Immobilization Of Ligands Research Articles

Novel fully-integrated biosensor for endotoxin detection via polymyxin B immobilization onto gold electrodes

Abstract. In this paper an electrochemical endotoxin biosensor consisting of an immobilized lipopolysaccharide (LPS) ligand, polymyxin B (PmB), is presented. Several parameters involved both in the device fabrication and in the detection process were analyzed to optimize the ligand immobilization and the interaction between PmB and LPS, aiming at increasing the sensitivity of the sensor. Different electrochemical pre-treatment procedures as well as the functionalization methods were studied and evaluated. The use of a SAM (self-assembled monolayer) to immobilize PmB and the quantification of the interactions via cyclic voltammetry allowed the development of a robust and simple device for in situ detection of LPS. Thus, the biosensor proposed in this work intends an approach to the demanding needs of the market for an integrated, portable and simple instrument for endotoxin detection.

Micropatterned designs of thermoresponsive surfaces for modulating cell behaviors

The chemistry and topography of the material surfaces have an important effect on cell behaviors. In this study, we reported the preparation of thermoresponsive micropatterned surfaces (TS) and galactosylated TS for modulating the adhesion/detachment of cells. A thickness of 1 µm of poly(N‐isopropylacrylamide) grafted layer was fabricated on the polystyrene surface with microgrooves using ultraviolet‐induced copolymerization. The thick grafted layer was in favor of the interactions between cells and materials. The following immobilization of galactose ligand with specific affinity to hepatocyte onto TS promoted the adhesion of human hepatocyte line (HL‐7702 cells). The microgrooves structure could facilitate cell adhesion and regulate the oriented growth of cells. Moreover, narrow grooves accelerated the spontaneous detachment of cells only by reducing temperature. Thus, micropatterned biofunctional designs with controlled geometrical features presented in this study have sufficient biofunctional activities in facilitating cell sheet engineering and regenerative medicine. Copyright © 2013 John Wiley & Sons, Ltd.

Fluorescent cellulose aerogels containing covalently immobilized (ZnS)x(CuInS2)1-x/ZnS (core/shell) quantum dots.

Photoluminiscent (PL) cellulose aerogels of variable shape containing homogeneously dispersed and surface-immobilized alloyed (ZnS)x(CuInS2)1−x/ZnS (core/shell) quantum dots (QD) have been obtained by (1) dissolution of hardwood prehydrolysis kraft pulp in the ionic liquid 1-hexyl-3-methyl-1H-imidazolium chloride, (2) addition of a homogenous dispersion of quantum dots in the same solvent, (3) molding, (4) coagulation of cellulose using ethanol as antisolvent, and (5) scCO2 drying of the resulting composite aerogels. Both compatibilization with the cellulose solvent and covalent attachment of the quantum dots onto the cellulose surface was achieved through replacement of 1-mercaptododecyl ligands typically used in synthesis of (ZnS)x(CuInS2)1−x/ZnS (core–shell) QDs by 1-mercapto-3-(trimethoxysilyl)-propyl ligands. The obtained cellulose—quantum dot hybrid aerogels have apparent densities of 37.9–57.2 mg cm−3. Their BET surface areas range from 296 to 686 m2 g−1 comparable with non-luminiscent cellulose aerogels obtained via the NMMO, TBAF/DMSO or Ca(SCN)2 route. Depending mainly on the ratio of QD core constituents and to a minor extent on the cellulose/QD ratio, the emission wavelength of the novel aerogels can be controlled within a wide range of the visible light spectrum. Whereas higher QD contents lead to bathochromic PL shifts, hypsochromism is observed when increasing the amount of cellulose at constant QD content. Reinforcement of the cellulose aerogels and hence significantly reduced shrinkage during scCO2 drying is a beneficial side effect when using α-mercapto-ω-(trialkoxysilyl) alkyl ligands for QD capping and covalent QD immobilization onto the cellulose surface.

