On-chip measurements of cell compressibility via acoustic radiation

Measurements of mechanical properties of biological cells are of great importance because changes in these properties can be strongly associated with the progression of cell differentiation and cell diseases. Although state of the art methods, such as atomic force microscopy, optical tweezers and micropipette aspiration, have been widely used to measure the mechanical properties of biological cells, all these methods involve direct contact with the cell and the measurements could be affected by the contact or any local deformation. In addition, all these methods typically deduced the Young's modulus of the cells based on their measurements. Herein, we report a new method for fast and direct measurement of the compressibility or bulk modulus of various cell lines on a microchip. In this method, the whole cell is exposed to acoustic radiation force without any direct contact. The method exploits the formation of an acoustic standing wave within a straight microchannel. When the polystyrene beads and cells are introduced into the channel, the acoustic radiation force moves them to the acoustic pressure node and the movement speed is dependent on the compressibility. By fitting the experimental and theoretical trajectories of the beads and the cells, the compressibility of the cells can be obtained. We find that the compressibility of various cancer cells (MCF-7: 4.22 ± 0.19 × 10(-10) Pa(-1), HEPG2: 4.28 ± 0.12 × 10(-10) Pa(-1), HT-29: 4.04 ± 0.16 × 10(-10) Pa(-1)) is higher than that of normal breast cells (3.77 ± 0.09 × 10(-10) Pa(-1)) and fibroblast cells (3.78 ± 0.17 × 10(-10) Pa(-1)). This work demonstrates a novel acoustic-based method for on-chip measurements of cell compressibility, complementing existing methods for measuring the mechanical properties of biological cells.     

Gellan beads as a transparent media for protein immobilization and affinity capture

Gellan gum beads are presented as a novel substrate for protein immobilization and immobilized protein activity measurements. The optical transparency of the gellan beads down to 200 nm provides a method for direct quantitation of the amount of protein immobilized onto the beads. The ability to utilize these beads in a non-aqueous activation step allowed for a fourfold increase in the amount of protein immobilized, and this method was used to immobilize Protein A onto gellan beads at a final yield of 1.42+/-0.07 mg of Protein A/g of beads. The optical transparency also allowed for detection of the activity of the immobilized Protein A simply by measuring the absorbance of the beads following capture of rabbit IgG. This activity measurement method was compared with a traditional method utilizing the amount of protein remaining in solution after the IgG capture step. The traditional method yielded an activity measurement of 10.9+/-0.2 mg IgG/mg of Protein A, while the absorbance method showed an activity of only 7.5+/-0.3 mg IgG/mg of Protein A. The difference can be explained by the more direct measurement used in the absorbance method. The optical transparency of the beads was also evaluated in a fluorescence based IgG capture experiment, showing that detection of fluorescent IgG captured on the beads was possible with no interference from the beads.     

Estimation of cell surface associated protease activity and its application to lymphocytes.

A new method has been developed to estimate proteolytic activity available at the cell surface. Radioiodinated protein substrates are covalently linked to modified polystyrene-divinylbenzene beads with various diameters. These beads are presented to viable cells. Secreted enzyme activity is estimated when no contact occurs between beads and cells. Surface associated proteolytic activity is estimated by the increased rate of iodinated peptide release due to a contact between beads and cells. This method was applied to various lymphocyte preparations. In the absence of serum, mouse spleen lymphocytes produce three- to fourfold higher proteolytic activity than lymph node cells. This activity is completely inhibited by serum diluted 1:10. Since the proteolysis is so marked in the case of spleen cells, one must conclude that lymphocytes removed from the serum and treated in buffered mediums at 37 degrees C have enzymatically altered surface properties. Cell surface associated enzyme activity was measured using rat lymph node lymphocytes with less than 0.1% contamination by granulocytes. This predominantly thymus derived, T cell population had 30% increase in proteolysis due to contact between cells and solid-phase localized substrate of casein. The released enzymatic activity was inhibited by diisopropylfluorophosphate, but its effect on the surface associated enzyme activity remains questionable since it perturbs several membrane functions.     

