Cell lysis and protein extraction in a microfluidic device with detection by a fluorogenic enzyme assay

Kinetic detection of hydrogen peroxide in single horseradish peroxidase-concentrated silica particle using confocal fluorescence microspectroscopic measurement

In the present study, we propose a scheme for detecting H2O2 by using horseradish peroxidase (HRP) adsorbed onto single silica particles and fluorescence microspectroscopy. When the silica particles were immersed in an HRP solution, the HRP concentration in the silica particles increased by a factor of 690 compared to that in the bulk aqueous solution because HRP was adsorbed on the silica surface. When a single particle containing HRP was added to a mixed solution of H2O2 and Amplex Red, fluorescence from resorufin, which was produced by the reaction of HRP, H2O2, and Amplex Red, was observed. The fluorescence from the resorufin in the particles increased after a single particle was added to the solution, and the release of resorufin was observed. As the concentration of H2O2 (CH2O2) decreased, the time it takes for fluorescence intensity to reach its maximum was shorter. The detection limit for H2O2 in the present system was 980 nM. The reaction behavior of a single silica particle was evaluated using a spherical diffusion model, which explains the approximate concentration change of resorufin in the silica particle. The proposed method has the advantages of simple sample preparation and detection, low sample consumption, and a short detection time.

Space in cancer biology: its role and implications

Tumor cells present complex behaviors in their interactions with other cells. This intricate behavior is driving the need to develop new tools to understand these ecosystems. The surge of spatial technologies allows evaluation of the complexity of relationships between cells present in a tumor, giving insights about tumor heterogeneity and the tumor microenvironment while providing clinically relevant metrics for tumor classification. In this review, we describe key results obtained using spatial techniques, present recent advances in methods to uncover spatially relevant biological significance, and summarize their main characteristics. We expect spatial technologies to significantly broaden our understanding of tumor biology and to generate clinically relevant tools that will ultimately impact personalized medicine.

Polydimethylsiloxane microstructure-induced acoustic streaming for enhanced ultrasonic DNA fragmentation on a microfluidic chip

Next-generation sequencing (NGS) is an essential technology for DNA identification in genomic research. DNA fragmentation is a critical step for NGS and doing this on-chip is of great interest for future integrated genomic solutions. Here we demonstrate fast acoustofluidic DNA fragmentation via ultrasound-actuated elastic polydimethylsiloxane (PDMS) microstructures that induce acoustic streaming and associated shear forces when placed in the field of an ultrasonic transducer. Indeed, acoustic streaming locally generates high tensile stresses that can mechanically stretch and break DNA molecule chains. The improvement in efficiency of the on-chip DNA fragmentation is due to the synergistic effect of these tensile stresses and ultrasonic cavitation phenomena. We tested these microstructure-induced effects in a DNA-containing microfluidic channel both experimentally and by simulation. The DNA fragmentation process was evaluated by measuring the change in the DNA fragment size over time. The chip works well with both long and short DNA chains; in particular, purified lambda (λ) DNA was cut from 48.5 kbp to 3 kbp in one minute with selected microstructures and further down to 300 bp within two and a half minutes. The fragment size of mouse genomic DNA was reduced from 1.4 kbp to 400 bp in one minute and then to 200 bp in two and a half minutes. The DNA fragmentation efficiency of the chip equipped with the PDMS microstructures was twice that of the chip without the microstructures. Exhaustive comparison shows that the on-chip fragmentation performance reaches the level of high-end professional standards. Recently, DNA fragmentation was shown to be enhanced using vibrating air microbubbles when the chip was placed in an acoustic field. We think the microbubble-free microstructure-based device we present is easier to operate and more reliable, as it avoids microbubble preparation and maintenance, while showing high DNA fragmentation performance.

Microfluidic devices for studying bacterial taxis, drug testing and biofilm formation

Some bacteria have coevolved to establish symbiotic or pathogenic relationships with plants, animals or humans. With human association, the bacteria can cause a variety of diseases. Thus, understanding bacterial phenotypes at the single-cell level is essential to develop beneficial applications. Traditional microbiological techniques have provided great knowledge about these organisms; however, they have also shown limitations, such as difficulties in culturing some bacteria, the heterogeneity of bacterial populations or difficulties in recreating some physical or biological conditions. Microfluidics is an emerging technique that complements current biological assays. Since microfluidics works with micrometric volumes, it allows fine-tuning control of the test conditions. Moreover, it allows the recruitment of three-dimensional (3D) conditions, in which several processes can be integrated and gradients can be generated, thus imitating physiological 3D environments. Here, we review some key microfluidic-based studies describing the effects of different microenvironmental conditions on bacterial response, biofilm formation and antimicrobial resistance. For this aim, we present different studies classified into six groups according to the design of the microfluidic device: (i) linear channels, (ii) mixing channels, (iii) multiple floors, (iv) porous devices, (v) topographic devices and (vi) droplet microfluidics. Hence, we highlight the potential and possibilities of using microfluidic-based technology to study bacterial phenotypes in comparison with traditional methodologies.

