Linker-free Functionalization of Phosphorene Nanosheets by Sialic Acid Biomolecules

The importance of sialic acid on cell functions has been recently unveiled, and consequently, great attention has been paid to its interaction with tumor cells. In this line of research, we have realized phosphorene nanosheets functionalized with sialic acid molecules for biological applications with no need for another linker molecule. The formation of phosphorene sheets is feasible by using hydrogen plasma treatment and conversion of amorphous phosphorus on silicon substrates into highly crystalline nanosheets. Through immersion of these freshly prepared nanosheets into an aqueous solution containing sialic acid molecules, the formation of chemical binding between biomolecules and P atoms is initiated to form a carpet-like coverage. We have studied these structures by using Raman spectroscopy, electron microscopy, FTIR-ATR spectroscopy, and X-ray photoelectron spectroscopy. While XPS supports the passivation of sialic-activated phosphorene nanosheets (SAP) against oxidation in air or aqueous solutions, the FTIR analysis corroborates the evolution of P-O-C and P-C bonds between such biomolecules and the sheet surface. Moreover, the high-resolution TEM images demonstrate a considerable reduction in the lattice spacing from 0.32 nm for pristine phosphorene to 0.30 nm. Similarly, Raman spectroscopy depicts a shift in A2g in-plane vibrations, owing to the evolution of stress in the passivated sheets. To investigate their biocompatibility, we examined the toxicity of these bioactivated structures and observed no or little sign of toxicity. For the latter evaluation, we exploited MTT, flow cytometry, and animal models for in vivo investigations.

Experimental and molecular dynamics studies of an ultra-fast sequential hydrogen plasma process for fabricating phosphorene-based sensors

Low concentration phosphorene-based sensors have been fabricated using a facile and ultra-fast process which is based on an exfoliation-free sequential hydrogen plasma treatment to convert the amorphous phosphorus thin film into mono- or few-layered phosphorene sheets. These sheets have been realized directly on silicon substrates followed by the fabrication of field-effect transistors showing the low leakage current and reasonable mobility for the nano-sensors. Being capable of covering the whole surface of the silicon substrate, red phosphorus (RP) coated substrate has been employed to achieve large area phosphorene sheets. Unlike the available techniques including mechanical exfoliation, there is no need for any exfoliation and/or transfer step which is significant progress in shortening the device fabrication procedure. These phosphorene sheets have been examined using transmission electron microscopy (TEM), Scanning electron microscopy (SEM), Raman spectroscopy and atomic-force microscopy (AFM). Electrical output in different states of the crystallization as well as its correlation with the test parameters have been also extensively used to examine the evolution of the phosphorene sheets. By utilizing the fabricated devices, the sensitivity of the phosphorene based-field effect transistors to the soluble L-Cysteine in low concentrations has been studied by measuring the FET response to the different concentrations. At a gate voltage of - 2.5 V, the range of 0.07 to 0.60 mg/ml of the L-Cysteine has been distinguishably detected presenting a gate-controlled sensor for a low-concentration solution. A reactive molecular dynamics simulation has been also performed to track the details of this plasma-based crystallization. The obtained results showed that the imparted energy from hydrogen plasma resulted in a phase transition from a system containing red phosphorus atoms to the crystal one. Interestingly and according to the simulation results, there is a directional preference of crystal growth as the crystalline domains are being formed and RP atoms are more likely to re-locate in armchair than in zigzag direction.

Antimony doped SnO2nanowire@C core-shell structure as a high-performance anode material for lithium-ion battery

SnO₂is considered as one of the high specific capacity anode materials for Lithium-ion batteries. However, the low electrical conductivity of SnO₂limits its applications. This manuscript reports a simple and efficient approach for the synthesis of Sb-doped SnO₂nanowires (NWs) core and carbon shell structure which effectively enhances the electrical conductivity and electrochemical performance of SnO₂nanostructures. Sb doping was performed during the vapor-liquid-solid synthesis of SnO₂NWs in a horizontal furnace. Subsequently, carbon nanolayer was coated on the NWs using the DC Plasma Enhanced Chemical Vapor Deposition approach. The carbon-coated shell improves the Solid-Electrolyte Interphase stability and alleviates the volume expansion of the anode electrode during charging and discharging. The Sb-doped SnO₂core carbon shell anode showed the superior specific capacity of 585 mAhg^-1after 100 cycles at the current density of 100 mA g^-1, compared to the pure SnO₂NWs electrode. The cycle stability evaluation revealed that the discharge capacity of pure SnO₂NWs and Sb doped SnO₂NWs electrodes were dropped to 52 and 152 mAh g^-1after100th cycles. The process of Sb doping and carbon nano shielding of SnO₂nanostructures is proposed for noticeable improvement of the anode performance for SnO₂based materials.