Concanavalin A Binding on PHEMA Beads and Their Interactions with Myeloma Cells

The aim of this study is to prepare concanavalin A (Con A) bound poly(2-hydroxy ethyl methacrylate) (PHEMA) beads for cell affinity chromatography. In the first step, PHEMA beads were produced by suspension polymerization, and activated by cyanogen bromide (CNBr) in an alkaline medium (pH 11.5), and then, the bio-ligand “Con A” was attached by covalent binding onto the CNBr activated beads. PHEMA beads were characterized by scanning electron microscopy (SEM), surface area and pore size measurements. The PHEMA beads have a spherical shape and porous structure. The specific surface area of the PHEMA beads was found to be 39.7 m²/g with a size range of 150–200 μm in diameter and the swelling ratio was 55%. The amount of bound Con A was controlled by changing pH and the initial concentrations of CNBr and Con A. The non-specific adsorption of Con A on the plain PHEMA beads was 0.1 mg/g. The maximum Con A binding was 4.8 mg/g at pH 7.25. Both plain and Con A bound PHEMA beads were interacted first with the myeloma cell suspension in phosphate buffer. Myeloma cell attachment was very low for the plain PHEMA beads, while the number of myeloma cells attached increased almost 20 fold when the Con A bound beads were used. In order to look at whether or not the interaction of the Con A bound PHEMA beads and myeloma cells are affected from the biological molecules and other cells in the medium. We selected sheep blood itself as the medium, and mixed with the myeloma cell suspension and changed the environment. Cell adhesion decreased but not very significantly by changing the medium from simple buffer to sheep blood.     

Cell mechanics using atomic force microscopy-based single-cell compression

We report herein the establishment of a single-cell compression method based on force measurements in atomic force microscopy (AFM). The high-resolution bright-field or confocal laser scanning microscopy guides the location of the AFM probe and then monitors the deformation of cell shape, while microsphere-modified AFM probes compress the cell and measure the force. Force and deformation profiles of living cells reveal a cubic relationship at small deformation (<30%), multiple peaks at 30-70% compression, and a rapid increase at over 80% deformation. The initial compression may be described qualitatively and quantitatively using a simple model of a nonpermeable balloon filled with incompressible fluid. Stress peaks reflect cell membrane rupture, followed by the deformation and rupture of intracellular components, beyond which the cell responses become irreversible. The Young's modulus and bending constant of living cell membranes are extracted from the balloon models, with 10-30 MPa and 17-52 kT, respectively. The initial compression of dead and fixed cells is modeled using Hertzian contact theory, assuming that the cell is a homogeneous sphere. Dead cells exhibit a cytoskeleton elasticity of 4-7.5 kPa, while fixation treatment leads to a dramatic increase in the cytoskeletal Young's modulus (150-230 kPa) due to protein cross-linking by imine bonds. These results demonstrate the high sensitivity of the single-cell compression method to the molecular-level structural changes of cells, which suggests a new generic platform for investigating cell mechanics in tissue engineering and cancer research.     

Photo‐switchable spiropyran immobilized polystyrene beads using catechol chemistry

Catechol and spiropyran functional groups were conjugated to a polymer backbone, allowing immobilization on polystyrene beads (PS beads). The final product was capable of stably reproducing the optical properties of spiropyran. Through the outstanding surface adhesion properties of the catechol functional group, spiropyran was immobilized on PS beads. Switchable photoluminescence in the spiropyran coated PS bead surfaces was observed depending on irradiation with either UV or visible light. The surfaces of the PS beads were morphologically examined by field emission scanning electron microscopy and X‐ray photoelectron spectroscopy was used for characterization of the constituent atoms. Furthermore, UV–Vis and fluorescence spectroscopy were used to confirm conversion between the spiropyran (SP) and merocyanine (MC) forms through UV or visible light irradiation on SP, while fluorescent images for both SP and MC were studied using confocal laser scanning microscopy. The confocal images of the SP‐PS beads system onto MDAMB‐231 cells under UV and visible light indicate the cellular uptake by emerging color within the cytoplasm. Advancing study, the remaining catechol groups can confers adhesive properties, given by contact angle data of various coated surfaces film. These stimuli‐responsive coatings are compatible as drawing switchable photochromic material on versatile substrate shown in confocal images of propylene film. Overall, this great water solubility and biocompatibility PS beads system also showed potential as cell bio‐imaging light stimuli responsive material, and the benefits of this system can also possibly address coat able advanced material for a wide range of surface light sensor applications. Copyright © 2017 John Wiley & Sons, Ltd.     

