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Control over orientation and conformation of surface-immobilized proteins, determining their biological activity, plays a critical role in biointerface engineering. Specific protein state can be achieved with adjusted surface preparation and immobilization conditions through different types of protein-surface and protein-protein interactions, as outlined in this work. Time-of-flight secondary ion mass spectroscopy, combining surface sensitivity with excellent chemical specificity enhanced by multivariate data analysis, is the most suited surface analysis method to provide information about protein state. This work highlights recent applications of the multivariate principal component analysis of TOF-SIMS spectra to trace orientation and conformation changes of various proteins (antibody, bovine serum albumin, and streptavidin) immobilized by adsorption, specific binding, and covalent attachment on different surfaces, including self-assembled monolayers on silicon, solution-deposited polythiophenes, and thermo-responsive polymer brushes. Multivariate TOF-SIMS results correlate well with AFM data and binding assays for antibody-antigen and streptavidin-biotin recognition. Additionally, several novel extensions of the multivariate TOF-SIMS method are discussed. Graphical abstract [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Shape-controlled synthesis of Ag-NPs in grafted temperature-responsive brushes. • Strong impact of the composition of grafted brushes on the shape of the Ag-NPs. • Temperature-induced changes in morphology of coatings with Ag-NPs. • Strong influence of temperature on optical effects of the Ag-NPs. Abstract The polymeric coatings of poly(4-vinylpyridine), poly(oligo(ethylene glycol)ethyl ether methacrylate246) and poly(4-vinylpyridine -co- oligo(ethylene glycol)ethyl ether methacrylate246) attached to glass using oligoperoxide initiator were successfully fabricated and then silver ions were immobilized in coatings. Silver nanoparticles were included in polymer matrixes using sodium borohydride as reducing agent of the immobilized silver ions. The composition and morphology of resulting coatings were analyzed. First, strong impact of the chemical nature of the grafted polymer brushes on the shape of the silver nanoparticles (sphere-like shape, nanorods and weakly branched dendritic nanostructures) was shown. In addition, the influence of the temperature on coating morphology and optical effects of the silver nanoparticles were demonstrated using Atomic Force Microscopy and UV–VIS spectroscopy. [ABSTRACT FROM AUTHOR]

Abstract: The origin and formation of the dipole moment at the interface of metal electrode and thin organic film is crucial for the fabrication of high‐performance organic electronic devices. In this work, model polymer multilayer systems are studied in which interfaces are modified heterogeneously with thiol‐based self‐assembled monolayers (SAM). Due to the presence of polar terminal group (‐COOH) in SAM and polar pendant groups (‐COOH, ‐C(O)OCH3) within studied polymers, it is pointed out that the resultant interface energetics differ from the expected ones as one would expect from the chemical character of the self‐assembled molecules used to tune junction properties. This is discussed in terms of inter‐association and depolarization effects between polymer and thiol modified substrate. The presented model systems may serve as an interaction reference for SAMs and semiconducting polymers containing similar moieties, utilized for the fabrication of organic electronic devices. [ABSTRACT FROM AUTHOR]

In this paper the combined effect of elasticity and chemical properties of the substrate on cellular behavior is applied to control the spatial arrangement of bladder cancer cells (HCV29). For this purpose regular and isotropic patterns of polystyrene (PS) are fabricated on a soft polydimethylsiloxane (PDMS) matrix. The topography and chemical composition of the patterns are determined using atomic force microscopy (AFM) and time-of-flight secondary ion mass spectrometry (ToF-SIMS), respectively, whereas fluorescence microscopy provides information on cellular location. Obtained results show that cells locate preferentially on the soft PDMS matrix whereas the stiffer and presenting weaker adhesive properties PS regions remain unoccupied. This effect may be used for spatial control of adhesion and proliferation of cells over the large areas. [ABSTRACT FROM AUTHOR]

Many of bioelectronic and biosensor applications are based on poly(3-alkylthiophenes), conducting and solution-processable polymers. The most facile approach for the fabrication of such devices relies on biofunctionalization of P3AT surfaces with antibodies through adsorption. The success of this approach depends critically on antibody orientation that affects its biorecognition. As demonstrated here both these features are controlled by the surface structure of spin-cast P3ATs. In particular, a multi-technique and multivariate study that involved Atomic Force Microscopy, Grazing Incidence X-ray Diffraction, Angle-Resolved X-ray Photoelectron Spectroscopy, Enzyme-Linked ImmunoSorbent Assay, and Time-of-Flight Secondary Ion Mass Spectrometry combined with Principal Component Analysis is conducted in order to deduce the crystalline texture of three P3AT polymers as well as its effect on orientation of adsorbed rabbit immunoglobulin (IgG) molecules. An edge-on crystalline texture is concluded for regioregular poly(3-butylthiophene) (RP3BT) and poly(3-hexylthiophene) (RP3HT), while amorphous morphology is inferred for poly(3-butylthiophene) (P3BT). In addition, end-on and head-on orientations similar for all P3ATs were concluded, based on the amount of adsorbed rabbit IgG molecules. Examination of amino acids characteristic for F(ab’) 2 and Fc fragments, and dominant in the external regions of adsorbed immunoglobulin molecules, points to end-on IgG alignment on RP3BT and RP3HT, but not on P3BT. Moreover, the binding of an anti-rabbit IgG antibody on the absorbed rabbit IgG is higher (up to 71%) when the biorecognition reactions are performed on regioregular rather than regiorandom P3AT surfaces. In particular, the highest biorecognition efficiency and IgG orientational order is observed for the RP3BT surfaces with the more developed crystallinity. [ABSTRACT FROM AUTHOR]

Time-of-flight-secondary ion mass spectrometry (TOF-SIMS) mass spectra measurements combined with an appropriate sample preparation protocol are the powerful tools to obtain unique information about the chemical composition of biological materials. In our studies, two questions were addressed, i.e., whether it is possible to develop a fixative-based sample preparation protocol and whether it allows one to distinguish between cells originating from various stages of cancer progression. Therefore, four human bladder cancer cell lines (with distinct malignancy degree) have been investigated. A chemical fixation protocol has been used for TOF-SIMS measurements, and mass spectra were obtained using a Bi3+ primary ion beam. The principal component analysis (PCA) has been applied to analyze the whole range of mass spectra (without preselection of any particular masses) using two approaches of data preprocessing, namely, mean centering and autoscaling. The PC3 versus PC2 plot has showed significant differences between nonmalignant cancer cells and the cancerous ones for both of preprocessing approaches. The analysis of mass spectra of human bladder cells allows one tofind a list of mass peaks with intensities significantly larger in cancerous bladder cells compared to nonmalignant cell cancer of the ureter (HCV29 cells). These findings show that TOF-SIMS in combination with PCA can be used to identify reference, human bladder cells from cancerous ones. [ABSTRACT FROM AUTHOR]

