Dielectrophoretic isolation of DNA and nanoparticles from blood

Dielectrophoretic trapping of nanosized biomolecules on plasmonic nanohole arrays for biosensor applications: simple fabrication and visible-region detection

Surface plasmon resonance is an optical phenomenon that can be applied for label-free, real-time sensing to directly measure biomolecular interactions and detect biomarkers in solutions. Previous studies using plasmonic nanohole arrays have monitored and detected various biomolecules owing to the propagating surface plasmon polaritons (SPPs). Extraordinary optical transmission (EOT) that occurs in the near-infrared (NIR) and infrared (IR) regions is usually used for detection. Although these plasmonic nanohole arrays improve the sensitivity and throughput for biomolecular detection, these arrays have the following disadvantages: (1) molecular diffusion in the solution (making the detection of biomolecules difficult), (2) the device fabrication's complexities, and (3) expensive equipments for detection in the NIR or IR regions. Therefore, there is a need to fabricate plasmonic nanohole arrays as biomolecular detection platforms using a simple and highly reproducible procedure based on other SPP modes in the visible region instead of the EOT in the NIR or IR regions while suppressing molecular diffusion in the solution. In this paper, we propose the combination of a polymer-based gold nanohole array (Au NHA) obtained through an easy process as a simple platform and dielectrophoresis (DEP) as a biomolecule manipulation method. This approach was experimentally demonstrated using SPP and LSPR modes (not EOT) in the visible region and simple, label-free, rapid, cost-effective trapping and enrichment of nanoparticles (trapping time: <50 s) and bovine serum albumin (trapping time: <1000 s) was realized. These results prove that the Au NHA-based DEP devices have great potential for real-time digital and Raman bioimaging, in addition to biomarker detection.

Dielectrophoresis: An Approach to Increase Sensitivity, Reduce Response Time and to Suppress Nonspecific Binding in Biosensors?

The performance of receptor-based biosensors is often limited by either diffusion of the analyte causing unreasonable long assay times or a lack of specificity limiting the sensitivity due to the noise of nonspecific binding. Alternating current (AC) electrokinetics and its effect on biosensing is an increasing field of research dedicated to address this issue and can improve mass transfer of the analyte by electrothermal effects, electroosmosis, or dielectrophoresis (DEP). Accordingly, several works have shown improved sensitivity and lowered assay times by order of magnitude thanks to the improved mass transfer with these techniques. To realize high sensitivity in real samples with realistic sample matrix avoiding nonspecific binding is critical and the improved mass transfer should ideally be specific to the target analyte. In this paper we cover recent approaches to combine biosensors with DEP, which is the AC kinetic approach with the highest selectivity. We conclude that while associated with many challenges, for several applications the approach could be beneficial, especially if more work is dedicated to minimizing nonspecific bindings, for which DEP offers interesting perspectives.

Effective Separation of Cancer-Derived Exosomes in Biological Samples for Liquid Biopsy: Classic Strategies and Innovative Development

Liquid biopsy has remarkably facilitated clinical diagnosis and surveillance of cancer via employing a non-invasive way to detect cancer-derived components, such as circulating tumor DNA and circulating tumor cells from biological fluid samples. The cancer-derived exosomes, which are nano-sized vesicles secreted by cancer cells have been investigated in liquid biopsy as their important roles in intracellular communication and disease development have been revealed. Given the challenges posed by the complicated humoral microenvironment, which contains a variety of different cells and macromolecular substances in addition to the exosomes, it has attracted a large amount of attention to effectively isolate exosomes from collected samples. In this review, the authors aim to analyze classic strategies for separation of cancer-derived exosomes, giving an extensive discussion of advantages and limitations of these methods. Furthermore, the innovative multi-strategy methods to realize efficient isolation of cancer-derived exosomes in practical applications are also presented. Additionally, the possible development trends of exosome separation in to the future is discussed in this review.

Electrokinetic separation of cfDNA in insulator-based dielectrophoresis systems: a linear model of cfDNA and investigation of effective parameters

In this study, a comprehensive numerical simulation was done to investigate the electrokinetic translocation of cfDNA molecule as well as the possibility of its detection and separation in insulator based dielectrophoresis (iDEP) systems. Modeling was done for the first time by solving the Poisson equation for the electrical potential, Naiver-Stokes (NS) equation for the fluid flow and energy equation for the heat transfer in the system and considering a coarse-grained bead-spring model to describe the conformational and geometrical changes of cfDNA molecule. The effect of the geometrical parameters of the system, the initial orientation of the molecule, electrical conductivity of the solution and zeta potential of the wall was investigated on the translocation and the minimum voltage required for cfDNA trapping. When the ratio of the inlet height to the constriction zone height is large enough, cfDNA molecules cannot pass through the nanopore and trap in the constriction zone. Also, it was found that the electrical conductivity of the solution is a limiting parameter to directly isolate cfDNA from pure plasma without dilution due to significant increase in the temperature of the system. Our results demonstrate the enormous potential of iDEP systems for rapid detection of cfDNA from diluted plasma under special electrical potential and geometrical parameters of the iDEP systems.

