Differences in subcellular distribution and toxicity of green and red emitting CdTe quantum dots

Induction of autophagy in porcine kidney cells by quantum dots: a common cellular response to nanomaterials?

Quantum dots (QDs) are being investigated as novel in vivo imaging agents. The leaching of toxic metals from these QDs in biological systems is of great concern. This study compared the cytotoxic mechanisms of two QD species made of different core materials (cadmium selenide [CdSe] vs. indium gallium phosphide [InGaP]) but similar core sizes (5.1 vs. 3.7 nm) and surface compositions (both ZnS capped, lipid-coated and pegylated). The CdSe QD was found to be 10-fold more toxic to porcine renal proximal tubule cells (LLC-PK1) than the InGaP QD on a molar basis, as determined by MTT assay (48 h IC(50) 10nM for CdSe vs. 100nM for InGaP). Neither of the QD species induced appreciable oxidative stress, as determined by lipid peroxide and reduced glutathione content, suggesting that toxicity was not metal associated. In agreement, treatment of cells with CdSe QDs was not associated with changes in metallothionein-IA (MT-IA) gene expression or Cd-associated caspase 3 enzyme activation. By contrast, incubation of the LLC-PK1 cells with the InGaP QD resulted in a dramatic increase in MT-IA expression by 21- and 43-fold, at 8 and 24 h, respectively. The most remarkable finding was evidence of extensive autophagy in QD-treated cells, as determined by Lysotracker Red dye uptake, TEM, and LC3 immunobloting. Autophagy induction has also been described for other nanomaterials and may represent a common cellular response. These data suggest that QD cytotoxicity is dependent upon properties of the particle as a whole, and not exclusively the metal core materials.

Surface-structure-regulated cell-membrane penetration by monolayer-protected nanoparticles

Nanoscale objects are typically internalized by cells into membrane-bounded endosomes and fail to access the cytosolic cell machinery. Whereas some biomacromolecules may penetrate or fuse with cell membranes without overt membrane disruption, no synthetic material of comparable size has shown this property yet. Cationic nano-objects pass through cell membranes by generating transient holes, a process associated with cytotoxicity. Studies aimed at generating cell-penetrating nanomaterials have focused on the effect of size, shape and composition. Here, we compare membrane penetration by two nanoparticle 'isomers' with similar composition (same hydrophobic content), one coated with subnanometre striations of alternating anionic and hydrophobic groups, and the other coated with the same moieties but in a random distribution. We show that the former particles penetrate the plasma membrane without bilayer disruption, whereas the latter are mostly trapped in endosomes. Our results offer a paradigm for analysing the fundamental problem of cell-membrane-penetrating bio- and macro-molecules.

Tumor targeting using liposomal antineoplastic drugs

During the last years, liposomes (microparticulate phospholipid vesicles) have been used with growing success as pharmaceutical carriers for antineoplastic drugs. Fields of application include lipid-based formulations to enhance the solubility of poorly soluble antitumor drugs, the use of pegylated liposomes for passive targeting of solid tumors as well as vector-conjugated liposomal carriers for active targeting of tumor tissue. Such formulation and drug targeting strategies enhance the effectiveness of anticancer chemotherapy and reduce at the same time the risk of toxic side-effects. The present article reviews the principles of different liposomal technologies and discusses current trends in this field of research.

Assessment of cytotoxicity of quantum dots and gold nanoparticles using cell-based impedance spectroscopy

A continuous online technique based on electric cell-substrate impedance sensing (ECIS) was demonstrated for measuring the concentration and time response function of fibroblastic V79 cells exposed to nanomaterials such as quantum dots (QDs) and fluorescent gold nanoparticles. The half-inhibition concentration, (ECIS50), the required concentration to attain 50% inhibition of the cytotoxic response, was estimated from the response function to ascertain cytotoxicity during the course of measurement. The ECIS50 values agreed well with the results obtained using the standard neutral red assay. Cadmium selenide quantum dots showed direct cytotoxicity with the ECIS assay. For the cadmium telluride quantum dots, significant toxicity could be assigned to free cadmium, although additional toxicity could be attributed to the QDs per se. The QDs synthesized with indium gallium phosphide and the fluorescent gold nanoparticles were not cytotoxic.

Mechanism of antimicrobial activity of CdTe quantum dots

The antimicrobial activity and mechanism of CdTe quantum dots (QDs) against Escherichia coli were investigated in this report. Colony-forming capability assay and atomic force microscopy (AFM) images show that the QDs can effectively kill the bacteria in a concentration-dependent manner. Results of photoluminescence spectrophotometry, confocal microscopy, and antioxidative response tests indicate that the QDs bind with bacteria and impair the functions of a cell's antioxidative system, including down-regulations of antioxidative genes and decreases of antioxidative enzymes activities. The oxidative damage of protein and lipid is also observed with thiobarbituric reacting substances and protein carbonyl assays, respectively. On the basis of these results, it is proposed that the mechanism of the antimicrobial activity of CdTe QDs involves QDs-bacteria association and a reactive oxygen species-mediated pathway. Thus, CdTe QDs could have the potential to be formulated as a novel antimicrobial material with excellent optical properties.