Bubble-enhanced ultrasonic microfluidic chip for rapid DNA fragmentation

DNA fragmentation is an essential process in developing genetic sequencing strategies, genetic research, as well as for the diagnosis of diseases with a genetic signature like cancer. Efficient on-chip DNA fragmentation protocols would be beneficial to process integration and open new opportunities for microfluidics in genetic applications. Here we present an acoustic microfluidic chip comprising an array of ultrasound-actuated microbubbles located at dedicated positions adjacent to a channel containing the DNA sample solution. The efficiency of the on-chip DNA fragmentation process arises mainly from tensile forces generated by acoustic streaming near the oscillating bubble interfaces, as well as a synergistic effect of streaming stress and ultrasonic cavitation. Acoustic microstreaming and the pressure distribution in the DNA channel were assessed by finite element simulation. We characterized the bubble-enhanced effect by measuring gene fragment size distributions with respect to different ultrasound parameters. For optimized on-chip conditions, purified lambda (λ) DNA (48.5 kbp) could be disrupted to fragments with an average size of 2 kbp after 30 s and down to 300 bp after 90 s. Mouse genomic DNA (1.4 kbp) fragmentation size decreased to 500 bp in 30 s and reduced further to 250 bp in 90 s. Bubble-induced fragmentation was more than 3 times faster than without bubbles. On-chip performance and process yield were found to be comparable to a sophisticated high-end commercial system. In this view, our new bubble-enhanced microfluidic approach is a promising tool for current and next generation sequencing platforms with high efficiency and good capacity. Moreover, the availability of an efficient on-chip DNA fragmentation process opens perspectives for implementing full molecular protocols on a single microfluidic platform.

Portable Pathogen Diagnostics Using Microfluidic Cartridges Made from Continuous Liquid Interface Production Additive Manufacturing

Biomedical diagnostics based on microfluidic devices have the potential to significantly benefit human health; however, the manufacturing of microfluidic devices is a key limitation to their widespread adoption. Outbreaks of infectious disease continue to demonstrate the need for simple, sensitive, and translatable tests for point-of-care use. Additive manufacturing (AM) is an attractive alternative to conventional approaches for microfluidic device manufacturing based on injection molding; however, there is a need for development and validation of new AM process capabilities and materials that are compatible with microfluidic diagnostics. In this paper, we demonstrate the development and characterization of AM cartridges using continuous liquid interface production (CLIP) and investigate process characteristics and capabilities of the AM microfluidic device manufacturing. We find that CLIP accurately produces microfluidic channels as small as 400 μm and that it is possible to routinely produce fluid channels as small as 100 μm with high repeatability. We also developed a loop-mediated isothermal amplification (LAMP) assay for detection of E. coli from whole blood directly on the CLIP-based AM microfluidic cartridges, with a 50 cfu/μL limit of detection, validating the use of CLIP processes and materials for pathogen detection. The portable diagnostic platform presented in this paper could be used to investigate and validate other AM processes for microfluidic diagnostics and could be an important component of scaling up the diagnostics for current and future infectious diseases and pandemics.

Analysis of the Biochemical Reaction Status by Real-Time Monitoring Molecular Diffusion Behaviors Using a Transistor Biosensor Integrated with a Microfluidic Channel

Traditional methods of monitoring biochemical reactions measure certain detectable reagents or products while assuming that the undetectable species follow the stoichiometry of the reactions. Here, based upon the metal-oxide thin-film transistor (TFT) biosensor, we develop a real-time molecular diffusion model to benchmark the concentration of the reagents and products. Using the nicotinamide adenine dinucleotide (NADH)-oxaloacetic acid with the enzyme of malate dehydrogenase as an example, mixtures of different reagent concentrations were characterized to extract the ratio of remaining concentrations between NAD⁺ and NADH. We can thus obtain the apparent equilibrium constant of the reaction, (8.06 ± 0.61) × 10⁴. Because the whole analysis was conducted using a TFT sensor fabricated using a semiconductor process, our approach has the advantages of exploring biochemical reaction kinetics in a massively parallel manner.

Rapid Manufacturing of Multilayered Microfluidic Devices for Organ on a Chip Applications

Microfabrication and Polydimethylsiloxane (PDMS) soft-lithography techniques became popular for microfluidic prototyping at the lab, but even after protocol optimization, fabrication is yet a long, laborious process and partly user-dependent. Furthermore, the time and money required for the master fabrication process, necessary at any design upgrade, is still elevated. Digital Manufacturing (DM) and Rapid-Prototyping (RP) for microfluidics applications arise as a solution to this and other limitations of photo and soft-lithography fabrication techniques. Particularly for this paper, we will focus on the use of subtractive DM techniques for Organ-on-a-Chip (OoC) applications. Main available thermoplastics for microfluidics are suggested as material choices for device fabrication. The aim of this review is to explore DM and RP technologies for fabrication of an OoC with an embedded membrane after the evaluation of the main limitations of PDMS soft-lithography strategy. Different material options are also reviewed, as well as various bonding strategies. Finally, a new functional OoC device is showed, defining protocols for its fabrication in Cyclic Olefin Polymer (COP) using two different RP technologies. Different cells are seeded in both sides of the membrane as a proof of concept to test the optical and fluidic properties of the device.

