Identification of the main mixing process in the synthesis of alloy nanoparticles by laser ablation of compacted micropowder mixtures

Alloy nanoparticles offer the possibility to tune functional properties of nanoscale structures. Prominent examples of tuned properties are the local surface plasmon resonance for sensing applications and adsorption energies for applications in catalysis. Laser synthesis of colloidal nanoparticles is well suited for generating alloy nanoparticles of desired compositions. Not only bulk alloys but also compacted mixtures of single-metal micropowders can serve as ablation targets. However, it is still unknown how mixing of the individual metals transfers from the micro- to the nanoscale. This work experimentally contributes to the elucidation of the mixing processes during the laser-based synthesis of alloy nanoparticles. Key parameters, such as the initial state of mixing in the ablation target, the laser pulse duration, the laser spot size, and the ablation time, are varied. Experiments are performed on a cobalt-iron alloy, relevant for application in oxidation catalysis, in ethanol. The extent of mixing in the targets after ablation and in individual nanoparticles are studied by energy-dispersive X-ray spectroscopy and by cyclic voltammetry at relevant conditions for the oxygen evolution reaction, as model reaction. The results point at the benefits of well pre-mixed ablation targets and longer laser pulse durations for the laser-based synthesis of alloy nanoparticles. Graphical abstract

Nanotechnology in veterinary medicine: a review

ABSTRACT: The purpose of this review was to address the applicability of nanotechnology in veterinary medicine, with an emphasis on research in Brazil from 2013 to 2020. Firstly, we introduced to the general aspects of applicability of nanotechnology in veterinary medicine, and lately we pointed the research involving nanoscience performed in Brazil, in the studied period. Nanotechnology is the field of science that has the capacity to organize matter in nanoscale structures (1 to 100 nm), enabling innovations in different areas including biotechnology, agriculture, disease diagnosis, food and clothing industry, electronics, and pharmacological therapies. In veterinary medicine, several studies are being carried out in the world, mainly in the areas that involve search of new treatment options and the development of immunotherapy, as well as in the diagnosis of diseases. In Brazil, it is clear that the use of nanotechnology in veterinary medicine is still incipient, but it can be considered a growing area. In addition, several points have to be reflected and researched, including some adverse effects and implications to validate the safe use of nanotechnology in veterinary medicine. Therefore, this review highlighted the nanotechnology as a promise alternative in the current context of Brazilian technological innovation involving animal health, as well as a possible diagnostic tool and highlighting its potential therapeutic use in disease control in veterinary medicine. Regarding future perspectives, we believed that greater investment in science and technology could contribute to the advancement and strengthening of nanotechnology in Brazil.

Progress in design, nanofabrication and performance of metalenses

Metalens has been shown to overcome the diffraction limit of conventional optical lenses to achieve sub-wavelength resolution. Due to its planar structure and lightweight, metalens has the potential applications in the manufacture of flat lenses for cameras and other high resolution imaging optics. However, currently reported metalenses have low focusing efficiencies: 26% - 68% in THz and GHz range, 1% - 91% in near infrared range (NIR), and 5% - 91.6% in the visible range. Far field imaging in the visible light is essential for use in camera and mobile phones, which requires a complex metalens structure with multi-layers of alternating metal and dielectric layers. Most of the reported metalenses work in a single wavelength, mainly due to the high dispersion characteristics of the diffractive metalenses. It remains a challenge to realize high resolution imaging for a wide wavelength band in particular in the visible range. In this review, we report the state-of-the-art in metalens design principle, types of nanoscale structures, and various fabrication processes. We introduce femtosecond laser direct writing based on two-photon polymerization as an emerging nanofabrication technology. We provide an overview of the optical performance of the recently-reported metalenses and elaborate the major research and engineering challenges and future prospects.

Nanoscale structures and materials from the self-assembly of polypeptides and DNA

: The use of biological molecules with programmable self-assembly properties is an attractive route to functional nanomaterials. Proteins and peptides have been used extensively for these systems due to their biological relevance and large number of supramolecular motifs, but it is still difficult to build highly anisotropic and programmable nanostructures due to their high complexity. Oligonucleotides, by contrast, have the advantage of programmability and reliable assembly, but lack biological and chemical diversity. In this review, we discuss systems that merge protein or peptide self-assembly with the addressability of DNA. We outline the various self-assembly motifs used, the chemistry for linking polypeptides with DNA, and the resulting nanostructures that can be formed by the interplay of these two molecules. Finally, we close by suggesting some interesting future directions in hybrid polypeptide-DNA nanomaterials, and potential applications for these exciting hybrids.

