Microchip Electrophoresis Profiling of Aβ Peptides in the Cerebrospinal Fluid of Patients with Alzheimer’s Disease

Modular microfluidic system for on-chip extraction, preconcentration and detection of the cytokine biomarker IL-6 in biofluid

The cytokine interleukin 6 (IL-6) is involved in the pathogenesis of different inflammatory diseases, including cancer, and its monitoring could help diagnosis, prognosis of relapse-free survival and recurrence. Here, we report an innovative microfluidic approach that uses the fluidization of magnetic beads to specifically extract, preconcentrate and fluorescently detect IL-6 directly on-chip. We assess how the physical properties of the beads can be tuned to improve assay performance by enhancing mass transport, reduce non-specific binding and multiply the detection signal threefold by transitioning between packed and fluidization states. With the integration of a full ELISA protocol in a single microfluidic chamber, we show a twofold reduction in LOD compared to conventional methods along with a large dynamic range (10 pg/mL to 2 ng/mL). We additionally demonstrate its application to IL-6 detection in undiluted serum samples.

Advanced Human BBB-on-a-Chip: A New Platform for Alzheimer's Disease Studies

The blood-brain barrier (BBB) is a unique vascular structure that serves as a molecular transport gateway for the maintenance of brain homeostasis. Chronic disruption or breakdown of the BBB reportedly leads to neurodegenerative diseases. Nonetheless, research on human BBB pathophysiology and drug development remains highly dependent on studies using inherently different animals. Moreover, more studies have shown that animal models are not appropriate in modeling Alzheimer's disease (AD), underlining the importance of in vitro models of the human BBB with physiological relevance. In this review, recent advances in human BBB-on-a-chip technologies are highlighted and their potential for pathogenesis studies and drug prescreening for AD treatment are discussed.

Recent Electrokinetic and Microfluidic Strategies for Detection of Amyloid Beta Peptide Biomarkers: Towards Molecular Diagnosis of Alzheimer's Disease

Among all neurodegenerative diseases, Alzheimer's Disease (AD) is the most prevalent worldwide, with a huge burden to the society and no efficient AD treatment so far. Continued efforts have been being made towards early and powerful diagnosis of AD, in the hope for a successful set of clinical trials and subsequently AD curative treatment. Towards this aim, detection and quantification of amyloid beta (Aβ) peptides in cerebrospinal fluid (CSF) and other biofluids, which are established and validated biomarkers for AD, have drawn attention of the scientific community and industry over almost two decades. In this work, an overview on our major contributions over 15 years to develop different electrokinetic and microfluidic strategies for Aβ peptides detection and quantification is reported. Accordingly, discussions and viewpoints on instrumental and methodological developments for microscale electrophoresis, microfluidic designs and immuno-enrichment / assays on magnetic beads in microchannels for tracing Aβ peptides in CSF are given in this review.

Microfluidics-Based Systems in Diagnosis of Alzheimer's Disease and Biomimetic Modeling

Early detection and accurate diagnosis of Alzheimer’s disease (AD) is essential for patient care and disease treatment. Microfluidic technology is emerging as an economical and versatile platform in disease detection and diagnosis. It can be conveniently integrated with nanotechnology and/or biological models for biomedical functional and pre-clinical treatment study. These strengths make it advantageous in disease biomarker detection and functional analysis against a wide range of biological backgrounds. This review highlights the recent developments and trends of microfluidic applications in AD research. The first part looks at the principles and methods for AD diagnostic biomarker detection and profiling. The second part discusses how microfluidic chips, especially organ-on-a-chip platforms, could be used as an independent approach and/or integrated with other technologies in AD biomimetic functional analysis.

