Assessment of cytocompatibility of surface-modified CdSe/ZnSe quantum dots for BALB/3T3 fibroblast cells

Study of the Structure and Properties of ZnS Utilized in a Fluorescence Biosensor

ZnS materials have been widely used in fluorescence biosensors to characterize different types of stem cells due to their excellent fluorescence effect. In this study, ZnS was prepared by vulcanizing nano-Zn particles synthesized using a DC arc plasma. The composition and structure of the ZnS materials were studied by X-ray diffraction (XRD), and their functional group information and optical properties were investigated by using IR spectrophotometry and UV-vis spectrophotometry. It has been found that the synthesized materials consist of Zn, cubic ZnS, and hexagonal ZnS according to the vulcanization parameters. Crystalline ZnS was gradually transformed from a cubic to a hexagonal structure, and the cycling properties first increase, then decrease with increasing sulfurization temperature. There is an optimal curing temperature giving the best cycling performance and specific capacity: the material sulfurized thereat mainly consists of cubic β-ZnS phase with a small quantity of Zn and hexagonal α-ZnS. The cubic phase ZnS has better conductivity than hexagonal ZnS, as evinced by electrochemical impedance spectroscopy (EIS). The ZnS (as prepared) shows board absorption, which can be used in fluorescence biosensors in cell imaging systems.

Toxicity evaluation of cadmium-containing quantum dots: A review of optimizing physicochemical properties to diminish toxicity

Fluorescent quantum dots (QDs) have received extensive attention because of their excellent optical properties and wide utilization in biological and biomedical areas. Nonetheless, there have been intense concerns on the cytotoxicity assessment of cadmium-containing QDs due to free cadmium ions release and nano-size effects. This paper reviews the representative synthetic strategies for preparation of cadmium-containing QDs and their applications. Then the toxicity assessments of QDs from cell studies to animal models are discussed, which can aid in improving our understanding of the cytotoxicity of QDs, and the toxicity mechanism is proposed. Several critical physicochemical properties of QDs are discussed and suggestions are provided for optimizing QDs design in view of minimal cytotoxicity. Finally, accurate detection techniques and systematic methodologies for the toxicity assessment of QDs are expected to achieve further breakthroughs in the future, especially in-situ, real-time, and rapid quantitative analysis methods.

Toxicity of different types of quantum dots to mammalian cells in vitro: An update review

Currently, there are a great quantity type of quantum dots (QDs) that has been developed by researchers. Depending on the core material, they can be roughly divided into cadmium, silver, indium, carbon and silicon QDs. And studies on the toxicity of QDs are also increasing rapidly, but in vivo tests in model animals fail to reach a consistent conclusion. Therefore, we review the literatures dealing with the cytotoxicity of QDs in mammalian cells in vitro. After a short summary of the application characteristics of five types of QDs, the fate of QDs in cells will be discussed, ranging from the uptake, transportation, sublocation and excretion. A substantial part of the review will be focused on in vitro toxicity, in which the type of QDs is combined with their adverse effect and toxic mechanism. Because of their different luminescent properties, different subcellular fate, and different degree of cytotoxicity, we provide an overview on the balance of optical stability and biocompatibility of QDs and give a short outlook on future direction of cytotoxicology of QDs.

Toxic effects and involved molecular pathways of nanoparticles on cells and subcellular organelles

Owing to the increasing application of engineered nanoparticles (NPs), besides the workplace, human beings are also exposed to NPs from nanoproducts through the skin, respiratory tract, digestive tract and vein injection. This review states pathways of cellular uptake, subcellular distribution and excretion of NPs. The uptake pathways commonly include phagocytosis, micropinocytosis, clathrin- and caveolae-mediated endocytosis, scavenger receptor-related pathway, clathrin- or caveolae-independent pathway, and direct penetration or insertion. Then the ability of NPs to decrease cell viability and metabolic activity, change cell morphology, and destroy cell membrane, cytoskeleton and cell function was presented. In addition, the lowest dose decreasing cell metabolic viability compared with the control or IC₅₀ of silver, titanium dioxide, zinc oxide, carbon black, carbon nanotubes, silica, silicon NPs and cadmium telluride quantum dots to some cell lines was gathered. Next, this review attempts to increase our understanding of NP-caused adverse effects on organelles, which have implications in mitochondrial dysfunction, endoplasmic reticulum stress and lysosomal rupture. In particular, the disturbance of mitochondrial biogenesis and mitochondrial dynamic fusion-fission, mitophagy and cytochrome c-dependent apoptosis are involved. In addition, prolonged endoplasmic reticulum stress will result in apoptosis. Rupture of the lysosomal membrane was associated with inflammation, and both induction of autophagy and blockade of autophagic flow can result in cytotoxicity. Finally, the network mechanism of the combined action of multiple organelle dysfunction, apoptosis, autophagy and oxidative stress was discussed.