Label-Free Isolation of Exosomes Using Microfluidic Technologies

Exosomes are cell-derived structures packaged with lipids, proteins, and nucleic acids. They exist in diverse bodily fluids and are involved in physiological and pathological processes. Although their potential for clinical application as diagnostic and therapeutic tools has been revealed, a huge bottleneck impeding the development of applications in the rapidly burgeoning field of exosome research is an inability to efficiently isolate pure exosomes from other unwanted components present in bodily fluids. To date, several approaches have been proposed and investigated for exosome separation, with the leading candidate being microfluidic technology due to its relative simplicity, cost-effectiveness, precise and fast processing at the microscale, and amenability to automation. Notably, avoiding the need for exosome labeling represents a significant advance in terms of process simplicity, time, and cost as well as protecting the biological activities of exosomes. Despite the exciting progress in microfluidic strategies for exosome isolation and the countless benefits of label-free approaches for clinical applications, current microfluidic platforms for isolation of exosomes are still facing a series of problems and challenges that prevent their use for clinical sample processing. This review focuses on the recent microfluidic platforms developed for label-free isolation of exosomes including those based on sieving, deterministic lateral displacement, field flow, and pinched flow fractionation as well as viscoelastic, acoustic, inertial, electrical, and centrifugal forces. Further, we discuss advantages and disadvantages of these strategies with highlights of current challenges and outlook of label-free microfluidics toward the clinical utility of exosomes.

Emerging on-chip electrokinetic based technologies for purification of circulating cancer biomarkers towards liquid biopsy: A review

Early detection of cancer can significantly reduce mortality and save lives. However, the current cancer diagnosis is highly dependent on costly, complex, and invasive procedures. Thus, a great deal of effort has been devoted to exploring new technologies based on liquid biopsy. Since liquid biopsy relies on detection of circulating biomarkers from biofluids, it is critical to isolate highly purified cancer-related biomarkers, including circulating tumor cells (CTCs), cell-free nucleic acids (cell-free DNA and cell-free RNA), small extracellular vesicles (exosomes), and proteins. The current clinical purification techniques are facing a number of drawbacks including low purity, long processing time, high cost, and difficulties in standardization. Here, we review a promising solution, on-chip electrokinetic-based methods, that have the advantage of small sample volume requirement, minimal damage to the biomarkers, rapid, and label-free criteria. We have also discussed the existing challenges of current on-chip electrokinetic technologies and suggested potential solutions that may be worthy of future studies.

Acoustofluidic medium exchange for preparation of electrocompetent bacteria using channel wall trapping

Comprehensive integration of process steps into a miniaturised version of synthetic biology workflows remains a crucial task in automating the design of biosystems. However, each of these process steps has specific demands with respect to the environmental conditions, including in particular the composition of the surrounding fluid, which makes integration cumbersome. As a case in point, transformation, i.e. reprogramming of bacteria by delivering exogenous genetic material (such as DNA) into the cytoplasm, is a key process in molecular engineering and modern biotechnology in general. Transformation is often performed by electroporation, i.e. creating pores in the membrane using electric shocks in a low conductivity environment. However, cell preparation for electroporation can be cumbersome as it requires the exchange of growth medium (high-conductivity) for low-conductivity medium, typically performed via multiple time-intensive centrifugation steps. To simplify and miniaturise this step, we developed an acoustofluidic device capable of trapping the bacterium Escherichia coli non-invasively for subsequent exchange of medium, which is challenging in acoustofluidic devices due to detrimental acoustic streaming effects. With an improved etching process, we were able to produce a thin wall between two microfluidic channels, which, upon excitation, can generate streaming fields that complement the acoustic radiation force and therefore can be utilised for trapping of bacteria. Our novel design robustly traps Escherichia coli at a flow rate of 10 μL min^-1 and has a cell recovery performance of 47 ± 3% after washing the trapped cells. To verify that the performance of the medium exchange device is sufficient, we tested the electrocompetence of the recovered cells in a standard transformation procedure and found a transformation efficiency of 8 × 10⁵ CFU per μg of plasmid DNA. Our device is a low-volume alternative to centrifugation-based methods and opens the door for miniaturisation of a plethora of microbiological and molecular engineering protocols.

Analytical Technologies for Liquid Biopsy of Subcellular Materials

Liquid biopsy markers, which can be secured from a simple blood draw or other biological samples, are used to manage a variety of diseases and even monitor for bacterial or viral infections. Although there are several different types of liquid biopsy markers, the subcellular ones, including cell-free DNA, microRNA, extracellular vesicles, and viral particles, are evolving in terms of their utility. A challenge with liquid biopsy markers is that they must be enriched from the biological sample prior to analysis because they are a vast minority in a mixed population, and potential interferences may be present in the sample matrix that can inhibit profiling the molecular cargo from the subcellular marker. In this article, we discuss existing and developing analytical enrichment platforms used to isolate subcellular liquid biopsy markers, and discuss their figures of merit such as recovery, throughput, and purity.