Continuous electrical lysis of cancer cells in a microfluidic device with passivated interdigitated electrodes

Cell lysis is a critical step in genomics for the extraction of cellular components of downstream assays. Electrical lysis (EL) offers key advantages in terms of speed and non-interference. Here, we report a simple, chemical-free, and automated technique based on a microfluidic device with passivated interdigitated electrodes with DC fields for continuous EL of cancer cells. We show that the critical problems in EL, bubble formation and electrode erosion that occur at high electric fields, can be circumvented by passivating the electrodes with a thin layer (∼18 μm) of polydimethylsiloxane. We present a numerical model for the prediction of the transmembrane potential (TMP) at different coating thicknesses and voltages to verify the critical TMP criterion for EL. Our simulations showed that the passivation layer results in a uniform electric field in the electrode region and offers a TMP in the range of 5-7 V at an applied voltage of 800 V, which is well above the critical TMP (∼1 V) required for EL. Experiments revealed that lysis efficiency increases with an increase in the electric field (E) and residence time (tr): a minimum E ∼ 105 V/m and tr ∼ 1.0 s are required for efficient lysis. EL of cancer cells is demonstrated and characterized using immunochemical staining and compared with chemical lysis. The lysis efficiency is found to be ∼98% at E = 4 × 105 V/m and tr = 0.72 s. The efficient recovery of genomic DNA via EL is demonstrated using agarose gel electrophoresis, proving the suitability of our method for integration with downstream on-chip assays.

Microbial lipases and their industrial applications: a comprehensive review

Lipases are very versatile enzymes, and produced the attention of the several industrial processes. Lipase can be achieved from several sources, animal, vegetable, and microbiological. The uses of microbial lipase market is estimated to be USD 425.0 Million in 2018 and it is projected to reach USD 590.2 Million by 2023, growing at a CAGR of 6.8% from 2018. Microbial lipases (EC 3.1.1.3) catalyze the hydrolysis of long chain triglycerides. The microbial origins of lipase enzymes are logically dynamic and proficient also have an extensive range of industrial uses with the manufacturing of altered molecules. The unique lipase (triacylglycerol acyl hydrolase) enzymes catalyzed the hydrolysis, esterification and alcoholysis reactions. Immobilization has made the use of microbial lipases accomplish its best performance and hence suitable for several reactions and need to enhance aroma to the immobilization processes. Immobilized enzymes depend on the immobilization technique and the carrier type. The choice of the carrier concerns usually the biocompatibility, chemical and thermal stability, and insolubility under reaction conditions, capability of easy rejuvenation and reusability, as well as cost proficiency. Bacillus spp., Achromobacter spp., Alcaligenes spp., Arthrobacter spp., Pseudomonos spp., of bacteria and Penicillium spp., Fusarium spp., Aspergillus spp., of fungi are screened large scale for lipase production. Lipases as multipurpose biological catalyst has given a favorable vision in meeting the needs for several industries such as biodiesel, foods and drinks, leather, textile, detergents, pharmaceuticals and medicals. This review represents a discussion on microbial sources of lipases, immobilization methods increased productivity at market profitability and reduce logistical liability on the environment and user.

Digital Manufacturing for Microfluidics

The microfluidics field is at a critical crossroads. The vast majority of microfluidic devices are presently manufactured using micromolding processes that work very well for a reduced set of biocompatible materials, but the time, cost, and design constraints of micromolding hinder the commercialization of many devices. As a result, the dissemination of microfluidic technology-and its impact on society-is in jeopardy. Digital manufacturing (DM) refers to a family of computer-centered processes that integrate digital three-dimensional (3D) designs, automated (additive or subtractive) fabrication, and device testing in order to increase fabrication efficiency. Importantly, DM enables the inexpensive realization of 3D designs that are impossible or very difficult to mold. The adoption of DM by microfluidic engineers has been slow, likely due to concerns over the resolution of the printers and the biocompatibility of the resins. In this article, we review and discuss the various printer types, resolution, biocompatibility issues, DM microfluidic designs, and the bright future ahead for this promising, fertile field.

Cell Lysis Based on an Oscillating Microbubble Array

Cell lysis is a process of breaking cell membranes to release intracellular substances such as DNA, RNA, protein, or organelles from a cell. The detection of DNA, RNA, or protein from the lysed cells is of importance for cancer diagnostics and drug screening. In this study, we develop a microbubble array that enables the realization of multiple cell lysis induced by the shear stress resulting from the individual oscillating microbubbles. The oscillating microbubbles in the channel have similar vibration amplitudes, and the intracellular substances can be released from the individual cells efficiently. Moreover, the efficiency of cell lysis increases with increments of input voltage and sonication time. By means of DNA agarose-gel electrophoresis, a sufficient extraction amount of DNA released from the lysed cells can be detected, and there is no significant difference in lysis efficiency when compared to cell lysis achieved using commercial kits. With the advantages of the simple manufacturing process, low cost, high efficiency, and high speed, this device can serve as an efficient and versatile tool for the single-cell sequencing of cell biology research, disease diagnosis, and stem cell therapy.

Versatile biomanufacturing through stimulus-responsive cell-material feedback

Small-scale production of biologics has great potential for enhancing the accessibility of biomanufacturing. By exploiting cell-material feedback, we have designed a concise platform to achieve versatile production, analysis and purification of diverse proteins and protein complexes. The core of our technology is a microbial swarmbot, which consists of a stimulus-sensitive polymeric microcapsule encapsulating engineered bacteria. By sensing the confinement, the bacteria undergo programmed partial lysis at a high local density. Conversely, the encapsulating material shrinks responding to the changing chemical environment caused by cell growth, squeezing out the protein products released by bacterial lysis. This platform is then integrated with downstream modules to enable quantification of enzymatic kinetics, purification of diverse proteins, quantitative control of protein interactions and assembly of functional protein complexes and multienzyme metabolic pathways. Our work demonstrates the use of the cell-material feedback to engineer a modular and flexible platform with sophisticated yet well-defined programmed functions.

