Surface engineering of quantum dots for in vivo vascular imaging

Surface engineering of quantum dots for in vivo imaging

The aim of this study was to investigate the effect of gluconic acid (GA) conjugation on the biodistribution of cysteamine-capped quantum dots (amino-QDots) in vivo. Cadmium selenide/zinc sulfide (CdSe/ZnS) was capped with cysteamine through a thiol exchange method, and different amounts of GA were conjugated to the amine groups of cysteamine via the formation of an amide bond. The emission maxima of the synthesized QDots, the amino-QDots and the GA-conjugated amine-QDots (GA-QDots) were located at 720, 600 and 610 nm, respectively. In the cell viability studies, the GA-QDots showed very low toxicity against CHO cells as compared to the cytotoxicity of the amino-QDots. The QDots were next intravenously injected into normal mice and then we performed ex vivo optical imaging. The majority of the amino-QDots were accumulated in the lung. In contrast, the GA-QDots were cleared out of the body through the kidney. Therefore, we expect that the conjugation of GA onto the amino-QDots can create opportunities for using amino-QDots for in vivo imaging.

Intravital imaging of embryonic and tumor neovasculature using viral nanoparticles

Viral nanoparticles are a novel class of biomolecular agents that take advantage of the natural circulatory and targeting properties of viruses to allow the development of therapeutics, vaccines and imaging tools. We have developed a multivalent nanoparticle platform based on the cowpea mosaic virus (CPMV) that facilitates particle labeling at high density with fluorescent dyes and other functional groups. Compared with other technologies, CPMV-based viral nanoparticles are particularly suited for long-term intravital vascular imaging because of their biocompatibility and retention in the endothelium with minimal side effects. The stable, long-term labeling of the endothelium allows the identification of vasculature undergoing active remodeling in real time. In this study, we describe the synthesis, purification and fluorescent labeling of CPMV nanoparticles, along with their use for imaging of vascular structure and for intravital vascular mapping in developmental and tumor angiogenesis models. Dye-labeled viral nanoparticles can be synthesized and purified in a single day, and imaging studies can be conducted over hours, days or weeks, depending on the application.

Delivering quantum dots to cells: bioconjugated quantum dots for targeted and nonspecific extracellular and intracellular imaging

Bioconjugated nanomaterials offer endless opportunities to advance both nanobiotechnology and biomedical technology. In this regard, semiconductor nanoparticles, also called quantum dots, are of particular interest for multimodal, multifunctional and multiplexed imaging of biomolecules, cells, tissues and animals. The unique optical properties, such as size-dependent tunable absorption and emission in the visible and NIR regions, narrow emission and broad absorption bands, high photoluminescence quantum yields, large one- and multi-photon absorption cross-sections, and exceptional photostability are the advantages of quantum dots. Multimodal imaging probes are developed by interfacing the unique optical properties of quantum dots with magnetic or radioactive materials. Besides, crystalline structure of quantum dots adds scope for high-contrast X-ray and TEM imaging. Yet another unique feature of a quantum dot is its spacious and flexible surface which is promising to integrate multiple ligands and antibodies and construct multi-functional probes for bioimaging. In this critical review, we will summarize recent advancements in the preparation of biocompatible quantum dots, bioconjugation of quantum dots, and applications of quantum dots and their bioconjugates for targeted and nonspecific imaging of extracellular and intracellular proteins, organelles and functions (181 references).

In vivo tumor-targeted fluorescence imaging using near-infrared non-cadmium quantum dots