Label-free CRP detection using optical biosensor with one-step immobilization of antibody on nitrocellulose membrane

To assess the potential of using the MCLW sensor as a label-free optical biosensor system for clinical diagnosis, we evaluated the potential of detecting C-reactive protein (CRP) in a diluted real serum sample by using nitrocellulose as an adlayer. Nitrocellulose was coated on the MCLW sensor chip via spin coating and the CRP antibody was directly immobilized on the sensor surface by hydrophobic physical adsorption. Biosensing using the nitrocellulose surface is highly convenient and does not require any additional treatment for the immobilization of ligand. We optimized the condition for the deposition of nitrocellulose on the MCLW sensor chip with the goal of generating the largest signal difference of the sample against the control signal. In addition, label-free immunosensing of CRP was achieved using the nitrocellulose-coated MCLW sensor in real time. As a result, we were able to quantitatively detect CRP in a human serum within a concentration range of 0.1–10μg/mL.

Sequential Nucleophilic Substitutions Permit Orthogonal Click Functionalization of Multicomponent PEG Brushes

Multicomponent poly(ethylene glycol) (PEG) brushes (i.e., ≥ 2 adjacent PEG brushes) can be used to engineer culture substrates with microscale, nonfouling regions decorated with covalently immobilized ligands that mediate biospecific interactions. However, synthesizing such brushes with orthogonal immobilization chemistries to permit differential biofunctionalization is nontrivial and often requires synthesis of PEG-co-polymers. To simplify synthesis and enhance the versatility of such substrates, we developed a protocol for generating orthogonal click-functionalized multicomponent PEG brushes using sequential nucleophilic substitutions by sodium azide, ethanolamine, and propargylamine. The novel application of propargylamine-mediated substitution functionalizes PEG brushes with acetylene groups, and for the first time, ethanolamine-mediated substitution is shown to be sufficient for passivating the "living" polymer chain ends between brush synthesis steps. Thus, our multicomponent PEG brushes present dual orthogonal chemistries (i.e., azido and acetylene groups) for ligand immobilization via versatile copper-free click reactions, which are useful for in situ surface modifications during cell culture.

Notch-HES1 signaling axis controls hemato-endothelial fate decisions of human embryonic and induced pluripotent stem cells

AbstractNotch signaling regulates several cellular processes including cell fate decisions and proliferation in both invertebrates and mice. However, comparatively less is known about the role of Notch during early human development. Here, we examined the function of Notch signaling during hematopoietic lineage specification from human pluripotent stem cells of both embryonic and adult fibroblast origin. Using immobilized Notch ligands and small interfering RNA to Notch receptors we have demonstrated that Notch1, but not Notch2, activation induced hairy and enhancer of split 1 (HES1) expression and generation of committed hematopoietic progenitors. Using gain- and loss-of-function approaches, this was shown to be attributed to Notch-signaling regulation through HES1, which dictated cell fate decisions from bipotent precursors either to the endothelial or hematopoietic lineages at the clonal level. Our study reveals a previously unappreciated role for the Notch pathway during early human hematopoiesis, whereby Notch signaling via HES1 represents a toggle switch of hematopoietic vs endothelial fate specification.

Dextran–Lipase Conjugates as Tools for Low Molecular Weight Ligand Immobilization in Microarray Development

The development of effective array biosensors relies heavily on careful control of the density of surface-immobilized ligands on the transducing platform. In this paper we describe the synthesis of new dextran-lipase conjugates for use in immobilizing low molecular weight haptens onto glass planar waveguides for immunosensor development. The conjugates were synthesized by immobilizing bacterial thermoalkalophilic lipases (Geobacillus thermocatenulatus lipase 2, BTL2) on agarose macroporous beads, followed by covalent coupling to dextran networks of variable molecular weight (1500-40000). The chimeras were immobilized via nonspecific hydrophobic interactions onto glass planar waveguides modified with 1,1,1,3,3,3-hexamethyldisilazane to obtain highly ordered and homogeneous molecular architectures as confirmed by atomic force microscopy. Microcystin LR (MCLR) was covalently bound to the dextran-BTL2 conjugates. The usefulness of this approach in immunosensor development was demonstrated by determining amounts of MCLR down to a few picograms per liter with an automated array biosensor and evanescent wave excitation for fluorescence measurements of attached DyLight649-labeled secondary antibody. Modifying BTL2 with dextrans of an increased molecular weight (>6000) provided surfaces with an increased loading capacity that was ascribed to the production of three-dimensional surfaces by the effect of analyte binding deep in the volume, leading to expanded dynamic ranges (0.09-136.56 ng L(-1)), lower limits of detection (0.007 ± 0.001 ng L(-1)), and lower IC50 values (4.4 ± 0.7 ng L(-1)). These results confirm the effectiveness of our approach for the development of high-performance biosensing platforms.

