Applications of microfluidics and microchip electrophoresis for potential clinical biomarker analysis

Capillary electrophoresis-mass spectrometry for protein analyses under native conditions: Current progress and perspectives

Native mass spectrometry is a rapidly emerging technique for fast and sensitive structural analysis of protein constructs, maintaining the protein higher order structure. The coupling with electromigration separation techniques under native conditions enables the characterization of proteoforms and highly complex protein mixtures. In this review, we present an overview of current native CE-MS technology. First, the status of native separation conditions is described for capillary zone electrophoresis (CZE), affinity capillary electrophoresis (ACE), and capillary isoelectric focusing (CIEF), as well as their chip-based formats, including essential parameters such as electrolyte composition and capillary coatings. Further, conditions required for native ESI-MS of (large) protein constructs, including instrumental parameters of QTOF and Orbitrap systems, as well as requirements for native CE-MS interfacing are presented. On this basis, methods and applications of the different modes of native CE-MS are summarized and discussed in the context of biological, medical, and biopharmaceutical questions. Finally, key achievements are highlighted and concluded, while remaining challenges are pointed out.

Application of microfluidic technology based on surface-enhanced Raman scattering in cancer biomarker detection: A review

With the continuous discovery and research of predictive cancer-related biomarkers, liquid biopsy shows great potential in cancer diagnosis. Surface-enhanced Raman scattering (SERS) and microfluidic technology have received much attention among the various cancer biomarker detection methods. The former has ultrahigh detection sensitivity and can provide a unique fingerprint. In contrast, the latter has the characteristics of miniaturization and integration, which can realize accurate control of the detection samples and high-throughput detection through design. Both have the potential for point-of-care testing (POCT), and their combination (lab-on-a-chip SERS (LoC-SERS)) shows good compatibility. In this paper, the basic situation of circulating proteins, circulating tumor cells, exosomes, circulating tumor DNA (ctDNA), and microRNA (miRNA) in the diagnosis of various cancers is reviewed, and the detection research of these biomarkers by the LoC-SERS platform in recent years is described in detail. At the same time, the challenges and future development of the platform are discussed at the end of the review. Summarizing the current technology is expected to provide a reference for scholars engaged in related work and interested in this field.

A review of electrophoretic separations in temperature-responsive Pluronic thermal gels

Gel electrophoresis is a ubiquitous bioanalytical technique used in research laboratories to validate protein and nucleic acid samples. Polyacrylamide and agarose have been the gold standard gel materials for decades, but an alternative class of polymer has emerged with potentially superior performance. Pluronic thermal gels are water-soluble polymers that possess the unique ability to undergo a change in viscosity in response to changing temperature. Thermal gels can reversibly convert between low-viscosity liquids and high-viscosity solid gels using temperature as an adjustable parameter. The properties of thermal gels provide unmatched flexibility as a dynamic separations matrix to measure analytes ranging from small molecules to cells. This review article describes the physical and chemical properties of Pluronic thermal gels to provide a fundamental overview of polymer behavior. The performance of thermal gels is then reviewed to highlight their applications as a gel matrix for electrokinetic separations in capillary, microfluidic, and slab gel formats. The use of dynamic temperature-responsive gels in bioanalytical separations is an underexplored area of research but one that holds exciting potential to achieve performance unattainable with conventional static polymers.

Particle Counting Methods Based on Microfluidic Devices

Particle counting serves as a pivotal constituent in diverse analytical domains, encompassing a broad spectrum of entities, ranging from blood cells and bacteria to viruses, droplets, bubbles, wear debris, and magnetic beads. Recent epochs have witnessed remarkable progressions in microfluidic chip technology, culminating in the proliferation and maturation of microfluidic chip-based particle counting methodologies. This paper undertakes a taxonomical elucidation of microfluidic chip-based particle counters based on the physical parameters they detect. These particle counters are classified into three categories: optical-based counters, electrical-based particle counters, and other counters. Within each category, subcategories are established to consider structural differences. Each type of counter is described not only in terms of its working principle but also the methods employed to enhance sensitivity and throughput. Additionally, an analysis of future trends related to each counter type is provided.

Advances in TB testing

Globally, tuberculosis (TB) was the leading cause of death from a single infectious agent until the coronavirus (COVID-19) pandemic. In 2020, an estimated 10 million people fell ill with TB and a total of 1.5 million people died from the disease. About one-quarter of the global population, almost two billion people, is estimated to be latently infected with Mycobacterium tuberculosis (MTB). Although latent TB infection (LTBI) is asymptomatic and noncontagious, about 5-10% of LTBI patients have a lifetime risk of progression to active TB. The diagnosis and treatment of active cases are extremely vital for TB control programs. However, achieving the End TB goal of 2035 without the ability to identify and treat the pool of latently infected individuals will be a big challenge. To do so, improved technology to provide more accurate diagnostic tools and accessibility are crucial. Therefore, this chapter covers the current WHO-endorsed tests and advances in diagnostic and screening tests for active and latent TB.