Silica- and alkoxysilane-coated ultrasmall superparamagnetic iron oxide particles: a promising tool to label cells for magnetic resonance imaging

In this study silica- and alkoxysilane-coated ultrasmall superparamagnetic iron oxide (USPIO) particles were synthesized, and their ability to label immortalized progenitor cells for magnetic resonance imaging (MRI) was compared. USPIO particles were synthesized by coprecipitation of ferric and ferrous salts. Subsequently, the particles were coated with silica, (3-aminopropyl)trimethoxysilane (APTMS), and [N-(2-aminoethyl)-3-aminopropyl]trimethoxysilane (AEAPTMS). The size of the USPIO particles was about 10 nm without a significant increase in diameter after coating. The highest T2 relaxivity was achieved for silica-coated USPIO particles, 339.80 +/- 0.22 s-1 mM-1, as compared with APTMS- and AEAPTMS-coated ones, reaching 134.40 +/- 0.01 and 84.79 +/- 0.02 s-1 mM-1, respectively. No toxic effects on the cells could be detected by trypan blue, TUNEL, and MTS assays. Uptake of USPIO particles was evaluated by Prussian blue staining, transmission electron microscopy, T2-MR relaxometry, and mass spectrometry. It was found that cell uptake of the different USPIO particles increased for longer incubation times and higher doses. Maximum cellular iron concentrations of 42.1 +/- 4.0 pg/cell (silica-coated USPIO particles), 37.1 +/- 3.5 pg/cell (APTMS-coated USPIO particles), and 32.7 +/- 4.0 pg/cell (AEAPTMS-coated USPIO particles) were achieved after incubation of the cells with USPIO particles at a dose of 3 micromol/mL for 6 h. The decrease of the T2 relaxation time of the cell pellets was most pronounced for cells incubated with silica-coated USPIO particles followed by APTMS- and AEAPTMS-coated particles, respectively. In gelatin gels even small clusters of labeled cells were detected by 1.5 T MRI, and significant changes in the T2 relaxation times of the gels were determined for 10000 labeled cells/mL for all particles. In summary, as compared with APTMS- and AEAPTMS-coated particles, silica-coated USPIO particles provide the highest T2 relaxivity and most effectively reduce the T2 relaxation time of immortalized progenitor cells after internalization. This suggests silica-coated USPIO particles are most suited for cell labeling approaches in MRI.     

Covalently Bound Antibody on Polystyrene Latex Beads: Formation, Stability, and Use in Analyses of White Blood Cell Populations

CD4 or CD8 antibodies were covalently bound to latex beads by reaction of activated CD4 or CD8 monoclonal antibodies with 2-μm-diameter, 1,3-diaminopropane (DAP) coupled, polystyrene aldehyde/sulfate latex beads. Spectrophotometric analyses of the filtrates of the antibody-bead conjugation mixtures for unreacted antibody allowed construction of binding curves of antibody for the polystyrene bead surface and evaluation of binding constants for association of antibody with bead, ranging from 1.5x10(7) to 1.6x10(7) M(-1) for CD4 and CD8 antibodies. The reaction of the antibody thiol group with the activated maleimide group on the bead at pH 7.2-7.3 was complete within 10-15 min. The kinetics of CD4 or CD8 monoclonal antibody displacement from the surface of covalently conjugated antibody-polystyrene latex beads was followed as a function of temperature (5, 22, and 37 degrees C) and the nature of the final diluent for the antibody-coated beads by measuring the concentration of antibody in the filtrates of conjugated beads by an ELISA (enzyme-linked immunosorbent assay). The displacement reaction showed a pseudo-zero-order dependence of the rate, with constants, k(1), ranging from 0.65x10(-17) to 270x10(-17) M s(-1). The functionality of antibody-coated beads suspended in various media was also monitored in a biological cell assay with whole blood. The cell assay depends on forming a layer of beads around targeted lymphocytes to distinguish them from nontargeted lymphocytes by differences in dc or rf conductivity or median angle light scatter. Covalently bound CD4 and CD8 antibody beads stored in one set of media at 5, 22, and 37 degrees C over a period of 16 weeks showed excellent results in the STKS assay with various blood donors, which correlated well (correlation coefficients of 0.99 for CD4 data and 0.93 for CD8 data) with reference results obtained with fluorescent markers by flow cytometry. Covalently bound CD4/CD8 beads stored for 2 weeks in BSA buffer at 5-37 degrees C performed equally well in providing accurate values of the percentage of CD4- or CD8-positive cells in the total white blood cell population, whereas the same beads stored in the 47-50 degrees C range showed some failures in performance. Comparison with antibody concentrations in filtrates of adsorbed antibody-bead suspensions showed 2- to 10-fold greater amounts of free antibody at comparable elapsed time, media, and temperature conditions. A threshold of 1-2 μg/mL of free antibody was necessary before adverse effects on the biological cell assay were noticeable. Copyright 2001 Academic Press.     

