Green- and red-fluorescent nanospheres for the detection of cell surface receptors by flow cytometry

Preparation of fluorescence-encoded microbeads with large encoding capacities and application of suspension array technology

This research study reported a type of reconstructed polystyrene microbeads for fluorescence encoding in suspension array technology (SAT). The present study improved their surface functionalization and compatibility with dyes.

Temperature Response of Rhodamine B-Doped Latex Particles. From Solution to Single Particles

Nanoparticle-based temperature imaging is an emerging field of advanced applications. Herein, the sensitivity of the fluorescence of rhodamine B-doped latex nanoparticles toward temperature is described. Submicrometer size latex particles were prepared by a surfactant-free emulsion polymerization method that allowed a simple and inexpensive way to incorporate rhodamine B into the nanoparticles. Also, rhodamine B-coated latex nanoparticles dispersed in water were prepared in order to address the effect of the dye location in the nanoparticles on their temperature dependence. A better linearity of the temperature dependence emission of the rhodamine B-embedded latex particles, as compared to that of free rhodamine B dyes or rhodamine B-coated latex particles, is observed. Temperature-dependent fluorescence measurements by fluorescent confocal microscopy on individual rhodamine B-embedded latex particles were found similar to those obtained for fluorescent latex nanoparticles in solution, indicating that these nanoparticles could be good candidates to probe thermal processes as nanothermometers.

Nanotoxicity: An Interplay of Oxidative Stress, Inflammation and Cell Death

Nanoparticles are emerging as a useful tool for a wide variety of biomedical, consumer and instrumental applications that include drug delivery systems, biosensors and environmental sensors. In particular, nanoparticles have been shown to offer greater specificity with enhanced bioavailability and less detrimental side effects as compared to the existing conventional therapies in nanomedicine. Hence, bionanotechnology has been receiving immense attention in recent years. However, despite the extensive use of nanoparticles today, there is still a limited understanding of nanoparticle-mediated toxicity. Both in vivo and in vitro studies have shown that nanoparticles are closely associated with toxicity by increasing intracellular reactive oxygen species (ROS) levels and/or the levels of pro-inflammatory mediators. The homeostatic redox state of the host becomes disrupted upon ROS induction by nanoparticles. Nanoparticles are also known to up-regulate the transcription of various pro-inflammatory genes, including tumor necrosis factor-α and IL (interleukins)-1, IL-6 and IL-8, by activating nuclear factor-kappa B (NF-κB) signaling. These sequential molecular and cellular events are known to cause oxidative stress, followed by severe cellular genotoxicity and then programmed cell death. However, the exact molecular mechanisms underlying nanotoxicity are not fully understood. This lack of knowledge is a significant impediment in the use of nanoparticles in vivo. In this review, we will provide an assessment of signaling pathways that are involved in the nanoparticle- induced oxidative stress and propose possible strategies to circumvent nanotoxicity.

Core–shell microspheres by dispersion polymerization as promising delivery systems for proteins

Functional poly(methyl methacrylate) core-shell microspheres were prepared by dispersion polymerization. An appropriate selection of experimental parameters and in particular of the initiator and stabilizer amount and of the medium solvency power allowed a monodisperse sample as large as 600 nm to be prepared. To this purpose, low initiator concentration, high steric stabilizer amount and a low solvency power medium were employed. The microspheres present a core-shell structure in which the outer shell is constituted by the steric stabilizer which affords carboxylic groups able to interact with basic proteins, such as trypsin, whose adsorption is essentially driven by the carboxylic group density in the microsphere shell. Finally, fluorescent microspheres were prepared for biodistribution studies and shown to be readily taken up by the cells both in vitro and in vivo. These results suggest that these microspheres are promising delivery systems for the development of novel protein-based vaccines.

Poly(ethyl cyanoacrylate) colloidal particles tagged with Rhodamine 6G: preparation and physicochemical characterization

This paper describes the preparation and characterization of poly(ethyl cyanoacrylate) colloidal particles loaded with the organic fluorophore Rhodamine 6G. We studied the physicochemical properties of the colloidal particles: morphology, size-distribution, ζ-potential, fluorescent properties and photobleaching upon UV-light illumination. The properties of the obtained colloidal particles, as well as the dye loading efficiency, were found to depend on the concentrations of ethyl cyanoacrylate monomer and Rhodamine 6G in the polymerization medium. The fluorophore release from the colloidal particles in aqueous buffer is also studied.

