Nanoporous elements in microfluidics for multiscale manipulation of bioparticles

Visualization and Analysis of Mapping Knowledge Domain of Fluid Flow Related to Microfluidic Chip

Microfluidic chips are important tools to study the microscopic flow of fluid. To better understand the research clues and development trends related to microfluidic chips, a bibliometric analysis of microfluidic chips was conducted based on 1115 paper records retrieved from the Web of Science Core Collection database. CiteSpace and VOSviewer software were used to analyze the distribution of annual paper quantity, country/region distribution, subject distribution, institution distribution, major source journals distribution, highly cited papers, coauthor cooperation relationship, research knowledge domain, research focuses, and research frontiers, and a knowledge domain map was drawn. The results show that the number of papers published on microfluidic chips increased from 2010 to 2023, among which China, the United States, Iran, Canada, and Japan were the most active countries in this field. The United States was the most influential country. Nanoscience, energy, and chemical industry and multidisciplinary materials science were the main fields of microfluidic chip research. Lab on a Chip, Microfluidics and Nanofluidics, and Journal of Petroleum Science and Engineering were the main sources of papers published. The fabrication of chips, as well as their applications in porous media flow and multiphase flow, is the main knowledge domain of microfluidic chips. Micromodeling, fluid displacement, wettability, and multiphase flow are the research focuses in this field currently. The research frontiers in this field are enhanced oil recovery, interfacial tension, and stability.

Novel Isolating Approaches to Circulating Tumor Cell Enrichment Based on Microfluidics: A Review

Circulating tumor cells (CTCs), derived from the primary tumor and carrying genetic information, contribute significantly to the process of tumor metastasis. The analysis and detection of CTCs can be used to assess the prognosis and treatment response in patients with tumors, as well as to help study the metastatic mechanisms of tumors and the development of new drugs. Since CTCs are very rare in the blood, it is a challenging problem to enrich CTCs efficiently. In this paper, we provide a comprehensive overview of microfluidics-based enrichment devices for CTCs in recent years. We explore in detail the methods of enrichment based on the physical or biological properties of CTCs; among them, physical properties cover factors such as size, density, and dielectric properties, while biological properties are mainly related to tumor-specific markers on the surface of CTCs. In addition, we provide an in-depth description of the methods for enrichment of single CTCs and illustrate the importance of single CTCs for performing tumor analyses. Future research will focus on aspects such as improving the separation efficiency, reducing costs, and increasing the detection sensitivity and accuracy.

Seamless Integration of Rapid Separation and Ultrasensitive Detection for Complex Biological Samples Using Multistage Annular Functionalized Carbon Nanotube Arrays

Efficient separation, enrichment, and detection of bacteria in diverse media are pivotal for identifying bacterial diseases and their transmission pathways. However, conventional bacterial detection methods that split the separation and detection steps are plagued by prolonged processing times. Herein, a multistage annular functionalized carbon nanotube array device designed for the seamless integration of complex biological sample separation and multimarker detection is introduced. This device resorts to the supersmooth fluidity of the liquid sample in the carbon nanotubes interstice through rotation assistance, achieving the ability to quickly separate impurities and capture biomarkers (1 mL sample cost time of 2.5 s). Fluid dynamics simulations show that the reduction of near-surface hydrodynamic resistance drives the capture of bacteria and related biomarkers on the functionalized surface of carbon nanotube in sufficient time. When further assembled as an even detection device, it exhibited fast detection (<30 min), robust linear correlation (101-107 colony-forming units [CFU] mL-1, R2 = 0.997), ultrasensitivity (limit of detection = 1.7 CFU mL-1), and multitarget detection (Staphylococcus aureus, extracellular vesicles, and enterotoxin proteins). Collectively, the material and system offer an expanded platform for real-time diagnostics, enabling integrated rapid separation and detection of various disease biomarkers.

Biporous silica nanostructure-induced nanovortex in microfluidics for nucleic acid enrichment, isolation, and PCR-free detection

Efficient pathogen enrichment and nucleic acid isolation are critical for accurate and sensitive diagnosis of infectious diseases, especially those with low pathogen levels. Our study introduces a biporous silica nanofilms-embedded sample preparation chip for pathogen and nucleic acid enrichment/isolation. This chip features unique biporous nanostructures comprising large and small pore layers. Computational simulations confirm that these nanostructures enhance the surface area and promote the formation of nanovortex, resulting in improved capture efficiency. Notably, the chip demonstrates a 100-fold lower limit of detection compared to conventional methods used for nucleic acid detection. Clinical validations using patient samples corroborate the superior sensitivity of the chip when combined with the luminescence resonance energy transfer assay. The enhanced sample preparation efficiency of the chip, along with the facile and straightforward synthesis of the biporous nanostructures, offers a promising solution for polymer chain reaction-free detection of nucleic acids.

Spatio-temporal programming of lyotropic phase transition in nanoporous microfluidic confinements

HYPOTHESIS

The nanoporous polydimethylsiloxane (PDMS) surfaces of a rectangular microfluidic channel, selectively uptakes water molecules, concentrating the solute molecules in an aqueous phase, that could drive phase transitions. Factors such as surface wettability, channel geometry, the surface-to-volume ratio, and surface topography of the confinements could play a key role in tuning the phase transitions spatio-temporally.

EXPERIMENTS

Using a lyotropic chromonic liquid crystal as model biological material, confined within nanoporous microfluidic environments, we study molecular assembly driven by nanoporous substrates. By combining timelapse polarized imaging, quantitative image processing, and a simple mathematical model, we analyze the phase transitions and construct a master diagram capturing the role of surface wettability, channel geometry and embedded topography on programmable lyotropic phase transitions.

FINDINGS

Intrinsic PDMS nanoporosity and confinement cross-section, together with the imposed wettability regulate the rate of the N-M phase transition; whereas the microfluidic geometry and embedded topography enable phase transition at targeted locations. We harness the emergent long-range order during N-M transition to actuate elasto-advective transport of embedded micro-cargo, demonstrating particle manipulation concepts governed by tunable phase transitions. Our results present a programmable physical route to material assembly in microfluidic environment, and offer a new paradigm for assembling genetic components, biological cargo, and minimal synthetic cells.