Synthesis, characterization and antibacterial activity of Zn(II) coordination polymer

In this study, the zinc(II)-based coordination polymer, [Zn(CPDA)(NO₃)₂)](CPDA = 1,2-cyclopentanedicarboxylic acid) (1), had been successfully synthesized according to the hydrothermal method. Afterwards, 1 had been characterized by means of single crystal and power X-ray diffraction, elemental analysis, thermogravimetric analysis and infrared spectrum techniques. In addition, the antibacterial activities in vitro had been evaluated towards Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), respectively, through the growth inhibition and inhibition zone experimental methods. Our results indicated that 1 had displayed favorable antibacterial activity compared with the Zinc nitrate and the CPDA ligand. These findings had revealed that the antibacterial mechanism of 1 might be correlated with the production of reactive oxygen species (ROS) in cells.

Nanostructured surfaces for analysis of anticancer drug and cell diagnosis based on electrochemical and SERS tools

Discovering new anticancer drugs and screening their efficacy requires a huge amount of resources and time-consuming processes. The development of fast, sensitive, and nondestructive methods for the in vitro and in vivo detection of anticancer drugs' effects and action mechanisms have been done to reduce the time and resources required to discover new anticancer drugs. For the in vitro and in vivo detection of the efficiency, distribution, and action mechanism of anticancer drugs, the applications of electrochemical techniques such as electrochemical cell chips and optical techniques such as surface-enhanced Raman spectroscopy (SERS) have been developed based on the nanostructured surface. Research focused on electrochemical cell chips and the SERS technique have been reviewed here; electrochemical cell chips based on nanostructured surfaces have been developed for the in vitro detection of cell viability and the evaluation of the effects of anticancer drugs, which showed the high capability to evaluate the cytotoxic effects of several chemicals at low concentrations. SERS technique based on the nanostructured surface have been used as label-free, simple, and nondestructive techniques for the in vitro and in vivo monitoring of the distribution, mechanism, and metabolism of different anticancer drugs at the cellular level. The use of electrochemical cell chips and the SERS technique based on the nanostructured surface should be good tools to detect the effects and action mechanisms of anticancer drugs.

EGF receptor lysosomal degradation is delayed in the cells stimulated with EGF-Quantum dot bioconjugate but earlier key events of endocytic degradative pathway are similar to that of native EGF

Quantum dots (QDs) complexed to ligands recognizing surface receptors undergoing internalization are an attractive tool for live cell imaging of ligand-receptor complexes behavior and for specific tracking of the cells of interest. However, conjugation of quasi-multivalent large QD-particle to monovalent small growth factors like EGF that bound their tyrosine-kinase receptors may affect key endocytic events tightly bound to signaling. Here, by means of confocal microscopy we have addressed the key endocytic events of lysosomal degradative pathway stimulated by native EGF or EGF-QD bioconjugate. We have demonstrated that the decrease in endosome number, increase in mean endosome integrated density and the pattern of EEA1 co-localization with EGF-EGFR complexes at early stages of endocytosis were similar for the both native and QD-conjugated ligands. In both cases enlarged hollow endosomes appeared after wortmannin treatment. This indicates that early endosomal fusions and their maturation proceed similar for both ligands. EGF-QD and native EGF similarly accumulated in juxtanuclear region, and live cell imaging of endosome motion revealed the behavior described elsewhere for microtubule-facilitated motility. Finally, EGF-QD and the receptor were found in lysosomes. However, degradation of receptor part of QD-EGF-EGFR-complex was delayed compared to native EGF, but not inhibited, while QDs fluorescence was detected in lysosomes even after 24 hours. Importantly, in HeLa and A549 cells the both ligands behaved similarly. We conclude that during endocytosis EGF-QD behaves as a neutral marker for degradative pathway up to lysosomal stage and can also be used as a long-term cell marker.

