A surface plasmon field-enhanced fluorescence reversible split aptamer biosensor

Surface plasmon field-enhanced fluorescence is reported for the readout of a heterogeneous assay that utilizes low affinity split aptamer ligands. Weak affinity ligands that reversibly interact with target analytes hold potential for facile implementation in continuous monitoring biosensor systems. This functionality is not possible without the regeneration of more commonly used assays relying on high affinity ligands and end-point measurement. In fluorescence-based sensors, the use of low affinity ligands allows avoiding this step but it imposes a challenge associated with the weak optical response to the specific capture of the target analyte which is also often masked by a strong background. The coupling of fluorophore labels with a confined field of surface plasmons is reported for strong amplification of the fluorescence signal emitted from the sensor surface and its efficient discrimination from the background. This optical scheme is demonstrated for time-resolved analysis of chosen model analytes - adenoside and adenosine triphosphate - with a split aptamer that exhibits an equilibrium affinity binding constant between 0.73 and 1.35 mM. The developed biosensor enables rapid and specific discrimination of target analyte concentration changes from low μM to mM in buffer as well as in 10% serum.

Sculpting nanoparticle dynamics for single-bacteria-level screening and direct binding-efficiency measurement

Particle trapping and binding in optical potential wells provide a versatile platform for various biomedical applications. However, implementation systems to study multi-particle contact interactions in an optical lattice remain rare. By configuring an optofluidic lattice, we demonstrate the precise control of particle interactions and functions such as controlling aggregation and multi-hopping. The mean residence time of a single particle is found considerably reduced from 7 s, as predicted by Kramer’s theory, to 0.6 s, owing to the mechanical interactions among aggregated particles. The optofluidic lattice also enables single-bacteria-level screening of biological binding agents such as antibodies through particle-enabled bacteria hopping. The binding efficiency of antibodies could be determined directly, selectively, quantitatively and efficiently. This work enriches the fundamental mechanisms of particle kinetics and offers new possibilities for probing and utilising unprecedented biomolecule interactions at single-bacteria level.

Optical trapping is a versatile tool for biomedical applications. Here, the authors use an optofluidic lattice to achieve controllable multi-particle hopping and demonstrate single-bacteria-level screening and measurement of binding efficiency of biological binding agents through particle-enabled bacteria hopping.

High-resolution and multi-range particle separation by microscopic vibration in an optofluidic chip

An optofluidic chip is demonstrated in experiments for high-resolution and multi-range particle separation through the optically-induced microscopic vibration effect, where nanoparticles are trapped in loosely overdamped optical potential wells created with combined optical and fluidic constraints. It is the first demonstration of separating single nanoparticles with diameters ranging from 60 to 100 nm with a resolution of 10 nm. Nanoparticles vibrate with an amplitude of 3-7 μm in the loosely overdamped potential wells in the microchannel. The proposed optofluidic device is capable of high-resolution particle separation at both nanoscale and microscale without reconfiguring the device. The separation of bacteria from other larger cells is accomplished using the same chip and operation conditions. The unique trapping mechanism and the superb performance in high-resolution and multi-range particle separation of the proposed optofluidic chip promise great potential for a diverse range of biomedical applications.

Correction: Optofluidic lens with low spherical and low field curvature aberrations

Correction for 'Optofluidic lens with low spherical and low field curvature aberrations' by H. T. Zhao et al., Lab Chip, 2016, 16, 1617-1624.

Optofluidic lens with low spherical and low field curvature aberrations

This paper reports an optofluidic lens with low spherical and low field curvature aberrations through the desired refractive index profile by precisely controlling the mixing between ethylene glycol and deionized water in an optofluidic chip. The experimental results demonstrate that the spherical aberration is reduced to 19.5 μm and the full width at half maximum of the focal point is 7.8 μm with a wide divergence angle of 35 degrees. In addition, the optofluidic lens can focus light at different off-axis positions on the focal plane with Δx' < 6.8 μm and at opposite transverse positions with |Δy - Δy'| < 5.7 μm. This is the first demonstration of a special optofluidic lens that significantly reduces both the spherical and field curvature aberrations, which enhances the focusing power and facilitates multiple light source illumination using a single lens. It is anticipated to have high potential for applications such as on-chip light manipulation, sample illumination and multiplexed detection.

