Vertical Nanopillars Research Articles

Scalable and Robust Hollow Nanopillar Electrode for Enhanced Intracellular Action Potential Recording.

Electrophysiology is a unique biomarker of the electrogenic cells that can perform a disease investigation or drug assessment. In the recent decade, vertical nanoelectrode arrays can successfully achieve a high-quality intracellular electrophysiological study in electrogenic cells and their networks. However, a high success rate and high-quality and long-term intracellular recording using low-cost nanostructures is still a considerable challenge. Herein, we develop a scalable and robust hollow nanopillar electrode to achieve enhanced intracellular recording of cardiomyocytes. The template-based synthesis of vertical hollow nanopillars is compatible with large-scale and efficient microfabrication processes and is convenient to regulate the geometry of hollow nanopillars. Compared with the conventional same-size planar electrode, the regulating height of a hollow nanopillar can achieve high-quality and prolonged intracellular recordings, which can improve the cell-electrode interface for tight coupling and effective electroporation. It is demonstrated that the geometry regulation of a nanostructure is a powerful strategy to enhance intracellular recording.

Broadband Nanoscale Surface‐Enhanced Raman Spectroscopy by Multiresonant Nanolaminate Plasmonic Nanocavities on Vertical Nanopillars

AbstractSurface‐enhanced Raman spectroscopy (SERS) has become a sensitive detection technique for biochemical analysis. Despite significant research efforts, most SERS substrates consisting of single‐resonant plasmonic nanostructures on the planar surface suffer from limitations of narrowband SERS operation and unoptimized nano‐bio interface with living cells. Here, it is reported that nanolaminate plasmonic nanocavities on 3D vertical nanopillar arrays can support a broadband SERS operation with large enhancement factors (>106) under laser excitations at 532, 633, and 785 nm. The multi‐band Raman mapping measurements show that nanolaminate plasmonic nanocavities on vertical nanopillar arrays exhibit broadband uniform SERS performance with diffraction‐limited resolution at a single nanopillar footprint. By selective exposure of embedded plasmonic hotspots in individual metal–insulator–metal (MIM) nanogaps, nanoscale broadband SERS operation at the single MIM nanocavity level with visible and near‐infrared (vis–NIR) excitations is demonstrated. Numerical studies reveal that nanolaminate plasmonic nanocavities on vertical nanopillars can support multiple hybridized plasmonic modes to concentrate optical fields across a broadband wavelength range from 500 to 900 nm at the nanoscale.

Large-Area Nanopillar Arrays by Glancing Angle Deposition with Tailored Magnetic Properties.

Ferromagnetic films down to thicknesses of tens of nanometers and composed by polycrystalline Fe and Fe2O3 nanopillars are grown in large areas by glancing angle deposition with magnetron sputtering (MS-GLAD). The morphological features of these films strongly depend on the growth conditions. Vertical or tilted nanopillars have been fabricated depending on whether the substrate is kept rotating azimuthally during deposition or not, respectively. The magnetic properties of these nanopillars films, such as hysteresis loops squareness, adjustable switching fields, magnetic anisotropy and coercivity, can be tuned with the specific morphology. In particular, the growth performed through a collimator mask mounted onto a not rotating azimuthally substrate produces almost isolated well-defined tilted nanopillars that exhibit a magnetic hardening. The first-order reversal curves diagrams and micromagnetic simulations revealed that a growth-induced uniaxial anisotropy, associated with an anisotropic surface morphology produced by the glancing angle deposition in the direction perpendicular to the atomic flux, plays an important role in the observed magnetic signatures. These results demonstrate the potential of the MS-GLAD method to fabricate nanostructured films in large area with tailored structural and magnetic properties for technological applications.

Surface modification of ZnO nanopillars to enhance the sensitivity towards methane: The studies of experimental and first-principle simulation

The versatile patterned micro-shell fully covered with ZnO vertical nanopillars of length 2 µm and diameter 100 nm have been successfully synthesized and employed as a CH4 sensor. The sample has been characterized by Field Emission Scanning Electron Microscope (FE-SEM) and X-ray Diffraction (XRD). The bandgap of synthesized ZnO nanopillars has been calculated by using UV–visible spectroscopy and found to be 3.37 eV. Marvelous sensor response of ZnO nanopillars was observed for UV light and found to be 302 with a response time of ~ 1 s. ZnO nanopillars have an excellent sensing property so they can detect CH4 at a low concentration (100 ppm) at room temperature. Under UV light, it exhibited higher performance with an outstanding characteristic with an adequate gas sensor response 1.02 at 100 ppm of methane gas with response/recovery time ~ 132/13 s. The characteristics of ZnO and CH4 molecules were also calculated by first-principles based on density functional theory (DFT). The comparison of ZnO binding energy before and after interaction of methane gas molecule was calculated and found to be 3.68 eV and 3.1904 eV respectively, which show -0.7021 eV absorbance energy. Experimental and theoretical studied evidence that ZnO molecules have an excellent bustle with CH4 molecules.