This article reported the high tumor targeting efficacy of RGD peptide labeled near-infrared (NIR) non-cadmium quantum dots (QDs). After using poly(ethylene glycol) to encapsulate InAs/InP/ZnSe QDs (emission maximum at about 800 nm), QD800-PEG dispersed well in PBS buffer with the hydrodynamic diameter (HD) of 15.9 nm and the circulation half-life of approximately 29 min. After coupling QD800-PEG with arginine-glycine-aspartic acid (RGD) or arginine-alanine-aspartic acid (RAD) peptides, we used nude mice bearing subcutaneous U87MG tumor as models to test tumor-targeted fluorescence imaging. The results indicated that the tumor uptake of QD800-RGD is much higher than those of QD800-PEG and QD800-RAD. The semiquantitative analysis of the region of interest (ROI) showed a high tumor uptake of 10.7 +/- 1.5%ID/g in mice injected with QD800-RGD, while the tumor uptakes of QD800-PEG and QD800-RAD were 2.9 +/- 0.3%ID/g and 4.0 +/- 0.5%ID/g, respectively, indicating the specific tumor targeting of QD800-RGD. The high reproducibility of bioconjunction between QDs and the RGD peptide and the feasibility of QD-RGD bioconjugates as tumor-targeted fluorescence probes warrant the successful application of QDs for in vivo molecular imaging.

Surface modification, functionalization and bioconjugation of colloidal inorganic nanoparticles

Inorganic colloidal nanoparticles are very small, nanoscale objects with inorganic cores that are dispersed in a solvent. Depending on the material they consist of, nanoparticles can possess a number of different properties such as high electron density and strong optical absorption (e.g. metal particles, in particular Au), photoluminescence in the form of fluorescence (semiconductor quantum dots, e.g. CdSe or CdTe) or phosphorescence (doped oxide materials, e.g. Y(2)O(3)), or magnetic moment (e.g. iron oxide or cobalt nanoparticles). Prerequisite for every possible application is the proper surface functionalization of such nanoparticles, which determines their interaction with the environment. These interactions ultimately affect the colloidal stability of the particles, and may yield to a controlled assembly or to the delivery of nanoparticles to a target, e.g. by appropriate functional molecules on the particle surface. This work aims to review different strategies of surface modification and functionalization of inorganic colloidal nanoparticles with a special focus on the material systems gold and semiconductor nanoparticles, such as CdSe/ZnS. However, the discussed strategies are often of general nature and apply in the same way to nanoparticles of other materials.

Biocompatible near-infrared quantum dots as ultrasensitive probes for long-term in vivo imaging applications

A facile synthesis method to produce monodisperse, biocompatible, lysine crosslinked mercaptoundecanoic acid (MUA) CdSe(0.25)Te(0.75)/CdS near-infrared (NIR) quantum dots and use them as probes to study their long term in vivo distribution, clearance, and toxicity is presented. Large signal enhancements are demonstrated by these quantum dots, which enables their use as efficient and sensitive probes for live-animal imaging. An important finding is that mice intravenously injected with approximately 10.5 mg kg(-1) of NIR QDs survive for more than three months without any apparent adverse effect to their health. Furthermore, it is determined that there is a significant reduction in the number of the QDs in the liver and spleen three months post injection. In addition, histological analysis of heart, kidney, liver, spleen, and lung tissue indicates that there are no acute toxic effects from these lysine cross-linked MUA NIR QDs. This study suggests that these NIR QDs can be potentially used for long-term targeted imaging and therapy studies in vivo.

Clathrin-mediated endocytosis of quantum dot-peptide conjugates in living cells

Efficient intracellular delivery of quantum dots (QDs) and unravelling the mechanism underlying the intracellular delivery are essential for advancing the applications of QDs toward in vivo imaging and therapeutic interventions. Here, we show that clathrin-mediated endocytosis is the most important pathway for the intracellular delivery of peptide-conjugated QDs. We selected an insect neuropeptide, namely, allatostatin (AST1, APSGAQRLYG FGL-NH(2)), conjugated it with CdSe-ZnS QDs, and investigated the intracellular delivery of the conjugate in living cells such as human epidermoid ovarian carcinoma cells (A431) and mouse embryonic fibroblast cells (3T3). We selected AST1 to investigate the intracellular delivery of QDs because we recently found it to be efficient for delivering QDs in living mammalian cells. Also, the receptors of AST1 in insects show functional and sequence similarity to G-protein-coupled galanin receptors in mammals. We employed flow cytometry and fluorescence microscopy and investigated the contributions of clathrin-mediated endocytosis, receptor-mediated endocytosis, and charge-based cell penetration or transduction to the intracellular delivery of QD-AST1 conjugates. Interestingly, the intracellular delivery was suppressed by approximately 57% when we inhibited the regulatory enzyme phosphoinositide 3-kinase (PI3K) with wortmannin and blocked the formation of clathrin-coated vesicles. In parallel, we investigated clathrin-mediated endocytosis by colocalizing QD560-labeled clathrin heavy-chain antibody and QD605-AST1. We also estimated galanin receptor-mediated endocytosis of QD-AST1 at <10% by blocking the cells with a galanin antagonist and transduction at <30% by both removing the charge of the peptide due to arginine and suppressing the cell-surface charge due to glycosaminoglycan. In short, the current work shows that multiple pathways are involved in the intracellular delivery of peptide-conjugated QDs, among which clathrin-mediated endocytosis is the most important.