Microfluidic platform for rapid screening of bacterial cell lysis

Over the past decade significant progress has been found in the upstream production processes, shifting the main bottlenecks in current manufacturing platforms for biopharmaceuticals towards the downstream processing. Challenges in the purification process include reducing the production costs, developing robust and efficient purification processes as well as integrating both upstream and downstream processes. Microfluidic technologies have recently emerged as effective tools for expediting bioprocess design in a cost-effective manner, since a large number of variables can be evaluated in a small time frame, using reduced volumes and manpower. Their modularity also allows to integrate different unit operations into a single chip, and consequently to evaluate the effect of each stage on the overall process efficiency. This paper describes the development of a diffusion-based microfluidic device for the rapid screening of continuous chemical lysis conditions. The release of a recombinant green fluorescent protein (GFP) expressed in Escherichia coli (E. coli) was used as model system due to the simple evaluation of cell growth and product concentration by fluorescence. The concept can be further applied to any biopharmaceutical production platform. The microfluidic device was successfully used to test the lytic effect of both enzymatic and chemical lysis solutions, with lysis efficiency of about 60% and close to 100%, respectively, achieved. The microfluidic technology also demonstrated the ability to detect potential process issues, such as the increased viscosity related with the rapid release of genomic material, that can arise for specific lysis conditions and hinder the performance of a bioprocess. Finally, given the continuous operation of the lysis chip, the microfluidic technology has the potential to be integrated with other microfluidic modules in order to model a fully continuous biomanufacturing process on a chip.

Converting Any Faradaic Current Generated at an Electrode under Potentiostatic Control into a Remote Fluorescence Signal

We describe the development of an original faradaic current-to-fluorescence conversion scheme. The proposed instrumental strategy consists of coupling the electrochemical reaction of any species at an electrode under potentiostatic control with the fluorescence emission of a species produced at the counter electrode. In order to experimentally validate this scheme, the fluorogenic species resazurin is chosen as a fluorescent reporter molecule, and its complex reduction mechanism is first studied in unprecedented detail. This kinetic study is carried out by recording simultaneous cyclic voltammograms and voltfluorograms at the same electrode. Numerical simulations are used to account for the experimental current and fluorescence signals, to analyze their degree of correlation, and to decipher their relation to resazurin reduction kinetics. It is then shown that, provided that the reduction of resazurin takes place at a micrometer-sized electrode, the fluorescence emission perfectly tracks the faradaic current. By implementing this ideal configuration at the counter electrode of a potentiostatic setup, it is finally demonstrated that the oxidation reaction of a nonfluorescent species at the working electrode can be quantitatively transduced into simultaneous emission of fluorescence.

Engineering Nanowire-Mediated Cell Lysis for Microbial Cell Identification

Researchers have demonstrated great promise for inorganic nanowire use in analyzing cells or intracellular components. Although a stealth effect of nanowires toward cell surfaces allows preservation of the living intact cells when analyzing cells, as a completely opposite approach, the applicability to analyze intracellular components through disrupting cells is also central to understanding cellular information. However, the reported lysis strategy is insufficient for microbial cell lysis due to the cell robustness and wrong approach taken so far ( i. e., nanowire penetration into a cell membrane). Here we propose a nanowire-mediated lysis method for microbial cells by introducing the rupture approach initiated by cell membrane stretching; in other words, the nanowires do not penetrate the membrane, but rather they break the membrane between the nanowires. Entangling cells with the bacteria-compatible and flexible nanowires and membrane stretching of the entangled cells, induced by the shear force, play important roles for the nanowire-mediated lysis to Gram-positive and Gram-negative bacteria and yeast cells. Additionally, the nanowire-mediated lysis is readily compatible with the loop-mediated isothermal amplification (LAMP) method because the lysis is triggered by simply introducing the microbial cells. We show that an integration of the nanowire-mediated lysis with LAMP provides a means for a simple, rapid, one-step identification assay (just introducing a premixed solution into a device), resulting in visual chromatic identification of microbial cells. This approach allows researchers to develop a microfluidic analytical platform not only for microbial cell identification including drug- and heat-resistance cells but also for on-site detection without any contamination.

Microfluidic reactors for advancing the MS analysis of fast biological responses

The response of cells to physical or chemical stimuli is complex, unfolding on time-scales from seconds to days, with or without de novo protein synthesis, and involving signaling processes that are transient or sustained. By combining the technology of microfluidics that supports fast and precise execution of a variety of cell handling operations, with that of mass spectrometry detection that facilitates an accurate and complex characterization of the protein complement of cells, in this work, we developed a platform that supports (near) real-time sampling and proteome-level capturing of cellular responses to a perturbation such as treatment with mitogens. The geometric design of the chip supports three critical features: (a) capture of a sufficient number of cells to meet the detection limit requirements of mass spectrometry instrumentation, (b) fluid delivery for uniform stimulation of the resident cells, and (c) fast cell recovery, lysis and processing for accurate sampling of time-sensitive cellular responses to a stimulus. COMSOL simulations and microscopy were used to predict and evaluate the flow behavior inside the microfluidic device. Proteomic analysis of the cellular extracts generated by the chip experiments revealed that the identified proteins were representative of all cellular locations, exosomes, and major biological processes related to proliferation and signaling, demonstrating that the device holds promising potential for integration into complex lab-on-chip work-flows that address systems biology questions. The applicability of the chips to study time-sensitive cellular responses is discussed in terms of technological challenges and biological relevance.

