Sharp Nanoscale Research Articles

Extraction and identification of steroidal saponins from Polygonatum cyrtonema Hua using natural deep eutectic solvent-synergistic quartz sand-assisted extraction method.

In this study, quartz sand with particularly sharp nanoscale edges acted like a nanoscale knife physically cut cells of Polygonatum cyrtonema Hua into nanosized particles and was synergized with natural deep eutectic solvent to extract steroidal saponins of Polygonatum cyrtonema Hua. The natural deep eutectic solvent (choline chloride-lactic acid)-synergistic quartz sand-assisted extraction was optimized using response surface methodology. The steroidal saponins purified with AB-8 macroporous resin were identified using ultra-high-performance liquid chromatography-triple time of flight mass spectrometry. The results showed that the experimental total saponins content value (36.97±0.12mg dioscin equivalent/g dry weight) at optimal extraction conditions with a temperature of 68°C, a rotational speed of 20 400rpm, shear time of 4.3min, the liquid-solid ratio of 38ml/g, was close to the maximum possible theoretical value (36.64mg dioscin equivalent/g dry weight). A total of 20 steroidal saponins were identified, among which the content of (25R)-Kingianoside E was the highest (102.66±3.47mg/g). Furthermore, a new steroid saponin (3β,25S)-26-(β-D-glucopyranosyloxy)-22-hydroxyfurost-5-en-3-yl 4-O-β-D-glucopyranosyl-β-D-galactopyranoside+Glc was found for the first time. These results revealed that natural deep eutectic solvent-synergistic quartz sand-assisted extraction was an efficient and green method to extract a variety of steroidal saponins.

You shall not pass: Ti nanospike-based sterilizer in fluid flow reactor

We report the laser-ablative fabrication of antibacterial nanostructures, combining mechanical and chemotoxic effects, by femto- and nanosecond laser ablation and their testing on Staphylococcus aureus and Pseudomonas aeruginosa strains. A Ti surface, covered with nanospikes and periodical surface ripples, provides a strong anti-biofilm effect, and the addition of cytotoxic nanoparticles (NPs) (Ag, Se) enhances the overall bactericidal activities. A flow reactor, including Ti nanospike-covered wafers as a through-flow sterilizer, allowed reduction of the bacterial population by two orders. Several types of nanostructures with/without biofilms were characterized by scanning electron microscopy and energy-dispersive x-ray spectroscopy. Their antibacterial properties were demonstrated by standard live/dead tests and were suggested to originate from the combined chemical toxicity of NPs and mechanical damage caused by sharp nanoscale relief on Ti.

Binary Spiky/Spherical Nanoparticle Films with Hierarchical Micro/Nanostructures for High-Performance Flexible Pressure Sensors.

Flexible pressure sensors have been widely explored for their versatile applications in electronic skins, wearable healthcare monitoring devices, and robotics. However, fabrication of sensors with characteristics such as high sensitivity, linearity, and simple fabrication process remains a challenge. Therefore, we propose herein a highly flexible and sensitive pressure sensor based on a conductive binary spiky/spherical nanoparticle film that can be fabricated by a simple spray-coating method. The sea-urchin-shaped spiky nanoparticles are based on the core-shell structures of spherical silica nanoparticles decorated with conductive polyaniline spiky shells. The simple spray coating of binary spiky/spherical nanoparticles enables the formation of uniform conductive nanoparticle-based films with hierarchical nano/microstructures. The two differently shaped particles-based films (namely sea-urchin-shaped and spherical) when interlocked face-to-face to form a bilayer structure can be used as a highly sensitive piezoresistive pressure sensor. Our optimized pressure sensor exhibits high sensitivity (17.5 kPa-1) and linear responsivity over a wide pressure range (0.008-120 kPa), owing to the effects of stress concentration and gradual deformation of the hierarchical microporous structures with sharp nanoscale tips. Moreover, the sensor exhibits high durability over 6000 repeated cycles and practical applicability in wearable devices that can be used for healthcare monitoring and subtle airflow detection (1 L/min).