Fluorescent DNA nanotags based on a self-assembled DNA tetrahedron

Progress in fluorescence detection and imaging technologies depends on the availability of fluorescent labels with strong light absorption/emission characteristics. We have synthesized intercalator dye arrays on a compact 3-dimensional DNA-tetrahedron nanostructure. The template tolerates the structural distortions introduced by intercalation and allows concentration of multiple fluorophores within a small volume, resulting in brightly fluorescent nanotags with effective extinction coefficients in the order of 10(6) M(-1) cm(-1). Efficient energy transfer from intercalated donor dyes to covalently attached acceptor dyes in the nanotags allows the emission wavelength to be shifted to the red relative to the excitation light, providing wavelength tunability. The compact nature of the supramolecular DNA tetrahedron also provides a protective medium for the fluorophores, leading to improved photostability and enhanced resistance to nuclease digestion, relative to one- or two-dimensional nanotags described previously.

Targeting cancer stem cells with monoclonal antibodies: a new perspective in cancer therapy and diagnosis

This review discusses some of the impacts that biotechnology, genomics and nanotechnology convergence should have on future cancer management, in particular, the development of innovative diagnostic and therapeutic approaches based on monoclonal antibodies (mAbs) and cancer stem cells. Emergent therapeutic strategies in cancer have been focusing on the use of mAbs to stimulate an immune response against tumors, to block signaling pathways, or to refine delivery of cytotoxic agents. Now that cancer stem cells are being identified and characterized in different tumor types, their relevance to cancer physiopathology is becoming evident, making them natural targets for mAb development. Cancer stem cells are postulated to be responsible for tumor development, metastasis and relapse after conventional therapies. Therefore, mAbs targeting specific antigens and related pathways altered in cancer stem cells should facilitate earlier diagnosis through molecular imaging techniques and more efficient destruction of tumor initiating cells, thus improving clinical outcome.

Biotinylation and characterization of Cryptococcus neoformans cell surface proteins

AIMS

To develop a novel procedure for isolating and characterizing cryptococcal cell-surface proteins using biotinylation, fluorescein isothiocyanate (FITC)-streptavidin, flow cytometry and associated ligand-receptor analysis, confocal microscopy and electrophoretic separation.

METHODS AND RESULTS

Cell proteins of both acapsulate and encapsulated Cryptococcus neoformans cells were labelled using sulfo-NHS-biotin which, in turn, was complexed with FITC-streptavidin. Resulting cell population fluorescence supported visualization of cell-surface protein distribution by confocal microscopy, as well as evaluation of protein exposure by flow cytometry and the calculation of the ligand-binding determinants EC(50), F(max) and H(n). Biotinylation of cell-surface proteins also supported their isolation by affinity chromatography and characterization by SDS/PAGE. Ligand-binding determinants, such as EC(50) values, indicated that acapsulate and stationary phase cells have greatest affinity for biotin. F(max) values demonstrated greatest protein exposure among stationary phase cells; in turn, encapsulated cells expose more protein than acapsulate counterparts. H(n) values of below unity potentially confirm the complex multi-receptor nature of biotin binding to cryptococcal cell surfaces under investigation. Fluorescence visualization showed marked but localized fluorescence indicative of protein exposure around sites of cell division. In turn, biotinylation of cell-surface proteins and their release under reducing conditions demonstrated at least two noncovalently linked proteinaceous entities, of 43 and 57 kDa, exposed on acapsulate cryptococcal cell walls.

CONCLUSIONS

A novel method for identifying, in situ, cell-surface proteins exposed by C. neoformans was established. This novel technique was successfully implemented using both acapsulate and encapsulated C. neoformans cells, both were found to have dynamic and markedly localized protein distribution around sites of cell division and associated cell wall trauma.