Fluorescence intensity and intermittency as tools for following dopamine bioconjugate processing in living cells

CdSe/ZnS quantum dots (QDs) conjugated to biomolecules that quench their fluorescence, particularly dopamine, have particular spectral properties that allow determination of the number of conjugates per particle, namely, photoenhancement and photobleaching. In this work, we quantify these properties on a single-particle and ensemble basis in order to evaluate their usefulness as a tool for indicating QD uptake, breakdown, and processing in living cells. This creates a general framework for the use of fluorescence quenching and intermittency to better understand nanoparticle-cell interactions.

Air pollution, ultrafine and nanoparticle toxicology: cellular and molecular interactions

Nanotechnology is involved with the creation and/or manipulation of materials at the nanometer (nm) scale, and has arisen as a consequence of the novel properties that materials exhibit within the "nano" size range. The attraction of producing, and exploiting nanparticles (NPs; one dimension less than 100 nm) is a consequence of the fact that the properties are often strikingly different from bulk forms composed from the same material. As a consequence, the field of nanotechnology has generated substantial interest resulting in incorporation of NPs into a wide variety of products including electronics, food, clothing, medicines, cosmetics and sporting equipment. While there is general recognition that nanotechnology has the potential to advance science, quality of life and to generate substantial financial gains, a number of reports suggest that potential toxicity should be considered in order to allow the safe and sustainable development of such products. For example, substances which are ordinarily innocuous can elicit toxicity due to the altered chemical and physical properties that become evident within nano dimensions leading to potentially detrimental consequences for the producer, consumer or environment. Research into respirable air pollution particles (PM10) has focused on the role of ultrafine particle (diameter less than 100 nm) in inducing oxidative stress leading to inflammation and resulting in exacerbation of preexisting respiratory and cardiovascular disease. Epidemiological studies have repeatedly found a positive correlation between the level of particulate air pollution and increased morbidity and mortality rates in both adults and children. Such studies have also identified a link between respiratory ill health and the number of ambient ultrafine particles. In vivo and in vitro toxicology studies confirm that for low solubility, low toxicity materials such as TiO2, carbon black and polystyrene beads, ultrafine particles are more toxic and inflammogenic than fine particles. In many of these studies the term "ultrafine particle" can be directly exchanged for nanoparticle, as these particles are manufactured industrially. In such studies the NPs generate reactive oxygen species (ROS) to a greater extent than larger particles leading to increased transcription of pro-inflammatory mediators via intracellular signaling pathways including calcium and oxidative stress. To date, only limited NP compositions and structures have been tested, including materials such as carbon, polystyrene beads and TiO2 as surrogate particles that aimed to represent particulate air pollution. All of these materials are generally low toxicity and low solubility. Much work is required to identify whether the conclusions made for such materials can be extrapolated to engineered nanoparticles varying not only in size but also, shape, composition, structure, surface area, surface coating, and aggregation state. Therefore, it is necessary to reveal if the diversity of NPs available will confer to a varied extent and mechanisms of toxicity.

The large-scale digital cell analysis system: an open system for nonperturbing live cell imaging

The Large-Scale Digital Cell Analysis System (LSDCAS) was designed to provide a highly extensible open source live cell imaging system. Analysis of cell growth data has demonstrated a lack of perturbation in cells imaged using LSDCAS, through reference to cell growth data from cells growing in CO(2) incubators. LSDCAS consists of data acquisition, data management and data analysis software, and is currently a Core research facility at the Holden Comprehensive Cancer Center at the University of Iowa. Using LSDCAS analysis software, this report and others show that although phase-contrast imaging has no apparent effect on cell growth kinetics and viability, fluorescent image acquisition in the cell lines tested caused a measurable level of growth perturbation using LSDCAS. This report describes the current design of the system, reasons for the implemented design, and details its basic functionality. The LSDCAS software runs on the GNU/Linux operating system, and provides easy to use, graphical programs for data acquisition and quantitative analysis of cells imaged with phase-contrast or fluorescence microscopy (alone or in combination), and complete source code is freely available under the terms of the GNU Public Software License at the project website (http://lsdcas.engineering.uiowa.edu).

Nonfunctionalized nanocrystals can exploit a cell's active transport machinery delivering them to specific nuclear and cytoplasmic compartments

We use high content cell analysis, live cell fluorescent imaging, and transmission electron microscopy approaches combined with inhibitors of cellular transport and nuclear import to conduct a systematic study of the mechanism of interaction of nonfunctionalized quantum dots (QDs) with live human blood monocyte-derived primary macrophages and cell lines of phagocytic, epithelial, and endothelial nature. Live human macrophages are shown to be able to rapidly uptake and accumulate QDs in distinct cellular compartment specifically to QDs size and charge. We show that the smallest QDs specifically target histones in cell nuclei and nucleoli by a multistep process involving endocytosis, active cytoplasmic transport, and entering the nucleus via nuclear pore complexes. Treatment of the cells with an anti-microtubule agent nocodazole precludes QDs cytoplasmic transport whereas a nuclear import inhibitor thapsigargin blocks QD import into the nucleus. These results demonstrate that the nonfunctionalized QDs exploit the cell's active transport machineries for delivery to specific intranuclear destinations.

