Less common applications of monoliths: I. Microscale protein mapping with proteolytic enzymes immobilized on monolithic supports

Affinity monolith chromatography: A review of general principles and recent developments

Affinity monolith chromatography (AMC) is a liquid chromatographic technique that utilizes a monolithic support with a biological ligand or related binding agent to isolate, enrich, or detect a target analyte in a complex matrix. The target-specific interaction exhibited by the binding agents makes AMC attractive for the separation or detection of a wide range of compounds. This article will review the basic principles of AMC and recent developments in this field. The supports used in AMC will be discussed, including organic, inorganic, hybrid, carbohydrate, and cryogel monoliths. Schemes for attaching binding agents to these monoliths will be examined as well, such as covalent immobilization, biospecific adsorption, entrapment, molecular imprinting, and coordination methods. An overview will then be given of binding agents that have recently been used in AMC, along with their applications. These applications will include bioaffinity chromatography, immunoaffinity chromatography, immobilized metal-ion affinity chromatography, and dye-ligand or biomimetic affinity chromatography. The use of AMC in chiral separations and biointeraction studies will also be discussed.

Flow-through enzymatic reactors using polymer monoliths: From motivation to application

The application of monolithic materials as carriers for enzymes has rapidly expanded to the realization of flow-through analysis and bioconversion processes. This expansion is partly attributed to the absence from diffusion limitation in many monoliths-based enzyme reactors. Particularly, the relatively ease of introducing functional groups renders polymer monoliths attractive as enzyme carriers. After summarizing the motivation to develop enzymatic reactors using polymer monoliths, this review reports the most recent applications of such reactors. Besides, the present review focuses on the crucial characteristics of polymer monoliths affecting the immobilization of enzymes and the processing parameters dictating the performance of the resulting enzymatic reactors. This review is intended to provide a guideline for designing and applying flow-through enzymatic reactors using polymer monoliths.

Enzymatic Bioreactors: An Electrochemical Perspective

Biocatalysts provide a number of advantages such as high selectivity, the ability to operate under mild reaction conditions and availability from renewable resources that are of interest in the development of bioreactors for applications in the pharmaceutical and other sectors. The use of oxidoreductases in biocatalytic reactors is primarily focused on the use of NAD(P)-dependent enzymes, with the recycling of the cofactor occurring via an additional enzymatic system. The use of electrochemically based systems has been limited. This review focuses on the development of electrochemically based biocatalytic reactors. The mechanisms of mediated and direct electron transfer together with methods of immobilising enzymes are briefly reviewed. The use of electrochemically based batch and flow reactors is reviewed in detail with a focus on recent developments in the use of high surface area electrodes, enzyme engineering and enzyme cascades. A future perspective on electrochemically based bioreactors is presented.

Confinement of Monolithic Stationary Phases in Targeted Regions of 3D-Printed Titanium Devices Using Thermal Polymerization

In this study, we have prepared thermally initiated polymeric monolithic stationary phases within discrete regions of 3D-printed titanium devices. The devices were created with controllable hot and cold regions. The monolithic stationary phases were first locally created in capillaries inserted into the channels of the titanium devices. The homogeneity of the monolith structure and the interface length were studied by scanning a capacitively coupled conductivity contactless detector (C4D) along the length of the capillary. Homogeneous monolithic structures could be obtained within a titanium device equipped with a hot and cold jacket connected to two water baths. The confinement method was optimized in capillaries. The sharpest interfaces (between monolith and empty channel) were obtained with the hot region maintained at 70 °C and the cold region at 4 or 10 °C, with the latter temperature yielding better repeatability. The optimized conditions were used to create monoliths bound directly to the walls of the titanium channels. The fabricated monoliths were successfully used to separate a mixture of four intact proteins using reversed-phase liquid chromatography. Further chromatographic characterization showed a permeability (Kf) of ∼4 × 10-15 m2 and a total porosity of 60%.

