Immunomicrospheres: reagents for cell labeling and separation

Microplastic pollution in soils, plants, and animals: A review of distributions, effects and potential mechanisms

Increasing production of synthetic plastics and poor management of plastic wastes have dramatically increased the amount of plastics in the environment. In 2014, at the first United Nations Environment Assembly, marine plastic waste pollution was listed as one of the 10 most pressing environmental issues. In addition, there is much plastic waste in terrestrial ecosystems due to substantial residues from agricultural mulching and packing. As a recently recognized pollutant, microplastics (MPs) have attracted significant attention from the public and various governments. Concentrations of MPs in the environment vary among locations, from <100 to >1 × 10⁶ particles per cubic meter. Many studies have addressed the impacts and potential mechanisms of MPs on the environment and organisms. Humans and other organisms can ingest or carry MPs in a variety of passive ways and these MPs can have a range of negative effects on metabolism, function, and health. Additionally, given their large surface area, MPs can sorb various pollutants, including heavy metals and persistent organic pollutants, with serious implications for animals and human wellbeing. However, due to their complexity and a lack of accurate determination methods, the systematic impacts of MP pollution on whole foodwebs are not clearly established. Therefore, this review summarizes current research advances in MP pollution, particularly the impact of MPs on soils, plants, and animals, and proposes potential future research prospects to better characterize MPs.

An overview of microplastic and nanoplastic pollution in agroecosystems

Microplastics and nanoplastics are emerging pollutants of global importance. They are small enough to be ingested by a wide range of organisms and at nano-scale, they may cross some biological barriers. However, our understanding of their ecological impact on the terrestrial environment is limited. Plastic particle loading in agroecosystems could be high due to inputs of some recycled organic waste and plastic film mulching, so it is vital that we develop a greater understanding of any potentially harmful or adverse impacts of these pollutants to agroecosystems. In this article, we discuss the sources of plastic particles in agroecosystems, the mechanisms, constraints and dynamic behaviour of plastic during aging on land, and explore the responses of soil organisms and plants at different levels of biological organisation to plastic particles of micro and nano-scale. Based on limited evidence at this point and understanding that the lack of evidence of ecological impact from microplastic and nanoplastic in agroecosystems does not equate to the evidence of absence, we propose considerations for addressing the gaps in knowledge so that we can adequately safeguard world food supply.

Synthesis and Characterization of Polystyrene Core/Polyacrolein Shell Latexes

The poly(styrene/acrolein) latexes were synthesized in an emul sifier-free emulsion-precipitation polymerization. Monodisperse particles from 0.30 μm to 0.52 μm, depending on the acrolein monomer feed, were obtained. More acrolein in the monomer feed yielded latex particles with smaller di ameters. Analyses indicate that the particles have a core-shell morphology. The core is rich in the hydrophobic (polystyrene) component whereas the shell is composed mainly of hydrophilic polyacrolein. Significant changes in polyacro lein in the latexes (from 0.03 to 0.28) has less influence on the composition of the shell (from 0.5 to 0.84, respectively). The surface of the latex particles is smooth and can be penetrated by 2,4-dinitrophenyl hydrazine to the depth from 1.5 to 3.5 Å. These poly(styrene/acrolein) latexes are capable of binding ca. 3 mg of human globulins or ca. 1 mg of human serum albumin on 1 m2 of the latex surface.

Fast and highly efficient purification of 6×histidine-tagged recombinant proteins by Ni-decorated MnFe2O4@SiO2@NH2@2AB as novel and efficient affinity adsorbent magnetic nanoparticles

A fast, convenient, and inexpensive method for the preparation of MnFe₂O₄@SiO₂@NH₂@2AB-Ni magnetic nanoparticles as an efficient and novel affinity adsorbent for the highly specific capture of 6×histidine-tagged recombinant protein-A is reported.

