Novel streptavidin-functionalized silicon nanowire arrays for CD4+ T lymphocyte separation

Simulation and fabrication of an integrating well-aligned silicon nanowires substrate for trapping circulating tumor cells labeled with Fe3O4 nanoparticles in a microfluidic device

Introduction: Circulating tumor cells (CTCs) are the transformed tumor cells that can penetrate into the bloodstream and are available at concentrations as low as 1-100 cells per milliliter. To trap CTCs in the blood, one valid and mature technique that has been developed is the magnetophoresis-based separation in a microfluidic channel. Recently, nanostructured platforms have also been developed to trap specific targeted and marker cells in the blood. We aimed to integrate both in one platform to improve trapping. Methods: Here, we developed a numerical scheme and an integrated device that considered the interaction between drag and magnetic forces on paramagnetic labeled cells in the fluid as well as interaction of these two forces with the adhesive force and the surface friction of the nanowires substrate. We aimed on developing a more advanced technique that integrated the magnetophoretic property of some Fe₃O₄ paramagnetic nanoparticles (PMNPs) with a silicon nanowires (SiNWs) substrate in a microfluidic device to trap MDA-MB231 cell lines as CTCs in the blood. Results: Simulation indicated assuming that the nanoparticles adhere perfectly to the white blood cells (WBCs) and the CTCs, the magnetic moment of the CTCs was almost one order of magnitude larger than that of the WBCs, so its attraction by the magnetic field was much higher. In general with significant statistics, the integrated device can trap almost all of the CTCs on the SiNWs substrate. In the experimental section, we took advantage of the integrated trapping techniques, including micropost barriers, magnetophoresis, and nanowires-based substrate to more effectively isolate the CTCs. Conclusion: The simulation indicated that the proposed device could almost trap all of the CTCs onto the SiNWs substrate, whereas trapping in flat substrates with magnetophoretic force was very low. As a result of the magnetic field gradient, magnetophoretic force was applied to the cells through the nanoparticles, which would efficiently drive down the nanoparticle-tagged cells. For the experimental validation, anti-EpCAM antibodies for specific binding to tumor cells were used. Using this specific targeting method and by statistically counting, it was shown that the proposed technique has excellent performance and results in the trapping efficiency of above 90%.

Oxide nanowire microfluidics addressing previously-unattainable analytical methods for biomolecules towards liquid biopsy

Nanowire microfluidics using a combination of self-assembly and nanofabrication technologies is expected to be applied to various fields due to its unique properties. We have been working on the fabrication of nanowire microfluidic devices and the development of analytical methods for biomolecules using the unique phenomena generated by the devices. The results of our research are not just limited to the development of nanospace control with "targeted dimensions" in "targeted arrangements" with "targeted materials/surfaces" in "targeted spatial locations/structures" in microfluidic channels, but also cover a wide range of analytical methods for biomolecules (extraction, separation/isolation, and detection) that are impossible to achieve with conventional technologies. Specifically, we are working on the extraction technology "the cancer-related microRNA extraction method in urine," the separation technology "the ultrafast and non-equilibrium separation method for biomolecules," and the detection technology "the highly sensitive electrical measurement method." These research studies are not just limited to the development of biomolecule analysis technology using nanotechnology, but are also opening up a new academic field in analytical chemistry that may lead to the discovery of new pretreatment, separation, and detection principles.

Bacterial-nanostructure interactions: The role of cell elasticity and adhesion forces

The attachment of single-celled organisms, namely bacteria and fungi, to abiotic surfaces is of great interest to both the scientific and medical communities. This is because the interaction of such cells has important implications in a range of areas, including biofilm formation, biofouling, antimicrobial surface technologies, and bio-nanotechnologies, as well as infection development, control, and mitigation. While central to many biological phenomena, the factors which govern microbial surface attachment are still not fully understood. This lack of understanding is a direct consequence of the complex nature of cell-surface interactions, which can involve both specific and non-specific interactions. For applications involving micro- and nano-structured surfaces, developing an understanding of such phenomenon is further complicated by the diverse nature of surface architectures, surface chemistry, variation in cellular physiology, and the intended technological output. These factors are extremely important to understand in the emerging field of antibacterial nanostructured surfaces. The aim of this perspective is to re-frame the discussion surrounding the mechanism of nanostructured-microbial surface interactions. Broadly, the article reviews our current understanding of these phenomena, while highlighting the knowledge gaps surrounding the adhesive forces which govern bacterial-nanostructure interactions and the role of cell membrane rigidity in modulating surface activity. The roles of surface charge, cell rigidity, and cell-surface adhesion force in bacterial-surface adsorption are discussed in detail. Presently, most studies have overlooked these areas, which has left many questions unanswered. Further, this perspective article highlights the numerous experimental issues and misinterpretations which surround current studies of antibacterial nanostructured surfaces.

