Water-soluble Semiconductor Quantum Dots Research Articles

A Review, Water-Soluble CuInS Quantum Dots, Strategies and Photoluminescence

Water-soluble semiconductor quantum dots (QDs) have become a unique field of materials science with great potential for applications in biomedical and optoelectronic devices. However, the more stable and bright QDs are the conventional QDs that contain toxic heavy metals such as Pb, Cd and Hg or the QDs that were synthesized in an organic phase. Hence, it is important to find an alternative material with similar optical properties and low cytotoxicity among these materials. Recently, hydrophilic CuInS2 (CIS) QDs have attracted a lot of interest due to their direct bandgap in the infrared region, large optical absorption coefficient, hydrophilicity, low cost and low toxic composition. These factors make them a good material for biomedical applications. This review starts with the origin characteristics of CIS QDs followed by various synthetic strategies, including synthesis in aqueous solvents and transformation from organic phase to water-soluble phase QDs. Then the tuning of their optical properties is discussed. The review then considers the strategies to improve the photoluminescence performances of CIS QDs.

Nano-Bio Interaction between Blood Plasma Proteins and Water-Soluble Silicon Quantum Dots with Enabled Cellular Uptake and Minimal Cytotoxicity.

A better understanding of the compatibility of water-soluble semiconductor quantum dots (QDs) upon contact with the bloodstream is important for biological applications, including biomarkers working in the first therapeutic spectral window for deep tissue imaging. Herein, we investigated the conformational changes of blood plasma proteins during the interaction with near-infrared light-emitting nanoparticles, consisting of Pluronic F127 shells and cores comprised of assembled silicon QDs terminated with decane monolayers. Albumin and transferrin have high quenching constants and form a hard protein corona on the nanoparticle. In contrast, fibrinogen has low quenching constants and forms a soft protein corona. A circular dichroism (CD) spectrometric study investigates changes in the protein’s secondary and tertiary structures with incremental changes in the nanoparticle concentrations. As expected, the addition of nanoparticles causes the denaturation of the plasma proteins. However, it is noteworthy that the conformational recovery phenomena are observed for fibrinogen and transferrin, suggesting that the nanoparticle does not influence the ordered structure of proteins in the bloodstream. In addition, we observed enabled cellular uptake (NIH3T3 Fibroblasts) and minimal cytotoxicity using different cell lines (HeLa, A549, and NIH3T3). This study offers a basis to design QDs without altering the biomacromolecule’s original conformation with enabled cellular uptake with minimal cytotoxicity.

Controlled Functionalization of Water-Soluble Semiconductor Quantum Dots for Bioconjugation

A one-step procedure using carbodiimide condensation was proposed for controlled functionalization of watersoluble semiconductor quantum dots (QDs) with azide groups. The changes of functional group surface density and ζ-potential could be controlled during modifi cation of anionic and analogous zwitterionic polymer-encapsulated CdSe/ZnS core–shell QDs. Ethanolamine-O-sulfate, aminotetraethylene glycol (H2N–TEG–OH), and aminotetraethylene glycol azide (H2N–TEG–N3) were used as modifiers. Functionalization was investigated by studying the conjugation kinetics of organic dye JOE to QDs using strain-promoted azide-alkyne cycloaddition (SPAAC). The reactivity of QDs in SPAAC was nearly proportional to the relative density of surface azides. The QD ζ-potential correlated with the ratio of modifiers. Azides on the QD surface could be easily transformed under mild conditions into primary amines using tris(2-carboxyethyl)phosphine as a reducing agent. The applicability of surface-functionalized QDs for bioconjugation was demonstrated via conjugation to fluorescent-dye-labeled bovine serum albumin.

Light-mediated effects of CdTe-MSA quantum dots on the autofluorescence of freshwater green microalgae: Spectroscopic studies