Background: The aim of the research presented here was to find a set of parameters enabling discrimination between three types of fibroblasts, i.e., healthy ones and those derived from two disorders mimicking each other: idiopathic pulmonary fibrosis (IPF), and nonspecific interstitial pneumonia (NSIP). Methods: The morphology and growth of cells were traced using fluorescence microscopy and analyzed quantitatively using cell proliferation and substrate cytotoxicity indices. The viability of cells was recorded using MTS assays, and their stiffness was examined using atomic force microscopy (AFM) working in force spectroscopy (FS) mode. To enhance any possible difference in the examined parameters, experiments were performed with cells cultured on substrates of different elasticities. Moreover, the chemical composition of cells was determined using time-of-flight secondary ion mass spectrometry (ToF-SIMS), combined with sophisticated analytical tools, i.e., Multivariate Curve Resolution (MCR) and Principal Component Analysis (PCA). Results: The obtained results demonstrate that discrimination between cell lines derived from healthy and diseased patients is possible based on the analysis of the growth of cells, as well as their physical and chemical properties. In turn, the comparative analysis of the cellular response to altered stiffness of the substrates enables the identification of each cell line, including distinguishing between IPF- and NSIP-derived fibroblasts. [ABSTRACT FROM AUTHOR]

The fibrotic fibroblasts derived from idiopathic pulmonary fibrosis (IPF) and nonspecific interstitial pneumonia (NSIP) are surrounded by specific environments, characterized by increased stiffness, aberrant extracellular matrix (ECM) composition, and altered lung architecture. The presented research was aimed at investigating the effect of biological, physical, and topographical modification of the substrate on the properties of IPF- and NSIP-derived fibroblasts, and searching for the parameters enabling their identification. Soft and stiff polydimethylsiloxane (PDMS) was chosen for the basic substrates, the properties of which were subsequently tuned. To obtain the biological modification of the substrates, they were covered with ECM proteins, laminin, fibronectin, and collagen. The substrates that mimicked the 3D structure of the lungs were prepared using two approaches, resulting in porous structures that resemble natural lung architecture and honeycomb patterns, typical of IPF tissue. The growth of cells on soft and stiff PDMS covered with proteins, traced using fluorescence microscopy, confirmed an altered behavior of healthy and IPF- and NSIP-derived fibroblasts in response to the modified substrate properties, enabling their identification. In turn, differences in the mechanical properties of healthy and fibrotic fibroblasts, determined using atomic force microscopy working in force spectroscopy mode, as well as their growth on 3D-patterned substrates were not sufficient to discriminate between cell lines. [ABSTRACT FROM AUTHOR]

A simple and efficient method for the synthesis of biodegradable, highly branched polycaprolactone (PCL) is presented. The solvent-free (bulk) reaction was carried out via ring opening polymerization (ROP), catalyzed by tin octanoate Sn(Oct)2, and it employed hyperbranched polyamide (HPPA) as a macro-initiator. The core–shell structure of the obtained products (PCL-HPPA), with the hyperbranched HPPA core and linear PCL chains as shell, was in the focus of the product characterization. 1H nuclear magnetic resonance (1H NMR) and elemental analysis confirmed the covalent incorporation of the HPPA in the products, as well as a high degree of grafting conversion of its amino functional groups. Confocal Raman Micro spectroscopy, and especially Time-of-Flight Secondary Ion Mass Spectrometry, further supported the existence of a core–shell structure in the products. Direct observation of macromolecules by means of cryogenic transmission electron microscopy, as well as gel permeation chromatography (GPC), suggested the existence of a minor 'aggregated' product fraction with multiple HPPA cores, which was attributed to transesterification reactions. Differential scanning calorimetry, as well as X-ray diffraction, demonstrated that the PCL-HPPA polymers displayed a similar degree of crystallinity to linear neat PCL, but that the branched products possessed smaller and less regular crystallites. [ABSTRACT FROM AUTHOR]

The unique features of poly[2‐(dimethylamino)ethyl methacrylate] (PDMAEMA), such as its sensitivity to external stimuli like pH and the presence of tertiary amine groups that can be easily quaternized to introduce antibacterial properties, make it a promising platform for biomedical applications. In this contribution, a facile, cost‐effective, and ecological procedure for controlled grafting of PDMAEMA brushes from a glass surface, both in mL and µL scale, is developed. This concept involves utilizing an aqueous solution of sunflower honey as a source of reducing sugars to accelerate surface‐initiated activators regenerated by electron transfer atom transfer radical polymerization. The PDMAEMA chains covalently grafted to the glass surface are then quaternized to form an antibacterial film. The thickness of the polymeric brush layer is determined by atomic force microscopy, while the chemical composition is analyzed by time of flight secondary ion mass spectrometry. Water contact angle measurements demonstrate the pH‐sensitivity of PDMAEMA pointing out the potential application of the prepared material as smart surfaces. Furthermore, the antibacterial tests against Gram‐positive and Gram‐negative bacteria strains are performed. The protein adsorption is used to evaluate the biocompatibility of the prepared surfaces. The resulting glass materials can serve as multifunctional surfaces for various purposes. [ABSTRACT FROM AUTHOR]

