Quantum dot-based cell motility assay

Nanomedicine and Early Cancer Diagnosis: Molecular Imaging using Fluorescence Nanoparticles

Incorporating nanotechnology into fluorescent imaging and magnetic resonance imaging (MRI) has shown promising potential for accurate diagnosis of cancer at an earlier stage than the conventional imaging modalities. Molecular imaging (MI) aims to quantitatively characterize, visualize, and measure the biological processes or living cells at molecular and genetic levels. MI modalities have been exploited in different applications including noninvasive determination and visualization of diseased tissues, cell trafficking visualization, early detection, treatment response monitoring, and in vivo visualization of living cells. High-affinity molecular probe and imaging modality to detect the probe are the two main requirements of MI. Recent advances in nanotechnology and allied modalities have facilitated the use of nanoparticles (NPs) as MI probes. Within the extensive group of NPs, fluorescent NPs play a prominent role in optical molecular imaging. The fluorescent NPs used in molecular and cellular imaging can be categorized into three main groups including quantum dots (QDs), upconversion, and dyedoped NPs. Fluorescent NPs have great potential in targeted theranostics including cancer imaging, immunoassay- based cells, proteins and bacteria detections, imaging-guided surgery, and therapy. Fluorescent NPs have shown promising potentials for drug and gene delivery, detection of the chromosomal abnormalities, labeling of DNA, and visualizing DNA replication dynamics. Multifunctional NPs have been successfully used in a single theranostic modality integrating diagnosis and therapy. The unique characteristics of multifunctional NPs make them potential theranostic agents that can be utilized concurrently for diagnosis and therapy. This review provides the state of the art of the applications of nanotechnologies in early cancer diagnosis focusing on fluorescent NPs, their synthesis methods, and perspectives in clinical theranostics.

Metabolic pathway for the universal fluorescent recognition of tumor cells

Quantification of circulating tumor cells (CTCs) in blood samples from cancer patients is a non-invasive approach to monitoring the status of the disease. Most of the methods proposed in the recent years are phenomenological and rely on the use of antibodies labelled with fluorophores, magnetic particles, or immobilized on surfaces to capture the CTCs. Herein, we designed and optimized a method that employs a glucose analogue labelled with a fluorophore which takes advantage of the different metabolic pathways of cancer cells to discern them from normal ones. Notably, we demonstrate that fluorescence signal in tumor cells can be greatly maximized by applying hyperoxia conditions without damaging the cells. These results are demonstrated by means of confocal fluorescence and flow-cytometry measurements in peripheral blood mononuclear cells (PBMC) extracted after Ficoll of human blood samples and spiked with a known concentration of MCF-7 tumor cells.

Dynamic Cellular Interactions with Extracellular Matrix Triggered by Biomechanical Tuning of Low-Rigidity, Supported Lipid Membranes

The behavior of cells in a tissue is regulated by chemical as well as physical signals arising from their microenvironment. While gel-based substrates have been widely used for mimicking a range of substrate rigidities, there is a need for the development of low rigidity substrates for mimicking the physical properties of soft tissues. In this study, the authors report the development of a supported lipid bilayer (SLB)-based low rigidity substrate for cell adhesion studies. SLBs are functionalized with either collagen I or fibronectin via covalent, amine coupling to a carboxyl group-modified lipid molecule. While the lipid molecules in the bilayer show long-range lateral mobility, the covalently functionalized extracellular matrix (ECM) proteins are immobile on the bilayer surface. Specific adhesion of cells results in an enrichment of the protein on the bilayer and the appearance of a zone of depletion around the cells. Further, the lateral reorganization of the ECM proteins is controlled by altering the fluidity of lipid molecules in the substrate. Thus, the experimental platform developed in this study can be utilized for addressing basic questions related to cell adhesion on low rigidity substrates as well as biomedical applications requiring adhesion of cells to low rigidity substrates.

Diverse Applications of Nanomedicine

The design and use of materials in the nanoscale size range for addressing medical and health-related issues continues to receive increasing interest. Research in nanomedicine spans a multitude of areas, including drug delivery, vaccine development, antibacterial, diagnosis and imaging tools, wearable devices, implants, high-throughput screening platforms, etc. using biological, nonbiological, biomimetic, or hybrid materials. Many of these developments are starting to be translated into viable clinical products. Here, we provide an overview of recent developments in nanomedicine and highlight the current challenges and upcoming opportunities for the field and translation to the clinic.

Three-dimensional cage-like microscaffolds for cell invasion studies

Cancer cell motility is one of the major events involved in metastatic process. Tumor cells that disseminate from a primary tumor can migrate into the vascular system and, being carried by the bloodstream, transmigrate across the endothelium, giving rise to a new tumor site. However, during the invasive process, tumor cells must pass through the extracellular matrix, whose structural and mechanical properties define the parameters of the migration process. Here, we propose 3D-complex cage-like microstructures, realized by two-photon (TP) direct laser writing (DLW), to analyze cell migration through pores significantly smaller than the cell nucleus. We found that the ability to traverse differently sized pores depends on the metastatic potential and on the invasiveness of the cell lines, allowing to establish a pore-area threshold value able to discriminate between non-tumorigenic and tumorigenic human breast cells.

