Boronate Affinity Fluorescent Nanoparticles for Förster Resonance Energy Transfer Inhibition Assay of cis-Diol Biomolecules

Förster resonance energy transfer (FRET) has been essential for many applications, in which an appropriate donor-acceptor pair is the key. Traditional dye-to-dye combinations remain the working horses but are rather nonspecifically susceptive to environmental factors (such as ionic strength, pH, oxygen, etc.). Besides, to obtain desired selectivity, functionalization of the donor or acceptor is essential but usually tedious. Herein, we present fluorescent poly(m-aminophenylboronic acid) nanoparticles (poly(mAPBA) NPs) synthesized via a simple procedure and demonstrate a FRET scheme with suppressed environmental effects for the selective sensing of cis-diol biomolecules. The NPs exhibited stable fluorescence properties, resistance to environmental factors, and a Förster distance comparable size, making them ideal donor for FRET applications. By using poly(mAPBA) NPs and adenosine 5'-monophosphate modified graphene oxide (AMP-GO) as a donor and an acceptor, respectively, an environmental effects-suppressed boronate affinity-mediated FRET system was established. The fluorescence of poly(mAPBA) NPs was quenched by AMP-GO while it was restored when a competing cis-diol compounds was present. The FRET system exhibited excellent selectivity and improved sensitivity toward cis-diol compounds. Quantitative inhibition assay of glucose in human serum was demonstrated. As many cis-diol compounds such as sugars and glycoproteins are biologically and clinically significant, the FRET scheme presented herein could find more promising applications.

Biomimetic water-collecting materials inspired by nature

Nowadays, water shortage is a severe issue all over the world, especially in some arid and undeveloped areas. Interestingly, a variety of natural creatures can collect water from fog, which can provide a source of inspiration to develop novel and functional water-collecting materials. Recently, as an increasingly hot research topic, bioinspired materials with the water collection ability have captured vast scientific attention in both practical applications and fundamental research studies. In this review, we summarize the mechanisms of water collection in various natural creatures and present the fabrications, functions, applications, and new developments of bioinspired materials in recent years. The theoretical basis related to the phenomenon of water collection containing wetting behaviors and water droplet transportations is described in the beginning, i.e., the Young's equation, Wenzel model, Cassie model, surface energy gradient model and Laplace pressure equation. Then, the water collection mechanisms of three typical and widely researched natural animals and plants are discussed and their corresponding bioinspired materials are simultaneously detailed, which are cactus, spider, and desert beetles, respectively. This is followed by introducing another eight animals and plants (butterfly, shore birds, wheat awns, green bristlegrass, the Cotula fallax plant, Namib grass, green tree frogs and Australian desert lizards) that are rarely reported, exhibiting water collection properties or similar water droplet transportation. Finally, conclusions and outlook concerning the future development of bioinspired fog-collecting materials are presented.

Monoclonal antibody capture from cell culture supernatants using epitope imprinted macroporous membranes

A straightforward epitope imprinting procedure is used to prepare IgG affinity membranes directly applicable to mAb capture under near process realistic conditions.

Boronate affinity materials for separation and molecular recognition: structure, properties and applications

Boronate affinity materials, as unique sorbents, have emerged as important media for the selective separation and molecular recognition of cis-diol-containing compounds. With the introduction of boronic acid functionality, boronate affinity materials exhibit several significant advantages, including broad-spectrum selectivity, reversible covalent binding, pH-controlled capture/release, fast association/desorption kinetics, and good compatibility with mass spectrometry. Because cis-diol-containing biomolecules, including nucleosides, saccharides, glycans, glycoproteins and so on, are the important targets in current research frontiers such as metabolomics, glycomics and proteomics, boronate affinity materials have gained rapid development and found increasing applications in the last decade. In this review, we critically survey recent advances in boronate affinity materials. We focus on fundamental considerations as well as important progress and new boronate affinity materials reported in the last decade. We particularly discuss on the effects of the structure of boronate ligands and supporting materials on the properties of boronate affinity materials, such as binding pH, affinity, selectivity, binding capacity, tolerance for interference and so on. A variety of promising applications, including affinity separation, proteomics, metabolomics, disease diagnostics and aptamer selection, are introduced with main emphasis on how boronate affinity materials can solve the issues in the applications and what merits boronate affinity materials can provide.

