Efficient, Low-Cost, and High-Throughput Sodium Dodecyl Sulfate (SDS) Removal from Protein Digests Using Weak-Anion Exchange.

Sodium dodecyl sulfate (SDS) plays a pivotal role in protein denaturation, tissue extraction, and protein mass-based electrophoretic separations. However, even modest concentrations of SDS can cause column overpressure, retention time shifts, and ionization signal suppression during liquid chromatography-tandem mass spectrometry (LC-MS/MS) analyses. Thus, SDS removal is a critical step for LC-MS/MS analysis of protein digests containing SDS.

Paper Spray Mass Spectrometry with On-Paper Electrokinetic Manipulations: Part-Per-Trillion Detection of Per/Polyfluoroalkyl Substances in Water and Opioids in Urine.

We developed a simple, paper-based device that enables sensitive detection by mass spectrometry (MS) without solid phase extraction or other sample preparation. Using glass fiber filter papers within a 3D printed holder, the device employs electrokinetic manipulations to stack, separate, and desalt charged molecules on paper prior to spray into the MS. Due to counter-balanced electroosmotic flow and electrophoresis, charged analytes stack on the paper and desalting occurs in minutes.

In-Membrane Enrichment and Peptic Digestion to Facilitate Analysis of Monoclonal Antibody Glycosylation.

The number of therapeutic monoclonal antibodies (mAbs) is growing rapidly due to their widespread use for treating various diseases and health conditions. Assessing the glycosylation profile of mAbs during production is essential to ensuring their safety and efficacy. This research aims to rapidly isolate and digest mAbs for liquid chromatography-tandem mass spectrometry (LC-MS/MS) identification of glycans and monitoring of glycosylation patterns, potentially during manufacturing.

Addressing Challenges in Ion-Selectivity Characterization in Nanopores.

Ion selectivity is the basis for designing smart nanopore/channel-based devices, e.g., ion separators and biosensors.

Rapid Quantitation of Various Therapeutic Monoclonal Antibodies Using Membranes with Fc-Specific Ligands.

Therapeutic monoclonal antibodies (mAbs) provide effective treatments for many diseases, including cancer, autoimmune disorders, and, lately, COVID-19. Monitoring the concentrations of mAbs is important during their production and subsequent processing. This work demonstrates a 5 min quantitation of most human immunoglobulin G (IgG) antibodies through capture of mAbs in membranes modified with ligands that bind to the fragment crystallizable (Fc) region.

Analysis of Protein Glycosylation after Rapid Digestion Using Protease-Containing Membranes in Spin Columns.

Glycosylation is an important protein post-translational modification that plays a pivotal role in the bioactivity of therapeutic proteins and in the infectivity of viral proteins. Liquid chromatography with tandem mass spectrometry readily identifies protein glycans with site specificity. However, the overnight incubation used in conventional in-solution proteolysis leads to high turnaround times for glycosylation analysis, particularly when sequential in-solution digestions are needed for site-specific glycan identification.

Online protein digestion in membranes between capillary electrophoresis and mass spectrometry.

This research employs pepsin-containing membranes to digest proteins online after a capillary electrophoresis (CE) separation and prior to tandem mass spectrometry. Proteolysis after the separation allows the peptides from a given protein to enter the mass spectrometer in a single plug. Thus, migration time can serve as an additional criterion for confirming the identification of a peptide.

Nanopores: synergy from DNA sequencing to industrial filtration - small holes with big impact.

Nanopores in thin membranes play important roles in science and industry. Single nanopores have provided a step-change in portable DNA sequencing and understanding nanoscale transport while multipore membranes facilitate food processing and purification of water and medicine. Despite the unifying use of nanopores, the fields of single nanopores and multipore membranes differ - to varying degrees - in terms of materials, fabrication, analysis, and applications.

Quantitation of Trastuzumab and an Antibody to SARS-CoV-2 in Minutes Using Affinity Membranes in 96-Well Plates.