Investigating Monoliths (Vinyl Azlactone-co-Ethylene Dimethacrylate) as a Support for Enzymes and Drugs, for Proteomics and Drug-Target Studies

Prior to mass spectrometry, on-line sample preparation can be beneficial to reduce manual steps, increase speed, and enable analysis of limited sample amounts. For example, bottom-up proteomics sample preparation and analysis can be accelerated by digesting proteins to peptides in an on-line enzyme reactor. We here focus on low-backpressure 100 μm inner diameter (ID) × 160 mm, 180 μm ID × 110 mm or 250 μm ID × 140 mm vinyl azlactone-co-ethylene dimethacrylate [poly(VDM-co-EDMA)] monoliths as supports for immobilizing of additional molecules (i.e., proteases or drugs), as the monolith was expected to have few unspecific interactions. For on-line protein digestion, monolith supports immobilized with trypsin enzyme were found to be suited, featuring the expected characteristics of the material, i.e., low backpressure and low carry-over. Serving as a functionalized sample loop, the monolith units were very simple to connect on-line with liquid chromatography. However, for on-line target deconvolution, the monolithic support immobilized with a Wnt pathway inhibitor was associated with numerous secondary interactions when exploring the possibility of selectively trapping target proteins by drug-target interactions. Our initial observations suggest that (poly(VDM-co-EDMA)) monoliths are promising for e.g., on-line bottom-up proteomics, but not a "fit-for-all" material. We also discuss issues related to the repeatability of monolith-preparations.

Isolation of anti-extra-cellular vesicle single-domain antibodies by direct panning on vesicle-enriched fractions

Background

The thorough understanding of the physiological and pathological processes mediated by extracellular vesicles (EVs) is challenged by purification methods which are cumbersome, not reproducible, or insufficient to yield homogeneous material. Chromatography based on both ion-exchange and immune-capture can represent an effective method to improve EV purification and successive analysis.

Methods

Cell culture supernatant was used as a model sample for assessing the capacity of anion-exchange chromatography to separate distinct EV fractions and to isolate nanobodies by direct panning on whole EVs to recover binders specific for the native conformation of EV-surface epitopes and suitable to develop EV immune-capture reagents.

Results

Anion-exchange chromatography of cell culture supernatant separated distinct protein-containing fractions and all of them were positive for CD9, a biomarker associated to some EVs. This suggested the existence of several EV fractions but did not help in separating EVs from other contaminants. We further isolated several nanobodies instrumental for implementing immune-affinity protocols. These were able to immobilize EVs from both cell culture supernatant and biological samples, to be used in ELISA, flow-cytometry, and immune-purification.

Conclusions

Here we report the first successful isolation of anti-EV nanobodies for the use in immunoaffinity-based EV capture by panning a phage library directly on partially purified EVs. This achievement paves the way for the application of direct EV panning for the discovery of novel antibody-vesicle surface biomarker pairs and represents the preliminary requirement for the development of selective immune-capture that, in combination with anion-exchange chromatography, can simplify the systematic stratification of EV sub-populations and their individual characterization.

Electronic supplementary material

The online version of this article (10.1186/s12934-017-0856-9) contains supplementary material, which is available to authorized users.

Polymer brush decorated nanoparticles immobilised on polymer monoliths for enhanced biopolymer elution

Polymer monoliths uniformly covered with polymer brush nanoparticles are fabricated and the elution properties investigated with myoglobin and blue dextran.

Polyethylenimine: a very useful ionic polymer in the design of immobilized enzyme biocatalysts

This review discusses the possible roles of polyethylenimine (PEI) in the design of improved immobilized biocatalysts from diverse perspectives.

Screening of tyrosinase inhibitors by capillary electrophoresis with immobilized enzyme microreactor and molecular docking

A new method for screening tyrosinase inhibitors from traditional Chinese medicines (TCMs) was successfully developed by capillary electrophoresis with reliable online immobilized enzyme microreactor (IMER). In addition, molecular docking study has been used for supporting inhibition interaction between enzyme and inhibitors. The IMER of tyrosinase was constructed at the outlet of the capillary by using glutaraldehyde as cross-linker. The parameters including enzyme reaction, separation of the substrate and product, and the performance of immobilized tyrosinase were investigated systematically. Because of using short-end injection procedure, the product and substrate were effectively separated within 2 min. The immobilized tyrosinase could remain 80% active for 30 days at 4°C. The Michaelis-Menten constant of tyrosinase was determined as 1.78 mM. Kojic acid, a known tyrosinase inhibitor, was used as a model compound for the validation of the inhibitors screening method. The half-maximal inhibitory concentration of kojic acid was 5.55 μM. The method was successfully applied for screening tyrosinase inhibitors from 15 compounds of TCM. Four compounds including quercetin, kaempferol, bavachinin, and bakuchiol were found having inhibitory potentials. The results obtained in this work were supported by molecular docking study.

Thiol–ene click chemistry for the design of diol porous monoliths with hydrophilic surface interaction ability: a capillary electrochromatography study

Thiol–ene click chemistry provides an efficient surface grafting strategy for designing diol monoliths meant for hydrophilic interaction capillary electrochromatography.