Talking to cells: semiconductor nanomaterials at the cellular interface

The interface of biological components with semiconductors is a growing field with numerous applications. For example, the interfaces can be used to sense and modulate the electrical activity of single cells and tissues. From the materials point of view, silicon is the ideal option for such studies due to its controlled chemical synthesis, scalable lithography for functional devices, excellent electronic and optical properties, biocompatibility and biodegradability. Recent advances in this area are pushing the bio-interfaces from the tissue and organ level to the single cell and sub-cellular regimes. In this progress report, we will describe some fundamental studies focusing on miniaturizing the bioelectric and biomechanical interfaces. Additionally, many of our highlighted examples involve freestanding silicon-based nanoscale systems, in addition to substrate-bound structures or devices; the former offers new promise for basic research and clinical application. In this report, we will describe recent developments in the interfacing of neuronal and cardiac cells and their networks. Moreover, we will briefly discuss the incorporation of semiconductor nanostructures for interfacing non-excitable cells in applications such as probing intracellular force dynamics and drug delivery. Finally, we will suggest several directions for future exploration.

Microfluidic channel-coupled 3D quartz nanohole arrays for high capture and release efficiency of BT20 cancer cells

Nanostructured materials, such as silicon nanowires, quartz nanostructures, and polymer-modified nanostructures, are a promising new class of materials for the capture and enumeration of very rare tumor cells, including circulating tumor cells (CTCs), to examine their biological characteristics in whole blood of cancer patients. These cells can then be used for transplantation, anti-tumor cell therapy, and cell-secreted protein studies. It is believed that 3-dimensional (3D) nanostructured substrates efficiently enhance cell capture yields due to the increased local contacts between the 3D nanostructures and extracellular extensions of the tumor cells. Recent studies have been performed with enhanced cell capture yields thanks to various nanostructured platforms; however, there remains an urgent need both to capture and release viable rare tumor cells for further molecular (i.e., protein) analysis and to develop patient-specific drugs. Here, we first demonstrate that our 3D quartz nanohole array (QNHA) tumor cell capture and release system allows us not only to selectively capture rare tumor cells, but also to release the cells with high capture and release rates. This system was developed using streptavidin (STR)-functionalized QNHA (STR-QNHA) with a microfluidic channel. Our system has ideal cell-separation yields of as high as 85-91% and high release rates of >90% for the BT20 cell line. We suggest that the use of a microfluidic channel technique coupled with a STR-QNHA cell capture and release chip (STR-QNHA cell chip) would be a powerful and simple process to evaluate the capture, enumeration, and release of CTCs from patient whole blood for studying further cell therapy and tumor-cell-secreted molecules.

Functionalization of nanotextured substrates for enhanced identification of metastatic breast cancer cells

Metastasis is the major cause of low survival rates among cancer patients. Once cancer cells metastasize, it is extremely difficult to contain the disease. We report on a nanotextured platform for enhanced detection of metastatic cells. We captured metastatic (MDA-MDB-231) and non-metastatic (MCF-7) breast cancer cells on anti-EGFR aptamer modified plane and nanotextured substrates. Metastatic cells were seen to change their morphology at higher rates when captured on nanotextured substrates than on plane substrates. Analysis showed statistically different morphological behaviors of metastatic cells that were very pronounced on the nanotextured substrates. Several distance matrices were calculated to quantify the dissimilarity of cell shape change. Nanotexturing increased the dissimilarity of the metastatic cells and as a result the contrast between metastatic and non-metastatic cells increased. Jaccard distance measurements found that the shape change ratio of the non-metastatic and metastatic cells was enhanced from 1:1.01 to 1:1.81, going from plane to nanotextured substrates. The shape change ratio of the non-metastatic to metastatic cells improved from 1:1.48 to 1:2.19 for the Hausdorff distance and from 1:1.87 to 1:4.69 for the Mahalanobis distance after introducing nanotexture. Distance matrix analysis showed that nanotexture increased the shape change ratios of non-metastatic and metastatic cells. Hence, the detectability of metastatic cells increased. These calculated matrices provided clear and explicit measures to discriminate single cells for their metastatic state on functional nanotextured substrates.