Evolution of large area TiS2-TiO2 heterostructures and S-doped TiO2 nano-sheets on titanium foils

We report a novel and facile method to synthesize sulfur-doped titanium oxide sheets and realize TiS2-TiO2 heterostructures by means of a sequential sulfurization and oxidation step in a dual-zone chemical vapor deposition furnace. The inclusion of chlorine and argon gases during the growth of such titanium-based compounds plays a critical role in the formation of desired geometries and crystalline structures. These heterostructures possess nano-whisker and nanosheet configurations, controlled by adjusting the growth parameters such as temperature, carrier gas and the sequencing between different steps of the growth. The evolution of these complex heterostructures has been investigated using Raman spectroscopy and EDS characterization. The presence of chlorine gas during the growth results in local TiS2 formation as well as faceted growth of TiO2 nanosheets through anatase to rutile phase change prohibition. The electron microscopy (TEM) images and diffraction pattern (SAED) characterization reveal the crystallinity and layered nature of grown structures, further demonstrating the 2D characteristics of S-doped nanosheets. The evolution of TiO2 on TiS2 heterostructures has also has been verified using XPS analysis. These highly featured nanostructures are suitable candidates to enhance the photocatalytic behavior of TiO2 nanostructures.

Controlled Plasma Thinning of Bulk MoS2 Flakes for Photodetector Fabrication

The electronic properties of layered materials are directly determined based on their thicknesses. Remarkable progress has been carried out on synthesis of wafer-scale atomically molybdenum disulfide (MoS2) layers as a two-dimensional material in the past few years in order to transform them into commercial products. Although chemical/mechanical exfoliation techniques are used to obtain a high-quality monolayer of MoS2, the lack of suitable control in the thickness and the lateral size of the flakes restrict their benefits. As a result, a straightforward, effective, and reliable approach is widely demanded to achieve a large-area MoS2 flake with control in its thickness for optoelectronic applications. In this study, thick MoS2 flakes are obtained by a short-time bath sonication in dimethylformamide solvent, which are thinned with the aid of a sequential plasma etching process using H2, O2, and SF6 plasma. A comprehensive study has been carried out on MoS2 flakes based on scanning electron microscopy, atomic force microscopy, Raman, transmission electron microscopy, and X-ray photoelectron microscopy measurements, which ultimately leads to a two-cycle plasma thinning method. In this approach, H2 is used in the passivation step in the first subcycle, and O2/SF6 plasma acts as an etching step for removing the MoS2 layers in the second subcycle. Finally, we show that this technique can be enthusiastically used to fabricate MoS2-based photodetectors with a considerable photoresponsivity of 1.39 A/W and a response time of 0.45 s under laser excitation of 532 nm.

Formation of large area WS2 nanosheets using an oxygen-plasma assisted exfoliation suitable for optical devices

We report a facile method to realize large area two-dimensional tungsten disulfide nanosheets. The formation of such large WS₂ sheets is feasible through sonication in water and dimethyl-sulfoxide (DMSO) solutions, leading to well-separated mono and few layer flakes. The exfoliation has been improved by extensive immersion in near-freezing water prior to probe sonication and subsequent addition of DMSO. By applying oxygen plasma before exfoliation, the size and distribution of sheets become more uniform and larger mono and double-layered structures with sizes of the order of 1 μm are achieved. Different analyses such as SEM, TEM, AFM, DLS and Raman spectroscopy have been employed to understand the mechanism of the exfoliation and study the effects of various parameters such as water temperature, duration and plasma power. The optical properties of WS₂ sheets have been examined with a 532 nm laser illumination and demonstrate superior responsivity and detectivity of 0.59 A W^-1 and 6.5 × 10¹⁰ cm Hz^1/2 W^-1, respectively.