Cyclic tensile strain increases interactions between human epidermal keratinocytes and quantum dot nanoparticles

The effects of quantum dots (QD) on cell viability have gained increasing interest due to many recent developments utilizing QD for pharmaceutical and biomedical applications. The potential use of QD nanoparticles as diagnostic, imaging, and drug delivery agents has raised questions about their potential for cytotoxicity. The objective of this study was to investigate the effects of applied strain on QD uptake by human epidermal keratinocytes (HEK). It was hypothesized that introduction of a 10% average strain to cell cultures would increase QD uptake. HEK were seeded at a density of 150,000 cells/mL on collagen-coated Flexcell culture plates (Flexcell Intl.). QD were introduced at a concentration of 3 nM and a 10% average strain was applied to the cells. After 4h of cyclic strain, the cells were examined for cell viability, QD uptake, and cytokine production. The results indicate that addition of strain results in an increase in cytokine production and QD uptake, resulting in irritation and a negative impact on cell viability. Application of physiological load conditions can increase cell membrane permeability, thereby increasing the concentration of QD nanoparticles in cells.

Quantum dots and multifunctional nanoparticles: new contrast agents for tumor imaging

Nanometer-sized particles, such as semiconductor quantum dots and iron oxide nanocrystals, have novel optical, electronic, magnetic or structural properties that are not available from either molecules or bulk solids. When linked with tumor-targeting ligands, such as monoclonal antibodies, peptide fragments of tumor-specific proteins or small molecules, these nanoparticles can be used to target tumor antigens (biomarkers) and tumor vasculatures with high affinity and specificity. In the mesoscopic size range of 5-100 nm diameter, quantum dots and related nanoparticles have large surface areas and functional groups that can be linked to multiple diagnostic (e.g., optical, radioisotopic or magnetic) and therapeutic (e.g., anticancer) agents. In this review, recent advances in the development and applications of bioconjugated quantum dots and multifunctional nanoparticles for in vivo tumor imaging and targeting are discussed.

Use of fluorescent quantum dot bioconjugates for cellular imaging of immune cells, cell organelle labeling, and nanomedicine: surface modification regulates biological function, including cytotoxicity

With the development of nanotechnology, nanoscale products that are smaller than several hundred nanometers have been applied to all areas of science and technology. Nanoscale products, including carbon nanotubes, fullerene derivatives, and nanocrystal quantum dots (QDs), are wide spread as novel tools in various fields, not only in materials engineering, electronics, plastics, and the automobile and aerospace industries, but also in molecular biology and medicine. At present, QDs have been widely used in biological and medical studies because of their superior photoemission and photostability. Although the physical and chemical properties of QDs have been circumstantially investigated, little is known about any harmful effects of QDs on human health. Here we report on the toxicity and biological behavior of QDs in vitro and in vivo. The toxicity of the core constituent chemicals such as cadmium and selenium has been identified. Recently, the surface molecules surrounding QDs have been intensively investigated. Accumulating evidence that toxic surface-covering molecules showed their cytotoxicity and biomolecules conjugated with QDs maintained their biological effects indicates that at least the biological properties of QDs are attributable to the QD-capping material rather than to the core metalloid complex itself.

An antibody-conjugated internalizing quantum dot suitable for long-term live imaging of cells

Quantum dots (QD) are fluorescent semiconductor nanocrystals that are emerging as superior alternatives to the conventional organic dyes used in biological applications. Although QDs offer several advantages over conventional fluorescent dyes, including greater photostability and a wider range of excitation and (or) emission wavelengths, their toxicity has been an issue in its wider use as an analytic, diagnostic and therapeutic tool. We prepared a conjugate QD with an internalizing antibody and demonstrated that the QD-antibody conjugate is efficiently internalized into cells and is visible even after multiple divisions. We demonstrate that the internalized QD is nontoxic to cells and provides a sensitive tool for long-term molecular imaging.

Persistent tissue kinetics and redistribution of nanoparticles, quantum dot 705, in mice: ICP-MS quantitative assessment

BACKGROUND

Quantum dots (QDs) are autofluorescent semiconductor nanocrystals that can be used for in vivo biomedical imaging. However, we know little about their in vivo disposition and health consequences.

OBJECTIVES

We assessed the tissue disposition and pharmacokinetics of QD705 in mice.

METHODS

We determined quantitatively the blood and tissue kinetics of QD705 in mice after single intravenous (iv) injection at the dose of 40 pmol for up to 28 days. Inductively coupled plasma-mass spectrometry (ICP-MS) measurement of cadmium was the primary method of quantification of QD705. Fluorescence light microscopy revealed the localization of QD705 in tissues.

RESULTS

Plasma half-life of QD705 in mice was short (18.5 hr), but ICP-MS analyses revealed QD705 persisted and even continued to increase in the spleen, liver, and kidney 28 days after an iv dose. Considerable time-dependent redistribution from body mass to liver and kidney was apparent between 1 and 28 days postdosing. The recoveries at both time points were near 100%; all QD705s reside in the body. Neither fecal nor urinary excretion of QD705 was detected appreciably in 28 days postdosing. Fluorescence microscopy demonstrated deposition of QD705 in the liver, spleen, and kidneys.