Lying low but ready for action: the quiescent muscle satellite cell

The muscle satellite cell is essential for skeletal muscle regeneration. It is located on the muscle fibre, under the basal lamina as a quiescent cell, which becomes activated after injury, when it leaves the fibre, proliferates, and either undergoes myogenesis to form new fibres or reconstitutes the satellite cell pool. In this review, we discuss the cellular environment of the quiescent cell, including the extracellular matrix, which constitutes its niche. Cell adhesion molecules and some signalling pathways reinforce its quiescent state, whereas other signals lead to activation. We discuss how the satellite cell is ready to respond with the appropriate receptors, but protects its quiescence by mechanisms that include immobilization of ligands by extracellular matrix components and synthesis of inhibitors for intracellular signalling pathways and for metalloproteinases that break down the matrix and promote ligand processing and receptor activation. The quiescent satellite cell is also well protected against toxins and oxidative stress. It has a low metabolic rate, as shown by few active mitochondria and anaerobic glycolysis. Different subpopulations of quiescent satellite cells can be distinguished on the basis of cell surface markers and stem cell-like properties. We discuss the latter in the context of the small proportion of satellite cells that express high levels of Pax7, or that are derived from cells that have never activated the Myf5 myogenic determination gene. However, many quiescent satellite cells transcribe Myf5, but do not enter myogenesis because of post-transcriptional regulation, which prevents Myf5 protein accumulation. Post-transcriptional regulation, through microRNA repression of a potential cell cycle activator, further illustrates how these cells are ready for action.

Surface modification methods to improve behavior of biosensor based on imaging ellipsometry

Surface modifications not only perform functions as ligand immobilization and biosensing interface formation, but also play a crucial role for inhibiting noise and enhance biosensor signal. After years of development, several surface modification methods designed for the biosensor based on imaging ellipsometry have become more and more practical and already been successfully implemented in the detection of various biomolecules. Some typical surface modification approaches are reviewed.

Polymer-supported chiral α-amino amides for the asymmetric addition of diethylzinc to aldehydes: Transforming an inactive homogeneous system into an efficient catalyst

A series of polymer-supported α-amino amides derived from natural amino acids have been easily synthesized and fully characterized. Their chiral Zn (II) complexes catalyzed the enantioselective addition of diethylzinc to aldehydes to form chiral secondary alcohols in high yields and enantioselectivities up to 95% were obtained. The results showed that the immobilization of this chiral ligand onto a polymeric matrix transforms the inactive homogeneous system into an efficient catalyst. Moreover, the supported catalyst could be re-used at least five times without any significant loss of catalytic activity.

Glycosylation of the polypropylene membrane surface via thiol–yne click chemistry for lectin adsorption

Glycosylated membrane, as one of the most important affinity membranes, permits affinity separation/purification of proteins based on carbohydrate–protein interactions. It is an important scientific issue to screen facile method for fabricating the glycosylated membrane surface with high glycosyl density. Such a surface can be fabricated by the direct covalent immobilization of carbohydrate ligands on the surfaces of microporous polypropylene membrane (MPPM). First, alkyne-functionalized membrane surface was fabricated by plasma pretreatment combined with UV-induced graft polymerization of 3-(trimethylsilyl) propargyl methacrylate. Then, the glycosylated membrane surface was directly fabricated with the thiol–yne click reaction to ensure rapid process, improved efficiency, and high glycosyl density. Chemical and physical properties of the membrane surface were characterized by ATR/FT-IR, XPS, FESEM and water contact angle measurement. Static lectin adsorption indicates that the glycosylated membrane can specifically adsorb lectin concanavalin A (Con A) other than peanut agglutinin (PNA). Break through curves from dynamic Con A adsorption show the membrane has unique properties such as strong specificity, high adsorption capacity, and reversible binding capability. We suggest that the prepared glycosylated membrane is of great potentials in affinity membrane chromatography for rapid and high-resolution separation/purification of lectins.

