Preparation and application of new monosized polymer particles

Soap-free synthesis for producing highly monodisperse, micrometer-sized polystyrene particles up to 6 μm

A soap-free emulsion polymerization method with the use of an amphoteric initiator, currently proposed by the authors for producing highly monodisperse, micrometer-sized polymer particles, was examined in the polymerization of styrene with a 2,2'-azobis [N-(2-carboxyethyl)-2-2-methylpropionamidine] hydrate initiator and an NH(4)OH/NH(4)Cl pH buffer. The pH buffer was used to control the electric surface potential of particles to maintain a stable dispersion of particles and to prevent generation of new particles during the polymerization. Addition of monomer to the reaction system during polymerization could enlarge the average size of polymer particles to 5.7 microm with a coefficient of variation of 1.5%, which is much less than the standard criteria of monodispersity, 10%.

Polymer Microgels: Reactors for Semiconductor, Metal, and Magnetic Nanoparticles

We report a strategy for the production of materials with structural hierarchy. The approach employs polymer microgels as templates for the synthesis of semiconductor, metal, or magnetic nanoparticles (NPs). We show that NPs with predetermined dimensions and size-dependent properties can be synthesized by using a very delicate balance between the reaction conditions, the composition and the structure of microgel templates, and the concentration of NPs in the microgel. Postheat treatment of microgels doped with semiconductor nanoparticles reduces NP polydispersity and allows control of their photoluminescence. Microgel templates are particularly beneficial in the synthesis of polymer microspheres heavily loaded with monodisperse superparamagnetic Fe(3)O(4) NPs. Hybrid submicrometer-size microgels have promising potential applications in photonics, catalysis, and separation technologies.

Analysis of networks based on styrene and divinylbenzene containing iron anchored using variable pressure scanning electron microscopy

There is great demand for the development of composite materials containing small metal or metal oxides particles, owing to their variable properties and wide application. However, microscopic evaluation of these materials using high-vacuum scanning electron microscopy is difficult because the samples must undergo a series of preparation steps to reach a high image quality and to avoid becoming shrunk inside the microscope vacuum chamber. Thus, in this study, we used variable pressure scanning electron microscopy to evaluate the morphology and iron distribution on the surface of magnetic microspheres based on poly(styrene-co-divinylbenzene). These materials were obtained by suspension copolymerization of styrene and divinylbenzene in the presence of fine iron particles. Energy-dispersive X-rays were also used to analyse distribution of the iron particles. The results indicate that, under the conditions used, magnetic microspheres with a relatively narrow size distribution were formed. Moreover, the micrographs show that agglomerated iron particles appeared only on the microsphere surface.

One-step quantitative thyrotropin assay for the detection of hypothyroidism in point-of-care conditions

OBJECTIVES

Different screening strategies for early diagnosis of hypothyroidism have been discussed increasingly. We demonstrate the applicability of a miniaturized microparticle assay format for rapid and quantitative determination of increased thyrotropin (TSH) concentrations in serum.

DESIGN AND METHODS

Porous microparticles were used as solid phase for a noncompetitive, one-step, kinetic immunoassay with varying incubation times and time-resolved fluorescence detection.

RESULTS

The analytical (mean of zero + 3 SD) and functional (CV <15%) detection limits were 1.5 and 6.0 mIU/L for 2-min, 0.5 and 1.5 mIU/L for 7-min, and 0.2 and 0.5 mIU/L for 15-min assays, respectively. A good correlation was found with the Chiron Diagnostics ACS:180 assay (slopes 0.885-1.051, y-intercepts < +/- 0.20 mIU/L, S(y logical or, bar below x) <or= 0.10 mIU/L, r > 0.98, n = 20).

CONCLUSION

The kinetic TSH assay provides reproducible and quantitative information on thyroid status within minutes and is applicable for the detection of hypothyroidism in point-of-care (POC) conditions.

Online automatic discrimination between solid and gaseous cerebral microemboli with the first multifrequency transcranial Doppler

BACKGROUND AND PURPOSE

The aim of this study was to assess the first multifrequency transcranial Doppler system that was specially developed to automatically detect and discriminate between solid and gaseous cerebral microemboli.

METHODS

The multifrequency transcranial Doppler instrumentation insonates simultaneously with 2.5 and 2.0 MHz. Differentiation between solid and gaseous microemboli is based on the principle that solid microemboli reflect more ultrasound at the higher than at the lower frequency, whereas the opposite is the case for gaseous microemboli. In the in vitro studies, 159 plastic spheres (50 or 80 micro m in diameter) and 105 gas bubbles (8 to 25 micro m) were studied in a pulsatile closed-loop system containing irodinium or pig blood. In vivo studies were carried out for 1 hour in 15 patients with mechanical heart valves and in 45 patients with carotid stenosis. This gave a total of 60 hours of online automatic monitoring in patients.