Surface functionalization of quantum dots for biological applications

Quantum dots are a group of inorganic nanomaterials exhibiting exceptional optical and electronic properties which impart distinct advantages over traditional fluorescent organic dyes in terms of tunable broad excitation and narrow emission spectra, signal brightness, high quantum yield and photo-stability. Aqueous solubility and surface functionalization are the most common problems for QDs employed in biological research. This review addresses the recent research progress made to improve aqueous solubility, functionalization of biomolecules to QD surface and the poorly understood chemistry involved in the steps of bio-functionalization of such nanoparticles.

Location deterministic biosensing from quantum-dot-nanowire assemblies

Semiconductor quantum dots (QDs) with high fluorescent brightness, stability, and tunable sizes, have received considerable interest for imaging, sensing, and delivery of biomolecules. In this research, we demonstrate location deterministic biochemical detection from arrays of QD-nanowire hybrid assemblies. QDs with diameters less than 10 nm are manipulated and precisely positioned on the tips of the assembled Gold (Au) nanowires. The manipulation mechanisms are quantitatively understood as the synergetic effects of dielectrophoretic (DEP) and alternating current electroosmosis (ACEO) due to AC electric fields. The QD-nanowire hybrid sensors operate uniquely by concentrating bioanalytes to QDs on the tips of nanowires before detection, offering much enhanced efficiency and sensitivity, in addition to the position-predictable rationality. This research could result in advances in QD-based biomedical detection and inspires an innovative approach for fabricating various QD-based nanodevices.

Assembly, characterization, and delivery of quantum dot labeled biotinylated lipid particles

Lipid nanoparticles composed of mixtures of PEGylated-lipids; cationic and neutral lipids prepared by detergent dialysis can encapsulate biological active molecules and show considerable potential as systemic therapeutic agents. Addition of biotinylated lipids to this formulation allows surface modification of these particles with a suitable ligand or probe conjugated to streptavidin for specific cell targeting. Monitoring long circulating particles and cellular uptake requires stable and bright fluorescent probes. Quantum dots (QDs) constitute a relatively new class of fluorescent probes that overcome the limitations of organic fluorophores in biological imaging applications. Here, a protocol for the encapsulation of QD655 (red) in biotinylated lipid particles (BLPs) prepared by a detergent dialysis technique is presented followed by characterization of the loaded liposomal vehicles. Then, a protocol for BLPs surface modification via biotin-streptavidin linkage with preformed complexes of ligand-QD525 (green) for specific cell targeting of the nanoparticle is detailed. Conditions for cell binding and uptake of two colors QD labeled BLPs as well as basic microscopic settings for confocal live cell imaging are described.

Fluorescence lifetime imaging microscopy in the medical sciences

The steady improvement in the imaging of cellular processes in living tissue over the last 10-15 years through the use of various fluorophores including organic dyes, fluorescent proteins and quantum dots, has made observing biological events common practice. Advances in imaging and recording technology have made it possible to exploit a fluorophore's fluorescence lifetime. The fluorescence lifetime is an intrinsic parameter that is unique for each fluorophore, and that is highly sensitive to its immediate environment and/or the photophysical coupling to other fluorophores by the phenomenon Förster resonance energy transfer (FRET). The fluorescence lifetime has become an important tool in the construction of optical bioassays for various cellular activities and reactions. The measurement of the fluorescence lifetime is possible in two formats; time domain or frequency domain, each with their own advantages. Fluorescence lifetime imaging applications have now progressed to a state where, besides their utility in cell biological research, they can be employed as clinical diagnostic tools. This review highlights the multitude of fluorophores, techniques and clinical applications that make use of fluorescence lifetime imaging microscopy (FLIM).

Nanotoxicology using the sea anemone Nematostella vectensis: from developmental toxicity to genotoxicology

Concomitant with the fast-growing advances in the synthesis and engineering of colloidal nanocrystals, an urgent evaluation of their toxicity on human beings and environment is strongly encouraged by public health organisations. Despite the in vitro approaches employed for toxicological screening of hazardous compounds, the use of simple and cost-effective living organisms may enormously contribute to solve unanswered questions related to embryotoxic and teratogenic effects of nanomaterials. Here, the sea anemone Nematostella vectensis (Cnidaria, Anthozoa) is presented as a novel model organism to profile bio/non-bio interactions and to show a comprehensive toxicological analysis performed on embryos, larvae and adults treated with fluorescent cadmium-based nanocrystals. Spanning from in vivo biodistribution to molecular investigations, different behaviours and effects depending on the composition and surface coatings are showed. Rod-shaped cadmium selenide/cadmium sulfide (CdSe/CdS) nanocrystals resulted in excellent imaging probes to track N. vectensis development with negligible adverse effects, while spherical CdTe nanocrystals severely impaired embryogenesis, resulting in aberrant phenotypes and deregulation of developmental genes, which raise severe worries for a safe use of this type of nanoparticles for human purposes and environmental contamination.

