Size-dependent long-term tissue response to biostable nanowires in the brain

AbstractNanostructured neural interfaces, comprising nanotubes or nanowires, have the potential to overcome the present hurdles of achieving stable communication with neuronal networks for long periods of time. This would have a strong impact on brain research. However, little information is available on the brain response to implanted high-aspect-ratio nanoparticles, which share morphological similarities with asbestos fibres. Here, we investigated the glial response and neuronal loss in the rat brain after implantation of biostable and structurally controlled nanowires of different lengths for a period up to one year post-surgery. Our results show that, as for lung and abdominal tissue, the brain is subject to a sustained, local inflammation when biostable and high-aspect-ratio nanoparticles of 5 μm or longer are present in the brain tissue. In addition, a significant loss of neurons was observed adjacent to the 10 μm nanowires after one year. Notably, the inflammatory response was restricted to a narrow zone around the nanowires and did not escalate between 12 weeks and one year. Furthermore, 2 μm nanowires did not cause significant inflammatory response nor significant loss of neurons nearby. The present results provide key information for the design of future neural implants based on nanomaterials

Fluorescence excitation enhancement by waveguiding nanowires

The optical properties of vertical semiconductor nanowires can allow an enhancement of fluorescence from surface-bound fluorophores, a feature proven useful in biosensing. One of the contributing factors to the fluorescence enhancement is thought to be the local increase of the incident excitation light intensity in the vicinity of the nanowire surface, where fluorophores are located. However, this effect has not been experimentally studied in detail to date. Here, we quantify the excitation enhancement of fluorophores bound to a semiconductor nanowire surface by combining modelling with measurements of fluorescence photobleaching rate, indicative of the excitation light intensity, using epitaxially grown GaP nanowires. We study the excitation enhancement for nanowires with a diameter of 50-250 nm and show that excitation enhancement reaches a maximum for certain diameters, depending on the excitation wavelength. Furthermore, we find that the excitation enhancement decreases rapidly within tens of nanometers from the nanowire sidewall. The results can be used to design nanowire-based optical systems with exceptional sensitivities for bioanalytical applications

Fluorescence Signal Enhancement in Antibody Microarrays Using Lightguiding Nanowires

Fluorescence-based detection assays play an essential role in the life sciences and medicine. To offer better detection sensitivity and lower limits of detection (LOD), there is a growing need for novel platforms with an improved readout capacity. In this context, substrates containing semiconductor nanowires may offer significant advantages, due to their proven light-emission enhancing, waveguiding properties, and increased surface area. To demonstrate and evaluate the potential of such nanowires in the context of diagnostic assays, we have in this work adopted a well-established single-chain fragment antibody-based assay, based on a protocol previously designed for biomarker detection using planar microarrays, to freestanding, SiO2-coated gallium phosphide nanowires. The assay was used for the detection of protein biomarkers in highly complex human serum at high dilution. The signal quality was quantified and compared with results obtained on conventional flat silicon and plastic substrates used in the established microarray applications. Our results show that using the nanowire-sensor platform in combination with conventional readout methods, improves the signal intensity, contrast, and signal-to-noise by more than one order of magnitude compared to flat surfaces. The results confirm the potential of lightguiding nanowires for signal enhancement and their capacity to improve the LOD of standard diagnostic assays

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

Interactions of nanowires with cells and tissue

III-V nanowires have tunable dimensions, between 40 nm and 100 nm in diameter and between 1 and 15 μm in length. Due to their small diameter, they are ideal candidates to interact with cells without detrimental effects on the cell viability. Nanowires can be used as sensors: in our case, we have shown that arrays of vertical gallium phosphide nanowires are promising materials for biosensing in membranes, neural implant development as well as for cellular mechanosensing. Moreover, due to the exceptional control one can achieve during synthesis over their geometrical and optical properties, III-V nanowires are ideal materials to investigate the interactions of high aspect ratio nanoparticles with living cells and tissue

Nanostructures for probing and transfecting living cells

Nanowires and nanotubes are very promising tools for biological applications. Their small dimensions, which are on the same length scale as many cell components, make them an ideal tool to probe and stimulate cells with minimal perturbation. Here, we present a review of our work towards using nanowires and nanotubes for biomedical applications, such as neural implant, mechanosensing, and cell transfection

STED Nanoscopy of Interfaces and Interactions between Nanostructure Arrays and Living Cells

STED Nanoscopy of Interfaces and Interactions between Nanostructure Arrays and Living Cells The specific arrangement of membrane lipids and proteins in a living cell at the interface to high-aspect ratio nanostructures (nanowires and nanostraws) is still unknown – as are the dynamic structural adaptations and molecular rearrangements of living cells in the vicinity of such nanostructures. Whether the nanostructures actually pierce through the cell membrane or how introduced changes in membrane curvature change the biophysical properties of the cell membrane is of particular interest for investigations of the efficacy and safety of nano-sized tissue implants and for studying the delivery of substances into living cells via hollow nanostraws. To elucidate these questions, STimulated Emission Depletion (STED) nanoscopy is the ideal technique because it is live-cell compatible, target-specific, and offers a lateral resolution on the protein level (<30 nm). Here we present STED based investigations of the live-cell membrane and the cytoskeletal Actin signal in the presence of hollow Alumina nanostraws with diameter of 100 nm. As cellular model system we chose the lung-cancer derived A549 culture cell line. The cells were incubated on the nanostraws and subsequently fluorescence-tagged with live-cell compatible labels targeting the cell membrane and filamentous Actin, respectively. We find that the cellular membrane forms ring structures of about 100 nm in diameter, wrapping tightly around the nanostraws. On the other hand, the Actin cytoskeleton forms intricate, coil-like nanometric structures around the nanostraws; these structures strongly vary in diameters between 250-600 nm and appear to widen with increasing distance from the nanostraw substrate. In addition, STED images of living cells stained for both membrane and Actin signal reveal a significant degree of co-localization at the apical cell membrane, i.e. further away from the nanostraws. This co-localization is almost entirely lost at the basal membrane close to the nanostraws which is due to a strongly reduced Actin signal on that side of the cell. In conclusion, our sub-diffraction STED imaging based investigations of the behavior of single living cells cultured on nanostraws reveals a strong response of the cellular membrane and the Actin cytoskeleton – two of the main structure-giving features of the cell. In a next step, we will extend our studies to additional scaffolding proteins to arrive at a more detailed map of the topology of living cells at the interface to nanostructures of different geometries