Large-area assembly of halloysite nanotubes for enhancing the capture of tumor cells

Here, polystyrene sulfonate sodium (PSS) modified Halloysite nanotubes (HNTs) were self-assembled into a patterned coating on a glass substrate with ordered nanotube arrays in a slit-like confined space. The microstructure of the formed patterned HNTs coating was investigated. The formed strips are more regular and almost parallel to each other with an increase in HNTs concentration. The HNTs coating formed from the 2% PSS-HNTs dispersion has the maximum nanotube alignment degree. The patterned HNTs coating was employed to capture tumor cells. The tumor cells can be captured by the HNTs coating effectively compared with a smooth glass surface due to the enhanced topographic interactions between the HNTs coating and cancer cells. The HNTs coating prepared from the 2% PSS-HNTs dispersion has the highest capture yield which is due to the ordered nanotube arrangement and the appropriate surface roughness. The HNTs coating was further conjugated with anti-EpCAM, which leads to the capture yield of MCF-7 cells reaching 92% within 3 h. The HNTs coating can capture 8 MCF-7 cells from 1 mL artificial blood samples spiked with 10 MCF-7 cells, showing the promising applications of HNTs in clinical circulating tumor cell capture for early diagnosis and monitoring of cancer patients.

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.

Dual-Functional Lipid Coating for the Nanopillar-Based Capture of Circulating Tumor Cells with High Purity and Efficiency

Clinical studies of circulating tumor cells (CTC) have stringent demands for high capture purity and high capture efficiency. Nanostructured surfaces have been shown to significantly increase the capture efficiency yet suffer from low capture purity. Here we introduce a dual-functional lipid coating on nanostructured surfaces. The lipid coating serves both as an effective passivation layer that helps prevent nonspecific cell adhesion and as a functionalized layer for antibody-based specific cell capture. In addition, the fluidity of lipid bilayers enables antibody clustering that enhances the cell-surface interaction for efficient cell capture. As a result, the lipid-coating method helps promote both the capture efficiency and capture purity of nanostructure-based CTC capture.

Bioprobes Based on Aptamer and Silica Fluorescent Nanoparticles for Bacteria Salmonella typhimurium Detection

In this study, we have developed an efficient method based on single-stranded DNA (ssDNA) aptamers along with silica fluorescence nanoparticles for bacteria Salmonella typhimurium detection. Carboxyl-modified Tris(2,2'-bipyridyl)dichlororuthenium(II) hexahydrate (RuBPY)-doped silica nanoparticles (COOH-FSiNPs) were prepared using reverse microemulsion method, and the streptavidin was conjugated to the surface of the prepared COOH-FSiNPs. The bacteria S. typhimurium was incubated with a specific ssDNA biotin-labeled aptamer, and then the aptamer-bacteria conjugates were treated with the synthetic streptavidin-conjugated silica fluorescence nanoprobes (SA-FSiNPs). The results under fluorescence microscopy show that SA-FSiNPs can be applied effectively for the labeling of bacteria S. typhimurium with great photostable property. To further verify the specificity of SA-FSiNPs out of multiple bacterial conditions, variant concentrations of bacteria mixtures composed of bacteria S. typhimurium, Escherichia coli, and Bacillus subtilis were treated with SA-FSiNPs.In addition, the feasibility of SA-FSiNPs for bacteria S. typhimurium detection in chicken samples was assessed. All the results display that the established aptamer-based nanoprobes exhibit the superiority for bacteria S. typhimurium detection, which is referentially significant for wider application prospects in pathogen detection.

Effect of graphene oxide ratio on the cell adhesion and growth behavior on a graphene oxide-coated silicon substrate

Control of living cells on biocompatible materials or on modified substrates is important for the development of bio-applications, including biosensors and implant biomaterials. The topography and hydrophobicity of substrates highly affect cell adhesion, growth, and cell growth kinetics, which is of great importance in bio-applications. Herein, we investigate the adhesion, growth, and morphology of cultured breast cancer cells on a silicon substrate, on which graphene oxides (GO) was partially formed. By minimizing the size and amount of the GO-containing solution and the further annealing process, GO-coated Si samples were prepared which partially covered the Si substrates. The coverage of GO on Si samples decreases upon annealing. The behaviors of cells cultured on two samples have been observed, i.e. partially GO-coated Si (P-GO) and annealed partially GO-coated Si (Annealed p-GO), with a different coverage of GO. Indeed, the spreading area covered by the cells and the number of cells for a given culture period in the incubator were highly dependent on the hydrophobicity and the presence of oxygenated groups on GO and Si substrates, suggesting hydrophobicity-driven cell growth. Thus, the presented method can be used to control the cell growth via an appropriate surface modification.