Mesoporous zirconium titanium oxides. Part 2: Synthesis, porosity, and adsorption properties of beads

Mesoporous zirconium titanium mixed-oxide beads having disordered wormhole textures and mole fractions of Zr (x) ranging from x=0.25 to 0.67 have been prepared. The bead preparation method combined the forced hydrolysis of mixtures of zirconium-titanium alkoxides in the presence of long-chain carboxylates with external gelation. Uniformly sized beads could be produced in the size range 0.5-1.1 mm by varying the droplet size and viscosity of the mixed-oxide sol, thus making them suitable for large-scale column chromatographic applications. The beads exhibited narrow pore size distributions with similar mean pore diameters of around 3.7 nm. The specific surface areas of the beads were linked to the Zr mole fraction in the precursor solution and were generally greater than 350 m2/g for x=0.5. A combination of scanning transmission electron microscopy and X-ray absorption fine structure analysis indicated that the pore walls of the beads were composed of atomically dispersed Zr and Ti to form a continuous network of Zr-O-Ti bonds. Mass transport in the beads was evaluated by monitoring the kinetics of vanadate and vanadyl adsorption at pH 10.5 and 0.87, respectively.     

Electrochemiluminescent determination of cancer cells based on aptamers, nanoparticles, and magnetic beads

Herein we report a polymerase chain reaction (PCR)-free electrochemiluminescence (ECL) approach that uses ECL nanoprobes for the determination of cancer cells with high sensitivity. The ECL nanoprobe consists of gold nanoparticles (AuNPs), linker DNA, and tris(2,2'-bipyridyl)ruthenium (TBR)-labeled signal DNA. The linker DNA and signal DNA were modified on the surface of the AuNPs through Au-S bonds. The linker DNA can partly hybridize with the aptamers of cancer cells loaded onto the magnetic beads (MB1) to construct the magnetic biocomplexes. In the presence of the cancer cells, the aptamers conjugated with the cancer cells with higher affinity. The ECL nanoprobe was released from the biocomplexes and subsequently hybridized with the capture DNA loaded onto another magnetic bead (MB2) to form the magnetic nanocomposite. The nanocomposites can be easily separated and firmly attached to an electrode on account of their excellent magnetic properties. The ECL intensity of the TBR loaded onto the nanocomposites directly reflected the amount of cancer cells. By using cell lines of Burkitt's lymphoma (Ramos cells) as a model, the ECL response was proportional to the cell concentration in the range from 5 to 100 cells ml(-1); a limit of detection as low as 5 cells ml(-1) of Ramos cells could be achieved. The proposed method described here is ideal for the diagnosis of cancers due to its high sensitivity, simplicity, and low cost.     

