Quantum dots are powerful multipurpose vital labeling agents in zebrafish embryos

Zebrafish: A Promising Real-Time Model System for Nanotechnology-Mediated Neurospecific Drug Delivery

Delivering drugs to the brain has always remained a challenge for the research community and physicians. The blood-brain barrier (BBB) acts as a major hurdle for delivering drugs to specific parts of the brain and the central nervous system. It is physiologically comprised of complex network of capillaries to protect the brain from any invasive agents or foreign particles. Therefore, there is an absolute need for understanding of the BBB for successful therapeutic interventions. Recent research indicates the strong emergence of zebrafish as a model for assessing the permeability of the BBB, which is highly conserved in its structure and function between the zebrafish and mammals. The zebrafish model system offers a plethora of advantages including easy maintenance, high fecundity and transparency of embryos and larvae. Therefore, it has the potential to be developed as a model for analysing and elucidating the permeability of BBB to novel permeation technologies with neurospecificity. Nanotechnology has now become a focus area within the industrial and research community for delivering drugs to the brain. Nanoparticles are being developed with increased efficiency and accuracy for overcoming the BBB and delivering neurospecific drugs to the brain. The zebrafish stands as an excellent model system to assess nanoparticle biocompatibility and toxicity. Hence, the zebrafish model is indispensable for the discovery or development of novel technologies for neurospecific drug delivery and potential therapies for brain diseases.

Fluorescent nanoparticles as tools in ecology and physiology

Fluorescent nanoparticles (FNPs) have been widely used in chemistry and medicine for decades, but their employment in biology is relatively recent. Past reviews on FNPs have focused on chemical, physical or medical uses, making the extrapolation to biological applications difficult. In biology, FNPs have largely been used for biosensing and molecular tracking. However, concerns over toxicity in early types of FNPs, such as cadmium-containing quantum dots (QDs), may have prevented wide adoption. Recent developments, especially in non-Cd-containing FNPs, have alleviated toxicity problems, facilitating the use of FNPs for addressing ecological, physiological and molecule-level processes in biological research. Standardised protocols from synthesis to application and interdisciplinary approaches are critical for establishing FNPs in the biologists' tool kit. Here, we present an introduction to FNPs, summarise their use in biological applications, and discuss technical issues such as data reliability and biocompatibility. We assess whether biological research can benefit from FNPs and suggest ways in which FNPs can be applied to answer questions in biology. We conclude that FNPs have a great potential for studying various biological processes, especially tracking, sensing and imaging in physiology and ecology.

Quantum Dots: An Emerging Tool for Point-of-Care Testing

Quantum dots (QDs) are semiconductor crystals in the nanodimension having unique optical and electronic properties that differ from bulk material due to quantum mechanics. The QDs have a narrow emission peak, size-dependent emission wavelength, and broad excitation range which can be utilized for diverse biomedical applications such as molecular imaging, biosensing, and diagnostic systems. This article reviews the current developments of biomedical applications of QDs with special reference to point-of-care testing.

Time-Gated FRET Nanoprobes for Autofluorescence-Free Long-Term In Vivo Imaging of Developing Zebrafish

The zebrafish is an important vertebrate model for disease, drug discovery, toxicity, embryogenesis, and neuroscience. In vivo fluorescence microscopy can reveal cellular and subcellular details down to the molecular level with fluorescent proteins (FPs) currently the main tool for zebrafish imaging. However, long maturation times, low brightness, photobleaching, broad emission spectra, and sample autofluorescence are disadvantages that cannot be easily overcome by FPs. Here, a bright and photostable terbium-to-quantum dot (QD) Förster resonance energy transfer (FRET) nanoprobe with narrow and tunable emission bands for intracellular in vivo imaging is presented. The long photoluminescence (PL) lifetime enables time-gated (TG) detection without autofluorescence background. Intracellular four-color multiplexing with a single excitation wavelength and in situ assembly and FRET to mCherry demonstrate the versatility of the TG-FRET nanoprobes and the possibility of in vivo bioconjugation to FPs and combined nanoprobe-FP FRET sensing. Upon injection at the one-cell stage, FRET nanoprobes can be imaged in developing zebrafish embryos over seven days with toxicity similar to injected RNA and strongly improved signal-to-background ratios compared to non-TG imaging. This work provides a strategy for advancing in vivo fluorescence imaging applications beyond the capabilities of FPs.

Functional optical coherence tomography and photoacoustic microscopy imaging for zebrafish larvae

We present a dual modality functional optical coherence tomography and photoacoustic microscopy (OCT-PAM) system. The photoacoustic modality employs an akinetic optical sensor with a large imaging window. This imaging window enables direct reflection mode operation, and a seamless integration of optical coherence tomography (OCT) as a second imaging modality. Functional extensions to the OCT-PAM system include Doppler OCT (DOCT) and spectroscopic PAM (sPAM). This functional and non-invasive imaging system is applied to image zebrafish larvae, demonstrating its capability to extract both morphological and hemodynamic parameters in vivo in small animals, which are essential and critical in preclinical imaging for physiological, pathophysiological and drug response studies.