Rational design of multivalent biosensor surfaces to enhance viral particle capture

Viral particles bind to receptors through multivalent protein interactions. Such high avidity interactions on sensor surfaces are less studied. In this work, three polyelectrolytes that can form biosensing surfaces with different interfacial characteristics in probe density and spatial arrangement were designed. Quartz crystal microbalance, interferometry and atomic force microscopy were used to study their surface density and binding behaviors with proteins and virus particles. A multivalent adsorption kinetic model was developed to estimate the number of bonds from the viral particles bound to the polyelectrolyte surfaces. Experimental results show that the heterogeneous 3D surface with jagged forest-like structure enhances the virus capture ability by maximizing the multivalent interactions. As a proof of concept, specific coronavirus detection was achieved in spiked swab samples. These results indicate the importance of both probe density and their spatial arrangement on the sensing performance, which could be used as a guideline for rational biosensing surface design.

Isolation, Detection and Analysis of Circulating Tumour Cells: A Nanotechnological Bioscope

Cancer is one of the dreaded diseases to which a sizeable proportion of the population succumbs every year. Despite the tremendous growth of the health sector, spanning diagnostics to treatment, early diagnosis is still in its infancy. In this regard, circulating tumour cells (CTCs) have of late grabbed the attention of researchers in the detection of metastasis and there has been a huge surge in the surrounding research activities. Acting as a biomarker, CTCs prove beneficial in a variety of aspects. Nanomaterial-based strategies have been devised to have a tremendous impact on the early and rapid examination of tumor cells. This review provides a panoramic overview of the different nanotechnological methodologies employed along with the pharmaceutical purview of cancer. Initiating from fundamentals, the recent nanotechnological developments toward the detection, isolation, and analysis of CTCs are comprehensively delineated. The review also includes state-of-the-art implementations of nanotechnological advances in the enumeration of CTCs, along with future challenges and recommendations thereof.

Fluid nanoporous microinterface enables multiscale-enhanced affinity interaction for tumor-derived extracellular vesicle detection

Tumor-derived extracellular vesicles (T-EVs) represent valuable markers for tumor diagnosis and treatment guidance. However, nanoscale sizes and the low abundance of marker proteins of T-EVs restrict interfacial affinity reaction, leading to low isolation efficiency and detection sensitivity. Here, we engineer a fluid nanoporous microinterface (FluidporeFace) in a microfluidic chip by decorating supported lipid bilayers (SLBs) on nanoporous herringbone microstructures with a multiscale-enhanced affinity reaction for efficient isolation of T-EVs. At the microscale level, the herringbone micropattern promotes the mass transfer of T-EVs to the surface. At the nanoscale level, nanoporousity can overcome boundary effects for close contact between T-EVs and the interface. At the molecular level, fluid SLBs afford clustering of recognition molecules at the binding site, enabling multivalent binding with an ∼83-fold increase of affinity compared with the nonfluid interface. With the synergetic enhanced mass transfer, interface contact, and binding affinity, FluidporeFace affords ultrasensitive detection of T-EVs with a limit of detection of 10 T-EVs μL −1 , whose PD-L1 expression levels successfully distinguish cancer patients from healthy donors. We expect this multiscale enhanced interfacial reaction strategy will inspire the biosensor design and expand liquid biopsy applications, especially for low-abundant targets in clinical samples.

Ultrasensitive Analysis of Exosomes Using a 3D Self-Assembled Nanostructured SiO2 Microfluidic Chip

Conventional microfluidics with a solid mixer for exosome detection is constrained by the low binding efficiency of the solid-liquid boundary effects and reduced sensitivity of individual markers. Here, we report a 3D-SiO₂ porous chip that combines nanoscale porous characteristics and multiple exosome specific markers to greatly improve the sensitivity for biosensing. The lower limit of detection was 220 particles/μL exosomes in PBS. We applied the 3D-SiO₂ porous chip for prostate cancer (PCa) staging in mice and early detection of clinical PCa patients. The developed method could significantly differentiate the different stages of PCa in mice and improve the early detection rate in clinical patients. Expression of multiple specific markers in clinical serum samples identified disease fingerprints, alongside histological results, which supports the potential application of exosomes as a noninvasive surrogate biopsy for PCa.

Vertically Aligned Carbon Nanotubes as a Unique Material for Biomedical Applications

Vertically aligned carbon nanotubes (VACNTs), a unique classification of CNT, highly oriented and normal to the respective substrate, have been heavily researched over the last two decades. Unlike randomly oriented CNT, VACNTs have demonstrated numerous advantages making it an extremely desirable nanomaterial for many biomedical applications. These advantages include better spatial uniformity, increased surface area, greater susceptibility to functionalization, improved electrocatalytic activity, faster electron transfer, higher resolution in sensing, and more. This Review discusses VACNT and its utilization in biomedical applications particularly for sensing, biomolecule filtration systems, cell stimulation, regenerative medicine, drug delivery, and bacteria inhibition. Furthermore, comparisons are made between VACNT and its traditionally nonaligned, randomly oriented counterpart. Thus, we aim to provide a better understanding of VACNT and its potential applications within the community and encourage its utilization in the future.

