Advances in and prospects of microchip liquid chromatography

Bone and Joint-on-Chip Platforms: Construction Strategies and Applications

Organ-on-a-chip, also known as "tissue chip," is an advanced platform based on microfluidic systems for constructing miniature organ models in vitro. They can replicate the complex physiological and pathological responses of human organs. In recent years, the development of bone and joint-on-chip platforms aims to simulate the complex physiological and pathological processes occurring in human bones and joints, including cell-cell interactions, the interplay of various biochemical factors, the effects of mechanical stimuli, and the intricate connections between multiple organs. In the future, bone and joint-on-chip platforms will integrate the advantages of multiple disciplines, bringing more possibilities for exploring disease mechanisms, drug screening, and personalized medicine. This review explores the construction and application of Organ-on-a-chip technology in bone and joint disease research, proposes a modular construction concept, and discusses the new opportunities and future challenges in the construction and application of bone and joint-on-chip platforms.

Trends and challenges in microfluidic methods for protein manipulation-A review

Proteins are important molecules involved in an immensely large number of biological processes. Being capable of manipulating proteins is critical for developing reliable and affordable techniques to analyze and/or detect them. Such techniques would enable the production of therapeutic agents for the treatment of diseases or other biotechnological applications (e.g., bioreactors or biocatalysis). Microfluidic technology represents a potential solution to protein manipulation challenges because of the diverse phenomena that can be exploited to achieve micro- and nanoparticle manipulation. In this review, we discuss recent contributions made in the field of protein manipulation in microfluidic systems using different physicochemical principles and techniques, some of which are miniaturized versions of already established macro-scale techniques.

Rubik's Cube as Reconfigurable Microfluidic Platform for Rapid Setup and Switching of Analytical Devices

Microfluidics technology plays an important role in modern analytical instruments, while the modular design of microfluidics facilitates the reconfiguration of analytical instrument functions, making it possible to deploy on-demand systems in the field. However, modular design also faces the challenges such as connection reliability and reconfiguration convenience. Inspired by the self-locking structure of the Rubik's cube, a modular, reconfigurable microfluidic instrument architecture is proposed in this paper. The system has a self-locking structure of Rubik's cube components and an O-ring-based alignment and sealing mechanism, which enables reliable interconnection and rapid rearrangement of microfluidic modules by simply rotating the faces of the microfluidic cube. In addition, the system is capable of integrating a variety of customized modules to perform analysis tasks. A proof-of-concept application of detecting multiple pollutants in water is demonstrated to show the reconfigurable characteristics of the system. The findings of this paper provide a new idea for the design of microfluidic analytical instrument architectures.

Nano liquid chromatography, an updated review

Low flow chromatography has a rich history of innovation but has yet to reach widespread implementation in bioanalytical applications. Improvements in pump technology, microfluidic connections, and nano-electrospray sources for mass spectrometry have laid the groundwork for broader application, and innovation in this space has accelerated in recent years. This article reviews the instrumentation used for nano-flow liquid chromatography , the types of columns employed, and strategies for multi-dimensionality of separations, which is key to the future state of the technique to the high-throughput needs of modern bioanalysis. An update of the current applications where nano-LC is widely used, such as proteomics and metabolomics, is discussed. But the trend towards biopharmaceutical development of increasingly complex, targeted, and potent therapeutics for the safe treatment of disease drives the need for ultimate selectivity and sensitivity of our analytical platforms for targeted quantitation in a regulated space. The selectivity needs are best addressed by mass spectrometric detection, especially at high resolutions, and exquisite sensitivity is provided by nano-electrospray ionization as the technology continues to evolve into an accessible, robust, and easy to use platform.

Microfluidic chips: recent advances, critical strategies in design, applications and future perspectives

Microfluidic chip technology is an emerging tool in the field of biomedical application. Microfluidic chip includes a set of groves or microchannels that are engraved on different materials (glass, silicon, or polymers such as polydimethylsiloxane or PDMS, polymethylmethacrylate or PMMA). The microchannels forming the microfluidic chip are interconnected with each other for desired results. This organization of microchannels trapped into the microfluidic chip is associated with the outside by inputs and outputs penetrating through the chip, as an interface between the macro- and miniature world. With the help of a pump and a chip, microfluidic chip helps to determine the behavioral change of the microfluids. Inside the chip, there are microfluidic channels that permit the processing of the fluid, for example, blending and physicochemical responses. Microfluidic chip has numerous points of interest including lesser time and reagent utilization and alongside this, it can execute numerous activities simultaneously. The miniatured size of the chip fastens the reaction as the surface area increases. It is utilized in different biomedical applications such as food safety sensing, peptide analysis, tissue engineering, medical diagnosis, DNA purification, PCR activity, pregnancy, and glucose estimation. In the present study, the design of various microfluidic chips has been discussed along with their biomedical applications.