Impact of nanomaterials on ecosystems: Mechanistic aspects in vivo

Nanotechnologies are becoming increasingly popular in modern era of human development in every aspect of life. Their impact on our ecosystem in air, soil, and water is largely unknown because of the limited amount of information available, and hence, they require considerable attention. This account highlights the important routes of nanomaterials toxicity in air, soil, and water, their possible impact on the ecosystem and aquatic life. The mechanistic aspects have been focused on the size, shape, and surface modifications of nanomaterials. The preventive measures and future directions along with appropriate designs and implementation of nanotechnologies have been proposed so as to minimize the interactions of nanomaterials with terrestrial flora and aquatic life. Specifically, the focus largely remains on the toxicity of metallic nanoparticles such as gold (Au) and silver (Ag) because of their applications in diverse fields. The account lists some prominent mechanistic routes of nanotoxicity along with in vivo experimental results based on the fundamental understanding that how nanometallic surfaces interact with plant as well as animal biological systems. The appropriate modifications of the nanometallic surfaces with biocompatible molecules are considered to be the most effective preventive measures to reduce the nanotoxicity.

Nanomaterials meet zebrafish: Toxicity evaluation and drug delivery applications

With the rapid development of engineered nanomaterials for various applications, in vivo toxicological studies for evaluating the potential hazardous effects of nanomaterials on environmental and human safety are in urgent need. Zebrafish has long been considered as the "gold standard" for biosafety assessments of chemicals and pollutants due to its high fecundity, cost-effectiveness, well-characterized developmental stages, optical transparency, and so forth. Thus, zebrafish holds great potential for high-throughput nanotoxicity screening. In this review, we summarize the in vivo toxicological profiles of different nanomaterials, including Ag nanoparticles (NPs), CuO NPs, silica NPs, polymeric NPs, quantum dots, nanoscale metal-organic frameworks, etc, in zebrafish and focus on how the physicochemical properties (e.g., size, surface charge, and surface chemistry) of these nanomaterials influence their biosafety. In addition, we also report the recent advances of the in vivo delivery of nanopharmaceuticals using zebrafish as the model organism for therapeutic assessment, biodistribution tracking, and the controlled release of loaded drugs. Limitations and special considerations of zebrafish model are also discussed. Overall, zebrafish is expected to serve as a high-throughput screening platform for nanotoxicity and drug delivery assessment, which may instruct the design of safe nanomaterials and more effective nanomedicines.

Intracellular Delivery by Membrane Disruption: Mechanisms, Strategies, and Concepts

Intracellular delivery is a key step in biological research and has enabled decades of biomedical discoveries. It is also becoming increasingly important in industrial and medical applications ranging from biomanufacture to cell-based therapies. Here, we review techniques for membrane disruption-based intracellular delivery from 1911 until the present. These methods achieve rapid, direct, and universal delivery of almost any cargo molecule or material that can be dispersed in solution. We start by covering the motivations for intracellular delivery and the challenges associated with the different cargo types-small molecules, proteins/peptides, nucleic acids, synthetic nanomaterials, and large cargo. The review then presents a broad comparison of delivery strategies followed by an analysis of membrane disruption mechanisms and the biology of the cell response. We cover mechanical, electrical, thermal, optical, and chemical strategies of membrane disruption with a particular emphasis on their applications and challenges to implementation. Throughout, we highlight specific mechanisms of membrane disruption and suggest areas in need of further experimentation. We hope the concepts discussed in our review inspire scientists and engineers with further ideas to improve intracellular delivery.

Zebrafish as a Model to Evaluate Nanoparticle Toxicity

Nanoparticles are increasingly being developed for in vivo use, from targeted drug delivery to diagnostics, where they have enormous potential, while they are also being used for a variety of applications that can result in environmental exposure for humans. Understanding how specific nanoparticles interact with cells and cell systems is essential to gauge their safety with respect to either clinical or environmental exposure. Zebrafish is being increasingly employed as a model to evaluate nanoparticle biocompatibility. This review describes this model and how it can be used to assess nanoparticle toxicity at multiple levels, including mortality, teratogenicity, immunotoxicity, genotoxicity, as well as alterations in reproduction, behavior and a range of other physiological readouts. This review also provides an overview of studies using this model to assess the toxicity of metal, metal oxide and carbon-based nanoparticles. It is anticipated that this information will inform research aimed at developing biocompatible nanoparticles for a range of uses.