Interfacing Inorganic Nanowire Arrays and Living Cells for Cellular Function Analysis

Inorganic nanowires are among the most attractive functional materials, which have emerged in the past two decades. They have demonstrated applications in information technology and energy conversion, but their utility in biological or biomedical research remains relatively under-explored. Although nanowire-based sensors have been frequently reported for biomolecular detection, interfacing nanowire arrays and living mammalian cells for the direct analysis of cellular functions is a very recent endeavor. Cell-penetrating nanowires enabled effective delivery of biomolecules, electrical and optical stimulation and recording of intracellular signals over a long period of time. Non-penetrating, high-density nanowire arrays display rich interactions between the nanostructured substrate and the micro/nanoscale features of cell surfaces. Such interactions enable efficient capture of rare cells including circulating tumor cells and trafficking leukocytes from complex biospecimens. It also serves as a platform for probing cell traction force and neuronal guidance. The most recent advances in the field that exploits nanowire arrays (both penetrating and non-penetrating) to perform rapid analysis of cellular functions potentially for disease diagnosis and monitoring are reviewed.

Biosensors for Cell Analysis

Biosensors first appeared several decades ago to address the need for monitoring physiological parameters such as oxygen or glucose in biological fluids such as blood. More recently, a new wave of biosensors has emerged in order to provide more nuanced and granular information about the composition and function of living cells. Such biosensors exist at the confluence of technology and medicine and often strive to connect cell phenotype or function to physiological or pathophysiological processes. Our review aims to describe some of the key technological aspects of biosensors being developed for cell analysis. The technological aspects covered in our review include biorecognition elements used for biosensor construction, methods for integrating cells with biosensors, approaches to single-cell analysis, and the use of nanostructured biosensors for cell analysis. Our hope is that the spectrum of possibilities for cell analysis described in this review may pique the interest of biomedical scientists and engineers and may spur new collaborations in the area of using biosensors for cell analysis.

Single-Crystalline, Nanoporous Gallium Nitride Films With Fine Tuning of Pore Size for Stem Cell Engineering

Single-crystalline nanoporous gallium nitride (GaN) thin films were fabricated with the pore size readily tunable in 20-100 nm. Uniform adhesion and spreading of human mesenchymal stem cells (hMSCs) seeded on these thin films peak on the surface with pore size of 30 nm. Substantial cell elongation emerges as pore size increases to ∼80 nm. The osteogenic differentiation of hMSCs occurs preferentially on the films with 30 nm sized nanopores, which is correlated with the optimum condition for cell spreading, which suggests that adhesion, spreading, and stem cell differentiation are interlinked and might be coregulated by nanotopography.

Interactions between semiconductor nanowires and living cells

Semiconductor nanowires are increasingly used for biological applications and their small dimensions make them a promising tool for sensing and manipulating cells with minimal perturbation. In order to interface cells with nanowires in a controlled fashion, it is essential to understand the interactions between nanowires and living cells. The present paper reviews current progress in the understanding of these interactions, with knowledge gathered from studies where living cells were interfaced with vertical nanowire arrays. The effect of nanowires on cells is reported in terms of viability, cell-nanowire interface morphology, cell behavior, changes in gene expression as well as cellular stress markers. Unexplored issues and unanswered questions are discussed.

Tunable high aspect ratio polymer nanostructures for cell interfaces

Nanoscale topographies and chemical patterns can be used as synthetic cell interfaces with a range of applications including the study and control of cellular processes. Herein, we describe the fabrication of high aspect ratio nanostructures using electron beam lithography in the epoxy-based polymer SU-8. We show how nanostructure geometry, position and fluorescence properties can be tuned, allowing flexible device design. Further, thiol-epoxide reactions were developed to give effective and specific modification of SU-8 surface chemistry. SU-8 nanostructures were made directly on glass cover slips, enabling the use of high resolution optical techniques such as live-cell confocal, total internal reflection and 3D structured illumination microscopy to investigate cell interactions with the nanostructures. Details of cell adherence and spreading, plasma membrane conformation and actin organization in response to high aspect ratio nanopillars and nanolines were investigated. The versatile structural and chemical properties combined with the high resolution cell imaging capabilities of this system are an important step towards the better understanding and control of cell interactions with nanomaterials.

Nanotopographic Biomaterials for Isolation of Circulating Tumor Cells

Circulating tumor cells (CTCs) shed from the primary tumor mass and circulating in the bloodstream of patients are believed to be vital to understand of cancer metastasis and progression. Capture and release of CTCs for further enumeration and molecular characterization holds the key for early cancer diagnosis, prognosis and therapy evaluation. However, detection of CTCs is challenging due to their rarity, heterogeneity and the increasing demand of viable CTCs for downstream biological analysis. Nanotopographic biomaterial-based microfluidic systems are emerging as promising tools for CTC capture with improved capture efficiency, purity, throughput and retrieval of viable CTCs. This review offers a brief overview of the recent advances in this field, including CTC detection technologies based on nanotopographic biomaterials and relevant nanofabrication methods. Additionally, the possible intracellular mechanisms of the intrinsic nanotopography sensitive responses that lead to the enhanced CTC capture are explored.