Benzoboroxole-functionalized magnetic core/shell microspheres for highly specific enrichment of glycoproteins under physiological conditions

Efficient enrichment of specific glycoproteins from complex biological samples is of great importance towards the discovery of disease biomarkers in biological systems. Recently, phenylboronic acid-based functional materials have been widely used for enrichment of glycoproteins. However, such enrichment was mainly carried out under alkaline conditions, which is different to the status of glycoproteins in neutral physiological conditions and may cause some unpredictable degradation. In this study, on-demand neutral enrichment of glycoproteins from crude biological samples is accomplished by utilizing the reversible interaction between the cis-diols of glycoproteins and benzoboroxole-functionalized magnetic composite microspheres (Fe3O4/PAA-AOPB). The Fe3O4/PAA-AOPB composite microspheres are deliberately designed and constructed with a high-magnetic-response magnetic supraparticle (MSP) core and a crosslinked poly(acrylic acid) (PAA) shell anchoring abundant benzoboroxole functional groups on the surface. These nanocomposites possessed many merits, such as large enrichment capacity (93.9 mg/g, protein/beads), low non-specific adsorption, quick enrichment process (10 min) and magnetic separation speed (20 s), and high recovery efficiency. Furthermore, the as-prepared Fe3O4/PAA-AOPB microspheres display high selectivity to glycoproteins even in the E. coli lysate or fetal bovine serum, showing great potential in the identify of low-abundance glycoproteins as biomarkers in real complex biological systems for clinical diagnoses.

Uniform magnetic core/shell microspheres functionalized with Ni2+-iminodiacetic acid for one step purification and immobilization of his-tagged enzymes

A facile approach has been developed to synthesize Fe3O4/PMG (poly (N,N'-methylenebisacrylamide-co-glycidyl methacrylate)) core/shell microspheres using distillation-precipitation polymerization. Treating PMG shell with iminodiacetic acid (IDA) and Ni2+ yields composite microspheres of Fe3O4/PMG/IDA-Ni2+. The Ni2+ ions loaded on the surface of microspheres provide abundant docking sites for immobilization of histidine-tagged proteins. The high saturation magnetization of Fe3O4/PMG (23 emu/g), determined by vibrating sample magnetometer (VSM), allows an easy separation of the microspheres from solution under an external magnetic field. The composite microspheres were used to purify two His-tagged cellulolytic enzymes (Cel48F and Cel9G) directly from crude cell lysates with high binding affinity, capacity, and specificity. The microspheres can be recycled for many times without significant loss of binding capacity to enzymes. The immobilized enzymes on the surface of microspheres well retain their biological activities in degradation of cellulose. These materials show great potential in the biomedical and biotechnological applications that require low-cost purification of recombinant proteins and instant enzyme immobilization at an industrial scale.

Selective individual primary cell capture using locally bio-functionalized micropores

Background

Solid-state micropores have been widely employed for 6 decades to recognize and size flowing unlabeled cells. However, the resistive-pulse technique presents limitations when the cells to be differentiated have overlapping dimension ranges such as B and T lymphocytes. An alternative approach would be to specifically capture cells by solid-state micropores. Here, the inner wall of 15-µm pores made in 10 µm-thick silicon membranes was covered with antibodies specific to cell surface proteins of B or T lymphocytes. The selective trapping of individual unlabeled cells in a bio-functionalized micropore makes them recognizable just using optical microscopy.

Methodology/Principal Findings

We locally deposited oligodeoxynucleotide (ODN) and ODN-conjugated antibody probes on the inner wall of the micropores by forming thin films of polypyrrole-ODN copolymers using contactless electro-functionalization. The trapping capabilities of the bio-functionalized micropores were validated using optical microscopy and the resistive-pulse technique by selectively capturing polystyrene microbeads coated with complementary ODN. B or T lymphocytes from a mouse splenocyte suspension were specifically immobilized on micropore walls functionalized with complementary ODN-conjugated antibodies targeting cell surface proteins.

Conclusions/Significance

The results showed that locally bio-functionalized micropores can isolate target cells from a suspension during their translocation throughout the pore, including among cells of similar dimensions in complex mixtures.