Simultaneous synthesis of modified Binol-periodic mesoporous organosilica SBA-15 type material. Application as catalysts in asymmetric sulfoxidation reactions

The synthesis of a chiral periodic mesoporous organosilica (chiral PMO) SBA-15 type, using a bis-silylated Binol precursor, has been studied through two different heterogenization routes. On the one hand, the immobilization of a (R)-(+)-1,1′-bi-2-naphthol (Binol) derivative was accomplished by following a standard multistep synthesis methodology. On the other hand, a new route consisting of an easy one-step synthesis was developed achieving a simultaneous formation of mesoporous structure and Binol chiral ligand immobilization in the walls. The addition of KCl “salting out” electrolytes favored the micellization, obtaining the well-ordered chiral PMO materials. The thioanisole asymmetric oxidation reaction was used to validate the enantio-catalysts activity. The materials synthesized by the multistep method reached yield and enantiomeric excess of 41 and 15 %, respectively, while the synthesized one-pot chiral PMO materials achieved up to 58 and 42 %, respectively. This difference could be attributed to a more homogenous distribution of the chiral moiety as well as the simultaneous micellization and formation of the siliceous mesostructure, in the one-pot procedure. This promotes higher reagents accessibility to the active center, and therefore an enhancement of the chiral induction. Thereby, materials with Binol ligand incorporated into the three-dimensional silica framework were successfully accomplished.

The influence of matrix properties on growth and morphogenesis of human pancreatic ductal epithelial cells in 3D

A highly tunable synthetic biomimetic hydrogel platform was developed to study the growth and morphogenesis of pancreatic ductal epithelial cells (PDEC) under the influence of a myriad of instructive cues. A PDEC line, PANC-1, was used as a model system to illustrate the importance of matrix compositions on cell fate determination. PANC-1 is an immortalized ductal epithelial cell line widely used in the study of pancreatic tumor cell behaviors. PANC-1 cells are also increasingly explored as a potential cell source for endocrine differentiation. Thus far, most studies related to PANC-1, among other PDEC lines, are performed on 2D culture surfaces. Here, we evaluated the effect of matrix compositions on PANC-1 cell growth and morphogenesis in 3D. Specifically, PANC-1 cells were encapsulated in PEG-based hydrogels prepared by step-growth thiol-ene photopolymerization. It was found that thiol-ene hydrogels provided a cytocompatible environment for encapsulation and 3D culture of PANC-1 cells. In contrast to a monolayer morphology on 2D culture surfaces, PANC-1 cells formed clusters in 3D thiol-ene hydrogels within 4 days of culture. After culturing for 10 days, however, the growth and structures of these clusters were significantly impacted by gel matrix properties, including sensitivity of the matrix to proteases, stiffness of the matrix, and ECM-mimetic motifs. The use of matrix metalloproteinase (MMP) sensitive linker or the immobilization of fibronectin-derived RGDS ligand in the matrix promoted PANC-1 cell growth and encouraged them to adopt ductal cyst-like structures. On the other hand, the encapsulated cells formed smaller and more compact aggregates in non-MMP responsive gels. The incorporation of laminin-derived YIGSR peptide did not enhance cell growth and caused the cells to form compact aggregates. Immobilized YIGSR also enhanced the expression of epithelial cell markers including β-catenin and E-cadherin. These studies have established PEG-peptide hydrogels formed by thiol-ene photo-click reaction as a suitable platform for studying and manipulating pancreatic epithelial cell growth and morphogenesis in 3D.