CONCLUSION

Judging from the continued increase in the liver (29-42% of the administered dose), kidney (1.5-9.2%), and spleen (4.8-5.2%) between 1 and 28 days without any appreciable excretion, QD705 has a very long half-life, potentially weeks or even months, in the body and its health consequences deserve serious consideration.

From diagnostics to therapy: Prospects of quantum dots

Quantum dots (QDs) are among the most promising items in the nanomedicine toolbox. These nanocrystal fluorophores have several potential medical applications including nanodiagnostics, imaging, targeted drug delivery, and photodynamic therapy. The diverse potential applications of QDs are attributed to their unique optical properties including broad-range excitation, size-tunable narrow emission spectra, and high photostability. The size and composition of QDs can be varied to obtain the desired emission properties a makes them amenable for simultaneous detection of multiple targets. Also, numerous surface functionalizations can be used to adapt QDs to the needed application. Recent reports have shown successful use of QDs in various medical applications. With respect to in vivo applications, caution must be exercised with QDs due to their toxic components. Development of appropriate health and safety regulations and resolution of intellectual property issues are necessary for commercialization. In light of these obstacles however, QDs appear to be too valuable to nanomedicine to dismiss, and will eventually come into routine practical use.

What do we (need to) know about the kinetic properties of nanoparticles in the body?

Nowadays the development and applications of nanotechnology are of major importance in both industrial and consumer areas. However, the knowledge on human exposure and possible toxicity of nanotechnology products is limited. To understand the mechanism of toxicity, thorough knowledge of the toxicokinetic properties of nanoparticles is warranted. There is a need for information on the absorption, distribution, metabolism and excretion (ADME) of nanoparticles and validated detection methods of these man-made nanoparticles. Determination of the ADME properties of nanoparticles requires specialised detection methods in different biological matrices (e.g. blood and organs). In this paper, the current knowledge on the kinetic properties of nanoparticles is reviewed. Moreover, knowledge gaps from a kinetic point of view (detection, dose, ADME processes) are identified.

Toxicity of luminescent silica nanoparticles to living cells

Luminescent nanomaterials can provide high-intensity and photostable luminescent signals when used as labeling materials for the determination of trace amounts of analytes. However, a major concern that has arisen is whether the nanomaterials cause toxic effects in living systems. Here, we address this problem through a systematic investigation of the cytotoxicity and genotoxicity of luminescent silica nanoparticles. These nanoparticles are intensely luminescent labeling materials for ultrasensitive determination of biological samples. The investigation of genotoxicity of the nanomaterials was carried out from two perspectives. First, the integrity of the DNA was examined by detecting DNA base modification, strand breaks, and increased DNA repair activity to recover the damage. Second, different sets of cellular DNAs, including nuclear DNA extracts and the whole genomic DNAs, were examined. Furthermore, to fully assess DNA damage by the nanoparticles, isolated genomic DNAs were directly exposed to the nanoparticles. The cytotoxicity of the nanoparticle was detected by measuring the cell proliferation rate, cell death, and death patterns (necrosis and apoptosis) after the nanoparticle treatments. Results show no significant toxic effects due to the luminescent nanoparticles at the molecular and cellular levels below a concentration of 0.1 mg/mL. Our study indicates that the luminescent silica nanoparticle is a promising labeling reagent for various biomedical applications.

Luminescent silica nanobeads: characterization and evaluation as efficient cytoplasmatic transporters for T-lymphocytes

We report the fabrication and characterization of neutravidin-conjugated silica nanobeads doped with a ruthenium-complex luminophore and functionalized with antihuman CD3, antihuman CD28, and an acid-sensitive polymer. We observed that the nanobeads were readily delivered into Jurkat T leukemia cells by endocytosis, transported into lysosomes and subsequently into the cytoplasm as revealed by pH-sensitive luminescence. Since signs of cytotoxicity were not observed, the reported nanobeads could be an excellent and nontoxic building block for efficient intracellular transporters.

Infrared-emitting colloidal nanocrystals: synthesis, assembly, spectroscopy, and applications

Semiconductor nanocrystals produced by means of colloidal chemistry in a solvent medium are an attractive class of nanometer-sized building blocks from which to create complex materials with unique properties for a variety of applications. Their optical and electronic properties can be tailored easily, both by their chemical composition and particle size. While colloidal nanocrystals emitting in the infrared region have seen a burst of attention during the last decade there is clearly a paucity of review articles covering their synthesis, assembly, spectroscopic characterization, and applications. This Review comprehensively addresses these topics for II-VI, III-V, and IV-VI nanocrystals, examples being HgTe and Cd(x)Hg(1-) (x)Te, InP and InAs, and PbS, PbSe, and PbTe, respectively. Among the applications discussed here are optical amplifier media for telecommunications systems, electroluminescence devices, and noninvasive optical imaging in biology.