The water-soluble semiconductor quantum dots (QDs) serve as optically detectable models of nanoparticles and are commonly applied as photoluminescent markers in biological systems. The unicellular algae represent a popular model system suitable to evaluate pollution-induced effects. There is growing experimental evidence that release of metal ions cannot account for potential toxicity of metal containing nanoparticles, however, the underlying mechanisms are not clearly understood. Surrounding environment and illumination conditions are among the most important factors affecting the stability of QDs as well as the interaction between nanoparticles and cells such as microalgae. The measurements of changes in photoluminescence (PL) of QDs and autofluorescence (AF) of microalgae can thus be used as a non-invasive screening method for detecting mutual effects of nanoparticles and algae cells on each other under natural conditions.In this study, CdTe quantum dots (a peak of PL at 550 nm) capped with a mercaptosuccinic acid (MSA) were introduced into aqueous ionic medium containing wild type green freshwater microalgae Scenedesmus and Chlorella sp. cells under artificial and natural ambient illumination. The spectroscopy and microscopy techniques were applied to observe both the influence of the microalgae on the spectral properties of negatively charged CdTe-MSA quantum dots and the effects of nanoparticles on the microalgae. The presence of algae cells revealed a protecting effect on both medium-dependent and radiation-induced changes in photoluminescence properties of QDs, which could be related with the increased stability of the capping layer. The effects on cellular AF intensity and the interaction of QDs with cellular surface depended on type of microalgae. The observed changes in AF spectral properties and AF induction signals can't be explained only by the photodegradation of QDs and have revealed the ability of nanoparticles to retard the photoadaptation of wild type microalgae under naturally varying illumination conditions.

Interaction of Globular Plasma Proteins with Water-Soluble CdSe Quantum Dots.

The interactions between water-soluble semiconductor quantum dots [hydrophilic 3-mercaptopropionic acid (MPA)-coated CdSe] and three globular plasma proteins, namely, bovine serum albumin (BSA), β-lactoglobulin (β-Lg) and human serum albumin (HSA), are investigated. Acidic residues of protein molecules form electrostatic interactions with these quantum dots (QDs). To determine the stoichiometry of proteins bound to QDs, we used dynamic light scattering (DLS) and zeta potential techniques. Fluorescence resonance energy transfer (FRET) experiments revealed energy transfer from tryptophan residues in the proteins to the QD particles. Quenching of the intrinsic fluorescence of protein molecules was noticed during this binding process (hierarchy HSA<β-Lg <BSA, lower binding affinity for hydrophobic protein molecules). Upon binding with QD particles, the protein molecules underwent substantial conformational changes at the secondary-structure level (50 % helicity lost), due to loss in hydration.

Nanomaterial antennae in photo-delivery of bioactive molecules

Our laboratory has developed photochemical strategies for delivery of NO and CO to physiological targets that allow control of the location, timing, and dosage of such delivery. We have explored the photoreactions of the iron/sulfur/nitrosyl clusters Fe 2 (μ-SR) 2 (NO) 4 and the Cr (III) nitrito complex trans- Cr (cyclam) ( ONO ) 2 + that release NO under visible irradiation but not at longer wavelengths. Thus, we have designed new supramolecular assemblies with water-soluble semiconductor quantum dots and lanthanide near-IR upconversion materials to serve as antennae for photosensitization of reactions from analogous precursors and increase rates of NO release using longer wavelength visible light. Certain antennae have high two photon cross-sections, a feature that allows use of NIR light (where tissue transmission is maximized) to sensitize photoreactions of these systems.

Synthesis of Mercaptosuccinic Acid/MercaptoPolyhedral Oligomeric Silsesquioxane Coated Cadmium Telluride Quantum Dots in Cell Labeling Applications

An aqueous synthesis method to obtain highly luminescent cadmium telluride nanocrystals is described. We have shown water-soluble semi-conductor quantum dots with high photoluminescence quantum yield have great potential for biological applications. The spectral properties of these nanocrystals can be easily tuned according to their particle size to yield multicolours simultaneously by a single excitation light source. A stable precursor material sodium tellurite is utilised instead of the traditional oxygen sensitive NaHTe or H2Te as Te source. We have introduced mercaptosuccinic acid and propylisobutyl polyhedral oligomeric silsesquioxane nanoparticles as novel capping agents to stabilize the nanocrystals, synthesized in borate-citrate buffering system. Inclusion of propylisobutyl polyhedral oligomeric silsesquioxane nanoparticles in the capping procedure showed enhanced stability and biocompatibility. The presence of mercaptosuccinic acid/propylisobutyl polyhedral oligomeric silsesquioxane coatings was confirmed by Fourier Transform Infrared spectroscopy and average sizes of 2-5 nm by transmission electron microscopy measurements. The functionalized and targeted quantum dots detected cancer cell death on exposure to some anticancer drugs. Studies have indicated that apoptotic cells can activate signaling pathways in dendritic cells via ligation of surface receptors. Cells treated with specific class of pro-apototic drug such as anthracyclines mount an anti-tumour immune response when introduced into mice. Apoptotic cells may be immunogenic or non-immunogenic depending on the presence of calreticulin on the plasma membrane of dying tumour cells. Here the confocal microscopy showed localization of conjugated mercaptosuccinic acid/propylisobutyl polyhedral oligomeric silsesquioxane cadmium telluride quantum dots on MCF-7 cells when exposed to cadmium ions at 50 microM, compared to coated quantum dots. We have used cadmium ions as a model drug as certain anticancer drugs (anthracyclines) induce translocation of calreticulin to the cell membrane, an indicator of apoptosis. Antibodies generated against a peptide to human calreticulin and conjugated to quantum dots detected the protein on cell membrane of stimulated cells were visualized by confocal microscopy. Stimulating natural immune response, against tumours has enormous potential to improve current regimens of cancer detection and therapy.