Direct detection by atomic force microscopy of single bond forces associated with the rupture of discrete charge-transfer complexes

Atomic force microscopy (AFM) was used to measure the chemical binding force of discrete electron donor-acceptor complexes formed at the interface between proximal self-assembled monolayers (SAMs). Derivatives of the well-known electron donor N,N,N',N'-tetramethylphenylenediamine (TMPD) and the electron acceptor 7,7,8,8-tetracyanoquinodimethane (TCNQ) were immobilized on Au-coated AFM tips and substrates by formation of SAMs of N,N,N'-trimethyl-N'-(10-thiodecyl)-1,4-phenylenediamine (I) and bis(10-(2-((2,5-cyclohexadiene-1,4-diylidene)dimalonitrile))decyl) disulfide (II), respectively. Pull-off forces between modified tips and substrates were measured under CHCl(3) solvent. The mean pull-off forces associated with TMPD/TCNQ microcontacts were more than an order of magnitude larger than the pull-off forces for TMPD/TMPD and TCNQ/TCNQ microcontacts, consistent with the presence of specific charge-transfer interactions between proximal TMPD donors and TCNQ acceptors. Furthermore, histograms of pull-off forces for TMPD/TCNQ contacts displayed 70 +/- 15 pN periodicity, assigned to the rupture of individual TMPD-TCNQ donor-acceptor (charge-transfer) complexes. Both the mean pull-off force and the 70 pN force quantum compare favorably with a contact mechanics model that incorporates the effects of discrete chemical bonds, solvent surface tensions, and random contact area variations in consecutive pull-offs. From the 70 pN force quantum, we estimate the single bond energy to be approximately 4-5 kJ/mol, in reasonable agreement with thermodynamic data. These experiments establish that binding forces due to discrete chemical bonds can be detected directly in AFM pull-off measurements employing SAM modified probes and substrates. Because SAMs can be prepared with a wide range of exposed functional groups, pull-off measurements between SAM-coated tips and substrates may provide a general strategy for directly measuring binding forces associated with a variety of simple, discrete chemical bonds, e.g., single hydrogen bonds.     

Surface modification of glass beads with poly(acrylic acid)

Non‐porous P₂ glass beads were etched with sodium hydroxide to increase the number of silanol groups that could be used to modify the surface. The etched glass beads were then functionalized with 3‐aminopropyltriethoxysilane (APS) and/or glycidoxypropyltrimethoxysilane (GPS). The surface of the glass beads were further modified with poly(acrylic acid) (PAA) by reacting the carboxyl groups on PAA with the amino groups of the pregrafted APS. The chemical modifications were characterized by FT‐IR spectroscopy, particle size analyzer and tensiometry for contact angle and porosity measurements. Five different molecular weight PAA polymers ranging from 2000 to 3,000,000 were grafted with less than expected increase of grafted PAA with molecular weight. The amount of APS and PAA on the surface was determined from thermogravimetric analysis and elemental analysis data. The surface properties of the surface modified glass beads were determined by measuring water and hexane penetration rate and contact angle. The surface morphology was examined by scanning electron microscopy. Copyright © 2006 John Wiley & Sons, Ltd.     

Synthesis of crosslinked resin based on methacrylamide, styrene and divinylbenzene obtained from polymerization in aqueous suspension

A series of porous copolymer beads based on methacrylamide (MA), styrene and divinylbenzene (DVB) was prepared by aqueous suspension polymerization in the presence of diluents to act as precipitants. As MA is totally soluble into aqueous phase, the use of two types of phase transfer agent was investigated, namely: TritonX-100^TM [polyoxyethylene-(10)-isooctylphenyl-ether] and tetrabutylammonium perchlorate. The effect of the diluents on the surface appearance and the porous structure of copolymer beads was studied. Suitable particle stabilisation was achieved by using a combination of two suspension agents, namely: gelatin and 2-hydroxy-ethyl-cellulose. The network resins were characterized by optical and scanning electron microscopy, IR spectroscopy, elemental analysis (CHN), apparent density, swelling in different solvents and specific area by BET method. It was observed that the MA incorporation was more effective when Triton^TM was employed as phase transfer agent.     