Intensive epidermal adsorption and specific venous deposition of carboxyl quantum dots in zebrafish early-life stages

To properly assess the environmental risk of quantum dots (QDs), it is necessary to determine their fate in living organisms, including adsorption, distribution and bioaccumulation under representative environmental or physiological conditions. We comprehensively investigated the fate of QDs with carboxyl terminal functional groups (carboxyl-QDs) in zebrafish (Danio rerio) embryo and larvae subjected to either waterborne exposure or cardiovascular system microinjection. On waterborne exposure, carboxyl-QDs exhibited an intensive adsorption and accumulation in the chorion of embryos, and their predominate target organs were the gill and intestinal tract in larvae. On microinjection, carboxyl-QDs were rapidly delivered into the cardiovascular system and specifically deposited in veins and the capillary network system of zebrafish larvae, but not in the arterial system. Taken together, we found that the exact tissue condition including epidermal structures, mucus secretion and vascular microstructures strongly affected the adsorption, uptake and distribution of carboxyl-QDs in zebrafish. This work highlights the intensive tissue epidermal adsorption and accumulation of carboxyl-QDs and their specific vein and capillary deposition in the cardiovascular system in zebrafish early-life stages.

Development of a zebrafish sepsis model for high-throughput drug discovery

Sepsis is a leading cause of death worldwide. Current treatment modalities remain largely supportive. Intervention strategies focused on inhibiting specific mediators of the inflammatory host response have been largely unsuccessful, a consequence of an inadequate understanding of the complexity and heterogeneity of the innate immune response. Moreover, the conventional drug development pipeline is time consuming and expensive and the low success rates associated with cell-based screens underline the need for whole organism screening strategies, especially for complex pathological processes. Here, we established an LPS-induced zebrafish endotoxemia model, which exhibits the major hallmarks of human sepsis including, edema and tissue/organ damage, increased vascular permeability and vascular leakage accompanied by an altered expression of cellular junction proteins, increased cytokine expression, immune cell activation and ROS production, reduced circulation and increased platelet aggregation. We tested the suitability of the model for phenotype-based drug screening using three primary readouts: mortality, vascular leakage, and ROS production. Preliminary screening identified fasudil, a drug known to protect against vascular leakage in murine models, as a lead hit thereby validating the utility of our model for sepsis drug screens. This zebrafish sepsis model has the potential to rapidly analyze sepsis associated pathologies and cellular processes in the whole organism, as well as to screen and validate large numbers of compounds that can modify sepsis pathology in vivo.

Quantum dots: bright and versatile in vitro and in vivo fluorescence imaging biosensors

Colourful cells and tissues: semiconductor quantum dots and their versatile applications in multiplexed bioimaging research.

Reverse genetic morpholino approach using cardiac ventricular injection to transfect multiple difficult-to-target tissues in the zebrafish larva

The zebrafish is an important model to understand the cell and molecular biology of organ and appendage regeneration. However, molecular strategies to employ reverse genetics have not yet been adequately developed to assess gene function in regeneration or tissue homeostasis during larval stages after zebrafish embryogenesis, and several tissues within the zebrafish larva are difficult to target. Intraventricular injections of gene-specific morpholinos offer an alternative method for the current inability to genomically target zebrafish genes in a temporally controlled manner at these stages. This method allows for complete dispersion and subsequent incorporation of the morpholino into various tissues throughout the body, including structures that were formerly impossible to reach such as those in the larval caudal fin, a structure often used to noninvasively research tissue regeneration. Several genes activated during larval finfold regeneration are also present in regenerating adult vertebrate tissues, so the larva is a useful model to understand regeneration in adults. This morpholino dispersion method allows for the quick and easy identification of genes required for the regeneration of larval tissues as well as other physiological phenomena regulating tissue homeostasis after embryogenesis. Therefore, this delivery method provides a currently needed strategy for temporal control to the evaluation of gene function after embryogenesis. 

Counterion-enhanced cyanine dye loading into lipid nano-droplets for single-particle tracking in zebrafish

Superior brightness of fluorescent nanoparticles places them far ahead of the classical fluorescent dyes in the field of biological imaging. However, for in vivo applications, inorganic nanoparticles, such as quantum dots, are limited due to the lack of biodegradability. Nano-emulsions encapsulating high concentrations of organic dyes are an attractive alternative, but classical fluorescent dyes are inconvenient due to their poor solubility in the oil and their tendency to form non-fluorescent aggregates. This problem was solved here for a cationic cyanine dye (DiI) by substituting its perchlorate counterion for a bulky and hydrophobic tetraphenylborate. This new dye salt, due to its exceptional oil solubility, could be loaded at 8 wt% concentration into nano-droplets of controlled size in the range 30-90 nm. Our 90 nm droplets, which contained >10,000 cyanine molecules, were >100-fold brighter than quantum dots. This extreme brightness allowed, for the first time, single-particle tracking in the blood flow of live zebrafish embryo, revealing both the slow and fast phases of the cardiac cycle. These nano-droplets showed minimal cytotoxicity in cell culture and in the zebrafish embryo. The concept of counterion-based dye loading provides a new effective route to ultra-bright lipid nanoparticles, which enables tracking single particles in live animals, a new dimension of in vivo imaging.