Lateral flow colloidal gold-based immunoassay for pesticide

In recent years, immunochromatographic lateral flow test strips are used as a popular diagnostic tool. There are two formats (noncompetitive and competitive) in gold-based immunoassay. Noncompetitive gold-based immunoassay also called sandwich assay is applied for the detection of large molecular mass. For small molecular mass such as pesticide, competitive format of lateral flow colloidal gold-based immunoassay is described in this chapter. The preparation of gold colloidal and the conjugation between antibody and gold colloidal are described. Hi-flow plus nitrocellulose membranes are separately coated with goat anti-rabbit IgG (control line) and hapten-OVA conjugate (test line). Thus, the degree of intensity of color of the test line is the reverse of the concentration of pesticide in the sample and the visual result is immediately observable. Colloidal gold-based immunoassay can also be applied for multianalysis in one test strip if the detected targets show different physico-chemical properties and their haptens show great differences in chemical structure.

Facile route to enzyme immobilization: core-shell nanoenzyme particles consisting of well-defined poly(methyl methacrylate) cores and cellulase shells

A one-step method for preparing cellulase-immobilized nanoparticles that consist of well-defined poly(methyl methacrylate) (PMMA) cores and cellulase shells has been developed. The core-shell nanoparticles are synthesized from a direct graft copolymerization of methyl methacrylate (MMA) from cellulase in an aqueous medium. Particle formation strongly depends on the surface nature of the cellulase (e.g., pH of reaction media) and MMA to cellulase weight ratio. Under optimized conditions, high MMA conversions (>90%) were achieved, and the PMMA-cellulase nanoparticles produced were very stable with narrow size distributions ( Dv/Dn < 1.20). Particle sizes in the range between 80 and 124 nm (volume average diameter) could be tailored by a variation of cellulase concentration. Transmission electron microscopy micrographs revealed that the nanoparticle had a well-defined PMMA core which was evenly coated with cellulase shell. Study of cellulase activity of the PMMA-cellulase nanoparticles indicated that even though activity of immobilized cellulase on the nanoparticles was 41% less than that of the native cellulase after the polymerization, the immobilized cellulase showed improved properties such as broader working pH range and better thermal stability. Other important advantages of this approach include that the PMMA-cellulase nanoparticles could be produced in high concentrations (up to 18% w/w solids content) and the nanoparticles have thick and evenly distributed enzyme shells. Thus, this method may provide a new commercially viable route to the immobilization of thermally stable enzyme to form nanoenzyme particles.

Gold nanoparticles bound on microgel particles and their application as an enzyme support

Submicron-sized poly(N-isopropyl acrylamide)/polyethyleneimine core-shell microgels were prepared in aqueous media by using tert-butyl hydroperoxide (TBHP) as an initiator, and then the gold nanoparticles (∼8 nm) were formed on the surface of the microgels. The amino groups on the polyethyleneimine (PEI) chains act as the binder for the assembly of the gold nanoparticles/microgel complex. In aqueous media the microgels are highly stable with the gold nanoparticles on their extended PEI chains, and this multi-scale nanoparticle complex can be recovered from water and redispersed in water. The nanogold/microgel particles were conjugated with the enzymes horseradish peroxidase (HRP) and urease. It is found that under identical assay conditions the enzyme/nanogold/microgel systems exhibit enhanced biocatalytic activity over free enzymes in solution, especially at lower enzyme concentrations. In addition, compared to free HRP, the HRP/nanogold/microgel systems show higher activity at varied pHs and temperatures, as well as higher storage stability. Thus the novel nanogold/microgel particles can serve as an excellent support for enzymes.

Thermodynamic and kinetic analysis of the interaction between hepatitis B surface antibody and antigen on a gold electrode modified with cysteamine and colloidal gold via electrochemistry

Hepatitis B surface antibody (HBsAb) was immobilized to the surface of a gold electrode modified with cysteamine and colloidal gold as matrices to detect hepatitis B surface antigen (HBsAg). Differential pulse voltammetry (DPV) method was used for the investigation of the specific interaction between the immobilized HBsAb and HBsAg in solution, which was followed as a change of peak current in DPV with time. With the modified gold electrode, the differences in affinity of HBsAb with HBsAg at the temperatures of 37 and 40 degrees C were easily distinguished and the kinetic rate constants (k(ass) and k(diss)) and kinetic affinity constant K were determined from the curves of current versus time. In addition, the thermodynamic constants, DeltaG, DeltaH and DeltaS, of the interaction at 37 degrees C were calculated, which were -56.65, -64.54 and -25.45 kJ mol(-1), respectively.