Microfluidics as a Novel Tool for Biological and Toxicological Assays in Drug Discovery Processes: Focus on Microchip Electrophoresis

The last decades of biological, toxicological, and pharmacological research have deeply changed the way researchers select the most appropriate 'pre-clinical model'. The absence of relevant animal models for many human diseases, as well as the inaccurate prognosis coming from 'conventional' pre-clinical models, are among the major reasons of the failures observed in clinical trials. This evidence has pushed several research groups to move more often from a classic cellular or animal modeling approach to an alternative and broader vision that includes the involvement of microfluidic-based technologies. The use of microfluidic devices offers several benefits including fast analysis times, high sensitivity and reproducibility, the ability to quantitate multiple chemical species, and the simulation of cellular response mimicking the closest human in vivo milieu. Therefore, they represent a useful way to study drug-organ interactions and related safety and toxicity, and to model organ development and various pathologies 'in a dish'. The present review will address the applicability of microfluidic-based technologies in different systems (2D and 3D). We will focus our attention on applications of microchip electrophoresis (ME) to biological and toxicological studies as well as in drug discovery and development processes. These include high-throughput single-cell gene expression profiling, simultaneous determination of antioxidants and reactive oxygen and nitrogen species, DNA analysis, and sensitive determination of neurotransmitters in biological fluids. We will discuss new data obtained by ME coupled to laser-induced fluorescence (ME-LIF) and electrochemical detection (ME-EC) regarding the production and degradation of nitric oxide, a fundamental signaling molecule regulating virtually every critical cellular function. Finally, the integration of microfluidics with recent innovative technologies-such as organoids, organ-on-chip, and 3D printing-for the design of new in vitro experimental devices will be presented with a specific attention to drug development applications. This 'composite' review highlights the potential impact of 2D and 3D microfluidic systems as a fast, inexpensive, and highly sensitive tool for high-throughput drug screening and preclinical toxicological studies.

An ultrasensitive microchip electrophoresis chemiluminescence assay platform for detection of trace biomolecules

An ultrasensitive microchip electrophoresis chemiluminescence (MCE-CL) assay platform based on separation assisted cascade signal amplification was developed for detection of trace biomolecules. In this work, the aptamer was used as a target probe to bind target molecule and triggering cascade signal amplification reaction. The horseradish peroxide labeled DNA (HRP-DNA) was used as signal probe, utilizing nucleic acid hybridization and exonuclease cutting technology realized ultrasensitive detection of biomolecules on the MCE-CL assay platform. Taking gamma interferon (IFN-γ) as a model analyte, the linear range for IFN-γ detection is 8.0 × 10^-15-1.0 × 10^-8 M, the detection limit is 1.6 fM, which is six orders magnitude lower than that of without signal amplification. The proposed method was successfully applied for the quantification of IFN-γ in human plasma samples. It was demonstrated that the MCE-CL assay platform was quick, sensitive, and highly selective. It may serve as a tool for clinical analysis of IFN-γ to assist in the diagnosis of disease.

Array of multifunctional polymers for localized immobilization of biomolecules on microarray substrates

The performance of microarray assays results from the optimization of several parameters: in particular, the physical-chemical properties of the surface play a pivotal role in determining the robustness of the technology. Usually, microarray substrates are entirely modified with coatings able to bind, covalently or not, bioprobes. Here we present a new, fully automated approach for the immobilization of biomolecules, based on the deposition of pL amounts of water solutions of DMA based copolymers on an uncoated surface, followed by the deposition, on the same spot, of the probe. Starting from a common precursor, polymers with different characteristics and functionalities are obtained by post-polymerization modification and by combining different monomers during the synthesis. This strategy, allows to functionalize and tailor the surface properties of discrete areas of the same array with different chemistries, that coexist on a single substrate. As a consequence, probes with different functionalities are bound simultaneously to neutral, positively, negatively charged, hydrophobic, hydrophilic polymers, in micrometer-sized spots. The proposed polymer array, applicable to both DNA or protein, offers advantages in terms of time and costs reduction, since pretreatment and coating steps are totally avoided, and the requested polymer amount is extremely low. Moreover, it provides a strategy perfectly suitable for miniaturization applicable to integrated biosensors or Lab-on-a-chip devices.