Demarcating the membrane damage for the extraction of functional mitochondria

Defective mitochondria have been linked to several critical human diseases such as neurodegenerative disorders, cancers and cardiovascular disease. However, the detailed characterization of mitochondria has remained relatively unexplored, largely due to the lack of effective extraction methods that may sufficiently retain the functionality of mitochondria, particularly when limited amount of sample is considered. In this study, we explore the possibility of modulating hydrodynamic stress through a cross-junction geometry at microscale to selectively disrupt the cellular membrane while mitochondrial membrane is secured. The operational conditions are empirically optimized to effectively shred the cell membranes while keeping mitochondria intact for the model mammalian cell lines, namely human embryonic kidney cells, mouse muscle cells and neuroblastoma cells. Unsurprisingly, the disruption of cell membranes with higher elastic moduli (neuroblastoma) requires elevated stress. This study also presents a comparative analysis of total protein yield and concentrations of extracted functional mitochondria with two commercially available mitochondria extraction approaches, the Dounce Homogenizer and the Qproteome® Mitochondria Isolation Kit, in a range of cell concentrations. Our findings show that the proposed "microscale cell shredder" yields at least 40% more functional mitochondria than the two other approaches and is able to preserve the morphological integrity of extracted mitochondria, particularly at low cell concentrations (5-20 × 104 cells/mL). Characterized by its capability of rapidly processing a limited quantity of samples (200 μL), demarcating the membrane damage through the proposed microscale cell shredder represents a novel strategy to extract subcellular organelles from clinical samples.

The Many Roads to an Ideal Paper-based Device

The recent Zika and Ebola virus outbreaks highlight the need for low-cost diagnostics that can be rapidly deployed and used outside of established clinical infrastructure. This demand for robust point-of-care (POC) diagnostics is further driven by the increasing burden of drug-resistant diseases, concern for food and water safety, and bioterrorism. As has been discussed in previous chapters, paper-based tests provide a simple and compelling solution to such needs.

A Laser-Engraving Technique for Portable Micropneumatic Oscillators

Microfluidic automation technology is at a stage where the complexity and cost of external hardware control often impose severe limitations on the size and functionality of microfluidic systems. Developments in autonomous microfluidics are intended to eliminate off-chip controls to enable scalable systems. Timing is a fundamental component of the digital logic required to manipulate fluidic flow. The authors present a self-driven pneumatic ring oscillator manufactured by assembling an elastomeric sheet of polydimethylsiloxane (PDMS) between two laser-engraved polymethylmethacrylate (PMMA) layers via surface activation through treatment with 3-aminopropyltriethoxysilane (APTES). The frequency of the fabricated oscillators is in the range of 3⁻7.5 Hz with a maximum of 14 min constant frequency syringe-powered operation. The control of a fluidic channel with the oscillator stages is demonstrated. The fabrication process represents an improvement in manufacturability compared to previous molding or etching approaches, and the resulting devices are inexpensive and portable, making the technology potentially applicable for wider use.

Rheological Droplet Interface Bilayers (rheo-DIBs): Probing the Unstirred Water Layer Effect on Membrane Permeability via Spinning Disk Induced Shear Stress

A new rheological droplet interface bilayer (rheo-DIB) device is presented as a tool to apply shear stress on biological lipid membranes. Despite their exciting potential for affecting high-throughput membrane translocation studies, permeability assays conducted using DIBs have neglected the effect of the unstirred water layer (UWL). However as demonstrated in this study, neglecting this phenomenon can cause significant underestimates in membrane permeability measurements which in turn limits their ability to predict key processes such as drug translocation rates across lipid membranes. With the use of the rheo-DIB chip, the effective bilayer permeability can be modulated by applying shear stress to the droplet interfaces, inducing flow parallel to the DIB membranes. By analysing the relation between the effective membrane permeability and the applied stress, both the intrinsic membrane permeability and UWL thickness can be determined for the first time using this model membrane approach, thereby unlocking the potential of DIBs for undertaking diffusion assays. The results are also validated with numerical simulations.

Implementation of antimicrobial peptides for sample preparation prior to nucleic acid amplification in point-of-care settings

BACKGROUND

A variety of sample preparation techniques are used prior to nucleic acid amplification. However, their efficiency is not always sufficient and nucleic acid purification remains the preferred method for template preparation. Purification is difficult and costly to apply in point-of-care (POC) settings and there is a strong need for more robust, rapid, and efficient biological sample preparation techniques in molecular diagnostics.

METHODS

Here, the authors applied antimicrobial peptides (AMPs) for urine sample preparation prior to isothermal loop-mediated amplification (LAMP). AMPs bind to many microorganisms such as bacteria, fungi, protozoa and viruses causing disruption of their membrane integrity and facilitate nucleic acid release.

RESULTS

The authors show that incubation of E. coli with antimicrobial peptide cecropin P1 for 5 min had a significant effect on the availability of template DNA compared with untreated or even heat treated samples resulting in up to six times increase of the amplification efficiency.