Adhesion of CdTe quantum dots on model membranes and internalization into RBL-2H3 cells

Quantum dots (QDs) have attracted broad attention due to their special optical properties and promising prospect in medical and biological applications. However, the process of QDs on cell membrane is worth further investigations because such process may lead to harmful effects on organisms and also important for QD application. In this study, adhesion of amino- and carboxyl-coated CdTe QDs (A-QDs and C-QDs) on cell membrane and the subsequent internalization are studied using a series of endocytosis-free model membranes, including giant and small unilamellar vesicles, supported lipid bilayers and giant plasma membrane vesicles (GPMVs). The adhered QD amounts on model membranes are quantified by a quartz crystal microbalance. The CdTe QD adhesion on model membranes is governed by electrostatic forces. Positively charged A-QDs adhere on GPMV surface and passively penetrate the plasma membrane via endocytosis-free mechanism, but negatively charged C-QDs cannot. Rat basophilic leukemia (RBL-2H3) cells are exposed to CdTe QDs to monitor the QD internalization process. Both A- and C-QDs are internalized by RBL-2H3 cells mainly via endocytosis. CdTe QDs do not accumulate on the plasma membrane of living cells due to the fast endocytosis and the weakened electrostatic attraction in biological medium, resulting in low chance of passive penetration. The suspended cells after trypsin digestion take more QDs than the adherent cells. A-QDs cause lower cell viability than C-QDs, probably because the approach of positively charged QDs to cells is favored and the smaller aggregates of A-QDs.

Meta-analysis of cellular toxicity for cadmium-containing quantum dots

Understanding the relationships between the physicochemical properties of engineered nanomaterials and their toxicity is critical for environmental and health risk analysis. However, this task is confounded by material diversity, heterogeneity of published data and limited sampling within individual studies. Here, we present an approach for analysing and extracting pertinent knowledge from published studies focusing on the cellular toxicity of cadmium-containing semiconductor quantum dots. From 307 publications, we obtain 1,741 cell viability-related data samples, each with 24 qualitative and quantitative attributes describing the material properties and experimental conditions. Using random forest regression models to analyse the data, we show that toxicity is closely correlated with quantum dot surface properties (including shell, ligand and surface modifications), diameter, assay type and exposure time. Our approach of integrating quantitative and categorical data provides a roadmap for interrogating the wide-ranging toxicity data in the literature and suggests that meta-analysis can help develop methods for predicting the toxicity of engineered nanomaterials.

Immunotoxicity assessment of CdSe/ZnS quantum dots in macrophages, lymphocytes and BALB/c mice

BACKGROUND

The toxicity of CdSe/ZnS quantum dots (QDs) in the environment and biological systems has become a major concern for the nanoparticle community. However, the potential toxicity of QDs on immune cells and its corresponding immune functions remains poorly understood. In this study, we investigated the immunotoxicity of CdSe/ZnS QDs using the in vitro in macrophages and lymphocytes and in vivo in BALB/c mice.

RESULTS

Our results indicated that macrophages treated with 1.25 or 2.5 nM QDs exhibited decreased cell viability, increased levels of reactive oxygen species (ROS), elevated apoptotic events, altered phagocytic ability, and decreased release of TNF-α and IL-6 by upon subsequent stimulation with Lipopolysaccharide (LPS). In contrast, lymphocytes exposed to QDs exhibited enhanced cell viability, increased release of TNF-α and IL-6 following exposure with CpG-ODN, and decreased transformation ability treatment in response to LPS. To study the in vivo effects in mice, we showed that QDs injection did not cause significant changes to body weight, hematology, organ histology, and phagocytic function of peritoneal macrophages in QDs-treated mice. In addition, the QDs formulation accumulated in major immune organs for more than 42 days. Lymphocytes from QDs-treated mice showed reduced cell viability, changed subtype proportions, increased TNF-α and IL-6 release, and reduced transformation ability in response to LPS.

CONCLUSIONS

Taken together, these results suggested that exposures to CdSe/ZnS QDs could suppress immune-defense against foreign stimuli, which in turn could result in increased susceptibility of hosts to diseases.

Fabrication of AIE-active amphiphilic fluorescent polymeric nanoparticles through host–guest interaction

Novel polymeric luminescent nanoprobes with aggregation induced emission (AIE) properties were fabricatedviahost–guest interaction between the β-CD pendant copolymers and adamantane-terminated AIE dye.