Automated fluorescence quantification of extracellular vesicles collected from blood plasma using dielectrophoresis

Tumor-secreted exosomes and other extracellular vesicles (EVs) in circulation contain valuable biomarkers for early cancer detection and screening. We have previously demonstrated collection of cancer-derived nanoparticles (NPs) directly from whole blood and plasma with a chip-based technique that uses a microelectrode array to generate dielectrophoretic (DEP) forces. This technique enables direct recovery of NPs from whole blood and plasma. The biomarker payloads associated with collected particles can be detected and quantified with immunostaining. Accurately separating the fluorescence intensity of stained biomarkers from background (BG) levels becomes a challenge when analyzing the blood from early-stage cancer patients in which biomarker concentrations are low. To address this challenge, we developed two complementary techniques to standardize the quantification of fluorescently immunolabeled biomarkers collected and concentrated at predictable locations within microfluidic chips. The first technique was an automated algorithm for the quantitative analysis of fluorescence intensity at collection regions within the chip compared to levels at adjacent regions. The algorithm used predictable locations of particle collection within the chip geometry to differentiate regions of collection and BG. We successfully automated the identification and removal of optical artifacts from quantitative calculations. We demonstrated that the automated system performs nearly the same as a human user following a standard protocol for manual artifact removal with Pearson's r-values of 0.999 and 0.998 for two different biomarkers (n = 36 patients). We defined a usable dynamic range of fluorescence intensities corresponding to 1 to 2000 arbitrary units (a.u.). Fluorescence intensities within the dynamic range increased linearly with respect to exposure time and particle concentration. The second technique was the implementation of an internal standard to adjust levels of biomarker fluorescence based on the relative collection efficiency of the chip. Use of the internal standard reduced variability in measured biomarker levels due to differences in chip-to-chip collection efficiency, especially at low biomarker concentrations. The internal standard did not affect linear trends between fluorescence intensity and exposure time. Adjustments using the internal standard improved linear trends between fluorescence intensity and particle concentration. The optical quantification techniques described in this paper can be easily adapted for other lab-on-a-chip platforms that have predefined regions of biomarker or particle collection and that rely on fluorescence detection.

Dielectrophoresis: Developments and applications from 2010 to 2020

The 20th century has seen tremendous innovation of dielectrophoresis (DEP) technologies, with applications being developed in areas ranging from industrial processing to micro- and nanoscale biotechnology. From 2010 to present day, there have been 981 publications about DEP. Of over 2600 DEP patents held by the United States Patent and Trademark Office, 106 were filed in 2019 alone. This review focuses on DEP-based technologies and application developments between 2010 and 2020, with an aim to highlight the progress and to identify potential areas for future research. A major trend over the last 10 years has been the use of DEP techniques for biological and clinical applications. It has been used in various forms on a diverse array of biologically derived molecules and particles to manipulate and study them including proteins, exosomes, bacteria, yeast, stem cells, cancer cells, and blood cells. DEP has also been used to manipulate nano- and micron-sized particles in order to fabricate different structures. The next 10 years are likely to see the increase in DEP-related patent applications begin to result in a greater level of technology commercialization. Also during this time, innovations in DEP technology will likely be leveraged to continue the existing trend to further biological and medical-focused applications as well as applications in microfabrication. As a tool leveraged by engineering and imaginative scientific design, DEP offers unique capabilities to manipulate small particles in precise ways that can help solve problems and enable scientific inquiry that cannot be addressed using conventional methods.

Microfluidic Isolation and Enrichment of Nanoparticles

Over the past decades, nanoparticles have increased in implementation to a variety of applications ranging from high-efficiency electronics to targeted drug delivery. Recently, microfluidic techniques have become an important tool to isolate and enrich populations of nanoparticles with uniform properties (e.g., size, shape, charge) due to their precision, versatility, and scalability. However, due to the large number of microfluidic techniques available, it can be challenging to identify the most suitable approach for isolating or enriching a nanoparticle of interest. In this review article, we survey microfluidic methods for nanoparticle isolation and enrichment based on their underlying mechanisms, including acoustofluidics, dielectrophoresis, filtration, deterministic lateral displacement, inertial microfluidics, optofluidics, electrophoresis, and affinity-based methods. We discuss the principles, applications, advantages, and limitations of each method. We also provide comparisons with bulk methods, perspectives for future developments and commercialization, and next-generation applications in chemistry, biology, and medicine.

Continuous Enrichment and Separation of Nanoparticles via Acoustic Streaming

Enrichment and separation of Micro/Nano-scale specimens are fundamental requirements in biomedical researches. In this paper, we demonstrated a simple and efficient microfluidic chip for the continuous enrichment and separation of nanoscale polystyrene particles using the acoustic streaming induced by gigahertz(GHz) bulk acoustic waves(BAW). The bulk acoustic resonator released ultrahigh frequency (2GHz) acoustic waves into the fluid and triggered the acoustic streaming. The nanoparticles were continuous concentrated and segregated by the combination action of the viscosity force and the acoustic radiation force. The separation of 300 and 100 nm particles was achieved with the high purity (92.4%). These data contribute proof-in-principle that acoustic streaming is a label-free strategy that can be used to enrich and separate nanoscale specimens with high efficiency.