CONCLUSION

These results show that AMPs treatment is a very efficient sample preparation technique that is suitable for application prior to nucleic acid amplification directly within biological samples. Furthermore, the entire process of AMPs treatment was performed at room temperature for 5 min thereby making it a good candidate for use in POC applications.

A Review on Macroscale and Microscale Cell Lysis Methods

The lysis of cells in order to extract the nucleic acids or proteins inside it is a crucial unit operation in biomolecular analysis. This paper presents a critical evaluation of the various methods that are available both in the macro and micro scale for cell lysis. Various types of cells, the structure of their membranes are discussed initially. Then, various methods that are currently used to lyse cells in the macroscale are discussed and compared. Subsequently, popular methods for micro scale cell lysis and different microfluidic devices used are detailed with their advantages and disadvantages. Finally, a comparison of different techniques used in microfluidics platform has been presented which will be helpful to select method for a particular application.

A mechanical cell disruption microfluidic platform based on an on-chip micropump

Cell disruption plays a vital role in detection of intracellular components which contain information about genetic and disease characteristics. In this paper, we demonstrate a novel microfluidic platform based on an on-chip micropump for mechanical cell disruption and sample transport. A 50 μl cell sample can be effectively lysed through on-chip multi-disruption in 36 s without introducing any chemical agent and suffering from clogging by cellular debris. After 30 cycles of circulating disruption, 80.6% and 90.5% cell disruption rates were achieved for the HEK293 cell sample and human natural killer cell sample, respectively. Profiting from the feature of pump-on-chip, the highly integrated platform enables more convenient and cost-effective cell disruption for the analysis of intracellular components.

Multifunctional, inexpensive, and reusable nanoparticle-printed biochip for cell manipulation and diagnosis

Isolation and characterization of rare cells and molecules from a heterogeneous population is of critical importance in diagnosis of common lethal diseases such as malaria, tuberculosis, HIV, and cancer. For the developing world, point-of-care (POC) diagnostics design must account for limited funds, modest public health infrastructure, and low power availability. To address these challenges, here we integrate microfluidics, electronics, and inkjet printing to build an ultra-low-cost, rapid, and miniaturized lab-on-a-chip (LOC) platform. This platform can perform label-free and rapid single-cell capture, efficient cellular manipulation, rare-cell isolation, selective analytical separation of biological species, sorting, concentration, positioning, enumeration, and characterization. The miniaturized format allows for small sample and reagent volumes. By keeping the electronics separate from microfluidic chips, the former can be reused and device lifetime is extended. Perhaps most notably, the device manufacturing is significantly less expensive, time-consuming, and complex than traditional LOC platforms, requiring only an inkjet printer rather than skilled personnel and clean-room facilities. Production only takes 20 min (vs. up to weeks) and $0.01-an unprecedented cost in clinical diagnostics. The platform works based on intrinsic physical characteristics of biomolecules (e.g., size and polarizability). We demonstrate biomedical applications and verify cell viability in our platform, whose multiplexing and integration of numerous steps and external analyses enhance its application in the clinic, including by nonspecialists. Through its massive cost reduction and usability we anticipate that our platform will enable greater access to diagnostic facilities in developed countries as well as POC diagnostics in resource-poor and developing countries.

Electrophoretic Concentration and Electrical Lysis of Bacteria in a Microfluidic Device Using a Nanoporous Membrane

Pathogenic bacteria such as Escherichia coli O157, Salmonella and Campylobacter are the main causes for food and waterborne illnesses. Lysis of these bacteria is an important component of the sample preparation for molecular identification of these pathogens. The pathogenicity of these bacteria is so high that they cause illness at very low concentrations (1–10 CFU/100 mL). Hence, there is a need to develop methods to collect a small number of such bacterial cells from a large sample volume and process them in an automated reagent-free manner. An electrical method to concentrate the bacteria and lyse them has been chosen here as it is reagent free and hence more conducive for online and automated sample preparation. We use commercially available nanoporous membranes sandwiched between two microfluidic channels to create thousands of parallel nanopore traps for bacteria, electrophoretically accumulate and then lyse them. The nanopores produce a high local electric field for lysis at moderate applied voltages, which could simplify instrumentation and enables lysis of the bacteria as it approaches them under an appropriate range of electric field (>1000 V/cm). Accumulation and lysis of bacteria on the nanoporous membrane is demonstrated by using the LIVE/DEAD BacLight Bacterial Viability Kit and quantified by fluorescence intensity measurements. The efficiency of the device was determined through bacterial culture of the lysate and was found to be 90% when a potential of 300 V was applied for 3 min.

Spontaneous and specific binding of enterohemorrhagic Escherichia coli to overoxidized polypyrrole-coated microspheres

Specific identification of enterohemorrhagic Escherichia coli was achieved using microspheres coated with overoxidized polypyrrole.

Merging orthogonal microfluidic flows to generate multi-profile concentration gradients

This work describes a novel microfluidic device capable of generating multi-profile gradients that include sigmoidal, parabolic, and exponential concentration variations across its main channel.