DNA binding and photocleavage in vitro by new dirhodium(II) dppz complexes: correlation to cytotoxicity and photocytotoxicity

Two new dirhodium(II) complexes possessing the intercalating dppz ligand (dppz = dipyrido[3,2-a:2',3'-c]phenazine), cis-[Rh(2)(mu-O(2)CCH(3))(2)(dppz)(eta(1)-O(2)CCH(3))(CH(3)OH)](+) (1) and cis-[Rh(2)(mu-O(2)CCH(3))(2)(dppz)(2)](2+) (2), were synthesized and characterized as potential agents for photochemotherapy. Various techniques show that 1 binds to DNA through intercalation, although some aggregation of the complex on the DNA surface is also present. In contrast, 2 does not intercalate between the DNA bases; however, strong hypochromic behavior is observed in the presence of DNA, which can be attributed to intermolecular pi-stacking of 2 enhanced by the polyanion. The apparent DNA binding constants determined using optical titrations are compared to those from dialysis experiments. Both complexes photocleave pUC18 plasmid in vitro under irradiation with visible light (lambda(irr) >or= 395 nm, 15 min), resulting in the nicked, circular form. Greater photocleavage is observed for 1 relative to 2, which may be due to the ability of 1 to intercalate between the DNA bases. The cytotoxicity toward human skin cells (Hs-27) measured as the concentration at which 50% cell death is recorded, LC(50), was found to be 135 +/- 8 microM for 2 in the dark (30 min), which is significantly lower than those of 1 (LC(50) = 27 +/- 2 microM) and Rh(2)(O(2)CCH(3))(4) (LC(50) = 15 +/- 2 microM). Irradiation of cell cultures containing 1 and Rh(2)(O(2)CCH(3))(4) with visible light (400-700 nm, 30 min) has little effect on their cytotoxicity, with LC(50) values of 21 +/- 3 and 13 +/- 2 microM, respectively. Interestingly, a 3.4-fold increase in the toxicity of 2 is observed when the cell cultures are irradiated (400-700 nm, 30 min), resulting in LC(50) = 39 +/- 1 microM. The greater toxicity of 1 compared to 2 in the dark may be related to the ability of the former compound to intercalate between the DNA bases. The lower cytotoxicity of 2, together with its significantly greater photocytotoxicity, makes this complex a potential agent for photodynamic therapy (PDT). These results suggest that intercalation or strong DNA binding may not be a desirable property of a potential PDT agent.     

Cell adhesion on nanofibrous polytetrafluoroethylene (nPTFE)

Here, we described the in vitro biocompatibility of a novel nanostructured surface composed of PTFE as a potential polymer for the prevention of adverse host reactions to implanted devices. The foreign body response is characterized at the tissue-material interface by several layers of macrophages and large multinucleated cells known as foreign body giant cells (FBGC), and a fibrous capsule. The nanofibers of nanofibrous PTFE (nPTFE) range in size from 20 to 30 nm in width and 3-4 mm in length. Glass surfaces coated with nPTFE (produced by jet-blowing of PTFE 601A) were tested under in vitro conditions to characterize the amount of protein adsorption, cell adhesion, and cell viability. We have shown that nPTFE adsorbs 495 +/- 100 ng of bovine serum albumin (BSA) per cm2. This level was considerably higher than planar PTFE, most likely due to the increase in hydrophobicity and available surface area, both a result of the nanoarchitecture. Endothelial cells and macrophages were used to determine the degree of cell adsorption on the surface of the nanostructured polymer. Both cell types were significantly more round and occupied less area on nPTFE as compared to tissue culture polystyrene (TCPS). Furthermore, a larger majority of the cells on the nPTFE were dead compared to TCPS, at dead-to-live ratios of 778 +/- 271 to 1 and 23 +/- 5.6 to 1, respectively. Since there was a high amount of cell death (due to either apoptosis or necrosis), and the foreign body response is a form of chronic inflammation, an 18 cytokine Luminex panel was performed on the supernatant from macrophages adherent on nPTFE and TCPS. As a positive control for inflammation, lipopolysaccharide (LPS) was added to macrophages on TCPS to estimate the maximum inflammation response of the macrophages. From the data presented with respect to IL-1, TNF-alpha, IFN-gamma, and IL-5, we concluded that nPTFE is nonimmunogenic and should not yield a huge inflammatory response in vivo, and cell death observed on the surface of nPTFE was likely due to apoptosis resulting from the inability of cells to spread on these surface. On the basis of the production of IL-1, IL-6, IL-4, and GM-CSF, we concluded that FBGC formation on nPTFE may be decreased as compared to materials known to elicit FBGC formation in vivo.     