Rapid and simple preparation of thiol-ene emulsion-templated monoliths and their application as enzymatic microreactors

A novel, rapid and simple method for the preparation of emulsion-templated monoliths in microfluidic channels based on thiol-ene chemistry is presented. The method allows monolith synthesis and anchoring inside thiol-ene microchannels in a single photoinitiated step. Characterization by scanning electron microscopy showed that the methanol-based emulsion templating process resulted in a network of highly interconnected and regular thiol-ene beads anchored solidly inside thiol-ene microchannels. Surface area measurements indicate that the monoliths are macroporous, with no or little micro- or mesopores. As a demonstration, galactose oxidase and peptide-N-glycosidase F (PNGase F) were immobilized at the surface of the synthesized thiol-ene monoliths via two different mechanisms. First, cysteine groups on the protein surface were used for reversible covalent linkage to free thiol functional groups on the monoliths. Second, covalent linkage was achieved via free primary amino groups on the protein surface by means of thiol-ene click chemistry and l-ascorbic acid linkage. Thus prepared galactose oxidase and PNGase F microreactors demonstrated good enzymatic activity in a galactose assay and the deglycosilation of ribonuclease B, respectively.

A lateral electrophoretic flow diagnostic assay

Immunochromatographic assays are a cornerstone tool in disease screening. To complement existing lateral flow assays (based on wicking flow) we introduce a lateral flow format that employs directed electrophoretic transport. The format is termed a "lateral e-flow assay" and is designed to support multiplexed detection using immobilized reaction volumes of capture antigen. To fabricate the lateral e-flow device, we employ mask-based UV photopatterning to selectively immobilize unmodified capture antigen along the microchannel in a barcode-like pattern. The channel-filling polyacrylamide hydrogel incorporates a photoactive moiety (benzophenone) to immobilize capture antigen to the hydrogel without a priori antigen modification. We report a heterogeneous sandwich assay using low-power electrophoresis to drive biospecimen through the capture antigen barcode. Fluorescence barcode readout is collected via a low-resource appropriate imaging system (CellScope). We characterize lateral e-flow assay performance and demonstrate a serum assay for antibodies to the hepatitis C virus (HCV). In a pilot study, the lateral e-flow assay positively identifies HCV+ human sera in 60 min. The lateral e-flow assay provides a flexible format for conducting multiplexed immunoassays relevant to confirmatory diagnosis in near-patient settings.

A surface-enhanced Raman scattering optrode prepared by in situ photoinduced reactions and its application for highly sensitive on-chip detection

A surface-enhanced Raman scattering (SERS)-active optical fiber sensor combining the optical fiber waveguide with various SERS substrates has been a powerful analytical tool for in situ and long-distance SERS detection with high sensitivity. The design and modification of a high-quality SERS-active sensing layer are important topics in the development of novel SERS-active optical fiber sensors. Here, we prepared a highly sensitive SERS-active optrode by in situ fabrication of a three-dimensional porous structure on the optical fiber end via a photoinduced polymerization reaction, followed by the growth of photochemical silver nanoparticles above the porous polymer material. The fabrication process is rapid (finished within 1 h) and can be on line under light control. The porous structure supports vast silver nanoparticles, which allows for strong electromagnetic enhancement of SERS. Interestingly, the preparation of this SERS optrode and its utilization for SERS detection can all be conducted in a microfluidic chip. The qualitative and quantitative on-chip SERS sensing of organic pollutants and pesticides has been achieved by this SERS optrode-integrated microfluidic chip, and its high detection sensitivity makes it a promising factor in the analysis of liquid systems.

One-pot preparation of glutathione-silica hybrid monolith for mixed-mode capillary liquid chromatography based on "thiol-ene" click chemistry

A novel glutathione (GSH)-silica hybrid monolithic column synthesized via a combination of thiol-ene click reaction and one-pot process was described, where thiol-end GSH organic monomer and 2,2-azobisisobutyronitrile (AIBN) were mixed with hydrolyzed tetramethyloxysilane (TMOS) and γ-methacryloxypropyltrimethoxysilane (γ-MAPS) and then introduced into a fused-silica capillary for simultaneous polycondensation and "thiol-ene" click reaction to form the GSH-silica hybrid monolith. The effects of the molar ratio of TMOS/γ-MAPS, the amount of GSH, and the volume of porogen on the morphology, permeability and pore properties of the prepared GSH-silica hybrid monoliths were studied in detail. A uniform monolithic network with high porosity was obtained. A series of test compounds including alkylbenzenes, amides, and anilines were used to evaluate the retention behaviors of the GSH-silica hybrid monolithic column. The results demonstrated that the prepared GSH-silica hybrid monolith exhibited multiple interactions including hydrophobicity, hydrophilicity, as well as cation exchange interaction. The run-to-run, column-to-column and batch-to-batch reproducibilities of the GSH-silica hybrid monolith for phenols' retention were satisfactory with the relative standard deviations (RSDs) less than 1.3% (n=5), 2.6% (n=3) and 3.2% (n=3), respectively, indicating the effectiveness and practicability of the proposed method. In addition, the GSH-silica hybrid monolith was applied to the separation of nucleotides, peptides and protein tryptic digests, respectively. The successful applications suggested the potential of the GSH-silica hybrid monolith in complex sample analysis.