You shall not pass: titanium and silver nanospikes-based flow-through filter for liquid sterilization

Antibacterial nanostructures were written on the surface of a silver (Ag) film and titanium (Ti) wafer using femtosecond laser ablation. The bactericidal properties were tested on S. aureus and P. aeruginosa bacterial strains. The resulting nanostructures were characterized by scanning electron microscopy (SEM). A flow-through filter, based on Ag plates with nanospikes, used as a sterilization of the liquid, led to the almost complete death of bacteria. It is assumed that the antibacterial properties are due to mechanical damage caused by the sharp nanoscale relief.

A bacterial misericorde: laser-generated silicon nanorazors with embedded biotoxic nanoparticles combat the formation of durable biofilms

A combined mechano- and chemo-bactericidal nanomorphology, consisting of periodical surface structures on silicon with deposited nanoparticles of selenium, tellurium oxide, antimony oxide and silver, was fabricated via laser ablation in deionized water with femto- and nanosecond laser systems. The resulting functional surfaces were tested against the formation of Staphylococcus aureus biofilms, and their morphology and elemental composition was characterized with scanning electron microscopy and energy-dispersive x-ray and Raman spectroscopy. Antibacterial properties were suggested to originate from the combined chemical toxicity of nanoparticles and the mechanical damage caused by the sharp nanoscale relief on silicon.

Intracellular Photothermal Delivery for Suspension Cells Using Sharp Nanoscale Tips in Microwells.

Efficient intracellular delivery of biomolecules into cells that grow in suspension is of great interest for biomedical research, such as for applications in cancer immunotherapy. Although tremendous effort has been expended, it remains challenging for existing transfer platforms to deliver materials efficiently into suspension cells. Here, we demonstrate a high-efficiency photothermal delivery approach for suspension cells using sharp nanoscale metal-coated tips positioned at the edge of microwells, which provide controllable membrane disruption for each cell in an array. Self-aligned microfabrication generates a uniform microwell array with three-dimensional nanoscale metallic sharp tip structures. Suspension cells self-position by gravity within each microwell in direct contact with eight sharp tips, where laser-induced cavitation bubbles generate transient pores in the cell membrane to facilitate intracellular delivery of extracellular cargo. A range of cargo sizes were tested on this platform using Ramos suspension B cells with an efficiency of >84% for Calcein green (0.6 kDa) and >45% for FITC-dextran (2000 kDa), with retained viability of >96% and a throughput of >100 000 cells delivered per minute. The bacterial enzyme β-lactamase (29 kDa) was delivered into Ramos B cells and retained its biological activity, whereas a green fluorescence protein expression plasmid was delivered into Ramos B cells with a transfection efficiency of >58%, and a viability of >89% achieved.

Plasmonic nano-protrusions: hierarchical nanostructures for single-molecule Raman spectroscopy

Classical methods for enhancing the electromagnetic field from substrates for spectroscopic applications, such as surface-enhanced Raman spectroscopy (SERS), have involved the generation of hotspots through directed self-assembly of nanoparticles or by patterning nanoscale features using expensive nanolithography techniques. A novel large-area, cost-effective soft lithographic technique involving glancing angle deposition (GLAD) of silver on polymer gratings is reported here. This method produces hierarchical nanostructures with high enhancement factors capable of analyzing single-molecule SERS. The uniform ordered and patterned nanostructures provide extraordinary field enhancements that serve as excitatory hotspots and are herein interrogated by SERS. The high spatial homogeneity of the Raman signal and signal enhancement over a large area from a self-assembled monolayer (SAM) of 2-naphthalenethiol demonstrated the uniformity of the hotspots. The enhancement was shown to have a critical dependence on the underlying nanostructure via the surface energy landscape and GLAD angles for a fixed deposition thickness, as evidenced by atomic force microscopy and scanning electron microscopy surface analysis of the substrate. The nanostructured surface leads to an extremely concentrated electromagnetic field at sharp nanoscale peaks, here referred to as ‘nano-protrusions’, due to the coupling of surface plasmon resonance (SPR) with localized SPR. These nano-protrusions act as hotspots which provide Raman enhancement factors as high as 108 over a comparable SAM on silver. Comparison of our substrate with the commercial substrate Klarite™ shows higher signal enhancement and minimal signal variation with hotspot spatial distribution. By using the proper plasmon resonance angle corresponding to the laser source wavelength, further enhancement in signal intensity can be achieved. Single-molecule Raman spectra for rhodamine 6G are obtained from the best SERS substrate (a GLAD angle of 60°). The single-molecule spectrum is invariant over the substrate, due to the patterned ordered nanostructures (nano-protrusions).