Cell refractive index for cell biology and disease diagnosis: past, present and future

Cell refractive index is a key biophysical parameter, which has been extensively studied. It is correlated with other cell biophysical properties including mechanical, electrical and optical properties, and not only represents the intracellular mass and concentration of a cell, but also provides important insight for various biological models. Measurement techniques developed earlier only measure the effective refractive index of a cell or a cell suspension, providing only limited information on cell refractive index and hence hindering its in-depth analysis and correlation. Recently, the emergence of microfluidic, photonic and imaging technologies has enabled the manipulation of a single cell and the 3D refractive index of a single cell down to sub-micron resolution, providing powerful tools to study cells based on refractive index. In this review, we provide an overview of cell refractive index models and measurement techniques including microfluidic chip-based techniques for the last 50 years, present the applications and significance of cell refractive index in cell biology, hematology, and pathology, and discuss future research trends in the field, including 3D imaging methods, integration with microfluidics and potential applications in new and breakthrough research areas.

Correlation between surface chemistry and settlement behaviour in barnacle cyprids (Balanus improvisus)

In laboratory-based biofouling assays, the influence of physico-chemical surface characteristics on barnacle settlement has been tested most frequently using the model organism Balanus amphitrite (= Amphibalanus amphitrite). Very few studies have addressed the settlement preferences of other barnacle species, such as Balanus improvisus (= Amphibalanus improvisus). This study aimed to unravel the effects of surface physico-chemical cues, in particular surface-free energy (SFE) and surface charge, on the settlement of cyprids of B. improvisus. The use of well-defined surfaces under controlled conditions further facilitates comparison of the results with recent similar data for B. amphitrite. Zero-day-old cyprids of B. improvisus were exposed to a series of model surfaces, namely self-assembled monolayers (SAMs) of alkanethiols with varying end-groups, homogenously applied to gold-coated polystyrene (PS) Petri dishes. As with B. amphitrite, settlement of cyprids of B. improvisus was influenced by both SFE and charge, with higher settlement on low-energy (hydrophobic) surfaces and negatively charged SAMs. Positively charged SAMs resulted in low settlement, with intermediate settlement on neutral SAMs of similar SFE. In conclusion, it is demonstrated that despite previous suggestions to the contrary, these two species of barnacle show similar preferences in response to SFE; they also respond similarly to charge. These findings have positive implications for the development of novel antifouling (AF) coatings and support the importance of consistency in substratum choice for assays designed to compare surface preferences of fouling organisms.

Interactions of zoospores of Ulva linza with arginine-rich oligopeptide monolayers

We recently reported on the strong interactions of zoospores of the green alga, Ulva linza with an arginine-rich oligopeptide self-assembled monolayer (SAM) [Biofouling 2008, 24, 303-312], where the arginine-rich peptide induced not only high spore settlement, but also a form of abnormal settlement, or "pseudo-settlement", whereby a proportion of spores do not go through the normal process of surface exploration, adhesive exocytosis, and loss of flagella. Further, it was demonstrated that both the total number of settled spores and the fraction of pseudosettled spores were related to the surface density of the arginine-rich peptide. Here we present a further investigation of the interactions of zoospores of Ulva with a set of oligomeric, de novo designed, arginine-rich peptides, specifically aimed to test the effect of peptide primary structure on the interaction. Via variations in the peptide length and by permutations in the amino acid sequences, we gain further insight into the spore-surface interactions. The interpretation of the biological assays is supported by physicochemical characterization of the SAMs using infrared spectroscopy, ellipsometry, and contact angle measurements. Results confirm the importance of arginine residues for the anomalous pseudosettlement, and we found that settlement is modulated by variations in both the total length and peptide primary structure. To elucidate the causes of the anomalous settlement and the possible relation to peptide-membrane interactions, we also compared the settlement of the "naked" zoospores of Ulva (which present a lipoprotein membrane to the exterior without a discrete polysaccharide cell wall), with the settlement of diatoms (unicellular algae that are surrounded by a silica cell wall), onto the peptide SAMs. Cationic SAMs do not notably affect settlement (attachment), adhesion strength, or viability of diatom cells, suggesting that the effect of the peptides on zoospores of Ulva is mediated via specific peptide-membrane interactions.

Anomalous settlement behavior of Ulva linza zoospores on cationic oligopeptide surfaces

Identification of settlement cues for marine fouling organisms opens up new strategies and methods for biofouling prevention, and enables the development of more effective antifouling materials. To this end, the settlement behaviour of zoospores of the green alga Ulva linza onto cationic oligopeptide self-assembled monolayers (SAMs) has been investigated. The spores interact strongly with lysine- and arginine-rich SAMs, and their settlement appears to be stimulated by these surfaces. Of particular interest is an arginine-rich oligopeptide, which is effective in attracting spores to the surface, but in a way which leaves a large fraction of the settled spores attached to the surface in an anomalous fashion. These 'pseudo-settled' spores are relatively easily detached from the surface and do not undergo the full range of cellular responses associated with normal commitment to settlement. This is a hitherto undocumented mode of settlement, and surface dilution of the arginine-rich peptide with a neutral triglycine peptide demonstrates that both normal and anomalous settlement is proportional to the surface density of the arginine-rich peptide. The settlement experiments are complemented with physical studies of the oligopeptide SAMs, before and after extended immersion in artificial seawater, using infrared spectroscopy, null ellipsometry and contact angle measurements.