Fate of micelles and quantum dots in cells

Micelles and quantum dots have been used as experimental drug delivery systems and imaging tools both in vitro and in vivo. Investigations of their fate at the subcellular level require different surface-core modifications. Among the most common modifications are those with fluorescent probes, dense-core metals or radionucleids. Cellular fate of several fluorescent probes incorporated into poly(caprolactone)-b-copolymer micelles (PCL-b-PEO) was followed by confocal microscopy, and colloidal gold incorporated in poly 4-vinyl pyridine-PEO micelles were developed to explore micelle fate by electron microscopy. More recently, we have examined quantum dots (QDs) as the next-generation-labels for cells and nanoparticulate drug carriers amenable both to confocal and electron microscopic analyses. Effects of QDs at the cellular and subcellular levels and their integrity were studied. Results from different studies suggest that size, charge and surface manipulations of QDs may play a role in their subcellular distribution. Examples of pharmacological agents incorporated into block copolymer micelles, administered or attached to QD surfaces show how the final biological outcome (e.g. cell death, proliferation or differentiation) depends on physical properties of these nanoparticles.

Long-term exposure to CdTe quantum dots causes functional impairments in live cells

Several studies suggested that the cytotoxic effects of quantum dots (QDs) may be mediated by cadmium ions (Cd2+) released from the QDs cores. The objective of this work was to assess the intracellular Cd2+ concentration in human breast cancer MCF-7 cells treated with cadmium telluride (CdTe) and core/shell cadmium selenide/zinc sulfide (CdSe/ZnS) nanoparticles capped with mercaptopropionic acid (MPA), cysteamine (Cys), or N-acetylcysteine (NAC) conjugated to cysteamine. The Cd2+ concentration determined by a Cd2+-specific cellular assay was below the assay detection limit (<5 nM) in cells treated with CdSe/ZnS QDs, while in cells incubated with CdTe QDs, it ranged from approximately 30 to 150 nM, depending on the capping molecule. A cell viability assay revealed that CdSe/ZnS QDs were nontoxic, whereas the CdTe QDs were cytotoxic. However, for the various CdTe QD samples, there was no dose-dependent correlation between cell viability and intracellular [Cd2+], implying that their cytotoxicity cannot be attributed solely to the toxic effect of free Cd2+. Confocal laser scanning microscopy of CdTe QDs-treated cells imaged with organelle-specific dyes revealed significant lysosomal damage attributable to the presence of Cd2+ and of reactive oxygen species (ROS), which can be formed via Cd2+-specific cellular pathways and/or via CdTe-triggered photoxidative processes involving singlet oxygen or electron transfer from excited QDs to oxygen. In summary, CdTe QDs induce cell death via mechanisms involving both Cd2+ and ROS accompanied by lysosomal enlargement and intracellular redistribution.

Quantum dot-induced cell death involves Fas upregulation and lipid peroxidation in human neuroblastoma cells

Background

Neuroblastoma, a frequently occurring solid tumour in children, remains a therapeutic challenge as existing imaging tools are inadequate for proper and accurate diagnosis, resulting in treatment failures. Nanoparticles have recently been introduced to the field of cancer research and promise remarkable improvements in diagnostics, targeting and drug delivery. Among these nanoparticles, quantum dots (QDs) are highly appealing due to their manipulatable surfaces, yielding multifunctional QDs applicable in different biological models. The biocompatibility of these QDs, however, remains questionable.

Results

We show here that QD surface modifications with N-acetylcysteine (NAC) alter QD physical and biological properties. In human neuroblastoma (SH-SY5Y) cells, NAC modified QDs were internalized to a lesser extent and were less cytotoxic than unmodified QDs. Cytotoxicity was correlated with Fas upregulation on the surface of treated cells. Alongside the increased expression of Fas, QD treated cells had increased membrane lipid peroxidation, as measured by the fluorescent BODIPY-C₁₁ dye. Moreover, peroxidized lipids were detected at the mitochondrial level, contributing to the impairment of mitochondrial functions as shown by the MTT reduction assay and imaged with confocal microscopy using the fluorescent JC-1 dye.

Conclusion

QD core and surface compositions, as well as QD stability, all influence nanoparticle internalization and the consequent cytotoxicity. Cadmium telluride QD-induced toxicity involves the upregulation of the Fas receptor and lipid peroxidation, leading to impaired neuroblastoma cell functions. Further improvements of nanoparticles and our understanding of the underlying mechanisms of QD-toxicity are critical for the development of new nanotherapeutics or diagnostics in nano-oncology.

Surface Coatings Determine Cytotoxicity and Irritation Potential of Quantum Dot Nanoparticles in Epidermal Keratinocytes

Quantum dot (QD) nanoparticles have potential applications in nanomedicine as drug delivery vectors and diagnostic agents, but the skin toxicity and irritation potential of QDs are unknown. Human epidermal keratinocytes (HEKs) were used to assess if QDs with different surface coatings would cause differential effects on HEK cytotoxicity, proinflammatory cytokine release, and cellular uptake. Commercially available QDs of two different sizes, QD 565 and QD 655, with neutral (polyethylene glycol (PEG)), cationic (PEG-amine), or anionic (carboxylic acid) coatings were utilized. Live cell imaging and transmission electron microscopy were used to determine that all QDs localized intracellularly by 24 hours, with evidence of QD localization in the nucleus. Cytotoxicity and release of the proinflammatory cytokines IL-1beta, IL-6, IL-8, IL-10, and tumor necrosis factor-alpha were assessed at 24 and 48 hours. Cytotoxicity was observed for QD 565 and QD 655 coated with carboxylic acids or PEG-amine by 48 hours, with little cytotoxicity observed for PEG-coated QDs. Only carboxylic acid-coated QDs significantly increased release of IL-1beta, IL-6, and IL-8. These data indicate that QD surface coating is a primary determinant of cytotoxicity and immunotoxicity in HEKs, which is consistent across size. However, uptake of QDs by HEKs is independent of surface coating.