Bifurcations in flows of complex fluids around microfluidic cylinders

Flow around a cylinder is a classical problem in fluid dynamics and also one of the benchmarks for testing viscoelastic flows. The problem is of wide relevance to understanding many microscale industrial and biological processes and applications, such as porous media and mucociliary flows. In recent years, we have developed model microfluidic geometries consisting of very slender cylinders fabricated in glass by selective laser-induced etching. The cylinder radius is small compared with the channel width, which allows the effects of the stagnation points in the flow to dominate over the effects of squeezing between the cylinder and the channel walls. Furthermore, the cylinders are contained in high aspect ratio microchannels that render the flow field approximately two-dimensional (2D) and therefore conveniently permit comparison between experiments and 2D numerical simulations. A number of different viscoelastic fluids including wormlike micellar and various polymer solutions have been tested in our devices. Of particular interest to us has been the occurrence of a striking, steady-in-time, flow asymmetry that occurs for certain non-Newtonian fluids when the dimensionless Weissenberg number (quantifying the importance of elastic over viscous forces in the flow) increases above a critical value. In this perspective review, we present a summary of our key findings related to this novel flow instability and present our current understanding of the mechanism for its onset and growth. We believe that the same fundamental mechanism may also underlie some important non-Newtonian phenomena observed in viscoelastic flows around particles, drops, and bubbles, or through geometries composed of multiple bifurcation points such as cylinder arrays and other porous media. Knowledge of the instability we discuss will be important to consider in the design of optimally functional lab-on-a-chip devices in which viscoelastic fluids are to be used.

A Novel Microfluidic Chip for Fast, Sensitive Quantification of Plasma Extracellular Vesicles as Biomarkers in Patients With Osteosarcoma

Plasma circulating extracellular vesicle (EV) has emerged as a promising biomarker for diagnosis and prognosis of various epithelial tumors. However, fast and efficient capture of EVs with microfluidic chip in sarcoma remains to be established. Herein, we reported a ZnO-nanorods integrated (ZNI) microfluidic chip, where EV capture antibody was uniformly grafted to the surface of the ZnO-nanorods of the chip to enhance the plasma turbulence formation and the capture efficiency at the micro-scale. Based on osteosarcoma (OS) cell line, we demonstrated that a combination of CD81 and CD63 antibody on ZNI chip yielded the greatest amount of total EVs, with an extra sensitive limit of detection (LOD) of ~10⁴ particles mL^-1. Furthermore, the addition of fluorescent labeling of Vimentin (VIM), a previously reported sarcoma cell surface biomarker, could enabled the dual visualization of total plasma EVs and VIM-positive EVs from OS patients' plasma. Based on our ZNI chip, we found that the amount of plasma total EVs was significantly different between OS and healthy donors (1562 a.u. versus 639 a.u., p< 0.05), but not between metastatic and nonmetastatic OS (p> 0.05). Interestingly, patients with metastatic disease had a significantly greater amount of VIM-positive EVs (1411 a.u. versus 231 a.u.., p< 0.05) and increased VIM-positive/total EVs ratio (0.943 versus 0.211, p< 0.05) in comparison with the nonmetastatic counterpart. Therefore, our ZNI microfluidic chip has great potential for the fast quantification of plasma EVs, and the microfluidic-based quantification of total and VIM-positive EVs might serve as a promising biomarker for the diagnosis and surveillance in OS patients.

Exosomal analysis: Advances in biosensor technology

Exosomes, a subtype of extracellular vesicle secreted by cells, have been a subject of intense research interest. Unfortunately, a simple and reliable method to separate exosomes has yet to be developed. As can be expected, the lack of a standardized method for extraction and purification has contributed to suboptimal inter-laboratory correlation and difficulty in comparison studies. Traditional techniques such as centrifugation, immunoaffinity and size exclusion chromatography, suffer from low purity and tend to be labor intensive thus making their use limited. To mitigate these drawbacks, an integrated biosensor-based exosome separation and detection has recently been developed. In this review, we examine five biosensors that use a variety of detection technology (colorimetric, fluorescent, surface plasmon resonance, surface-enhanced Raman scattering and electrochemical) and propose thoughts on standardization of exosomal analysis.

Aptamer-based nanostructured interfaces for the detection and release of circulating tumor cells

Analysis of circulating tumor cells (CTCs) can provide significant clinical information for tumors, which has proven to be helpful for cancer diagnosis, prognosis monitoring, treatment efficacy, and personalized therapy. However, CTCs are an extremely rare cell population, which challenges the isolation of CTCs from patient blood. Over the last few decades, many strategies for CTC detection have been developed based on the physical and biological properties of CTCs. Among them, nanostructured interfaces have been widely applied as CTC detection platforms to overcome the current limitations associated with CTC capture. Furthermore, aptamers have attracted significant attention in the detection of CTCs due to their advantages, including good affinity, low cost, easy modification, excellent stability, and low immunogenicity. In addition, effective and nondestructive release of CTCs can be achieved by aptamer-mediated methods that are used under mild conditions. Herein, we review some progress in the detection and release of CTCs through aptamer-functionalized nanostructured interfaces.

Carbon nanotubes for rapid capturing of SARS-COV-2 virus: revealing a mechanistic aspect of binding based on computational studies

We investigate the binding interactions of synthesized multi-walled carbon nanotubes (MWCNTs) with SARS-CoV-2 virus. Two essential components of the SARS-CoV-2 structure i.e.6LU7 (main protease of SARS-CoV-2) and 6LZG (spike receptor-binding domain complexed with its receptor ACE2) were used for computational studies. MWCNTs of different morphologies (zigzag, armchair and chiral) were synthesized through a thermal chemical vapour deposition process as a function of pyrolysis temperature. A direct correlation between radius to volume ratio of the synthesized MWCNTs and the binding energies for all three (zigzag, armchair and chiral) conformations were observed in our computational studies. Our result suggests that MWCNTs interact with the active sites of the main protease along with the host angiotensin-converting enzyme2 (ACE2) receptors. Furthermore, it is also observed that MWCNTs have significant binding affinities towards SARS-CoV-2. However, the highest free binding energy of -87.09 kcal mol-1 with 6LZG were shown by the armchair MWCNTs with SARS-CoV-2 through the simulated molecular dynamic trajectories, which could alter the SARS-CoV-2 structure with higher accuracy. The radial distribution function also confirms the density variation as a function of distance from a reference particle of MWCNTs for the study of interparticle interactions of the MWCNT and SARS-CoV-2. Due to these interesting attributes, such MWCNTs could find potential application in personal protective equipment (PPE) and diagnostic kits.