Synthetic de novo designed polypeptides for control of nanoparticle assembly and biosensing

This contribution describes how de novo designed synthetic helix–loop–helix polypeptides are utilized to control the assembly of gold nanoparticles and as scaffolds for biosensing. The synthetic polypeptides are designed to fold into a four-helix bundle upon dimerization. When immobilized on gold nanoparticles, dimerization and folding occur between peptides on neighbouring particles as an effect of particle aggregation and the folded polypeptides are rigid enough to keep the particles separated at a distance corresponding to the size of the four-helix bundle. Moreover, peptide dimerization offers a convenient route to assemble nanoparticles into hybrid multilayers on planar substrates. The drastic change in the resonance conditions of the localized nanoparticle surface plasmon upon particle aggregation is shown to be useful for optical detection of biomolecular interactions.

Molecular Orientation in Helical and All-Trans Oligo(ethylene glycol)-Terminated Assemblies on Gold: Results of ab Initio Modeling

The structural properties of self-assembled monolayers (SAMs) of oligo(ethylene glycol) (OEG)-terminated and amide-containing alkanethiols (HS(CH(2))(15)CONH(CH(2)CH(2)O)(6)H and related molecules with shorter alkyl or OEG portions) on gold are addressed. Optimized geometry of the molecular constituents, characteristic vibration frequencies, and transition dipole moments are obtained using density-functional theory methods with gradient corrections. These data are used to simulate IR reflection-absorption (RA) spectra associated with different OEG conformations. It is shown that the positions and relative intensities of all characteristic peaks in the fingerprint region are accurately reproduced by the model spectra within a narrow range of the tilt and rotation angles of the alkyl plane, which turns out to be nearly the same for the helical and all-trans OEG conformations. In contrast, the tilt of the OEG axis changes considerably under conformational transition from helical to all-trans OEG. By means of ab initio modeling, we also clarify other details of the molecular structure and orientation, including lateral hydrogen bonding, the latter of which is readily possessed by the SAMs in focus. These results are crucial for understanding phase and folding characteristics of OEG SAMs and other complex molecular assemblies. They are also expected to contribute to an improved understanding of the interaction with water, ions, and ultimately biological macromolecules.

Alpha-helix-inducing dimerization of synthetic polypeptide scaffolds on gold

Designed, synthetic polypeptides that assemble into four-helix bundles upon dimerization in solution were studied with respect to folding on planar gold surfaces. A model system with controllable dimerization properties was employed, consisting of negatively and positively charged peptides. Circular dichroism spectroscopy and surface plasmon resonance based measurements showed that at neutral pH, the peptides were able to form heterodimers in solution, but unfavorable electrostatic interactions prevented the formation of homodimers. The dimerization propensity was found to be both pH- and buffer-dependent. A series of infrared absorption-reflection spectroscopy experiments of the polypeptides attached to planar gold surfaces revealed that if the negatively charged peptide was immobilized from a loading solution where it was folded, its structure was retained on the surface provided it had a cysteine residue available for anchoring to gold. If it was immobilized as random coil, it remained unstructured on the surface but was able to fold through heterodimerization if subsequently exposed to a positively charged polypeptide. When the positively charged peptide was immobilized as random coil, heterodimerization could not be induced, probably because of high-affinity interactions between the charged primary amine groups and the gold surface. These observations are intended to pave the way for future engineering of functional surfaces based on polypeptide scaffolds where folding is known to be crucial for function.

Masticatory and nutritional aspects on fixed and removable partial dentures

The aim of the present study was to evaluate mastication, food selection and nutritional aspects in two groups of persons restored with fixed (FPD, N=44) and removable (RPD, N=40) partial dentures respectively. The subjects were part of a cohort study of 67-68-year-old men living in Malmö, Sweden. The two groups were very similar regarding social factors and the inclusion criteria were chosen so that the groups were very equal regarding oral factors, apart from the difference in fixed and removable partial dentures. The number of natural teeth, number of replaced teeth and occlusal contacts did not differ significantly between the two groups, nor did the distribution of maxillary and mandibular dentures. A comprehensive examination of several general health factors included a home interview of dietary habits. A clinical examination included a 20-minute oral examination with registration of number of teeth, FPDs, RPDs, and occlusal contacts. It also included masticatory tests: chewing gum colour mixing, chewing gum bolus shaping, and swallowing threshold (number of strokes to the first swallow of an almond). The consumption of hard and soft foods was revealed by the dietary interview as well as the intake of energy and some nutrients. There was a significant difference between the groups regarding the capacity to mix the two-coloured chewing gum, to shape the chewing gum bolus and in the consumption of hard foods. There was no difference in the swallowing threshold and the consumption of soft foods. The intake of energy and nutrients did not differ significantly between the groups. The differences in masticatory capacity found thus seem to have little, if any, effect on the factors of importance for general health. A reasonable explanation for the differences found is that artificial teeth that are well retained, such as FPDs, make more active chewing possible than do removable, and often somewhat loose-fitting partial dentures.

