Nanofluidics in hollow nanowires

Uptake of nanowires by human lung adenocarcinoma cells

Semiconductor nanowires are increasingly used in optoelectronic devices. However, their effects on human health have not been assessed fully. Here, we investigate the effects of gallium phosphide nanowires on human lung adenocarcinoma cells. Four different geometries of nanowires were suspended in the cell culture for 48 hours. We show that cells internalize the nanowires and that the nanowires have no effect on cell proliferation rate, motility, viability and intracellular ROS levels. By blocking specific internalization pathways, we demonstrate that the nanowire uptake is the result of a combination of processes, requiring dynamin and actin polymerization, which suggests an internalization through macropinocytosis and phagocytosis.

Nanoplasmonic Sensor Detects Preferential Binding of IRSp53 to Negative Membrane Curvature

Biosensors based on plasmonic nanostructures are widely used in various applications and benefit from numerous operational advantages. One type of application where nanostructured sensors provide unique value in comparison with, for instance, conventional surface plasmon resonance, is investigations of the influence of nanoscale geometry on biomolecular binding events. In this study, we show that plasmonic "nanowells" conformally coated with a continuous lipid bilayer can be used to detect the preferential binding of the insulin receptor tyrosine kinase substrate protein (IRSp53) I-BAR domain to regions of negative surface curvature, i.e., the interior of the nanowells. Two different sensor architectures with and without an additional niobium oxide layer are compared for this purpose. In both cases, curvature preferential binding of IRSp53 (at around 0.025 nm^-1 and higher) can be detected qualitatively. The high refractive index niobium oxide influences the near field distribution and makes the signature for bilayer formation less clear, but the contrast for accumulation at regions of negative curvature is slightly higher. This work shows the first example of analyzing preferential binding of an average-sized and biologically important protein to negative membrane curvature in a label-free manner and in real-time, illustrating a unique application for nanoplasmonic sensors.

Single cell analysis of proliferation and movement of cancer and normal-like cells on nanowire array substrates

Nanowires are presently investigated in the context of various biological and medical applications. In general, these studies are population-based, which results in sub-populations being overlooked. Here, we present a single cell analysis of cell cycle and cell movement parameters of cells seeded on nanowires using digital holographic microscopy for time-lapse imaging. MCF10A normal-like human breast epithelial cells and JIMT-1 breast cancer cells were seeded on glass, flat gallium phosphide (GaP), and on vertical GaP nanowire arrays. The cells were monitored individually using digital holographic microscopy for 48 h. The data show that cell division is affected in cells seeded on flat GaP and nanowires compared to glass, with much fewer cells dividing on the former two substrates compared to the latter. However, MCF10 cells that are dividing on glass and flat GaP substrates have similar cell cycle time, suggesting that distinct cell subpopulations are affected differently by the substrates. Altogether, the data highlight the importance of performing single cell analysis to increase our understanding of the versatility of cell behavior on different substrates, which is relevant in the design of nanowire applications.

Morphology of living cells cultured on nanowire arrays with varying nanowire densities and diameters

Vertical nanowire arrays are increasingly investigated for their applications in steering cell behavior. The geometry of the array is an important parameter, which influences the morphology and adhesion of cells. Here, we investigate the effects of array geometry on the morphology of MCF7 cancer cells and MCF10A normal-like epithelial cells. Different gallium phosphide nanowire array-geometries were produced by varying the nanowire density and diameter. Our results show that the cell size is smaller on nanowires compared to flat gallium phosphide. The cell area decreases with increasing the nanowire density on the substrate. We observed an effect of the nanowire diameter on MCF10A cells, with a decreased cell area on 40 nm diameter nanowires, compared to 60 and 80 nm diameter nanowires in high-density arrays. The focal adhesion morphology depends on the extent to which cells are contacting the substrate. For low nanowire densities and diameters, cells are lying on the substrate and we observed large focal adhesions at the cell edges. In contrast, for high nanowire densities and diameters, cells are lying on top of the nanowires and we observed point-like focal adhesions distributed over the whole cell. Our results constitute a step towards the ability to fine-tune cell behavior on nanowire arrays.

High-Efficiency Gene Transfection of Cells through Carbon Nanotube Arrays

Introducing nucleic acids into mammalian cells is a crucial step to elucidate biochemical pathways, and to modify gene expression and cellular development in immortalized cells, primary cells, and stem cells. Current transfection technologies are time consuming and limited by the size of genetic cargo, the inefficient introduction of test molecules into large populations of target cells, and the cytotoxicity of the techniques. A novel method of introducing genes and biomolecules into tens of thousands of mammalian cells has been developed through an array of aligned hollow carbon nanotubes, manufactured by template-based nanofabrication processes, to achieve rapid high-efficiency transfer with low cytotoxicity. The utilization of carbon nanotube arrays for gene transfection overcomes molecular weight limits of current technologies and can be adapted to deliver drugs or proteins in addition to nucleic acids.