Traditional vs. Microfluidic Synthesis of ZnO Nanoparticles

Microfluidics provides a precise synthesis of micro-/nanostructures for various applications, including bioengineering and medicine. In this review article, traditional and microfluidic synthesis methods of zinc oxide (ZnO) are compared concerning particle size distribution, morphology, applications, reaction parameters, used reagents, and microfluidic device materials. Challenges of traditional synthesis methods are reviewed in a manner where microfluidic approaches may overcome difficulties related to synthesis precision, bulk materials, and reproducibility.

Microfluidic assessment of nutritional biomarkers: Concepts, approaches and advances

Among various approaches to understand the health status of an individual, nutritional biomarkers can provide valuable information, particularly in terms of deficiencies, if any, and their severity. Commonly, the approach revolves around molecular sciences, and the information gained can support prognosis, diagnosis, remediation, and impact assessment of therapies. Microfluidic platforms can offer benefits of low sample and reagent requirements, low cost, high precision, and lower detection limits, with simplicity in handling and the provision for complete automation and integration with information and communication technologies (ICTs). While several advances are being made, this work details the underlying concepts, with emphasis on different point-of-care devices for the analysis of macro and micronutrient biomarkers. In addition, the scope of using different wearable microfluidic sensors for real-time and noninvasive determination of biomarkers is detailed. While several challenges remain, a strong focus is given on recent advances, presenting the state-of-the-art of this field. With more such biomarkers being discovered and commercialization-driven research, trends indicate the wide prospects of this advancing field in supporting clinicians, food technologists, nutritionists, and others.

Sequential storage and release of microdroplets

Droplet microfluidic methods have opened up the possibility of studying a plethora of phenomena ranging from biological to physical or chemical processes at ultra low volumes and high throughput. A key component of such approaches is the ability to trap droplets for observation, and many device architectures for achieving this objective have been developed. A challenge with such approaches is, however, recovering the droplets following their confinement for applications involving further analysis. Here, we present a device capable of generating, confining and releasing microdroplets in a sequential manner. Through a combination of experimental and computational simulations, we shed light on the key features required for successful droplet storage and retrieval. Moreover, we explore the effect of the flow rate of the continuous phase on droplet release, determining that a critical rate is needed to ensure complete droplet deformation through constrictions holding the droplets in place prior to release. Finally, we find that once released, droplets can be retrieved and collected off chip. The ability to generate, store and sequentially release droplets renders such a device particularly promising for future applications where reactions may not only be monitored on-chip, but droplets can also be retrieved for further analysis, facilitating new exploratory avenues in the fields of analytical chemistry and biology.

Moving forward with isoprostanes, neuroprostanes and phytoprostanes: where are we now?

Polyunsaturated fatty acids (PUFAs) are essential components in eukaryotic cell membrane. They take part in the regulation of cell signalling pathways and act as precursors in inflammatory metabolism. Beside these, PUFAs auto-oxidize through free radical initiated mechanism and release key products that have various physiological functions. These products surfaced in the early nineties and were classified as prostaglandin isomers or isoprostanes, neuroprostanes and phytoprostanes. Although these molecules are considered robust biomarkers of oxidative damage in diseases, they also contain biological activities in humans. Conceptual progress in the last 3 years has added more understanding about the importance of these molecules in different fields. In this chapter, a brief overview of the past 30 years and the recent scope of these molecules, including their biological activities, biosynthetic pathways and analytical approaches are discussed.

Rapid and simple pressure-sensitive adhesive microdevice fabrication for sequence-specific capture and fluorescence detection of sepsis-related bacterial plasmid gene sequences

Microbial resistance to currently available antibiotics poses a great threat in the global fight against infections. An important step in determining bacterial antibiotic resistance can be selective DNA sequence capture and fluorescence labeling. In this paper, we demonstrate the fabrication of simple, robust, inexpensive microfluidic devices for DNA capture and fluorescence detection of a model antibiotic resistance gene sequence. We laser micromachined polymethyl methacrylate microchannels and enclosed them using pressure-sensitive adhesive tapes. We then formed porous polymer monoliths with DNA capture probes in these microchannels and used them for sequence-specific capture, fluorescent labeling, and laser-induced fluorescence detection of picomolar (pM) concentrations of synthetic and plasmid antibiotic resistance gene targets. The relative fluorescence for the elution peaks increased with loaded target DNA concentration. We observed higher fluorescence signal and percent recovery for synthetic target DNA compared to plasmid DNA at the same loaded target concentration. A non-target gene was used for control experiments and produced < 3% capture relative to the same concentration of target. The full analysis process including device fabrication was completed in less than 90 min with a limit of detection of 30 pM. The simplicity of device fabrication and good DNA capture selectivity demonstrated herein have potential for application with processes for bacterial plasmid DNA extraction and single-particle counting to facilitate determination of antibiotic susceptibility. Graphical abstract.