Urine biopsy technologies: Cancer and beyond

Since the discovery of circulating tumor cells in 1869, technological advances in the study of biomarkers from liquid biopsy have made it possible to diagnose disease in a less invasive way. Although blood-based liquid biopsy has been used extensively for the detection of solid tumors and immune diseases, the potential of urine-based liquid biopsy has not been fully explored. Advancements in technologies for the harvesting and analysis of biomarkers are providing new opportunities for the characterization of other disease types. Liquid biopsy markers such as exfoliated bladder cancer cells, cell-free DNA (cfDNA), and exosomes have the potential to change the nature of disease management and care, as they allow a cost-effective and convenient mode of patient monitoring throughout treatment. In this review, we addressed the advancement of research in the field of disease detection for the key liquid biopsy markers such as cancer cells, cfDNA, and exosomes, with an emphasis on urine-based liquid biopsy. First, we highlighted key technologies that were widely available and used extensively for clinical urine sample analysis. Next, we presented recent technological developments in cell and genetic research, with implications for the detection of other types of diseases, besides cancer. We then concluded with some discussions on these areas, emphasizing the role of microfluidics and artificial intelligence in advancing point-of-care applications. We believe that the benefits of urine biopsy provide diagnostic development potential, which will pave opportunities for new ways to guide treatment selections and facilitate precision disease therapies.

A Review on Microdevices for Isolating Circulating Tumor Cells

Cancer metastasis is the primary cause of high mortality of cancer patients. Enumeration of circulating tumor cells (CTCs) in the bloodstream is a very important indicator to estimate the therapeutic outcome in various metastatic cancers. The aim of this article is to review recent developments on the CTC isolation technologies in microdevices. Based on the categories of biochemical and biophysical isolation approaches, a literature review and in-depth discussion will be included to provide an overview of this challenging topic. The current excellent developments suggest promising CTC isolation methods in order to establish a precise indicator of the therapeutic outcome of cancer patients.

Recent Advances in Microfluidic Platforms Applied in Cancer Metastasis: Circulating Tumor Cells' (CTCs) Isolation and Tumor-On-A-Chip

Cancer remains the leading cause of death worldwide despite the enormous efforts that are made in the development of cancer biology and anticancer therapeutic treatment. Furthermore, recent studies in oncology have focused on the complex cancer metastatic process as metastatic disease contributes to more than 90% of tumor-related death. In the metastatic process, isolation and analysis of circulating tumor cells (CTCs) play a vital role in diagnosis and prognosis of cancer patients at an early stage. To obtain relevant information on cancer metastasis and progression from CTCs, reliable approaches are required for CTC detection and isolation. Additionally, experimental platforms mimicking the tumor microenvironment in vitro give a better understanding of the metastatic microenvironment and antimetastatic drugs' screening. With the advancement of microfabrication and rapid prototyping, microfluidic techniques are now increasingly being exploited to study cancer metastasis as they allow precise control of fluids in small volume and rapid sample processing at relatively low cost and with high sensitivity. Recent advancements in microfluidic platforms utilized in various methods for CTCs' isolation and tumor models recapitulating the metastatic microenvironment (tumor-on-a-chip) are comprehensively reviewed. Future perspectives on microfluidics for cancer metastasis are proposed.

Circulating Tumor Cell Enrichment Technologies

Circulating tumor cells (CTCs) are responsible for the metastatic spread of cancer and therefore are extremely valuable not only for basic research on cancer metastasis but also as potential biomarkers in diagnosing and managing cancer in the clinic. While relatively non-invasive access to the blood tissue presents an opportunity, CTCs are mixed with approximately billion-times more-populated blood cells in circulation. Therefore, the accuracy of technologies for reliable enrichment of the rare CTC population from blood samples is critical to the success of downstream analyses. The focus of this chapter is to provide the reader an overview of significant advances made in the development of diverse CTC enrichment technologies by presenting the strengths of individual techniques in addition to specific challenges remaining to be addressed.

Hybrid negative enrichment of circulating tumor cells from whole blood in a 3D-printed monolithic device

Isolation and analysis of circulating tumor cells (CTCs) from blood samples present exciting opportunities for basic cancer research and personalized treatment of the disease. While microchip-based negative CTC enrichment offers both sensitive microfluidic cell screening and unbiased selection, conventional microchips are inherently limited by their capacity to deplete a large number of normal blood cells. In this paper, we use 3D printing to create a monolithic device that combines immunoaffinity-based microfluidic cell capture and a commercial membrane filter for negative enrichment of CTCs directly from whole blood. In our device, stacked layers of chemically-functionalized microfluidic channels capture millions of white blood cells (WBCs) in parallel without getting saturated and the leuko-depleted blood is post-filtered with a 3 μm-pore size membrane filter to eliminate anucleated blood cells. This hybrid negative enrichment approach facilitated direct extraction of viable CTCs off the chip on a membrane filter for downstream analysis. Immunofluorescence imaging of enriched cells showed ∼90% tumor cell recovery rate from simulated samples spiked with prostate, breast or ovarian cancer cells. We also demonstrated the feasibility of our approach for processing clinical samples by isolating prostate cancer CTCs directly from a 10 mL whole blood sample.

Tangential Flow Microfiltration for Viral Separation and Concentration

Microfluidic devices that allow biological particle separation and concentration have found wide applications in medical diagnosis. Here we present a viral separation polydimethylsiloxane (PDMS) device that combines tangential flow microfiltration and affinity capture to enrich HIV virus in a single flow-through fashion. The set-up contains a filtration device and a tandem resistance channel. The filtration device consists of two parallel flow channels separated by a polycarbonate nanoporous membrane. The resistance channel, with dimensions design-guided by COMSOL simulation, controls flow permeation through the membrane in the filtration device. A flow-dependent viral capture efficiency is observed, which likely reflects the interplay of several processes, including specific binding of target virus, physical deposition of non-specific particles, and membrane cleaning by shear flow. At the optimal flow rate, nearly 100% of viral particles in the permeate are captured on the membrane with various input viral concentrations. With its easy operation and consistent performance, this microfluidic device provides a potential solution for HIV sample preparation in resource-limited settings.