Boronate-Affinity Glycan-Oriented Surface Imprinting: A New Strategy to Mimic Lectins for the Recognition of an Intact Glycoprotein and Its Characteristic Fragments

Lectins possess unique binding properties and are of particular value in molecular recognition. However, lectins suffer from several disadvantages, such as being hard to prepare and showing poor storage stability. Boronate-affinity glycan-oriented surface imprinting was developed as a new strategy for the preparation of lectin-like molecularly imprinted polymers (MIPs). The prepared MIPs could specifically recognize an intact glycoprotein and its characteristic fragments, even within a complex sample matrix. Glycan-imprinted MIPs could thus prove to be powerful tools for important applications such as proteomics, glycomics, and diagnostics.

Facile synthesis of zwitterionic polymer-coated core-shell magnetic nanoparticles for highly specific capture of N-linked glycopeptides

Highly selective and efficient capture of glycosylated proteins and peptides from complex biological samples is of profound significance for the discovery of disease biomarkers in biological systems. Recently, hydrophilic interaction liquid chromatography (HILIC)-based functional materials have been extensively utilized for glycopeptide enrichment. However, the low amount of immobilized hydrophilic groups on the affinity material has limited its specificity, detection sensitivity and binding capacity in the capture of glycopeptides. Herein, a novel affinity material was synthesized to improve the binding capacity and detection sensitivity for glycopeptides by coating a poly(2-(methacryloyloxy)ethyl)-dimethyl-(3-sulfopropyl) ammonium hydroxide (PMSA) shell onto Fe3O4@SiO2 nanoparticles, taking advantage of reflux-precipitation polymerization for the first time (denoted as Fe3O4@SiO2@PMSA). The thick polymer shell endows the nanoparticles with excellent hydrophilic property and several functional groups on the polymer chains. The resulting Fe3O4@SiO2@PMSA demonstrated an outstanding ability for glycopeptide enrichment with high selectivity, extremely high detection sensitivity (0.1 fmol), large binding capacity (100 mg g(-1)), high enrichment recovery (above 73.6%) and rapid magnetic separation. Furthermore, in the analysis of real complicated biological samples, 905 unique N-glycosylation sites from 458 N-glycosylated proteins were reliably identified in three replicate analyses of a 65 μg protein sample extracted from mouse liver, showing the great potential of Fe3O4@SiO2@PMSA in the detection and identification of low-abundance N-linked glycopeptides in biological samples.

Characterization of the binding strengths between boronic acids and cis-diol-containing biomolecules by affinity capillary electrophoresis

The affinity of boronic acids toward cis-diol-containing biomolecules has found wide applications in many fields, such as sensing, separation, drug delivery, and functional materials. A sound understanding of the binding interactions will greatly facilitate exquisite applications of this chemistry. Traditional techniques are associated with some apparent drawbacks, so they are only applicable to a limited range of boronic acids and cis-diol-containing biomolecules. This chapter describes an affinity capillary electrophoresis (ACE) method for the characterization of the binding strengths between boronic acids and cis-diol-containing biomolecules. As compared with existing approaches, such as (11)B NMR, the ACE method exhibits several significant advantages: (1) possibility of simultaneous study of multiple interactions, (2) low requirement on the purity of the binding species, (3) widely applicable to almost all types of cis-diol-containing compounds and boronic acids, and (4) high accuracy and precision.