Pharmacokinetics-On-a-Chip: In Vitro Microphysiological Models for Emulating of Drugs ADME

Despite many ongoing efforts across the full spectrum of pharmaceutical and biotech industries, drug development is still a costly undertaking that involves a high risk of failure during clinical trials. Animal models played vital roles in understanding the mechanism of human diseases. However, the use of these models has been a subject of heated debate, particularly due to ethical matters and the inevitable pathophysiological differences between animals and humans. Current in vitro models lack the sufficient functionality and predictivity of human pharmacokinetics and toxicity, therefore, are not capable to fully replace animal models. The recent development of micro-physiological systems has shown great potential as indispensable tools for recapitulating key physiological parameters of humans and providing in vitro methods for predicting the pharmacokinetics and pharmacodynamics in humans. Integration of Absorption, Distribution, Metabolism, and Excretion (ADME) processes within one close in vitro system is a paramount development that would meet important unmet pharmaceutical industry needs. In this review paper, synthesis of the ADME-centered organ-on-a-chip technology is systemically presented from what is achieved to what needs to be done, emphasizing the requirements of in vitro models that meet industrial needs in terms of the structure and functions.

Design of Microchannel Suitable for Packing with Anion Exchange Resins: Uranium Separation from Seawater Containing a Large Amount of Cesium

We present a resin-packed microchannel that can reduce the radiation exposure risk and secondary radioactive wastes during uranium (U) separation by downscaling the separation using a microchip. Two types of microchips were designed to densely pack the microchannels with resins. The microchannels had almost the same cross-sectional area, but different outer circumferences. A satisfactory separation performance could be obtained by arranging more than ca. 10 resins along the depth and width of the microchannels. A resin-packed microchannel is an effective separation technique for determining the U concentration via inductively coupled plasma mass spectrometry owing to its ability to avoid the contamination of equipment by cesium, and to reduce the matrix effect. The size of the separation site was scaled down to <1/5000 compared to commonly used counterparts. The radiation exposure risk and secondary radioactive wastes can be reduced by 10- and 800-fold, respectively, using a resin-packed microchannel.

[Recent advances in microchip liquid chromatography]

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Low-cost and open-source strategies for chemical separations

In recent years, a trend toward utilizing open access resources for laboratory research has begun. Open-source design strategies for scientific hardware rely upon the use of widely available parts, especially those that can be directly printed using additive manufacturing techniques and electronic components that can be connected to low-cost microcontrollers. Open-source software eliminates the need for expensive commercial licenses and provides the opportunity to design programs for specific needs. In this review, the impact of the "open-source movement" within the field of chemical separations is described, primarily through a comprehensive look at research in this area over the past five years. Topics that are covered include general laboratory equipment, sample preparation techniques, separations-based analysis, detection strategies, electronic system control, and software for data processing. Remaining hurdles and possible opportunities for further adoption of open-source approaches in the context of these separations-related topics are also discussed.

Chip-based ion chromatography (chip-IC) with a sensitive five-electrode conductivity detector for the simultaneous detection of multiple ions in drinking water

The emerging need for accurate, efficient, inexpensive, and multiparameter monitoring of water quality has led to interest in the miniaturization of benchtop chromatography systems. This paper reports a chip-based ion chromatography (chip-IC) system in which the microvalves, sample channel, packed column, and conductivity detector are all integrated on a polymethylmethacrylate (PMMA) chip. A laser-based bonding technique was developed to guarantee simultaneous robust sealing between the homogeneous and heterogeneous interfaces. A five-electrode-based conductivity detector was presented to improve the sensitivity for nonsuppressed anion detection. Common anions (F^-, Cl^-, NO₃ ^-, and SO₄ ^2-) were separated in less than 8 min, and a detection limit (LOD) of 0.6 mg L^-1 was achieved for SO₄ ^2-. Tap water was also analyzed using the proposed chip-IC system, and the relative deviations of the quantified concentration were less than 10% when compared with that a commercial IC system.