Dielectrophoretic Manipulation of Cancer Cells and Their Electrical Characterization

Electromanipulation and electrical characterization of cancerous cells is becoming a topic of high interest as the results reported to date demonstrate a good differentiation among various types of cells from an electrical viewpoint. Dielectrophoresis and broadband dielectric spectroscopy are complementary tools for sorting, identification, and characterization of malignant cells and were successfully used on both primary tumor cells and culture cells as well. However, the literature is presenting a plethora of studies with respect to electrical evaluation of these type of cells, and this review is reporting a collection of information regarding the functioning principles of different types of dielectrophoresis setups, theory of cancer cell polarization, and electrical investigation (including here the polarization mechanisms). The interpretation of electrical characteristics against frequency is discussed with respect to interfacial/Maxwell-Wagner polarization and the parasitic influence of electrode polarization. Moreover, the electrical equivalent circuits specific to biological cells polarizations are discussed for a good understanding of the cells' morphology influence. The review also focuses on advantages of specific low-conductivity buffers employed currently for improving the efficiency of dielectrophoresis and provides a set of synthesized data from the literature highlighting clear differentiation between the crossover frequencies of different cancerous cells.

Biological applications of microchip electrophoresis with amperometric detection: in vivo monitoring and cell analysis

Microchip electrophoresis with amperometric detection (ME-EC) is a useful tool for the determination of redox active compounds in complex biological samples. In this review, a brief background on the principles of ME-EC is provided, including substrate types, electrode materials, and electrode configurations. Several different detection approaches are described, including dual-channel systems for dual-electrode detection and electrochemistry coupled with fluorescence and chemiluminescence. The application of ME-EC to the determination of catecholamines, adenosine and its metabolites, and reactive nitrogen and oxygen species in microdialysis samples and cell lysates is also detailed. Lastly, approaches for coupling of ME-EC with microdialysis sampling to create separation-based sensors that can be used for near real-time monitoring of drug metabolism and neurotransmitters in freely roaming animals are provided. Graphical abstract.

Protein Discrimination Using a Fluorescence-Based Sensor Array of Thiacarbocyanine-GUMBOS

Sensitive and selective detection of proteins from complex samples has gained substantial interest within the scientific community. Early and precise detection of key proteins plays an important role in potential clinical diagnosis, treatment of different diseases, and proteomic research. In the study reported here, six different compounds belonging to a group of uniform materials based on organic salts (GUMBOS) have been synthesized using three thiacarbocyanine (TC) dyes and employed as fluorescent sensors. Fluorescence properties of micro- and nanoaggregates of these TC-based GUMBOS formed in phosphate buffer solutions are studied in the absence and presence of seven proteins. Fluorescence response patterns of these TC-based GUMBOS were analyzed by linear discriminant analysis (LDA). The constructed LDA model allowed discrimination of these seven proteins at various concentrations with 100% accuracy. The sensing and discrimination abilities of these TC-based GUMBOS were further evaluated in mixtures of two major proteins, i.e., human serum albumin and hemoglobin. Fluorescence response patterns of these mixtures were analyzed by LDA. This model allowed discrimination of various mixtures with 100% accuracy. Moreover, spiked urine samples were prepared and the responses of these sensors were collected and analyzed by LDA. Remarkably, discrimination of these seven proteins was also achieved with 100% accuracy.

A Two-Dimensional Affinity Capture and Separation Mini-Platform for the Isolation, Enrichment, and Quantification of Biomarkers and Its Potential Use for Liquid Biopsy

Biomarker detection for disease diagnosis, prognosis, and therapeutic response is becoming increasingly reliable and accessible. Particularly, the identification of circulating cell-free chemical and biochemical substances, cellular and subcellular entities, and extracellular vesicles has demonstrated promising applications in understanding the physiologic and pathologic conditions of an individual. Traditionally, tissue biopsy has been the gold standard for the diagnosis of many diseases, especially cancer. More recently, liquid biopsy for biomarker detection has emerged as a non-invasive or minimally invasive and less costly method for diagnosis of both cancerous and non-cancerous diseases, while also offering information on the progression or improvement of disease. Unfortunately, the standardization of analytical methods to isolate and quantify circulating cells and extracellular vesicles, as well as their extracted biochemical constituents, is still cumbersome, time-consuming, and expensive. To address these limitations, we have developed a prototype of a portable, miniaturized instrument that uses immunoaffinity capillary electrophoresis (IACE) to isolate, concentrate, and analyze cell-free biomarkers and/or tissue or cell extracts present in biological fluids. Isolation and concentration of analytes is accomplished through binding to one or more biorecognition affinity ligands immobilized to a solid support, while separation and analysis are achieved by high-resolution capillary electrophoresis (CE) coupled to one or more detectors. When compared to other existing methods, the process of this affinity capture, enrichment, release, and separation of one or a panel of biomarkers can be carried out on-line with the advantages of being rapid, automated, and cost-effective. Additionally, it has the potential to demonstrate high analytical sensitivity, specificity, and selectivity. As the potential of liquid biopsy grows, so too does the demand for technical advances. In this review, we therefore discuss applications and limitations of liquid biopsy and hope to introduce the idea that our affinity capture-separation device could be used as a form of point-of-care (POC) diagnostic technology to isolate, concentrate, and analyze circulating cells, extracellular vesicles, and viruses.