Quantum dot mediated imaging of atherosclerosis

The progression of atherosclerosis is associated with leukocyte infiltration within lesions. We describe a technique for the ex vivo imaging of cellular recruitment in atherogenesis which utilizes quantum dots (QD) to color-code different cell types within lesion areas. Spectrally distinct QD were coated with the cell-penetrating peptide maurocalcine to fluorescently-label immunomagnetically isolated monocyte/macrophages and T lymphocytes. QD-maurocalcine bioconjugates labeled both cell types with a high efficiency, preserved cell viability, and did not perturb native leukocyte function in cytokine release and endothelial adhesion assays. QD-labeled monocyte/macrophages and T lymphocytes were reinfused in an ApoE(-/-) mouse model of atherosclerosis and age-matched controls and tracked for up to four weeks to investigate the incorporation of cells within aortic lesion areas, as determined by oil red O (ORO) and immunofluorescence ex vivo staining. QD-labeled cells were visible in atherosclerotic plaques within two days of injection, and the two cell types colocalized within areas of subsequent ORO staining. Our method for tracking leukocytes in lesions enables high signal-to-noise ratio imaging of multiple cell types and biomarkers simultaneously within the same specimen. It also has great utility in studies aimed at investigating the role of distinct circulating leukocyte subsets in plaque development and progression.

Direct magnetic separation of immune cells from whole blood using bacterial magnetic particles displaying protein G

Direct separation of target cells from mixed population, such as peripheral blood, umbilical cord blood, and bone marrow, is an essential technique for various therapeutic or diagnosis applications. In this study, novel particles were fabricated, and direct magnetic separation of immune cells from whole blood using such particles was performed. The magnetotactic bacterium Magnetospirillum magneticum AMB-1 synthesizes intracellular bacterial magnetic particles (BacMPs), and protein G was expressed on the surface of the BacMPs by gene fusion techniques with anchor proteins isolated from BacMP membrane. The BacMPs displaying protein G (protein G-BacMPs) had high binding capabilities to a wide range of antibody types, and various versions of protein G-BacMPs binding with different anti-CD monoclonal antibodies were constructed. Consequently, direct magnetic separation of immune cells from whole blood using protein G-BacMPs binding with anti-CD monoclonal antibodies was demonstrated. B lymphocytes (CD19+ cells) or T lymphocytes (CD3+ cells), which represent less than 0.05% in whole blood cells, were successfully separated at a purity level of more than 96%. This level was superior to that from previous reports using other magnetic separation approaches. The results of this study demonstrate the utility of protein G-BacMP and this particle may become a powerful tool for various therapeutic or diagnosis applications.

Quantum dots for live cell and in vivo imaging

In the past few decades, technology has made immeasurable strides to enable visualization, identification, and quantitation in biological systems. Many of these technological advancements are occurring on the nanometer scale, where multiple scientific disciplines are combining to create new materials with enhanced properties. The integration of inorganic synthetic methods with a size reduction to the nano-scale has lead to the creation of a new class of optical reporters, called quantum dots. These semiconductor quantum dot nanocrystals have emerged as an alternative to organic dyes and fluorescent proteins, and are brighter and more stable against photobleaching than standard fluorescent indicators. Quantum dots have tunable optical properties that have proved useful in a wide range of applications from multiplexed analysis such as DNA detection and cell sorting and tracking, to most recently demonstrating promise for in vivo imaging and diagnostics. This review provides an in-depth discussion of past, present, and future trends in quantum dot use with an emphasis on in vivo imaging and its related applications.