Laser Fabrication of Nanoholes on Silica through Surface Window Assisted Nano-Drilling (SWAN)

Nano-structures have significant applications in many fields such as chip fabrications, nanorobotics, and solar cells. However, realizing nanoscale structures on hard and brittle materials is still challenging. In this paper, when processing the silica surface with a tightly focused Bessel beam, the smallest nanohole with ~20 nm diameter has been realized by precisely controlling the interior and superficial interaction of the silica material. An effective surface window assisted nano-drilling (SWAN) mechanism is proposed to explain the generation of such a deep subwavelength structure, which is supported by the simulation results of energy depositions.

Demonstration of thermal modulation using nanoscale and microscale structures for ultralarge pixel array photothermal transducers

Large-pixel-array infrared emitters are attractive in the applications of infrared imaging and detection. However, the array scale has been restricted in traditional technologies. Here, we demonstrated a light-driven photothermal transduction approach for an ultralarge pixel array infrared emitter. A metal-black coating with nanoporous structures and a silicon (Si) layer with microgap structures were proposed to manage the thermal input and output issues. The effects of the nanoscale structures in the black coating and microscale structures in the Si layer were investigated. Remarkable thermal modulation could be obtained by adjusting the nanoscale and microscale structures. The measured stationary and transient results of the fabricated photothermal transducers agreed well with the simulated results. From the input view, due to its wide spectrum and high absorption, the black coating with nanoscale structures contributed to a 5.6-fold increase in the temperature difference compared to that without the black coating. From the output view, the microgap structures in the Si layer eliminated the in-plane thermal crosstalk. The temperature difference was increased by 340% by modulating the out-of-plane microstructures. The proposed photothermal transducer had a rising time of 0.95 ms and a falling time of 0.53 ms, ensuring a fast time response. This method is compatible with low-cost and mass manufacturing and has promising potential to achieve ultralarge-array pixels beyond ten million.

Artifact removal in the contour areas of SAXS-CT images by Tikhonov-L1 minimization

Small-angle X-ray scattering (SAXS) coupled with computed tomography (CT), denoted SAXS-CT, has enabled the spatial distribution of the characteristic parameters (e.g. size, shape, surface, length) of nanoscale structures inside samples to be visualized. In this work, a new scheme with Tikhonov regularization was developed to remove the effects of artifacts caused by streak scattering originating from the reflection of the incident beam in the contour regions of the sample. The noise due to streak scattering was successfully removed from the sinogram image and hence the CT image could be reconstructed free from artifacts in the contour regions.

Simultaneous multicolor DNA-PAINT without sequential fluid exchange using spectral demixing

Several variants of multicolor single-molecule localization microscopy (SMLM) have been developed to resolve the spatial relationship of nanoscale structures in biological samples. The oligonucleotide-based SMLM approach DNA-PAINT robustly achieves nanometer localization precision and can be used to count binding sites within nanostructures. However, multicolor DNA-PAINT has primarily been realized by Exchange-PAINT that requires sequential exchange of the imaging solution and thus leads to extended acquisition times. To alleviate the need for fluid exchange and to speed up the acquisition of current multichannel DNA-PAINT, we here present a novel approach that combines DNA-PAINT with simultaneous multicolor acquisition using spectral demixing (SD). By using newly designed probes and a novel multichannel registration procedure we achieve simultaneous multicolor SD-DNA-PAINT with minimal crosstalk. We demonstrate high localization precision (3 - 6 nm) and multicolor registration of dual and triple-color SD-DNA-PAINT by resolving patterns on DNA origami nanostructures and cellular structures.

Intense XUV pulses from a compact HHG setup using a single harmonic

We report on a compact and spectrally intense extreme-ultraviolet (XUV) source, which is based on high-harmonic generation (HHG) driven by 395 nm pulses. In order to minimize the XUV virtual source size and to maximize the XUV flux, HHG is performed several Rayleigh lengths away from the driving laser focal plane in a high-density gas jet. As a result, a high focused XUV intensity of 5 × 1013 W/cm2 is achieved, using a beamline with a length of only two meters and a modest driving laser pulse energy of 3 mJ. The high XUV intensity is demonstrated by performing a nonlinear ionization experiment in argon, using an XUV spectrum that is dominated by a single harmonic at 22 eV. Ion charge states up to Ar3+ are observed, which requires the absorption of at least four XUV photons. The high XUV intensity and the narrow bandwidth are ideally suited for a variety of applications including photoelectron spectroscopy, the coherent control of resonant transitions and the imaging of nanoscale structures.

Event-triggered STED imaging

The observation of protein organization during cellular signalling calls for imaging methods with increased spatial and temporal resolution. STED nanoscopy can access dynamics of nanoscale structures in living cells. However, the available number of recordable frames is often limited by photo-bleaching. Here, we present an automated method, event-triggered STED, which instantly (< 40 ms) images synaptic proteins with high spatial and temporal resolution (~30 nm, 2.5 Hz) in small regions upon and at the site of local calcium sensing.