A web-based automated machine learning platform to analyze liquid biopsy data

Liquid biopsy (LB) technologies continue to improve in sensitivity, specificity, and multiplexing and can measure an ever growing library of disease biomarkers. However, clinical interpretation of the increasingly large sets of data these technologies generate remains a challenge. Machine learning is a popular approach to discover and detect signatures of disease. However, limited machine learning expertise in the LB field has kept the discipline from fully leveraging these tools and risks improper analyses and irreproducible results. In this paper, we develop a web-based automated machine learning tool tailored specifically for LB, where machine learning models can be built without the user's input. We also incorporate a differential privacy algorithm, designed to limit the effects of overfitting that can arise from users iteratively developing a panel with feedback from our platform. We validate our approach by performing a meta-analysis on 11 published LB datasets, and found that we had similar or better performance compared to those reported in the literature. Moreover, we show that our platform's performance improved when incorporating information from prior LB datasets, suggesting that this approach can continue to improve with increased access to LB data. Finally, we show that by using our platform the results achieved in the literature can be matched using 40% of the number of subjects in the training set, potentially reducing study cost and time. This self-improving and overfitting-resistant automatic machine learning platform provides a new standard that can be used to validate machine learning works in the LB field.

Recent Advances and Applications of Microfluidic Capillary Electrophoresis: A Comprehensive Review (2017-Mid 2019)

Microfluidic capillary electrophoresis (MCE) is the novel technique resulted from the CE mininaturization as planar separation and analysis device. This review presents and discusses various application fields of this advanced technology published in the period 2017 till mid-2019 in eight different sections including clinical, biological, single cell analysis, environmental, pharmaceuticals, food analysis, forensic and ion analysis. The need for miniaturization of CE and the consequence advantages achieved are also discussed including high-throughput, miniaturized detection, effective separation, portability and the need for micro- or even nano-volume of samples. Comprehensive tables for the MCE applications in the different studied fields are provided. Also, figure comparing the number of the published papers applying MCE in the eight discussed fields within the studied period is included. The future investigation should put into consideration the possibility of replacing conventional CE with the MCE after proper validation. Suitable validation parameters with their suitable accepted ranges should be tailored for analysis methods utilizing such unique technique (MCE).

Rapid Ultrasensitive Gel-Free Immunoblotting with Magnetic Labels

Immunoblotting is widely used for the detection of proteins using specific antibodies. We present here a new immunoblotting method, which is characterized by exceptional sensitivity, rapidness, and low consumption of antibodies. A thin conductive layer between touching hydrophilic cellulose membranes instead of polyacrylamide gel is used for the electrophoretic separation of proteins. Contrary to common Western blotting, the separation occurs in nondenaturing conditions. The membrane surface is smoothed by deposition of the cellulose layer and modified with azidophenyl groups, allowing for the photochemical in situ immobilization of proteins, which are carried out after the electrophoresis. Thus, the additional step of transferring the protein from the gel onto the membrane is eliminated. Specific protein bands are then visualized by decoration with magnetic beads. The limit of detection of interleukin IL-1β reaches 0.3 fg or ∼10⁴ molecules, whereas the total blotting time is about 5 min. The application of the technique is demonstrated by the detection of IL-1β, total IgA, and IgA specific to Mycobacterium tuberculosis antigen in the exhaled breath samples, obtained from healthy subjects and tuberculosis patients.

Label-Free Analysis of Protein Aggregation and Phase Behavior

Phase transitions of protein molecules are central to biological function and malfunction. One such transition commonly encountered in nature is the conversion of soluble monomeric states into solid phases, which include crystals and amyloid fibrils, the latter of which are associated with the onset and development of neurodegenerative diseases. Monitoring aggregate formation and protein phase behavior is essential in gaining mechanistic insights into these fundamental processes. Fluorescence techniques have proven invaluable in observing biological molecules; yet, most such approaches rely on the use of an extrinsic fluorophore that binds to the molecule of interest, the installation of which can perturb the molecular systems under study. However, most proteins also possess aromatic amino acids within their peptide sequence and therefore exhibit intrinsic fluorescence. Here, we show that by measuring in space and time tryptophan autofluorescence for three proteins, reconstituted silk fibroin, β-lactoglobulin, and lysozyme, fibrillar self-assembly can be monitored accurately and without the need for extrinsic dyes. When fibrillar protein self-assembly takes place, hydrophobic burial occurs, resulting in the minimization of exposed tryptophan residues to the solvent and consequently leading to an increase in protein autofluorescence. Moreover, by employing a droplet-microfluidic approach to confine protein self-assembly in space, we demonstrate that intrinsic fluorescence can be used to image protein nanofibrils in a label-free manner and that the microstructural analysis obtained from intrinsic fluorescence microscopy correlates well with that from samples treated with extrinsic dyes. Finally, our results show that protein autofluorescence is not limited to the observation of β-sheet-rich structures, but can also be used to distinguish between different types of solid phases including spherulites and crystals, making this approach suitable for overall characterization of protein phase transition phenomena.