Abstract We characterize an approach enabling dual protein positioning over broad polymer areas based on subsequent selective adsorption of two fluorescently labelled lectins, Concanavalin A (Con A) and Lentil Lectin (LcH), on self-assembled gradient patterns of thermoresponsive poly(N-isopropyl acrylamide) (PNIPAM) and polystyrene (PS) polymers blend, prepared by horizontal dipping technique. The film morphologies of gradient samples prior dual selective protein adsorption are mapped with scanning microscopy (AFM) and secondary ion mass spectrometry (ToF-SIMS), whereas adsorbed proteins are imaged with fluorescence microscope. ToF-SIMS analysis reveals surface composition consisting of PNIPAM-rich domains in PS-rich matrix. The two-step protein adsorption experiment results in selective adsorption of Con A and LcH to PNIPAM- and PS-rich phases, respectively. Integral geometry approach is used to compare quantitatively morphology of polymer patterns varied in domain size due to horizontal dipping casting. Minkowski measures are also used to compare quantitatively fluorescence micrographs of protein patches with SIMS images of original isotropic polymer patterns. It confirms that PNIPAM domains size increases with increasing speed. Further, Minkowski analysis unveiled that adsorbed proteins cover about 60–70% of polymer surface. What is more fluorescence micrographs acknowledge both no lectins contamination and no adsorption to interphase areas. Additionally, protein displacement effect is observed. Graphical abstract Unlabelled Image Highlights • Gradient patterns of thermoresponsive polymer as supports for dual protein positioning. • Subsequent lectin adsorption allows fabrication of dual protein patterns. • Proteins displacement events were observed. • 'Protein affinity' is one of key factors responsible for the Vroman-like effect. [ABSTRACT FROM AUTHOR]

The novel temperature-responsive poly(cholesteryl methacylate) (PChMa) coatings derived from renewable sources were synthesized and characterized. Temperature induced changes in wettability were accompanied by surface roughness modifications, traced with AFM. Topographies recorded for temperatures increasing from 5 to 25 °C showed a slight but noticeable increase of calculated root mean square (RMS) roughness by a factor of 1.5, suggesting a horizontal rearrangement in the structure of PChMa coatings. Another structural reordering was observed in the 55–85 °C temperature range. The recorded topography changed noticeably from smooth at 55 °C to very structured and rough at 60 °C and returned eventually to relatively smooth at 85 °C. In addition, temperature transitions of PChMa molecules were revealed by DSC measurements. The biocompatibility of the PChMa-grafted coatings was shown for cultures of granulosa cells and a non malignant bladder cancer cell (HCV29 line) culture. [ABSTRACT FROM AUTHOR]

Among the various biomarkers that are used to diagnose or monitor disease, extracellular vesicles (EVs) represent one of the most promising targets in the development of new therapeutic strategies and the application of new diagnostic methods. The detection of circulating platelet-derived microvesicles (PMVs) is a considerable challenge for laboratory diagnostics, especially in the preliminary phase of a disease. In this study, we present a multistep approach to immobilizing and detecting PMVs in biological samples (microvesicles generated from activated platelets and human platelet-poor plasma) on functionalized silicon substrate. We describe the application of time-of-flight secondary ion mass spectrometry (TOF-SIMS) and spectroscopic ellipsometry methods to the detection of immobilized PMVs in the context of a novel imaging flow cytometry (ISX) technique and atomic force microscopy (AFM). This novel approach allowed us to confirm the presence of the abundant microvesicle phospholipids phosphatidylserine (PS) and phosphatidylethanolamine (PE) on a surface with immobilized PMVs. Phosphatidylcholine groups (CHN; CHPNO ) were also detected. Moreover, we were able to show that ellipsometry permitted the immobilization of PMVs on a functionalized surface to be evaluated. The sensitivity of the ISX technique depends on the size and refractive index of the analyzed microvesicles. [ABSTRACT FROM AUTHOR]

Fluorinated polymers have unique wettability and protein adsorption properties. The site-specific alteration of these properties could expand their application to different research areas. In this work, a fluorinated homopolymer and two of its copolymers with 4-vinylbenzyl glycidyl ether (VBGE) are synthesized by free radical polymerization. The produced polymers are then used to develop resist formulations by the addition of a photoacid generator. Films of these formulations are exposed to ultraviolet radiation through a binary mask and heated to create the pattern. It is found that the water contact angle values of the exposed films areas are reduced compared to those of the unexposed ones, with the exception of pentafluorophenyl methacrylate (PFMA) homopolymer film. This is attributed to the reaction of the epoxy groups creating x-links and producing hydroxyl groups and the cleavage of the pentafluorophenyl group from the ester group leading to carboxylic acid groups. Both modifications on the exposed areas are verified by FTIR spectroscopy and ToF-SIMS analysis. In addition, the biomolecules adsorption ability of the exposed area is increasing 10–15 times compared to the unexposed one for the PFMA homopolymer and the PFMA/VBGE 1:1 copolymer. Thus, the proposed polymers and patterning procedure could find application to spatially directed immobilization of biomolecules and/or cells onto a surface for both biosensing and tissue engineering purposes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Application of poly(4-vinyl pyridine) layers cross-linked with transition metal complexes as active layers in biomedical sensors. • Sensitivity of the coatings to the presence of proteins and cells in different concentrations verified by impedance spectroscopy. • Different detection limits for different transition metals. • High selectivity of the coatings toward the defined analyte confirmed by the specific antigen–antibody immunoreaction. • Conductive response of a bilayer system that mimics Organic Field Effect Transistor. The possibility of application of poly(4-vinyl pyridine) layers cross-linked with transition metal complexes as active layers in biomedical sensors was tested. The successful modification of the P4VP coating with CuBr 2 or ZnBr 2 was verified using time of flight - secondary ion mass spectrometry and X-ray photoelectron spectroscopy. The topography and wettability of the coatings were examined by using atomic force microscopy and water contact angles measurements, respectively. Tests of biological activity of coatings indicated strong protein adsorption, good biocompatibility, and no antimicrobial activity. The potential of the coatings to be used as active layers of biosensors was verified, by systematic impedance-based measurements, which showed the sensitivity of the P4VP:CuBr 2 coatings to the presence of proteins and cells in different concentrations. The high selectivity of the coatings toward the defined analyte was confirmed by the specific antigen–antibody immunoreaction, and the possibility of in situ monitoring of protein adsorption and cell adhesion also for individual cells was presented. Finally, the conductive response of a bilayer system that mimics Organic Field Effect Transistor was shown. These results point to a great potential for both coatings to serve as active layers of sensitive and highly selective biosensors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Architecture of PS-PGL copolymers influences its properties in thin films. • Copolymer with coil-brush structure reorients PGL segments in aqueous solution. • Reorientation of PGL chains to the film surface significantly reduces BSA adsorption. • Protein molecules due to adsorption to polymer film reduce mobility of polymer blocks. The effect of the architecture of amphiphilic polystyrene-b-polyglycidol and polystyrene-b-(polyglycidol-g-polyglycidol) copolymers on their behavior in thin films and interaction with the protein has been studied. The properties of the copolymer films surface were investigated before and after incubation in water and aqueous solution of PBS buffer. Surface sensitive techniques: time-of-flight secondary ion mass spectrometry, atomic force microscopy, and contact angle measurements show the differences in film surfaces behavior depending on the copolymer architecture. It was found that exposure of the coil-brush copolymer to an aqueous solution reoriented the PGL segments, changing the properties of the surface layer. Greater exposure of antifouling PGL chains at the surface of the copolymer film modified the interaction with bovine serum albumin, significantly reducing its adsorption. In contrast, no changes in the orientation of the PGL chains were observed after incubation of the copolymer films in an aqueous solution of protein in PBS buffer. This suggests that protein adsorption to the thin copolymer film blocks the conformational changes of the copolymer chains and reduces their mobility under the protein molecules. [ABSTRACT FROM AUTHOR]