"Microchip Electrophoresis," with Respect to "Profiling of Aβ Peptides in the Cerebrospinal Fluid of Patients with Alzheimer's Disease"

Aggregation of beta-amyloid peptides especially Aβ1-42 in amyloid plaques is one of the major neuropathological events in Alzheimer's disease. This event is normally accompanied by a relative reduction of the concentration of Aβ1-42 in the cerebrospinal fluid (CSF) of patient developing the signs of Alzheimer's disease. Here, we describe methods for isolation and for microchip gel electrophoresis of Aβ peptides in polydimethylsiloxane (PDMS) microfluidic chip. The method was applied to compare the relative concentration of Aβ1-42 with other Aβ peptides, for example, Aβ 1-40 in CSF. In order to increase the sensitivity of detection, Aβ peptides in the CSF samples were first captured and concentrated using magnetic beads coated with specific anti-Aβ antibodies.

Recent advances in protein analysis by capillary and microchip electrophoresis

This review article describes the significant recent advances in the analysis of proteins by capillary and microchip electrophoresis during the period from mid-2014 to early 2017. This review highlights the progressions, new methodologies, innovative instrumental modifications, and challenges for efficient protein analysis in human specimens, animal tissues, and plant samples. The protein analysis fields covered in this review include analysis of native, reduced, and denatured proteins in addition to Western blotting, protein therapeutics and proteomics.

The severe impact of in vivo-like microfluidic flow and the influence of gemini surfactants on amyloid aggregation of hen egg white lysozyme

The formation of amyloid plaques is being intensively studied, as this process underlies severe human diseases, including Alzheimer's disease, and the exact mechanism of this specific aggregation has not been resolved yet.

Solid supports for extraction and preconcentration of proteins and peptides in microfluidic devices: A review

Determination of proteins and peptides is among the main challenges of today's bioanalytical chemistry. The application of microchip technology in this field is an exhaustively developed concept that aims to create integrated and fully automated analytical devices able to quantify or detect one or several proteins from a complex matrix. Selective extraction and preconcentration of targeted proteins and peptides especially from biological fluids is of the highest importance for a successful realization of these microsystems. Incorporation of solid structures or supports is a convenient solution employed to face these demands. This review presents a critical view on the latest achievements in sample processing techniques for protein determination using solid supports in microfluidics. The study covers the period from 2006 to 2015 and focuses mainly on the strategies based on microbeads, monolithic materials and membranes. Less common approaches are also briefly discussed. The reviewed literature suggests future trends which are discussed in the concluding remarks.

Field amplified sample stacking of amyloid beta (1-42) oligomers using capillary electrophoresis

Oligomeric forms of the amyloid beta (Aβ) protein have been indicated to be an important factor in the development of Alzheimer's disease (AD). Since the oligomeric forms of Aβ can vary in size and conformation, it is vital to understand the early stages of Aβ aggregation in order to improve the care and treatment of patients with AD. This is the first study to determine the effect of field amplified sample stacking (FASS) on the separation of oligomeric forms of Aβ1-42 using capillary electrophoresis (CE) with ultraviolet (UV) detection. UV-CE was able to separate two different species of Aβ1-42 oligomers (<7 mers and 7-22 mers). Although FASS required the use of a higher ionic strength buffer, Aβ1-42 oligomers had the same aggregation behavior as under the non-FASS conditions with only small changes in the amounts of oligomers observed. In general, FASS provided smaller peak widths (>75% average reduction) and increased peak heights (>60% average increase) when compared to non-FASS conditions. UV-CE with FASS also provided higher resolution between the Aβ1-42 oligomers for all aggregation time points studied. In addition, Congo red and Orange G inhibition studies were used to help evaluate the conformation of the observed species. This work demonstrates the ability of UV-CE employing FASS to provide higher resolution between oligomeric forms of Aβ1-42 without significantly altering their aggregation.

Magnetic Particle Plug-Based Assays for Biomarker Analysis

Conventional immunoassays offer selective and quantitative detection of a number of biomarkers, but are laborious and time-consuming. Magnetic particle-based assays allow easy and rapid selection of analytes, but still suffer from the requirement of tedious multiple reaction and washing steps. Here, we demonstrate the trapping of functionalised magnetic particles within a microchannel for performing rapid immunoassays by flushing consecutive reagent and washing solutions over the trapped particle plug. Three main studies were performed to investigate the potential of the platform for quantitative analysis of biomarkers: (i) a streptavidin-biotin binding assay; (ii) a sandwich assay of the inflammation biomarker, C-reactive protein (CRP); and (iii) detection of the steroid hormone, progesterone (P4), towards a competitive assay. Quantitative analysis with low limits of detection was demonstrated with streptavidin-biotin, while the CRP and P4 assays exhibited the ability to detect clinically relevant analytes, and all assays were completed in only 15 min. These preliminary results show the great potential of the platform for performing rapid, low volume magnetic particle plug-based assays of a range of clinical biomarkers via an exceedingly simple technique.