Long-term stability of Cu surface nanotips

Sharp nanoscale tips on the metal surfaces of electrodes enhance locally applied electric fields. Strongly enhanced electric fields trigger electron field emission and atom evaporation from the apexes of nanotips. Together, these processes may explain electric discharges in the form of small local arcs observed near metal surfaces in the presence of electric fields, even in ultra-high vacuum conditions. In the present work, we investigate the stability of nanoscale tips by means of computer simulations of surface diffusion processes on copper, the main material used in high-voltage electronics. We study the stability and lifetime of thin copper (Cu) surface nanotips at different temperatures in terms of diffusion processes. For this purpose we have developed a surface kinetic Monte Carlo (KMC) model where the jump processes are described by tabulated precalculated energy barriers. We show that tall surface features with high aspect ratios can be fairly stable at room temperature. However, the stability was found to depend strongly on the temperature: 13 nm nanotips with the major axes in the crystallographic directions were found to flatten down to half of the original height in less than 100 ns at temperatures close to the melting point, whereas no significant change in the height of these nanotips was observed after 10 at room temperature. Moreover, the nanotips built up along the crystallographic directions were found to be significantly more stable than those oriented in the or crystallographic directions. The proposed KMC model has been found to be well-suited for simulating atomic surface processes and was validated against molecular dynamics simulation results via the comparison of the flattening times obtained by both methods. We also note that the KMC simulations were two orders of magnitude computationally faster than the corresponding molecular dynamics calculations.

Process-Structure-Properties Relationship of Electrodeposited Au Thin Film Used in Thermoelectric Power Generation Device

An effective thermoelectric (TE) power source consists of TE modules and thermal management device. The TE modules must be connected electrically in series on both the top and bottom surface with bridging metal interconnects that must maintain low contact resistance with high mechanical strength while operating at high current densities and temperature gradients. Due to its low emissivity, excellent electronic, and mechanical properties, Au coatings can be used for interconnect metallization and heat mitigation in TE modules and thermal management devices respectively. In this study, we report on the successful synthesis of perfectly coherent and atomically sharp nanoscale growth twin boundaries (figure 1(e&f)) and the introduction of highly crystalline atomic structure (figure 1(f)) in the interior of each grain of Au electrodeposits using pulsed electrodeposition from an additive stable cyanide gold bath. The increase in sharpness of nanoscale twin boundaries resulted in improved mechanical and electronic properties in Au electrodeposits1. During the study of nucleation and growth mechanism of Au electrodeposition process, we established that both instantaneous and progressive nucleation modes could be achieved depending on the overpotential used during deposition. Instantaneous nucleation was observed at lower overpotentials (≥ -0.75 V vs Ag/AgCl) while progressive nucleation occurred at larger overpotentials (< -0.75 V vs Ag/AgCl). We then compared direct (DC) and pulse current (PC) electrodeposition modes and their effects on mechanical and electronic properties of the electrodeposits. We determined that the use of large overpotentials (≤ -0.9 V vs Ag/AgCl) successfully produced films with enhanced properties. Compared to films generated using DC electrodeposition, pulsed Au coatings had improved physical and electronic properties with emissivity as low as 0.006, contact resistance five times less, hardness and electrical conductivity twice as much. We also found that long pulse on-times (≥ 2ms) and a small duty cycle (10%) were needed to produce smooth, porous free(figure 1(b&c)), highly crystalline, strongly textured, low emissivity, reduced contact resistance, enhanced electrical conductivity, and mechanically strong Au electrodeposits. Reference 1. L. Lu, Y. F. Shen, X. H. Chen, L. H. Qian, and K. Lu, Science, 304 (5669), 422-426 (2004). Figure 1

