiative lifetime, nonradiative lifetime, average lifetime, QY, radiative recombination, and nonradiative recombination rates have been analyzed.

(Invited) Simulation of CdSe Based Quantum Dot Hybrid Light Emitting Diodes Using Tcad Continuous Models

Organic-inorganic hybrid quantum dot (QD) based light emitting diodes (LEDs) have been investigated. Stacked hybrid QD LED structures, based on cadmium selenide QD with cadmium sulfide barrier shells, have been fabricated at the Universtiat Rovira i Virgili using spin coating techniques. These have been modelled, with Technology Computer Aided Design (TCAD) software, using two different carrier conduction models. Two quantum confinements models are used to predict the electronic transport through these stacks. A 1D simulation of a stack with a single QD mono-layer, using the Silvaco Radiant tool based on the Atlas engine, is reported. This approach allows device designers to optimise the current density and spectral response as a function of QD radius (as shown in the figure) and transport layer thicknesses. Furthermore, a second approach using a 3D QD simulation in which the user can investigate the effect of the QD radius and barrier layer thickness on the carrier confinement in the structures is shown. This work demonstrates the capability of 1D simulations, using the Radiant software tool, to model the behavior of single QD mono-layer structures. The user friendly input graphical user interface, as well as the speed of the simulation, helps to iterate the design quickly to optimise QD size and transport layer thicknesses for maximum intensity at the desired spectral output. Figure 1

Synthesis and characterization of cadmium selenide quantum dots doped by europium and investigation of their chemiluminescence properties and antibacterial activities.

Nanoparticles of cadmium selenide (CdSe) doped with europium, were synthesized as stabilizing agents using thioglycolic acid ligand. This method is based on the enhancing effect of CdSe quantum dots (QDs) doped with europium on chemiluminescence (CL) emission. This emission was generated by mixing CdSe QDs with manganese (II), iron (II) and chrome (II) sulfates as catalysts in the presence of hydrogen peroxide (H2 O2 ). The structural characteristics and morphology of these nanoparticles were investigated by scanning electron microscopy, Fourier transform infrared spectroscopy, ultraviolet-visible absorption spectroscopy, X-ray pattern and dynamic light scattering methods. The CdSe QDs doped with europium were used as the sensitizer in a luminol-hydrogen peroxide CL system. The sensitized CdSe QDs were analyzed for antibacterial activity against Gram-positive or Gram-negative bacteria. The results showed that the CdSe QDs are effective against all the studied bacteria, effectiveness was especially higher for Bacillus subtilis.

Photolytic C–O Bond Cleavage with Quantum Dots

Quantum dots are used as photoredox catalysts to drive bond cleavage in lignin model substrates. Cadmium selenide quantum dots selectively cleave C–O bonds with yields comparable to the best transi...

English

Cadmium selenide quantum dots (CdSe QDs) were synthesized by using Providencia vermicola BGRW, which has discriminatory ability to resist many metals such as Selenium, Cadmium, Silver, Zinc, Copper, Lead, Nickel, Cobalt and Bismuth metals. BGRW was able to grow in the presence of 6 mM of CdCl2. The best conditions for extra/intracellular CdSe QDs synthesis were 0.1 mM SeO2: 0.9 mM CdCl2, 37°C, pH 9 within 24 h. The biosynthesis of CdSe QDs was monitored by UV–Visible spectrum that showed surface plasmon resonance (SPR) peaks at 388 nm. Depending on fluorescence property of quantum dots, photoluminescence characteristics of the biogenic CdSe QDs were at 385 nm. Further characterization of synthesized CdSe QDs was carried out using the X-ray Diffraction (XRD), Transmission Electron Microscope (TEM) and Fourier Transform Infrared (FTIR) spectroscopy. TEM and XRD analysis revealed that CdSe QDs was cubic in shape with a size range of ∼2 to 4 nm. EDS analysis confirmed the composition of QDs from cadmium and selenium ions. FTIR spectroscopy confirmed the presence of proteins as the stabilizing agent surrounding the quantum dots. Key words: Quantum dots, cadmium selenide quantum dots, capping agent, transmission electron microscope, fluorescence spectroscopy, X-ray and FTIR analysis.