Detection of cell-free DNA nanoparticles in insulator based dielectrophoresis systems

In this paper, a semi-analytical investigation was performed to study the effect of the geometrical parameters of insulator-based dielectrophoresis (iDEP) systems for cell free DNA (cfDNA) trapping. For this purpose, first electrical potential and fluid flow fields were calculated by solving the governing equations including Poisson and Navier-stokes equations with appropriate boundary conditions (BCs) and then a Lagrangian approach was utilized to analyze the motion of cfDNA under the most important forces affected on it including Brownian, Drag, electrophoresis and dielectrophoresis (DEP) forces. The effect of the different parameters such as the electrical conductivity of the medium, shape and geometrical parameters of the insulators on the dielectrophoretic behavior of cfDNA was studied and the optimal value of these parameters was presented. Finally, in order to predict the minimum voltage required for cfDNA trapping, artificial neural network (ANN) was utilized and a relation between input and output parameters was introduced.

An electrophoretic DNA extraction device using a nanofilter for molecular diagnosis of pathogens

Rapid and efficient nucleic acid (NA) extraction and concentration are required for point-of-care analysis in order to prevent an epidemic/pandemic disease outbreak. Typical silica-based NA extraction methods have limitations such as being time-consuming, requiring human intervention, and resulting in a low recovery yield. In this study, we have developed a pathogenic DNA extraction device based on electrokinetic separation incorporated with a silicon nitride (SiNx) nanofilter, which expedites the DNA extraction procedure with advantages of being convenient, efficient, and inexpensive. This DNA extraction device consists of a computer numerical control (CNC) milled-Teflon gadget with a cis-chamber as a cell lysate reservoir and a trans-chamber as a elution solution reservoir, with the SiNx nanofilter being inserted between the two chambers. The SiNx nanofilter was fabricated using a photolithographic method in conjunction with nanoimprinting. Approximately 7.2 million nanopores of 220 nm diameter were located at the center of the nanofilter. When a DC electric field is applied through the nanopores, DNA is transferred from the cis-chamber to the trans-chamber to isolate the DNA from the cell debris. To demonstrate the DNA extraction performance, we measured the absorbances at 260 and 280 nm and performed a real-time polymerase chain reaction (real-time PCR) using the recovered DNA to verify its feasibility for downstream genetic analysis. Moreover, the DNA extraction device was successfully operated using a 1.5 V alkaline battery, which verifies the portability of the device for point-of-care testing. Such an advanced DNA extraction system can be utilized in various fields including clinical analysis, pathogen detection, forensic analysis, and on-site detection.

Direct electrophoretic microRNA preparation from clinical samples using nanofilter membrane

A method to directly collect negatively charged nucleic acids, such as DNA and RNA, in the biosamples simply by applying an electric field in between the sample and collection buffer separated by the nanofilter membrane is proposed. The nanofilter membrane was made of low-stress silicon nitride with a thickness of 100 nm, and multiple pores were perforated in a highly arranged pattern using nanoimprint technology with a pore size of 200 nm and a pore density of 7.22 × 108/cm2. The electrophoretic transport of hsa-mir-93-5p across the membrane was confirmed in pure microRNA (miRNA) mimic solution using quantitative reverse transcription-polymerase chain reactions (qRT-PCR). Consistency of the collected miRNA quantity, stability of the system during the experiment, and yield and purity of the prepared sample were discussed in detail to validate the effectiveness of the electrical protocol. Finally, in order to check the applicability of this method to clinical samples, liquid biopsy process was demonstrated by evaluating the miRNA levels in sera of hepatocellular carcinoma patients and healthy controls. This efficient system proposed a simple, physical idea in preparation of nucleic acid from biosamples, and demonstrated its compatibility to biological downstream applications such as qRT-PCR as the conventional nucleic acid extraction protocols.

High-Performance Nucleic Acid Sensors for Liquid Biopsy Applications

Circulating tumour nucleic acids (ctNAs) are released from tumours cells and can be detected in blood samples, providing a way to track tumors without requiring a tissue sample. This "liquid biopsy" approach has the potential to replace invasive, painful, and costly tissue biopsies in cancer diagnosis and management. However, a very sensitive and specific approach is required to detect relatively low amounts of mutant sequences linked to cancer because they are masked by the high levels of wild-type sequences. This review discusses high-performance nucleic acid biosensors for ctNA analysis in patient samples. We compare sequencing- and amplification-based methods to next-generation sensors for ctDNA and ctRNA (including microRNA) profiling, such as electrochemical methods, surface plasmon resonance, Raman spectroscopy, and microfluidics and dielectrophoresis-based assays. We present an overview of the analytical sensitivity and accuracy of these methods as well as the biological and technical challenges they present.

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.

Transverse dielectrophoretic-based DNA nanoscale confinement

Confinement of single molecules within nanoscale environments is crucial in a range of fields, including biomedicine, genomics, and biophysics. Here, we present a method that can concentrate, confine, and linearly stretch DNA molecules within a single optical field of view using dielectrophoretic (DEP) force. The method can convert an open surface into one confining DNA molecules without a requirement for bonding, hydrodynamic or mechanical components. We use a transverse DEP field between a top coverslip and a bottom substrate, both of which are coated with a transparent conductive material. Both layers are attached using double-sided tape, defining the chamber. The nanofeatures lie at the “floor” and do not require any bonding. With the application of an alternating (AC) electric field (2 V_p-p) between the top and bottom electrodes, a DEP field gradient is established and used to concentrate, confine and linearly extend DNA in nanogrooves as small as 100-nm in width. We also demonstrate reversible loading/unloading of DNA molecules into nanogrooves and nanopits by switching frequency (between 10 kHz to 100 kHz). The technology presented in this paper provides a new method for single-molecule trapping and analysis.