Fabrication of quantum dot microarrays using electron beam lithography for applications in analyte sensing and cellular dynamics

Quantum dot (QD) based micro-/nanopatterned arrays are of broad interest in applications ranging from electronics, photonics, to sensor devices for biomedical purposes. Here, we report on a rapid, physico-chemically mild approach to generate high fidelity micropattern arrays of prefunctionalized water-soluble quantum dots using electron beam lithography. We show that such patterns retain their fluorescence and bioaffinity upon electron beam lithography and, based on the streptavidin-biotin interaction, allow for detection of proteins, colloidal gold nanoparticles and magnetic microparticles. Furthermore, we demonstrate the applicability of QD based microarray patterns differing in their shape (circles, squares, grid-like), size (from 1 to 10 μm) and pitch distance to study the adhesion, spreading and migration of human blood derived neutrophils. Using live cell confocal fluorescence microscopy, we show that pattern geometry and pitch distance influence the adhesion, spreading and migratory behavior of neutrophils. Research reported in this work paves the way for producing QD microarrays with multiplexed functionalities relevant for applications in analyte sensing and cellular dynamics.

[Nanotechnology: a big revolution from the small world]

Nanotechnology is a multidisciplinary field originating from the interaction of several different disciplines, such as engineering, physics, biology and chemistry. New materials and devices effectively interact with the body at molecular level, yielding a brand new range of highly selective and targeted applications designed to maximize the therapeutic efficiency while reducing the side effects. Liposomes, quantum dots, carbon nanotubes and superparamagnetic nanoparticles are among the most assessed nanotechnologies. Meanwhile, other futuristic platforms are paving the way toward a new scientific paradigm, able to deeply change the research path in the medical science. The growth of nanotechnology, driven by the dramatic advances in science and technology, clearly creates new opportunities for the development of the medical science and disease treatment in human health care. Despite the concerns and the on-going studies about their safety, nanotechnology clearly emerges as holding the promise of delivering one of the greatest breakthroughs in the history of medical science.

Hetero-multinuclear ruthenium(III)/platinum(II) complexes that potentially exhibit both antimetastatic and antineoplastic properties

Hetero-multinuclear, platinum/ruthenium species were synthesized and tested for their effect on the motility of A549 (nonsmall cell lung) and MDA-MB-231 (breast) cancer cells and for their ability to inhibit DNA mobility using gel electrophoresis. It was found that the Ru(2)Pt trinuclear species [Na(2)]{[Ru(III)Cl(4)(DMSO-S)(-μ-pyz)](2)Pt(II)Cl(2)}, AH197, was much more efficient at inhibiting cell motility than [C(3)N(2)H(5)][Ru(III)Cl(4)(DMSO-S)(C(3)N(2)H(4))], NAMI-A, while the dinuclear RuPt species [K][Ru(III)Cl(4)(DMSO-S)(-μ-pyz)Pt(II)(DMSO-S)Cl(2)], IT127, was slightly better than NAMI-A. However, the dinuclear species retarded the electrophoretic mobility of DNA greater than both the trinuclear complex and cisplatin. The metal complexes and their respective BSA protein/metal adducts were studied by X-ray absorption spectroscopy. The spectra led to the conclusion that BSA donor atoms have substituted for the chloride ligands and perhaps the DMSO ligands.

Luminescent quantum dots for molecular toxicology

Recent developments in nanotechnology have made available a host of new approaches for the improved quantitative detection of biomarkers due to the enhanced sensitivity of nanoparticle-based assays. The majority of molecular toxicology studies revolve around sensitive measurement of cell-death (apoptosis) and cell-health biomarkers present in living cells or formalin-fixed and paraffin embedded (FFPE) tissue samples. In this regard, semi-conductor quantum dots (QDs) which exhibit high brightness, photo-stability and degree of multiplexing, are predicted to have a significant impact on research in molecular toxicology. Due to these superior photophysical properties of QDs as compared to traditional fluorophores and the unsurpassed versatility of QDs as enabling components for new assays, these nanoparticles promise to facilitate new discoveries in molecular toxicology. Indeed, multiplexed QD-based assays have been incorporated into cell imaging, flow cytometry and other homogenized sample-based assays for detecting multiple biomarkers including those associated with cell injury and apoptosis.

Semiconductor quantum dots for biomedicial applications

Semiconductor quantum dots (QDs) are nanometre-scale crystals, which have unique photophysical properties, such as size-dependent optical properties, high fluorescence quantum yields, and excellent stability against photobleaching. These properties enable QDs as the promising optical labels for the biological applications, such as multiplexed analysis of immunocomplexes or DNA hybridization processes, cell sorting and tracing, in vivo imaging and diagnostics in biomedicine. Meanwhile, QDs can be used as labels for the electrochemical detection of DNA or proteins. This article reviews the synthesis and toxicity of QDs and their optical and electrochemical bioanalytical applications. Especially the application of QDs in biomedicine such as delivering, cell targeting and imaging for cancer research, and in vivo photodynamic therapy (PDT) of cancer are briefly discussed.