Exploring arrays of vertical one-dimensional nanostructures for cellular investigations

The endeavor of exploiting arrays of vertical one-dimensional (1D) nanostructures (NSs) for cellular applications has recently been experiencing a pronounced surge of activity. The interest is rooted in the intrinsic properties of high-aspect-ratio NSs. With a height comparable to a mammalian cell, and a diameter 100-1000 times smaller, NSs should intuitively reach far into a cell and, due to their small diameter, do so without compromising cell health. Single NSs would thus be expedient for measuring and modifying cell response. Further organization of these structures into arrays can provide up-scaled and detailed spatiotemporal information on cell activity, an achievement that would entail a massive leap forward in disease understanding and drug discovery. Numerous proofs-of-principle published recently have expanded the large toolbox that is currently being established in this rapidly advancing field of research. Encouragingly, despite the diversity of NS platforms and experimental conditions used thus far, general trends and conclusions from combining cells with NSs are beginning to crystallize. This review covers the broad spectrum of NS materials and dimensions used; the observed cellular responses with specific focus on adhesion, morphology, viability, proliferation, and migration; compares the different approaches used in the field to provide NSs with the often crucial cytosolic access; covers the progress toward biological applications; and finally, envisions the future of this technology. By maintaining the impressive rate and quality of recent progress, it is conceivable that the use of vertical 1D NSs may soon be established as a superior choice over other current techniques, with all the further benefits that may entail.

Stem-loop DNA-assisted silicon nanowires-based biochemical sensors with ultra-high sensitivity, specificity, and multiplexing capability

A class of stem-loop DNA-assisted silicon nanowires (SiNWs)-based fluorescent biosensor is presented in this report. Significantly, the sensor enables rapid and sensitive detection of DNA targets with a concentration as low as 1 pM. Moreover, the large planar surface of SiNWs facilitates simultaneous assembly with different DNA strands, which is favorable for multiplexed DNA detection. On the other hand, the SiNWs-based sensor is highly efficacious for detecting heavy metal ions. Mercury ions (Hg(2+)) of low concentrations (e.g., 5 pM) are readily identified from its mixture with over 10 kinds of interfering metal ions, even in real water samples. Given that SiNWs can be fabricated in a facile, reproducible and low-cost manner, this kind of SiNWs-based high-performance sensor is expected to be a practical analytical tool for a variety of biological and environment-protection applications.

Nanowire array chips for molecular typing of rare trafficking leukocytes with application to neurodegenerative pathology

Despite the presence of the blood-brain barrier (BBB) that restricts the entry of immune cells and mediators into the central nervous system (CNS), a small number of peripheral leukocytes can traverse the BBB and infiltrate into the CNS. The cerebrospinal fluid (CSF) is one of the major routes through which trafficking leukocytes migrate into the CNS. Therefore, the number of leukocytes and their phenotypic compositions in the CSF may represent important sources to investigate immune-to-brain interactions or diagnose and monitor neurodegenerative diseases. Due to the paucity of trafficking leucocytes in the CSF, a technology capable of efficient isolation, enumeration, and molecular typing of these cells in the clinical settings has not been achieved. In this study, we report on a biofunctionalized silicon nanowire array chip for highly efficient capture and multiplexed phenotyping of rare trafficking leukocytes in small quantities (50 microliters) of clinical CSF specimens collected from neurodegenerative disease patients. The antibody coated 3D nanostructured materials exhibited vastly improved rare cell capture efficiency due to high-affinity binding and enhanced cell-substrate interactions. Moreover, our platform creates multiple cell capture interfaces, each of which can selectively isolate specific leukocyte phenotypes. A comparison with the traditional immunophenotyping using flow cytometry demonstrated that our novel silicon nanowire-based rare cell analysis platform can perform rapid detection and simultaneous molecular characterization of heterogeneous immune cells. Multiplexed molecular typing of rare leukocytes in CSF samples collected from Alzheimer's disease patients revealed the elevation of white blood cell counts and significant alterations in the distribution of major leukocyte phenotypes. Our technology represents a practical tool for potentially diagnosing and monitoring the pathogenesis of neurodegenerative diseases by allowing an effective hematological analysis of the CSF from patients.