Protein-Directed Immobilization of Phosphocholine Ligands on a Gold Surface for Multivalent C-Reactive Protein Binding

The preparation of a synthetic receptor for multivalent protein binding by a directed immobilization of bifunctional ligands was demonstrated using pentameric C-reactive protein (CRP) and a thiolated phosphocholine-containing ligand on a gold surface. CRP consisting of five identical, noncovalently linked subunits and having five phosphocholine-binding sites on the same face was complexed with 12-mercaptododecylphosphocholine. The complexes were reacted with a gold surface, which was blocked with BSA or 2-mercaptoethanol to avoid non-specific binding. CRP binding to the molecularly imprinted monolayer was investigated by surface plasmon resonance, exhibiting high sensitivity with a detection limit as low as 1 pM (0.12 ng/mL) and binding affinity (K(A) ~ 10(-7)-10(-9) M(-1)) comparable to that of immobilized anti- CRP.

Photochemically-Driven Methods for the <i>In Situ</i> and Site-Specific Fabrication of Monolithic-Based Electrochromatographic Microsystems

This paper reports on the in-situ synthesis of reactive polymeric monolith and its subsequent surface functionalization. Poly (N-acryloyloxysuccinimide-co-ethylene dimethacrylate) was prepared through free radical photopolymerization of the respective monomers. The grafting procedure is based on the preliminary grafting of alkyne units on the monolith surface and the further radical photoaddition of functional thiol molecules. Implementation of UV-driven polymerization and grafting methods enabled the locally controlled immobilization of generic monolith within the confines of the capillary channel, and the site-specific immobilization of ligands on the pore surface of the monolith. Our results suggest that such a synthesis methodology is promising for integrating multiple analytical modules within microstructures for on-line analysis.

Investigation of palladium(II) detection and recovery using ligand modified conjugate adsorbent

This study aims to develop a highly selective ligand modified conjugate adsorbent to investigate the selective and sensitive detection and recovery of Pd(II) ions. The conjugate adsorbent was prepared by synthesized 3-(((5-ethoxybenzenethiol)imino)methyl)-salicylic acid ligand immobilization onto mesoporous silica monoliths carriers. The Pd(II) complexation with functional groups in ligand was enhanced the color formation and adsorption corresponding to formation of [Pd(II)-ligand]n+ complexes. Optimum conditions were evaluated as a function of pH, adsorbent dosage, contact time, selectivity and adsorption isotherms models. The data revealed that conjugate adsorbent offered simple and one-step ultra-trace detection procedure without using high tech instruments. This adsorbent was worked well in acidic media for selective take up of Pd(II). The isotherms data showed that the maximum uptake of Pd(II) was as high as 164.20mg/g. Different compositions of eluting solution were tested for the recovery of Pd(II) from conjugate adsorbent. It was found that 0.5MHCl was eluted all of the undesired trace metal ions, while HCl–thiourea was an effective eluent for Pd(II) from conjugate adsorbent. The regenerated adsorbent remained high selective to Pd(II) recovery and exhibited almost the same adsorption capacity as the fresh conjugate adsorbent. The adsorbent was stable without significant loss of adsorption and recovery efficiencies even after several cycles. Therefore, ligand modified conjugate adsorbent is a useful and cost-effective adsorbent for the recovery of precious Pd(II) metal from metal refining processes.

Site-specific peptide and protein immobilization on surface plasmon resonance chips via strain-promoted cycloaddition

Surface plasmon resonance (SPR) is a powerful label-free diagnostic tool to study biomolecular interactions. However, one of the drawbacks of SPR is the lack of controlled immobilization of ligands on the sensor surface. We have developed a modular platform for the fast, reagent-free and site-specific immobilization of azide-containing ligands by strain-promoted cycloaddition onto a cyclooctyne-modified SPR sensor surface. The usefulness of the concept was shown in a study with a papain model system, and up to 150 experiments were performed without loss of surface quality. Furthermore, azide-containing green fluorescent protein (GFP) was also effectively immobilized. Taken together, cyclooctyne-modified SPR chips enable smooth and site-selective immobilization of ligands and prove to be more robust than traditionally functionalized systems.