Three multi-step multi-molecular approaches using the biotin–streptavidin system to contact-print DNA arrays on SiO2 surfaces modified with (3-glycidoxypropyl)trimethoxysilane are examined after each deposition/reaction step by atomic force microscopy, X-ray photoelectron spectroscopy and time of flight secondary ion mass spectrometry. Surface modification involves the spotting of preformed conjugates of biotinylated oligonucleotides with streptavidin onto surfaces coated with biotinylated bovine serum albumin b-BSA (approach I) or the spotting of biotinylated oligonucleotides onto a streptavidin coating, the latter prepared through a reaction with immobilized b-BSA (approach II) or direct adsorption (approach III). AFM micrographs, quantified by autocorrelation and height histogram parameters (e.g. roughness), reveal uniform coverage after each modification step with distinct nanostructures after the reaction of biotinylated BSA with streptavidin or of a streptavidin conjugate with biotinylated oligonucleotides. XPS relates the immobilization of biomolecules with covalent binding to the epoxy-silanized surface. Protein coverage, estimated from photoelectron attenuation, shows that regarding streptavidin the highest and the lowest immobilization efficiency is achieved by following approaches I and III, respectively, as confirmed by TOF-SIMS microanalysis. The size of the DNA spot reflects the contact radius of the printed droplet and increases with protein coverage (and roughness) prior to the spotting, as epoxy-silanized surfaces are hardly hydrophilic. Representative TOF-SIMS images show sub-millimeter spots: uniform for approach I, doughnut-like (with a small non-zero minimum) for approach II, both with coffee-rings or peak-shaped for approach III. Spot features, originating from pinned contact lines and DNA surface binding and revealed by complementary molecular distributions (all material, DNA, streptavidin, BSA, epoxy, SiO2), indicate two modes of droplet evaporation depending on the details of each applied approach. [ABSTRACT FROM AUTHOR]

Polylactic acid (PLA), a polymer derived from renewable resources, is gaining increasing attention in the development of biomedical devices due to its cost-effectiveness, low immunogenicity, and biodegradability. However, its inherent hydrophobicity remains a problem, leading to poor cell adhesion features. On this basis, the aim of this work was to develop a method for functionalizing the surface of PLA films with a biopolymer, chitosan (CH), which was proved to be a material with intrinsic cell adhesive properties, but whose mechanical properties are insufficient to be used alone. The combination of the two polymers, PLA as a bulk scaffold and CH as a coating, could be a promising combination to develop a scaffold for cell growth. The modification of PLA films involved several steps: aminolysis followed by bromination to graft amino and then bromide groups, poly(glycidyl methacrylate) (PGMA) grafting by surface-initiated supplemental activator and reducing agent atom transfer radical polymerization (SI-SARA ATRP) and finally the CH grafting. To prove the effective adhesive properties, conjugated and non-conjugated films were tested in vitro as substrates for neuronal cell growth using differentiated neurons from human induced pluripotent stem cells. The results demonstrated enhanced cell growth in the presence of CH. [Display omitted] • Functionalization of PLA films with chitosan is developed. • Grafting is performed by SI-SARA ATRP. • The functionalized films prove to be efficient scaffolds for neuronal cell growth. [ABSTRACT FROM AUTHOR]

The effect of temperature and buffer solutions with different pH (often used in biomedical applications) on the behavior of POEGMA brush coatings, synthesized without incorporated functional groups, was for the first time studied in details using water contact angle (CA) measurements and atomic force microscopy (AFM). Thermal response of grafted brush-coatings based on poly(oligo(ethylene glycol) methacrylate)s (POEGMA)s is driven by lower critical solution temperature (LCST) phenomenon. Obtained CA and AFM results suggest strong impact of the buffer solutions on the values of LCST transition and contact angle ranges, as well as on coatings morphology. In turn, ellipsometry data reflect penetration of salt ions from buffer solutions into brush-coatings. In contrast to "typical" behavior of POEGMA coatings in water, different mechanisms available below LCST in the buffer solutions destroy hydrated layers surrounding POEGMA macromolecules leading to their collapse. [ABSTRACT FROM AUTHOR]

[Display omitted] • Complex polymer structures were grafted on PEEK to increase its biocompatibility. • SI-ATRP was used to synthesize hydrophilic polymer brushes over 300 nm. • High density of functional groups enhanced the formation of 3D HAp layers. • Extensive analysis of product hints its high potential of use in implantology. In the search of the ideal bone implant material, surface initiated atom transfer radical polymerization (SI-ATRP) techniques were successfully employed to modify the polyetheretherketone (PEEK) surface with complex architecture nanolayers featuring hydrophilic poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) or poly(2-hydroxyethyl methacrylate) (PHEMA) branches. As a result, polymer layers with height up to over 300 nm were synthesized to decrease the water contact angle from 92.8° to 23.0°. In-depth analysis of layer topography, structure and elemental composition realized with atomic force microscopy (AFM), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), time-of-flight secondary ions mass spectroscopy (TOF-SIMS) and X-ray photon spectroscopy (XPS) confirmed successful surface modification. Additionally, to demonstrate the applicability of proposed PEEK functionalization, the biomineralization assay in simulated body fluid (SBF) solution was conducted. The high density of hydroxyl and amine groups in branched polymer brushes structure enhanced the rate of hydroxyapatites (HAp) formation substantially. Compared to untreated PEEK, modification with polymer brushes resulted in the creation of cauliflower-like structures with high specific surface area and Ca/P ratio equal to 1.83–1.87 for PEEK grafted with brushes composed of PHEMA backbone segment and PDMAEMA or PHEMA as block polymer branches (PEEK- g -PHEMA- g -PDMAEMA or PEEK- g -PHEMA- g -PHEMA) after 2 weeks. Finally, the process of the hydroxyapatite formation and increase of the layer thickness in a range of 14 days to 6 weeks of immersion in SBF was thoroughly visualized by scanning electron microscopy (SEM). [ABSTRACT FROM AUTHOR]