Inorganic-organic hybrid nanomaterials for therapeutic and diagnostic imaging applications

Nanotechnology offers outstanding potential for future biomedical applications. In particular, due to their unique characteristics, hybrid nanomaterials have recently been investigated as promising platforms for imaging and therapeutic applications. This class of nanoparticles can not only retain valuable features of both inorganic and organic moieties, but also provides the ability to systematically modify the properties of the hybrid material through the combination of functional elements. Moreover, the conjugation of targeting moieties on the surface of these nanomaterials gives them specific targeted imaging and therapeutic properties. In this review, we summarize the recent reports in the synthesis of hybrid nanomaterials and their applications in biomedical areas. Their applications as imaging and therapeutic agents in vivo will be highlighted.

Semiconductor quantum dots as fluorescent probes for in vitro and in vivo bio-molecular and cellular imaging

Over the years, biological imaging has seen many advances, allowing scientists to unfold many of the mysteries surrounding biological processes. The ideal imaging resolution would be in nanometres, as most biological processes occur at this scale. Nanotechnology has made this possible with functionalised nanoparticles that can bind to specific targets and trace processes at the cellular and molecular level. Quantum dots (QDs) or semiconductor nanocrystals are luminescent particles that have the potential to be the next generation fluorophores. This paper is an overview of the basics of QDs and their role as fluorescent probes for various biological imaging applications. Their potential clinical applications and the limitations that need to be overcome have also been discussed.

Getting across the plasma membrane and beyond: intracellular uses of colloidal semiconductor nanocrystals

Semiconductor nanocrystals (NCs) are increasingly being used as photoluminescen markers in biological imaging. Their brightness, large Stokes shift, and high photostability compared to organic fluorophores permit the exploration of biological phenomena at the single-molecule scale with superior temporal resolution and spatial precision. NCs have predominantly been used as extracellular markers for tagging and tracking membrane proteins. Successful internalization and intracellular labelling with NCs have been demonstrated for both fixed immunolabelled and live cells. However, the precise localization and subcellular compartment labelled are less clear. Generally, live cell studies are limited by the requirement of fairly invasive protocols for loading NCs and the relatively large size of NCs compared to the cellular machinery, along with the subsequent sequestration of NCs in endosomal/lysosomal compartments. For long-period observation the potential cytotoxicity of cytoplasmically loaded NCs must be evaluated. This review focuses on the challenges of intracellular uses of NCs.

Emerging nanotechnology-based strategies for the identification of microbial pathogenesis

Infectious diseases are still a major healthcare problem. From food intoxication and contaminated water, to hospital-acquired diseases and pandemics, infectious agents cause disease throughout the world. Despite advancements in pathogens' identification, some of the gold-standard diagnostic methods have limitations, including laborious sample preparation, bulky instrumentation and slow data readout. In addition, new field-deployable diagnostic modalities are urgently needed in first responder and point-of-care applications. Apart from compact, these sensors must be sensitive, specific, robust and fast, in order to facilitate detection of the pathogen even in remote rural areas. Considering these characteristics, researchers have utilized innovative approaches by employing the unique properties of nanomaterials in order to achieve detection of infectious agents, even in complex media like blood. From gold nanoparticles and their plasmonic shifts to iron oxide nanoparticles and changes in magnetic properties, detection of pathogens, toxins, antigens and nucleic acids has been achieved with impressive detection thresholds. Additionally, as bacteria become resistant to antibiotics, nanotechnology has achieved the rapid determination of bacterial drug susceptibility and resistance using novel methods, such as amperometry and magnetic relaxation. Overall, these promising results hint to the adoption of nanotechnology-based diagnostics for the diagnosis of infectious diseases in diverse settings throughout the globe, preventing epidemics and safeguarding human and economic wellness.

Quantum dot-based HIV capture and imaging in a microfluidic channel

Globally, over 33.2 million people who mostly live in developing countries with limited access to the appropriate medical care suffer from the human immunodeficiency virus (HIV) infection. We developed an on-chip HIV capture and imaging method using quantum dots (Qdots) from fingerprick volume (10 microl) of unprocessed HIV-infected patient whole blood in anti-gp120 antibody-immobilized microfluidic chip. Two-color Qdots (Qdot525 and Qdot655 streptavidin conjugates) were used to identify the captured HIV by simultaneous labeling the envelope gp120 glycoprotein and its high-mannose glycans. This dual-stain imaging technique using Qdots provides a new and effective tool for accurate identification of HIV particles from patient whole blood without any pre-processing. This on-chip HIV capture and imaging platform creates new avenues for point-of-care diagnostics and monitoring applications of infectious diseases.