Exploring the cellular and tissue uptake of nanomaterials in a range of biological samples using multimodal nonlinear optical microscopy

The uptake of nanomaterials (NMs) by cells is critical in determining their potential biological impact, whether beneficial or detrimental. Thus, investigation of NM internalization by cells is a common consideration in hazard and efficacy studies. There are currently a number of approaches that are routinely used to investigate NM-cell interactions, each of which have their own advantages and limitations. Ideally, imaging modalities used to investigate NM uptake by cells should not require the NM to be labelled (e.g. with fluorophores) to facilitate its detection. We present a multimodal imaging approach employing a combination of label-free microscopies that can be used to investigate NM-cell interactions. Coherent anti-Stokes Raman scattering microscopy was used in combination with either two-photon photoluminescence or four-wave mixing (FWM) to visualize the uptake of gold or titanium dioxide NMs respectively. Live and fixed cell imaging revealed that NMs were internalized by J774 macrophage and C3A hepatocyte cell lines (15-31 μg ml(-1)). Sprague Dawley rats were exposed to NMs (intratracheal instillation, 62 μg) and NMs were detected in blood and lung leucocytes, lung and liver tissue, demonstrating that NMs could translocate from the exposure site. Obtained data illustrate that multimodal nonlinear optical microscopy may help overcome current challenges in the assessment of NM cellular uptake and biodistribution. It is therefore a powerful tool that can be used to investigate unlabelled NM cellular and tissue uptake in three dimensions, requires minimal sample preparation, and is applicable to live and fixed cells.

Red fluorescent cross-linked glycopolymer nanoparticles based on aggregation induced emission dyes for cell imaging

Aggregation induced emission dye based cross-linked fluorescent glycopolymer nanoparticles with red emission: their synthesis, characterization and application for cell imaging.

Fabrication of photostable PEGylated polymer nanoparticles from AIE monomer and trimethylolpropane triacrylate

Fabrication of biocompatible and photostable PEGylated nanoparticles from AIE monomer and trimethylolpropane triacrylate for cellular imaging.

Preparation of biocompatible and photostable PEGylated red fluorescent nanoparticles for cellular imaging

Biocompatible and photostable PEGylated red fluorescent nanoparticles were preparedviasurface-initiated ATRP and their cellular imaging application was successfully demonstrated.

The interactions between CdSe quantum dots and yeast Saccharomyces cerevisiae: adhesion of quantum dots to the cell surface and the protection effect of ZnS shell

The interactions between quantum dots (QDs) and biological systems have attracted increasing attention due to concerns on possible toxicity of the nanoscale materials. The biological effects of CdSe QDs and CdSe/ZnS QDs with nearly identical hydrodynamic size on Saccharomyces cerevisiae were investigated via microcalorimetric, spectroscopic and microscopic methods, demonstrating a toxic order CdSe>CdSe/ZnS QDs. CdSe QDs damaged yeast cell wall and reduced the mitochondrial membrane potential. Noteworthy, adhesion of QDs to the yeast cell surface renders this work a good example of interaction site at cell surface, and the epitaxial coating of ZnS could greatly reduce the toxicity of Cd-containing QDs. These results will contribute to the safety evaluation of quantum dots, and provide valuable information for design of nanomaterials.

The effect of nanoparticle degradation on amphiphilic polymer-coated quantum dot toxicity: the importance of particle functionality assessment in toxicology [corrected]

Colloidal semiconductor nanoparticles (quantum dots) have attracted a lot of interest in technological and biomedical research, given their potent fluorescent properties. However, the use of heavy-metal-containing nanoparticles remains an issue of debate. The possible toxic effects of quantum dots remain a hot research topic and several questions such as possible intracellular degradation of quantum dots and the effect thereof on both cell viability and particle functionality remain unresolved. In the present work, amphiphilic polymer [corrected] coated CdSe/ZnS quantum dots were synthesized and characterized, after which their effects on cultured cells were evaluated using a multiparametric setup. The data reveal that the quantum dots are taken up through endocytosis and when exposed to the low pH of the endosomal structures, they partially degrade and release cadmium ions, which lowers their fluorescence intensity and augments particle toxicity. Using the multiparametric method, the quantum dots were evaluated at non-toxic doses in terms of their ability to visualize labeled cells for longer time periods. The data revealed that comparing different particles in terms of their applied dose is challenging, likely due to difficulties in obtaining accurate nanoparticle concentrations, but evaluating particle toxicity in terms of their biological functionality enables an easy and straightforward comparison.