Rapid Isolation and Detection of Exosomes and Associated Biomarkers from Plasma

Exosomes found in the circulation are a primary source of important cancer-related RNA and protein biomarkers that are expected to lead to early detection, liquid biopsy, and point-of-care diagnostic applications. Unfortunately, due to their small size (50-150 nm) and low density, exosomes are extremely difficult to isolate from plasma. Current isolation methods are time-consuming multistep procedures that are unlikely to translate into diagnostic applications. To address this issue, we demonstrate the ability of an alternating current electrokinetic (ACE) microarray chip device to rapidly isolate and recover glioblastoma exosomes from undiluted human plasma samples. The ACE device requires a small plasma sample (30-50 μL) and is able to concentrate the exosomes into high-field regions around the ACE microelectrodes within 15 min. A simple buffer wash removes bulk plasma materials, leaving the exosomes concentrated on the microelectrodes. The entire isolation process and on-chip fluorescence analysis is completed in less than 30 min which enables subsequent on-chip immunofluorescence detection of exosomal proteins, and provides viable mRNA for RT-PCR analysis. These results demonstrate the ability of the ACE device to streamline the process for isolation and recovery of exosomes, significantly reducing the number of processing steps and time required.

Impact of surface roughness on Dielectrophoretically assisted concentration of microorganisms over PCB based platforms

This article presents a PCB based microfluidic platform for performing a dielectrophoretic capture of live microorganisms over inter-digitated electrodes buried under layers of different surface roughness values. Although dielectrophoresis has been extensively studied earlier over silicon and polymer surfaces with printed electrodes the issue of surface roughness particularly in case of buried electrodes has been seldom investigated. We have addressed this issue through a layer of spin coated PDMS (of various surface roughness) that is used to cover the printed electrodes over a printed circuit board. The roughness in the PDMS layer is generally defined by the roughness of the FR4 base which houses the printed electrodes as well as other structures. Possibilities arising out of COMSOL simulations have been well validated experimentally in this work.

The ePrep-System: A new electrophoretic approach for DNA isolation from biological samples

We present a new free-flow electrophoretic separation system that extends the established concepts of nucleic acid migration in an electric field to a broadly applicable preparative scale. The system comprises a disposable flow tube in which the target nucleic acids are separated from impurities by a balanced combination of electrophoretic migration and counter-streaming electroosmotic flow under the influence of an applied external electric field. Despite the complex theoretical background the introduced electrophoretic technology offers simple hardware setup and handling protocols. A variable number of small and disposable flow tubes can be processed in parallel, which largely eliminates the cumulative increase in extraction times inherent to batch processing methods and allows faster throughput of intermediate sample numbers. We demonstrate easy isolation of nucleic acids without user interaction during the run by using existing and well established lysis chemistries. Sample loading is realized by concentrated transfer of DNA-loaded magnetic beads from a lysis reaction into the extraction flow tube. The present study centers on the development of a functional model for the device and the flow tube as well as a preliminary standard extraction protocol. The system is compatible with a broad range of sample types and we present proof of principle data demonstrating its suitability for biomarker detection in translational research applications.

DNA dielectrophoresis: Theory and applications a review

Dielectrophoresis is the migration of an electrically polarizable particle in an inhomogeneous electric field. This migration can be exploited for several applications with (bio)molecules or cells. Dielectrophoresis is a noninvasive technique; therefore, it is very convenient for (selective) manipulation of (bio)molecules or cells. In this review, we will focus on DNA dielectrophoresis as this technique offers several advantages in trapping and immobilization, separation and purification, and analysis of DNA molecules. We present and discuss the underlying theory of the most important forces that have to be considered for applications with dielectrophoresis. Moreover, a review of DNA dielectrophoresis applications is provided to present the state-of-the-art and to offer the reader a perspective of the advances and current limitations of DNA dielectrophoresis.

Dielectrophoresis for Biomedical Sciences Applications: A Review

Dielectrophoresis (DEP) is a label-free, accurate, fast, low-cost diagnostic technique that uses the principles of polarization and the motion of bioparticles in applied electric fields. This technique has been proven to be beneficial in various fields, including environmental research, polymer research, biosensors, microfluidics, medicine and diagnostics. Biomedical science research is one of the major research areas that could potentially benefit from DEP technology for diverse applications. Nevertheless, many medical science research investigations have yet to benefit from the possibilities offered by DEP. This paper critically reviews the fundamentals, recent progress, current challenges, future directions and potential applications of research investigations in the medical sciences utilizing DEP technique. This review will also act as a guide and reference for medical researchers and scientists to explore and utilize the DEP technique in their research fields.

Dielectrophoretic recovery of DNA from plasma for the identification of chronic lymphocytic leukemia point mutations

Aim

Circulating cell free (ccf) DNA contains information about mutations affecting chronic lymphocytic leukemia (CLL). The complexity of isolating DNA from plasma inhibits the development of point-of-care diagnostics. Here, we introduce an electrokinetic method that enables rapid recovery of DNA from plasma.