From immobilized cells to motile cells on a bed-of-nails: effects of vertical nanowire array density on cell behaviour

The field of vertical nanowire array-based applications in cell biology is growing rapidly and an increasing number of applications are being explored. These applications almost invariably rely on the physical properties of the nanowire arrays, creating a need for a better understanding of how their physical properties affect cell behaviour. Here, we investigate the effects of nanowire density on cell migration, division and morphology for murine fibroblasts. Our results show that few nanowires are sufficient to immobilize cells, while a high nanowire spatial density enables a ”bed-of-nails” regime, where cells reside on top of the nanowires and are fully motile. The presence of nanowires decreases the cell proliferation rate, even in the “bed-of-nails” regime. We show that the cell morphology strongly depends on the nanowire density. Cells cultured on low (0.1 μm⁻²) and medium (1 μm⁻²) density substrates exhibit an increased number of multi-nucleated cells and micronuclei. These were not observed in cells cultured on high nanowire density substrates (4 μm⁻²). The results offer important guidelines to minimize cell-function perturbations on nanowire arrays. Moreover, these findings offer the possibility to tune cell proliferation and migration independently by adjusting the nanowire density, which may have applications in drug testing.

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.

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.

Fluid and highly curved model membranes on vertical nanowire arrays

Sensing and manipulating living cells using vertical nanowire devices requires a complete understanding of cell behavior on these substrates. Changes in cell function and phenotype are often triggered by events taking place at the plasma membrane, the properties of which are influenced by local curvature. The nanowire topography can therefore be expected to greatly affect the cell membrane, emphasizing the importance of studying membranes on vertical nanowire arrays. Here, we used supported phospholipid bilayers as a model for biomembranes. We demonstrate the formation of fluid supported bilayers on vertical nanowire forests using self-assembly from vesicles in solution. The bilayers were found to follow the contours of the nanowires to form continuous and locally highly curved model membranes. Distinct from standard flat supported lipid bilayers, the high aspect ratio of the nanowires results in a large bilayer surface available for the immobilization and study of biomolecules. We used these bilayers to bind a membrane-anchored protein as well as tethered vesicles on the nanowire substrate. The nanowire-bilayer platform shown here can be expanded from fundamental studies of lipid membranes on controlled curvature substrates to the development of innovative membrane-based nanosensors.

Fluorescent nanowire heterostructures as a versatile tool for biology applications

Nanowires are increasingly used in biology, as sensors, as injection devices, and as model systems for toxicity studies. Currently, in situ visualization of nanowires in biological media is done using organic dyes, which are prone to photobleaching, or using microscopy methods which either yield poor resolution or require a sophisticated setup. Here we show that inherently fluorescent nanowire axial heterostructures can be used to localize and identify nanowires in cells and tissue. By synthesizing GaP-GaInP nanowire heterostructures, with nonfluorescent GaP segments and fluorescent GaInP segments, we created a barcode labeling system enabling the distinction of the nanowire morphological and chemical properties using fluorescence microscopy. The GaInP photoluminescence stability, combined with the fact that the nanowires can be coated with different materials while retaining their fluorescence, make these nanowires promising tools for biological and nanotoxicological studies.

Ultra low-loss, isotropic optical negative-index metamaterial based on hybrid metal-semiconductor nanowires

Recently, many fascinating properties predicted for metamaterials (negative refraction, superlensing, electromagnetic cloaking,…) were experimentally demonstrated. Unfortunately, the best achievements have no direct translation to the optical domain, without being burdened by technological and conceptual difficulties. Of particular importance within the realm of optical negative-index metamaterials (NIM), is the issue of simultaneously achieving strong electric and magnetic responses and low associated losses. Here, hybrid metal-semiconductor nanowires are proposed as building blocks of optical NIMs. The metamaterial thus obtained, highly isotropic in the plane normal to the nanowires, presents a negative index of refraction in the near-infrared, with values of the real part well below -1, and extremely low losses (an order of magnitude better than present optical NIMs). Tunability of the system allows to select the operating range in the whole telecom spectrum. The design is proven in configurations such as prisms and slabs, directly observing negative refraction.

Hollow nanoneedle array and its utilization for repeated administration of biomolecules to the same cells

We present a novel hollow nanoneedle array (NNA) device capable of simultaneously delivering diverse cargo into a group of cells in a culture over prolonged periods. The silica needles are fed by a common reservoir whose content can be replenished and modified in real time while maintaining contact with the same cells. The NNA, albeit its submicrometer features, is fabricated in a silicon-on-insulator wafer using conventional, large scale, silicon technology. 3T3-NIH fibroblast cells and HEK293 human embryonic kidney cells are shown to grow and proliferate successfully on the NNAs. Cargo delivery from the reservoir through the needles to a group of HEK293 cells in the culture is demonstrated by repeated administration of fluorescently labeled dextran to the same cells and transfection with DNA coding for red fluorescent protein. The capabilities demonstrated by the NNA device open the door to large scale studies of the effect of selected cells on their environment as encountered, for instance, in the study of cell-fate decisions, the role of cell-autonomous versus nonautonomous mechanisms in developmental biology, and in the study of excitable cell-networks.