Surface Texturing of Si with Periodically Arrayed Oblique Nanopillars to Achieve Antireflection.

Si surfaces were texturized with periodically arrayed oblique nanopillars using slanted plasma etching, and their optical reflectance was measured. The weighted mean reflectance (Rw) of the nanopillar-arrayed Si substrate decreased monotonically with increasing angles of the nanopillars. This may have resulted from the increase in the aspect ratio of the trenches between the nanopillars at oblique angles due to the shadowing effect. When the aspect ratios of the trenches between the nanopillars at 0° (vertical) and 40° (oblique) were equal, the Rw of the Si substrates arrayed with nanopillars at 40° was lower than that at 0°. This study suggests that surface texturing of Si with oblique nanopillars reduces light reflection compared to using a conventional array of vertical nanopillars.

Scalable fabrication and electrical contact formation process for vertically oriented silicon nanopillars in trenches

Vertical silicon nano-pillars (Si N-Pls) inside the cylindrical trenches have been fabricated as a prospective platform for the development of silicon nanowire based devices. Deep reactive ion etching (DRIE) has been used to etch these features in a silicon substrate. In the present case, the fabricated Si N-Pls are ~15 μm in length and 200–500 nm in diameter, while the trenches are of the diameter 12–25 μm. Alumina (Al2O3) discs of 50 nm thickness and diameter in the range of 200–500 nm, obtained via e-beam evaporation, have been used as a hard mask for defining the Si N-Pls during DRIE. Further, a proof of concept has been provided for obtaining electrical contact to the top-ends of these vertically oriented nano-pillars. The proposed platform involving nano-pillars in trenches can be extended for realizing microfluidic-channels containing an array of vertically oriented and electrically addressable silicon nanowires for several applications including chemical sensing.

Intracellular Recording of Human Cardiac Action Potentials on Market-Available Multielectrode Array Platforms.

High quality attenuated intracellular action potentials from large cell networks can be recorded on multi-electrode arrays by means of 3D vertical nanopillars using electrical pulses. However, most of the techniques require complex 3D nanostructures that prevent the straightforward translation into marketable products and the wide adoption in the scientific community. Moreover, 3D nanostructures are often delicate objects that cannot sustain several harsh use/cleaning cycles. On the contrary, laser optoacoustic poration allows the recording of action potentials on planar nanoporous electrodes made of noble metals. However, these constraints of the electrode material and morphology may also hinder the full exploitation of this methodology. Here, we show that optoacoustic poration is also very effective for porating cells on a large family of MEA electrode configurations, including robust electrodes made of nanoporous titanium nitride or disordered fractal-like gold nanostructures. This enables the recording of high quality cardiac action potentials in combination with optoacoustic poration, providing thus attenuated intracellular recordings on various already commercial devices used by a significant part of the research and industrial communities.

Photo‐Tunable Supramolecular Ultrathin Surfaces for Simultaneous Homeotropic Anchoring and Superfast Switching of Liquid Crystals

AbstractPhoto‐tunable supramolecular ultrathin surfaces functionalized with a soft ultraviolet (UV) treatment of star‐shaped reactive amphiphiles are fabricated to simultaneously afford homeotropic anchoring of liquid crystals (LCs) and improve the LC switching performance. Photochemically functionalized ultrathin surfaces are generated by cross‐linking star‐shaped amphiphilic monomers in the self‐assembled monolayers with retention of cluster structure under electric field. Since these star‐shaped amphiphiles can construct the close‐packed self‐organized molecular layer with an alkyl brush at the interface between indium tin oxide and LCs through intermolecular hydrogen bonding, they might make elegant alignment surfaces for the homeotropic anchoring of LCs to provide a new type of vertical alignment layer. It is experimentally revealed that supramolecular ultrathin layers with vertical nanopillars form hydrophobic surface, and afford a stable and uniform homeotropic alignment of LCs even in high‐temperature environment. Furthermore, a soft UV irradiation on the self‐assembled ultrathin surfaces under electric field yields superfast responsive cross‐linked ultrathin surfaces with low power consumption compared to conventional polyimide layer. Notably, this controlled methodology offers advantages of simplicity, low‐cost, and scalability in the fabrication of functional alignment surfaces without the need of complex manufacturing steps.