We have investigated the formation of surface nanostructures caused by early-stage wear of polystyrene (PS) and poly(n -butyl methacrylate) (PnBMA) thin films as pure materials, or mixed in the form of a 1:1 blend. To this end, atomic force microscopy (AFM) was used to repeatedly scratch the sample surfaces, measure the accompanying friction forces, and image the resulting features. In the very first stage ordered ripples are formed in all cases. As the process goes on, hillocks are nucleated on the crests of the ripples, and progressively released in the form of nanoplastics while the ripples become wider and less regular. On the blend surface the more compliant PnBMA presents more corrugated ripple structures and larger friction oscillations than PS in the beginning, but the scenario becomes again more complex as the wear test is repeated and the original 'rim and hole' geometry of the blend is disrupted. Quite noticeably, the wear damage is reduced if the surfaces are scraped forth and back and not only in one direction. The influence of the scan pattern (distance between scan lines) and of the normal force (well below and above the force threshold of about 50 nN leading to surface ripples in the first stage) have been also addressed. • Evolution of early-stage wear on a polymer blend is characterized on the nanoscale. • Hillocks are nucleated from the surface ripples formed in the very first stage. • As the process goes on the hillocks are released in the form of nanoplastics. • Wear is reduced if the polymer blend is scraped forth and back. [ABSTRACT FROM AUTHOR]

In the presented work "smart" antibacterial surfaces based on silver nanoparticles (AgNPs) embedded in temperature-responsive poly(di(ethylene glycol)methyl ether methacrylate) - (POEGMA188) as well as poly(4-vinylpyridine) – (P4VP) coatings attached to a glass surface were successfully prepared. The composition, thickness, morphology and wettability of the resulting coatings were analyzed using ToF-SIMS, XPS, EDX, ellipsometry, AFM, SEM and CA measurements, respectively. Temperature-switched killing of the bacteria was tested against Escherichia coli ATCC 25922 (representative of Gram-negative bacteria) and Staphylococcus aureus ATCC 25923 (representative of Gram-positive bacteria) at 4 and 37 °C. In general at 4 °C no significant difference was observed between the amounts of bacteria accounted on the grafted brush coatings and within the control sample. In contrast, at 37 °C almost no bacteria were visible for temperature-responsive coating with AgNPs, whereas the growth of bacteria remains not disturbed for "pure" coating, indicating strong temperature-dependent antibacterial properties of AgNPs integrated into brushes. Unlabelled Image • "Command" surfaces were successfully fabricated. • Thermo-switchable antibacterial activity was shown. • Antibacterial properties for different type of bacteria were demonstrated. [ABSTRACT FROM AUTHOR]

Time-of-flight secondary ion mass spectrometry has been employed to examine, with biomolecular discrimination, sensing arm areas (20 μm × 600 μm) of integrated onto silicon chips Mach-Zehnder interferometers aiming to optimize their biofunctionalization with regard to indirect immunochemical (competitive) detection of ochratoxin A. Sensing areas are examined after: modification with (3-aminopropyl)triethoxysilane, spotting of OTA-ovalbumin conjugate (probe) from solutions with different concentration, blocking with bovine serum albumin, reaction with OTA-specific mouse monoclonal antibody followed by goat anti-mouse IgG secondary antibody. Component mass loadings of all proteins involved in immunodetection are determined from TOF-SIMS micro-analysis combined with ellipsometry of planar surfaces. These data show that partial desorption of surface-bound probe and blocking protein takes place upon primary immunoreaction to a degree that depends on probe concentration in spotting solution. Taking into account this desorption, apparent binding stoichiometry of both antibodies in immune complexes formed onto chip surface is determined more accurately than the respective evaluation based on real-time sensor response. In addition, mass loadings for probe and secondary antibody is observed to saturate for optimum probe concentrations. Also, principal component analysis of TOF-SIMS data could resolve both immunoreactions and biofunctionalization and discriminate surfaces prepared with optimum probe concentrations from those prepared using suboptimum ones. [ABSTRACT FROM AUTHOR]

[Display omitted] • pH-response of complex architecture polymer brushes generated via low-ppm SI-ATRP. • Polyelectrolyte nanolayers as complex architecture brushes were grated from Si wafer. • Sequential SI-ATRP in microliter-scale applied as novel tool for surface nanoengineering. • 20 μL/cm2 of reaction mixture resulted in effective synthesis of amphiphilic polymer brushes. The article presents a step-by-step protocol, designed on the basis of principles of green chemistry, for the synthesis of polymer brushes with complex structure via surface-initiated atom transfer radical polymerization (SI-ATRP) approach. The selection of anionic (poly(acrylic acid), PAA) and cationic (poly(2-(dimethylamino)ethyl methacrylate, PDMAEMA) macromolecular chains enabled the formation of ampholytic polymer coating on silicon (Si) substrates. Scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) analyses confirmed changes in the structure of the synthesized nanolayer at each step of the surface modification. Finally, the synthesis protocol was rescaled presenting an extremely economically and environmentally beneficial procedure for the synthesis of Si wafers grafted with brushes composed of poly(2-hydroxyethyl methacrylate) (PHEMA) core and PDMAEMA and PAA as block polymer branches (Si- g -PHEMA- g -(PDMAEMA- b -PAA)) with application of microliter volumes of reactants. [ABSTRACT FROM AUTHOR]