An integrated microfluidic device for solid-phase extraction and spectrophotometric detection of opium alkaloids in urine samples

A novel lab-on-chip integrated microfluidic device for solid-phase extraction (SPE) and spectrophotometric detection of morphine (MOR), codeine (COD), and papaverine (PAP) was developed. The extracted analytes were analyzed with a miniature UV-Vis spectrophotometer. The SPE adsorptive phase composed of polyurethane/polyaniline (PU/PANI) nanofibers was fabricated by electrospinning and in situ oxidative polymerization techniques. The sorbent was characterized by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The main factors of extraction such as desorption conditions, pH, salt effect, and extraction time were investigated. The partial least square (PLS) regression was applied to improve the quantification of analytes. The linear dynamic ranges (LDRs) for MOR, COD, and PAP were 4-240, 4-210, and 1-150 ng mL^-1, respectively. Finally, the proposed method was successfully applied for the determination of MOR, COD, and PAP in human urine samples and the extraction recoveries were obtained in the range of 66.7-85.0% with RSDs < 8.3%.

Separation Phenomena in Tailored Micro- and Nanofluidic Environments

Separations of bioanalytes require robust, effective, and selective migration phenomena. However, due to the complexity of biological matrices such as body fluids or tissue, these requirements are difficult to achieve. The separations field is thus constantly evolving to develop suitable methods to separate biomarkers and fractionate biospecimens for further interrogation of biomolecular content. Advances in the field of microfabrication allow the tailored generation of micro- and nanofluidic environments. These can be exploited to induce interactions and dynamics of biological species with the corresponding geometrical features, which in turn can be capitalized for novel separation approaches. This review provides an overview of several unique separation applications demonstrated in recent years in tailored micro- and nanofluidic environments. These include electrokinetic methods such as dielectrophoresis and electrophoresis, but also rather nonintuitive ratchet separation mechanisms, continuous flow separations, and fractionations such as deterministic lateral displacement, as well as methods employing entropic forces for separation.

Capillary electrophoresis of small ions and molecules in less conventional human body fluid samples: A review

In recent years, advances in sensitive analytical techniques have encouraged the analysis of various compounds in biological fluids. While blood serum, blood plasma and urine still remain the golden standards in clinical, toxicological and forensic science, analyses of other body fluids, such as breast milk, exhaled breath condensate, sweat, saliva, amniotic fluid, cerebrospinal fluid, or capillary blood in form of dried blood spots are becoming more popular. This review article focuses on capillary electrophoresis and microchip electrophoresis of small ions and molecules (e.g. inorganic cations/anions, basic/acidic drugs, small acids/bases, amino acids, peptides and other low molecular weight analytes) in various less conventional human body fluids and hopes to stimulate further interest in the field.

Rapid quantification of aloin A and B in aloe plants and aloe-containing beverages, and pharmaceutical preparations by microchip capillary electrophoresis with laser induced fluorescence detection

A microchip capillary electrophoresis coupled with laser induced fluorescence detection method for the fast determination of aloin was developed and comprehensively applied for the quantification of aloin A and B present in seven aloe plant species, 42 aloin-containing crude drugs, ten aloe pharmaceutical preparations, and four aloe gel-containing functional foods. The excitation and emission wavelengths for detection of both aloins were set at 473 and 520 nm, respectively. Sample analysis on a 35 mm length of glass microchip channel was completed within 40 s. An interference study indicated that the other main anthraquinones present in the samples did not interrupt with the target aloins detection, demonstrating the good selectivity of this method. It is demonstrated that this method is fast, facile, and specific for determination of aloin A and B from matrix samples which can be applied to the quality control of a wide varieties of aloe species and aloe-derived products.

Toward miniaturized analysis of chemical identity and purity of radiopharmaceuticals via microchip electrophoresis