Nanomechanical Characterization of Vertical Nanopillars Using an MEMS-SPM Nano-Bending Testing Platform.

Nanomechanical characterization of vertically aligned micro- and nanopillars plays an important role in quality control of pillar-based sensors and devices. A microelectromechanical system based scanning probe microscope (MEMS-SPM) has been developed for quantitative measurement of the bending stiffness of micro- and nanopillars with high aspect ratios. The MEMS-SPM exhibits large in-plane displacement with subnanometric resolution and medium probing force beyond 100 micro-Newtons. A proof-of-principle experimental setup using an MEMS-SPM prototype has been built to experimentally determine the in-plane bending stiffness of silicon nanopillars with an aspect ratio higher than 10. Comparison between the experimental results and the analytical and FEM evaluation has been demonstrated. Measurement uncertainty analysis indicates that this nano-bending system is able to determine the pillar bending stiffness with an uncertainty better than 5%, provided that the pillars’ stiffness is close to the suspending stiffness of the MEMS-SPM. The MEMS-SPM measurement setup is capable of on-chip quantitative nanomechanical characterization of pillar-like nano-objects fabricated out of different materials.

Zinc Oxide Nanostructures Doped with Transition Metals: Fabrication and Properties

ZnO nanostructured films doped with Co and Ni deposited by hydrothermal method on silicon substrates covered with undoped ZnO sublayer were studied. SEM images of the films demonstrated them to consist of densely packed vertical nanopillars. Doping ZnO films with Ni or Co at concentrations up to [Formula: see text][Formula: see text]cm[Formula: see text] quenches their UV-excited photoluminescence. The doping also leads to the slight ferromagnetic behavior of ZnO.

Improved recovery time and sensitivity to H2 and NH3 at room temperature with SnOx vertical nanopillars on ITO

Nanostructured SnO2 is a promising material for the scalable production of portable gas sensors. To fully exploit their potential, these gas sensors need a faster recovery rate and higher sensitivity at room temperature than the current state of the art. Here we demonstrate a chemiresistive gas sensor based on vertical SnOx nanopillars, capable of sensing < 5 ppm of H2 at room temperature and 10 ppt at 230 °C. We test the sample both in vacuum and in air and observe an exceptional improvement in the performance compared to commercially available gas sensors. In particular, the recovery time for sensing NH3 at room temperature is more than one order of magnitude faster than a commercial SnO2 sensor. The sensor shows an unique combination of high sensitivity and fast recovery time, matching the requirements on materials expected to foster widespread use of portable and affordable gas sensors.

Biofunctionalized 3D Nanopillar Arrays Fostering Cell Guidance and Promoting Synapse Stability and Neuronal Activity in Networks.

A controlled geometry of in vitro neuronal networks allows investigation of the cellular mechanisms that underlie neuron-to-neuron and neuron–extracellular matrix interactions, which are essential to biomedical research. Herein, we report a selective guidance of primary hippocampal neurons by using arrays of three-dimensional vertical nanopillars (NPs) functionalized with a specific adhesion-promoting molecule—poly-dl-ornithine (PDLO). We show that 90% of neuronal cells are guided exclusively on the combinatorial PDLO/NP substrate. Moreover, we demonstrate the influence of the interplay between nanostructures and neurons on synapse formation and maturation, resulting in increased expression of postsynaptic density-95 protein and enhanced network cellular activity conferred by the endogenous c-fos expression. Successful guidance to foster synapse stability and cellular activity on multilevel cues of surface topography and chemical functionalization suggests the potential to devise technologies to control neuronal growth on nanostructures for tissue engineering, neuroprostheses, and drug development.