Microfluidic technologies for circulating tumor cell isolation

Metastasis is the main cause of tumor-related death, and the dispersal of tumor cells through the circulatory system is a critical step in the metastatic process. Early detection and analysis of circulating tumor cells (CTCs) is therefore important for early diagnosis, prognosis, and effective treatment of cancer, enabling favorable clinical outcomes in cancer patients. Accurate and reliable methods for isolating and detecting CTCs are necessary to obtain this clinical information. Over the past two decades, microfluidic technologies have demonstrated great potential for isolating and detecting CTCs from blood. The present paper reviews current advanced microfluidic technologies for isolating CTCs based on various biological and physical principles, and discusses their fundamental advantages and drawbacks for subsequent cellular and molecular assays. Owing to significant genetic heterogeneity among CTCs, microfluidic technologies for isolating individual CTCs have recently been developed. We discuss these single-cell isolation methods, as well as approaches to overcoming the limitations of current microfluidic CTC isolation technologies. Finally, we provide an overview of future innovative microfluidic platforms.

Ultrasensitive detection of circulating exosomes with a 3D-nanopatterned microfluidic chip

The performance of current microfluidic methods for exosome detection is constrained by boundary conditions, as well as fundamental limits to microscale mass transfer and interfacial exosome binding. Here, we show that a microfluidic chip designed with self-assembled three-dimensional herringbone nanopatterns can detect low levels of tumour-associated exosomes in plasma (10 exosomes μl^-1, or approximately 200 vesicles per 20 μl of spiked sample) that would otherwise be undetectable by standard microfluidic systems for biosensing. The nanopatterns promote microscale mass transfer, increase surface area and probe density to enhance the efficiency and speed of exosome binding, and permit drainage of the boundary fluid to reduce near-surface hydrodynamic resistance, thus promoting particle-surface interactions for exosome binding. We used the device for the detection-in 2 μl plasma samples from 20 ovarian cancer patients and 10 age-matched controls-of exosome subpopulations expressing CD24, epithelial cell adhesion molecule and folate receptor alpha proteins, and suggest exosomal folate receptor alpha as a potential biomarker for early detection and progression monitoring of ovarian cancer. The nanolithography-free nanopatterned device should facilitate the use of liquid biopsies for cancer diagnosis.

A carbon nanotube integrated microfluidic device for blood plasma extraction

Blood is a complex fluid consisting of cells and plasma. Plasma contains key biomarkers essential for disease diagnosis and therapeutic monitoring. Thus, by separating plasma from the blood, it is possible to analyze these biomarkers. Conventional methods for plasma extraction involve bulky equipment, and miniaturization constitutes a key step to develop portable devices for plasma extraction. Here, we integrated nanomaterial synthesis with microfabrication, and built a microfluidic device. In particular, we designed a double-spiral channel able to perform cross-flow filtration. This channel was constructed by growing aligned carbon nanotubes (CNTs) with average inter-tubular distances of ~80 nm, which resulted in porosity values of ~93%. During blood extraction, these aligned CNTs allow smaller molecules (e.g., proteins) to pass through the channel wall, while larger molecules (e.g., cells) get blocked. Our results show that our device effectively separates plasma from blood, by trapping blood cells. We successfully recovered albumin -the most abundant protein inside plasma- with an efficiency of ~80%. This work constitutes the first report on integrating biocompatible nitrogen-doped CNT (CN_xCNT) arrays to extract plasma from human blood, thus widening the bio-applications of CNTs.

Engineering Concepts in Stem Cell Research

The field of regenerative medicine integrates advancements made in stem cells, molecular biology, engineering, and clinical methodologies. Stem cells serve as a fundamental ingredient for therapeutic application in regenerative medicine. Apart from stem cells, engineering concepts have equally contributed to the success of stem cell based applications in improving human health. The purpose of various engineering methodologies is to develop regenerative and preventive medicine to combat various diseases and deformities. Explosion of stem cell discoveries and their implementation in clinical setting warrants new engineering concepts and new biomaterials. Biomaterials, microfluidics, and nanotechnology are the major engineering concepts used for the implementation of stem cells in regenerative medicine. Many of these engineering technologies target the specific niche of the cell for better functional capability. Controlling the niche is the key for various developmental activities leading to organogenesis and tissue homeostasis. Biomimetic understanding not only helped to improve the design of the matrices or scaffolds by incorporating suitable biological and physical components, but also ultimately aided adoption of designs that helped these materials/devices have better function. Adoption of engineering concepts in stem cell research improved overall achievement, however, several important issues such as long-term effects with respect to systems biology needs to be addressed. Here, in this review the authors will highlight some interesting breakthroughs in stem cell biology that use engineering methodologies.

Micropatterned macroporous structures in microfluidic devices for viral separation from whole blood

Separation and enrichment of bio-nanoparticles from cell suspensions and blood are critical steps in many chemical and biomedical practices. We demonstrate here the design and fabrication of a microfluidic immunochromatographic device incorporating regular and multiscale monolithic structures to capture viruses from blood. The device contains micropatterned arrays of macroporous materials to perform size-exclusion and affinity chromatography in a simple flow-through process. The microscale gaps in the array allow the passage of cells while the macroporous matrices promote viral capture. Computational analyses reveal that fluid permeation into the porous matrices is controllable by the micropattern shape, separation distance and dimensions. Experimental analyses using blood samples containing human immunodeficiency viruses (HIV) as a model system further prove significantly improved viral capture efficiency using devices incorporating multiscale structures than those containing solid micropatterns. Such microfluidic devices with regular and multiscale structures have a potential for the separation and concentration of a wide range of bio-nanoparticles as well as macromolecules from complex mixtures containing both nano- and micro-sized species.