An integrated microfluidic chip for immunocapture, preconcentration and separation of β-amyloid peptides

We present an integrated microfluidic chip for detection of β-amyloid (Aβ) peptides. Aβ peptides are major biomarkers for the diagnosis of Alzheimer's disease (AD) in its early stages. This microfluidic device consists of three main parts: (1) An immunocapture microcolumn based on self-assembled magnetic beads coated with antibodies specific to Aβ peptides, (2) a nano-porous membrane made of photopolymerized hydrogel for preconcentration, and (3) a microchip electrophoresis (MCE) channel with fluorescent detection. Sub-milliliter sample volume is either mixed off-chip with antibody coated magnetic beads and injected into the device or is injected into an already self-assembled column of magnetic beads in the microchannel. The captured peptides on the beads are then electrokinetically eluted and re-concentrated onto the nano-membrane in a few nano-liters. By integrating the nano-membrane, total assay time was reduced and also off-chip re-concentration or buffer exchange steps were not needed. Finally, the concentrated peptides in the chip are separated by electrophoresis in a polymer-based matrix. The device was applied to the capture and MCE analysis of differently truncated peptides Aβ (1-37, 1-39, 1-40, and 1-42) and was able to detect as low as 25 ng of synthetic Aβ peptides spiked in undiluted cerebrospinal fluid (CSF). The device was also tested with CSF samples from healthy donors. CSF samples were fluorescently labelled and pre-mixed with the magnetic beads and injected into the device. The results indicated that Aβ1-40, an important biomarker for distinguishing patients with frontotemporal lobe dementia from controls and AD patients, was detectable. Although the sensitivity of this device is not yet enough to detect all Aβ subtypes in CSF, this is the first report on an integrated or semi-integrated device for capturing and analyzing of differently truncated Aβ peptides. The method is less demanding and faster than the conventional Western blotting method currently used for research.

Neutral polymers as coatings for high resolution electrophoretic separation of Aβ peptides on glass microchips

This study reports a comparison of the performances of two neutral polymers, poly ethylene-oxide (PEO) and poly(dimethylacrylamide-co-allyl glycidyl ether) (EpDMA), in glass microchips to achieve zone electrophoresis separation of several truncated forms of beta amyloid (Aβ) peptides, sharing very similar structures. The peptides were derivatized by FluoProbes 488 NHS to allow their fluorescence detection. Two protocols based either on PEO or EpDMA led to good pH stabilities in addition to a significant reduction of the electroosmotic flow. These two polymer coatings allowed repeatable analyses and high resolution for the simultaneous analysis of three Aβ peptides, Aβ 1-38, Aβ 1-40 and Aβ 1-42, considered as potential biomarkers of Alzheimer's disease. A recovery study showed that EpDMA was superior in reducing the adsorption of the Aβ peptides on the coated inner wall. Finally, the separation method relying on the EpDMA coated microchips was validated as linear using a calibration curve and the LOD was estimated to be close to 200 nM. Despite very short migration distances, different N-terminal or C-terminal truncated Aβ peptides, corresponding to promising biomarker combinations for the future diagnostic, were fully resolved. The method was successfully applied to detect these peptides in spiked cerebrospinal fluid and has provided a first achievement towards the development of a microsystem that would integrate preconcentration and separation steps.