Sugar-boronate ester scaffold tethered pyridyl-imine palladium(ii) complexes: synthesis and their in vitro anticancer evaluation

The anticancer activity of sugar-boronate ester containing palladium(ii) complexes is reported.

Fabrication of a dendrimer-modified boronate affinity material for online selective enrichment of cis-diol-containing compounds and its application in determination of nucleosides in urine

A high binding capacity dendrimer-modified boronate affinity material (SiO₂@dBA) was synthesized and coupled with large-volume injection/online column-switching solid phase extraction to facilitate the determination process of cis-diols.

Selective extraction based on poly(MAA-VB-EGMDA) monolith followed by HPLC for determination of hordenine in plasma and urine samples

Hordenine is an active compound found in several foods, herbs and beer. In this work, a novel sorbent was fabricated for selective solid-phase extraction (SPE) of hordenine in biological samples. The organic polymer sorbent was synthesized in one step in the plastic barrel of a syringe by a pre-polymerization solution consisting of methacrylic acid (MAA), 4-vinylphenylboronic acid (VB) and ethylene glycol dimethacrylate (EGDMA). The conditions for preparation were optimized to generate a poly(MAA-VB-EGMDA) monolith with good permeability. The monolith exhibited good enrichment efficiency towards hordenine. By using tyramine as the internal standard, a poly(MAA-VB-EGMDA)-based SPE-HPLC method was established for analysis of hordenine. Conditions for SPE, including volume of eluting solvent, pH of sample solution, sampling rate and sample volume, were optimized. The proposed SPE-HPLC method presented good linearity (R(2)  = 0.9992) within 10-2000 ng/mL and the detection limits was 3 ng/mL, which is significantly more sensitive than reported methods. The method was also applied in plasma and urine samples; good capability of removing matrices was observed, while hordenine in low content was well extracted and enriched. The recoveries were from 90.6 to 94.7% and from 89.3 to 91.5% for the spiked plasma and urine samples, respectively, with the relative standard deviations <4.7%.

Self-oriented nanoparticles for site-selective immunoglobulin G recognition via epitope imprinting approach

Molecular imprinting is a polymerization technique that provides synthetic analogs for template molecules. Molecularly imprinted polymers (MIPs) have gained much attention due to their unique properties such as selectivity and specificity for target molecules. In this study, we focused on the development of polymeric materials with molecular recognition ability, so molecular imprinting was combined with miniemulsion polymerization to synthesize self-orienting nanoparticles through the use of an epitope imprinting approach. Thus, L-lysine imprinted nanoparticles (LMIP) were synthesized via miniemulsion polymerization technique. Immunoglobulin G (IgG) was then bound to the cavities that specifically formed for L-lysine molecules that are typically found at the C-terminus of the Fc region of antibody molecules. The resulting nanoparticles makes it possible to minimize the nonspecific interaction between monomer and template molecules. In addition, the orientation of the entire IgG molecule was controlled, and random imprinting of the IgG was prevented. The optimum conditions were determined for IgG recognition using the imprinted nanoparticles. The selectivity of the nanoparticles against IgG molecules was also evaluated using albumin and hemoglobin as competitor molecules. In order to show the self-orientation capability of imprinted nanoparticles, human serum albumin (HSA) adsorption onto both the plain nanoparticles and immobilized nanoparticles by anti-human serum albumin antibody (anti-HSA antibody) was also carried out. Due to anti-HSA antibody immobilization on the imprinted nanoparticles, the adsorption capability of nanoparticles against HSA molecules vigorously enhanced. It is proved that the oriented immobilization of antibodies was appropriately succeeded.