Enhanced Isolation and Release of Circulating Tumor Cells Using Nanoparticle Binding and Ligand Exchange in a Microfluidic Chip

The detection of rare circulating tumor cells (CTCs) in the blood of cancer patients has the potential to be a powerful and noninvasive method for examining metastasis, evaluating prognosis, assessing tumor sensitivity to drugs, and monitoring therapeutic outcomes. In this study, we have developed an efficient strategy to isolate CTCs from the blood of breast cancer patients using a microfluidic immune-affinity approach. Additionally, to gain further access to these rare cells for downstream characterization, our strategy allows for easy detachment of the captured CTCs from the substrate without compromising cell viability or the ability to employ next generation RNA sequencing for the identification of specific breast cancer genes. To achieve this, a chemical ligand-exchange reaction was engineered to release cells attached to a gold nanoparticle coating bound to the surface of a herringbone microfluidic chip (NP-^HBCTC-Chip). Compared to the use of the unmodified ^HBCTC-Chip, our approach provides several advantages, including enhanced capture efficiency and recovery of isolated CTCs.

Label-Free Virus Capture and Release by a Microfluidic Device Integrated with Porous Silicon Nanowire Forest

Viral diseases are perpetual threats to human and animal health. Detection and characterization of viral pathogens require accurate, sensitive, and rapid diagnostic assays. For field and clinical samples, the sample preparation procedures limit the ultimate performance and utility of the overall virus diagnostic protocols. This study presents the development of a microfluidic device embedded with porous silicon nanowire (pSiNW) forest for label-free size-based point-of-care virus capture in a continuous curved flow design. The pSiNW forests with specific interwire spacing are synthesized in situ on both bottom and sidewalls of the microchannels in a batch process. With the enhancement effect of Dean flow, this study demonstrates that about 50% H5N2 avian influenza viruses are physically trapped without device clogging. A unique feature of the device is that captured viruses can be released by inducing self-degradation of the pSiNWs in physiological aqueous environment. About 60% of captured viruses can be released within 24 h for virus culture, subsequent molecular diagnosis, and other virus characterization and analyses. This device performs viable, unbiased, and label-free virus isolation and release. It has great potentials for virus discovery, virus isolation and culture, functional studies of virus pathogenicity, transmission, drug screening, and vaccine development.

Microfluidic devices with templated regular macroporous structures for HIV viral capture

There is a need to develop inexpensive, portable and easy-to-use devices for viral sample processing for resource-limited settings. Here we offer a solution to efficient virus capture by incorporating macroporous materials with regular structures into microfluidic devices for affinity chromatography. Two-dimensional simulations were first conducted to investigate the effects of two structures, a nanopost array and a spherical pore network, on nanoparticle capture. Then, the two structures were created in polymers by templating anodic aluminum oxide films and 3D close-packed silica particles, respectively. When the microdevices containing functionalized porous materials were tested for human immunodeficiency virus (HIV) isolation, capture efficiencies of 80-99% were achieved under a continuous flow. Comparatively, functionalized flatbed microchannels captured around 10% of HIV particles. As the characteristic dimensions of the nanostructures are tunable, such devices can be adapted for the capture of different submicron bioparticles. The high capture efficiency and easy-to-operate nature suit the needs of resource-limited settings and may find applications in point-of-care diagnostics.

Tunable and label-free virus enrichment for ultrasensitive virus detection using carbon nanotube arrays

Viral infectious diseases can erupt unpredictably, spread rapidly, and ravage mass populations. Although established methods, such as polymerase chain reaction, virus isolation, and next-generation sequencing have been used to detect viruses, field samples with low virus count pose major challenges in virus surveillance and discovery. We report a unique carbon nanotube size-tunable enrichment microdevice (CNT-STEM) that efficiently enriches and concentrates viruses collected from field samples. The channel sidewall in the microdevice was made by growing arrays of vertically aligned nitrogen-doped multiwalled CNTs, where the intertubular distance between CNTs could be engineered in the range of 17 to 325 nm to accurately match the size of different viruses. The CNT-STEM significantly improves detection limits and virus isolation rates by at least 100 times. Using this device, we successfully identified an emerging avian influenza virus strain [A/duck/PA/02099/2012(H11N9)] and a novel virus strain (IBDV/turkey/PA/00924/14). Our unique method demonstrates the early detection of emerging viruses and the discovery of new viruses directly from field samples, thus creating a universal platform for effectively remediating viral infectious diseases.

Nanotechnology for enrichment and detection of circulating tumor cells

Circulating tumor cells (CTCs) are a hallmark of invasive behavior of cancer, responsible for the development of metastasis. Their detection and analysis have significant impacts in cancer biology and clinical practice. However, CTCs are rare events and contain heterogeneous subpopulations, requiring highly sensitive and specific techniques to identify and capture CTCs with high efficiency. Nanotechnology shows strong promises for CTC enrichment and detection owning to the unique structural and functional properties of nanoscale materials. In this review, we discuss the CTC enrichment and detection technologies based on a variety of functional nanosystems and nanostructured substrates, with the goal to highlight the role of nanotechnology in the advancement of basic and clinical CTC research.

Flow cytometry using Brillouin imaging and sensing via time-resolved optical (BISTRO) measurements

A novel concept of Brillouin imaging and sensing via time-resolved optical (BISTRO) measurements is introduced for flow cytometry applications. The system affords robust, maintenance-free and high-speed elasticity-sensitive measurements.

A Cellular Compatible Chitosan Nanoparticle Surface for Isolation and In Situ Culture of Rare Number CTCs

Circulating tumor cell (CTC) isolation has attracted a great deal of research interest in recent years. However, there are still some challenges, including purity as well as viability of the captured CTCs, resulting from nanoscale structures and inorganic nanomaterials. Here, a chitosan nanoparticle surface is first fabricated by electrospray to provide a cellular compatible interface. The "soft" substrate, further modified by polyethylene glycol (PEG) as an antifouling molecule and DNA aptamer as a specific capture molecule, has a hydrophilic nature and is capable of specific capture of viable rare CTCs from artificial white blood cell (WBC) samples. Furthermore, a subsequent in situ culture strategy based on the developed cellular compatible soft interface is introduced for further purification and proliferation of the captured rare number target cells. The WBCs are weeded out after 2 d, and after a 7 d proliferation nearly 200 MCF-7 cells are obtained from 7 target cells with more than 90% purity. This work provides a promising strategy for viable isolation and purification of rare CTCs and it has great potential for achieving clinical validity.