Synthesis and characterization of europium(III) nanoparticles for time-resolved fluoroimmunoassay of prostate-specific antigen

Recent advances in the fabrication and bioconjugation of nanometre-sized lanthanide(III) chelate particles have led to robust high specific activity labels. This paper describes the synthesis and characterization of lanthanide(III) nanoparticle labels and the use of a nanoparticle in a bioaffinity assay system. Two europium(III) nanoparticles were prepared using an extremely simple, inexpensive and fast agglomeration strategy. A silica-stabilized nanoparticle was synthesized from hydrophobic tris(dibenzoylmethane)-mono(phenanthroline) and tris(dibenzoylmethane)-mono(5-aminophenanthroline) europium(III) chelates in aqueous solution. In addition, a naphthoyl trifluoroacetone:tri-n-octylphosphineoxide:sodium dodecyl sulfate europium(III) complex was agglomerated in water. The particle sizes ranged from 62 to 140 nm in diameter. The silica-stabilized particle was further coated with a monoclonal antibody. The analytical performance of the bioconjugated nanoparticle label was evaluated in a model sandwich immunoassay of prostate-specific antigen. The detection limit of human prostate-specific antigen was 28 ng l(-1), 850 fM, in a microtiter plate format using time-resolved fluorometry. The coefficient of variation ranged from 1 to 9%. The novel nanoparticle label improves the specific activity of existing lanthanide(III) nanoparticle labels and simplifies the preparation route. In addition, prepared high-density nanoparticle labels using lanthanide(III) chelates or other specific fluorochromes have potential applications in a number of other fields.

Application of electrochemical impedance spectroscopy for monitoring allergen–antibody reactions using gold nanoparticle-based biomolecular immobilization method

Gold nanoparticles were used to enhance the immobilization amount and retain the immunoactivity of recombinant dust mite allergen Der f2 immobilized on a glassy carbon electrode (GCE). The interaction between allergen and antibody was studied by electrochemical impedance spectroscopy (EIS). Self-assembled Au colloid layer (ø=16nm) deposited on (3-mercaptopropyl)trimethoxysilane (MPTS)-modified GCE offered a basis to control the immobilization of allergen Der f2. The impedance measurements were based on the charge transfer kinetics of the [Fe(CN)(6)](3-/4-) redox pair, compared with bare GCE, the immobilization of allergen Der f2 and the allergen-antibody interaction that occurred on the electrode surface altered the interfacial electron transfer resistance and thereby slowed down the charge transfer kinetics by reducing the active area of the electrode or by preventing the redox species in electrolyte solution from approaching the electrode. The interactions of allergen with various concentrations of monoclonal antibody were also monitored through the change of impedance response. The results showed that the electron transfer resistance increased with increasing concentrations of monoclonal antibody.

Composite Magnetic Particles as Carriers for Laccase fromTrametes versicolor

In this paper we report a study of laccase immobilisation on different kinds of carrier particles. The immobilisation of enzyme on the particle surface with respect to the immobilisation efficiency and the properties of the immobilised enzymes is discussed. The immobilisation of laccase on polystyrene particles bearing reactive beta-diketone groups is characterised by high efficiency, but grafting of the enzyme increases the stability of the colloidal system, which makes the separation/purification procedure difficult. Additionally, the extreme colloidal stability of the immobilisates hinders the application of such particles with immobilised enzymes in some applications where the recycling of the enzyme should be performed. It has been found that hybrid PS-AAEM particles equipped with maghemite show similar immobilisation efficiency to that of their analogues without maghemite and can additionally be manipulated in magnetic fields. The activity of the immobilised laccase is much higher in the pH region 5-7 and the temperature range 50-70 degrees C as compared with that of the free enzyme. Immobilised enzymes also exhibit much better storage stability.