Nanoparticles for optical molecular imaging of atherosclerosis

Molecular imaging contributes to future personalized medicine dedicated to the treatment of cardiovascular disease, the leading cause of mortality in industrialized countries. Endoscope-compatible optical imaging techniques would offer a stand-alone alternative and high spatial resolution validation technique to clinically accepted imaging techniques in the (intravascular) assessment of vulnerable atherosclerotic lesions, which are predisposed to initiate acute clinical events. Efficient optical visualization of molecular epitopes specific for vulnerable atherosclerotic lesions requires targeting of high-quality optical-contrast-enhancing particles. In this review, we provide an overview of both current optical nanoparticles and targeting ligands for optical molecular imaging of atherosclerotic lesions and speculate on their applicability in the clinical setting.

Quantum dots for live cell and in vivo imaging

In the past few decades, technology has made immeasurable strides to enable visualization, identification, and quantitation in biological systems. Many of these technological advancements are occurring on the nanometer scale, where multiple scientific disciplines are combining to create new materials with enhanced properties. The integration of inorganic synthetic methods with a size reduction to the nano-scale has lead to the creation of a new class of optical reporters, called quantum dots. These semiconductor quantum dot nanocrystals have emerged as an alternative to organic dyes and fluorescent proteins, and are brighter and more stable against photobleaching than standard fluorescent indicators. Quantum dots have tunable optical properties that have proved useful in a wide range of applications from multiplexed analysis such as DNA detection and cell sorting and tracking, to most recently demonstrating promise for in vivo imaging and diagnostics. This review provides an in-depth discussion of past, present, and future trends in quantum dot use with an emphasis on in vivo imaging and its related applications.

Quantum dots for live cell and in vivo imaging

In the past few decades, technology has made immeasurable strides to enable visualization, identification, and quantitation in biological systems. Many of these technological advancements are occurring on the nanometer scale, where multiple scientific disciplines are combining to create new materials with enhanced properties. The integration of inorganic synthetic methods with a size reduction to the nano-scale has lead to the creation of a new class of optical reporters, called quantum dots. These semiconductor quantum dot nanocrystals have emerged as an alternative to organic dyes and fluorescent proteins, and are brighter and more stable against photobleaching than standard fluorescent indicators. Quantum dots have tunable optical properties that have proved useful in a wide range of applications from multiplexed analysis such as DNA detection and cell sorting and tracking, to most recently demonstrating promise for in vivo imaging and diagnostics. This review provides an in-depth discussion of past, present, and future trends in quantum dot use with an emphasis on in vivo imaging and its related applications.

Multifunctional Nanoparticles as Biocompatible Targeted Probes for Human Cancer Diagnosis and Therapy

The use of nanoparticles in biological application has been rapidly advancing toward practical applications in human cancer diagnosis and therapy. Upon linking the nanoparticles with biomolecules, they can be used to locate cancerous area as well as for traceable drug delivery with high affinity and specificity. In this review, we discuss the engineering of multifunctional nanoparticle probes and their use in bioimaging and nanomedicine.

Functionalized-quantum-dot-liposome hybrids as multimodal nanoparticles for cancer

Functionalized-quantum-dot-liposome (f-QD-L) hybrid nanoparticles are engineered by encapsulating poly(ethylene glycol)-coated QD in the internal aqueous phase of different lipid bilayer vesicles. f-QD-L maintain the QD fluorescence characteristics as confirmed by fluorescence spectroscopy, agarose gel electrophoresis, and confocal laser scanning microscopy. Cationic f-QD-L hybrids lead to dramatic improvements in cellular binding and internalization in tumor-cell monolayer cultures. Deeper penetration into three-dimensional multicellular spheroids is obtained for f-QD-L by modifying the lipid bilayer characteristics of the hybrid system. f-QD-L are injected intratumorally into solid tumor models leading to extensive fluorescent staining of tumor cells compared to injections of the f-QD alone. f-QD-L hybrid nanoparticles constitute a versatile tool for very efficient labeling of cells ex vivo and in vivo, particularly when long-term imaging and tracking of cells is sought. Moreover, f-QD-L offer many opportunities for the development of combinatory therapeutic and imaging (theranostic) modalities by incorporating both drug molecules and QD within the different compartments of a single vesicle.