In vivo cell biology in zebrafish - providing insights into vertebrate development and disease

Over the past decades, studies using zebrafish have significantly advanced our understanding of the cellular basis for development and human diseases. Zebrafish have rapidly developing transparent embryos that allow comprehensive imaging of embryogenesis combined with powerful genetic approaches. However, forward genetic screens in zebrafish have generated unanticipated findings that are mirrored by human genetic studies: disruption of genes implicated in basic cellular processes, such as protein secretion or cytoskeletal dynamics, causes discrete developmental or disease phenotypes. This is surprising because many processes that were assumed to be fundamental to the function and survival of all cell types appear instead to be regulated by cell-specific mechanisms. Such discoveries are facilitated by experiments in whole animals, where zebrafish provides an ideal model for visualization and manipulation of organelles and cellular processes in a live vertebrate. Here, we review well-characterized mutants and newly developed tools that underscore this notion. We focus on the secretory pathway and microtubule-based trafficking as illustrative examples of how studying cell biology in vivo using zebrafish has broadened our understanding of the role fundamental cellular processes play in embryogenesis and disease.

Non-mammalian vertebrate embryos as models in nanomedicine

Various in vivo biological models have been proposed for studying the interactions of nano-materials in biological systems. Unfortunately, the widely used small mammalian animal models (rodents) are costly and labor intensive and generate ethical issues and antagonism from the anti-vivisectionist movement. Recently, there has been increasing interest in the scientific community in the interactions between nano-materials and non-mammalian developmental organisms, which are now being recognized as valid models for the study of human disease. This review examines and discusses the biomedical applications and the interaction of nano-materials with embryonic systems, focusing on non-mammalian vertebrate models, such as chicken, zebrafish and Xenopus.

FROM THE CLINICAL EDITOR

Animal models are critical components of preclinical biomedical research. This review discusses the feasibility and potential applications of non-mammalian vertebral animals, such as zebrafish, xenopus, and chicken as animal models in nanomedicine research.

Quantum Dots Do Not Alter the Differentiation Potential of Pancreatic Stem Cells and Are Distributed Randomly among Daughter Cells

With the increasing relevance of cell-based therapies, there is a demand for cell-labeling techniques for in vitro and in vivo studies. For the reasonable tracking of transplanted stem cells in animal models, the usage of quantum dots (QDs) for sensitive cellular imaging has major advances. QDs could be delivered to the cytoplasm of the cells providing intense and stable fluorescence. Although QDs are emerging as favourable nanoparticles for bioimaging, substantial investigations are still required to consider their application for adult stem cells. Therefore, rat pancreatic stem cells (PSCs) were labeled with different concentrations of CdSe quantum dots (Qtracker 605 nanocrystals). The QD labeled PSCs showed normal proliferation and their usual spontaneous differentiation potential in vitro. The labeling of the cell population was concentration dependent, with increasing cell load from 5 nM QDs to 20 nM QDs. With time-lapse microscopy, we observed that the transmission of the QD particles during cell divisions was random, appearing as equal or unequal transmission to daughter cells. We report here that QDs offered an efficient and nontoxic way to label pancreatic stem cells without genetic modifications. In summary, QD nanocrystals are a promising tool for stem cell labeling and facilitate tracking of transplanted cells in animal models.

From seeing to believing: labelling strategies for in vivo cell-tracking experiments

Intravital microscopy has become increasingly popular over the past few decades because it provides high-resolution and real-time information about complex biological processes. Technological advances that allow deeper penetration in live tissues, such as the development of confocal and two-photon microscopy, together with the generation of ever-new fluorophores that facilitate bright labelling of cells and tissue components have made imaging of vertebrate model organisms efficient and highly informative. Genetic manipulation leading to expression of fluorescent proteins is undoubtedly the labelling method of choice and has been used to visualize several cell types in vivo. This approach, however, can be technically challenging and time consuming. Over the years, several dyes have been developed to allow rapid, effective and bright ex vivo labelling of cells for subsequent transplantation and imaging. Here, we review and discuss the advantages and limitations of a number of strategies commonly used to label and track cells at high resolution in vivo in mouse and zebrafish, using fluorescence microscopy. While the quest for the perfect label is far from achieved, current reagents are valuable tools enabling the progress of biological discovery, so long as they are selected and used appropriately.