Protein adsorption to oligo(ethylene glycol) self-assembled monolayers: experiments with fibrinogen, heparinized plasma, and serum

Low protein adsorption is believed advantageous for blood-contacting materials and ethylene glycols (EG)-based polymeric compounds are often attached to surfaces for this purpose. In the present study, the adsorption of fibrinogen, serum, and plasma were studied by ellipsometry on a series of well-defined oligo(EG) terminated alkane-thiols self-assembled on gold. The layers were prepared with compounds of the general structure HS-(CH2)15-CONH-EGn, where n = 2, 4, and 6. Methoxy-terminated tri(EG) undecanethiol and hydroxyl-terminated hexadecanethiol self-assembled monolayers (SAMs) were used as references. The results clearly demonstrate that the adsorption depends on the experimental conditions with small amounts of fibrinogen adsorbing from a single protein solution, but larger amounts of proteins from serum and plasma. The adsorption of fibrinogen and blood plasma decreased with an increasing number of EG repeats and was temperature-dependent. Significantly less serum adsorbed to methoxy tri(EG) than to hexa(EG) and more proteins remained on the latter surface after incubation in a sodium dodecyl sulfate (SDS) solution, indicating a looser protein binding to the methoxy-terminated surface. All surfaces adsorbed complement factor 3 (C3) from serum and plasma, although no surface-mediated complement activation was observed. The present study points to the importance of a careful choice of the protein model system before general statements regarding the protein repellant properties of potential surfaces can be made.

Electrochemical evaluation of the interfacial capacitance upon phosphorylation of amino acid analogue molecular films

An approach based on electrochemistry to differentiate between phosphorylated and nonphosphorylated amino acid analogues adsorbed on gold is presented. Analogues of serine, threonine, and tyrosine, containing thiohexadecyl headgroups, were synthesized and assembled on gold, and the surface capacitance was evaluated using electrochemical impedance spectroscopy. A procedure for deprotection of tert-butyl phosphate protecting groups, on the monolayer, is also described. Characterizations of the assembled analogues by cyclic voltammetry, infrared spectroscopy, and ellipsometry are used to confirm the insulating properties of the monolayers and the outcome of surface modifications. The results from cyclic voltammetry show good insulating properties for the monolayers even after phosphate deprotection. The infrared measurements reveal well-ordered monolayers, and the thickness from ellipsometry is in good agreement with expectations from molecular modeling. The impedance experiments show a capacitance increase up to 0.6 microF/cm2 as phosphate groups are introduced. The results in this study indicate the possibility of using a surface chemical and impedance spectroscopy approach to detect the kinase/phosphatase activity and kinetics involved in phosphorylation reactions.

Subtle differences in dissociation rates of interactions between destabilized human carbonic anhydrase II mutants and immobilized benzenesulfonamide inhibitors probed by a surface plasmon resonance biosensor

The development of commercial biosensors based on surface plasmon resonance has made possible careful characterization of biomolecular interactions. Here, a set of destabilized human carbonic anhydrase II (HCA II) mutants was investigated with respect to their interaction kinetics with two different immobilized benzenesulfonamide inhibitors. Point mutations were located distantly from the active site, and the destabilization energies were up to 23 kJ/mol. The dissociation rate of wild-type HCA II, as determined from the binding to the inhibitor with higher affinity, was 0.019 s(-1). For the mutants, dissociation rates were faster (0.022-0.025 s(-1)), and a correlation between faster dissociation and a high degree of destabilization was observed. We interpreted these results in terms of increased dynamics of the tertiary structures of the mutants. This interpretation was supported by entropy determinations, showing that the entropy of the native structure significantly increased upon destabilization of the protein molecule. Our findings demonstrate the applicability of modern biosensor technology in the study of subtle details in molecular interaction mechanisms, such as the long-range effect of point mutations on interaction kinetics.