Unraveling the effects of siRNA carrier systems on cell physiology: a multiparametric approach demonstrated on dextran nanogels

Aim: The extent of cell–nanoparticle interactions between a polycationic siRNA nanocarrier system (dextran nanogels) and cultured cells was analyzed. Materials & methods: A multiparametric methodology is introduced to examine the cytotoxic effects of a model siRNA carrier (dextran nanogels) on different cell types, including primary human cells. Using this methodology, the nontoxic concentration of nanogels could be defined and the mechanisms contributing to their toxic profile were unraveled. Results: Above the toxicity threshold, nanogels were found to induce oxidative stress and destabilize the plasma membrane. Furthermore, nanogel-induced cellular stress led to DNA damage, impeded cell functionality and intracellular signaling, resulting in unspecific regulation of gene expression. Conclusion: This methodology shows that current toxicity assays such as the 3-(4,5-dimethylthiazol-2yl-)-2,5-diphenyl tetrazolium bromide assay are not adequate to assess the full spectrum of cell–nanoparticle interactions and more in-depth studies are required.

Original submitted 8 May 2012; Revised submitted 3 December 2012; Published online 12 June 2013

Cadmium sulfate and CdTe-quantum dots alter DNA repair in zebrafish (Danio rerio) liver cells

Increasing use of quantum dots (QDs) makes it necessary to evaluate their toxicological impacts on aquatic organisms, since their contamination of surface water is inevitable. This study compares the genotoxic effects of ionic Cd versus CdTe nanocrystals in zebrafish hepatocytes. After 24h of CdSO4 or CdTe QD exposure, zebrafish liver (ZFL) cells showed a decreased number of viable cells, an accumulation of Cd, an increased formation of reactive oxygen species (ROS), and an induction of DNA strand breaks. Measured levels of stress defense and DNA repair genes were elevated in both cases. However, removal of bulky DNA adducts by nucleotide excision repair (NER) was inhibited with CdSO4 but not with CdTe QDs. The adverse effects caused by acute exposure of CdTe QDs might be mediated through differing mechanisms than those resulting from ionic cadmium toxicity, and studying the effects of metallic components may be not enough to explain QD toxicities in aquatic organisms.

Lysine-based surfactants in nanovesicle formulations: the role of cationic charge position and hydrophobicity in in vitro cytotoxicity and intracellular delivery

Understanding nanomaterial interactions within cells is of increasing importance for assessing their toxicity and cellular transport. Here, the authors developed nanovesicles containing bioactive cationic lysine-based amphiphiles and assessed whether these cationic compounds increase the likelihood of intracellular delivery and modulate toxicity. Different cytotoxic responses were found among the formulations, depending on surfactant, cell line and endpoint assayed. The induction of mitochondrial dysfunction, oxidative stress and apoptosis were the general mechanisms underlying cytotoxicity. Fluorescence microscopy analysis demonstrated that nanovesicles were internalised by HeLa cells and evidenced that their ability to release endocytosed materials into cell cytoplasm depends on the structural parameters of amphiphiles. The cationic charge position and hydrophobicity of surfactants determine the nanovesicle interactions within the cell and, thus, the resulting toxicity and intracellular behaviour after cell uptake of the nanomaterial. The insights into some toxicity mechanisms of these new nanomaterials contribute in reducing the uncertainty surrounding their potential health hazards.

Linseed oil based nanocapsules as delivery system for hydrophobic quantum dots

In the present work, the CdSe/ZnS hydrophobic quantum dots were embedded within the polyelectrolyte nanocapsules. The core of the capsules, which consists of a mixture of the linseed oil with chloroform, was prepared using the spontaneous emulsification technique. The obtained emulsions were stabilized with lecithin and encapsulated using the layer-by-layer (LbL) adsorption of polyelectrolytes. The pair of biocompatible polyelectrolytes was used: the cationic poly-l-lysine hydrobromide (PLL) together with the anionic poly-d-glutamic acid sodium salt. The saturation LbL method, which is based on the stepwise formation of consecutive layers on the initial emulsion without the intermediate rinsing step, was applied to form the capsule shells. Their growth was evidenced by the capsule size and electrophoretic mobility measurements. The emulsion and the capsules were deposited on a mica surface and the deposit topology was examined by the means of atomic force microscopy (AFM). The presence of quantum dots within the oil cores was confirmed by recording the fluorescent spectra of the samples containing CdSe/ZnS. In order to evaluate cytotoxicity of the capsules, their influence on the viability of mouse embryonic fibroblasts was examined using the MTT test, followed by optical-microscope observation of morphology of the cells after hematoxylin-eosin staining.