Conjugation of quantum dots on carbon nanotubes for medical diagnosis and treatment

Cancer is one of the leading causes of death worldwide and early detection provides the best possible prognosis for cancer patients. Nanotechnology is the branch of engineering that deals with the manipulation of individual atoms and molecules. This area of science has the potential to help identify cancerous cells and to destroy them by various methods such as drug delivery or thermal treatment of cancer. Carbon nanotubes (CNT) and quantum dots (QDs) are the two nanoparticles, which have received considerable interest in view of their application for diagnosis and treatment of cancer. Fluorescent nanoparticles known as QDs are gaining momentum as imaging molecules with life science and clinical applications. Clinically they can be used for localization of cancer cells due to their nano size and ability to penetrate individual cancer cells and high-resolution imaging derived from their narrow emission bands compared with organic dyes. CNTs are of interest to the medical community due to their unique properties such as the ability to deliver drugs to a site of action or convert optical energy into thermal energy. By attaching antibodies that bind specifically to tumor cells, CNTs can navigate to malignant tumors. Once at the tumor site, the CNTs enter into the cancer cells by penetration or endocytosis, allowing drug release, and resulting in specific cancer cell death. Alternatively, CNTs can be exposed to near-infrared light in order to thermally destroy the cancer cells. The amphiphilic nature of CNTs allows them to penetrate the cell membrane and their large surface area (in the order of 2600 m²/g) allows drugs to be loaded into the tube and released once inside the cancer cell. Many research laboratories, including our own, are investigating the conjugation of QDs to CNTs to allow localization of the cancer cells in the patient, by imaging with QDs, and subsequent cell killing, via drug release or thermal treatment. This is an area of huge interest and future research and therapy will focus on the multimodality of nanoparticles. In this review, we seek to explore the biomedical applications of QDs conjugated to CNTs, with a particular emphasis on their use as therapeutic platforms in oncology.

Highly lipophilic fluorescent dyes in nano-emulsions: towards bright non-leaking nano-droplets

Dye-loaded lipid nano-droplets present an attractive alternative to inorganic nanoparticles, as they are composed of non-toxic biodegradable materials and easy to prepare. However, to achieve high fluorescence brightness, the nano-droplets have to be heavily loaded with the dyes avoiding fluorescence self-quenching and release (leakage) of the encapsulated dyes from the nano-droplets in biological media. In the present work, we have designed highly lipophilic fluorescent derivatives of 3-alkoxyflavone (F888) and Nile Red (NR668) that can be encapsulated in the lipophilic core of stable nano-emulsion droplets at exceptionally high concentrations in the oil core, i.e. up to 170 mM and 17 mM, respectively, corresponding to ~ 830 and 80 dyes per 40-nm droplet. Despite this high loading, these dyes keep high fluorescence quantum yield and thus, provide high nano-droplet brightness, probably due to their bulky structure preventing self-quenching. Moreover, simultaneous encapsulation of both dyes at high concentrations in single nano-droplets allows observation of FRET. FRET and fluorescence correlation spectroscopy (FCS) studies showed that NR668 release in the serum-containing medium is very slow, while the reference hydrophobic dye Nile Red leaks immediately. This drastic difference in the leakage profile between NR668 and Nile Red was confirmed by in vitro cellular studies as well as by in vivo angiography imaging on zebrafish model, where the NR668-loaded nano-droplets remained in the blood circulation, while the parent Nile Red leaked rapidly from the droplets distributing all over the animal body. This study suggests new molecular design strategies for obtaining bright nano-droplets without dye leakage and their use as efficient and stable optical contrast agents in vitro and in vivo.

Stable, compact, bright biofunctional quantum dots with improved peptide coating

We developed a new peptide, natural phytochelatin (PC), which tightly binds to CdSe/ZnS quantum dots' (QDs) surfaces and renders them water-soluble. Coating QDs with this flexible and all-hydrophilic peptide offers high colloidal stability, adds only 0.8-0.9 nm to the radius of the particles (as compared to their original inorganic radius), preserves very high quantum yield (QY) in water, and affords facile bioconjugation with various functional groups. We demonstrate specific targeting (with minimal nonspecific binding) of such fluorescein-conjugated QDs to ScFv-fused mouse prion protein expressed in live N2A cells. We also demonstrated homogeneous in vivo biodistribution with no significant toxicity in live zebrafish.