Differential interaction of magnetic nanoparticles with tumor cells and peripheral blood cells

PURPOSE

The separation of tumor cells from healthy cells is a vital problem in oncology and hematology, especially from peripheral blood. Magnetic assisted cell sorting (MACS) is a possibility to fulfill these needs.

METHODS

Tumor cell lines and leukocytes from peripheral blood were incubated with carboxymethyl dextran-coated magnetic nanoparticles under various conditions and separated by MACS.

RESULTS

We studied the interaction of magnetic nanoparticles devoid of antibodies with healthy and tumor cells. The magnetic nanoparticles interact with tumor cells and leukocytes and are located predominantly within the cell cytoplasm. Incubation of cell culture cells with magnetic nanoparticles led to a labeling of these cells without reduced biological properties for at least 14 days. The interaction of the magnetic nanoparticles with cells depends on several factors. The ionic strength (osmolality) of the solvent plays an important role. We could show that an increase in osmolality led to a dramatic reduction of labeled leukocytes. Tumor cells, however, are mildly affected. This could be detected not only in pure cultures of tumor cells or leukocytes but also in mixed cell populations.

CONCLUSION

This observation gives us the opportunity to selectively label and separate tumor cells but not leukocytes from the peripheral blood.

Colloidal gold nanoparticle modified carbon paste interface for studies of tumor cell adhesion and viability

A non-toxic biomimetic interface for immobilization of living cells and electrochemical exogenous effect study of cell viability was constructed by mixing colloidal gold nanoparticles in carbon paste. A new approach to study the effects of anti-tumor drug and other exogenous factors on cell viability was proposed. The nanoparticles were efficient for preserving the activity of immobilized living cells and preventing their leakage from the electrode surface. The immobilized living AsPC-1 cells (pancreatic adenocarcinoma cells derived from ascites) exhibited an irreversible voltammetric response related to the oxidation of guanine. The presence of guanine was verified by liquid chromatography-mass spectrometry. The contents of guanine in cytoplasm of each AsPC-1 and normal pancreatic cell were detected to be 370 and 22amol, respectively. The cytotoxic effect of adriamycin resulted in a decrease in peak current of guanine. The optimal exogenous factors that affected cell viability, including pH, temperature and salt concentration of electrolyte, were just consistent with cell growth conditions in culture. This simple and rapid method could be applied for the electrochemical investigation of exogenous effect and characterization of the viability of living cells.

A cell behavior screen: identification, sorting, and enrichment of cells based on motility

BACKGROUND

Identifying and isolating cells with specific behavioral characteristics will facilitate the understanding of the molecular basis regulating these behaviors. Although many approaches exist to characterize cell motility, retrieving cells of specific motility following analysis remains challenging.

RESULTS

Cells migrating on substrates coated with fluorescent microspheres generate non-fluorescent tracks as they move and ingest the spheres. The area cleared by each cell allows for quantitation of single cell and population motility; because individual cell fluorescence is proportional to motility, cells can be sorted according to their degree of movement. Using this approach, we sorted a glioblastoma cell line into high motility and low motility populations and found stable differences in motility following sorting.

CONCLUSION

We describe an approach to identify, sort, and enrich populations of cells possessing specific levels of motility. Unlike existing assays of cell motility, this approach enables recovery of characterized cell populations, and can enable screens to identify factors that might regulate motility differences even within clonal population of cells.

Gold-nanoparticle-assisted oligonucleotide immobilisation for improved DNA detection

Colloidal gold nanoparticles are investigated as a potential scaffold for the assisted immobilisation of probe oligonucleotides on silicon surfaces. A preliminary study is devoted to the examination of the immobilisation of DNA-modified gold nanoparticles as a function of time, concentration, salt and pH. The DNA-modified nanoparticles self-assembled onto solid surfaces in a three-dimensional self-assembled architecture. The functionalised surfaces are evaluated in diagnostic assays, where their potential to improve the efficiency of the hybridisation reaction is tested. The system utilising DNA-modified nanoparticles produced an enhancement in the hybridisation efficiency and the sensitivity limit by a factor 10 to 100 as compared to a conventional DNA immobilisation system on a planar surface.