Parallel affinity-based isolation of leukocyte subsets using microfluidics: application for stroke diagnosis

We report the design and performance of a polymer microfluidic device that can affinity select multiple types of biological cells simultaneously with sufficient recovery and purity to allow for the expression profiling of mRNA isolated from these cells. The microfluidic device consisted of four independent selection beds with curvilinear channels that were 25 μm wide and 80 μm deep and were modified with antibodies targeting antigens specifically expressed by two different cell types. Bifurcated and Z-configured device geometries were evaluated for cell selection. As an example of the performance of these devices, CD4+ T-cells and neutrophils were selected from whole blood as these cells are known to express genes found in stroke-related expression profiles that can be used for the diagnosis of this disease. CD4+ T-cells and neutrophils were simultaneously isolated with purities >90% using affinity-based capture in cyclic olefin copolymer (COC) devices with a processing time of ∼3 min. In addition, sufficient quantities of the cells could be recovered from a 50 μL whole blood input to allow for reverse transcription-polymerase chain reaction (RT-PCR) following cell lysis. The expression of genes from isolated T-cells and neutrophils, such as S100A9, TCRB, and FPR1, was evaluated using RT-PCR. The modification and isolation procedures demonstrated here can also be used to analyze other cell types as well where multiple subsets must be interrogated.

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.

Temperature-dependent thermal conductivities of 1D semiconducting nanowires via four-point-probe 3-ω method

We report on a systematic study of the thermal transport characteristics of both as-grown zinc oxide and gallium nitride nanowires (NWs) via the four-point-probe 3-ω method in the temperature range 130-300 K. Both as-grown NWs were synthesized by a vapor-liquid-solid growth mechanism, and show clear n-type semiconducting behavior without any defects, which enables both the NWs to be promising candidates for thermoelectric materials. To measure the thermal conductivities of both NWs with lower heat loss and measurement errors, the suspended structures were formed by a combination of an e-beam lithography process and a random dispersion method. The measured thermal conductivities of both NWs are greatly reduced compared to their bulk materials due to the enhanced phonon scattering via the size effect and dopants (impurities). Furthermore, we observed that the Umklapp peaks of both NWs are shifted to a higher temperature than those of their bulk counterparts, indicating that phonon-boundary scattering dominates over other phonon scattering due to the size effect.

Collective behaviors of mammalian cells on amine-coated silicon nanowires

Intensive studies with vertical nanowire (NW) arrays have illustrated broad implications for manipulating mammalian cells in vitro, but how cellular responses are influenced by the presence of NWs has not been thoroughly investigated. Here, we address collective cellular behaviors, including surface area of cells, membrane trafficking, focal adhesion distribution and dynamics, and cytoskeletal protein distribution on amine-coated silicon (Si) NWs with different physical properties. The degree of HeLa cell spreading was inversely proportional to the surface area occupied by the NWs, which was not affected by manipulation of membrane trafficking dynamics. In the presence of a diffusive focal complex around the NWs, strong, well organized focal adhesion was hardly visible on the NWs, implying that the cells were interacting weakly with the NW-embedded surface. Furthermore, we found that actin filament formation of the cells on long NWs was not favorable, and this could explain our observation of reduced cell spreading, as well as the decreased number of focal adhesion complexes. Taken together, our results suggest that cells can survive on silicon NWs by adjusting their morphology and adhesion behavior through actively organizing these molecules.

Specific rare cell capture using micro-patterned silicon nanowire platform

We report on the rapid and direct quantification of specific cell captures using a micro-patterned streptavidin (STR)-functionalized silicon nanowire (SiNW) platform, which was prepared by Ag-assisted wet chemical etching and a photo-lithography process. This platform operates by high-affinity cell capture rendered by the combination of antibody-epithelial cell surface-binding, biotin-streptavidin binding, and the topologically enhanced cell-substrate interaction on a 3-dimensional SiNWs array. In this work, we developed a micro-patterned nanowire platform, with which we were able to directly evaluate the performance enhancement due to nanotopography. An excellent capture efficiency of ~96.6±6.7%, which is the highest value achieved thus far for the targeting specific A549 cells on a selective area of patterned SiNWs, is demonstrated. Direct comparison between the nanowire region and the planar region on the same substrate indicates dramatically elevated cell-capture efficiency on nanotopological surface identical surface chemistry (<2% cell-capture efficiency). An excellent linear response was seen for quantifying captured A549 cells with respect to loaded cells. This study suggests that the micro-patterned STR-functionalized SiNWs platform provides additional advantage for detecting rare cells populations in a more quantitative and specific manner.

Silicon nanowire based single-molecule SERS sensor

One-dimensional nanowire (NW) optical sensors have attracted great attention as promising nanoscale tools for applications such as probing inside living cells. However, achieving single molecule detection on NW sensors remains an interesting and unsolved problem. In the present paper, we investigate single-molecule detection (SMD) on a single SiNW based surface-enhanced Raman scattering (SERS) sensor, fabricated by controllably depositing silver nanoparticles on a SiNW (AgNP-SiNW). Both Raman spectral blinking and bi-analyte approaches are performed in aqueous solution to investigate SMD on individual SiNW SERS sensors. The results extend the functions of the SiNW sensor to SMD and provide insight into the molecule level illustration on the sensing mechanism of the nanowire sensor.