A high-density poly(ethylene glycol) polymer brush for immobilization on glass-type surfaces

Label-free heterogeneous phase detection critically depends on the properties of the interfacial layer. We have obtained high-density monomolecular poly(ethylene glycol) (PEG) layers by solvent-free coupling of homo-bifunctional PEGs (2,000 g/mol) at 75 degrees C to silica surfaces silanized with glycidyloxipropyltrimethoxysilane (GOPTS). Characterization by ellipsometry and contact angles revealed that PEG layers up to 3.4 ng/mm2 with low roughness and flexibility were obtained. Specific and non-specific binding at these PEG surfaces was monitored by reflectometric interference spectroscopy (RIfS). No significant non-specific adsorption upon incubation of 1 mg/ml ovalbumin was detectable (< 10 pg/mm2), and 150 pg/mm2 upon incubation of 10% calf serum, less than 10% of the amount adsorbed to the solely silanized surfaces. The terminal functional groups of the PEG layers were utilized to couple ligands and a protein. Specific protein interaction with these immobilized compounds was detected with saturation loadings in the range of protein monolayers (2-4 ng/mm2). The excellent functional properties, the high stability of the layers, the generic and practical coupling procedure and the versatility for immobilizing compounds of very different functionality make these PEG layers very attractive for application in label-free detection with silica or metal-oxide based transducers.

Sensitivity deviation: instrumental linearity errors that influence concentration analyses and kinetic evaluation of biomolecular interactions

Many scientific instruments utilise multiple element detectors, e.g. CCD's or photodiode arrays, to monitor the change in a position of an optical pattern. For example. instruments for affinity biosensing based on surface plasmon resonance (SPR) or resonant mirror are equipped with such detectors. An important and desired property of these bioanalytical instruments is that the calculation of the movement or change in shape follows the true change. This is often not the case and it may lead to linearity errors, and to sensitivity errors. The sensitivity is normally defined as the slope of the calibration curve. A new parameter is introduced to account for the linearity errors, the sensitivity deviation, defined as the deviation from the undistorted slope of the calibration curve. The linearity error and the sensitivity deviation are intimately related and the sensitivity deviation may lead to misinterpretation of kinetic data, mass transport limitations and concentration analyses. Because the linearity errors are small (e.g. 10 pg/mm2 of biomolecules on the sensor surface) with regard to the dynamic range (e.g. 30,000 pg/mm2), they can be difficult to discover. However, the linearity errors are often not negligible with regard to a typical response (e.g. 0-100 pg/mm2). and may therefore cause serious problems. A method for detecting linearity errors is outlined. Further on, this paper demonstrates how integral linearity errors of less than 1% can result in a sensitivity deviation of 10%, a value that in our opinion cannot be ignored in biospecific interaction analysis (BIA). It should also be stressed out that this phenomenon also occurs in other instruments using array detectors.

Synthesis of a series of oligo(ethylene glycol)-terminated alkanethiol amides designed to address structure and stability of biosensing interfaces

A strategy for the synthesis of a series of closely related oligo(ethylene glycol)-terminated alkanethiol amides (principally HS(CH(2))(m)CONH(CH(2)CH(2)O)(n)H; m = 2, 5, 11, 15, n = 1, 2, 4, 6, 8, 10, 12) and analogous esters has been developed. These compounds were made to study the structure and stability of self-assembled monolayers (SAMs) on gold in the prospect of designing new biosensing interfaces. For this purpose, monodisperse heterofunctional oligo(ethylene glycols) with up to 12 units were prepared. Selective monoacylation of the symmetrical tetra- and hexa(ethylene glycol) diols as their mesylates with the use of silver(I) oxide was performed. The synthetic approach was based on carbodiimide couplings of various oligo(ethylene glycol) derivatives to omega-(acetylthio) carboxylic acids via a terminal amino or hydroxyl function. SAM structures on gold were studied with respect to thickness, wettability (water contact angles approximately 30 degrees ), and conformation. A good fit was obtained for the relation between monolayer thickness (d) and the number of units in the oligo(ethylene glycol) chain (n): d = 2.8n + 21.8 (A). Interestingly, the corresponding infrared spectroscopy analysis showed a dramatic change in conformation of the oligomeric chains from all-trans (n = 4) to helical (n > or = 6) conformation. A crystalline helical structure was observed in the SAMs for n > 6.

Comparison of surface plasmon resonance and quartz crystal microbalance in the study of whole blood and plasma coagulation

The coagulation of blood plasma and whole blood was studied with a surface plasmon resonance (SPR) based device and a quartz crystal microbalance instrument with energy dissipation detection (QCM-D). The SPR and QCM-D response signals were similar in shape but differing in time scales, reflecting differences in detection mechanisms. The QCM-D response time was longer than SPR, as a physical coupling of the sample to the substrate is required for molecules to be detected by the QCM-method. Change of sample properties within the evanescent field is sufficient for detection with SPR. Both the SPR signals and the QCM-D frequency and dissipation shifts showed dependency on concentrations of coagulation activator and sensitivity to heparin additions. The ratio of dissipation to frequency shifts, commonly considered to reflect viscoelastic properties of the sample, varied with the concentration of activator in blood plasma but not in whole blood. Additions of heparin to the thromboplastin activated whole blood sample, however, made the ratio variation reoccur. Implications of these observations for the understanding of the blood coagulation processes as well as the potential of the two methods in the clinic and in research are discussed.