Novel approach for improving the performance of Si-based anodes in lithium-ion batteries

Herein, we report successful deposition of aluminum oxide films on the silicon nanowires (SiNWs) to realize core-shell silicon-based lithium-ion battery anodes. By means of reactive ion etching, it has been possible to form an ultra-thin layer of Al₂O₃ on SiNWs through hydrogen plasma. This deposition technique leads to the formation of tiny holes on the surface of the Al₂O₃ layer while introducing the pore sites into the inner silicon material without damaging the whole structure. SiNW@Al₂O₃ core-shell nanostructures were used as the effective anode materials and showed a superior electrochemical performance compared to conventional SiNWs. Our electrode exhibited the high first cycle specific discharge capacity of 3936 mAh g^-1 at a rate of C/16 as well as high rate capability. Furthermore, this anode electrode showed less than 6% degradation of specific capacity over 120 cycles at high rate density of 2C and it delivers high reversible capacity of 965 mAh g^-1. The improvement in the electrochemical properties of our electrode is achieved due to both a high specific capacity of Si core and the effect of aluminum oxide shell on active material cycling stability.

Sequential Solvent Exchange Method for Controlled Exfoliation of MoS2 Suitable for Phototransistor Fabrication

In this study, flakes of molybdenum disulfide (MoS₂) with controlled size and thickness are prepared through sequential solvent exchange method by sonication in dimethylformamide (DMF) and N-methyl-2-pyrrolidone (NMP) solvents. While NMP acts more effectively in reducing the thickness of flakes, DMF shows better potential in conserving the lateral size of nanosheets. The distribution of size and thickness of nanoflakes as a function of sonication time verifies that extended sonication results in dramatic drop of the dimension of the exfoliated flakes. This technique leads to the formation of few-layered MoS₂ flakes without further drop of their lateral dimensions. It has been observed that by exposing the bulk MoS₂ powders to oxygen plasma, the exfoliation process is accelerated without converting to 2H-MoS₂ structures. Finally, a phototransistor has been fabricated based on few-layered MoS₂ layers with a field effect mobility of ∼2.1 cm² V^-1 s^-1 showing a high response to laser excitation of 532 nm wavelength.

Nanoelectromechanical Chip (NELMEC) Combination of Nanoelectronics and Microfluidics to Diagnose Epithelial and Mesenchymal Circulating Tumor Cells from Leukocytes

An integrated nano-electromechanical chip (NELMEC) has been developed for the label-free distinguishing of both epithelial and mesenchymal circulating tumor cells (ECTCs and MCTCs, respectively) from white blood cells (WBCs). This nanoelectronic microfluidic chip fabricated by silicon micromachining can trap large single cells (>12 µm) at the opening of the analysis microchannel arrays. The nature of the captured cells is detected using silicon nanograss (SiNG) electrodes patterned at the entrance of the channels. There is an observable difference between the membrane capacitance of the ECTCs and MCTCs and that of WBCs (measured using SiNG electrodes), which is the key indication for our diagnosis. The NELMEC chip not only solves the problem of the size overlap between CTCs and WBCs but also detects MCTCs without the need for any markers or tagging processes, which has been an important problem in previously reported CTC detection systems. The great conductivity of the gold-coated SiNG nanocontacts as well as their safe penetration into the membrane of captured cells, facilitate a precise and direct signal extraction to distinguish the type of captured cell. The results achieved from epithelial (MCF-7) and mesenchymal (MDA-MB231) breast cancer cells circulated in unprocessed blood suggest the significant applications for these diagnostic abilities of NELMEC.

A single-cell correlative nanoelectromechanosensing approach to detect cancerous transformation: monitoring the function of F-actin microfilaments in the modulation of the ion channel activity

Cancerous transformation may be dependent on correlation between electrical disruptions in the cell membrane and mechanical disruptions of cytoskeleton structures. Silicon nanotube (SiNT)-based electrical probes, as ultra-accurate signal recorders with subcellular resolution, may create many opportunities for fundamental biological research and biomedical applications. Here, we used this technology to electrically monitor cellular mechanosensing. The SiNT probe was combined with an electrically activated glass micropipette aspiration system to achieve a new cancer diagnostic technique that is based on real-time correlation between mechanical and electrical behaviour of single cells. Our studies demonstrated marked changes in the electrical response following increases in the mechanical aspiration force in healthy cells. In contrast, such responses were extremely weak for malignant cells. Confocal microscopy results showed the impact of actin microfilament remodelling on the reduction of the electrical response for aspirated cancer cells due to the significant role of actin in modulating the ion channel activity in the cell membrane.