Determination of a threshold dose to reduce or eliminate CdTe-induced toxicity in L929 cells by controlling the exposure dose

With the widespread use of quantum dots (QDs), the likelihood of exposure to quantum dots has increased substantially. The application of quantum dots in numerous biomedical areas requires detailed studies on their toxicity. In this study, we aimed to determine the threshold dose which reduced or eliminated CdTe-induced toxicity in L929 cells by controlling the exposure dose. We established a cellular model of acute exposure to CdTe QDs. Cells were exposed to different concentrations of CdTe QDs (2.2 nm and 3.5 nm) followed by illustrative cytotoxicity analysis. The results showed that low concentrations of CdTe QDs (under 10 µg/mL) promoted cell viability, caused no obvious effect on the rate of cell apoptosis, intracellular calcium levels and changes in mitochondrial membrane potential, while high concentrations significantly inhibited cell viability. In addition, reactive oxygen species in the 10 µg/mL-treated group was significantly reduced compared with the control group. In summary, the cytotoxicity of CdTe QDs on L929 cell is dose-dependent, time-dependent and size-dependent. Low concentrations of CdTe QDs (below 10 µg/mL) may be nontoxic and safe in L929 cells, whereas high concentrations (above 10 µg/mL) may be toxic resulting in inhibition of proliferation and induction of apoptosis in L929 cells.

Biophysical responses upon the interaction of nanomaterials with cellular interfaces

The explosion of study of nanomaterials in biological applications (the nano-bio interface) can be ascribed to nanomaterials' growing importance in diagnostics, therapeutics, theranostics (therapeutic diagnostics), and targeted modulation of cellular processes. However, a growing number of critics have raised concerns over the potential risks of nanomaterials to human health and safety. It is essential to understand nanomaterials' potential toxicity before they are tested in humans. These risks are complicated to unravel, however, because of the complexity of cells and their nanoscale macromolecular components, which enable cells to sense and respond to environmental cues, including nanomaterials. In this Account, we explore these risks from the perspective of the biophysical interactions between nanomaterials and cells. Biophysical responses to the uptake of nanomaterials can include conformational changes in biomolecules like DNA and proteins, and changes to the cellular membrane and the cytoskeleton. Changes to the latter two, in particular, can induce changes in cell elasticity, morphology, motility, adhesion, and invasion. This Account reviews what is known about cells' biophysical responses to the uptake of the most widely studied and used nanoparticles, such as carbon-based, metal, metal-oxide, and semiconductor nanomaterials. We postulate that the biophysical structure impairment induced by nanomaterials is one of the key causes of nanotoxicity. The disruption of cellular structures is affected by the size, shape, and chemical composition of nanomaterials, which are also determining factors of nanotoxicity. Currently, popular nanotoxicity characterizations, such as the MTT and lactate dehydrogenase (LDH) assays, only provide end-point results through chemical reactions. Focusing on biophysical structural changes induced by nanomaterials, possibly in real-time, could deepen our understanding of the normal and altered states of subcellular structures and provide useful perspective on the mechanisms of nanotoxicity. We strongly believe that biophysical properties of cells can serve as novel and noninvasive markers to evaluate nanomaterials' effect at the nano-bio interface and their associated toxicity. Better understanding of the effects of nanomaterials on cell structures and functions could help identify the required preconditions for the safe use of nanomaterials in therapeutic applications.

Facile synthesis and characterization of water soluble ZnSe/ZnS quantum dots for cellar imaging