Preparation of well-distributed titania nanopillar arrays on Ti6Al4V surface by induction heating for enhancing osteogenic differentiation of stem cells

Great effort has recently been devoted to the preparation of nanoscale surfaces on titanium-based implants to achieve clinically fast osteoinduction and osseointegration, which relies on the unique characteristics of the nanostructure. In this work, we used induction heating treatment (IHT) as a rapid oxidation method to fabricate a porous nanoscale oxide layer on the Ti6Al4V surface for better medical application. Well-distributed vertical nanopillars were yielded by IHT for 20–35 s on the alloy surface. The composition of the oxides contained rutile/anatase TiO2 and a small amount of Al2O3 between the TiO2 grain boundaries (GBs). This technology resulted in a reduction and subsequent increase of surface roughness of 26–32 nm when upregulating the heating time, followed by the successive enhancement of the thickness, wettability and adhesion strength of the oxidation layer to the matrix. The surface hardness also distinctly rose to 554 HV in the IHT-35 s group compared with the 350 HV of bare Ti6Al4V. The massive small-angle GBs in the bare alloy promoted the formation of nanosized oxide crystallites. The grain refinement and deformation texture reduction further improved the mechanical properties of the matrix after IHT. Moreover, in vitro experiments on a mesenchymal stem cell (BMSC) culture derived from human bone marrow for 1–7 days indicated that the nanoscale layers did not cause cytotoxicity, and facilitated cell differentiation in osteoblasts by enhancing the gene and osteogenesis-related protein expressions after 1–3 weeks of culturing. The increase of the IHT time slightly advanced the BMSC proliferation and differentiation, especially during long-term culture. Our findings provide strong evidence that IHT oxidation technology is a novel nanosurface modification technology, which is potentially promising for further clinical development.

Apatite-forming ability of hydrothermally deposited rutile nano-structural arrays with exposed {101} facets on Ti foil

Highly ordered TiO2 nano-pillar arrays were deposited on the Ti foils by a hydrothermal method, using aqueous solutions of TiOSO4. The vertical nano-pillars with diameters in tens of nanometers strongly attached on the Ti foil and densely covered the whole surface. The structural studies clearly showed that the nano-pillars were pure tetragonal rutile TiO2 phase. [001] was the preferential growth direction. Based on the experimental results, a model for the in situ deposition of TiO2 with high-energy facet exposed is given. The growth mechanism was interpreted in terms of the lattice matching between the growing nano-structural titania and Ti, and the thermodynamic stability of the rutile lattice planes. The obtained TiO2 crystallographic plane with high energy induced apatite nucleation in less than 1 day and exhibited good in vitro bioactivity.

Site-Controlled Growth of Monolithic InGaAs/InP Quantum Well Nanopillar Lasers on Silicon.

In this Letter, we report the site-controlled growth of InP nanolasers on a silicon substrate with patterned SiO2 nanomasks by low-temperature metal-organic chemical vapor deposition, compatible with silicon complementary metal-oxide-semiconductor (CMOS) post-processing. A two-step growth procedure is presented to achieve smooth wurtzite faceting of vertical nanopillars. By incorporating InGaAs multiquantum wells, the nanopillar emission can be tuned over a wide spectral range. Enhanced quality factors of the intrinsic InP nanopillar cavities promote lasing at 0.87 and 1.21 μm, located within two important optical telecommunication bands. This is the first demonstration of a site-controlled III-V nanolaser monolithically integrated on silicon with a silicon-transparent emission wavelength, paving the way for energy-efficient on-chip optical links at typical telecommunication wavelengths.

Vertical Nanopillars as Probes for in Situ Nuclear Mechanotransduction

The stability and deformability of the cell nucleus are important to many biological processes like migration, proliferation, polarization. When cells are exposed to mechanical force, the force will be transmitted via cytoskeleton to the nucleus, induce shape deformation of the nuclear envelopes, and even change the configurations of nucleoskeletons. However, current techniques for studying nuclear mechanics are limited for studying inducing the effects of subcellular force perturbation in live cells. Here we developed a novel assay of using vertical nanopillar arrays to study the mechanical coupling between cell nucleus and cytoskeleton in live cells. Our results showed that nanopillars can induce deformation of nuclear envelope. By changing the geometry of the nanopillars or the stiffness of the nucleus, we can control the degree of nuclear deformation. Also, cytoskeletons such as actin and intermediate filaments were showed to play important roles in inducing and preventing nuclear deformation, respectively. Furthermore, we showed that mechanical perturbation of the nuclear envelope can cause the reorganization of nuclear lamina, which give the clue that cell nucleus itself may be able to sense and respond to mechanical signals. Overall, vertical nanopillars provide a long-term and non-invasive force to create a subcellular nuclear perturbation, and can be used as a tool for studying nuclear mechanotransduction in live cells.