Immunofluorescence detection with quantum dot bioconjugates for hepatoma in vivo

The use of highly specific and highly sensitive immunofluorescent probes is a promising approach for biomedical imaging in living tissue. We focus on immunofluorescence with quantum dot bioconjugates for hepatoma detection in vivo. We synthesized specific immunofluorescent probes by linking quantum dots to AFP (alpha-fetoprotein) antibody for specific binding AFP-an important marker for hepatocellular carcinoma cell lines. In in vivo studies, the characteristic quantum dot (QD) fluorescent property is exhibited by the QDs-Anti-AFP probes in tumor and they demonstrate active tumor targeting and spectroscopic hepatoma imaging with an integrated fluorescence imaging system. We investigate the inhomogeneous distribution of the QDs-Anti-AFP probes in tumor by using a site-by-site measurement method to test their ability for distribution studies of cancer cells. These results demonstrate the practicality of QD bioconjugates as attractive fluorescent probes for biomedical detection.

Syntheses, X-ray structures and AACVD studies of group 11 ditelluroimidodiphosphinate complexes

Reactions of Na(tmeda)[N((i)Pr(2)PTe)(2)] with CuCl, AgI or AuCl (in the presence of PPh(3)) in THF produced the coinage metal ditelluroimidodiphosphinate complexes {Cu[N((i)Pr(2)PTe)(2)]}(3), (5), {Ag[N((i)Pr(2)PTe)(2)]}(6) (6) and Au(PPh(3))[N((i)Pr(2)PTe)(2)] (7), respectively. Complexes 5, 6 and 7 were characterized in the solid state by X-ray crystallography. Complex 5 is trimeric and exhibits a highly distorted Cu(3)Te(3) ring. In contrast, the Ag(I) complex 6 is a hexamer, and forms a twelve-membered Ag(6)Te(6) ring. The replacement of the (i)Pr groups on phosphorus by Ph results in an intriguing structural change to a tetramer with a boat-shaped Ag(4)Te(4) ring in {Ag[N(Ph(2)PTe)(2)}(4).2THF (8). The gold(I) complex 7 is monomeric. Aerosol-assisted chemical vapour deposition (AACVD) of compounds 5, 6 and 7 yields CuTe, Ag(7)Te(4), AuTe(2) and Au films, respectively. The films were grown at temperatures of 300-500 degrees C and characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive analysis of X-rays (EDAX).

Self-assembled quantum dot-peptide bioconjugates for selective intracellular delivery

We demonstrate the use of self-assembled luminescent semiconductor quantum dot (QD)-peptide bioconjugates for the selective intracellular labeling of several eukaryotic cell lines. A bifunctional oligoarginine cell penetrating peptide (based on the HIV-1 Tat protein motif) bearing a terminal polyhistidine tract was synthesized and used to facilitate the transmembrane delivery of the QD bioconjugates. The polyhistidine sequence allows the peptide to self-assemble onto the QD surface via metal-affinity interactions while the oligoarginine sequence allows specific QD delivery across the cellular membrane and intracellular labeling as compared to nonconjugated QDs. This peptide-driven delivery is concentration-dependent and thus can be titrated. Upon internalization, QDs display a punctate-like staining pattern in which some, but not all, of the QD signal is colocalized within endosomes. The effects of constant versus limited exposure to QD-peptide conjugates on cellular viability are evaluated by a metabolic specific assay, and clear differences in cytotoxicity are observed. The efficacy of using peptides for selective intracellular delivery is highlighted by performing a multicolor QD labeling, where we found that the presence or absence of peptide on the QD surface controls cellular uptake.

Quantum dots for human mesenchymal stem cells labeling. A size-dependent autophagy activation

Lately certain cytotoxicity of quantum dots (QDs) and some deleterious effects of labeling procedure on stem cells differentiation abilities were shown. In the present study we compared cytotoxicity and intracellular processing of two different-sized protein-conjugated QDs after labeling of the human mesenchymal stem cells (hMSC). An asymmetrical intracellular uptake of red (605 nm) and green (525 nm) quantum dots was observed. We describe for the first time a size-dependent activation of autophagy, caused by nanoparticles.

In vivo selection of phage for the optical imaging of PC-3 human prostate carcinoma in mice

There is an increasing medical need to detect and spatially localize early and aggressive forms of prostate cancer. Affinity ligands derived from bacteriophage (phage) library screens can be developed to molecularly target prostate cancer with fluorochromes for optical imaging. Toward this goal, we used in vivo phage display and a newly described micropanning assay to select for phage that extravasate and bind human PC-3 prostate carcinoma xenografts in severe combined immune deficiency mice. One resulting phage clone (G1) displaying the peptide sequence IAGLATPGWSHWLAL was fluorescently labeled with the near-infrared fluorophore AlexaFluor 680 and was evaluated both in vitro and in vivo for its ability to bind and target PC-3 prostate carcinomas. The fluorescently labeled phage clone (G1) had a tumor-to-muscle ratio of approximately 30 in experiments. In addition, prostate tumors (PC-3) were readily detectable by optical-imaging methods. These results show proof of principle that disease-specific library-derived fluorescent probes can be rapidly developed for use in the early detection of cancers by optical means.