Single-particle-frit-based packed columns for microchip chromatographic analysis of neurotransmitters

The fabrication of effective microchip liquid chromatography (LC) systems tends to be limited by the availability of suitable chromatographic columns. Herein, we developed a glass microchip LC system in which porous single-particle silica was adopted as frits and a freeze-thaw valve was utilized to achieve sample injection without interfering with sampling. The fabrication of single-particle-frit-based packed columns did not require an additional packing channel, thus avoiding dead volumes within the channel interface that can influence chromatographic separation. Further, the length of the packed column could be adjusted using the location of single-particle frits within the column channel. The fabricated frits exhibited high mechanical strength, good permeability, and tolerance for high pressures during chromatographic separation. In particular, the developed microchip LC system was able to withstand high separation pressures of more than 5000 psi. The microchip LC system was applied to the separation of neurotransmitters. Three different monoamine neurotransmitters were completely separated within 5 min with theoretical plate numbers on the order of 100,000 plates m^-1. The microchip LC system has a potential for application in a variety of fields including environmental analysis, food safety, drug analysis, and biomedicine.

Analytical techniques for metabolomic studies: a review

Metabolomics is the comprehensive study of small-molecule metabolites. Obtaining a wide coverage of the metabolome is challenging because of the broad range of physicochemical properties of the small molecules. To study the compounds of interest spectroscopic (NMR), spectrometric (MS) and separation techniques (LC, GC, supercritical fluid chromatography, CE) are used. The choice for a given technique is influenced by the sample matrix, the concentration and properties of the metabolites, and the amount of sample. This review discusses the most commonly used analytical techniques for metabolomic studies, including their advantages, drawbacks and some applications.

Current developments in LC-MS for pharmaceutical analysis

Liquid chromatography (LC) based techniques in combination with mass spectrometry (MS) detection have had a large impact on the development of new pharmaceuticals in the past decades.

Automation of mass spectrometric detection of analytes and related workflows: A review

The developments in mass spectrometry (MS) in the past few decades reveal the power and versatility of this technology. MS methods are utilized in routine analyses as well as research activities involving a broad range of analytes (elements and molecules) and countless matrices. However, manual MS analysis is gradually becoming a thing of the past. In this article, the available MS automation strategies are critically evaluated. Automation of analytical workflows culminating with MS detection encompasses involvement of automated operations in any of the steps related to sample handling/treatment before MS detection, sample introduction, MS data acquisition, and MS data processing. Automated MS workflows help to overcome the intrinsic limitations of MS methodology regarding reproducibility, throughput, and the expertise required to operate MS instruments. Such workflows often comprise automated off-line and on-line steps such as sampling, extraction, derivatization, and separation. The most common instrumental tools include autosamplers, multi-axis robots, flow injection systems, and lab-on-a-chip. Prototyping customized automated MS systems is a way to introduce non-standard automated features to MS workflows. The review highlights the enabling role of automated MS procedures in various sectors of academic research and industry. Examples include applications of automated MS workflows in bioscience, environmental studies, and exploration of the outer space.

Experimental and numerical study of band-broadening effects associated with analyte transfer in microfluidic devices for spatial two-dimensional liquid chromatography created by additive manufacturing

Conventional one-dimensional column-based liquid chromatographic (LC) systems do not offer sufficient separation power for the analysis of complex mixtures. Column-based comprehensive two-dimensional liquid chromatography offers a higher separation power, yet suffers from instrumental complexity and long analysis times. Spatial two-dimensional liquid chromatography can be considered as an alternative to column-based approaches. The peak capacity of the system is ideally the product of the peak capacities of the two dimensions, yet the analysis time remains relatively short due to parallel second-dimension separations. Aspects affecting the separation efficiency of this type of systems include flow distribution to homogeneously distribute the mobile phase for the second-dimension (²D) separation, flow confinement during the first-dimension (¹D) separation, and band-broadening effects during analyte transfer from the ¹D separation channel to the ²D separation area. In this study, the synergy between computational fluid dynamics (CFD) simulations and rapid prototyping was exploited to address band broadening during the ²D development and analyte transfer from ¹D to ²D. Microfluidic devices for spatial two-dimensional liquid chromatography were designed, simulated, 3D-printed and tested. The effects of presence and thickness of spacers in the ²D separation area were addressed and leaving these out proved to be the most efficient solution regarding band broadening reduction. The presence of a stationary-phase material in the ¹D channel had a great effect on the analyte transfer from the ¹D to the ²D and the resulting band broadening. Finally, pressure limit of the fabricated devices and printability are discussed.