SIGNIFICANCE AND IMPACT OF THE STUDY

A novel procedure, employing a versatile combination of flow cytometry, ligand-receptor analysis, confocal microscopy and biotinylation, supported the characterization and isolation of cryptococcal cell-surface proteins.

Tandem dye acceptor used to enhance upconversion fluorescence resonance energy transfer in homogeneous assays

In fluorescence resonance energy transfer (FRET)-based assays, spectral separation of acceptor emission from donor emission is a common problem affecting the assay sensitivity. The challenge derives from small Stokes shifts characteristic to conventional fluorescent dyes resulting in leakage of donor emission to the measurement window intended only to collect the acceptor emission. We have studied a FRET-based homogeneous bioaffinity assay utilizing a tandem dye acceptor with a large pseudo-Stokes shift (139 nm). The tandem dye was constructed using B-phycoerythrin as an absorber and multiple Alexa Fluor 680 dyes as emitters. As a donor, we employed upconverting phosphor particles, which uniquely emit at visible wavelengths under low-energy infrared excitation enabling the fluorescence measurements free from autofluorescence even without time-resolved detection. With the tandem dye, it was possible to achieve four times higher signal from a single binding event compared to the conventional Alexa Fluor 680 dye alone. Tandem dyes are widely used in cytometry and other multiplex purposes, but their applications can be expanded to fluorescence-based homogeneous assays. Both the optimal excitation and emission wavelengths of tandem dye can be tuned to a desired region by choosing appropriate fluorophores enabling specifically designed acceptor dyes with large Stokes shift.

The Enhancement Effect of Gold Nanoparticles in Drug Delivery and as Biomarkers of Drug-Resistant Cancer Cells

The enhancement effect of 3-mercaptopropionic acid capped gold nanoparticles (NPs) in drug delivery and as biomarkers of drug-resistant cancer cells has been demonstrated through fluorescence microscopy and electrochemical studies. The results of cell viability experiments and confocal fluorescence microscopy studies illustrate that these functionalized Au NPs could play an important role in efficient drug delivery and biomarking of drug-resistant leukemia K562/ADM cells. This could be explored as a novel strategy to inhibit multidrug resistance in targeted tumor cells and as a sensitive method for the early diagnosis of certain cancers. Our observations also indicate that the interaction between the functionalized Au NPs and biologically active molecules on the surface of leukemia cells may contribute the observed enhancement in cellular drug uptake.

Nanoparticles: pharmacological and toxicological significance

Nanoparticles are tiny materials (<1000 nm in size) that have specific physicochemical properties different to bulk materials of the same composition and such properties make them very attractive for commercial and medical development. However, nanoparticles can act on living cells at the nanolevel resulting not only in biologically desirable, but also in undesirable effects. In contrast to many efforts aimed at exploiting desirable properties of nanoparticles for medicine, there are limited attempts to evaluate potentially undesirable effects of these particles when administered intentionally for medical purposes. Therefore, there is a pressing need for careful consideration of benefits and side effects of the use of nanoparticles in medicine. This review article aims at providing a balanced update of these exciting pharmacological and potentially toxicological developments. The classes of nanoparticles, the current status of nanoparticle use in pharmacology and therapeutics, the demonstrated and potential toxicity of nanoparticles will be discussed.

High-performance fluorescent particles prepared via miniemulsion polymerization

Highly fluorescent polymer particles were prepared with Eu beta-diketonates complex as a fluorophore by miniemulsion polymerization technique. Eu beta-diketonates complex has a long decay time, a large Stokes shift, and very narrow emission bands in comparison with other organic fluorescent compounds. Aqueous miniemulsion was prepared by mixing monomer, crosslinker, hydrophobe, and Eu beta-diketonates complex and then putting the mixture into an aqueous solution of surfactant, followed by ultrasonication. An aqueous solution of initiator was added to the miniemulsion to obtain fluorescent polymer particles, which were monodispersed without aggregation. Particle size was decreased to deca-nano scale by increasing the amount of surfactant. Fluorescent intensity was increased by using Eu beta-complex coordinated with additional ligand. Further fluorescence quantum yields and fluorescent properties in the presence of DNA were investigated to the confirm superiority of Eu beta-diketonates complexes in polymer particles.