Quantitation of therapeutic monoclonal antibodies (mAbs) in human serum could ensure that patients have adequate levels of mAbs for effective treatment. This research describes the use of affinity, glass-fiber membranes in a 96-well-plate format for rapid (<5 min) quantitation of the therapeutic mAb trastuzumab and a mAb against the SARS-CoV-2 spike protein. Adsorption of a poly(acrylic acid)-containing film in membrane pores and activation of the -COOH groups in the film enable covalent-linking of affinity peptides or proteins to the membrane.

Electroblotting through Enzymatic Membranes to Enhance Molecular Tissue Imaging.

MALDI-TOF mass spectrometry imaging (MSI) is a powerful tool for studying biomolecule localization in tissue. Protein distributions in tissue provide important histological information; however, large proteins exhibit a high limit of detection in MALDI-MS when compared to their corresponding smaller proteolytic peptides. As a result, several techniques have emerged to digest proteins into more detectable peptides for imaging.

Determination of the Serum Concentrations of the Monoclonal Antibodies Bevacizumab, Rituximab, and Panitumumab Using Porous Membranes Containing Immobilized Peptide Mimotopes.

Effective monoclonal antibody (mAb) therapies require a threshold mAb concentration in patient serum. Moreover, the serum concentration of the mAb Bevacizumab should reside in a specific range to avoid side effects. Methods for conveniently determining the levels of mAbs in patient sera could allow for personalized dosage schedules that lead to more successful treatments.

Highly Rectifying Fluidic Diodes Based on Asymmetric Layer-by-Layer Nanofilms on Nanochannel Membranes.

Nanochannel-based fluidic diodes display ion selectivity and ion current rectification (ICR), which may prove to be important in energy-harvesting devices and biosensors. This paper reports asymmetric functionalization of the outer surface of a flexible nanochannel polymer membrane to create fluidic diodes that give ICR. Layer-by-layer (LbL) adsorption with cross-linking of only the underlying part of the polyelectrolyte nanofilm leads to a porosity step across the film.

Membrane-Based Affinity Purification to Identify Target Proteins of a Small-Molecule Drug.

Identifying the target proteins of small-molecule drug candidates is important for determining their molecular mechanisms of action. Porous membranes derivatized with such small molecules may provide an attractive target-identification platform due to a high protein-capture efficiency during flow through membrane pores. This work employs carbonic anhydrase II (CAII) binding to immobilized 4-(2-aminoethyl)benzenesulfonamide (AEBSA) to examine the efficiency and selectivity of affinity capture in modified membranes.

Flow through negatively charged, nanoporous membranes separates Li and K due to induced electromigration.

Flow through negatively charged nanopores separates Li and K with selectivities of up to 70 and Li passages from 20% to above 100%. Remarkably, both the Li/K selectivity and Li passage initially increase with flow rate, breaking the permeability/selectivity trade-off. Modelling demonstrates that flow through the membranes creates electric fields that retard transport of cations.

Oil droplet behavior on model nanofiltration membrane surfaces under conditions of hydrodynamic shear and salinity.

Hypotheses: Oil droplet stability and electrical charge, and membrane's affinity for oil govern droplet attachment to a membrane surface. Moderate droplet-surface affinity encourages surface coalescence and removal of droplets to help maintain the membrane relatively oil-free.

Experiments: Droplet attachment onto model nanofiltration membranes was studied, in situ and in real time, using the Direct Observation Through the Membrane method.

A Limiting Case of Constant Counterion Electrochemical Potentials in the Membrane for Examining Ion Transfer at Ion-Exchange Membranes and Patches.

Ion passage through ion-exchange membranes is vital in electrodialysis desalination, batteries and fuel cells, and water splitting. Simplified models of ion transport through such membranes frequently assume complete exclusion of co-ions (ions with the same sign of charge as the fixed charge in the membrane) from the membrane. However, a second assumption of constant counterion electrochemical potentials across the membrane leads to simple analytical expressions for ion fluxes and transmembrane potentials.

Modelling nanofiltration of electrolyte solutions.

This review critically examines current models for nanofiltration (NF) of electrolyte solutions. We start from linear irreversible thermodynamics, we derive a basic equation set for ion transfer in terms of gradients of ion electrochemical potentials and transmembrane volume flux. These equations are extended to the case of significant differences of thermodynamic forces across the membrane (continuous version of irreversible thermodynamics) and solved in quadratures for single salts and trace ions added to single salts in the case of macroscopically-homogeneous membranes.

