Coupling Microchip Electrospray Ionization Devices with High Pressure Mass Spectrometry

Characterization of bispecific antigen-binding biotherapeutic fragmentation sites using microfluidic capillary electrophoresis coupled to mass spectrometry (mCZE-MS)

Fragmentation of therapeutic proteins is a potential critical quality attribute (CQA) that can occur in vivo or during manufacturing or storage due to enzymatic and non-enzymatic degradation pathways, such as hydrolysis, peroxide mediation, and acid/metal catalysis. Characterization of the fragmentation pattern of a therapeutic protein is traditionally accomplished using capillary gel electrophoresis with UV detection under both non-reducing and reducing conditions (nrCGE and rCGE). However, such methods are incompatible with direct coupling to mass spectrometry (MS) due to the use of anionic surfactants, e.g., sodium dodecyl sulfate (SDS). Here, we present a novel method to characterize size-based fragmentation variants of a new biotherapeutic kind using microfluidic ZipChip® capillary zone electrophoresis (mCZE) system interfaced with mass spectrometry (MS) to determine the molecular masses of fragments. A new modality of immuno-oncology therapy, bispecific antigen-binding biotherapeutic, was chosen to investigate its fragmentation pattern using mCZE-MS for the first time, according to our knowledge. Bispecific antigen-binding biotherapeutic samples from different stages of downstream column purification and forced degradation conditions were analyzed. The results were cross-validated with denaturing size-exclusion chromatography-mass spectrometry and conventional rSDS-CGE. In this study, we demonstrated that mCZE-MS could separate and characterize 12-40 kDa bispecific antigen-binding biotherapeutic fragments rapidly (within ≤12 minutes), with higher resolution and better sensitivity than traditional LC-MS methods.

Concepts and recent advances in microchip electrophoresis coupled to mass spectrometry: Technologies and applications

The online coupling of microchip electrophoresis (ME) as a fast, highly efficient, and low-cost miniaturized separation technique to mass spectrometry (MS) as an information-rich and sensitive characterization technique results in ME-MS an attractive tool for various applications. In this paper, we review the basic concepts and latest advances in technology for ME coupled to MS during the period of 2016-2021, covering microchip materials, structures, fabrication techniques, and interfacing to electrospray ionization (ESI)-MS and matrix-assisted laser desorption/ionization-MS. Two critical issues in coupling ME and ESI-MS include the electrical connection used to define the electrophoretic field strength along the separation channel and the generation of the electrospray for MS detection, as well as, a miniaturized ESI-tip. The recent commercialization of ME-MS in zone electrophoresis and isoelectric focusing modes has led to the widespread application of these techniques in academia and industry. Here we summarize recent applications of ME-MS for the separation and detection of antibodies, proteins, peptides, carbohydrates, metabolites, and so on. Throughout the paper these applications are discussed in the context of benefits and limitations of ME-MS in comparison to alternative techniques.

Microfluidic Platform for Time-Resolved Characterization of Protein Higher-Order Structures and Dynamics Using Top-Down Mass Spectrometry

Characterization of protein higher-order structures and dynamics is essential for understanding the biological functions of proteins and revealing the underlying mechanisms. Top-down mass spectrometry (MS) accesses structural information at both the intact protein level and the peptide fragment level. Native top-down MS allows analysis of a protein complex's architecture and subunits' identity and modifications. Top-down hydrogen/deuterium exchange (HDX) MS offers high spatial resolution for conformational or binding interface analysis and enables conformer-specific characterization. A microfluidic chip can provide superior performance for front-end reactions useful for these MS workflows, such as flexibility in manipulating multiple reactant flows, integrating various functional modules, and automation. However, most microchip-MS devices are designed for bottom-up approaches or top-down proteomics. Here, we demonstrate a strategy for designing a microchip for top-down MS analysis of protein higher-order structures and dynamics. It is suitable for time-resolved native MS and HDX MS, with designs aiming for efficient ionization of intact protein complexes, flexible manipulation of multiple reactant flows, and precise control of reaction times over a broad range of flow rates on the submicroliter per minute scale. The performance of the prototype device is demonstrated by measurements of systems including monoclonal antibodies, antibody-antigen complexes, and coexisting protein conformers. This strategy may benefit elaborate structural analysis of biomacromolecules and inspire method development using the microchip-MS approach.

Interfacing microfluidics with information-rich detection systems for cells, bioparticles, and molecules

The development of elegant and numerous microfluidic manipulations has enabled significant advances in the processing of small volume samples and the detection of minute amounts of biomaterials. Effective isolation of single cells in a defined volume as well as manipulations of complex bioparticle or biomolecule mixtures allows for the utilization of information-rich detection methods including mass spectrometry, electron microscopy imaging, and amplification/sequencing. The art and science of translating biosamples from microfluidic platforms to highly advanced, information-rich detection system is the focus of this review, where we term the translation between the microfluidics elements to the external world “off-chipping.” When presented with the challenge of presenting sub-nanoliter volumes of manipulated sample to a detection scheme, several delivery techniques have been developed for effective analysis. These techniques include spraying (electrospray, nano-electrospray, pneumatic), meniscus-defined volumes (droplets, plugs), constrained volumes (narrow channels, containers), and phase changes (deposition, freezing). Each technique has been proven effective in delivering highly defined samples from microfluidic systems to the detection elements. This review organizes and presents selective publications that illustrate the advancements of these delivery techniques with respect to the type of sample analyzed, while introducing each strategy and providing historical perspective. The publications highlighted in this review were chosen due to their significance and relevance in the development of their respective off-chip technique.