Delivering quantum dots into cells: strategies, progress and remaining issues

The use of semiconductor quantum dots (QDs) in biological sensing and labeling continues to grow with each year. Current and projected applications include use as fluorescent labels for cellular labeling, intracellular sensors, deep-tissue and tumor imaging agents, sensitizers for photodynamic therapy, and more recently interest has been sparked in using them as vectors for studying nanoparticle-mediated drug delivery. Many of these applications will ultimately require the QDs to undergo targeted intracellular delivery, not only to specific cells, but also to a variety of subcellular compartments and organelles. It is apparent that this issue will be critical in determining the efficacy of using QDs, and indeed a variety of other nanoparticles, for these types of applications. In this review, we provide an overview of the current methods for delivering QDs into cells. Methods that are covered include facilitated techniques such as those that utilize specific peptide sequences or polymer delivery reagents and active methods such as electroporation and microinjection. We critically examine the benefits and liabilities of each strategy and illustrate them with selected examples from the literature. Several important related issues such as QD size and surface coating, methods for QD biofunctionalization, cellular physiology and toxicity are also discussed. Finally, we conclude by providing a perspective of how this field can be expected to develop in the future.

Absorption of semiconductor nanocrystals by the aquatic invertebrate Ceriodaphnia dubia

When incubated with nanomolar concentrations of fluorescent semiconductor nanocrystals in moderately hard water the fluorescence of living Ceriodaphnia dubia increased. Average pixel intensity of exposed animals was greater than that of unexposed animals and increased in a dose and exposure time-dependent-manner. Internal structures were clearly visible in exposed and unexposed animals but fluorescence was most intense in the region of the abdominal appendages of exposed animals. Since these nanoparticles contain significant quantities of the toxic metals cadmium and selenium, their accumulation from aquatic environments by this standard test organism has significant implications about their potential environmental toxicity.

Quantum dots – Nano-sized probes for the exploration of cellular and intracellular targeting

Nanoparticles emerged as promising tool in drug targeting, since, after appropriate modification, they are able to deliver their payload to specific sites, like tissues, cells, or even certain cellular organelles. In this context, the delivery of nanoparticles from the circulation into the target cells represents a crucial step. Here, model drug delivery systems such as quantum dots are ideal candidates to elucidate this process in more detail, since they provide outstanding features like a small and uniform size, unique optical properties for most sensitive detection and modifiable surfaces. Recent progress in the surface chemistry of quantum dots expanded their use in biological applications, reduced their cytotoxicity and rendered quantum dots a powerful tool for the investigation of distinct cellular processes, like uptake, receptor trafficking and intracellular delivery. In this review, we will not only describe the ideal attributes of QDs for biological applications and imaging but also their distinct specific and non-specific pathways into the cells as well as their intracellular fate.

Molecular profiling of single cancer cells and clinical tissue specimens with semiconductor quantum dots

Semiconductor quantum dots (QDs) are a new class of fluorescent labels with broad applications in biomedical imaging, disease diagnostics, and molecular and cell biology. In comparison with organic dyes and fluorescent proteins, quantum dots have unique optical and electronic properties such as size-tunable light emission, improved signal brightness, resistance against photobleaching, and simultaneous excitation of multiple fluorescence colors. Recent advances have led to multifunctional nanoparticle probes that are highly bright and stable under complex in vitro and in vivo conditions. New designs involve encapsulating luminescent QDs with amphiphilic block copolymers, and linking the polymer coating to tumor-targeting ligands and drug-delivery functionalities. These improved QDs have opened new possibilities for real-time imaging and tracking of molecular targets in living cells, for multiplexed analysis of biomolecular markers in clinical tissue specimens, and for ultrasensitive imaging of malignant tumors in living animal models. In this article, we briefly discuss recent developments in bioaffinity QD probes and their applications in molecular profiling of individual cancer cells and clinical tissue specimens.

Are quantum dots ready for in vivo imaging in human subjects?

Nanotechnology has the potential to profoundly transform the nature of cancer diagnosis and cancer patient management in the future. Over the past decade, quantum dots (QDs) have become one of the fastest growing areas of research in nanotechnology. QDs are fluorescent semiconductor nanoparticles suitable for multiplexed in vitro and in vivo imaging. Numerous studies on QDs have resulted in major advancements in QD surface modification, coating, biocompatibility, sensitivity, multiplexing, targeting specificity, as well as important findings regarding toxicity and applicability. For in vitro applications, QDs can be used in place of traditional organic fluorescent dyes in virtually any system, outperforming organic dyes in the majority of cases. In vivo targeted tumor imaging with biocompatible QDs has recently become possible in mouse models. With new advances in QD technology such as bioluminescence resonance energy transfer, synthesis of smaller size non-Cd based QDs, improved surface coating and conjugation, and multifunctional probes for multimodality imaging, it is likely that human applications of QDs will soon be possible in a clinical setting.