Materials & methods

ccf-DNA was isolated from 25 µl of CLL plasma using dielectrophoresis. The DNA was used for PCR amplification, sequencing and analysis.

Results

The ccf-DNA collected from plasma of 5 CLL patients revealed identical mutations to those previously identified by extracting DNA from CLL cells from the same patients.

Conclusion

Rapid dielectrophoresis isolation of ccf-DNA directly from plasma provides sufficient amounts of DNA to use for identification of point mutations in genes associated with CLL progression.

Increasing local density and purity of molecules/bacteria on a sensing surface from diluted blood using 3D hybrid electrokinetics

We present a long-range and selective nanocolloid/molecular/bacteria concentrator based on 3D hybrid AC electrokinetics (ACEK) that includes AC dielectrophoresis (DEP) and biased AC electroosmosis (ACEO). Through a convergency comb-shaped electrode design, this long-range ACEO allows the effective transport of a high number of targets into the centre of the detection zone. In the proposed 3D hybrid electrokinetics model, 3D ACEO provides long-range transportation, and the 3D DEP provides an effective separation mechanism. Thus, detection targets ranging from nanoscale to micrometers could be selectively concentrated long-range from diluted blood. The proposed design was used for selectively concentrating nanocolloids and bacteria in the diluted blood sample, respectively. Compared to a 3D short-range dipolar electrode configuration, the detection limit of long-range 3D convergency tripolar electrode configuration is one order of magnitude higher. The result also shows that the 3D hybrid ACEK demonstrated a higher purity of any plane above the electrode, which compared positively to the same design of a 2D hybrid ACEK. The concentration factor of the proposed 3D hybrid electrokinetics device increased by several orders of local density and raised the local purity at least 6 orders (from 0.05% to greater than 99.9%). The chip is capable of making a DNA/protein/bacterial aggregate characterized by high local density and purity for further molecular and bacteria detection/analysis.

Recovery of Drug Delivery Nanoparticles from Human Plasma Using an Electrokinetic Platform Technology

The effect of complex biological fluids on the surface and structure of nanoparticles is a rapidly expanding field of study. One of the challenges holding back this research is the difficulty of recovering therapeutic nanoparticles from biological samples due to their small size, low density, and stealth surface coatings. Here, the first demonstration of the recovery and analysis of drug delivery nanoparticles from undiluted human plasma samples through the use of a new electrokinetic platform technology is presented. The particles are recovered from plasma through a dielectrophoresis separation force that is created by innate differences in the dielectric properties between the unaltered nanoparticles and the surrounding plasma. It is shown that this can be applied to a wide range of drug delivery nanoparticles of different morphologies and materials, including low-density nanoliposomes. These recovered particles can then be analyzed using different methods including scanning electron microscopy to monitor surface and structural changes that result from plasma exposure. This new recovery technique can be broadly applied to the recovery of nanoparticles from high conductance fluids in a wide range of applications.

Detecting cancer biomarkers in blood: challenges for new molecular diagnostic and point-of-care tests using cell-free nucleic acids

As we move into the era of individualized cancer treatment, the need for more sophisticated cancer diagnostics has emerged. Cell-free (cf) nucleic acids (cf-DNA, cf-RNA) and other cellular nanoparticulates are now considered important and selective biomarkers. There is great hope that blood-borne cf-nucleic acids can be used for 'liquid biopsies', replacing more invasive tissue biopsies to analyze cancer mutations and monitor therapy. Conventional techniques for cf-nucleic acid biomarker isolation from blood are generally time-consuming, complicated and expensive. They require relatively large blood samples, which must be processed to serum or plasma before isolation of biomarkers can proceed. Such cumbersome sample preparation also limits the widespread use of powerful, downstream genomic analyses, including PCR and DNA sequencing. These limitations also preclude rapid, point-of-care diagnostic applications. Thus, new technologies that allow rapid isolation of biomarkers directly from blood will permit seamless sample-to-answer solutions that enable next-generation point-of-care molecular diagnostics.

Focusing and continuous separation of microparticles by insulator-based dielectrophoresis (iDEP) in stair-shaped microchannel

Focusing and separation of microparticles in a complex mixture have had wide applications in chemistry, biology, medicine, etc. This work presents a numerical and experimental investigation on focusing and continuous separation of microparticles in a geometrically optimized arrangement of steps in the form of a staircase using insulator-based dielectrophoresis (iDEP) mechanism. First, a detailed finite element analysis was performed on important parameters in the focusing and separation of microparticles, such as geometry of stair-shaped microchannel, total voltage, and voltage difference applied to reservoirs. The optimum parameters obtained from numerical analysis were used for experimental work. Theoretically, predicted microparticle trajectories are in good agreement with experimentally observed ones. Experimental and numerical results show that the performance of focusing of microparticles enhances with growth of the total voltage (in a constant voltage difference) and decreases with voltage difference. The fabricated iDEP microchip enhances the performance of focusing and separation of microparticles due to its stair-shaped microchannel and therefore operates at low DC total applied voltages of 90-110 V.