Peptide-Based Affinity Adsorbents with High Binding Capacity for the Purification of Monoclonal Antibodies

High binding capacity and selectivity are key features for the successful application of affinity adsorbents for antibody purification. This study presents the development of affinity resins based on hexapeptide ligand HWRGWV for recovering monoclonal antibodies from cell culture fluids. Methods are presented for the immobilization of the peptide ligand and its variants on polymethacrylate and agarose based chromatographic supports using two main coupling strategies. The first one involves the formation of a peptide bond between the amino groups on the substrate and the peptide C-terminus activated with the uronium coupling agent HATU. The second approach involves resin activation with iodoacetic acid, followed by coupling of a cysteine-terminated variant of the ligand to form a thioether bond. The reaction conditions of peptide coupling were optimized to maximize the binding capacity of the resulting adsorbents. The peptide resins were characterized by measuring their static IgG binding capacities. The measured static binding capacity ranged from 35 to 48 mg/mL. The dynamic binding capacities (DBC) of four selected adsorbents were also determined, and they ranged from of 35 to 42 mg/mL with a 5-min residence time. All the resins exhibited high selectivity toward the Fc fragment of IgG. The affinity resins were used to purify two MAbs, a chimeric IgG1 and a humanized IgG4, from commercial CHO cell culture fluids. The resulting yields and purities for both MAbs were found to be in the range of 87–93% and >94%, respectively, which compare well with the purity and yield values obtained using commercially available Protein A media. Finally, the peptide resin with the highest IgG binding capacity, HWRGWVC-WorkBeads, was tested for 20 DBC cycles which included cleaning in place with 0.1 M NaOH after every cycle. The resin showed a high degree of reusability and alkaline stability, as it maintained 90% of its initial capacity.

Quartz crystal microbalance immunosensor for the quantification of immunoglobulin G in bovinemilk

The development of precise and sensitive methods for milk analysis remains a challenging task in the milk quality control field. A piezoelectric immunosensor was developed for the real-time quantification of immunoglobulin G (IgG) in bovine milk and colostrum. The sensing surface was designed with rabbit antibovine IgG as the detecting molecule, coupled onto a carboxymethyl dextran-coated gold crystal. Total binding and non-specific binding were measured using a quartz crystal microbalance with dissipation (QCM-D). Conditions of analysis, including ligand immobilization, dilution ratio of milk, salinity, and pH of the dilution buffer were optimized by Doehlert experimental design in order to enhance the detection specificity. The performances of the optimized immunosensor were evaluated. The standard curve was established from QCM-D responses and was linear until an IgG concentration of 2500ng/mL, with a detection limit of 46ng/mL. The total assay time is 5min per sample, including the regeneration step. The intra- and inter-assay variation coefficients were equal to or below 4.7and 6.1%, respectively. The sensing surface was stable for 100 analyses. This technique was successfully applied to the detection of colostrum addition in milk, with a minimum threshold of 0.1%. This new IgG quantification method is particularly interesting as a cost-effective and time-saving alternative for the dairy analytical laboratories when compared with the existing quantification methods.

Nanofibrous structured biomimetic strategies for skin tissue regeneration

Mimicking porous topography of natural extracellular matrix is advantageous for successful regeneration of damaged tissues or organs. Nanotechnology being one of the most promising and growing technology today shows an extremely huge potential in the field of tissue engineering. Nanofibrous structures that mimic the native extracellular matrix and promote the adhesion of various cells are being developed as tissue-engineered scaffolds for skin, bone, vasculature, heart, cornea, nervous system, and other tissues. A range of novel biocomposite materials has been developed to enhance the bioactive or therapeutic properties of these nanofibrous scaffolds via surface modifications, including the immobilization of functional cell-adhesive ligands and bioactive molecules such as drugs, enzymes, and cytokines. In skin tissue engineering, usage of allogeneic skin is avoided to reestablish physiological continuity and also to address the challenge of curing acute and chronic wounds, which remains as the area of exploration with various biomimetic approaches. Two-dimensional, three-dimensional scaffolds and stem cells are presently used as dermal regeneration templates for the treatment of full-thickness skin defects resulting from injuries and severe burns. The present review elaborates specifically on the fabrication of nanofibrous structured strategies for wound dressings, wound healing, and controlled release of growth factors for skin tissue regeneration.