Imaging the lateral diffusion of membrane molecules with quantum dots

This protocol describes a sensitive approach to tracking the motion of membrane molecules such as lipids and proteins with molecular resolution in live cells. This technique makes use of fluorescent semiconductor nanocrystals, quantum dots (QDs), as a probe to detect membrane molecules of interest. The photostability and brightness of QDs allow them to be tracked at a single particle level for longer periods than previous fluorophores, such as fluorescent proteins and organic dyes. QDs are bound to the extracellular part of the object to be followed, and their movements can be recorded with a fluorescence microscope equipped with a spectral lamp and a sensitive cooled charge-coupled device camera. The experimental procedure described for neurons below takes about 45 min. This technique is applicable to various cultured cells.

Semiconductor quantum rods as single molecule fluorescent biological labels

In this paper, we report the development of rod-shaped semiconductor nanocrystals (quantum rods) as fluorescent biological labels. Water-soluble biocompatible quantum rods have been prepared by surface silanization and applied for nonspecific cell tracking as well as specific cellular targeting. Quantum rods are brighter single molecule probes as compared to quantum dots. They have many potential applications as biological labels in situations where their properties offer advantages over quantum dots.

Quantum dots for cancer molecular imaging

Quantum dots (QDs), tiny light-emitting particles on the nanometer scale, are emerging as a new class of fluorescent probes for biomolecular and cellular imaging. In comparison with organic dyes and fluorescent proteins, quantum dots have unique optical and electronic properties such as size-tunable light emission, improved signal brightness, resistance against photobleaching, and simultaneous excitation of multiple fluorescence colors. These properties are most promising for improving the sensitivity of molecular imaging and quantitative cellular analysis by 1-2 orders of magnitude. Recent advances have led to multifunctional nanoparticle probes that are highly bright and stable under complex in-vivo conditions. A new structural design involves encapsulating luminescent QDs with amphiphilic block copolymers, and linking the polymer coating to tumor-targeting ligands and drug-delivery functionalities. Polymer-encapsulated QDs are essentially nontoxic to cells and small animals, but their long-term in-vivo toxicity and degradation need more careful studies. Nonetheless, bioconjugated QDs have raised new possibilities for ultrasensitive and multiplexed imaging of molecular targets in living cells and animal models.

Altered membrane dynamics of quantum dot-conjugated integrins during osteogenic differentiation of human bone marrow derived progenitor cells

Functionalized quantum dots offer several advantages for tracking the motion of individual molecules on the cell surface, including selective binding, precise optical identification of cell surface molecules, and detailed examination of the molecular motion without photobleaching. We have used quantum dots conjugated with integrin antibodies and performed studies to quantitatively demonstrate changes in the integrin dynamics during osteogenic differentiation of human bone marrow derived progenitor cells (BMPCs). Consistent with the unusually strong BMPC adhesion previously observed, integrins on the surface of undifferentiated BMPC were found in clusters and the lateral diffusion was slow (e.g., approximately 10(-11) cm2/s). At times as early as those after a 3-day incubation in the osteogenic differentiation media, the integrin diffusion coefficients increased by an order of magnitude, and the integrin dynamics became indistinguishable from that measured on the surface of terminally differentiated human osteoblasts. Furthermore, microfilaments in BMPCs consisted of atypically thick bundles of stress fibers that were responsible for restricting the integrin lateral mobility. Studies using laser optical tweezers showed that, unlike fully differentiated osteoblasts, the BMPC cytoskeleton is weakly associated with its cell membrane. Based on these findings, it appears likely that the altered integrin dynamics is correlated with BMPC differentiation and that the integrin lateral mobility is restricted by direct links to microfilaments.

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.

Quantum dots based probes conjugated to annexin V for photostable apoptosis detection and imaging

Quantum dots (Qdots) are nanoparticles exhibiting fluorescent properties that can be used for cell staining. We present here the development of quantum dots conjugated to Annexin V for specific targeting of apoptotic cells, for both apoptosis detection and staining of apoptotic "living" cells. For that purpose, Qdots Streptavidin Conjugates are coupled to biotinylated Annexin V, a 35-kDa protein which specifically recognizes and binds to phosphatidylserine (PS) moieties present on the outer membrane of apoptotic cells and not on healthy or necrotic cells. By using Annexin V, our Qdots probes are made specific for apoptotic cells. Staining of apoptotic cells was checked using fluorescence and confocal microscopy techniques and nonfixed cells. It is shown here that Qdots are insensitive to bleaching after prolonged exposure as opposed to organic dyes. This makes Qdots excellent candidates to continuously follow fast changes occurring at the membrane of apoptotic cells and facilitates time-lapse imaging as they alleviate any bleaching issue.

Multicolor quantum dots for molecular diagnostics of cancer

In the pursuit of sensitive and quantitative methods to detect and diagnose cancer, nanotechnology has been identified as a field of great promise. Semiconductor quantum dots are nanoparticles with intense, stable fluorescence, and could enable the detection of tens to hundreds of cancer biomarkers in blood assays, on cancer tissue biopsies, or as contrast agents for medical imaging. With the emergence of gene and protein profiling and microarray technology, high-throughput screening of biomarkers has generated databases of genomic and expression data for certain cancer types, and has identified new cancer-specific markers. Quantum dots have the potential to expand this in vitro analysis, and extend it to cellular, tissue and whole-body multiplexed cancer biomarker imaging.