Thin-Film Transistor-Based Biosensors for Determining Stoichiometry of Biochemical Reactions

The enzyme kinetic in a biochemical reaction is critical to scientific research and drug discovery but can hardly be determined experimentally from enzyme assays. In this work, a charge-current transducer (a transistor) is proposed to evaluate the status of biochemical reaction by monitoring the electrical charge changes. Using the malate-aspartate shuttle as an example, a thin-film transistor (TFT)-based biosensor with an extended gold pad is demonstrated to detect the biochemical reaction between NADH and NAD⁺. The drain current change indicates the status of chemical equilibrium and stoichiometry.

Recent developments in nanowires for bio-applications from molecular to cellular levels

This review highlights the most promising applications of nanowires for bioanalytical chemistry and medical diagnostics. The materials discussed here are metal oxide and Si semiconductors, which are integrated with various microfluidic systems. Nanowire structures offer desirable advantages such as a very small diameter size with a high aspect ratio and a high surface-to-volume ratio without grain boundaries; consequently, nanowires are promising tools to study biological systems. This review starts with the integration of nanowire structures into microfluidic systems, followed by the discussion of the advantages of nanowire structures in the separation, manipulation and purification of biomolecules (DNA, RNA and proteins). Next, some representative nanowire devices are introduced for biosensors from molecular to cellular levels based on electrical and optical approaches. Finally, we conclude the review by highlighting some bio-applications for nanowires and presenting the next challenges that must be overcome to improve the capabilities of nanowire structures for biological and medical systems.

3D-Printed Microfluidics

The advent of soft lithography allowed for an unprecedented expansion in the field of microfluidics. However, the vast majority of PDMS microfluidic devices are still made with extensive manual labor, are tethered to bulky control systems, and have cumbersome user interfaces, which all render commercialization difficult. On the other hand, 3D printing has begun to embrace the range of sizes and materials that appeal to the developers of microfluidic devices. Prior to fabrication, a design is digitally built as a detailed 3D CAD file. The design can be assembled in modules by remotely collaborating teams, and its mechanical and fluidic behavior can be simulated using finite-element modeling. As structures are created by adding materials without the need for etching or dissolution, processing is environmentally friendly and economically efficient. We predict that in the next few years, 3D printing will replace most PDMS and plastic molding techniques in academia.

A bactericidal microfluidic device constructed using nano-textured black silicon

Nano-structured black silicon (bSi) was used as a substratum for the construction of a microfluidic device of the highly efficient bactericidal action of this nano-textured surface againstPseudomonas aeruginosabacteria.

Two-layer Lab-on-a-chip (LOC) with passive capillary valves for mHealth medical diagnostics

There is a new potential to address needs for medical diagnostics in Point-of-Care (PoC) applications using mHealth (Mobile computing, medical sensors, and communications technologies for health care), a mHealth based lab test will require a LOC to perform clinical analysis. In this work, we describe the design of a simple Lab-on-a-chip (LOC) platform for mHealth medical diagnostics. The LOC utilizes a passive capillary valve with no moving parts for fluid control using channels with very low aspect ratios cross sections (i.e., channel width ≫ height) achieved through transitions in the channel geometry via that arrest capillary flow. Using a CO2 laser in raster engraving mode, we have designed and fabricated an eight-channel LOC for fluorescence signal detection fabricated by engraving and combining just two polymer layers. Each of the LOC channels is capable of mixing two reagents (e.g., enzyme and substrate) for various assays. For mHealth detection, we used a mobile CCD detector equipped with LED multispectral illumination in the red, green, blue, and white range. This technology enables the development of low-cost LOC platforms for mHealth whose fabrication is compatible with standard industrial plastic fabrication processes to enable mass production of mHealth diagnostic devices, which may broaden the use of LOCs in PoC applications, especially in global health settings.

Microfluidic Platform for Studying Chemotaxis of Adhesive Cells Revealed a Gradient-Dependent Migration and Acceleration of Cancer Stem Cells

Recent studies reveal that solid tumors consist of heterogeneous cells with distinct phenotypes and functions. However, it is unclear how different subtypes of cancer cells migrate under chemotaxis. Here, we developed a microfluidic device capable of generating multiple stable gradients, culturing cells on-chip, and monitoring single cell migratory behavior. The microfluidic platform was used to study gradient-induced chemotaxis of lung cancer stem cell (LCSC) and differentiated LCSC (dLCSC) in real time. Our results showed the dynamic and differential response of both LCSC and dLCSC to chemotaxis, which was regulated by the β-catenin dependent Wnt signaling pathway. The microfluidic analysis showed that LCSC and dLCSC from the same origin behaved differently in the same external stimuli, suggesting the importance of cancer cell heterogeneity. We also observed for the first time the acceleration of both LCSC and dLCSC during chemotaxis caused by increasing local concentration in different gradients, which could only be realized through the microfluidic approach. The capability to analyze single cell chemotaxis under spatially controlled conditions provides a novel analytical platform for the study of cellular microenvironments and cancer cell metastasis.