Nanostructured substrates for isolation of circulating tumor cells

Circulating tumor cells (CTCs) originate from the primary tumor mass and enter into the peripheral bloodstream. CTCs hold the key to understanding the biology of metastasis and also play a vital role in cancer diagnosis, prognosis, disease monitoring, and personalized therapy. However, CTCs are rare in blood and hard to isolate. Additionally, the viability of CTCs can easily be compromised under high shear stress while releasing them from a surface. The heterogeneity of CTCs in biomarker expression makes their isolation quite challenging; the isolation efficiency and specificity of current approaches need to be improved. Nanostructured substrates have emerged as a promising biosensing platform since they provide better isolation sensitivity at the cost of specificity for CTC isolation. This review discusses major challenges faced by CTC isolation techniques and focuses on nanostructured substrates as a platform for CTC isolation.

Direct observation of CD4 T cell morphologies and their cross-sectional traction force derivation on quartz nanopillar substrates using focused ion beam technique

Direct observations of the primary mouse CD4 T cell morphologies, e.g., cell adhesion and cell spreading by culturing CD4 T cells in a short period of incubation (e.g., 20 min) on streptavidin-functionalized quartz nanopillar arrays (QNPA) using a high-content scanning electron microscopy method were reported. Furthermore, we first demonstrated cross-sectional cell traction force distribution of surface-bound CD4 T cells on QNPA substrates by culturing the cells on top of the QNPA and further analysis in deflection of underlying QNPA via focused ion beam-assisted technique.

Programmable fractal nanostructured interfaces for specific recognition and electrochemical release of cancer cells

Topographic recognition of cancer cells is triggered by fractal gold nanostructures (FAuNSs), leading to dramatically enhanced recognition capability and efficient release of cancer cells with little damage. The unique characteristic of FAuNSs is the similar fractal dimension of their surface and that of a cancer cell. The design of fractal nanostructures will open up opportunities for functional design of bio-interfaces for highly efficient recognition and release of disease-related rare cells, which will improve detection in a clinical environment.

Layer-by-layer assembly of a streptavidin-fibronectin multilayer on biotinylated TiO(X)

The biomodification of surfaces, especially titanium, is an important issue in current biomedical research. Regarding titanium, it is also important to ensure a specific protein modification of its surface because here protein binding that is too random can be observed. Specific nanoscale architectures can be applied to overcome this problem. As recently shown, streptavidin can be used as a coupling agent to immobilize biotinylated fibronectin (bFn) on a TiO(X) surface. Because of the conformation of adsorbed biotinylated fibronectin on a streptavidin monolayer, it is possible to adsorb more streptavidin and biotinylated fibronectin layers. On this basis, an alternating protein multilayer can be built up. In contrast to common layer-by-layer technology, in this procedure the mechanism of layer adsorption is very specific because of the interaction of biotin and streptavidin. In addition, we showed that the assembly of this multilayer system and its stability are dependent on the degree of labeling of biotinylated fibronectin. Hence we conclude that it is possible to build up well-defined nanoscale protein architectures by varying the degree of labeling of biotinylated fibronectin.

Statistical analysis of immuno-functionalized tumor-cell behaviors on nanopatterned substrates

Laser scanning cytometry has been proven as a powerful technology for high-content, high-throughput quantitative analysis of cellular functions in a fully automated manner. It utilizes a large-area fluorescence imaging scheme and rigorous image quantitation algorithms to enable informative analysis of cell samples attached to solid substrates. While this technology represents a powerful approach for high-content screening using cell lines, it has not been applied to the study of tumor-cell behaviors on these solid nanopatterned substrates after several hours of incubation. Herein, we statistically demonstrated functional cellular morphology information, including size, shape, and distribution of the captured cells after 0.5 to 45 h of incubation on nanopatterned substrates, such as silicon nanowires and quartz nanopillars, along with planar glass substrates. With increasing incubation time up to 45 h, we observed that the nanopatterned substrates could have not only increased adhesion and traction forces between cells and nanopatterned substrates, but also limited cell spreading on the substrates compared to the planar glass substrates. On the basis of our results, we suggest that the most important factors to influence the cell behaviors on the three solid substrates are the degree of dimension on cell behaviors and cell traction force.

Cell adhesion and migration on nanopatterned substrates and their effects on cell-capture yield

With scanning electron microscopy analysis, we investigated the role of nanoscale topography on cellular activities; e.g. cell adhesion and spreading by culturing A549 cells (human lung carcinoma cell line cells) for 1-48 h on three sets of nanostructures; quartz nanopillars (QNPs), silicon nanopillars and silicon nanowire (SiNW) arrays, along with planar glass substrates. We found that cells on QNP arrays developed a longer shape than those on SiNW arrays. In addition, we studied how cell morphologies influence the cell-capture yield on the three sets of nanostructures. This research showed that the filopodial formations were directing the cell-capture yield on nanostructured substrates. This finding implies the possibility of using nanoscale topography features to control the filopodial formation including extension and migration from the cells. Using streptavidin-functionalized SiNW substrate, we further demonstrated a substantially higher yield (~91.8 ± 5.9%) than the planar glass wafers (~24.1 ± 7.5%) in the range of 200-3000 cells.