Mass fabrication of integrated biosensors on silicon chips is facilitated by contact pin-printing, applied for biofunctionalization of individual Si 3 N 4 -based transducers at wafer-scale. To optimize the biofunctionalization for immunochemical (competitive) detection of fungicide thiabendazole (TBZ), Si 3 N 4 surfaces are modified with (3-aminopropyl)triethoxysilane and examined after: immobilization of BSA-TBZ conjugate (probe) from solutions with different concentration, blocking with bovine serum albumin (BSA), and immunoreaction with a mouse monoclonal antibody against TBZ. Nanostructure, surface density, probe composition and coverage uniformity of protein layers are evaluated with Atomic Force Microscopy, Spectroscopic Ellipsometry, Time-of-Flight Secondary Ion Mass Spectrometry and X-ray Photoelectron Spectroscopy. Contact pin-printing of overlapping probe spots is compared with hand spotted areas. Contact pin-printing resulted in two-fold increase of immobilized probe surface density as compared to hand spotting. Regarding BSA-TBZ immobilization, an incomplete monolayer develops into a bilayer as the concentration of BSA-TBZ molecules in the printing solution increases from 25 to 100 μg/mL. Upon blocking, however, a complete protein monolayer is formed for all the BSA-TBZ concentrations used. Free surface sites are filled with BSA for low surface coverage with BSA-TBZ, whereas loosely bound BSA-TBZ molecules are removed from the BSA-TBZ bilayer. As a consequence immunoreaction efficiency increases with the printing probe concentration. [ABSTRACT FROM AUTHOR]

The arrangement, composition and orientation of immunoreagents employed in an indirect immunoassay for determination of mycotoxin OchraToxin A (OTA) are specified for Si 3 N 4 substrate, aiming to imitate biosensor transducers made of the same material. Si 3 N 4 surfaces are examined after modification with (3-aminopropyl)triethoxysilane, spotting with OTA-ovalbumin conjugate (probe), blocking with bovine serum albumin, reaction with a mouse monoclonal antibody against OTA and, finally, reaction with a goat anti-mouse secondary antibody. Atomic force micrographs, their autocorrelation and height histogram parameters, show the stepwise development of a multi-component monolayer covered by groups of secondary antibody molecules. Time-Of-Flight Secondary Ion Mass Spectrometry reveals the composition of probe and blocking protein, as well as their partial desorption during the primary immunoreaction. Ellipsometry provides surface amount of all proteins, increasing step-by-step from 0.7 to 6.9 mg/m 2 . In addition, ellipsometry combined with TOF-SIMS reveals the mass loadings of different molecules in the intermediate and the final overlayer. Based on this, some orientations of the immobilized molecules are proposed and a molar ratio of ∼2.5 for secondary to primary antibody is calculated. The orientations of the primary and secondary antibody are further clarified by Principal Component Analysis of TOF-SIMS data, through which a side-on and a head-on orientation is deduced for the primary and the secondary antibody, respectively. These findings demonstrate how the combination of multiple surface analysis techniques can provide insight on the arrangement, composition and orientation of biomolecules in the course of multi-step procedures employed in biosensors. [ABSTRACT FROM AUTHOR]

[Display omitted] • ZrCu-based thin films on 316L steel and Ti6Al4V alloy were obtained using the cathodic arc technique. • ZrCu-based thin films exhibited amorphous structures. • ToF-SIMS analysis revealed high protein adsorption on Ti6Al4V alloy substrate. • The coatings deposited on 316L substrate showed significant signs of poor corrosion resistance compared to those on Ti64 substrate. In this study, ZrCu-based thin films were obtained using a PVD-cathodic arc technique, aiming to improve the surface properties of 316L stainless steel and Ti6Al4V implant materials. By combining their superior mechanical properties with the corrosion resistance of amorphous metallic glasses, the obtained ZrCu-based layers could be qualified as candidates for medical applications. Ca, Mo, Mg, Si and Sr additions to ZrCu structure were considered and the resulting ternary systems were subjected to a detailed investigation. Potentiodynamic polarization was employed to assess corrosion kinetics and their overall electrochemical behaviour after 1 h immersion in SBF solution, the experiments being conducted at human body temperature (37.0 ± 0.5 °C). Additionally, electrochemical impedance spectroscopy (EIS) was carried out for detecting fast changes of the system under investigation and to reveal in depth information related to coating/substrate–solution interface. For morphology and topography characterization before and after electrochemical tests, scanning electron microscopy was used. The results showed a dependence of mechanical properties on the used substrate: the hardness was higher and a better adhesion was achieved when Ti6Al4V was used. Immersion tests were also influenced by the substrate related outcome, since the coatings deposited on 316L substrate showed a significant degradation compared to those on Ti6Al4V substrate, where the apatite structure formed on the surface was more evident. ToF-SIMS analysis revealed protein adsorption enhanced for all applied coatings. [ABSTRACT FROM AUTHOR]

Elastic properties of the substrate have profound effect on adhesion and proliferation of cells. Here, we introduce a method to produce polydimethylsiloxane (PDMS) substrates with stiffness tuned monotonically from 1.67 to 0.24 MPa, by the time of UV irradiation adjusted up to 5 h. The Young’s modulus (determined by using nanoindenter) scales linearly with stiffness calculated using AFM-based force spectroscopy data. Such a relation enables the determination of the Young modulus from AFM force – distance curves also when the Herz model is not applicable. Our findings demonstrate that surface properties of PDMS substrates are not affected by the applied methodology of tuning substrate elasticity. Finally, the colorimetric proliferation assay (MTT) carried out for non-malignant (HCV29) and cancerous (T24) bladder cancer cells depicted a significant contribution of PDMS substrate elasticity to the behavior of cells. The softer PDMS substrate demonstrated excellent cytocompatibility whereas the stiff one is more cell-repellent. [ABSTRACT FROM AUTHOR]

Time-of-flight secondary ion mass spectrometry (imaging, micro-analysis) has been employed to evaluate biofunctionalization of the sensing arm areas of Mach-Zehnder interferometers monolithically integrated on silicon chips for the immunochemical (competitive) detection of bovine κ-casein in goat milk. Biosensor surfaces are examined after: modification with (3-aminopropyl)triethoxysilane, application of multiple overlapping spots of κ-casein solutions, blocking with 100-times diluted goat milk, and reaction with monoclonal mouse anti-κ-casein antibodies in blocking solution. The areas spotted with κ-casein solutions of different concentrations are examined and optimum concentration providing homogeneous coverage is determined. Coverage of biosensor surfaces with biomolecules after each of the sequential steps employed in immunodetection is also evaluated with TOF-SIMS, supplemented by Atomic force microscopy and X-ray photoelectron spectroscopy. Uniform molecular distributions are observed on the sensing arm areas after spotting with optimum κ-casein concentration, blocking and immunoreaction. The corresponding biomolecular compositions are determined with a Principal Component Analysis that distinguished between protein amino acids and milk glycerides, as well as between amino acids characteristic for Mabs and κ-casein, respectively. Use of the optimum conditions (κ-casein concentration) for functionalization of chips with arrays of ten Mach-Zehnder interferometers provided on-chips assays with dramatically improved both intra-chip response repeatability and assay detection sensitivity. [ABSTRACT FROM AUTHOR]