Trends in Upstream and Downstream Process Development for Antibody Manufacturing

A steady increase of product titers and the corresponding change in impurity composition represent a challenge for development and optimization of antibody production processes. Additionally, increasing demands on product quality result in higher complexity of processes and analytics, thereby increasing the costs for product work-up. Concentration and composition of impurities are critical for efficient process development. These impurities can show significant variations, which primarily depend on culture conditions. They have a major impact on the work-up strategy and costs. The resulting "bottleneck" in downstream processing requires new optimization, technology and development approaches. These include the optimization and adaptation of existing unit operations respective to the new separation task, the assessment of alternative separation technologies and the search for new methods in process development. This review presents an overview of existing methods for process optimization and integration and indicates new approaches for future developments.

Insights into the effect of nanoconfinement on molecular interactions

Being confined within nanoscale space, substances may exhibit unique physicochemical properties. The effect of nanoconfinement on molecular interactions is of significance, but a sound understanding has not been established yet. Here we present a quantitative study on boronate affinity (covalent) and electrostatic (non-covalent) interactions confined within mesoporous silica. We show that both interactions were enhanced by the confinement and that the enhancement depended on the closeness of the interacting location, as well as on the difference between the pore size and the molecular size. The overall enhancement could reach 3 orders of magnitude.

Stationary phases for the enrichment of glycoproteins and glycopeptides

The analysis of protein glycosylation is important for biomedical and biopharmaceutical research. Recent advances in LC-MS analysis have enabled the identification of glycosylation sites, the characterisation of glycan structures and the identification and quantification of glycoproteins and glycopeptides. However, this type of analysis remains challenging due to the low abundance of glycopeptides in complex protein digests, the microheterogeneity at glycosylation sites, ion suppression effects and the competition for ionisation by co-eluting peptides. Specific sample preparation is necessary for comprehensive and site-specific glycosylation analyses using MS. Therefore, researchers continue to pursue new columns to broaden their applications. The current manuscript covers recent literature published from 2008 to 2013. The stationary phases containing various chemical bonding methods or ligands immobilisation strategies on solid supports that selectively enrich N-linked or sialylated N-glycopeptides are categorised with either physical or chemical modes of binding. These categories include lectin affinity, hydrophilic interactions, boronate affinity, titanium dioxide affinity, hydrazide chemistry and other separation techniques. This review should aid in better understanding the syntheses and physicochemical properties of each type of stationary phases for enriching glycoproteins and glycopeptides.

Aminophenylboronic-acid-conjugated polyacrylic acid-Mn-doped ZnS quantum dot for highly sensitive discrimination of glycoproteins

Discrimination of glycoproteins with different glycans is a significant but difficult issue. We presented here a new strategy for strengthening the discrimination of glycoproteins by introducing a new signaling channel, fluorescence polarization (FP), into a "single probe with three signaling channels" sensor array. The single probe was aminophenylboronic-acid-conjugated poly(acrylic acid)-Mn-doped ZnS quantum dots, and the three signaling channels were FP, room temperature phosphorescence and light scattering. Ten glycoproteins, including ovalbumin, fibrinogen, transferrin, horseradish peroxidase, vascular endothelial growth factor, immunoglobulin G, avidin, hyaluronidase, cellulase R-10, and glucose oxidase, were involved for evaluating the discriminating capability. The introduction of the FP signaling channel improved the discriminating power of the sensor array, so that the 10 glycoproteins at 0.15 μM could be well discriminated both in PBS buffer and in the presence of human serum sample. The identification accuracy of the unknown samples was 96.25% (77 out of 80) at the 0.15 μM level and 97.50% (78 out of 80) at the 0.2 μM level. The integration of the signaling patterns with different responsive principles was demonstrated as the promising way to enhance the discrimination power of the single-probe-based sensor arrays.