Immobilization and biocatalytic activity of fungal protease on gold nanoparticle-loaded zeolite microspheres

Gold nanoparticles are excellent biocompatible surfaces for the immobilization of enzymes. However, separation of the gold nanoparticle-enzyme bioconjugate material from the reaction medium is often difficult. In this study, we investigate the assembly of the gold nanoparticles on the surface of the amine-functionalized zeolite microspheres in the formation of zeolite-gold nanoparticle "core-shell" structures and, thereafter, the use of this structure in immobilization of fungal protease. The assembly of gold nanoparticles on the zeolite surface occurs through the amine groups present in 3-aminopropyltrimethoxysilane (3-APTS). The fungal proteases bound to the massive "core-shell" structures were easily separated from the reaction medium by mild centrifugation and exhibited excellent reuse characteristics. The biocatalytic activity of fungal protease in the bioconjugate was marginally enhanced relative to the free enzyme in solution. The bioconjugate material also showed significantly enhanced pH and temperature stability and a shift in the optimum temperature of operation.

Application of impedance spectroscopy for monitoring colloid Au-enhanced antibody immobilization and antibody–antigen reactions

We used colloidal Au to enhance the amount of antibody immobilized on a gold electrode and ultimately monitored the interaction of antigen-antibody by impedance measurement. Self-assembly of 6 nm (diameter) colloidal Au onto the self-assembled monolayers (SAMs) of 4-aminothiophenol modified gold electrode resulted in an easier attachment of antibody. The redox reactions of [Fe(CN)6](4-)/[Fe(CN)6](3-) on the gold surface were blocked due to the procedures of self-assembly of 4-aminothiophenol and antibody immobilization, which were investigated by cyclic voltammetry and impedance spectroscopy. The interaction of antigen with grafted antibody recognition layers was carried out by soaking the modified electrode into a phosphate buffer at pH 7.4 with various concentrations of antigen at 37 degrees C for 30 min. The antibody recognition layers and their interactions with various concentrations of antigen could be detected by measurements of the impedance change. The results show that this method has good correlation for detection of Hepatitis B virus surface antigen in the range of 0.5-200 microg/l and a detection limit of about 50 ng/l.

Multistage magnetic and electrophoretic extraction of cells, particles and macromolecules

Improved techniques for separating cells, particles, and macromolecules (proteins) are increasingly important to biotechnology because separation is frequently the limiting factor for many biological processes. Manufacturers of new enzymes and pharmaceutical products require improved methods for recovering intact cells and intracellular products. Similarly isolation, purification, and concentration of many biomolecules produced in fermentation processes is extremely important. Often such downstream processing contributes a large portion of the product cost. In conventional methods like centrifugation and even modern methods like chromatography, scale-up problems are enormous, making them uneconomical and prohibitively expensive unless the product is of very high value. Therefore there has been a need for efficient and economical alternative approaches to bioseparation processes to eliminate, reduce, or facilitate solids handling. Magnetic and electric field assisted separations may hold considerable potential for providing a future major improvement in bioseparation technology. In the present review the merits and demerits of the existing methods are discussed. We present mainly our own research on the development of unified multistage extraction processes that are versatile enough to handle cells and particles as well as macromolecules as described below. We describe multistage methods, namely ADSEP (Advanced Separator), MAGSEP (Magnetic Separator), and ELECSEP (Electrophoretic Separator), for quantitatively separating cells, particles, and solutes by using magnetically and electrophoretically assisted extraction processes. To the best of our knowledge, multistage magnetic and electrophoretic separations have not been reported in the earlier literature. The theoretical underpinnings of these separations are crucial to their success and to the identification of their advantages over other separation processes in particular applications. Hence mathematical modeling is stressed here, presenting our own models while also reviewing models reported in the literature. We also present suggestions for future work while analyzing the scale-up and economic aspects of these extraction processes. Commercial uses of the magnetic and electrophoretic processes, having both ground- and space-based research elements, also are presented in this review.