Bioconjugated quantum dots for in vivo molecular and cellular imaging

Semiconductor quantum dots (QDs) are tiny light-emitting particles on the nanometer scale, and are emerging as a new class of fluorescent labels for biology and medicine. In comparison with organic dyes and fluorescent proteins, they have unique optical and electronic properties, with size-tunable light emission, superior signal brightness, resistance to photobleaching, and broad absorption spectra for simultaneous excitation of multiple fluorescence colors. QDs also provide a versatile nanoscale scaffold for designing multifunctional nanoparticles with both imaging and therapeutic functions. When linked with targeting ligands such as antibodies, peptides or small molecules, QDs can be used to target tumor biomarkers as well as tumor vasculatures with high affinity and specificity. Here we discuss the synthesis and development of state-of-the-art QD probes and their use for molecular and cellular imaging. We also examine key issues for in vivo imaging and therapy, such as nanoparticle biodistribution, pharmacokinetics, and toxicology.

The biocompatibility of quantum dot probes used for the targeted imaging of hepatocellular carcinoma metastasis

Semiconductor quantum dots (QDs) have several photo-physical advantages over organic dyes making them good markers in biomedical application. We used CdSe/ZnS QDs with maximum emission wavelength of 590nm (QD590) linked to alpha-fetoprotein (AFP) monoclonal antibody (Ab) to detect AFP in cytoplasm of human hepatocellular carcinoma (HCC) cell line HCCLM6. For the in vivo studies, we used QD-AFP-Ab probes for targeted imaging of human HCC xenograft growing in nude mice by injecting them into the tail vein. In addition, the cytotoxicity in vitro, the acute toxicity in vivo, the hemodynamics and tissue distribution of these probes were also investigated. The results in vitro and in vivo indicate that our QD-based probes have good stability, specificity and biocompatibility for ultrasensitive fluorescence imaging of molecular targets in our liver cancer model system.

Systematic investigation of preparing biocompatible, single, and small ZnS-Capped CdSe quantum dots with amphiphilic polymers

The successful transfer of nanoparticles between solvents is critical for many applications. We evaluated the impact of amphiphilic polymer composition on the size, transfer efficiency, and biocompatibility of tri-n-octylphosphine oxide/hexadecylamine-stabilized semiconductor ZnS-capped CdSe and CdS-capped CdTe(x)Se(1-x) quantum dots (QDs). We also investigated the adsorption of various proteins onto the surface of these QDs and studied the effect of surface chemistry on non-specific protein binding. The results from these studies will have implications in the design of QDs and other nanoparticles for biological and biomedical applications.

Semiconductor quantum dots and metal nanoparticles: syntheses, optical properties, and biological applications

We review the syntheses, optical properties, and biological applications of cadmium selenide (CdSe) and cadmium selenide-zinc sulfide (CdSe-ZnS) quantum dots (QDs) and gold (Au) and silver (Ag) nanoparticles (NPs). Specifically, we selected the syntheses of QDs and Au and Ag NPs in aqueous and organic phases, size- and shape-dependent photoluminescence (PL) of QDs and plasmon of metal NPs, and their bioimaging applications. The PL properties of QDs are discussed with reference to their band gap structure and various electronic transitions, relations of PL and photoactivated PL with surface defects, and blinking of single QDs. Optical properties of Ag and Au NPs are discussed with reference to their size- and shape-dependent surface plasmon bands, electron dynamics and relaxation, and surface-enhanced Raman scattering (SERS). The bioimaging applications are discussed with reference to in vitro and in vivo imaging of live cells, and in vivo imaging of cancers, tumor vasculature, and lymph nodes. Other aspects of the review are in vivo deep tissue imaging, multiphoton excitation, NIR fluorescence and SERS imaging, and toxic effects of NPs and their clearance from the body.