Applications of microfluidics and microchip electrophoresis for potential clinical biomarker analysis

This article reviews advances over the last five years in microfluidics and microchip-electrophoresis techniques for detection of clinical biomarkers. The variety of advantages of miniaturization compared with conventional benchtop methods for detecting biomarkers has resulted in increased interest in developing cheap, fast, and sensitive techniques. We discuss the development of applications of microfluidics and microchip electrophoresis for analysis of different clinical samples for pathogen identification, personalized medicine, and biomarker detection. We emphasize the advantages of microfluidic techniques over conventional methods, which make them attractive future diagnostic tools. We also discuss the versatility and adaptability of this technology for analysis of a variety of biomarkers, including lipids, small molecules, carbohydrates, nucleic acids, proteins, and cells. Finally, we conclude with a discussion of aspects that need to be improved to move this technology towards routine clinical and point-of-care applications.

Magneto-immunocapture with on-bead fluorescent labeling of amyloid-β peptides: towards a microfluidized-bed-based operation

Novel combination of Magneto-immunocapture and on-beads fluorescent labeling of Aβ peptides for their sensitive determination in cerebro spinal fluid samples.

Monodisperse carboxyl-functionalized poly(ethylene glycol)-coated magnetic poly(glycidyl methacrylate) microspheres: application to the immunocapture of β-amyloid peptides

Identification and evaluation of small changes in β-amyloid peptide (Aβ) levels in cerebrospinal fluid is of crucial importance for early detection of Alzheimer's disease. Microfluidic detection methods enable effective preconcentration of Aβ using magnetic microparticles coated with Aβ antibodies. Poly(glycidyl methacrylate) microspheres are coated with α-amino-ω-methoxy-PEG5000 /α-amino-ω-Boc-NH-PEG5000 Boc groups deprotected and NH2 succinylated to introduce carboxyl groups. Capillary electrophoresis with laser-induced fluorescence detection confirms the efficient capture of Aβ 1-40 peptides on the microspheres with immobilized monoclonal anti-Aβ 6E10. The capture specificity is confirmed by comparing Aβ 1-40 levels on the anti-IgG-immobilized particles used as a control.

Detection and quantification of plasma amyloid-β by selected reaction monitoring mass spectrometry

Amyloid-β (Aβ) in human plasma was detected and quantified by an antibody-free method, selected reaction monitoring mass spectrometry (SRM-MS) in the current study. Due to its low abundance, SRM-based quantification in 10 μL plasma was a challenge. Prior to SRM analysis, human plasma proteins as a whole were digested by trypsin and high pH reversed-phase liquid chromatography (RPLC) was used to fractionate the tryptic digests and to collect peptides, Aβ(1-5), Aβ(6-16), Aβ(17-28) and Aβ(29-40(42)) of either Aβ(1-40) or Aβ(1-42). Among those peptides, Aβ(17-28) was selected as a surrogate to measure the total Aβ level. Human plasma samples obtained from triplicate sample preparations were analyzed, obtaining 4.20 ng mL(-1) with a CV of 25.3%. Triplicate measurements for each sample preparation showed CV of <5%. Limit of quantification was obtained as 132 pM, which corresponded to 570 pg mL(-1) of Aβ(1-40). Until now, most quantitative measurements of Aβ in plasma or cerebrospinal fluid have required antibody-based immunoassays. Since quantification of Aβ by immunoassays is highly dependent on the extent of epitope exposure due to aggregation or plasma protein binding, it is difficult to accurately measure the actual concentration of Aβ in plasma. Our diagnostic method based on SRM using a surrogate peptide of Aβ is promising in that actual amounts of total Aβ can be measured regardless of the conformational status of the biomarker.

New non-covalent strategies for stable surface treatment of thermoplastic chips

In order to be more extensively used outside of research laboratories, lab-on-chip technologies must be mass-produced using low-cost materials such as thermoplastics. Thermoplastics, however, are generally hydrophobic in their native state, which makes them unsuitable for direct use with biological samples in aqueous solution, and thus require surface coating. This coating should be robust, inexpensive and simple to implement, in order not to hinder the industrial advantage of thermoplastic chips. Cyclic Olefin Copolymer (COC) is a particularly appealing polymer, but it is also difficult to functionalize due to its chemical inertness. Here we introduce and compare the performance of two new approaches for COC coating. One relies on the use of a commercial triblock copolymer, Pluronic® F127. The second approach uses new copolymers synthesized by radical polymerization, and consisting of a dimethylacrylamide (DMA) backbone carrying aliphatic side chains (C22). Two DMA-C22 copolymers were synthesized with various C22/DMA ratios: DMA-S at 0.175% and DMA-M at 0.35%. Different physicochemical properties of the polymers such as critical micellar concentration (CMC), water contact angle, electroosmosis were investigated. Coated COC chips were then tested for their ability to reduce the adsorption of proteins, microparticles, and for protein electrophoresis. For each application we found an optimal treatment protocol to considerably improve the performance of the thermoplastic chip. These treatments use physisorption in situ which requires no photografting or chemical reaction and can be performed by a simple incubation either after chip production, or just prior to use.