Chiral Stationary Phases for Liquid Chromatography: Recent Developments

The planning and development of new chiral stationary phases (CSPs) for liquid chromatography (LC) are considered as continuous and evolutionary issues since the introduction of the first CSP in 1938. The main objectives of the development strategies were to attempt the improvement of the chromatographic enantioresolution performance of the CSPs as well as enlarge their versatility and range of applications. Additionally, the transition to ultra-high-performance LC were underscored. The most recent strategies have comprised the introduction of new chiral selectors, the use of new materials as chromatographic supports or the reduction of its particle size, and the application of different synthetic approaches for preparation of CSPs. This review gathered the most recent developments associated to the different types of CSPs providing an overview of the relevant advances that are arising on LC.

Study of peak capacities generated by a porous layered radially elongated pillar array column coupled to a nano-LC system

The performance of a porous-layered radially elongated pillar (PLREP) array column in a commercial nano-LC system was examined by performing separation of alkylphenones and peptides.

Click chemistry at the microscale

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

Low-cost customizable microscale toolkit for rapid screening and purification of therapeutic proteins

Biopharmaceutical separations require tremendous amounts of optimization to achieve acceptable product purity. Typically, large volumes of reagents and biological materials are needed for testing different parameters, thus adding to the expense of biopharmaceutical process development. This study demonstrates a versatile and customizable microscale column (µCol) for biopharmaceutical separations using immobilized metal affinity chromatography (IMAC) as an example application to identify key parameters. µCols have excellent precision, efficiency, and reproducibility, can accommodate any affinity, ion-exchange or size-exclusion-based resin and are compatible with any high-performance liquid chromatography (HPLC) system. µCols reduce reagent amounts, provide comparable purification performance and high-throughput, and are easy to automate compared with current conventional resin columns. We provide a detailed description of the fabrication methods, resin packing methods, and µCol validation experiments using a conventional HPLC system. Finite element modeling using COMSOL Multiphysics was used to validate the experimental performance of the µCols. In this study, µCols were used for improving the purification achieved for granulocyte colony stimulating factor (G-CSF) expressed using a cell-free CHO in vitro translation (IVT) system and were compared to a conventional 1 ml IMAC column. Experimental data revealed comparable purity with a 10-fold reduction in the amount of buffer, resin, and purification time for the μCols compared with conventional columns for similar protein yields.

Microfluidic affinity separation chip for selective capture and release of label-free ovarian cancer exosomes

Exosomes are nanoscale vesicles found in many bodily fluids which play a significant role in cell-to-cell signaling and contain biomolecules indicative of their cells of origin. Recently, microfluidic devices have provided the ability to efficiently capture exosomes based on specific membrane biomarkers, but releasing the captured exosomes intact and label-free for downstream characterization and experimentation remains a challenge. We present a herringbone-grooved microfluidic device which is covalently functionalized with antibodies against general and cancer exosome membrane biomarkers (CD9 and EpCAM) to isolate exosomes from small volumes of high-grade serous ovarian cancer (HGSOC) serum. Following capture, intact exosomes are released label-free using a low pH buffer and immediately neutralized downstream to ensure their stability. Characterization of captured and released exosomes was performed using fluorescence microscopy, nanoparticle tracking analysis, flow-cytometry, and SEM. Our results demonstrate the successful isolation of intact and label-free exosomes, indicate that the amount of both total and EpCAM+ exosomes increases with HGSOC disease progression, and demonstrate the downstream internalization of isolated exosomes by OVCAR8 cells. This device and approach can be utilized for a nearly limitless range of downstream exosome analytical and experimental techniques, both on and off-chip.

Two-dimensional insertable separation tool (TWIST) for flow confinement in spatial separations

Spatial comprehensive two-dimensional liquid chromatography (^xLC×^xLC) may be an efficient approach to achieve high peak capacities in relatively short analysis times, thanks to parallel second-dimension separations [1,2]. A key issue to reach the potential of ^xLC×^xLC is to achieve adequate flow control and confinement of the analytes to the desired regions, i.e. confinement in the first-dimension direction and subsequently homogeneous flow in the second dimension. To achieve these goals we propose the TWIST concept (TWo-dimensional Insertable Separation Tool), a modular device that includes an internal first-dimension (¹D) part that is cylindrical and rotatable. This internal part features a series of through-holes, each of which is perpendicular to the direction of the ¹D flow. The internal part is inserted in the cylindrical casing of the external part. The internal diameter of the casing is marginally larger than the external diameter of the internal part. The external part also comprises a flow distributor and second-dimension (²D) channels. During the ¹D injection and development, the channel is placed in a position where the through-holes are facing the wall of the external part, such that the liquid remains confined within the ¹D channel. Thereafter, to realize the transfer to the second dimension (²D injection), the ¹D channel is rotated, so that the holes of the internal part are aligned with the holes on the external part, allowing a transversal flow of the ²D mobile phase from the distributor through the ¹D channel and eventually into the ²D area.