Miniaturized synthesis of positron emission tomography (PET) tracers is poised to offer numerous advantages including reduced tracer production costs and increased availability of diverse tracers. While many steps of the tracer production process have been miniaturized, there has been relatively little development of microscale systems for the quality control (QC) testing process that is required by regulatory agencies to ensure purity, identity, and biological safety of the radiotracer before use in human subjects. Every batch must be tested, and in contrast with ordinary pharmaceuticals, the whole set of tests of radiopharmaceuticals must be completed within a short-period of time to minimize losses due to radioactive decay. By replacing conventional techniques with microscale analytical ones, it may be possible to significantly reduce instrument cost, conserve lab space, shorten analysis times, and streamline this aspect of PET tracer production. We focus in this work on miniaturizing the subset of QC tests for chemical identity and purity. These tests generally require high-resolution chromatographic separation prior to detection to enable the approach to be applied to many different tracers (and their impurities), and have not yet, to the best of our knowledge, been tackled in microfluidic systems. Toward this end, we previously explored the feasibility of using the technique of capillary electrophoresis (CE) as a replacement for the "gold standard" approach of using high-performance liquid chromatography (HPLC) since CE offers similar separating power, flexibility, and sensitivity, but can readily be implemented in a microchip format. Using a conventional CE system, we previously demonstrated the successful separation of non-radioactive version of a clinical PET tracer, 3'-deoxy-3'-fluorothymidine (FLT), from its known by-products, and the separation of the PET tracer 1-(2'-deoxy-2'-fluoro-β-D-arabinofuranosyl)-cytosine (D-FAC) from its α-isomer, with sensitivity nearly as good as HPLC. Building on this feasibility study, in this paper, we describe the first effort to miniaturize the chemical identity and purity tests by using microchip electrophoresis (MCE). The fully automated proof-of-concept system comprises a chip for sample injection, a separation capillary, and an optical detection chip. Using the same model compound (FLT and its known by-products), we demonstrate that samples can be injected, separated, and detected, and show the potential to match the performance of HPLC. Addition of a radiation detector in the future would enable analysis of radiochemical identity and purity in the same device. We envision that eventually this MCE method could be combined with other miniaturized QC tests into a compact integrated system for automated routine QC testing of radiopharmaceuticals in the future. Graphical abstract Miniaturized quality control (QC) testing of batches of radiopharmaceuticals via microfluidic analysis. The proof-of-concept hybrid microchip electrophoresis (MCE) device demonstrated the feasibility of achieving comparable performance to conventional analytical instruments (HPLC or CE) for chemical purity testing.

Electrokinetically operated microfluidic devices for integrated immunoaffinity monolith extraction and electrophoretic separation of preterm birth biomarkers

Biomarkers are often present in complex biological fluids like blood, requiring multiple, slow sample preparation steps that pose limitations in simplifying analysis. Here we report integrated immunoaffinity extraction and separation devices for analysis of preterm birth biomarkers in a human blood serum matrix. A reactive polymer monolith was used for immobilization of antibodies for selective extraction of target preterm birth biomarkers. Microfluidic immunoaffinity extraction protocols were optimized and then integrated with microchip electrophoresis for separation. Using these integrated devices, a ∼30 min analysis was carried out on low nanomolar concentrations of two preterm birth biomarkers spiked in a human serum matrix. This work is a promising step towards the development of an automated, integrated platform for determination of preterm birth risk.

Recent trends in capillary electrophoresis for complex samples analysis: A review

CE has been a continuously evolving analytical methodology since its first introduction in the 1980s of the last century. The development of new CE separation procedures, the coupling of these systems to more sensitive and versatile detection systems, and the advances in miniaturization technology have allowed the application of CE to the resolution of new and complex analytical problems, overcoming the traditional disadvantages associated with this method. In the present work, different recent trends in CE and their application to the determination of high complexity samples (as biological fluids, individual cells, etc.) will be reviewed: capillary modification by different types of coatings, microfluidic CE, and online microextraction CE. The main advantages and disadvantages of the different proposed approaches will be discussed with examples of most recent applications.

Recent developments in capillary and microchip electroseparations of peptides (2015-mid 2017)

The review brings a comprehensive overview of recent developments and applications of high performance capillary and microchip electroseparation methods (zone electrophoresis, isotachophoresis, isoelectric focusing, affinity electrophoresis, electrokinetic chromatography, and electrochromatography) to analysis, microscale isolation, purification, and physicochemical and biochemical characterization of peptides in the years 2015, 2016, and ca. up to the middle of 2017. Advances in the investigation of electromigration properties of peptides and in the methodology of their analysis (sample preseparation, preconcentration and derivatization, adsorption suppression and EOF control, and detection) are described. New developments in particular CE and CEC methods are presented and several types of their applications to peptide analysis are reported: qualitative and quantitative analysis, determination in complex (bio)matrices, monitoring of chemical and enzymatical reactions and physical changes, amino acid, sequence and chiral analysis, and peptide mapping of proteins. Some micropreparative peptide separations are shown and capabilities of CE and CEC methods to provide important physicochemical characteristics of peptides are demonstrated.

Recent advances in CE and microchip-CE in clinical applications: 2014 to mid-2017

CE and microchip CE (ME) are powerful tools for the analysis of a number of different analytes and have been applied to a variety of clinical fields and human samples. This review will present an overview of the most recent applications of these techniques to different areas of clinical medicine during the period of 2014 to mid-2017. CE and ME have been applied to clinical chemistry, drug detection and monitoring, hematology, infectious diseases, oncology, endocrinology, neonatology, nephrology, and genetic screening. Samples examined range from serum, plasma, and urine to lest utilized materials such as tears, cerebral spinal fluid, sweat, saliva, condensed breath, single cells, and biopsy tissue. Examples of clinical applications will be given along with the various detection systems employed.