RESULTS

In the in vitro studies, 152 of the 159 (95.6%) plastic spheres were classified as solid, and 7 (4.4%) were classified as uncertain solid. Of the 105 gas bubbles, 99 (94.3%) were classified as gaseous and 6 (5.7%) as uncertain gaseous. Thus, correct classification was made for 251 (95.1%) of the 264 embolic events studied. A comparison between the automatic multifrequency discrimination and the known embolic classification gave a kappa value of 0.897 (P<0.0001). The multifrequency Doppler classified 433 (84.2%) of the 514 emboli detected in the mechanical heart valve patients as gaseous, 74 (14.4%) as solid, and 7 (1.4%) as uncertain (3 uncertain solid, 4 uncertain gas). Thirty-two emboli were detected in 17 (38%) of the 45 carotid stenosis patients; 30 (93.7%) were classified as solid and 2 (6.3%) as uncertain solid.

CONCLUSIONS

This study has shown that multifrequency transcranial Doppler can be used to automatically differentiate between solid and gaseous microemboli online. Most detected microemboli in this initial study of mechanical heart valves were classified as gaseous, whereas most were classified as solid in the patients with carotid stenosis.

Ultrarapid, Ultrasensitive One-Step Kinetic Immunoassay for C-Reactive Protein (CRP) in Whole Blood Samples: Measurement of the Entire CRP Concentration Range with a Single Sample Dilution

Background: Recently, measurement of very low concentrations of C-reactive protein (CRP) has gained popularity as a potential new means for predicting the risk of future cardiac complications. In this study, we demonstrate the feasibility of a kinetic, one-step microparticle assay for quantitative determination of extremely low and high CRP concentrations in the limited timeframe typical for point-of-care testing.

Methods: A noncompetitive, kinetic CRP immunoassay was developed that uses individual, porous microparticles as the solid phase. The microparticles were covalently coated with a monoclonal capture antibody, and the monoclonal detection antibody was labeled with europium. The one-step binding reaction was stopped by washing after 2 min of incubation, and the fluorescence signal of individual particles was measured.

Results: The analytical detection limit (mean of zero calibrator + 3 SD) was 0.00016 mg/L CRP. Clinical samples were diluted 400-fold before assay to cover the CRP concentration range of 0.064–1200 mg/L. The assay correlated well with the Dade Behring N High Sensitivity CRP assay (for 0–10 mg/L, r = 0.969, Sy|x = 0.68, n = 54; for 0–350 mg/L, r = 0.969, Sy|x = 11.7, n = 100). The within- and between-run CVs based on calculated concentrations were, respectively, 9–16% and 14% at 0.11 mg/L, 4.5–12% and 8.2% at 4.2 mg/L, and 3.5–6.3% and 4.4% at 105 mg/L, with a CV &lt;15% at 0.2 mg/L and above.

Conclusions: Use of the kinetic microparticle approach combined with time-resolved fluorometry allows ultrasensitive quantification of CRP in whole blood in 2 min with a linear assay range spanning more than four orders of magnitude.

Preparation of highly selective stationary phases for high-performance liquid chromatographic separation of enantiomers by direct copolymerization of monomers with single or twin chiral ligands

Uniformly sized macroporous polymer beads, which can be used as chiral stationary phase (CSP), have been prepared by the staged templated suspension polymerization process using chiral monomer as one of the copolymerization components. This approach enables the preparation of CSPs for which properties such as pore size, pore volume, surface area, chemistry, and chiral ligands can be tuned over a broad range. Several types of well-defined chiral monomers were prepared and allowed to assess synergistic effect of multiple selectors attached to a branched linker as well as the effect of the length and chemistry of the linker. Microscale batch screening was used for simple and rapid evaluation of selectivity. The most promising candidate CSPs were prepared on a larger scale and packed into HPLC columns. Their performance was demonstrated on the separation of racemic N-(3,5-dinitrobenzoyl)-alpha-amino acid alkylamides. The highest separation factors alpha of up to 27 were observed for CSPs prepared from monomers containing the branched spacer. These highly selective CSPs also enabled the separation of larger amounts of the target racemates upon column overload conditions.