Design of a multimodal colloidal polymeric drug delivery vesicle: A detailed pharmaceutical study

Over the past few years, numerous developments and design principle of smart nanomaterials have pioneered different delivery modalities and routes for efficient drug administration. Nanocarriers comprising of fluorescent biomarkers and drug molecule at the same platform are promising vesicles for passive targeting and drug delivery. Here, we report the detailed pharmaceutical study of a novel synthesized multimodal nanoclinic consisting of Polycaprolactone (PCL), a biodegradable polymer as drug matrix, Cadmium Selenide (CdSe) quantum dot as fluorescent marker and curcumin, a natural anti-cancer drug as drug molecule. This multimodal nanoclinic was synthesized by a modified miniemulsion technique and characterized by UV–Vis absorption and FTIR spectroscopy. The efficiency of this nano-vesicle was evaluated by in vitro experiments including drug release, cell cytotoxicity and uptake. Drug release profile was studied in PBS buffer and correlated with theoretical Higuchi modelling. MTT assay confirmed the bio-suitability of these nanocomposites. The fluorescence and confocal imaging show the successful uptake of this nanoclinic by human lung cancer cell line. These polymeric nanoparticles based system provide the promise for the design of next generation multimodal drug delivery modality.

Cadmium selenide quantum dots: Synthesis, characterization and their humidity and temperature sensing properties with poly-(dioctylfluorene)

In this paper, we report synthesis, thin film characteristics and sensing properties of cadmium selenide (CdSe) quantum dots (QDs) for enhancing the humidity and temperature sensing of a polymeric semiconductor poly-(9,9-di-n-octylfluorenyl-2,7-diyl) (F8). Transmission electron microscopy (TEM) has been performed to study the texture, distribution over surface and size of the synthesized CdSe QDs. TEM image revealed slightly non-uniform distribution of the QDs with an average size of 4 nm having three-dimensional quantum confinement features. Atomic force microscopy (AFM) is carried out to investigate the average grain size and surface roughness of the F8-CdSe nanocomposite film. To understand the role of CdSe QDs on the sensing properties of F8, a blend F8-CdSe QDs has been prepared at 10:1 wt-percent (wt%) of F8 and CdSe QDs, respectively, in chloroform. An Ag/F8-CdSe QDs/Ag surface-type sensor has been fabricated via spin coating F8-CdSe QDs nanocomposite on a 45 μm gap between the pre-patterned silver (Ag) electrodes on glass substrate. The fabricated Ag/F8-CdSe QDs/Ag sensor has been studied for humidity and temperature sensing by measuring capacitance (C) of the sensor as a function of humidity and temperature, respectively. The Ag/F8-CdSe QDs/Ag sensor exhibits enhancement in the sensing parameters such as response time and recovery time i.e., 9 s and 7 s, respectively, as compared to our previously studied Ag/F8/Ag sensor whose response and recovery time were 15 s and 7 s, respectively. This improvement is due to the addition of CdSe QDs in F8 polymer matrix which changes some of the important properties of the F8-CdSe QDs nanocomposite such as electron polarizability, polarity, hydrophobicity and size dependent properties. The role of porosity (P) in the sensing properties of the active film of Ag/F8-CdSe QDs/Ag device has also been explored. The Ag/F8-CdSe QDs/Ag based sensor shows approximately linear change in C as a function of humidity and temperature with wide range of sensitivity from 25 percent relative humidity (%RH) to 90%RH and from 16 to 186 °C, respectively.

Effect of the Polymer on the Photoluminescent Spectrum and Kinetics of Quantum Dots of Cadmium Selenide in Amorphous and Liquid Crystalline Polymer Matrices

Measurements of the photoluminescent spectra and kinetics, and of the excitation spectra of photoluminescence of CdSe nanoparticles embedded in various polymer matrices, show that using a liquid crystalline polymer as a matrix makes it possible to increase the lifetime of photoluminescence and the quantum yield of this process.

Application of aqueous phase CdSe quantum dots for formaldehyde sensing

Thioglycolic acid capped cadmium selenide (CdSe) quantum dots have been synthesised in aqueous phase and their optical properties have been studied using UV-visible absorption and fluorescence spectroscopy. Quantum dots have been characterised using TEM and XRD. The potential application of CdSe quantum dots are further studied using formaldehyde as a model compound. The sensing is based on fluorescence quenching of quantum dots in the presence of formaldehyde, and this work showed linearity in the range from 0.15 to 1.05 ppm, with a detection limit of 0.06 ppm.