The antibacterial action of silver is utilized in numerous consumer products and medical devices. Metallic silver, silver salts, and also silver nanoparticles are used for this purpose. The state of research on the effect of silver on bacteria, cells, and higher organisms is summarized. It can be concluded that the therapeutic window for silver is narrower than often assumed. However, the risks for humans and the environment are probably limited.

Silver as Antibacterial Agent: Ion, Nanoparticle, and Metal

Driven by functionality and purity demand for applications of inorganic nanoparticle colloids in optics, biology, and energy, their surface chemistry has become a topic of intensive research interest. Consequently, ligand-free colloids are ideal reference materials for evaluating the effects of surface adsorbates from the initial state for application-oriented nanointegration purposes. After two decades of development, laser synthesis and processing of colloids (LSPC) has emerged as a convenient and scalable technique for the synthesis of ligand-free nanomaterials in sealed environments. In addition to the high-purity surface of LSPC-generated nanoparticles, other strengths of LSPC include its high throughput, convenience for preparing alloys or series of doped nanomaterials, and its continuous operation mode, suitable for downstream processing. Unscreened surface charge of LSPC-synthesized colloids is the key to achieving colloidal stability and high affinity to biomolecules as well as support materials,...

Laser Synthesis and Processing of Colloids: Fundamentals and Applications

Laser ablation synthesis in liquid solution (LASiS) is a “green” technique that gives access to the preparation of a library of nanomaterials. Bare noble metal spherical particles, multiphase core–shell oxides, metal–semiconductor heterostructures, layered organometallic compounds and other complex nanostructures can be obtained with the same experimental set up, just by varying a few synthetic parameters. How to govern such versatility is one of the current challenges of LASiS and requires a thorough understanding of the physical and chemical processes involved in the synthesis. In this perspective, the fundamental mechanisms of laser ablation in liquids are summarized, organized according to their temporal sequence and correlated with relevant examples taken from the library of nanomaterials disclosed by LASiS, in order to show how synthesis parameters influence the composition and the structure of products. The resulting framework suggests that, to date, much attention has been devoted to the physical aspects of laser–matter interaction and to the characterization of the final products of the synthesis. Conversely, the clarification of chemical processes active during LASiS deserves more research efforts and requires the synergy among multiple investigation techniques.

What controls the composition and the structure of nanomaterials generated by laser ablation in liquid solution

Bubbles in liquids, soft and squeezy objects made of gas and vapour, yet so strong as to destroy any material and so mysterious as at times turning into tiny light bulbs, are the topic of the present report. Bubbles respond to pressure forces and reveal their full potential when periodically driven by sound waves. The basic equations for nonlinear bubble oscillation in sound fields are given, together with a survey of typical solutions. A bubble in a liquid can be considered as a representative example from nonlinear dynamical systems theory with its resonances, multiple attractors with their basins, bifurcations to chaos and not yet fully describable behaviour due to infinite complexity. Three stability conditions are treated for stable trapping of bubbles in standing sound fields: positional, spherical and diffusional stability. Chemical reactions may become important in that respect, when reacting gases fill the bubble, but the chemistry of bubbles is just touched upon and is beyond the scope of the present report. Bubble collapse, the runaway shrinking of a bubble, is presented in its current state of knowledge. Pressures and temperatures that are reached at this occasion are discussed, as well as the light emission in the form of short flashes. Aspherical bubble collapse, as for instance enforced by boundaries nearby, mitigates most of the phenomena encountered in spherical collapse, but introduces a new effect: jet formation, the self-piercing of a bubble with a high velocity liquid jet. Examples of this phenomenon are given from light induced bubbles. Two oscillating bubbles attract or repel each other, depending on their oscillations and their distance. Upon approaching, attraction may change to repulsion and vice versa. When being close, they also shoot self-piercing jets at each other. Systems of bubbles are treated as they appear after shock wave passage through a liquid and with their branched filaments that they attain in standing sound fields. The N-bubble problem is formulated in the spirit of the n-body problem of astrophysics, but with more complicated interaction forces. Simulations are compared with three-dimensional bubble dynamics obtained by stereoscopic high speed digital videography.

Physics of bubble oscillations

Review on magnetic nanoparticles for magnetic nanofluid hyperthermia application

Fabrication of silver nanoparticle colloids using ultrashort pulse laser ablation in water is studied. Ablation in liquid flow improves the reproducibility and increases the nanoparticle productivity by 380% compared to stationary liquid. Femtosecond laser ablation in water is 20% more efficient than picosecond laser ablation, but due to higher picosecond laser power (higher repetition rate), the nanoparticle productivity at the same pulse fluence is three times higher for picosecond laser ablation. With picosecond laser pulses, the maximum productivity of 8.6μg∕s is achieved at a pulse energy of 110μJ and repetition rate of 50kHz.