Off-line hyphenation of boronate affinity monolith-based extraction with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for efficient analysis of glycoproteins/glycopeptides

Boronate affinity materials have attracted increasing attentions as sample enrichment platforms for glycoproteomic analysis in recent years. However, most of the boronate affinity materials that have already employed for proteomic analysis are suffering from apparent disadvantages, such as alkaline pH for binding, weak affinity, and relatively poor selectivity. Benzoboroxoles are a unique class of boronic acids which have showed excellent binding properties for the recognition of cis-diol-containing compounds. Recently, a 3-carboxy-benzoboroxole-functionalized monolithic column had been reported and it had exhibited the best selectivity and affinity as well as the lowest binding pH among all reported boronate affinity monolithic columns. In this study, an off-line hyphenation of this boronate affinity monolithic column-based extraction with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was developed and the powerfulness of this hyphenated approach in the analysis of glycoproteins and glycopeptides in complex samples was investigated. The approach was first applied to the analysis of glycopeptides in the tryptic digest of horseradish peroxidase (HRP). Totally 22 glycopeptides were identified. To the best of our knowledge, this is the best performance among all the boronic acid-functionalized materials. We further employed this approach to the analysis of intact proteins in human saliva. Totally 6 intact glycoproteins were successfully identified. As comparison, when the samples were analyzed without extraction, only a few glycopeptides were identified from the tryptic digest of HRP while no glycoproteins were found from the saliva samples.

Pyridinylboronic acid-functionalized organic-silica hybrid monolithic capillary for the selective enrichment and separation of cis-diol-containing biomolecules at acidic pH

Boronate affinity chromatography (BAC) is a unique means for the selective separation and enrichment of 1,2 and 1,3 cis-diol-containing compounds. However, conventional boronate affinity materials require a basic binding pH (usually≥8.5), which gives rise to not only inconvenience in operation but also the risk of degradation of labile compounds. Although the applicable pH has been expanded to 5.0 in recent years, the current boronate affinity materials still fail to meet the acidic pH end of frequently used biosamples, particularly urine (pH 4.5). In this study, we report a 3-pyridylboronic acid-functionalized organic-silica hybrid monolithic capillary that exhibited a binding pH of 4.5, the lowest so far in BAC. Such a binding pH enabled direct extraction of cis-diol-containing biomolecules such as nucleosides from urine samples without pH adjustment. The boronate affinity monolithic capillary showed enhanced affinity toward negatively charged cis-diol-containing analytes such as ribonucleotides. Moreover, it could function as an anion exchanger at acidic pH (∼2). The column was found to retain multiple compounds from urine, which can be assumed to be at least mostly if not entirely cis-diol-containing compounds.

Nanoconfining affinity materials for pH-mediated protein capture–release

Based on the nanoconfinement effect, two new affinity materials that have a pH-responsive capture–release ability for proteins were developed.

Detection of boronic acids through excited-state intramolecular proton-transfer fluorescence

Boronic acids are versatile reagents for the chemical synthesis of organic molecules. They and other boron-containing compounds can be detected readily by the interruption of the excited-state intramolecular proton transfer (ESIPT) of 10-hydroxybenzo[h]quinolone. This method is highly sensitive and selective, and useful for monitoring synthetic reactions and detecting boron-containing compounds on a solid support.

Boronic Acid-based approach for separation and immobilization of glycoproteins and its application in sensing

Glycoproteins influence a broad spectrum of biological processes including cell-cell interaction, host-pathogen interaction, or protection of proteins against proteolytic degradation. The analysis of their glyco-structures and concentration levels are increasingly important in diagnosis and proteomics. Boronic acids can covalently react with cis-diols in the oligosaccharide chains of glycoproteins to form five- or six-membered cyclic esters. Based on this interaction, boronic acid-based ligands and materials have attracted much attention in both chemistry and biology as the recognition motif for enrichment and chemo/biosensing of glycoproteins in recent years. In this work, we reviewed the progress in the separation, immobilization and detection of glycoproteins with boronic acid-functionalized materials and addressed its application in sensing.