Particle electrophoresis of micrometric-sized superparamagnetic particles designed for magnetic purification of cells

Measuring the electrophoretic mobility of superparamagnetic particles (0.5-4.5 microns mean size) was undertaken to probe the coupling of lectins and antibodies to their surface. Coupling was either noncovalent (antigen-antibody and biotin-streptavidin linkage) or covalent (tosyl-activated beads). The direct observation of the electrophoresis of single particles illuminated in dark field and processed by image analysis allowed the determination of their apparent electrophoretic mobility. Mobilities ranged from -0.5 micron s-1/CmV-1 to +1 micron s-1/CmV-1 when measured at 20 degrees C in 0.15 M NaCl and 30 mg/mL sorbitol, pH 7.4. The relative standard deviation was less than 0.1%. Surface immobilization of charged proteins onto the superparamagnetic beads shifted their electrophoretic mobility up to 200%; this was also quantitatively correlated with some specific properties (enzymatic activity, antigen-binding activity, lectin-binding activity). Although particle electrophoresis has mainly been reported for the study of surface adsorption phenomenon, it may be a versatile tool for controlling covalent modifications of particles designed for therapeutical targeting or chromatographic use and may also apply to a quantitative analysis of ligand-binding interactions.

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

Fluorescent probes serve as sensitive tools for obtaining structural and functional information in cellular systems. In spite of the high sensitivity provided by fluorescent reagents, cell surface receptors expressed in low numbers often escape detection with commonly used fluorescent probes. R-Phycoerythrin (R-PE), a molecule with a very high quantum yield, is often the reagent of choice for the detection of such low abundance events. We have developed streptavidin conjugates of two highly fluorescent 35-40 nm diameter polystyrene nanospheres, the green fluorescent FluoSpheres (Ex/Em 505/515) and red fluorescent TransFluoSpheres (Ex/Em 488/645). Like R-PE, the new reagents have peak excitations near 488 nm but differ in their emission maxima; 515 nm for the green nanospheres, 645 nm for the red nanospheres and 575 nm for R-PE. Hence the nanospheres are detected by flow cytometry in channels capable of detecting green (FL1) and red (FL3) fluorescence, while R-PE is detected in channel FL2. These nanospheres were tested for the detection of the sparsely expressed epidermal growth factor receptor (EGFR) of NIH-3T3 cells and the densely expressed EGFR of A431 cells. Results indicate that the nanosphere reagents are more sensitive than fluorescein-streptavidin and at least comparable in sensitivity to R-PE-streptavidin. The simultaneous use of these nanospheres with R-PE was also studied by concurrent staining of the CD3 and CD4 receptors in JURKAT cells. Labeling of CD4 receptors with streptavidin nanospheres and CD3 receptors with the R-PE-anti-CD3 conjugate confirmed the suitability of using the new nanospheres in combination with R-PE in multicolor flow cytometry experiments. This paper thus describes the use of alternative tools with detection sensitivity comparable to that of R-PE, but detected in different channels than R-PE, permitting their simultaneous use with R-PE.

Surface modification of superparamagnetic nanoparticles (Ferrofluid) studied with particle electrophoresis: application to the specific targeting of cells

Colloidal aqueous suspension of superparamagnetic nanoparticles (9 nm in diameter) composed of maghemite (gamma Fe2O3) and forming an ionic ferrofluid in aqueous solution are covalently coupled with lectins, enzymes or antibodies, using specific thiol chemistry. The surface charge modifications of nanoparticles, caused by ligand coupling, were monitored by measuring their electrophoretic mobilities using laser-Doppler velocimetry. Particle electrophoretic mobility (PEM) changes are shown to correlate well with the amount of ligand fixed on the particles, as probed by its biological activity. The PEM method provides a useful tool to optimize ligand immobilization at the surface of nanoparticles, and may be advantageous when biological activity measurements are not convenient.