Alternate injections coupled with flow-gated capillary electrophoresis for rapid and accurate quantitative analysis of urine samples

Capillary electrophoresis (CE) is a powerful separation technique with advantages over HPLC in terms of separation efficiency, speed, and cost. However, CE suffers in poor reproducibility in quantitative chemical analysis, which is one of major drawbacks preventing its widespread use in routine analytical laboratories. Here we report a novel strategy to enhance the quantitative capability of flow-gated CE. The platform integrated dual flow branches to respectively supply a sample and its standard additions that were then alternately injected into a single capillary for rapid separations (typically 20-90 s). A micro-fabricated switch was used to enable the alternate injections. It was assumed that the analytical system maintained constant conditions during neighboring injections that served as external self-standards for quantitation. This strategy was expected to reduce uncertainties caused by the fluctuation in capillary conditions and the drift of detection systems. Experimental results demonstrated that the dual-branch flow-gated CE coupled with alternate injections significantly improved the reproducibility with respect to peak height ratios under deliberate variations in injection volumes, separation voltages, optical focusing, and laser power; and thus the interday precision was ensured. To demonstrate its applicability, cyanide and amino acids in human urine were quantified rapidly with the one-point standard addition method after fluorogenic derivatization with naphthalene-2,3-dicarboxaldehyde (NDA), and the measurement accuracy was validated by determining the recovery of standard cyanide added to a urinary matrix. This strategy would be valuable to enable the quantitative capability of flow-gated CE in the measurements of a broad range of analytes, especially those lacking suited internal standards.

Recent advances in microfluidic sample preparation and separation techniques for molecular biomarker analysis: A critical review

Microfluidics is a vibrant and expanding field that has the potential for solving many analytical challenges. Microfluidics show promise to provide rapid, inexpensive, efficient, and portable diagnostic solutions that can be used in resource-limited settings. Researchers have recently reported various microfluidic platforms for biomarker analysis applications. Sample preparation processes like purification, preconcentration and labeling have been characterized on-chip. Additionally, improvements in microfluidic separation techniques have been reported for molecular biomarkers. This review critically evaluates microfluidic sample preparation platforms and separation methods for biomarker analysis reported in the last two years. Key advances in device operation and ability to process different sample matrices in a variety of device materials are highlighted. Finally, current needs and potential future directions for microfluidic device development to realize its full diagnostic potential are discussed.

Integrated electrokinetically driven microfluidic devices with pH-mediated solid-phase extraction coupled to microchip electrophoresis for preterm birth biomarkers

Integration in microfluidics is important for achieving automation. Sample preconcentration integrated with separation in a microfluidic setup can have a substantial impact on rapid analysis of low-abundance disease biomarkers. Here, we have developed a microfluidic device that uses pH-mediated solid-phase extraction (SPE) for the enrichment and elution of preterm birth (PTB) biomarkers. Furthermore, this SPE module was integrated with microchip electrophoresis for combined enrichment and separation of multiple analytes, including a PTB peptide biomarker (P1). A reversed-phase octyl methacrylate monolith was polymerized as the SPE medium in polyethylene glycol diacrylate modified cyclic olefin copolymer microfluidic channels. Eluent for pH-mediated SPE of PTB biomarkers on the monolith was optimized using different pH values and ionic concentrations. Nearly 50-fold enrichment was observed in single channel SPE devices for a low nanomolar solution of P1, with great elution time reproducibility (<7% RSD). The monolith binding capacity was determined to be 400 pg (0.2 pmol). A mixture of a model peptide (FA) and a PTB biomarker (P1) was extracted, eluted, injected, and then separated by microchip electrophoresis in our integrated device with ∼15-fold enrichment. This device shows important progress towards an integrated electrokinetically operated platform for preconcentration and separation of biomarkers.

Recent Progress in Nanomaterial-Based Electrochemical Biosensors for Cancer Biomarkers: A Review

This article reviews recent progress in the development of nanomaterial-based electrochemical biosensors for cancer biomarkers. Because of their high electrical conductivity, high affinity to biomolecules, and high surface area-to-weight ratios, nanomaterials, including metal nanoparticles, carbon nanotubes, and graphene, have been used for fabricating electrochemical biosensors. Electrodes are often coated with nanomaterials to increase the effective surface area of the electrodes and immobilize a large number of biomolecules such as enzymes and antibodies. Alternatively, nanomaterials are used as signaling labels for increasing the output signals of cancer biomarker sensors, in which nanomaterials are conjugated with secondary antibodies and redox compounds. According to this strategy, a variety of biosensors have been developed for detecting cancer biomarkers. Recent studies show that using nanomaterials is highly advantageous in preparing high-performance biosensors for detecting lower levels of cancer biomarkers. This review focuses mainly on the protocols for using nanomaterials to construct cancer biomarker sensors and the performance characteristics of the sensors. Recent trends in the development of cancer biomarker sensors are discussed according to the nanomaterials used.