Sorption behaviour of fluoride on carboxylated cross-linked chitosan beads

Carboxylated cross-linked chitosan beads (CCB) showed a significant defluoridation capacity (DC) of 1385 mgF(-)/kg than the raw chitosan beads (CB) which displayed only 52 mgF(-)/kg. Sorption experiments were performed by varying contact time, pH, presence of co-anions and temperature. The nature and morphology of the sorbent were discussed using FTIR and SEM with EDAX analysis. The stability of the beads in solution was explained in terms of swelling ratio of the beads. The fluoride uptake onto CCB obeys both Freundlich and Langmuir isotherms. Thermodynamic studies revealed that the nature of fluoride sorption is spontaneous and endothermic. Sorption kinetics is mainly controlled by pseudo-second-order and intraparticle diffusion models. 0.1M HCl was identified as the best eluent. The suitability of CCB at field conditions has been tested with field sample collected from a nearby fluoride-endemic area.     

Nanoparticle flotation collectors: mechanisms behind a new technology

This is the first report describing a new technology where hydrophobic nanoparticles adsorb onto much larger, hydrophilic mineral particle surfaces to facilitate attachment to air bubbles in flotation. The adsorption of 46 nm cationic polystyrene nanoparticles onto 43 μm diameter glass beads, a mineral model, facilitates virtually complete removal of the beads by flotation. As little as 5% coverage of the bead surfaces with nanoparticles promotes high flotation efficiencies. The maximum force required to pull a glass bead from an air bubble interface into the aqueous phase was measured by micromechanics. The pull-off force was 1.9 μN for glass beads coated with nanoparticles, compared to 0.0086 μN for clean beads. The pull-off forces were modeled using Scheludko's classical expression. We propose that the bubble/bead contact area may not be dry (completely dewetted). Instead, for hydrophobic nanoparticles sitting on a hydrophilic surface, it is possible that only the nanoparticles penetrate the air/water interface to form a three-phase contact line. We present a new model for pull-off forces for such a wet contact patch between the bead and the air bubble. Contact angle measurements of both nanoparticle coated glass and smooth films from dissolved nanoparticles were performed to support the modeling.     

Adsorption of humic acid from aqueous solutions on crosslinked chitosan-epichlorohydrin beads: kinetics and isotherm studies

The adsorption of humic acid on crosslinked chitosan-epichlorohydrin (chitosan-ECH) beads was investigated. Chitosan-ECH beads were characterized by Fourier transform infrared spectroscopy (FTIR), surface area and pore size analyses, and scanning electron microscopy (SEM). Batch adsorption experiments were carried out and optimum humic acid adsorption on chitosan-ECH beads occurred at pH 6.0, agitation rate of 300 rpm and contact time of 50 min. Adsorption equilibrium isotherms were analyzed by Langmuir and Freundlich models. Freundlich model was found to show the best fit for experimental data while the maximum adsorption capacity determined from Langmuir model was 44.84 mg g(-1). The adsorption of humic acid on chitosan-ECH beads was best described with pseudo-first-order kinetic model. For desorption study, more than 60% of humic acid could be desorbed from the adsorbent using 1.0M HCl for 180 min.     

Evanescent-wave cavity ring-down investigation of polymer/solvent interactions

Evanescent-wave cavity ring-down spectroscopy (EW-CRDS) is used to measure interfacial phenomena when methanol or water is placed in contact with a film of poly(dimethylsiloxane) (PDMS), which is attached to the face of a fused-silica prism that constitutes part of a ring cavity. In the first few minutes after contact, the uptake of methanol is slower than that of water, but after this initial period the methanol diffuses more rapidly in the film than water does. Bulk weight-gain measurements confirm this result and yield diffusion coefficients of (25.1 +/- 0.7) x 10(-7) cm(2)/s for methanol in PDMS and (7 +/- 2) x 10(-7) cm(2)/s for water in PDMS. The interfacial optical losses found in the EW-CRDS measurements result primarily from scatter. In particular, we find that delamination of the film from the fused-silica substrate dominates the optical losses in the case of methanol. This conclusion is confirmed by separate surface plasmon resonance experiments.