Preparation of highly monodisperse poly(methyl methacrylate) particles incorporating fluorescent rhodamine 6G for colloidal crystals

Soap-free emulsion polymerization was extended to preparation of monodisperse poly(methyl methacrylate) (PMMA) particles incorporating rhodamine 6G (R6G) fluorescent molecules. The polymerization was conducted in the presence of an anionic monomer, p-styrenesulfonate (NaSS), which improved dispersion stability of the polymer particles. NaSS concentrations was ranged up to 2 mol/m3 H2O in the polymerization at 0.5 kmol/m3 H2O methyl methacrylate (MMA) monomer and 5 mol/m3 H2O potassium persulfate (KPS) initiator for R6G concentrations from 0.1 to 10 mol/m3-polymer. At R6G concentrations lower than 1.0 mol/m3-polymer, PMMA particles were highly monodisperse and incorporated most R6G molecules. The average sizes of PMMA particles were in a rage of 160-300 nm, and decreased with the concentration of NaSS. The high monodispersity of the particles enabled the fabrication of colloidal crystals of the particles with a vertical deposition method.

Studies on the potential use of CD38 expression as a marker for the efficacy of anti-retroviral therapy in HIV-1-infected patients in Thailand

The monitoring of the efficacy of anti-retroviral therapy (ART) is becoming an important issue in the developing world. The current use of CD4 counts, plasma viral loads, and monitoring of drug-resistant viruses are at present either uninformative or costly. Thus, more new cost-effective and practical techniques need to be established and implemented. Towards this goal, our lab has carried out studies on the potential use of CD38 frequency and density expression by flow analysis as a means to assess the efficacy of ART. Results of our studies using whole blood sample from normal healthy donors indicate that CD38 is expressed by a high frequency of not only CD4+ and CD8+ T cells but also most hematopoietic cell lineages analyzed. Detailed studies of CD38 expression along with other cell surface markers using whole blood sample from HIV-1-infected patients showed that the most discriminating change was the increased frequency and density of CD38 expression by CD3+CD8+ T cells. Of importance was our preliminary finding that a reversal of the increased frequency and density of CD38 expression by CD8+ T cells only appeared in the whole blood sample from patients who were responders to ART but not those who were drug failures. These initial data provide a platform and incentive for larger cohort studies including prospective pre- and post-ART for the institution of such monitoring techniques in resource limited settings.

Fluorescent nanometer microspheres as a reporter for sensitive detection of simulants of biological threats using multiplexed suspension arrays

We succeeded in using 40 nm FRET (fluorescence resonance energy transfer) microspheres conjugated to antibodies as the fluorescent reporters to perform the multiplexing suspension array measurements on two simulants of biological threats, ricin (A chain) and a crude spore preparation of Bacillus globigii (Bg). The microspheres were impregnated with two types of fluorophores in equal number (approximately 140 fluorophores in total per microsphere) and displayed bright PE-like fluorescence via a fluorescence resonance energy transfer mechanism. Activated microspheres (aldehyde groups) were directly coupled to antibodies and used to form sandwich-type immunoassays in a suspension array. For the crude preparations of Bg, the assay sensitivity using antibody-conjugated microspheres is an order of magnitude higher than that using the conventional fluorescent reporter, R-phycoerythrin (PE). Using the microspheres, Bg at the concentration of 5 ng/mL can be easily detected. For ricin, the assay sensitivity was similar to that obtained using PE as the reporter, but washing the reaction mixtures resulted in the fluorescence signals that were 2-3 times higher compared to those using PE. Ricin at a concentration of 1 ng/mL can be readily identified. Importantly, the two simulants do not interfere with each other in the multiplexing experiments. The 40 nm FRET microspheres are a new sensitive alternative as fluorescent reporters for detection in suspension arrays.