High Selectivities among Monovalent Cations in Dialysis through Cation-Exchange Membranes Coated with Polyelectrolyte Multilayers.

Cation-exchange membranes allow preferential passage of cations over anions, but they show minimal selectivity among cations, which limits their use in ion separations. Recent studies show that modification of cation-exchange membranes with polyelectrolyte multilayers leads to exceptional monovalent/divalent cation electrodialysis selectivities, but no studies report high selectivity among monovalent ions. This work demonstrates that adsorption of protonated poly(allylamine) (PAH)/poly(4-styrenesulfonate) (PSS) multilayers on Nafion membranes leads to high K/Li selectivities in Donnan dialysis, where K and Li ions in a source phase pass through the membrane and exchange with Na ions in a receiving phase.

Monoclonal Antibody Capture and Analysis Using Porous Membranes Containing Immobilized Peptide Mimotopes.

Rapid, convenient methods for monoclonal antibody (mAb) isolation are critical for determining the concentrations of therapeutic mAbs in human serum. This work uses porous nylon membranes modified with a HER2 peptide mimotope, KGSGSGSQLGPYELWELSH (KH19), for rapid affinity capture of Herceptin, a mAb used to treat breast cancer. Covalent linking of KH19 to poly(acrylic acid)-containing films in porous nylon leads to a Herceptin-binding capacity of 10 mg per mL of membrane and allows selective Herceptin capture from diluted (1:3) human serum in 5 min.

Enzyme-containing spin membranes for rapid digestion and characterization of single proteins.

Proteolytic digestion is an important step in characterizing protein sequences and post-translational modifications (PTMs) using mass spectrometry (MS). This study uses pepsin- or trypsin-containing spin membranes for rapid digestion of single proteins or simple protein mixtures prior to ultrahigh-resolution Orbitrap MS analysis. Centrifugation of 100 μL of pretreated protein solutions through the functionalized membranes requires less than 1 min and conveniently digests proteins into large peptides that aid in confirming specific protein sequence variations and PTMs.

Limited proteolysis in porous membrane reactors containing immobilized trypsin.

Proteolysis is often a critical step in protein characterization via mass spectrometry. Compared to complete digestion, limited proteolysis gives larger peptides, and the dominant cleavage sites may identify highly accessible, flexible protein regions. This paper explores controlled proteolysis in porous nylon membranes containing immobilized trypsin.

Elution Is a Critical Step for Recovering Human Adenovirus 40 from Tap Water and Surface Water by Cross-Flow Ultrafiltration.

Unlabelled: This paper examines the recovery of the enteric adenovirus human adenovirus 40 (HAdV 40) by cross-flow ultrafiltration and interprets recovery values in terms of physicochemical interactions of virions during sample concentration. Prior to ultrafiltration, membranes were either blocked by exposure to calf serum (CS) or coated with a polyelectrolyte multilayer (PEM). HAdV 40 is a hydrophobic virus with a point of zero charge between pH 4.

Layer-by-Layer Deposition with Polymers Containing Nitrilotriacetate, A Convenient Route to Fabricate Metal- and Protein-Binding Films.

This paper describes a convenient synthesis of nitrilotriacetate (NTA)-containing polymers and subsequent layer-by-layer adsorption of these polymers on flat surfaces and in membrane pores. The resulting films form NTA-metal-ion complexes and capture 2-3 mmol of metal ions per mL of film. Moreover, these coatings bind multilayers of polyhistidine-tagged proteins through association with NTA-metal-ion complexes.

Deviations from Electroneutrality in Membrane Barrier Layers: A Possible Mechanism Underlying High Salt Rejections.

Reverse osmosis and nanofiltration (NF) employ composite membranes whose ultrathin barrier layers are significantly more permeable to water than to salts. Although solution-diffusion models of salt transport through barrier layers typically assume ubiquitous electroneutrality, in the case of ultrathin selective skins and low ion partition coefficients, space-charge regions may occupy a significant fraction of the membrane barrier layer. This work investigates the implications of these deviations from electroneutrality on salt transport.