Enzyme immobilization in biosensor constructions: self-assembled monolayers of calixarenes containing thiols

Herein, an amperometric glucose oxidase (GOx) biosensor is presented using calixarenes as an immobilization matrix of the biomolecule.

Analytical silica monoliths with submicron macropores: current limitations to a direct morphology-column efficiency scaling

Shrinking the structural elements of a particulate bed or monolith (i.e., the particle or domain size) yields more efficient columns only when the homogeneity of the bed can be conserved in that process. We investigate this complex issue for a set of 2nd generation analytical silica monoliths with macropores reaching submicron dimensions using chromatographic methods, mercury intrusion porosimetry, scanning electron microscopy, and confocal laser scanning microscopy (CLSM), and present eddy dispersion simulations and a chord length distribution analysis for the CLSM-based physical reconstructions at macropore resolution. The combined results allow us to identify relevant morphological advances made from 1st to 2nd generation monoliths and additionally highlight the current limitations to a direct morphology-efficiency scaling with respect to the performance that can be accomplished in HPLC practice with these columns. Whereas the improvement in radial homogeneity from 1st to 2nd generation silica monoliths is represented by a dramatic increase in column efficiency, the further reduction of macropore size in the 2nd generation monoliths does not lead to the expected improvement of plate height data, although these monoliths realize submicron macropores at a simultaneously conserved bulk macropore space homogeneity and negligible radial heterogeneity. Our study implies that limitations to further improved column efficiency arise from the intrinsic border effects of the used 4.6mm i.d. analytical columns. This includes the sample distribution onto the monoliths and asynchronous sample collection through the endfittings at the column inlet and outlet, respectively. Only when these effects are reduced will additionally improved 2nd generation monoliths live up to column efficiencies, which are envisioned for them based on their morphological properties.

Affinity monolith chromatography: a review of principles and recent analytical applications

Affinity monolith chromatography (AMC) is a type of liquid chromatography that uses a monolithic support and a biologically related binding agent as a stationary phase. AMC is a powerful method for the selective separation, analysis, or study of specific target compounds in a sample. This review discusses the basic principles of AMC and recent developments and applications of this method, with particular emphasis being given to work that has appeared in the last 5 years. Various materials that have been used to prepare columns for AMC are examined, including organic monoliths, silica monoliths, agarose monoliths, and cryogels. These supports have been used in AMC for formats that have ranged from traditional columns to disks, microcolumns, and capillaries. Many binding agents have also been employed in AMC, such as antibodies, enzymes, proteins, lectins, immobilized metal ions, and dyes. Some applications that have been reported with these binding agents in AMC are bioaffinity chromatography, immunoaffinity chromatography or immunoextraction, immobilized-metal-ion affinity chromatography, dye-ligand affinity chromatography, chiral separations, and biointeraction studies. Examples are presented from fields that include analytical chemistry, pharmaceutical analysis, clinical testing, and biotechnology. Current trends and possible directions in AMC are also discussed.

Recent advances in preparation and application of hybrid organic-silica monolithic capillary columns

Hybrid organic-silica monolithic columns, regarded as a second generation of silica-based monoliths, have received much interest due to their unique properties over the pure silica-based monoliths. This review mainly focuses on development in the fields of preparation of hybrid monolithic columns in a capillary and their application for CEC and capillary liquid chromatography separation, as well as for sample pretreatment of solid-phase microextraction and immobilized enzyme reactor since July 2010. The preparation approaches are comprehensively summarized with three routes: (i) general sol-gel process using trialkoxysilanes and tetraalkoxysilanes as coprecursors; (ii) "one-pot" process of alkoxysilanes and organic monomers concomitantly proceeding sol-gel chemistry and free radical polymerization; and (iii) other polymerization approaches of organic monomers containing silanes. The modification of hybrid monoliths containing reactive groups to acquire the desired surface functionality is also described.