Monitoring the spreading stage of lung cells by silicon nanowire electrical cell impedance sensor for cancer detection purposes

We developed a silicon nanowire based electrical cell impedance sensor (SiNW-ECIS) as an instrument that detects cancerous cultured living lung cells by monitoring their spreading state at which the cells stretched and become extended on nanowires. Further current penetration into the extended membrane of malignant cells in respect to normal ones (In the first 6h after cells interaction with surface) are the key mechanism in our diagnosis procedure. The developed device applied to monitor the spreading-induced electrical differences between cancerous and normal lung cells in an integral fashion. Detection was performed so faster than the time required to complete cells mitosis. Morphology and architecture of doped Si nanowires covered microelectrodes observably enhance the contact area between cells and electrodes which support accurate signal recording from stretched cells as indicated by SEM and florescent images.

Permeation of nickel nanodots on carbon nanotubes: synthesis of 3D CNT-based nanomaterials

In this paper, we report the fabrication of three-dimensional (3D) hybrid carbon nanotubes (CNT)-based nanostructures. Secondary carbon nanotubes are grown on the hydrogenated and unzipped horizontal carbon nanotubes without any further catalyst deposition. Hydrogenation of horizontal CNTs leads to out-diffusion of Ni nanoparticles that were trapped within the walls of nanotubes during the original growth process. This out-diffusion effect, as permeation, leads to the formation of nickel dots at the surfaces of carbon nanotubes which acts as the catalyst for the growth of secondary nanotubes. By controlling the secondary growth condition, a variety of 3D structures could be achieved. The permeation effect and the evolution of secondary nanostructures are studied extensively by means of scanning electron microscopy, transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction analysis.

Cell-imprinted substrates act as an artificial niche for skin regeneration

Bioinspired materials can mimic the stem cell environment and modulate stem cell differentiation and proliferation. In this study, biomimetic micro/nanoenvironments were fabricated by cell-imprinted substrates based on mature human keratinocyte morphological templates. The data obtained from atomic force microscopy and field emission scanning electron microscopy revealed that the keratinocyte-cell-imprinted poly(dimethylsiloxane) casting procedure could imitate the surface morphology of the plasma membrane, ranging from the nanoscale to the macroscale, which may provide the required topographical cell fingerprints to induce differentiation. Gene expression levels of the genes analyzed (involucrin, collagen type I, and keratin 10) together with protein expression data showed that human adipose-derived stem cells (ADSCs) seeded on these cell-imprinted substrates were driven to adopt the specific shape and characteristics of keratinocytes. The observed morphology of the ADSCs grown on the keratinocyte casts was noticeably different from that of stem cells cultivated on the stem-cell-imprinted substrates. Since the shape and geometry of the nucleus could potentially alter the gene expression, we used molecular dynamics to probe the effect of the confining geometry on the chain arrangement of simulated chromatin fibers in the nuclei. The results obtained suggested that induction of mature cell shapes onto stem cells can influence nucleus deformation of the stem cells followed by regulation of target genes. This might pave the way for a reliable, efficient, and cheap approach of controlling stem cell differentiation toward skin cells for wound healing applications.

Single-cell resolution diagnosis of cancer cells by carbon nanotube electrical spectroscopy

We report the use of vertically aligned carbon nanotubes (VACNTs) as electrical endoscopes (biosensors) for cancer metastatic diagnosis at single-cell resolution. The device is based on direct signal extraction by means of vertically aligned conductive carbon nanotubes from a live cell membrane, which has been disrupted during carcinogenesis at its primary and progressive stages. The value of this electrical disruption depends on the cancer metastatic grade. In addition, the electrical resonance behavior of the cell, halted during cancer progression, could be monitored as a new cancer diagnostic profile. By taking a second derivative of the cell impedance with respect to applied frequency, we have arrived at a new spectroscopy tool for distinguishing cancerous stages of colon and breast carcinoma cells.

A nickel-gold bilayer catalyst engineering technique for self-assembled growth of highly ordered silicon nanotubes (SiNT)

We report the growth of vertically aligned high-crystallinity silicon nanotube (SiNT) arrays on silicon substrate by means of a Ni-Au bilayer catalyst engineering technique. Nanotubes were synthesized through solid-liquid-solid method as well as vapor-liquid-solid. A precise evaluation utilizing atomic force microscopy and lateral force microscopy describes that the gold profile in Ni regions leads to the construction of multiwall SiNTs. The agreement of the structural geometry and stiffness of the obtained SiNTs with previous theoretical predictions suggest sp(3) hybridization as the mechanism of tube formation. Apart from scanning electron and transmission electron microscopy techniques, photoluminescence spectroscopy (PL) has been conducted to investigate the formation of nanostructures. PL spectroscopy confirms the evolution of ultrafine walls of the silicon nanotubes, responsible for the observed photoemission properties.