Miniaturized high-performance liquid chromatography instrumentation

Miniaturized high performance liquid chromatography (HPLC) has attracted increasing attention for its potential in high-throughput analyses and point-of-care applications. In this review we highlight the recent advancements in HPLC system miniaturization. We focus on the major components that constitute these instruments along with their respective advantages and drawbacks as well as present a few representative miniaturized HPLC systems. We discuss briefly some of the applications and also anticipate the future development trends of these instrumental platforms.

Impact of diffusion on transverse dispersion in two-dimensional ordered and random porous media

Solute dispersion in fluid flow results from the interaction between advection and diffusion. The relative contributions of these two mechanisms to mass transport are characterized by the reduced velocity ν, also referred to as the Péclet number. In the absence of diffusion (i.e., when the solute diffusion coefficient D_{m}=0 and ν→∞), divergence-free laminar flow of an incompressible fluid results in a zero-transverse dispersion coefficient (D_{T}=0), both in ordered and random two-dimensional porous media. We demonstrate by numerical simulations that a more realistic realization of the condition ν→∞ using D_{m}≠0 and letting the fluid flow velocity approach infinity leads to completely different results for ordered and random two-dimensional porous media. With increasing reduced velocity, D_{T} approaches an asymptotic value in ordered two-dimensional porous media but grows linearly in disordered (random) structures depending on the geometrical disorder of a structure: a higher degree of heterogeneity results in a stronger growth of D_{T} with ν. The obtained results reveal that disorder in the geometrical structure of a two-dimensional porous medium leads to a growth of D_{T} with ν even in a uniform pore-scale advection field; however, lateral diffusion is a prerequisite for this growth. By contrast, in ordered two-dimensional porous media the presence of lateral diffusion leads to a plateau for the transverse dispersion coefficient with increasing ν.

Prototyping of thermoplastic microfluidic chips and their application in high-performance liquid chromatography separations of small molecules

The present paper discusses practical aspects of prototyping of microfluidic chips using cyclic olefin copolymer as substrate and the application in high-performance liquid chromatography. The developed chips feature a 60mm long straight separation channel with circular cross section (500μm i.d.) that was created using a micromilling robot. To irreversibly seal the top and bottom chip substrates, a solvent-vapor-assisted bonding approach was optimized, allowing to approximate the ideal circular channel geometry. Four different approaches to establish the micro-to-macro interface were pursued. The average burst pressure of the microfluidic chips in combination with an encasing holder was established at 38MPa and the maximum burst pressure was 47MPa, which is believed to be the highest ever report for these polymer-based microfluidic chips. Porous polymer monolithic frits were synthesized in-situ via UV-initiated polymerization and their locations were spatially controlled by the application of a photomask. Next, high-pressure slurry packing was performed to introduce 3μm silica reversed-phase particles as the stationary phase in the separation channel. Finally, the application of the chip technology is demonstrated for the separation of alkyl phenones in gradient mode yielding baseline peak widths of 6s by applying a steep gradient of 1.8min at a flow rate of 10μL/min.

Recent advances in capillary ultrahigh pressure liquid chromatography

In the twenty years since its initial demonstration, capillary ultrahigh pressure liquid chromatography (UHPLC) has proven to be one of most powerful separation techniques for the analysis of complex mixtures. This review focuses on the most recent advances made since 2010 towards increasing the performance of such separations. Improvements in capillary column preparation techniques that have led to columns with unprecedented performance are described. New stationary phases and phase supports that have been reported over the past decade are detailed, with a focus on their use in capillary formats. A discussion on the instrument developments that have been required to ensure that extra-column effects do not diminish the intrinsic efficiency of these columns during analysis is also included. Finally, the impact of these capillary UHPLC topics on the field of proteomics and ways in which capillary UHPLC may continue to be applied to the separation of complex samples are addressed.