'In parallel' interconnectivity of the dorsal longitudinal anastomotic vessels requires both VEGF signaling and circulatory flow

Blood vessels deliver oxygen, nutrients, hormones and immunity factors throughout the body. To perform these vital functions, vascular cords branch, lumenize and interconnect. Yet, little is known about the cellular, molecular and physiological mechanisms that control how circulatory networks form and interconnect. Specifically, how circulatory networks merge by interconnecting 'in parallel' along their boundaries remains unexplored. To examine this process we studied the formation and functional maturation of the plexus that forms between the dorsal longitudinal anastomotic vessels (DLAVs) in the zebrafish. We find that the migration and proliferation of endothelial cells within the DLAVs and their segmental (Se) vessel precursors drives DLAV plexus formation. Remarkably, the presence of Se vessels containing only endothelial cells of the arterial lineage is sufficient for DLAV plexus morphogenesis, suggesting that endothelial cells from the venous lineage make a dispensable or null contribution to this process. The discovery of a circuit that integrates the inputs of circulatory flow and vascular endothelial growth factor (VEGF) signaling to modulate aortic arch angiogenesis, together with the expression of components of this circuit in the trunk vasculature, prompted us to investigate the role of these inputs and their relationship during DLAV plexus formation. We find that circulatory flow and VEGF signaling make additive contributions to DLAV plexus morphogenesis, rather than acting as essential inputs with equivalent contributions as they do during aortic arch angiogenesis. Our observations underscore the existence of context-dependent differences in the integration of physiological stimuli and signaling cascades during vascular development.

Impact of silicon-based quantum dots on the antioxidative system in white muscle of Carassius auratus gibelio

Silicon-based quantum dots were intraperitoneally injected in individuals of Carassius auratus gibelio. Their effects on white muscle were investigated by following their distribution and impact on the antioxidative system. The GSH level significantly increased after 1 and 3 days of exposure by, respectively, 85.3 and 25.4%. Seven days later, GSH levels were similar to control concentrations. MDA concentration rose after three days by 46.9% and remained at the same level after 7 days. Protein thiol levels significantly decreased by 6.7 and 8.1% after 3 and 7 days, whereas advanced oxidation protein products increased by 12.7, respectively, 28.1% in the same time intervals. The protein reactive carbonyl groups were raised only after the first day of exposure and returned to the control level later on. SOD specific activity increased up to 48% after 7 days, while CAT activity increased by 328, 176, and 26% after 1, 3, and 7 days of treatment. GST specific activity was up-regulated by 87, 18, and 9%, while GR activity increased by 68, 34, and 9%. G6PD activity was up-regulated by 12, 22, and 50%, whereas GPx activity raised by 75 and 109% compared to control after, respectively, 1, 3, and 7 days. Our results suggest that oxidative stress induced by silicon-based quantum dots was not strong enough to cause permanent damage in the white muscle of crucian carp.

Near-Infrared Fluorescent Nanoprobes for in Vivo Optical Imaging

Near-infrared (NIR) fluorescent probes offer advantages of high photon penetration, reduced light scattering and minimal autofluorescence from living tissues, rendering them valuable for noninvasive mapping of molecular events, assessment of therapeutic efficacy, and monitoring of disease progression in animal models. This review provides an overview of the recent development of the design and optical property of the different classes of NIR fluorescent nanoprobes associated with in vivo imaging applications.

The primacy of physicochemical characterization of nanomaterials for reliable toxicity assessment: a review of the zebrafish nanotoxicology model

Engineered nanomaterials (ENMs) have become increasingly prevalent in the past two decades in academic, medical, commercial, and industrial settings. The unique properties imbued with nanoparticles, as the physiochemical properties change from the bulk material to the surface atoms, present unique and often challenging characteristics that larger macromolecules do not possess. While nanoparticle characteristics are indeed exciting for unique chemistries, surface properties, and diverse applications, reports of toxicity and environmental impacts have tempered this enthusiasm and given cause for an exponential increase for concomitant nanotoxicology assessment. Currently, nanotoxicology is a steadily growing with new literature and studies being published more frequently than ever before; however, the literature reveals clear, inconsistent trends in nanotoxicological assessment. At the heart of this issue are several key problems including the lack of validated testing protocols and models, further compounded by inadequate physicochemical characterization of the nanomaterials in question and the seminal feedback loop of chemistry to biology back to chemistry. Zebrafish (Danio rerio) are emerging as a strong nanotoxicity model of choice for ease of use, optical transparency, cost, and high degree of genomic homology to humans. This review attempts to amass all contemporary nanotoxicology studies done with the zebrafish and present as much relevant information on physicochemical characteristics as possible. While this report is primarily a physicochemical summary of nanotoxicity studies, we wish to strongly emphasize that for the proper evolution of nanotoxicology, there must be a strong marriage between the physical and biological sciences. More often than not, nanotoxicology studies are reported by groups dominated by one discipline or the other. Regardless of the starting point, nanotoxicology must be seen as an iterative process between chemistry and biology. It is our sincere hope that the future will introduce a paradigm shift in the approach to nanotoxicology with multidisciplinary groups for data analysis to produce predictive and correlative models for the end goal of rapid preclinical development of new therapeutics into the clinic or insertion into environmental protection.