Novel alignment coating with temperature-tuned anchoring for nematic liquid crystals (NLCs) was successfully fabricated in three step process, involving polymerization of poly(cholesteryl methacrylate) (PChMa) from oligoproxide grafted to the glass surface premodified with 3-aminopropyltriethoxysilane. Molecular composition, thickness, wettability of the PChMa coating and its alignment action for a NLC were examined with time of flight-secondary ion mass spectrometry, ellipsometry, contact angle measurements, polarization optical microscopy and commercially produced PolScope technique allowing for mapping of the optic axis and optical retardance within the microscope field view. We find that the PChMa coating provides a specific monotonous increase (decrease) in the tilt angle of the NLC director with respect to the substrates normal upon heating (cooling) referred to as anchoring tuning. [ABSTRACT FROM AUTHOR]

The methods of preparation and characterization of core-shell poly(styrene/α- tert -butoxy-ω-vinylbenzyl-polyglycidol) particles arranged in colloidal crystals are described. The particles were prepared via emulsifier free emulsion copolymerization of styrene and α- tert -butoxy-ω-vinylbenzyl-polyglycidol macromonomer in aqueous medium, initiated by potassium persulfate. The individual polymerizations differed in a way of addition of macromonomer to the polymerization mixture. The particles assemblies were characterized by atomic force microscopy, Secondary Ion Mass Spectrometry (SIMS) and X-ray Photoelectron Spectroscopy (XPS). In-depth distribution of chemical states was determined by XPS combined with argon gas cluster ion sputtering (Ar-GCIB). The morphology of microspheres assemblies reflected the composition of the entire particles. It was found that the method of macromonomer addition to the polymerization mixture affects the particles size, surface and overall morphology. The XPS profiles revealed the chemical composition of the particles arranged in multilayers. It was found that distribution of polyglycidol segments at the particles interfacial layer depends on the time and way of addition of macromonomer. The thickest outer layer composed from polystyrene-polyglycidol segments was obtained for particles when macromonomer was added at the beginning of polymerization. [ABSTRACT FROM AUTHOR]

There are several techniques like time of flight secondary ion mass spectrometry (ToF SIMS) that require a special protocol for preparation of biological samples, in particular, those containing single cells due to high vacuum conditions that must be kept during the experiment. Frequently, preparation methodology involves liquid nitrogen freezing what is not always convenient. In our studies, we propose and validate a protocol for preparation of single cells. It consists of four steps: (i) paraformaldehyde fixation, (ii) salt removal, (iii) dehydrating, and (iv) sample drying under ambient conditions. The protocol was applied to samples with single melanoma cells i.e. WM115 and WM266-4 characterized by similar morphology. The surface and internal structures of cells were monitored using atomic force, scanning electron and fluorescent microscopes, used to follow any potential protocol-induced alterations. To validate the proposed methodology for sample preparation, ToF SIMS experiments were carried out using C 60 + cluster ion beam. The applied principal component analysis (PCA) revealed that chemical changes on cell surface of melanoma cells were large enough to differentiate between primary and secondary tumor sites. Subject category : Mass spectrometry. [ABSTRACT FROM AUTHOR]

[Display omitted] • Preparation procedures of effective plasmonic probes for TERS measurements of DNA are developed. • Characterization of plasmonic properties of various types of TERS probes is demonstrated. • DNA – a standard sample for nanospectroscopic techniques. Tip-enhanced Raman (TER) spectroscopy combines the nanometric spatial resolution of atomic force microscopy (AFM) and the chemical sensitivity of Raman spectroscopy. Thus, it provides a unique possibility to obtain spectroscopic information on individual, nanometre-size molecules. The enhancement of Raman scattering cross-section requires modification of the AFM tip apex with a plasmonic nanostructure. Despite numerous advances of TERS research, attaining good reproducibility and stable enhancement is still challenging mainly due to the lack of optimized probes and sample preparation procedures. Moreover, current nanospectroscopic standard samples - carbon nanotubes (CNTs) have relatively simple chemical structure, and therefore, they are far from real-life analytes, especially biological samples. In this work we focus on the optimization of TERS technique for efficient DNA measurements, including: a preparation of atomically-flat gold substrates, fixative free deposition of DNA and optimization of TERS probe preparation. Here we demonstrate a comprehensive comparison of the efficacy of several types of TERS probes. Applying the systematic approach, we obtained reliable and reproducible TER spectra of DNA. Thus, we provide preparation procedures of a new standard TERS sample, TERS substrates and TERS probes. Our research provides a solid foundation for further research on DNA and its interaction with other biomolecules upon biologically significant processes such as DNA damage and repair. [ABSTRACT FROM AUTHOR]

Highlights: [•] Poly(N-methacryloyl-l-leucine) coatings were polymerized from peroxided substrate. [•] Temperature-responsive properties of the peptide-mimetic coating were discovered. [•] High affinity of PNML coating to two proteins: LcH and BSA was observed. [•] Excellent cytocompatibility of PNML coating was demonstrated for HEK 293 cells. [ABSTRACT FROM AUTHOR]

Highlights: [•] Poly(oligo(ethylene glycol) methacrylate) was polymerized from glass surface. [•] Thermal but also pH-response is observed. [•] Thermal sensitivity, observed in wettability, diminishes with decreasing pH. [•] Such transitions induce changes in protein adsorption. [Copyright &y& Elsevier]