Nanowire substrate-based laser scanning cytometry for quantitation of circulating tumor cells

We report on the development of a nanowire substrate-enabled laser scanning imaging cytometry for rare cell analysis in order to achieve quantitative, automated, and functional evaluation of circulating tumor cells. Immuno-functionalized nanowire arrays have been demonstrated as a superior material to capture rare cells from heterogeneous cell populations. The laser scanning cytometry method enables large-area, automated quantitation of captured cells and rapid evaluation of functional cellular parameters (e.g., size, shape, and signaling protein) at the single-cell level. This integrated platform was first tested for capture and quantitation of human lung carcinoma cells from a mixture of tumor cells and leukocytes. We further applied it to the analysis of rare tumor cells spiked in fresh human whole blood (several cells per mL) that emulate metastatic cancer patient blood and demonstrated the potential of this technology for analyzing circulating tumor cells in the clinical settings. Using a high-content image analysis algorithm, cellular morphometric parameters and fluorescence intensities can be rapidly quantitated in an automated, unbiased, and standardized manner. Together, this approach enables informative characterization of captured cells in situ and potentially allows for subclassification of circulating tumor cells, a key step toward the identification of true metastasis-initiating cells. Thus, this nanoenabled platform holds great potential for studying the biology of rare tumor cells and for differential diagnosis of cancer progression and metastasis.

Gold nanoparticles-decorated silicon nanowires as highly efficient near-infrared hyperthermia agents for cancer cells destruction

Near-infrared (NIR) hyperthermia agents are of current interest because they hold great promise as highly efficacious tools for cancer photothermal therapy. Although various agents have been reported, a practical NIR hyperthermia agent is yet unavailable. Here, we present the first demonstration that silicon nanomaterials-based NIR hyperthermia agent, that is, gold nanoparticles-decorated silicon nanowires (AuNPs@SiNWs), is capable of high-efficiency destruction of cancer cells. AuNPs@SiNWs are found to possess strong optical absorbance in the NIR spectral window, producing sufficient heat under NIR irradiation. AuNPs@SiNWs are explored as novel NIR hyperthermia agents for photothermal ablation of tumor cells. In particular, three different cancer cells treated with AuNPs@SiNWs were completely destructed within 3 min of NIR irradiation, demonstrating the exciting potential of AuNPs@SiNWs for NIR hyperthermia agents.

A quartz nanopillar hemocytometer for high-yield separation and counting of CD4(+) T lymphocytes

We report the development of a novel quartz nanopillar (QNP) array cell separation system capable of selectively capturing and isolating a single cell population including primary CD4(+) T lymphocytes from the whole pool of splenocytes. Integrated with a photolithographically patterned hemocytometer structure, the streptavidin (STR)-functionalized-QNP (STR-QNP) arrays allow for direct quantitation of captured cells using high content imaging. This technology exhibits an excellent separation yield (efficiency) of ~95.3 ± 1.1% for the CD4(+) T lymphocytes from the mouse splenocyte suspensions and good linear response for quantitating captured CD4(+) T-lymphoblasts, which is comparable to flow cytometry and outperforms any non-nanostructured surface capture techniques, i.e. cell panning. This nanopillar hemocytometer represents a simple, yet efficient cell capture and counting technology and may find immediate applications for diagnosis and immune monitoring in the point-of-care setting.

Preparation of anti-CD4 monoclonal antibody-conjugated magnetic poly(glycidyl methacrylate) particles and their application on CD4+ lymphocyte separation

Novel immunomagnetic particles have been prepared for separation of CD4(+) lymphocytes. The magnetic nanoparticles with a diameter of approximately 5-6 nm were first synthesized by co-precipitation from ferrous and ferric iron solutions and subsequently encapsulated with poly(glycidyl methacrylate) (PGMA) by precipitation polymerization. Monoclonal antibody specific to CD4 molecules expressed on CD4(+) lymphocytes was conjugated to the surface of magnetic PGMA particles through covalent bonding between epoxide functional groups on the particle surface and primary amine groups of the antibodies. The generated immunomagnetic particles have successfully separated CD4(+) lymphocytes from whole blood with over 95% purity. The results indicated that these particles can be employed for cell separation and provide a strong potential to be applied in various biomedical applications including diagnosis, and monitoring of human diseases.