Low level epifluorescent detection of nanoparticles and DNA on dielectrophoretic microarrays

Common epifluorescent microscopy lacks the sensitivity to detect low levels of analytes directly in clinical samples, such as drug delivery nanoparticles or disease related DNA biomarkers. Advanced systems such as confocal microscopes may improve detection, but several factors limit their applications. This study now demonstrates that combining an epifluorescent microscope with a dielectrophoretic (DEP) microelectrode array device enables the detection of nanoparticles and DNA biomarkers at clinically relevant levels. Using DEP microarray devices, nanoparticles and DNA biomarkers are rapidly isolated and concentrated onto specific microscopic locations where they are easily detected by epifluorescent microscopy. In this study, 40nm nanoparticles were detected down to 2-3 × 10(3) /ul levels and DNA was detected down to the 200 pg/ml level. The synergy of epifluorescent microscopy and DEP microarray devices provides a new paradigm for DNA biomarker diagnostics and the monitoring of drug delivery nanoparticle concentrations.

Dielectrophoretic isolation and detection of cancer-related circulating cell-free DNA biomarkers from blood and plasma

Conventional methods for the isolation of cancer-related circulating cell-free (ccf) DNA from patient blood (plasma) are time consuming and laborious. A DEP approach utilizing a microarray device now allows rapid isolation of ccf-DNA directly from a small volume of unprocessed blood. In this study, the DEP device is used to compare the ccf-DNA isolated directly from whole blood and plasma from 11 chronic lymphocytic leukemia (CLL) patients and one normal individual. Ccf-DNA from both blood and plasma samples was separated into DEP high-field regions, after which cells (blood), proteins, and other biomolecules were removed by a fluidic wash. The concentrated ccf-DNA was detected on-chip by fluorescence, and then eluted for PCR and DNA sequencing. The complete process from blood to PCR required less than 10 min; an additional 15 min was required to obtain plasma from whole blood. Ccf-DNA from the equivalent of 5 μL of CLL blood and 5 μL of plasma was amplified by PCR using Ig heavy-chain variable (IGHV) specific primers to identify the unique IGHV gene expressed by the leukemic B-cell clone. The PCR and DNA sequencing results obtained by DEP from all 11 CLL blood samples and from 8 of the 11 CLL plasma samples were exactly comparable to the DNA sequencing results obtained from genomic DNA isolated from CLL patient leukemic B cells (gold standard).

Rapid (<5 min) identification of pathogen in human blood by electrokinetic concentration and surface-enhanced Raman spectroscopy

This study reports a novel microfluidic platform for rapid and long-ranged concentration of rare-pathogen from human blood for subsequent on-chip surface-enhanced Raman spectroscopy (SERS) identification/discrimination of bacteria based on their detected fingerprints. Using a hybrid electrokinetic mechanism, bacteria can be concentrated at the stagnation area on the SERS-active roughened electrode, while blood cells were excluded away from this region at the center of concentric circular electrodes. This electrokinetic approach performs isolation and concentration of bacteria in about three minutes; the density factor is increased approximately a thousand fold in a local area of ~5000 μm² from a low bacteria concentration of 5 × 10³ CFU/ml. Besides, three genera of bacteria, S. aureus, E. coli, and P. aeruginosa that are found in most of the isolated infections in bacteremia were successfully identified in less than one minute on-chip without the use of any antibody/chemical immobilization and reaction processes.

Rapid electrokinetic isolation of cancer-related circulating cell-free DNA directly from blood

BACKGROUND

Circulating cell-free DNA (ccf-DNA) is becoming an important biomarker for cancer diagnostics and therapy monitoring. The isolation of ccf-DNA from plasma as a "liquid biopsy" may begin to replace more invasive tissue biopsies for the detection and analysis of cancer-related mutations. Conventional methods for the isolation of ccf-DNA from plasma are costly, time-consuming, and complex, preventing the use of ccf-DNA biomarkers for point-of-care diagnostics and limiting other biomedical research applications.

METHODS

We used an AC electrokinetic device to rapidly isolate ccf-DNA from 25 μL unprocessed blood. ccf-DNA from 15 chronic lymphocytic leukemia (CLL) patients and 3 healthy individuals was separated into dielectrophoretic (DEP) high-field regions, after which other blood components were removed by a fluidic wash. Concentrated ccf-DNA was detected by fluorescence and eluted for quantification, PCR, and DNA sequencing. The complete process, blood to PCR, required <10 min. ccf-DNA was amplified by PCR with immunoglobulin heavy chain variable region (IGHV)-specific primers to identify the unique IGHV gene expressed by the leukemic B-cell clone, and then sequenced.

RESULTS

PCR and DNA sequencing results obtained by DEP from 25 μL CLL blood matched results obtained by use of conventional methods for ccf-DNA isolation from 1 mL plasma and for genomic DNA isolation from CLL patient leukemic B cells isolated from 15-20 mL blood.

CONCLUSIONS

Rapid isolation of ccf-DNA directly from a drop of blood will advance disease-related biomarker research, accelerate the transition from tissue to liquid biopsies, and enable point-of-care diagnostic systems for patient monitoring.