Trap Effect of Three-Dimensional Fibers Network for High Efficient Cancer-Cell Capture

Cells are trapped: The 3D fibrous interfaces, including microfibers, nanofibers, and nanofibers/microbeads composite interfaces, are fabricated by electrospinning. After coated with anti-EpCAM, these 3D fibrous interfaces allow cancer cells to be firmly trapped into the networks that show the outstanding capability for cancer cell capture from real blood.

Emerging role of nanomaterials in circulating tumor cell isolation and analysis

Circulating tumor cells (CTCs) are low frequency cells found in the bloodstream after having been shed from a primary tumor. These cells are research targets because of the information they may potentially provide about both an individual cancer as well as the mechanisms through which cancer spreads in the process of metastasis. Established technologies exist for CTC isolation, but the recent progress and future of this field lie in nanomaterials. In this review, we provide perspective into historical CTC capture as well as current research being conducted, emphasizing the significance of the materials being used to fabricate these devices. The modern investigation into CTCs initially featured techniques that have since been commercialized. A major innovation in the field was the development of a microfluidic capture device, first fabricated in silicon and followed up with glass and thermopolymer devices. We then specifically highlight the technologies incorporating magnetic nanoparticles, carbon nanotubes, nanowires, nanopillars, nanofibers, and nanoroughened surfaces, graphene oxide and their fabrication methods. The nanoscale provides a new set of tools that has the potential to overcome current limitations associated with CTC capture and analysis. We believe the current trajectory of the field is in the direction of nanomaterials, allowing the improvements necessary to further CTC research.

Nanoelectronic impedance detection of target cells

Detection of cells is typically performed using optical fluorescence based techniques such as flow cytometry. Here we present the impedance detection of target cells using a nanoelectronic probe we have developed, which we refer to as the nanoneedle biosensor. The nanoneedle consists of a thin film conducting electrode layer at the bottom, an insulative oxide layer above, another conductive electrode layer above, and a protective oxide above. The electrical impedance is measured between the two electrode layers. Cells captured on the surface of the nanoneedle tip results in a decrease in the impedance across the sensing electrodes. The basic mechanisms behind the electrical response of cells in solution under an applied alternating electrical field stems from modulation of the relative permittivity at the interface. In this paper we discuss, the circuit model, the nanofabrication, and the testing and characterization of the sensor. We demonstrate proof of concept for detection of yeast cells with specificity. We envision the sensor presented in this paper to be combined with microfluidic pre-concentration technologies to develop low cost point-of-care diagnostic assays for the clinical setting.

Discontinuous nanoporous membranes reduce non-specific fouling for immunoaffinity cell capture

The microfluidic isolation of target cells using adhesion-based surface capture has been widely explored for biology and medicine. However, high-throughput processing can be challenging due to interfacial limitations such as transport, reaction, and non-specific fouling. Here, it is shown that antibody-functionalized capture surfaces with discontinuous permeability enable efficient target cell capture at high flow rates by decreasing fouling. Experimental characterization and theoretical modeling reveal that "wall effects" affect cell-surface interactions and promote excess surface accumulation. These issues are partially circumvented by reducing the transport and deposition of cells near the channel walls. Optimized microfluidic devices can be operated at higher cell concentrations with significant improvements in throughput.

Magneto-controllable capture and release of cancer cells by using a micropillar device decorated with graphite oxide-coated magnetic nanoparticles

Aiming to highly efficient capture and analysis of circulating tumor cells, a micropillar device decorated with graphite oxide-coated magnetic nanoparticles is developed for magneto-controllable capture and release of cancer cells. Graphite oxide-coated, Fe3 O4 magnetic nanoparticles (MNPs) are synthesized by solution mixing and functionalized with a specific antibody, following by the immobilization of such modified MNPs on our designed micropillar device. For the proof-of-concept study, a HCT116 colorectal cancer cell line is employed to exam the capture efficiency. Under magnetic field manipulation, the high density packing of antibody-modified MNPs on the micropillars increases the local concentration of antibody, as well as the topographic interactions between cancer cells and micropillar surfaces. The flow rate and the micropillar geometry are optimized by studying their effects on capture efficiency. Then, a different number of HCT116 cells spiked in two kinds of cell suspension are investigated, yielding capture efficiency >70% in culture medium and >40% in blood sample, respectively. Moreover, the captured HCT116 cells are able to be released from the micropillars with a saturated efficiency of 92.9% upon the removal of applied magnetic field and it is found that 78% of the released cancer cells are viable, making them suitable for subsequent biological analysis.

Quantitative microfluidic biomolecular analysis for systems biology and medicine

In the postgenome era, biology and medicine are rapidly evolving towards quantitative and systems studies of complex biological systems. Emerging breakthroughs in microfluidic technologies and innovative applications are transforming systems biology by offering new capabilities to address the challenges in many areas, such as single-cell genomics, gene regulation networks, and pathology. In this review, we focus on recent progress in microfluidic technology from the perspective of its applications to promoting quantitative and systems biomolecular analysis in biology and medicine.

Microfluidics for manipulating cells

Microfluidics, a toolbox comprising methods for precise manipulation of fluids at small length scales (micrometers to millimeters), has become useful for manipulating cells. Its uses range from dynamic management of cellular interactions to high-throughput screening of cells, and to precise analysis of chemical contents in single cells. Microfluidics demonstrates a completely new perspective and an excellent practical way to manipulate cells for solving various needs in biology and medicine. This review introduces and comments on recent achievements and challenges of using microfluidics to manipulate and analyze cells. It is believed that microfluidics will assume an even greater role in the mechanistic understanding of cell biology and, eventually, in clinical applications.