CdSe@CdS Core–Shell Quantum Dot-Polymer Multilayer Sensitized TiO&lt;SUB&gt;2&lt;/SUB&gt; for Photovoltaics

Colloidal CdSe@CdS core-shell quantum dots (QDs) have been prepared and exploited as inorganic dyes to sensitize a large-band-gap TiO2 layer for QD-sensitized solar cells. The sensitized films were prepared by alternating the layer-by-layer deposition of water-soluble semiconductor QDs and polycations over mesoscopic TiO2 films. The multilayer build-up, monitored by UV-vis spectroscopy shows an increase in the film absorbance with the number of adsorbed CdSe@CdS layers. The photoluminescence (PL) and photoelectrochemical properties of the multilayers were investigated. The photovoltaic performance of QD-sensitized solar cells is strongly dependent on the film structure and component. The incorporation of the electron mediators of [Co(Phen)3]2+ during the deposition process remarkably enhanced the photocurrent intensity in comparison to that in case of QD/polyelectrolyte multilayers.

Hybrid photovoltaic cells with II–VI quantum dot sensitizers fabricated by layer-by-layer deposition of water-soluble components

We present the fabrication of all solid state heterojunction photovoltaic devices consisting of TiO 2 films sensitized by colloidal CdSe and CdTe quantum dots (QDs) and a hole transport layer of the conjugated polymer poly(9,9-dioctyl-fluorene- co-N-(4-butylenphenyl)diphenylamine). The sensitized films were prepared by alternating the layer-by-layer deposition of TiO 2 nanoparticles, water-soluble semiconductor QDs and polycations. Photovoltaic devices sandwiched between fluorinated tin oxide and gold electrodes showed a high rectification ratio and photovoltages of up to 1.15 V. Effective sensitization was observed for CdSe QDs, while incorporated CdTe QDs apparently had no such effect. These findings are explained by confinement effects in QDs.

An Intrinsically Fluorescent Recognition Ligand Scaffold Based on Chaperonin Protein and Semiconductor Quantum‐Dot Conjugates

Genetic engineering of a novel protein-nanoparticle hybrid system with great potential for biosensing applications and for patterning of various types of nanoparticles is described. The hybrid system is based on a genetically modified chaperonin protein from the hyperthermophilic archaeon Sulfolobus shibatae. This chaperonin is an 18-subunit double ring, which self-assembles in the presence of Mg ions and ATP. Described here is a mutant chaperonin (His-beta-loopless, HBLL) with increased access to the central cavity and His-tags on each subunit extending into the central cavity. This mutant binds water-soluble semiconductor quantum dots, creating a protein-encapsulated fluorescent nanoparticle. The new bioconjugate has high affinity, in the order of strong antibody-antigen interactions, a one-to-one protein-nanoparticle stoichiometry, and high stability. By adding selective binding sites to the solvent-exposed regions of the chaperonin, this protein-nanoparticle bioconjugate becomes a sensor for specific targets.

Water-soluble Ag nanoclusters exhibit strong two-photon-induced fluorescence.

Water-soluble ssDNA-encapsulated Ag clusters exhibit large two-photon cross sections reaching 50 000 GM, with high quantum yields in the red and near-IR. Three distinct, spectrally pure, several atom clusters emitting at 660, 680, or 710 nm have been created with two-photon cross sections rivaling those of much larger water-soluble semiconductor quantum dots. Their stability, biocompatibility, and small size offer the promise of nontoxic, sensitive high-resolution biological imaging.

Semiconductor quantum dots and free radical induced DNA nicking

There is a growing interest in the use of semiconductor quantum dots as fluorescent markers in biological applications. However, there are concerns regarding the potential environmental impact and toxic nature of these nanomaterials. In this study, we have investigated the interaction of water-soluble semiconductor quantum dots with supercoiled DNA.