Optical and pharmacological tools to investigate the role of mitochondria during oxidative stress and neurodegeneration

Mitochondria are critical for cellular adenosine triphosphate (ATP) production; however, recent studies suggest that these organelles fulfill a much broader range of tasks. For example, they are involved in the regulation of cytosolic Ca(2+) levels, intracellular pH and apoptosis, and are the major source of reactive oxygen species (ROS). Various reactive molecules that originate from mitochondria, such as ROS, are critical in pathological events, such as ischemia, as well as in physiological events such as long-term potentiation, neuronal-vascular coupling and neuronal-glial interactions. Due to their key roles in the regulation of several cellular functions, the dysfunction of mitochondria may be critical in various brain disorders. There has been increasing interest in the development of tools that modulate mitochondrial function, and the refinement of techniques that allow for real time monitoring of mitochondria, particularly within their intact cellular environment. Innovative imaging techniques are especially powerful since they allow for mitochondrial visualization at high resolution, tracking of mitochondrial structures and optical real time monitoring of parameters of mitochondrial function. The techniques discussed include classic imaging techniques, such as rhodamine-123, the highly advanced semi-conductor nanoparticles (quantum dots), and wide field microscopy as well as high-resolution multiphoton imaging. We have highlighted the use of these techniques to study mitochondrial function in brain tissue and have included studies from our laboratories in which these techniques have been successfully applied.

Three-dimensional reconstruction of cell nuclei, internalized quantum dots and sites of lipid peroxidation

BACKGROUND

The purpose of the study was to develop and illustrate three-dimensional (3-D) reconstruction of nuclei and intracellular lipid peroxidation in cells exposed to oxidative stress induced by quantum dots. Programmed cell death is characterized by multiple biochemical and morphological changes in different organelles, including nuclei, mitochondria and lysosomes. It is the dynamics of the spatio-temporal changes in the signalling and morphological adaptations which will ultimately determine the 'shape' and fate of the cell.

RESULTS

We present new approaches to the 3-D reconstruction of organelle morphology and biochemical changes in confocal live-cell images. We demonstrate the 3-D shapes of nuclei, the 3-D intracellular distributions of QDs and the accompanying lipid-membrane peroxidation, and provide methods for quantification.

CONCLUSION

This study provides an approach to 3-D organelle and nanoparticle visualization in the context of cell death; however, this approach is also applicable more generally to investigating changes in organelle morphology in response to therapeutic interventions, stressful stimuli and internalized nanoparticles. Moreover, the approach provides quantitative data for such changes, which will help us to better integrate compartmentalization of subcellular events and to link morphological and biochemical changes with physiological outcomes.

Stable isotopic tracing-a way forward for nanotechnology

Numerous publications and reports have expressed health and safety concerns about the production and use of nanoparticles, especially in areas of exposure monitoring, personal use, and environmental fate and transport. We suggest that stable isotopic tracers, which have been used widely in the earth sciences and in metabolic and other health-related studies for several decades, could be used to address many of these issues. One such example we are pursuing is the use of stable isotopes to monitor dermal absorption of zinc and titanium oxides in sunscreen preparations and other personal care products. Other potential applications of this tracing approach are discussed.

Nanodiagnostics: a new frontier for clinical laboratory medicine

BACKGROUND

The use of nanotechnologies for diagnostic applications shows great promise to meet the rigorous demands of the clinical laboratory for sensitivity and cost-effectiveness. New nanodiagnostic tools include quantum dots (QDs), gold nanoparticles, and cantilevers. QDs, which are the most promising nanostructures for diagnostic applications, are semiconductor nanocrystals characterized by high photostability, single-wavelength excitation, and size-tunable emission. QDs and magnetic nanoparticles can be used for barcoding of specific analytes. Gold and magnetic nanoparticles are key components of the bio-barcode assay, which has been proposed as a future alternative to the PCR.

METHODS

We examined articles published over the past 10 years investigating the use of QDs, gold nanoparticles, cantilevers, and other nanotechnologies in promising diagnostic applications.

RESULTS

Several nanodiagnostic assays have been developed, including a QD-based assay capable of detecting biotinylated prostate-specific antigen (PSA) at 0.38 ng/L, a bio-barcode assay capable of detecting 30 amol/L PSA in a 10-microL sample, and another able to detect 50 molecules of the Alzheimer marker amyloid beta-derived diffusible ligand in 10 microL of cerebrospinal fluid.

CONCLUSIONS

Nanodiagnostics promise increased sensitivity, multiplexing capabilities, and reduced cost for many diagnostic applications as well as intracellular imaging. Further work is needed to fully optimize these diagnostic nanotechnologies for clinical laboratory setting and to address the potential health and environmental risks related to QDs.