Real-time clinical monitoring of biomolecules

Continuous monitoring of clinical biomarkers offers the exciting possibility of new therapies that use biomarker levels to guide treatment in real time. This review explores recent progress toward this goal. We initially consider measurements in body fluids by a range of analytical methods. We then discuss direct tissue measurements performed by implanted sensors; sampling techniques, including microdialysis and ultrafiltration; and noninvasive methods. A future directions section considers analytical methods at the cusp of clinical use.

Development of a magnetic immunosorbent for on-chip preconcentration of amyloid β isoforms: Representatives of Alzheimer's disease biomarkers

Determination of amyloid β (Aβ) isoforms and in particular the proportion of the Aβ 1-42 isoform in cerebrospinal fluid (CSF) of patients suspected of Alzheimer's disease might help in early diagnosis and treatment of that illness. Due to the low concentration of Aβ peptides in biological fluids, a preconcentration step prior to the detection step is often necessary. This study utilized on-chip immunoprecipitation, known as micro-immunoprecipitation (μIP). The technique uses an immunosorbent (IS) consisting of magnetic beads coated with specific anti-Aβ antibodies organized into an affinity microcolumn by a magnetic field. Our goal was to thoroughly describe the critical steps in developing the IS, such as selecting the proper beads and anti-Aβ antibodies, as well as optimizing the immobilization technique and μIP protocol. The latter includes selecting optimal elution conditions. Furthermore, we demonstrate the efficiency of anti-Aβ IS for μIP and specific capture of 5 Aβ peptides under optimized conditions using various subsequent analytical methods, including matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), capillary electrophoresis, microchip electrophoresis, and immunoblotting. Synthetic Aβ peptides samples prepared in buffer and spiked in human CSF were analyzed. Finally, on-chip immunoprecipitation of Aβ peptides in human CSF sample was performed.

Unraveling the early events of amyloid-β protein (Aβ) aggregation: techniques for the determination of Aβ aggregate size

The aggregation of proteins into insoluble amyloid fibrils coincides with the onset of numerous diseases. An array of techniques is available to study the different stages of the amyloid aggregation process. Recently, emphasis has been placed upon the analysis of oligomeric amyloid species, which have been hypothesized to play a key role in disease progression. This paper reviews techniques utilized to study aggregation of the amyloid-β protein (Aβ) associated with Alzheimer's disease. In particular, the review focuses on techniques that provide information about the size or quantity of oligomeric Aβ species formed during the early stages of aggregation, including native-PAGE, SDS-PAGE, Western blotting, capillary electrophoresis, mass spectrometry, fluorescence correlation spectroscopy, light scattering, size exclusion chromatography, centrifugation, enzyme-linked immunosorbent assay, and dot blotting.

Microchip electrophoresis, with respect to "profiling of Aβ peptides in the cerebrospinal fluid of patients with Alzheimer's disease"

Aggregation of beta amyloid peptides especially Aβ1-42 in amyloid plaques is one of the major -neuropathological events in Alzheimer's disease. This event is normally accompanied by a relative reduction of the concentration of Aβ1-42 in the cerebrospinal fluid (CSF) of patients developing the signs of Alzheimer's disease. Here, we describe a microchip gel electrophoresis method in a polydimethylsiloxane (PDMS) chip that enables rapid profiling of major Aβ peptides. The method was applied to compare the relative concentration of Aβ1-42 with other Aβ peptides, for example, Aβ 1-40 in CSF. In order to increase the sensitivity of detection, Aβ peptides in the CSF samples were first captured and concentrated using magnetic beads coated with specific anti-Aβ antibodies.