Novel volumetric method for highly repeatable injection in microchip electrophoresis

A novel injector for microchip electrophoresis (MCE) has been designed and evaluated that achieves very high repeatability of injection volume suitable for quantitative analysis. It eliminates the injection biases in electrokinetic injection and the dependence on pressure and sample properties in hydrodynamic injection. The microfluidic injector, made of poly(dimethylsiloxane) (PDMS), operates similarly to an HPLC injection valve. It contains a channel segment (chamber) with a well-defined volume that serves as an "injection loop". Using on-chip microvalves, the chamber can be connected to the sample source during the "loading" step, and to the CE separation channel during the "injection" step. Once the valves are opened in the second state, electrophoretic potential is applied to separate the sample. For evaluation and demonstration purposes, the microinjector was connected to a 75 μm ID capillary and UV absorbance detector. For single compounds, a relative standard deviation (RSD) of peak area as low as 1.04% (n = 11) was obtained, and for compound mixtures, RSD as low as 0.40% (n = 4) was observed. Using the same microchip, the performance of this new injection technique was compared to hydrodynamic injection and found to have improved repeatability and less dependence on sample viscosity. Furthermore, a non-radioactive version of the positron-emission tomography (PET) imaging probe, FLT, was successfully separated from its known 3 structurally-similar byproducts with baseline resolution, demonstrating the potential for rapid, quantitative analysis of impurities to ensure the safety of batches of short-lived radiotracers. Both the separation efficiency and injection repeatability were found to be substantially higher when using the novel volumetric injection approach compared to electrokinetic injection (performed in the same chip). This novel microinjector provides a straightforward way to improve the performance of hydrodynamic injection and enables extremely repeatable sample volume injection in MCE. It could be used in any MCE application where volume repeatability is needed, including the quantitation of impurities in pharmaceutical or radiopharmaceutical samples.

Rapid antibiotic sensitivity testing in microwell arrays

The widespread bacterial resistance to a broad range of antibiotics necessitates rapid antibiotic susceptibility testing before effective treatment could start in the clinic. Among resistant bacteria, Staphylococcus aureus is one of the most important, and Methicillin-resistant (MRSA) strains are a common cause of life threatening infections. However, standard susceptibility testing for S. aureus is time consuming and thus the start of effective antibiotic treatment is often delayed. To circumvent the limitations of current susceptibility testing systems, we designed an assay that enables measurements of bacterial growth with higher spatial and temporal resolution than standard techniques. The assay consists of arrays of microwells that confine small number of bacteria in small spaces, where their growth is monitored with high precision. These devices enabled us to investigate the effect of different antibiotics on S. aureus growth. We measured the Minimal Inhibitory Concentration (MIC) in less than 3 hours. In addition to being significantly faster than the 48 hours needed for traditional microbiological methods, the assay is also capable of differentiating the specific effects of different antibiotic classes on S. aureus growth. Overall, this assay has the potential to become a rapid, sensitive, and robust tool for use in hospitals and laboratories to assess antibiotic sensitivity.

On-Chip Fluorescent Labeling using Reversed-phase Monoliths and Microchip Electrophoretic Separations of Selected Preterm Birth Biomarkers

On-chip preconcentration, purification, and fluorescent labeling are desirable sample preparation steps to achieve complete automation in integrated microfluidic systems. In this work, we developed electrokinetically operated microfluidic devices for solid-phase extraction and fluorescent labeling of preterm birth (PTB) biomarkers. Reversed-phase monoliths based on different acrylate monomers were photopolymerized in cyclic olefin copolymer microdevices and studied for the selective retention and elution of a fluorescent dye and PTB biomarkers. Octyl methacrylate-based monoliths with desirable retention and elution characteristics were chosen and used for on-chip fluorescent labeling of three PTB biomarkers. Purification of on-chip labeled samples was done by selective elution of unreacted dye prior to sample. Automated and rapid on-chip fluorescent labeling was achieved with similar efficiency to that obtained for samples labeled off chip. Additionally, protocols for microchip electrophoresis of several off-chip-labeled PTB biomarkers were demonstrated in poly(methyl methacrylate) microfluidic devices. This study is an important step toward the development of integrated on-chip labeling and separation microfluidic devices for PTB biomarkers.

Analysis of proteins and peptides by electromigration methods in microchips

This review presents the developments and applications of microchip electromigration methods in the separation and analysis of peptides and proteins in the period 2011-mid-2016. The developments in sample preparation and preconcentration, microchannel material, and surface treatment are described. Separations by various microchip electromigration methods (zone electrophoresis in free and sieving media, affinity electrophoresis, isotachophoresis, isoelectric focusing, electrokinetic chromatography, and electrochromatography) are demonstrated. Advances in detection methods are reported and novel applications in the areas of proteomics and peptidomics, quality control of peptide and protein pharmaceuticals, analysis of proteins and peptides in biomatrices, and determination of physicochemical parameters are shown.

Deformability-Based Electrokinetic Particle Separation

Deformability is an effective property that can be used in the separation of colloidal particles and cells. In this study, a microfluidic device is proposed and tested numerically for the sorting of deformable particles of various degrees. The separation process is numerically investigated by a direct numerical simulation of the fluid–particle–electric field interactions with an arbitrary Lagrangian–Eulerian finite-element method. The separation performance is investigated with the shear modulus of particles, the strength of the applied electric field, and the design of the contracted microfluidic devices as the main parameters. The results show that the particles with different shear moduli take different shapes and trajectories when passing through a microchannel contraction, enabling the separation of particles based on their difference in deformability.