Suramin blocks nucleotide triphosphate binding to ribosomal protein L3 from Trypanoplasma borreli

Ribosomal protein L3 (L3) has been demonstrated to participate in formation of the peptidyltransferase center and is essential for its catalytic activity. In the present study we show that L3 is able to bind nucleotide triphosphates with high and specific affinity in vitro. L3 was serendipitously identified by screening of a genomic phage library from a primitive kinetoplastid flagellate Trypanoplasma borreli with the ATPase domain of the topoisomerase II gene as a probe. The cloned gene was overexpressed and purified as a his-tag fusion protein in E. coli. Radioligand binding experiments, using [gamma-35S]ATP, showed that L3 is able to bind ATP but also GTP and UTP with similar high affinity (IC50 50-100 nM), while it has no ATPase activity. Furthermore, we showed that L3 has more than 500-fold higher affinity for nucleotide triphosphates compared to the corresponding nucleotide monophosphates and diphosphates. Molecular genetic and biochemical analyses allowed us to localize the NTP binding domain of L3 to the N-terminal 296 residues. Suramin, a polysulfonated naphthylamine derivative of urea, known for its chemotherapeutic effects completely inhibited the binding of [gamma-35S]ATP at subclinical levels. Results obtained with surface plasmon resonance technology showed that suramin both forms weak multimolecular complexes with L3 and binds strongly to L3 in nearly stoichiometric amounts.

Blood plasma coagulation studied by surface plasmon resonance

A surface plasmon resonance (SPR) apparatus was used to investigate blood plasma coagulation in real time as a function of thromboplastin and heparin concentrations. The response curves were analyzed by curve fitting to a sigmoid curve equation, followed by extraction of the time constant. Clotting activation by thromboplastin resulted in increased time constant, as compared to spontaneously clotted plasma, in a dose dependent way. Addition of heparin to the thromboplastin-activated plasma counteracted this effect. Atomic force microscopy (AFM) pictures of sensor surfaces dried after completed clotting, revealed differences in fibrin network structures as a function of thromboplastin concentration, and the fiber thickness increased with decreased thromboplastin concentration. The physical reason for the SPR signal observed is ambiguous and is therefore discussed. However, the results summarized in the plots and the fibrin network properties observed by AFM correlate well with present common methods used to analyze blood coagulation.

Immobilized chicken antibodies improve the detection of serum antigens with surface plasmon resonance (SPR)

Surface plasmon resonance (SPR) and other refractive index and mass sensitive methods are, due to complement activation by mouse monoclonal antibodies and with concomitant high background signal, only rarely used for the detection of antibody-antigen interactions in the blood serum milieu. In the present study chicken IgY and mouse IgG were immobilized to a sensor chip CM5 dextran matrix and compared for their background signal and detection of serum antigen. Ellipsometry with antibodies adsorbed to methylated silicon surfaces was used as a complementary detection method. As expected, fundamental differences in binding properties between the two kinds of antibodies were observed. Mouse antibodies bound large quantities of human serum. Human C1q was detected on mouse IgG and the complement system was activated, as seen from the rapid C3 and properdin depositions. Chicken antibodies bound low quantities of human serum and no human C1q. Moreover, C3 and properdin deposited only after prolonged serum incubations. Addition of EDTA to serum reduced the background signal modestly for both IgG and IgY. Serum samples with different concentrations of human C3 were injected over surfaces with immobilized chicken anti-C3, and the response was measured by SPR. Small concentration differences (< 1.25 micrograms/ml) in a physiologically relevant range (1-40 micrograms/ml after 100 times dilution) could then be detected reproducibly. The SPR signal was totally obscured when a mouse monoclonal anti-C3 antibody was used for the detection.

Protein adsorption studies on model organic surfaces: an ellipsometric and infrared spectroscopic approach

The development of accurate analytical tools to control the interfacial properties of solid substrates is of importance for the design of new biomaterials, as well as for the understanding of biomolecular interactions on surfaces. Considerable research efforts are presently devoted to this area on different levels of molecular complexity, i.e. both in the presence and in the absence of the biomolecules. In this contribution we review briefly applications of infrared reflection-absorption spectroscopy (IRAS) and ellipsometry as tools for analysis of the chemical properties of model surfaces, and their biological response in vitro when in contact with blood plasma or serum, respectively. The strength of the combination of the techniques is demonstrated by determination of protein adsorption patterns on a series of chemically well-defined so-called self-assembled alkanethiolate monolayers (SAMs) of 16-thiohexadecanol (HS-(CH2)16-OH) and n-hexadecanethiol (HS-(CH2)15-CH3) on gold. The protein adsorption patterns after incubations in plasma were determined by the specific binding of antibodies to the surfaces.