Giga-pixel fluorescent imaging over an ultra-large field-of-view using a flatbed scanner

We demonstrate a new fluorescent imaging technique that can screen for fluorescent micro-objects over an ultra-wide field-of-view (FOV) of ~532 cm(2), i.e., 19 cm × 28 cm, reaching a space-bandwidth product of more than 2 billion. For achieving such a large FOV, we modified the hardware and software of a commercially available flatbed scanner, and added a custom-designed absorbing fluorescent filter, a two-dimensional array of external light sources for computer-controlled and high-angle fluorescent excitation. We also re-programmed the driver of the scanner to take full control of the scanner hardware and achieve the highest possible exposure time, gain and sensitivity for detection of fluorescent micro-objects through the gradient index self-focusing lens array that is positioned in front of the scanner sensor chip. For example, this large FOV of our imaging platform allows us to screen more than 2.2 mL of undiluted whole blood for detection of fluorescent micro-objects within <5 minutes. This high-throughput fluorescent imaging platform could be useful for rare cell research and cytometry applications by enabling rapid screening of large volumes of optically dense media. Our results constitute the first time that a flatbed scanner has been converted to a fluorescent imaging system, achieving a record large FOV.

Dielectrophoresis: an assessment of its potential to aid the research and practice of drug discovery and delivery

Dielectrophoresis (DEP) is an electrokinetic technique with proven ability to discriminate and selectively manipulate cells based on their phenotype and physiological state, without the need for biological tags and markers. The DEP response of a cell is predominantly determined by the physico-chemical properties of the plasma membrane, subtle changes of which can be detected from two so-called 'cross-over' frequencies, f(xo1) and f(xo2). Membrane capacitance and structural changes can be monitored by measurement of f(xo1) at sub-megahertz frequencies, and current indications suggest that f(xo2), located above 100 MHz, is sensitive to changes of trans-membrane ion fluxes. DEP lends itself to integration in microfluidic devices and can also operate at the nanoscale to manipulate nanoparticles. Apart from measurements of f(xo1) and f(xo2), other examples where DEP could contribute to drug discovery and delivery include its ability to: enrich stem cells according to their differentiation potential, and to engineer artificial cell structures and nano-structures.

A Universal Electrode Approach for Automated Electrochemical Molecular Analyses

Transforming microfluidics-based biosensing systems from laboratory research into clinical reality remains an elusive goal despite decades of intensive research. A fundamental obstacle for the development of fully automated microfluidic diagnostic systems is the lack of an effective strategy for combining pumping, sample preparation, and detection modules into an integrated biosensing platform. Herein, we report a universal electrode approach, which incorporates DC electrolytic pumping, AC electrokinetic sample preparation, and self-assembled monolayer based electrochemical sensing on a single microfluidic platform, to automate complicated molecular analysis procedures that will enable biosensing applications in non-traditional healthcare settings. Using the universal electrode approach, major microfluidic operations required in molecular analyses, such as pumping, mixing, washing, and sensing can be performed in a single platform. We demonstrate the universal electrode platform for detecting bacterial 16S rRNA, a phylogenetic marker, toward rapid diagnostics of urinary tract infection. Since only electronic interfaces are required to operate the platform, the universal electrode approach represents an effective system integration strategy to realize the potential of microfluidics in molecular diagnostics at the point of care.

Dielectrophoresis of lambda-DNA using 3D carbon electrodes

Carbon electrodes have recently been introduced as an alternative to metal electrodes and insulator structures for dielectrophoretic applications. Here, an experimental and theoretical study employing an array of 3D carbon electrodes contained in a microfluidic channel for the dielectrophoretic manipulation of DNA is presented. First evidence that carbon-electrode DEP can be used for the manipulation and trapping of biomolecules such as DNA is reported. In particular, the dielectrophoretic response of λ-DNA (48.5 kbp) under various frequencies and flow conditions necessary for retention of λ-DNA are studied. Negative DEP is observed at frequencies above 75 kHz and positive DEP is present in the range below 75 kHz and down to 5 kHz. We further implement a theoretical model to capture the experimental findings in sufficient detail. Our theoretical considerations based on reported scaling laws for linear and supercoiled DNA further suggest that carbon-electrode DEP devices could be employed in future analytical applications such as DNA preconcentration and fractionation.

Dielectrophoretic isolation and detection of cfc-DNA nanoparticulate biomarkers and virus from blood

Dielectrophoretic (DEP) microarray devices allow important cellular nanoparticulate biomarkers and virus to be rapidly isolated, concentrated, and detected directly from clinical and biological samples. A variety of submicron nanoparticulate entities including cell free circulating (cfc) DNA, mitochondria, and virus can be isolated into DEP high-field areas on microelectrodes, while blood cells and other micron-size entities become isolated into DEP low-field areas between the microelectrodes. The nanoparticulate entities are held in the DEP high-field areas while cells are washed away along with proteins and other small molecules that are not affected by the DEP electric fields. DEP carried out on 20 μL of whole blood obtained from chronic lymphocytic leukemia patients showed a considerable amount of SYBR Green stained DNA fluorescent material concentrated in the DEP high-field regions. Whole blood obtained from healthy individuals showed little or no fluorescent DNA materials in the DEP high-field regions. Fluorescent T7 bacteriophage virus could be isolated directly from blood samples, and fluorescently stained mitochondria could be isolated from biological buffer samples. Using newer DEP microarray devices, high-molecular-weight DNA could be isolated from serum and detected at levels as low as 8-16 ng/mL.