Strain Tuning and Strong Enhancement of Ionic Conductivity in SrZrO3–RE2O3 (RE = Sm, Eu, Gd, Dy, and Er) Nanocomposite Films

Fast ion transport channels at interfaces in thin films have attracted great attention due to a range of potential applications for energy materials and devices, for, solid oxide fuel cells, sensors, and memories. Here, it is shown that in vertical nanocomposite heteroepitaxial films of SrZrO3–RE2O3 (RE = Sm, Eu, Gd, Dy, and Er) the ionic conductivity of the composite can be tuned and strongly enhanced using embedded, stiff, and vertical nanopillars of RE2O3. With increasing lattice constant of RE2O3 from Er2O3 to Sm2O3, it is found that the tensile strain in the SrZrO3 increases proportionately, and the ionic conductivity of the composite increases accordingly, by an order of magnitude. The results here conclusively show, for the first time, that strain in films can be effectively used to tune the ionic conductivity of the materials.

Vertical nanopillars for in situ probing of nuclear mechanics in adherent cells

The mechanical stability and deformability of the cell nucleus are crucial to many biological processes, including migration, proliferation and polarization. In vivo, the cell nucleus is frequently subjected to deformation on a variety of length and time scales, but current techniques for studying nuclear mechanics do not provide access to subnuclear deformation in live functioning cells. Here we introduce arrays of vertical nanopillars as a new method for the in situ study of nuclear deformability and the mechanical coupling between the cell membrane and the nucleus in live cells. Our measurements show that nanopillar-induced nuclear deformation is determined by nuclear stiffness, as well as opposing effects from actin and intermediate filaments. Furthermore, the depth, width and curvature of nuclear deformation can be controlled by varying the geometry of the nanopillar array. Overall, vertical nanopillar arrays constitute a novel approach for non-invasive, subcellular perturbation of nuclear mechanics and mechanotransduction in live cells.

Self-organized fabrication of periodic arrays of vertical, ultra-thin nanopillars on GaAs surfaces

This paper presents a low-cost procedure that allows for self-organized fabrication of periodically arranged, sub-50 nm diameter, vertical-sidewall GaAs nanopillars on GaAs surfaces based on nanosphere lithography, and reactive ion etching (RIE). Monodispersed polystyrene (PS) sphere double layers are deposited from a colloidal suspension on pre-treated, hydrophilized GaAs substrates. Ni is thermally evaporated to act as a hard mask for subsequent RIE. Scanning electron microscopy reveals that the Ni nanoparticles left on the substrate after PS sphere removal have polygon-shaped in-plane cross-sections corresponding to the shape of the double layer mask openings. RIE using SiCl4 at low pressure and high power density leads to the formation of vertical nanopillars with circular to oval cross-sections, whose diameters are reduced by ∼1/3 compared to those of the Ni nanoparticles. These findings can be explained by plasma-enhanced surface diffusion and sputtering processes during RIE. The obtained GaAs nanopillars have an average diameter of only ∼23 nm, exhibit an excellent verticality with a sidewall angle of 88.9 ± 0.4° and planar top faces, as visible in transmission electron microscopy images.

At the Nano-Bio Interface: Probing Live Cells with Nano Sensors

The rapidly evolving field of nanotechnology creates new frontiers for biological sciences. Recently, we and other groups show that vertical nanopillars protruding from a flat surface support cell survival and can be used as subcellular sensors to probe biological processes in live cells. In particular, we are exploring nanopillars as electric sensor, optical sensors, and structural probes. As an electric sensor, nanopillars electrodes offer several advantages such as high sensitivity, subcellular spatial resolution, and precise control of the sensor geometry. A sensitive measurement of cellular electrical activities requires strong coupling between the cell membrane and the recording electrodes. We found that nanopillars electrodes deform the cell membrane inwards and induce negative curvature when the cell engulfs them, leading to a reduction of the membrane-electrode gap distance and a higher sealing resistance. The 3D topology of the nanopillars electrodes is crucial for its enhanced signal detection. A new approach explores nanoelectrodes of a new 3D geometry, namely nanotubes with hollow centers. The nanotube geometry further enhances membrane-electrode coupling efficiency and also significantly increases the time duration of intracellular access. Interestingly, nanopillars serve as focal adhesion points for cell attachment. The presence of high membrane curvature induced by vertical nanopillars or nanotubes affects the distribution of curvature-sensitive proteins. Those studies show a strong interplay between biological cells and nano-sized sensors, which is an essential consideration for future development of interfacing devices.