Mapping of monoclonal antibody- and receptor-binding domains on human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) using a surface plasmon resonance-based biosensor

An automated surface plasmon resonance (SPR)-based biosensor system has been used for mapping antibody and receptor-binding regions on the recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) molecule. A rabbit antimouse IgG1-Fc antibody (RAM.Fc) was coupled to an extended carboxymethylated-hydrogel matrix attached to a gold surface in order to capture an anti-rhGM-CSF monoclonal antibody (MAb) injected over the sensing layer. rhGM-CSF was subsequently injected and allowed to bind to this antibody. Multisite binding assays were then performed, by flowing sequentially other antibodies and peptides over the surface, and the capacity of the latter to interact with the entrapped rhGM-CSF in a multimolecular complex was monitored in real time with SPR. Eleven MAb (all IgG1K), were analyzed: respectively, four antipeptide MAb raised against three distinct epitopes of the cytokine (two clones against residues 14-24, that includes part of the first alpha-helix toward the N-terminal region; one clone against peptide 30-41, an intrahelical loop; and one clone against residues 79-91, including part of the third alpha-helix) and seven antiprotein MAbs raised against the entire rhGM-CSF, whose target native epitopes are still undetermined. In addition, the binding capacity to rhGM-CSF of a synthetic peptide, corresponding to residues 238-254 of the extracellular human GM-CSF receptor alpha-chain, endowed with rhGM-CSF binding activity, was tested. The results from experiments performed with the biosensor were compared with those obtained by a sandwich enzyme-linked immunosorbent assay (ELISA), using the same reagents. The features of the biosensor technology (fully automated, measure in real time, sharpened yes/no response, less background disturbances, no need for washing step or labeling of the reagent) offered several advantages in these studies of MAb immunoreactivity and epitope mapping, giving a much better resolution and enabling more distinct epitopes to be identified over ELISA.

Biosensing with surface plasmon resonance--how it all started

A subjective description is given of how the development of surface plasmon resonance for immunosensing began. The main differences between the initial experiments and a commercially available instrumentation are pointed out. For the practical use of surface oriented methods for biosensing it is noted that the arrangements around the optical system itself, such as the sensing chip or sample cell, are most important. It is concluded that the instrumentation developed can be used not only for immunosensing but also for "real time biospecific interaction analysis" in general. It is pointed out that the use of surface plasmon resonance for detection is only one possibility and that many new (optical) methods for real time biospecific interaction analysis have been and will be developed.

Oral bolus kneading and shaping measured with chewing gum

A masticatory test using two-colored chewing gum is presented and analyzed. Two separate parameters of chewing were studied on the same chewing gum bolus after 10 strokes of oral preparation, color mixing, and bolus shaping. The two parameters were evaluated in indices 1-5. A test series should preferably contain three chewing gums, and color mixing can be evaluated on six sides and shape-indexed for each bolus. The medians characterize the subjects' masticatory ability. Color mixing may relate, for example, to ensalivation of the food during chewing, and bolus shape may relate to preparation into a form suitable for swallowing. The tests were used on test subjects with different dental and denture status. Significant differences in both color mixing and shape indices were found between groups with different status. The method is discussed in relation to earlier types of tests, e.g., the comminution test mostly used hitherto.

Mastication with and without removable partial dentures: an intraindividual study

The chewing of 22 subjects, with a total of 27 removable partial dentures (RPD) that had been used for more than 6 months, was analyzed by four different methods. The study design was an intraindividual comparison of chewing, with and without the RPDs. Chewing tests were a color mixture of two-colored gums, chewing gum bolus shaping, comminution of Optosil silicone tablets, and number of chewing strokes to first swallow of an almond. The participants were also asked some standardized questions about their eating, biting, and chewing capacity. There was no significant difference in efficiency as measured by chewing gum color mixing, chewing gum shape, and pulverization of Optosil between chewing with and without the RPDs. Significantly more strokes were needed to swallow an almond without than with the RPD in place. With their RPDs in place, all subjects could chew a sandwich and an apple, and all but one could chew whole meat. The study shows that the chewing process should preferably not be analyzed by one method only.