Photophysics of dopamine-modified quantum dots and effects on biological systems

Semiconductor quantum dots (QDs) have been widely used for fluorescent labelling. However, their ability to transfer electrons and holes to biomolecules leads to spectral changes and effects on living systems that have yet to be exploited. Here we report the first cell-based biosensor based on electron transfer between a small molecule (the neurotransmitter dopamine) and CdSe/ZnS QDs. QD-dopamine conjugates label living cells in a redox-sensitive pattern: under reducing conditions, fluorescence is only seen in the cell periphery and lysosomes. As the cell becomes more oxidizing, QD labelling appears in the perinuclear region, including in or on mitochondria. With the most-oxidizing cellular conditions, QD labelling throughout the cell is seen. Phototoxicity results from the creation of singlet oxygen, and can be reduced with antioxidants. This work suggests methods for the creation of phototoxic drugs and for redox-specific fluorescent labelling that are generalizable to any QD conjugated to an electron donor.

Neuroscience nanotechnology: progress, opportunities and challenges

Nanotechnologies exploit materials and devices with a functional organization that has been engineered at the nanometre scale. The application of nanotechnology in cell biology and physiology enables targeted interactions at a fundamental molecular level. In neuroscience, this entails specific interactions with neurons and glial cells. Examples of current research include technologies that are designed to better interact with neural cells, advanced molecular imaging technologies, materials and hybrid molecules used in neural regeneration, neuroprotection, and targeted delivery of drugs and small molecules across the blood-brain barrier.

Unmodified cadmium telluride quantum dots induce reactive oxygen species formation leading to multiple organelle damage and cell death

Quantum dots (QDs) are luminescent nanoparticles with unique optical properties that have been exploited for single-cell and whole-animal imaging. When coated with proteins or biocompatible polymers, QDs are not deleterious to cells and organisms. However, when QDs are retained in cells or accumulated in the body for a long period of time, their coatings may be degraded, yielding "naked" QDs. Here, we show that "naked" QDs induce damage to the plasma membrane, mitochondrion, and nucleus, leading to cell death. Reactive oxygen species (ROS) are important players in mediating QD-induced cellular damage. QD-induced cytotoxicity can be reduced or even eliminated without covalent binding of protective agents to the QD surface. Results from these studies suggest the critical role of several subcellular compartments in QD-induced cytotoxicity and point toward multiple molecular targets in nonclassical apoptosis.

A toxicologic review of quantum dots: toxicity depends on physicochemical and environmental factors

As a growing applied science, nanotechnology has considerable global socioeconomic value, and the benefits afforded by nanoscale materials and processes are expected to have significant impacts on almost all industries and all areas of society. A diverse array of engineered nanoscale products and processes have emerged [e.g., carbon nanotubes, fullerene derivatives, and quantum dots (QDs)], with widespread applications in fields such as medicine, plastics, energy, electronics, and aerospace. With the nanotechnology economy estimated to be valued at dollar 1 trillion by 2012, the prevalence of these materials in society will be increasing, as will the likelihood of exposures. Importantly, the vastness and novelty of the nanotechnology frontier leave many areas unexplored, or underexplored, such as the potential adverse human health effects resulting from exposure to novel nanomaterials. It is within this context that the need for understanding the potentially harmful side effects of these materials becomes clear. The reviewed literature suggests several key points: Not all QDs are alike; engineered QDs cannot be considered a uniform group of substances. QD absorption, distribution, metabolism, excretion, and toxicity depend on multiple factors derived from both inherent physicochemical properties and environmental conditions; QD size, charge, concentration, outer coating bioactivity (capping material and functional groups), and oxidative, photolytic, and mechanical stability have each been implicated as determining factors in QD toxicity. Although they offer potentially invaluable societal benefits such as drug targeting and in vivo biomedical imaging, QDs may also pose risks to human health and the environment under certain conditions. Key words: environment, human health, nanomaterials, nanosized particles, nanotechnology, nanotoxicology, quantum dots, toxicology.

Penetration of Intact Skin by Quantum Dots with Diverse Physicochemical Properties

Skin is the largest organ of the body and is a potential route of exposure to engineered nanomaterials, but the permeability of the skin to these nanomaterials is unknown. We selected commercially available quantum dots (QD) of two core/shell sizes and shapes and three different surface coatings to determine if QD could penetrate intact skin in a size- or coating-dependent manner. Spherical 4.6 nm core/shell diameter QD 565 and ellipsoid 12 nm (major axis) by 6 nm (minor axis) core/shell diameter QD 655 with neutral (polyethylene glycol), anionic (carboxylic acids) or cationic (polyethylene glycol-amine) coatings were topically applied to porcine skin in flow-through diffusion cells at an occupationally relevant dose for 8 h and 24 h. Confocal microscopy revealed that spherical QD 565 of each surface coating penetrated the stratum corneum and localized within the epidermal and dermal layers by 8 h. Similarly, polyethylene glycol- and polyethylene glycol-amine-coated ellipsoid QD 655 localized within the epidermal layers by 8 h. No penetration of carboxylic acid-coated QD 655 was evident until 24 h, at which time localization in the epidermal layers was observed. This study showed that quantum dots of different sizes, shapes, and surface coatings can penetrate intact skin at an occupationally relevant dose within the span of an average-length work day. These results suggest that skin is surprisingly permeable to nanomaterials with diverse physicochemical properties and may serve as a portal of entry for localized, and possibly systemic, exposure of humans to QD and other engineered nanoscale materials.