Fluorescent nanoparticle probes for cancer imaging

Optical imaging technique has strong potential for sensitive cancer diagnosis, particularly at the early stage of cancer development. This is a sensitive, non-invasive, non-ionizing (clinically safe) and relatively inexpensive technique. Cancer imaging with optical technique however greatly relies upon the use of sensitive and stable optical probes. Unlike the traditional organic fluorescent probes, fluorescent nanoparticle probes such as dye-doped nanoparticles and quantum dots (Qdots) are bright and photostable. Fluorescent nanoparticle probes are shown to be very effective for sensitive cancer imaging with greater success in the cellular level. However, cancer imaging in an in vivo setup has been recently realized. There are several challenges in developing fluorescent nanoparticle probes for in vivo cancer imaging applications. In this review, we will discuss various aspects of nanoparticle design, synthesis, surface functionalization for bioconjugation and cancer cell targeting. A brief overview of in vivo cancer imaging with Qdots will also be presented.

A novel “sandwich” assay for quantifying chemo-regulated cell migration within 3-dimensional matrices: Wound healing cytokines exhibit distinct motogenic activities compared to the transmembrane assay

The extracellular matrix profoundly affects cellular response to soluble motogens. In view of this critical aspect of matrix functionality, we have developed a novel assay to quantify chemo-regulated cell migration within biologically relevant 3-dimensional matrices. In this "sandwich" assay, target cells are plated at the interface between an upper and lower matrix compartment, either in the presence of an isotropic (uniform) or anisotropic (gradient) spatial distribution of test motogen. Cell migration in response to the different conditions is ascertained by quantifying their subsequent disposition within the upper and lower matrix compartments. The objective of this study has been to compare the motogenic activities of platelet-derived growth factor (PDGF-AB) and transforming growth factor-beta isoforms (TGF-beta1, -beta2 and -beta3) in the sandwich assay and the commonly employed transmembrane assay. As previously reported, dermal fibroblasts exhibited a motogenic response to isotropic and anisotropic distributions of all tested cytokines in the transmembrane assay. In contrast, only PDGF-AB and TGF-beta3 were active in the sandwich assay, each eliciting directionally unbiased (symmetrical) migration into the upper and lower type I collagen matrices in response to an isotropic cytokine distribution and a directionally biased response to an anisotropic distribution. TGF-beta1 and -beta2 were completely devoid of motogenic activity. These results are consistent with the reported differential bioactivities of PDGF and TGF-beta3 compared to TGF-beta1 and -beta2 in animal models of wound healing and suggest that the sandwich assay provides a means of obtaining physiologically relevant data regarding chemo-regulated cell migration.

Semiconductor nanocrystals for biological imaging

Conventional organic fluorophores suffer from poor photo stability, narrow absorption spectra and broad emission spectra. Semiconductor nanocrystals, however, are highly photo-stable with broad absorption spectra and narrow size-tunable emission spectra. Recent advances in the synthesis of these materials have resulted in the generation of bright, sensitive, extremely photo-stable and biocompatible semiconductor fluorophores. Commercial availability facilitates their application in a variety of unprecedented biological experiments, including multiplexed cellular imaging, long-term in vitro and in vivo labeling, deep tissue structure mapping and single particle investigation of dynamic cellular processes. Semiconductor nanocrystals are one of the first examples of nanotechnology enabling a new class of biomedical applications.

Quantum dots as cellular probes

Robust and bright light emitters, semiconductor nanocrystals [quantum dots (QDs)] have been adopted as a new class of fluorescent labels. Six years after the first experiments of their uses in biological applications, there have been dramatic improvements in understanding surface chemistry, biocompatibility, and targeting specificity. Many studies have shown the great potential of using quantum dots as new probes in vitro and in vivo. This review summarizes the recent advances of quantum dot usage at the cellular level, including immunolabeling, cell tracking, in situ hybridization, FRET, in vivo imaging, and other related technologies. Limitations and potential future uses of quantum dot probes are also discussed.

Quantum Dot-Based Cell Motility Assay

Because of their favorable physical and photochemical properties, colloidal CdSe/ZnS-semiconductor nanocrystals (commonly known as quantum dots) have enormous potential for use in biological imaging. In this report, we present an assay that uses quantum dots as markers to quantify cell motility. Cells that are seeded onto a homogeneous layer of quantum dots engulf and absorb the nanocrystals and, as a consequence, leave behind a fluorescence-free trail. By subsequently determining the ratio of cell area to fluorescence-free track area, we show that it is possible to differentiate between invasive and noninvasive cancer cells. Because this assay uses simple fluorescence detection, requires no significant data processing, and can be used in live-cell studies, it has the potential to be a powerful new tool for discriminating between invasive and noninvasive cancer cell lines or for studying cell signaling events involved in migration.