Social network, social support and dental status in elderly Swedish men

The objective of this study was to investigate whether there were associations between different aspects of social network and social support and dental status. The study sample (n = 621) comprised a random half of all male residents in Malmö, Sweden, born in 1914. Five hundred (80.5%) participated. Eight conceptually different aspects of social networks and social support were measured, and all men were clinically examined regarding number of teeth, prevalence of removable dentures, fixed bridges and anterior open tooth spaces. We found that some aspects of dental status were associated with social class, while others were associated with different aspects of social network and social support. Prevalence of complete dentures and fixed bridges was strongly associated with social class, a low number of functioning teeth was associated with both low social class belonging and an insufficient social network and social support, while anterior open tooth spaces were associated mostly with an insufficient social network and social support. This study shows that there are significant associations between some aspects of dental status and the social network and social support of the individual, while other aspects of dental status are associated with social class, which from a psychosocial perspective contribute to a deeper understanding of the backgrounds of dental status.

In vitro plasma protein adsorption and kallikrein formation on 3-mercaptopropionic acid, L-cysteine and glutathione immobilized onto gold

3-Mercaptopropionic acid (MPA), L-cysteine (L-cys), and glutathione (GSH) monolayers were immobilized onto gold and used in in vitro protein tests. The surfaces were characterized with ellipsometry, static contact angle measurements, atomic force microscopy, and Fourier transform infrared reflection absorption spectroscopy (FT-IRAS). After incubations in human plasma and antibody solutions, the surface antisera binding patterns were determined with ellipsometry. Using serum instead of plasma, complement activation was studied in the same fashion. Activated coagulation Factor XII and kallikrein formation on the surfaces and in the plasma were studied using a kallikrein-specific colorimetric assay. 3-Mercaptopropionic acid indicated contact activation of coagulation but L-cysteine did not. Glutathione displayed low deposition of plasma proteins, large deposition of proteins from serum, and did not promote kallikrein formation. None of the surfaces could be attributed complement activating properties, as determined by antibody deposition. The present study demonstrates that surface biology in complex model systems can be conveniently studied in vitro through systematic and well defined surface modifications.

Chewing and the dimension of the pharyngoesophageal segment

Masticatory efficiency was evaluated in 21 adults for four chewing parameters: mixing of a color-patterned chewing gum mass, shaping of a chewing gum mass, particle reduction of a silicone tablet, and number of chewing strokes before the first swallow of an almond. The results of these tests were correlated with the dimension of the pharyngoesophageal (PE) segment during swallow of liquid barium and solid meat. The transverse width of the PE segment during swallow of liquid barium correlated significantly with the chewing parameters. The sagittal width of the PE segment during swallow of liquid barium correlated only weakly with the chewing parameters. The PE segment dimension during swallow of a solid meat bolus did not correlate with the chewing parameters. The results suggest that there is feedback during chewing and swallowing between the PE segment and the oral cavity.

Masticatory ability in experimentally induced xerostomia

The masticatory ability of 15 nondysphagic volunteers with complete natural dentition was tested using different chewing parameters including preparation of a two-color plastic chewing gum (bolus shape, and color mixture), particle reduction of a piece of silicone, and number of strokes before swallow of almonds. The tests were performed under conditions of normal salivation and experimental oral dryness caused by intramuscular injection of methylscopolamine. The chewing gum tests as well as the silicone particle reduction tests were not influenced by lack of salivation. The number of chewing strokes prior to the initiation of swallowing of almonds was significantly increased. Oral dryness seems to cause accumulation of particles in the oral cavity from friable food and the particulate material is not transported posteriorly into a "ready-to-swallow" positioning. The absorption of saliva by dry oral content such as an almond further impaired oral manipulation of food.

Teeth, tooth spaces, and prosthetic appliances in elderly men in Malmö, Sweden

A group of 483 men, all of whom were 68 or 69 yr old and had lived for a long time in the city of Malmö were examined with regard to number of teeth present, removable dentures, fixed bridges, and tooth spaces. 76.4% had one or more natural teeth remaining, 59.2% had removable dentures, and 0.2% were edentulous and without dentures. The mean number of teeth present in a fixed dentition calculated on dentate subjects was 16.21 +/- 8.02, including teeth replaced by pontics and 15.0 +/- 7.44 when natural teeth only were recorded. The number of bridges was high, 28.8% of natural dentate persons having bridgework. This cohort had fewer remaining teeth than in similar groups in other areas of Sweden, but more fixed bridges. 19.5% had open tooth spaces corresponding to one or more teeth in the visible parts of the dental arches. The availability of dentistry has been extremely good in Malmö and financial support for all types of dental care has been provided for all inhabitants since 1974. In spite of this, a low number of remaining teeth and many untreated tooth spaces in visible part of the dental arches were found, though on the other hand much fixed bridgework was found. It appears from the present study that the population tends to polarize into two groups, namely one group which takes advantage of the dental services and one which does not.