Investigating the genetics of visual processing, function and behaviour in zebrafish

Over the past three decades, the zebrafish has been proven to be an excellent model to investigate the genetic control of vertebrate embryonic development, and it is now also increasingly used to study behaviour and adult physiology. Moreover, mutagenesis approaches have resulted in large collections of mutants with phenotypes that resemble human pathologies, suggesting that these lines can be used to model diseases and screen drug candidates. With the recent development of new methods for gene targeting and manipulating or monitoring gene expression, the range of genetic modifications now possible in zebrafish is increasing rapidly. Combined with the classical strengths of the zebrafish as a model organism, these advances are set to substantially expand the type of biological questions that can be addressed in this species. In this review, we outline how the potential of the zebrafish can be harvested in the context of eye development and visual function. We review recent technological advances used to study the formation of the eyes and visual areas of the brain, visual processing on the cellular, subcellular and molecular level, and the genetics of visual behaviour in vertebrates.

Nanoimaging and neurological surgery

Over 32 million surgical procedures are performed in the United States each year. Increasingly, image guidance is used in order to aid in the surgical localization of pathology, minimization of incisions, and improvement of surgical intervention outcomes. A variety of imaging modalities using different portions of the electromagnetic spectrum are used in neurological surgery. These include wavelengths used in ultrasonography, optical, infrared, ionizing radiation, and magnetic resonance. The use of currently available image-guidance tools for neurological surgery is reviewed. Advances in nanoparticulates and their integration into the neurosurgical operating room environment are discussed.

Zebrafish as a good vertebrate model for molecular imaging using fluorescent probes

Fluorescent probes have been used extensively to monitor biomolecules and biologically relevant species in vitro and in vivo. A new trend in this area that has been stimulated by the desire to obtain more detailed information about the biological effects of analytes is the change from live cell to whole animal fluorescent imaging. Zebrafish has received great attention for live vertebrate imaging due to several noticeable advantages. In this tutorial review, recent advances in live zebrafish imaging using fluorescent probes, such as fluorescent proteins, synthetic fluorescent dyes and quantum dots, are highlighted.

Quantum dots brighten biological imaging

Quantum dots (QDs) are novel photostable semiconductor nanocrystals possessing wide excitation spectra and narrow, symmetrical emission spectra and can be conjugated to a wide range of biological targets, including proteins, antibodies and nucleic acid probes. These characteristics have provoked considerable interest in their use for bioimaging. Much investigation has been performed into their use for multiplex immunohistochemistry and in situ hybridisation which, when combined with multispectral imaging, has enabled quantitation and colocalisation of gene expression in clinical tissue. Many advances have recently been made using QDs for live cell and in vivo imaging, in which QD-labelled molecules can be tracked and visualised in 3-D. This review aims to outline the beneficial properties presented by QDs along with important advances in their biological application.

Multispectral fingerprinting for improved in vivo cell dynamics analysis

Background

Tracing cell dynamics in the embryo becomes tremendously difficult when cell trajectories cross in space and time and tissue density obscure individual cell borders. Here, we used the chick neural crest (NC) as a model to test multicolor cell labeling and multispectral confocal imaging strategies to overcome these roadblocks.

Results

We found that multicolor nuclear cell labeling and multispectral imaging led to improved resolution of in vivo NC cell identification by providing a unique spectral identity for each cell. NC cell spectral identity allowed for more accurate cell tracking and was consistent during short term time-lapse imaging sessions. Computer model simulations predicted significantly better object counting for increasing cell densities in 3-color compared to 1-color nuclear cell labeling. To better resolve cell contacts, we show that a combination of 2-color membrane and 1-color nuclear cell labeling dramatically improved the semi-automated analysis of NC cell interactions, yet preserved the ability to track cell movements. We also found channel versus lambda scanning of multicolor labeled embryos significantly reduced the time and effort of image acquisition and analysis of large 3D volume data sets.

Conclusions

Our results reveal that multicolor cell labeling and multispectral imaging provide a cellular fingerprint that may uniquely determine a cell's position within the embryo. Together, these methods offer a spectral toolbox to resolve in vivo cell dynamics in unprecedented detail.

In vivo imaging of zebrafish retinal cells using fluorescent coumarin derivatives

Background

The zebrafish visual system is a good research model because the zebrafish retina is very similar to that of humans in terms of the morphologies and functions. Studies of the retina have been facilitated by improvements in imaging techniques. In vitro techniques such as immunohistochemistry and in vivo imaging using transgenic zebrafish have been proven useful for visualizing specific subtypes of retinal cells. In contrast, in vivo imaging using organic fluorescent molecules such as fluorescent sphingolipids allows non-invasive staining and visualization of retinal cells en masse. However, these fluorescent molecules also localize to the interstitial fluid and stain whole larvae.