Involvement of CD14 and beta2-integrins in activating cells with soluble and particulate lipopolysaccharides and mannuronic acid polymers

Lipopolysaccharide (LPS) and related bacterial products can be recognized by host inflammatory cells in a particulate, bacterium-bound form, as well as in various soluble, released forms. In the present study we have compared the mechanisms used by LPS, detoxified LPS (DLPS), and mannuronic acid polymers (M-polymers), in solution or covalently linked to particles, in stimulating monocytes to tumor necrosis factor (TNF) production. The addition of recombinant LPS binding protein (LBP) and/or soluble CD14 (sCD14) enhanced the production of TNF from monocytes stimulated with soluble LPS, DLPS, or M-polymer, but did not affect the response to M-polymer or DLPS attached to particles. Treatment of monocytes with antibody to CD14, CD18, or CD11b showed that CD14, but not CR3 (CD11b/CD18), mediated monocyte TNF production in response to the soluble antigens. In contrast, anti-CD14, anti-CD11b and anti-CD18 monoclonal antibodies all inhibited the response to the particulate stimuli. On the other hand, B975, a synthetic analog of Rhodobacter capsulatus lipid A, completely abrogated the monocyte TNF response induced by LPS but did not affect the TNF induction by DLPS or M-polymer, either in soluble or particulate forms. These data demonstrate that the engagement of immune receptors by bacterial products such as LPS, DLPS, and M-polymer is dependent upon the presentation form of their constituent carbohydrates, and that factors such as aggregation state, acylation, carbohydrate chain length, and solid versus liquid phase of bacterial ligands influence the mechanisms used by cells in mediating proinflammatory responses.

Miniature Single-Particle Immunoassay for Prostate-specific Antigen in Serum Using Recombinant Fab Fragments

Background: Quantitative, miniaturized nucleic acid assays and immunoassays can be developed with single microparticles, microfluorometric detection, and intrinsically fluorescent lanthanide chelates in a multiple assay format to decrease reagent consumption, cost, and assay time. We used recombinant Fab fragments to capture and detect free and total prostate-specific antigen (PSA) from serum in a submicroliter volume single-particle immunoassay.

Methods: Genetically engineered thiol-Fab or thiolated monoclonal antibodies (mAbs) were covalently attached onto uniformly sized 60-μm maleimide-activated microparticles. Free and total PSA were detected with europium- or terbium-labeled Fab fragments on a single microparticle using a microfluorometer in a time-resolved mode.

Results: The detection limit of the free- and total-PSA assays (mean + 3 SD of zero calibrator) was 0.35 μg/L, with a total volume of 330 nL per particle. An excellent correlation was found in microparticle and microtiter-well assays for 21 serum samples: slopes for free and total PSA were 1.06 ± 0.03 and 1.03 ± 0.02, respectively (Sy|x = 0.084 and 0.057 μg/L), with intercepts of 0.013 ± 0.018 and 0.013 ± 0.017 μg/L (R &gt;0.99). Furthermore, the particle-immobilized Fab fragment had a PSA binding capacity 1.5-fold higher than the intact mAb capacity on a single microparticle. Capacity, kinetics, and sensitivity of the Fab fragment and intact mAb assays in the microparticle and microtiter well formats are discussed.

Conclusions: With site-specific (cysteine tail) covalent attachment of Fab fragments on a microparticle, subattomole amounts of PSA can be detected quantitatively.

The use of affinity adsorbents in expanded bed adsorption

The potential for the use of affinity ligands in expanded bed adsorption (EBA) procedures is reviewed. The use of affinity ligands in EBA may improve its use in direct recovery operations, as the enhanced selectivity of the adsorbent permits selective capture of the target from complex feedstocks and high degrees of purification. The properties of ligands suitable for use in EBA processes are identified and illustrated with examples. In addition to its use in the recovery of soluble products, such as proteins and nucleic acids, from particulate feedstocks, EBA can also be used to recover particulate entities, such as cells and packaged DNA (viruses and phages), from feedstocks. Affinity ligands coupled to appropriate chosen support materials will be required for such processes in order to achieve the necessary selectivity for the required particulate entity. The latter point is illustrated by the use of proteinaceous ligands immobilized to perfluorocarbon emulsions to achieve separations of microbial cells.

Polymer latexes for cell-resistant and cell-interactive surfaces

Novel polymer latexes were prepared that can be applied in several ways for the control and study of cell behavior on surfaces. Acrylic latexes with glass transitions ranging from -30 to 100 degrees C were synthesized by dispersion polymerization in a water and alcohol solution using an amphiphilic comb copolymer as a stabilizing agent. The comb had a poly(methyl methacrylate) backbone and hydrophilic poly(ethylene glycol) (PEG) side chains, which served to stabilize the dispersion and create a robust hydrophilic coating on the final latex particles. The end groups of the comb stabilizer can be selectively functionalized to obtain latex particles with a controlled density of ligands tethered to their surfaces. Latexes were prepared with adhesion peptides (RGD) linked to the surface of the acrylic beads to induce attachment and spreading of cells. Coalesced films obtained from the RGD-bearing latex particles promoted attachment of WT NR6 fibroblasts, while films from unmodified latex particles were resistant to these cells. Additionally, RGD-linked beads were embedded in cell-resistant comb polymer films to create cell-interactive surfaces with discrete clustered-ligand domains. Cell attachment and morphology were seen to vary with the surface density of the RGD-bearing latex beads.