Design and validation of a bifunctional ligand display system for receptor targeting

Here we developed a bacteriophage display particle designed to serve as a bifunctional entity that can target tumors while delivering an agent. We engineered a chimera phage vector containing a pIII-displayed alphav integrins-targeting moiety and a pVIII-displayed streptavidin binding adaptor moiety. By using the chimeric phage particle, targeting of alphav integrins on cells in culture and tumor-related blood vessels was shown through different applications, including luminescent quantum dots localization, surface plasmon resonance-based binding detection, and an in vivo tumor model. The strategy validated here will accelerate the discovery and characterization of receptor-ligand binding events in high throughput, and cell-specific delivery of diagnostics or therapeutics to organs of choice without the need for chemical conjugation.

Detection of low-abundance membrane markers by immunofluorescence—a comparison of alternative high-sensitivity methods and reagents

The analysis of membrane molecules using antibodies detected by immunofluorescence staining and flow cytometry is used widely in research and diagnostic immunology. Conventional staining techniques readily detect molecules present at concentrations of around 2000 molecules per cell, but some molecules are expressed and function at much lower abundance. We described previously a method for the detection of molecules present at 100 molecules per cell or less based on the use of phycoerythrin as the fluorophore, a three-layer amplification process, and careful selection of available reagents. In recent years, a number of new reagents, fluorophores and kits, have become available, some of them intended for high-sensitivity applications. In this paper, a number of these reagents have been compared with the published method. While some of the reagents gave variable results or high nonspecific staining in our hands, several reagents were comparable with the published method. Furthermore, the new fluorophores allow improved simultaneous detection of two low-abundance markers.

Nanoparticles in cancer therapy and diagnosis

Numerous investigations have shown that both tissue and cell distribution profiles of anticancer drugs can be controlled by their entrapment in submicronic colloidal systems (nanoparticles). The rationale behind this approach is to increase antitumor efficacy, while reducing systemic side-effects. This review provides an update of tumor targeting with conventional or long-circulating nanoparticles. The in vivo fate of these systems, after intravascular or tumoral administration, is discussed, as well as the mechanism involved in tumor regression. Nanoparticles are also of benefit for the selective delivery of oligonucleotides to tumor cells. Moreover, certain types of nanoparticles showed some interesting capacity to reverse MDR resistance, which is a major problem in chemotherapy. The first experiments, aiming to decorate nanoparticles with molecular ligand for 'active' targeting of cancerous cells, are also discussed here. The last part of this review focus on the application of nanoparticles in imaging for cancer diagnosis.

Current status of flow cytometry in cell and molecular biology

This review summarizes recent developments in flow cytometry (FC). It gives an overview of techniques currently available, in terms of apparatus and sample handling, a guide to evaluating applications, an overview of dyes and staining methods, an introduction to internet resources, and a broad listing of classic references and reviews in various fields of interest, as well as some recent interesting articles.

Utilization of kinetically enhanced monovalent binding affinity by immunoassays based on multivalent nanoparticle-antibody bioconjugates

The monovalent binding affinity of high binding site density nanoparticle-antibody bioconjugates is shown to exceed the intrinsic affinity of the original, monoclonal antibody. The nanoparticle-antibody bioconjugates were prepared by covalent coupling of antibodies to long-lifetime fluorescent, europium(III) chelate nanoparticles, 107 nm in diameter. Experiments were carried out in standard microtitration wells to determine solid-phase association and dissociation rate constants, nonspecific binding, and affinity constants of the various binding site density nanoparticle-antibody bioconjugates and the conventionally labeled monoclonal antibody. The affinity constant for monovalent binding of a high binding site density bioconjugate (5.4 x 10(10) M(-1)) was 8-fold higher than the intrinsic affinity of the antibody (6.6 x 10(9) M(-1)). The separately measured association (2.5 x 10(6) M(-1) s(-1)) and dissociation (3.7 x 10(-5) s(-1)) rate constants of the bioconjugate were 2-fold higher and 4-fold lower, respectively, compared to the antibody. The dependence of the association rate constant of the density of the binding sites enhanced the kinetics and the affinity of the high binding site density bioconjugates. The nanoparticle labels with high specific activity, low nonspecific binding, and enhanced binding affinity of the nanoparticle-antibody bioconjugates contribute to the design of the next generation immunoassays with extreme sensitivity.