Polyphenols attached graphene nanosheets for high efficiency NIR mediated photodestruction of cancer cells

Green tea-reduced graphene oxide (GT-rGO) sheets have been exploited for high efficiency near infrared (NIR) photothermal therapy of HT29 and SW48 colon cancer cells. The biocompatibility of GT-rGO sheets was investigated by means of MTT assays. The polyphenol constituents of GT-rGO act as effective targeting ligands for the attachment of rGO to the surface of cancer cells, as confirmed by the cell granularity test in flow cytometry assays and also by scanning electron microscopy. The photo-thermal destruction of higher metastatic cancer cells (SW48) is found to be more than 20% higher than that of the lower metastatic one (HT29). The photo-destruction efficiency factor of the GT-rGO is found to be at least two orders of magnitude higher than other carbon-based nano-materials. Such excellent cancer cell destruction efficiency provided application of a low concentration of rGO (3 mg/L) and NIR laser power density (0.25 W/cm(2)) in our photo-thermal therapy of cancer cells.

Gas sensing properties of branched carbon nanotube-based structures using a novel low voltage emission

Branched carbon nanostructures have been successfully grown on interdigital comb-like structures for a gas sensing application. Field emission scanning electron microscopy has been utilized to investigate the morphology and structure of the grown nanostructures at different stages of growth process. Tunneling current of the fabricated sensor has been measured when a monotonically increasing voltage is applied between the electrodes. The effect of exposure to three different gases on the measured current has been studied. A data processing on the measured current voltage characteristics results in the evolution of various peaks at distinct voltages which depends on the type of the gas.

Gradual tilting exposure photo and nano lithography technique

We report a novel tilting exposure photolithography (TEL) technique where gradual pattern displacement is employed to achieve high-resolution features over large areas with reasonable exposure times. A linear array with features of the order of 100 nm has been realized using this technique with standard blue-light LED sources. TEL can be useful in the visible and ultraviolet spectra to create two-dimensional periodic structures. The created structures include the nanometric array of spots and lines. The proposed technique can be used as a writing method where complex features can be generated by moving the sample-holding leading to serpentine nanometric linear arrays.

A vertically aligned carbon nanotube-based impedance sensing biosensor for rapid and high sensitive detection of cancer cells

A novel vertically aligned carbon nanotube based electrical cell impedance sensing biosensor (CNT-ECIS) was demonstrated for the first time as a more rapid, sensitive and specific device for the detection of cancer cells. This biosensor is based on the fast entrapment of cancer cells on vertically aligned carbon nanotube arrays and leads to mechanical and electrical interactions between CNT tips and entrapped cell membranes, changing the impedance of the biosensor. CNT-ECIS was fabricated through a photolithography process on Ni/SiO(2)/Si layers. Carbon nanotube arrays have been grown on 9 nm thick patterned Ni microelectrodes by DC-PECVD. SW48 colon cancer cells were passed over the surface of CNT covered electrodes to be specifically entrapped on elastic nanotube beams. CNT arrays act as both adhesive and conductive agents and impedance changes occurred as fast as 30 s (for whole entrapment and signaling processes). CNT-ECIS detected the cancer cells with the concentration as low as 4000 cells cm(-2) on its surface and a sensitivity of 1.7 × 10(-3)Ω cm(2). Time and cell efficiency factor (TEF and CEF) parameters were defined which describe the sensor's rapidness and resolution, respectively. TEF and CEF of CNT-ECIS were much higher than other cell based electrical biosensors which are compared in this paper.

High performance multilayered nano-crystalline silicon/silicon-oxide light-emitting diodes on glass substrates

A low-temperature hydrogenation-assisted sequential deposition and crystallization technique is reported for the preparation of nano-scale silicon quantum dots suitable for light-emitting applications. Radio-frequency plasma-enhanced deposition was used to realize multiple layers of nano-crystalline silicon while reactive ion etching was employed to create nano-scale features. The physical characteristics of the films prepared using different plasma conditions were investigated using scanning electron microscopy, transmission electron microscopy, room temperature photoluminescence and infrared spectroscopy. The formation of multilayered structures improved the photon-emission properties as observed by photoluminescence and a thin layer of silicon oxy-nitride was then used for electrical isolation between adjacent silicon layers. The preparation of light-emitting diodes directly on glass substrates has been demonstrated and the electroluminescence spectrum has been measured.