Chip-Based Capillary Zone Electrophoresis Mass Spectrometry for Rapid Resolution and Quantitation of Critical Quality Attributes in Protein Biotherapeutics

The aspiration of the multi-attribute method (MAM) is to utilize a single mass spectrometry-based method that can measure multiple attributes simultaneously, thus enabling data-driven decisions more quickly and efficiently. However, challenges associated with identifying and quantitating critical quality attributes such as asparagine deamidation and isoaspartic acid using conventional ultrahigh-pressure liquid chromatography (UHPLC) coupled to mass spectrometry have necessitated long gradients to ensure sufficient separation for quantitation. Microfluidic chip-based capillary zone electrophoresis mass spectrometry (CZE-MS) shows potential to enable rapid charge-based separation of peptide mixtures, and this approach was evaluated using multipeptide mixtures of synthetic peptides as well as digested protein therapeutics. In these experiments, repeatability, linearity, and peak-to-peak resolution of several peptide families containing asparagine deamidation and/or isoaspartic acid were demonstrated. In addition, a comparison of peptide map results acquired with both UHPLC-MS and CZE-MS for two enzymatically digested biological therapeutics showed comparable sequence coverage and quantitation results between the two approaches. As MAM becomes increasingly utilized for analysis of biological therapeutics, MS instrument demand will rapidly increase, resulting in a bottleneck. A CZE-based separation shows potential to alleviate this bottleneck by drastically increasing MAM throughput while providing results comparable to those acquired using conventional UHPLC separations.

Clinical Chemistry for Developing Countries: Mass Spectrometry

Early disease diagnosis is necessary to enable timely interventions. Implementation of this vital task in the developing world is challenging owing to limited resources. Diagnostic approaches developed for resource-limited settings have often involved colorimetric tests (based on immunoassays) due to their low cost. Unfortunately, the performance/sensitivity of such simplistic tests are often limited and significantly hinder opportunities for early disease detection. A new criterion for selecting diagnostic tests in low- and middle-income countries is proposed here that is based on performance-to-cost ratio. For example, modern mass spectrometry (MS) now involves analysis of the native sample in the open laboratory environment, enabling applications in many fields, including clinical research, forensic science, environmental analysis, and agriculture. In this critical review, we summarize recent developments in chemistry that enable MS to be applied effectively in developing countries. In particular, we argue that closed automated analytical systems may not offer the analytical flexibility needed in resource-limited settings. Alternative strategies proposed here have potential to be widely accepted in low- and middle-income countries through the utilization of the open-source ambient MS platform that enables microsampling techniques such as dried blood spot to be coupled with miniature mass spectrometers in a centralized analytical platform. Consequently, costs associated with sample handling and maintenance can be reduced by >50% of the total ownership cost, permitting analytical measurements to be operated at high performance-to-cost ratios in the developing world.

Capillary Electrophoresis-High Resolution Mass Spectrometry for Measuring In Vivo Arginine Isotope Incorporation in Alzheimer's Disease Mouse Models

Immune-based metabolic reprogramming of arginine utilization in the brain contributes to the neuronal pathology associated with Alzheimer's disease (AD). To enable our long-term goals of differentiation of AD mouse model genotypes, ages, and sexes based on activity of this pathway, we describe here the novel dosing (using uniformly labeled (¹³C₆¹⁵N₄) arginine) and analysis methods using capillary electrophoresis high-resolution accurate-mass mass spectrometry for isotope tracing of metabolic products of arginine. We developed a pseudoprimed infusion-dosing regimen, using repeated injections, to achieve a steady state of uniformly labeled arginine in 135-195 min post bolus dose. Incorporation of stable isotope labeled carbon and nitrogen from uniformly labeled arginine into a host of downstream metabolites was measured in vivo in mice using serially sampled dried blood spots from the tail. In addition to the dried blood spot time course samples, total isotope incorporation into arginine-related metabolites was measured in the whole brain and plasma after 285 min. Preliminary demonstration of the technique identified differences isotope incorporation in arginine metabolites between male and female mice in a mouse-model of sporadic Alzheimer's disease (APOE4/huNOS2). The technique described herein will permit arginine pathway activity differentiation between mouse genotypes, ages, sexes, or drug treatments in order to elucidate the contribution of this pathway to Alzheimer's disease.

Applications of Mass Spectrometry for Clinical Diagnostics: The Influence of Turnaround Time

This critical review discusses how the need for reduced clinical turnaround times has influenced chemical instrumentation. We focus on the development of modern mass spectrometry (MS) and its application in clinical diagnosis. With increased functionality that takes advantage of novel front-end modifications and computational capabilities, MS can now be used for non-traditional clinical analyses, including applications in clinical microbiology for bacteria differentiation and in surgical operation rooms. We summarize here recent developments in the field that have enabled such capabilities, which include miniaturization for point-of-care testing, direct complex mixture analysis via ambient ionization, chemical imaging and profiling, and systems integration.

Click chemistry at the microscale

This manuscript reviews recent developments in click chemistry in microscale systems.