A novel field ionization gas sensor based on self-organized CuO nanowire arrays

In this study, we present fabrication and characterization of a gas ionization sensor based on high aspect ratio one-dimensional CuO nanowires as the field enhancing medium. Self-organized arrays of CuO nanowires have been synthesized based on a low-cost thermal oxidation method and integrated into a gas ionization sensor (GIS). The self-organized arrays of CuO nanowires have been employed to detect the identity of several gas species such as He, Ar and CO at ambient temperature and pressure. The sharp nanoscale size of CuO tips provide very high electric fields at moderate voltages (less than 100V) and provoke the breakdown of different gases. The reduced breakdown current of the metal oxide CuO nanowire electrodes result in reduced structural deformation. The proposed GIS based on CuO nano-tips exhibits good repeatability and selectivity for various types of gases and their mixtures.

A tip for better sensing

Extremely sensitive and ultrasmall superconducting quantum interference devices can be fabricated on sharp nanoscale tips.

Synthesis of Nanoscale Tips Using Femtosecond Laser Radiation under Ambient Condition

We report a unique growth of platelet-shaped nanoscale tips of transparent dielectric using femtosecond laser radiation at MHz pulse repetition rate with nitrogen background gas flow under ambient condition. The tips grew with sharp nanoscale apex while their base and lengths are of the order of few hundred nanometers. In the absence of nitrogen, the irradiation leads to nanofibrous structure formation. The collision between the nitrogen gas atoms and the vapor species slows down plume expansion and lead to an increase of nanoparticles size. This prevents the fibrous structure formation and provides appropriate condition for nanoscale tips growth.

Growth of Single-Crystalline Wurtzite Aluminum Nitride Nanotips with a Self-Selective Apex Angle

Single-crystalline, hexagonal aluminum nitride nanotips are fabricated using a vapor-transport and condensation process (VTCP) on silicon substrates with or without a catalyst layer. The resultant tips have very sharp nanoscale apexes (∼1 nm). while their bases and lengths are up to hundreds of nanometers wide and several micrometers long, respectively. It has been demonstrated that the thickness of the gold-catalyst layer plays a critical role in controlling the size of the tip; in addition, a catalyst-free growth mode has been observed, which results in lesser control over the nanotip morphology. Nevertheless, a remarkably narrow distribution of the apex angle of the nanotips, regardless of whether or not a catalyst was used in the VTCP, has been obtained. Compared with the commonly observed ridge and pyramid structures, the nanotips produced by VTCP have higher angles (-81°) between the tilted (221) and the basal (001) planes that encase it. A mechanism for this self-selective apex angle in aluminum nitride nanotip growth is proposed.

Nanoscale gap fabrication and integration of carbon nanotubes by micromachining

This paper presents new techniques for fabricating nanoscale gaps based on microlithography and the assembly of a carbon nanotube (CNT) across a gap. A sharp nanoscale gap was fabricated by the controlled over-etching of an Al thin film. The etching process was monitored by measured resistance, and a nanoscale gap (∼20 nm) was fabricated. A rounded gap was also created by using a lift-off process on a bridge pattern with a metal layer. The smallest gap created by this method was 150 nm. An ac electric field was used to deposit single-walled carbon nanotubes (SWCNTs) dispersed in a liquid across the prepared gaps. A highly oriented assembly was obtained for the deposition across this round gap. It was also demonstrated that a single multi-walled carbon nanotube (MWCNT) could be directionally deposited across a microscale gap when guided by a biased ac electric field. Compared with chemical vapor deposition (CVD) methods, suggested assembly procedure can be performed at a room temperature, thus providing more process freedom. Various configurations for device application and fundamental experiments can be conceived using the proposed method.