Quantum dot bioconjugates for imaging, labelling and sensing

One of the fastest moving and most exciting interfaces of nanotechnology is the use of quantum dots (QDs) in biology. The unique optical properties of QDs make them appealing as in vivo and in vitro fluorophores in a variety of biological investigations, in which traditional fluorescent labels based on organic molecules fall short of providing long-term stability and simultaneous detection of multiple signals. The ability to make QDs water soluble and target them to specific biomolecules has led to promising applications in cellular labelling, deep-tissue imaging, assay labelling and as efficient fluorescence resonance energy transfer donors. Despite recent progress, much work still needs to be done to achieve reproducible and robust surface functionalization and develop flexible bioconjugation techniques. In this review, we look at current methods for preparing QD bioconjugates as well as presenting an overview of applications. The potential of QDs in biology has just begun to be realized and new avenues will arise as our ability to manipulate these materials improves.

Potentials and pitfalls of fluorescent quantum dots for biological imaging

Fluorescent semiconductor nanocrystals, known as quantum dots (QDs), have several unique optical and chemical features. These features make them desirable fluorescent tags for cell and developmental biological applications that require long-term, multi-target and highly sensitive imaging. The improved synthesis of water-stable QDs, the development of approaches to label cells efficiently with QDs, and improvements in conjugating QDs to specific biomolecules have triggered the recent explosion in their use in biological imaging. Although there have been many successes in using QDs for biological applications, limitations remain that must be overcome before these powerful tools can be used routinely by biologists.

Labelling of cells with quantum dots

Colloidal quantum dots are semiconductor nanocrystals well dispersed in a solvent. The optical properties of quantum dots, in particular the wavelength of their fluorescence, depend strongly on their size. Because of their reduced tendency to photobleach, colloidal quantum dots are interesting fluorescence probes for all types of labelling studies. In this review we will give an overview on how quantum dots have been used so far in cell biology. In particular we will discuss the biologically relevant properties of quantum dots and focus on four topics: labelling of cellular structures and receptors with quantum dots, incorporation of quantum dots by living cells, tracking the path and the fate of individual cells using quantum dot labels, and quantum dots as contrast agents.

Quantum dots for live cells, in vivo imaging, and diagnostics

Research on fluorescent semiconductor nanocrystals (also known as quantum dots or qdots) has evolved over the past two decades from electronic materials science to biological applications. We review current approaches to the synthesis, solubilization, and functionalization of qdots and their applications to cell and animal biology. Recent examples of their experimental use include the observation of diffusion of individual glycine receptors in living neurons and the identification of lymph nodes in live animals by near-infrared emission during surgery. The new generations of qdots have far-reaching potential for the study of intracellular processes at the single-molecule level, high-resolution cellular imaging, long-term in vivo observation of cell trafficking, tumor targeting, and diagnostics.

Cell migration/invasion assays and their application in cancer drug discovery

Invasive capacity is the single most important trait that distinguishes benign from malignant lesions. Tumour cells, during intravasation and extravasation of blood and lymphatic channels and when establishing colonies at secondary sites, must move through tissue boundaries that normal adult cells (other than, for example activated leukocytes) do not cross. Similar mechanisms are also utilised by activated endothelial cells during the generation of new blood vessels that enable the sustained growth and dissemination of tumours. It is now increasingly recognised that these processes--cell motility and invasion--might provide a rich source of novel targets for cancer therapy and that appropriate inhibitors may restrain both metastasis and neoangiogenesis. This new paradigm demands screening assays that can rapidly and quantitatively measure cell movement and the ability to traverse physiological barriers. We also need to consider whether simple reductionist in vitro approaches can reliably model the complexity of in vivo tumour invasion/neoangiogenesis. There are both opportunities and challenges ahead in developing a balanced portfolio of assays that will be able to evaluate accurately and finally deliver novel anti-invasive agents with therapeutic potential for clinical use.

Peptide-coated semiconductor nanocrystals for biomedical applications

We have developed a new functionalization approach for semiconductor nanocrystals based on a single-step exchange of surface ligands with custom-designed peptides. This peptide-coating technique yield small, monodisperse and very stable water-soluble NCs that remain bright and photostable. We have used this approach on several types of core and core-shell NCs in the visible and near-infrared spectrum range and used fluorescence correlation spectroscopy for rapid assessment of the colloidal and photophysical properties of the resulting particles. This peptide coating strategy has several advantages: it yields probes that are immediately biocompatible; it is amenable to improvements of the different properties (solubilization, functionalization, etc) via rational design, parallel synthesis, or molecular evolution; it permits the combination of several functions on individual NCs. These functionalized NCs have been used for diverse biomedical applications. Two are discussed here: single-particle tracking of membrane receptor in live cells and combined fluorescence and PET imaging of targeted delivery in live animals.

On the development of colloidal nanoparticles towards multifunctional structures and their possible use for biological applications

In this Review, we describe the synthesis of high-quality colloidal nanoparticles in organic solvents, the mechanisms by which they can be transferred into aqueous solution, and some of their applications in biology. In particular, we will place emphasis on the creation of multifunctional nanoparticles or nanoparticle assemblies.