Abstract: Poly(N-isopropylacrylamide) (PNIPAM) coatings attached to glass with novel approach involving polymerization from oligoperoxide grafted to surface with (3-aminopropyl)triethoxysilane exhibit not only temperature- but also pH-dependence of wettability and protein adsorption. Wettability and composition of coatings, fabricated with different polymerization times, were determined using contact angle measurements and Time Of Flight-Secondary Ion Mass Spectrometry (TOF-SIMS), respectively. Thermal response of wettability, measured between 20 and 40°C, was prominent at pH 9 and 7 and diminished or absent at pH 5 and 3. This indicates a transition between hydrated loose coils and hydrophobic collapsed chains that is blocked at low pH. Higher surface roughness and dramatically increased adsorption of model protein (lentil lectin labeled with fluorescein isothiocyanate) were observed with AFM and fluorescence microscopy to occur in hydrophobic phases (at pH 3, for pH varied at constant temperature of 22°C and at ∼33°C, for temperature varied at constant pH 9). Protein adsorption response to pH was confirmed by TOF-SIMS and Principal Component Analysis. [Copyright &y& Elsevier]

The impact of polymer stereoregularity on its interactions with peptides, proteins and bacteria strains was studied for three stereoregular forms of poly(tert-butyl methacrylate) (PtBMA): isotactic (iso), atactic (at) and syndiotactic (syn) PtBMA. Principal component analysis of the time-of-flight secondary ion mass spectrometry data recorded for thin polymer films indicated a different orientation of ester groups, which in the case of iso-PtBMA are exposed away from the surface whereas for at-PtBMA and syn-PtBMA these are located deeper within the film. This arrangement of chemical groups modified the interactions of iso-PtBMA with biomolecules when compared to at-PtBMA and syn-PtBMA. For peptides, the affected interactions were explained by the preferential hydrogen bonding and electrostatic interaction between the exposed polar ester groups of iso-PtBMA and positively charged peptides. In turn, for protein adsorption no impact on the amount of adsorbed proteins was observed. However, the polymer stereoregularity influenced the orientation of immunoglobulin G and induced conformational changes in bovine serum albumin structure. Moreover, the impact of polymer stereoregularity occurred equally for their interactions with Gram-positive bacteria (S. aureus) , which absorbed preferentially onto iso-PtBMA films as compared to two other stereoregularities. [Display omitted] • properties of polymer film surface can be modified by stereoregularity of polymer. • isotactic PtBMA expose more polar ester groups at the surface. • tacticity of polymer impact on conformation and orientation of adsorbed proteins. • presence of ester groups at the surface of iso-PtBMA modified bacterial adhesion. [ABSTRACT FROM AUTHOR]

In the present work, we have successfully prepared and characterized novel nanocomposite material exhibiting temperature-dependent surface wettability changes, based on grafted brush coatings of non-fouling poly(di(ethylene glycol)methyl ether methacrylate) (POEGMA) with the embedded CaCO3 nanoparticles. Grafted polymer brushes attached to the glass surface were prepared in a three-step process using atom transfer radical polymerization (ATRP). Subsequently, uniform CaCO3 nanoparticles (NPs) embedded in POEGMA-grafted brush coatings were synthesized using biomineralized precipitation from solutions of CaCl2 and Na2CO3. An impact of the low concentration of the embedded CaCO3 NPs on cell adhesion and growth depends strongly on the type of studied cell line: keratinocytes (HaCaT), melanoma (WM35) and osteoblastic (MC3T3-e1). Based on the temperature-responsive properties of grafted brush coatings and CaCO3 NPs acting as biologically active substrate, we hope that our research will lead to a new platform for tissue engineering with modified growth of the cells due to the release of biologically active substances from CaCO3 NPs and the ability to detach the cells in a controlled manner using temperature-induced changes of the brush. [ABSTRACT FROM AUTHOR]

The presented research aims to verify whether physicochemical properties of lung fibroblasts, modified by substrate stiffness, can be used to discriminate between normal and fibrotic cells from idiopathic pulmonary fibrosis (IPF). The impact of polydimethylsiloxane (PDMS) substrate stiffness on the physicochemical properties of normal (LL24) and IPF-derived lung fibroblasts (LL97A) was examined in detail. The growth and elasticity of cells were assessed using fluorescence microscopy and atomic force microscopy working in force spectroscopy mode, respectively. The number of fibroblasts, as well as their shape and the arrangement, strongly depends on the mechanical properties of the substrate. Moreover, normal fibroblasts remain more rigid as compared to their fibrotic counterparts, which may indicate the impairments of IPF-derived fibroblasts induced by the fibrosis process. The chemical properties of normal and IPF-derived lung fibroblasts inspected using time-of-flight secondary ion mass spectrometry, and analyzed complexly with principal component analysis (PCA), show a significant difference in the distribution of cholesterol and phospholipids. Based on the observed distinctions between healthy and fibrotic cells, the mechanical properties of cells may serve as prospective diagnostic biomarkers enabling fast and reliable identification of idiopathic pulmonary fibrosis (IPF). [ABSTRACT FROM AUTHOR]

• Aminosilane layer micropatterned with photolithography and oxygen plasma. • Selective adsorption of contact printed biotinylated-BSA onto the APTES stripes. • Step-by-step chemical imaging of APTES patterning and biofunctionalization. • Blocking the surface with BSA results in binary protein pattern. • Patterning demonstrated for on-chip interferometric biosensors detecting streptavidin. Time-of-flight secondary ion mass spectrometry has been employed to characterize micropatterning of aminosilane layer by photolithography and oxygen plasma treatment to achieve spatially selective biofunctionalization of Si 3 N 4 waveguides surface corresponding to the sensing arm area of Mach-Zehnder interferometric biosensors integrated on silicon-chip. Si 3 N 4 surface with (3-aminopropyl)triethoxysilane (APTES) layer was examined after photolithography, plasma treatment, photoresist removal, and after robotic spotting with biotinylated bovine serum albumin (BSA), blocking with BSA and specific binding of streptavidin. TOF-SIMS chemical imaging and microanalysis provided an inside view regarding the resolution and selectivity of surface modification after each step of both the APTES layer patterning and biofunctionalization procedures. More particular, the effective APTES removal and surface oxidization to create 20-µm wide APTES stripes through photolithography and oxygen plasma treatment was demonstrated. Exclusive adsorption of biotinylated-BSA on the APTES stripes through spotting of the patterned surface is then revealed, followed by a preferential but not exclusive BSA adsorption during the blocking step. The pattern was clearly developed through exclusive streptavidin binding to biotinylated-BSA only onto the APTES regions. The proposed spatially-selective biofunctionalization, performed with biotinylated-BSA, was demonstrated for the Si 3 N 4 waveguide surface of an integrated on chip interferometric biosensor sensing arm for the detection of streptavidin. [ABSTRACT FROM AUTHOR]