Results

We screened fluorescent coumarin derivatives that might preferentially stain neuronal cells including retinal cells. We identified four coumarin derivatives that could be used for in vivo imaging of zebrafish retinal cells. The retinas of living zebrafish could be stained by simply immersing larvae in water containing 1 μg/ml of a coumarin derivative for 30 min. By using confocal laser scanning microscopy, the lamination of the zebrafish retina was clearly visualized. Using these coumarin derivatives, we were able to assess the development of the zebrafish retina and the morphological abnormalities induced by genetic or chemical interventions. The coumarin derivatives were also suitable for counter-staining of transgenic zebrafish expressing fluorescent proteins in specific subtypes of retinal cells.

Conclusions

The coumarin derivatives identified in this study can stain zebrafish retinal cells in a relatively short time and at low concentrations, making them suitable for in vivo imaging of the zebrafish retina. Therefore, they will be useful tools in genetic and chemical screenings using zebrafish to identify genes and chemicals that may have crucial functions in the retina.

Biocompatibility and biodistribution of surface-enhanced Raman scattering nanoprobes in zebrafish embryos: in vivo and multiplex imaging

Nanoparticles are increasingly being used to investigate biological processes in various animal models due to their versatile chemical, unique optical, and multifunctional properties. In this report we address the biocompatibility and biodistribution of nanoparticle sensors used for Raman chemical imaging in live zebrafish (Danio rerio) embryos. Surface-enhanced Raman scattering (SERS) nanoprobes (NPs) comprising gold nanoparticles (AuNPs) as enhancing substrate and nonfluorescent Raman labels were synthesized and microinjected into zebrafish embryos at the one-cell stage. Raman mapping was performed to assess their distribution in various cell-types and tissues of developing embryo at five different stages between 6 and 96 hpf (hours post-fertilization). Biocompatibility and toxicity studies indicate that the NPs are not toxic and the embryos were found to exhibit normal morphological and gene expression in addition to the proper form and function of major organs such as the heart and vasculature (of 7 day old NPs injected zebrafish embryos). A multiplex in vivo detection protocol was developed by SERS imaging to demonstrate that multiple labels can be detected by Raman mapping in undifferentiated cells as they develop into distinct cell- and tissue-types. The present work is the first to report on multiplex Raman imaging of zebrafish embryos with potential implications in tracking tissue development and biological processes at single molecule sensitivity using appropriate target molecules in vivo.

Clinical potential of quantum dots

Advances in nanotechnology have led to the development of novel fluorescent probes called quantum dots. Quantum dots have revolutionalized the processes of tagging molecules within research settings and are improving sentinel lymph node mapping and identification in vivo studies. As the unique physical and chemical properties of these fluorescent probes are being unraveled, new potential methods of early cancer detection, rapid spread and therapeutic management, that is, photodynamic therapy are being explored. Encouraging results of optical and real time identification of sentinel lymph nodes and lymph flow using quantum dots in vivo models are emerging. Quantum dots have also superseded many of the limitations of organic fluorophores and are a promising alternative as a research tool. In this review, we examine the promising clinical potential of quantum dots, their hindrances for clinical use and the current progress in abrogating their inherent toxicity.

Nanotechnology and molecular cytogenetics: the future has not yet arrived

Quantum dots (QDs) are a novel class of inorganic fluorochromes composed of nanometer-scale crystals made of a semiconductor material. They are resistant to photo-bleaching, have narrow excitation and emission wavelengths that can be controlled by particle size and thus have the potential for multiplexing experiments. Given the remarkable optical properties that quantum dots possess, they have been proposed as an ideal material for use in molecular cytogenetics, specifically the technique of fluorescent in situ hybridisation (FISH). In this review, we provide an account of the current QD-FISH literature, and speculate as to why QDs are not yet optimised for FISH in their current form.

Prospects and developments in cell and embryo laser nanosurgery

Recently, there has been increasing interest in the application of femtosecond (fs) laser pulses to the study of cells, tissues and embryos. This review explores the developments that have occurred within the last several years in the fields of cell and embryo nanosurgery. Each of the individual studies presented in this review clearly demonstrates the nondestructiveness of fs laser pulses, which are used to alter both cellular and subcellular sites within simple cells and more complicated multicompartmental embryos. The ability to manipulate these model systems noninvasively makes applied fs laser pulses an invaluable tool for developmental biologists, geneticists, cryobiologists, and zoologists. We are beginning to see the integration of this tool into life sciences, establishing its status among molecular and genetic cell manipulation methods. More importantly, several studies demonstrating the versatility of applied fs laser pulses have established new collaborations among physicists, engineers, and biologists with the common intent of solving biological problems.