Adsorption and covalent immobilization of human serum albumin (HSA) and gamma globulins (gamma G) onto poly(styrene/acrolein) latexes with pyrene, dansyl, and 2,4-dinitrophenyl labels

The poly(styrene/acrolein) latexes (P(SA)1 and P(SA)2), differing in poly(acrolein) content, were synthesized by the emulsifier-less emulsion-precipitation polymerization of styrene and acrolein. The fraction of poly(acrolein) in the surface layer was 0.35 and 0.50, for the P(SA)1 and P(SA)2 latex, respectively. Latexes were labelled with 2,4-dinitrophenylhydrazine (DNPH), dansylhdrazine (DAH), and 1-aminopyrene (APY). Surface concentration of labels varied from 4.20.10(-7) mol m-2 (for APY label on P(SA)1 latex) to 1.54.10(-6) mol m-2 (for DNPH label on P(SA)2 latex) reflecting the fraction of polyacrolein in the surface layer and bulkiness of the label. The differences between adsorption and covalent immobilization of human serum albumin and gamma globulins onto the P(SA)2 latex and onto its derivatives labelled with the 2,4-dinitrophenyl (DNP), dansyl (DA), and pyrene (PY) groups were small. The observation conforms to the hypothesis that polyacrolein forms domains on the surface of the P(SA) latexes and that after labelling some aldehyde groups are still available for the covalent immobilization of proteins. Labelled and parent latexes were used in the model slide and turbidimetric aggregation tests for the goat anti-HSA. The fluorescent latexes, labelled with APY and DAH, and latexes labelled and with DNPH were found to be suitable for the model tests, similarly as the nonlabelled ones, however, some differences in the sensitivity, depending on the presence and the nature of labels, were noticed. The standard goat anti-HSA serum (Sigma) was detected at maximum dilution equal to 2000 in the slide test, and in the dilution region from 1.8.10(3) to 4.7.10(6) times in the turbidimetric test.

Monosize microbeads based on polystyrene and their modified forms for some selected medical and biological applications

Polymeric particles are produced by different polymerization techniques. Phase inversion (dispersion) polymerization is one of the recent techniques to obtain monosize polymeric microbeads in the size range of 1-50 microns. The size and monodispersity of these microbeads can be adjusted by using several solvent systems (e.g., alcohol-water mixtures) with different polarities and by changing the type and amount of monomer, initiator and stabilizer. Surfaces of these microbeads can be further modified by different techniques including coating with different copolymers. Monosize polymeric microbeads are widely used in medical and biological applications as carriers, such as in immunoassays and cell separation, in site-specific drug delivery systems, in nuclear medicine for diagnostic imaging, in studying the phagocytic process, in affinity separation of biological entities, etc. Here, some important aspects of the production of monosize microbeads based on polystyrene and their modified forms are briefly discussed, and some selected medical and biological applications are summarized.

Preparative continuous separation of biological particles by means of free-flow magnetophoresis in a free-flow electrophoresis chamber

For sorting, cells or cellular components can specifically be labeled by antibody-coated magnetic beads. We have developed a device for continuous magnetic sorting based on the flow-chamber of a free-flow electrophoresis system. Magnetically labeled particles are injected into a given continuously flowing chamber buffer and pass an inhomogeneous magnetic field, configurated perpendicular to the flow direction. According to its magnetic moment, the magnetic material is deviated into the direction of the magnetic forces, while nonmagnetic material passes the field without interaction. The magnetic forces can be changed with the electrical current of the solenoids producing the magnetic field. As in the free-flow electrophoresis system, the particle fractions are collected in different vials. On-line control of the experiments can be performed by an optical scanning system. Experiments with model particles achieved a sorting purity of more than 99% at a rate of up to 5 X 10(8) particles per hour. In experiments with blood cells, a high enrichment of either B-or-T-lymphocytes was obtained. In contrast to free-flow electrophoresis, there is no limitation, in principle, regarding the type of chamber buffer to be used. This allows an optimal adaptation of the buffer conditions to the requirements of vital sorting. The preliminary results so far confirm this conclusion.