Polymer Coatings in 3D-Printed Fluidic Device Channels for Improved Cellular Adherence Prior to Electrical Lysis

This paper describes the design and fabrication of a polyjet-based three-dimensional (3D)-printed fluidic device where poly(dimethylsiloxane) (PDMS) or polystyrene (PS) were used to coat the sides of a fluidic channel within the device to promote adhesion of an immobilized cell layer. The device was designed using computer-aided design software and converted into an .STL file prior to printing. The rigid, transparent material used in the printing process provides an optically transparent path to visualize endothelial cell adherence and supports integration of removable electrodes for electrical cell lysis in a specified portion of the channel (1 mm width × 0.8 mm height × 2 mm length). Through manipulation of channel geometry, a low-voltage power source (500 V max) was used to selectively lyse adhered endothelial cells in a tapered region of the channel. Cell viability was maintained on the device over a 5 day period (98% viable), though cell coverage decreased after day 4 with static media delivery. Optimal lysis potentials were obtained for the two fabricated device geometries, and selective cell clearance was achieved with cell lysis efficiencies of 94 and 96%. The bottleneck of unknown surface properties from proprietary resin use in fabricating 3D-printed materials is overcome through techniques to incorporate PDMS and PS.

Rapidly prototyped multi-scale electrodes to minimize the voltage requirements for bacterial cell lysis

Lab-on-a-chip systems used for nucleic acid based detection of bacteria rely on bacterial lysis for the release of cellular material. Although electrical lysis devices can be miniaturized for on-chip integration and reagent-free lysis, they often suffer from high voltage requirements, and rely on the use of off-chip voltage supplies. To overcome this barrier, we developed a rapid prototyping method for creating multi-scale electrodes that are structurally tuned for lowering the voltage needed for electrical bacterial lysis. These three-dimensional multi-scale electrodes – with micron scale reaction areas and nanoscale features – are fabricated using benchtop methods including craft cutting, polymer-induced wrinkling, and electrodeposition, which enable a lysis device to be designed, fabricated, and optimized in a matter of hours. These tunable electrodes show superior behaviour compared to lithographically-prepared electrodes in terms of lysis efficiency and voltage requirement. Successful extraction of nucleic acids from bacterial samples processed by these electrodes demonstrates the potential for these rapidly prototyped devices to be integrated within practical lab-on-a-chip systems.

All-in-one nanowire-decorated multifunctional membrane for rapid cell lysis and direct DNA isolation

This paper describes a handheld device that uses an all-in-one membrane for continuous mechanical cell lysis and rapid DNA isolation without the assistance of power sources, lysis reagents, and routine centrifugation. This nanowire-decorated multifunctional membrane was fabricated to isolate DNA by selective adsorption to silica surface immediately after disruption of nucleus membranes by ultrasharp tips of nanowires for a rapid cell lysis, and it can be directly assembled with commercial syringe filter holders. The membrane was fabricated by photoelectrochemical etching to create microchannel arrays followed by hydrothermal synthesis of nanowires and deposition of silica. The proposed membrane successfully purifies high-quality DNA within 5 min, whereas a commercial purification kit needs more than an hour.

Real-time digitization of metabolomics patterns from a living system using mass spectrometry

The real-time quantification of changes in intracellular metabolic activities has the potential to vastly improve upon traditional transcriptomics and metabolomics assays for the prediction of current and future cellular phenotypes. This is in part because intracellular processes reveal themselves as specific temporal patterns of variation in metabolite abundance that can be detected with existing signal processing algorithms. Although metabolite abundance levels can be quantified by mass spectrometry (MS), large-scale real-time monitoring of metabolite abundance has yet to be realized because of technological limitations for fast extraction of metabolites from cells and biological fluids. To address this issue, we have designed a microfluidic-based inline small molecule extraction system, which allows for continuous metabolomic analysis of living systems using MS. The system requires minimal supervision, and has been successful at real-time monitoring of bacteria and blood. Feature-based pattern analysis of Escherichia coli growth and stress revealed cyclic patterns and forecastable metabolic trajectories. Using these trajectories, future phenotypes could be inferred as they exhibit predictable transitions in both growth and stress related changes. Herein, we describe an interface for tracking metabolic changes directly from blood or cell suspension in real-time.

Fabrication of rigid microstructures with thiol-ene-based soft lithography for continuous-flow cell lysis

In this work, we introduce a method for the soft-lithography-based fabrication of rigid microstructures and a new, simple bonding technique for use as a continuous-flow cell lysis device. While on-chip cell lysis techniques have been reported previously, these techniques generally require a long on-chip residence time, and thus cannot be performed in a rapid, continuous-flow manner. Microstructured microfluidic devices can perform mechanical lysis of cells, enabling continuous-flow lysis; however, rigid silicon-based devices require complex and expensive fabrication of each device, while polydimethylsiloxane (PMDS), the most common material used for soft lithography fabrication, is not rigid and expands under the pressures required, resulting in poor lysis performance. Here, we demonstrate the fabrication of microfluidic microstructures from off-stoichiometry thiol-ene (OSTE) polymer using soft-lithography replica molding combined with a post-assembly cure for easy bonding. With finite element simulations, we show that the rigid microstructures generate an energy dissipation rate of nearly 10(7), which is sufficient for continuous-flow cell lysis. Correspondingly, with the OSTE device we achieve lysis of highly deformable MDA-MB-231 breast cancer cells at a rate of 85%, while a comparable PDMS device leads to a lysis rate of only 40%.

Spatially selecting a single cell for lysis using light-induced electric fields

An optoelectronic tweezing (OET) device, within an integrated microfluidic channel, is used to precisely select single cells for lysis among dense populations. Cells to be lysed are exposed to higher electrical fields than their neighbours by illuminating a photoconductive film underneath them. Using beam spot sizes as low as 2.5 μm, 100% lysis efficiency is reached in <1 min allowing the targeted lysis of cells.