Generation of nanoparticle colloids by picosecond and femtosecond laser ablations in liquid flow

Comparable low nanoparticle production is a weakness of femtosecond-pulsed laser ablation in liquids, but the process ablation rate can be maximized at optimal focusing conditions and liquid levels. Refraction at the air−liquid boundary, vaporization of the liquid, self-focusing, and optical breakdown in the liquid complicate the determination of these optimal parameters. A semiempirical method has been developed, allowing an a priori determination of the appropriate experimental setup (liquid layer over the target, focal length, and lens position) for efficient ablation. The presented work can be applied with high accuracy for tightly focused beams, whereas loosely focused ultrashort lasers should be avoided to induce effective fabrication of colloids via laser ablation in liquids.

Transfer-Matrix Method for Efficient Ablation by Pulsed Laser Ablation and Nanoparticle Generation in Liquids

Charged Pt-Ir alloy nanoparticles are generated through femtosecond laser ablation of a Pt₉Ir target in acetone without using chemical precursors or stabilizing agents. Preservation of the target's stoichiometry in the colloidal nanoparticles is confirmed by transmission electron microscopy (TEM)-energy-dispersive x-ray spectroscopy (EDX), high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM)-EDX elemental maps, high resolution TEM and selected area electron diffraction (SAED) measurements. Results are discussed with reference to thermophysical properties and the phase diagram. The nanoparticles show a lognormal size distribution with a mean Feret particle size of 26 nm. The zeta potential of -45 mV indicates high stability of the colloid with a hydrodynamic diameter of 63 nm. The charge of the particles enables electrophoretic deposition of nanoparticles, creating nanoscale roughness on three-dimensional PtIr neural electrodes within a minute. In contrast to coating with Pt or Ir oxides, this method allows modification of the surface roughness without changing the chemical composition of PtIr.

https://iopscience.iop.org/article/10.1088/0957-4484/22/14/145601/pdf

Stoichiometry of alloy nanoparticles from laser ablation of PtIr in acetone and their electrophoretic deposition on PtIr electrodes.

The generation of nonoxidized magnetic alloy nanoparticles is still a challenge using conventional chemical reduction methods. However, because these nanoparticles are currently attracting much attention, alternative methods are required. In this context, the applicability of femtosecond laser ablation, which has evolved as a powerful tool for the generation of colloidal metal nanoparticles, has been investigated using the example of Ni48Fe52 and Sm2Co17 ablation in cyclopentanone. Besides stability and size measurements, the focus has been placed on the analysis of the elemental composition of nanoparticles, which proved the preservation of the stoichiometry of the target in Ni−Fe nanoparticles but not in Sm−Co. It is assumed that this is due to a greater difference in the heat of evaporation of the bulk alloy components in Sm−Co than in Ni−Fe. Hence, the successful generation of magnetic alloy nanoparticles is possible for alloys composed of elements with similar heats of evaporation. This one-step appr...

Magnetic Alloy Nanoparticles from Laser Ablation in Cyclopentanone and Their Embedding into a Photoresist

Defined hydrodynamic properties of nanoparticle colloids are required for applications in dosimetry, rheology, or biosensing studies. During the generation of nanoparticles by laser ablation of a solid target in liquids, the temperature of the liquid increases, which may effect cavitation bubble and particle formation. We demonstrate that this temperature variation influences the hydrodynamic diameter of the resulting colloidal nanoparticles when a gold target is ablated by an IR femtosecond laser in water at different stabilized liquid temperatures in the range of 283−353 K. The maximum hydrodynamic diameter was observed at 330 K, the temperature at which the compressibility of water reaches its minimum. The formation of particles by condensation of ablated species in the liquid matrix or inside the confined cavitation bubble is discussed, as well as the influence of the physical properties of the liquid that vary with temperature, such as viscosity and compressibility. The reduction of the hydrodynamic ...

Ana Menéndez-Manjón

Papers

Generation of nanoparticle colloids by picosecond and femtosecond laser ablations in liquid flow

Transfer-Matrix Method for Efficient Ablation by Pulsed Laser Ablation and Nanoparticle Generation in Liquids

Stoichiometry of alloy nanoparticles from laser ablation of PtIr in acetone and their electrophoretic deposition on PtIr electrodes.

Magnetic Alloy Nanoparticles from Laser Ablation in Cyclopentanone and Their Embedding into a Photoresist

Influence of Water Temperature on the Hydrodynamic Diameter of Gold Nanoparticles from Laser Ablation