Efficient selection of glycoprotein-binding DNA aptamers via boronate affinity monolithic capillary

Systematic evolution of ligands by exponential enrichment (SELEX) is the workhorse method for selecting aptamers that are capable of binding target molecules from a random oligonucleic acid library. However, conventional SELEX methods are associated with apparent drawbacks including labor-intensive, time-consuming, large reagent consumption and strong nonspecific binding with separation media. Herein, we report a boronate affinity monolithic capillary-based SELEX approach for rapid selection of high-specificity glycoprotein-binding DNA aptamers. Boronate affinity monolithic capillary is an advanced functional material appeared in recent years, which allows for facile capture/release of glycoproteins in a pH-switchable fashion. By using boronate affinity monolithic capillary as a platform for target immobilization and aptamer isolation, the proposed SELEX method allowed for efficient selection of glycoprotein-binding aptamers by 6 rounds and the dissociation constants were at 10(-8) M level. Because of the employment of boronate affinity monolithic capillary, the new SELEX approach overcame the above-mentioned drawbacks and provided several significant advantages, including rapid selection speed (only 2 days were needed), high specificity toward the target molecules, and minute reagent consumption.

Separation and analysis of cis-diol-containing compounds by boronate affinity-assisted micellar electrokinetic chromatography

Cis-diol-containing compounds (CDCCs) are usually highly hydrophilic compounds and are therefore difficult to separate by conventional reversed-phase-based micellar electrokinetic chromatography (MEKC) due to poor selectivity. Here, we report a new method, called boronate affinity-assisted micellar electrokinetic chromatography (BAA-MEKC), to solve this issue. A boronic acid with a hydrophobic alkyl chain was added to the background electrolyte, which acted as a modifier to adjust the selectivity. CDCCs can covalently react with the boronic acid to form negatively charged surfactant-like complexes, which can partition into micelles formed with a cationic surfactant. Thus, CDCCs can be separated according to the differential partition constants of their boronic acid complexes between the micellar phase and the surrounding aqueous phase. To verify this method, eight nucleosides were employed as the test compounds and their separation confirmed that the combination of boronate affinity interaction with MEKC can effectively enhance the separation of CDCCs. The effects of experimental conditions on the separation were investigated. Finally, the BAA-MEKC method was applied to the separation and analysis of nucleosides extracted from human urine. BAA-MEKC exhibited better selectivity and improved separation as compared with conventional MEKC and CZE. Successful quantitative analysis of urinary nucleosides by BAA-MEKC was demonstrated.

Photolithographic boronate affinity molecular imprinting: a general and facile approach for glycoprotein imprinting

Better than expected: With a regular boronic acid as the functional monomer, a general and facile approach for glycoprotein imprinting exhibited several highly favorable features that are beyond normal expectation, which make the prepared MIPs feasible for the recognition of trace glycoproteins in complicated real samples.

A new soft lithographic route for the facile fabrication of hydrophilic sandwich microchips

Manufacturing materials are an essential element for the fabrication of microfluidic chips. PDMS, the most widely used polymeric material, is associated with apparent disadvantages such as hydrophobic nature, while other materials also suffer from some limitations. In this paper, a new soft lithographic route was proposed for the facile manufacturing of hydrophilic sandwich microchips, using bisphenol A based epoxy acrylate (BABEA) as a new patterning material. The BABEA copolymers are hydrophilic, highly transparent in visible range while highly untransparent when the wavelength is less than 290 nm, and of high replication fidelity. By combining with appropriate monomers, including glycidyl methacrylate, methylmethacrylate, and acrylic acid, the copolymers contain active functional groups, which allows for easy postmodification for desirable functional units. A fabrication procedure was proposed for manufacturing hybrid quartz/BABEA copolymer/quartz microchips. In the procedure, no micromachining equipments, wet etching, or imprinting techniques were involved, making the fabrication approach applicable in ordinary chemistry laboratories. The performance of the prepared microchips was demonstrated in terms of CIEF with UV-whole channel imaging detection. The hydrophilic microchannel ensures stable focusing while the polymeric middle layer acts as a perfectly aligned optical slit for whole channel UV absorbance detection.