Size-based hydrodynamic rare tumor cell separation in curved microfluidic channels

In this work, we propose a rapid and continuous rare tumor cell separation based on hydrodynamic effects in a label-free manner. The competition between the inertial lift force and Dean drag force inside a double spiral microchannel results in the size-based cell separation of large tumor cells and small blood cells. The mechanism of hydrodynamic separation in curved microchannel was investigated by a numerical model. Experiments with binary mixture of 5- and 15-μm-diameter polystyrene particles using the double spiral channel showed a separation purity of more than 95% at the flow rate above 30 ml/h. High throughput (2.5 × 10(8) cells/min) and efficient cell separation (more than 90%) of spiked HeLa cells and 20 × diluted blood cells was also achieved by the double spiral channel.

Bioinspired multivalent DNA network for capture and release of cells

Capture and isolation of flowing cells and particulates from body fluids has enormous implications in diagnosis, monitoring, and drug testing, yet monovalent adhesion molecules used for this purpose result in inefficient cell capture and difficulty in retrieving the captured cells. Inspired by marine creatures that present long tentacles containing multiple adhesive domains to effectively capture flowing food particulates, we developed a platform approach to capture and isolate cells using a 3D DNA network comprising repeating adhesive aptamer domains that extend over tens of micrometers into the solution. The DNA network was synthesized from a microfluidic surface by rolling circle amplification where critical parameters, including DNA graft density, length, and sequence, could readily be tailored. Using an aptamer that binds to protein tyrosine kinase-7 (PTK7) that is overexpressed on many human cancer cells, we demonstrate that the 3D DNA network significantly enhances the capture efficiency of lymphoblast CCRF-CEM cells over monovalent aptamers and antibodies, yet maintains a high purity of the captured cells. When incorporated in a herringbone microfluidic device, the 3D DNA network not only possessed significantly higher capture efficiency than monovalent aptamers and antibodies, but also outperformed previously reported cell-capture microfluidic devices at high flow rates. This work suggests that 3D DNA networks may have broad implications for detection and isolation of cells and other bioparticles.

Microfluidic transport in microdevices for rare cell capture

The isolation and capture of rare cells is a problem uniquely suited to microfluidic devices, in which geometries on the cellular length scale can be engineered and a wide range of chemical functionalizations can be implemented. The performance of such devices is primarily affected by the chemical interaction between the cell and the capture surface and the mechanics of cell-surface collision and adhesion. As rare cell-capture technology has been summarized elsewhere (E. D. Pratt et al., Chem. Eng. Sci. 2011, 66, 1508-1522), this article focuses on the fundamental adhesion and transport mechanisms in rare cell-capture microdevices, and explores modern device design strategies in a transport context. The biorheology and engineering parameters of cell adhesion are defined; adhesion models and reaction kinetics briefly reviewed. Transport at the microscale, including diffusion and steric interactions that result in cell motion across streamlines, is discussed. The review concludes by discussing design strategies with a focus on leveraging the underlying transport phenomena to maximize device performance.

Nanoporous micro-element arrays for particle interception in microfluidic cell separation

The ability to control cell-surface interactions in order to achieve binding of specific cell types is a major challenge for microfluidic immunoaffinity cell capture systems. In the majority of existing systems, the functionalized capture surface is constructed of solid materials, where flow stagnation at the solid-liquid interface is detrimental to the convection of cells to the surface. We study the use of ultra-high porosity (99%) nanoporous micro-posts in microfluidic channels for enhancing interception efficiency of particles in flow. We show using both modelling and experiment that nanoporous posts improve particle interception compared to solid posts through two distinct mechanisms: the increase of direct interception, and the reduction of near-surface hydrodynamic resistance. We provide initial validation that the improvement of interception efficiency also results in an increase in capture efficiency when comparing nanoporous vertically aligned carbon nanotube (VACNT) post arrays with solid PDMS post arrays of the same geometry. Using both bacteria (∼1 μm) and cancer cell lines (∼15 μm) as model systems, we found capture efficiency increases by 6-fold and 4-fold respectively. The combined model and experimental platform presents a new generation of nanoporous microfluidic devices for cell isolation.

Nanomaterials and lab-on-a-chip technologies

Lab-on-a-chip (LOC) platforms have become important tools for sample analysis and treatment with interest for DNA, protein and cells studies or diagnostics due to benefits such as the reduced sample volume, low cost, portability and the possibility to build new analytical devices or be integrated into conventional ones. These platforms have advantages of a wide set of nanomaterials (NM) (i.e. nanoparticles, quantum dots, nanowires, graphene etc.) and offer excellent improvement in properties for many applications (i.e. detectors sensitivity enhancement, biolabelling capability along with other in-chip applications related to the specificities of the variety of nanomaterials with optical, electrical and/or mechanical properties). This review covers the last trends in the use of nanomaterials in microfluidic systems and the related advantages in analytical and bioanalytical applications. In addition to the applications of nanomaterials in LOCs, we also discuss the employment of such devices for the production and characterization of nanomaterials. Both framed platforms, NMs based LOCs and LOCs for NMs production and characterization, represent promising alternatives to generate new nanotechnology tools for point-of-care diagnostics, drug delivery and nanotoxicology applications.

Full surface embedding of gold clusters on silicon nanowires for efficient capture and photothermal therapy of circulating tumor cells

We report on rapid thermal chemical vapor deposition growth of silicon nanowires (Si NWs) that contain a high density of gold nanoclusters (Au NCs) with a uniform coverage over the entire length of the nanowire sidewalls. The Au NC-coated Si NWs with an antibody-coated surface obtain the unique capability to capture breast cancer cells at twice the highest efficiency currently achievable (~88% at 40 min cell incubation time) from a nanostructured substrate. We also found that irradiation of breast cancer cells captured on Au NC-coated Si NWs with a near-infrared light resulted in a high mortality rate of these cancer cells, raising a fine prospect for simultaneous capture and plasmonic photothermal therapy for circulating tumor cells.