Strong fluorescence and low cytotoxicity ZnSe/ZnS quantum dots (QDs) were synthesized by a facile aqueous phase route. It overcame the defects such as instability and low quantum yield of the quantum dots synthesized by early aqueous phase route. L-Glutathione (GSH) and 3-mercaptopropaonic acid (MPA) were used as mixture stabilizers to synthesize high quality ZnSe/ZnS QDs. The samples were characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectrometry (XPS) and their optical properties were investigated by using UV-vis spectrophotometer, fluorescence spectrophotometer (FL), IR spectrophotometer and confocal laser scanning microscope. The synthesized ZnSe/ZnS QDs illuminated blue fluorescence under ultraviolet lamp. Its water-soluble property is excellent and the fluorescence intensity of ZnSe/ZnS QDs almost did not change after 4 months at room temperature. The average diameter of ZnSe/ZnS nanocrystals is about 3 nm and quantum yield (QY) could reach to 70.6% after repeat determination. Low cytotoxicity was ensured by investigated SCG7901 and RAW264.7 cells. In comparison with cadmium based nanocrystals, ZnSe/ZnS QDs posed low cytotoxicity. The cells viability remained 96.7% when the QDs concentration was increased to 10 μmol/L. The results in vitro indicate that ZnSe/ZnS QDs-based probes have good stability, low toxicity and biocompatibility for fluorescence imaging in cancer model system.

Size-dependent toxicity and cell interaction mechanisms of gold nanoparticles on mouse fibroblasts

Gold nanoparticles (AuNPs) are currently used in several fields including biomedical applications, although no conclusive information on their cytotoxicity is available. For this reason this work has investigated the effects of AuNPs in vitro on Balb/3T3 mouse fibroblasts. Results obtained exposing cells for 72 h to AuNPs 5 and 15 nm citrate stabilized, revealed cytotoxic effects only for AuNPs 5 nm at concentration ≥ 50 μM if measured by colony forming efficiency (CFE). To understand the differences in cytotoxicity observed for the two AuNPs sizes, we investigated the uptake and the intracellular distribution of the nanoparticles. By TEM it was observed that 5 and 15 nm AuNPs are internalized by Balb/3T3 cells and located within intracellular endosomal compartments. Quantification of the uptake by ICP-MS showed that AuNPs internalization enhanced even up to 72 h. Disruption of the actin cytoskeleton was evident, with cell footprints narrow and contracted; effects more remarkable in cells exposed to 5 nm AuNP. The mechanism of NPs cell internalization was investigated using immunocytochemistry and western blot. No significant effect was observed in the expression level of caveolin, while reduction of the expression and degradation of the clathrin heavy chain was observed in cells exposed for 72 h to AuNPs.

The combined influence of surface modification, size distribution, and interaction time on the cytotoxicity of CdTe quantum dots in PANC-1 cells

Mercaptopropionic acid (MPA) and cysteamine (Cys) capped CdTe quantum dots (QDs) were successfully prepared and used to investigate the combined influence of surface modification, size distribution, and interaction time on their cytotoxicity in human pancreatic carcinoma (PANC-1) cells. Results indicated that the smaller the size of MPA-CdTe QDs, the higher the cytotoxicity, which could be partly due to the difference of their distribution inside cells. Comparing with MPA-CdTe QDs, Cys-CdTe QDs had better cellular metabolizability and lower cytotoxicity. These QDs' cellular distribution and cytotoxicity were closely related to their interaction time with cells. Their cytotoxicity was found to be significantly enhanced with the increase of incubation time in medium. After QD treatments, the influence of recover time on the final cell viability was also dependent on the concentration and surface modification of QDs used in pretreatment. The combined influence of these factors discussed here might provide useful information for understanding and reducing the cytotoxicity of QDs in future biomedical applications.

Short ligands affect modes of QD uptake and elimination in human cells

In order to better understand nanoparticle uptake and elimination mechanisms, we designed a controlled set of small, highly fluorescent quantum dots (QDs) with nearly identical hydrodynamic size (8-10 nm) but with varied short ligand surface functionalization. The properties of functionalized QDs and their modes of uptake and elimination were investigated systematically by asymmetrical flow field-flow fractionation (AF4), confocal fluorescence microscopy, flow cytometry (FACS), and flame atomic absorption (FAA). Using specific inhibitors of cellular uptake and elimination machinery in human embryonic kidney cells (Hek 293) and human hepatocellular carcinoma cells (Hep G2), we showed that QDs of the same size but with different surface properties were predominantly taken up through lipid raft-mediated endocytosis, however, to significantly different extents. The latter observation infers the contribution of additional modes of QD internalization, which include X-AG cysteine transporter for cysteine-functionalized QDs (QD-CYS). We also investigated putative modes of QD elimination and established the contribution of P-glycoprotein (P-gp) transporter in QD efflux. Results from these studies show a strong dependence between the properties of QD-associated small ligands and modes of uptake/elimination in human cells.