Ze'ev Porat

Silver Nanoparticles Deposited on Porous Silicon as a Surface-Enhanced Raman Scattering (SERS) Active Substrate

Silver nanoparticles were deposited spontaneously from their aqueous solution on a porous silicon (PS) layer. The PS acts both as a reducing agent and as the substrate on which the nanoparticles nucleate. At higher silver ion concentrations, layers of nanoparticle aggregates were formed on the PS surface. The morphology of the metallic layers and their SERS activity were influenced by the concentrations of the silver ion solutions used for deposition. Raman measurements of rhodamine 6G (R6G) and crystal violet (CV) adsorbed on these surfaces showed remarkable enhancement of up to about 10 orders of magnitude.

Ultrasonic cavitation of molten gallium in water: entrapment of organic molecules in gallium microspheres

Simultaneous formation of gallium microspheres and entrapment of organic materials within them can be accomplished by applying ultrasonic energy to a heated solution of the organic substance that contains the molten metal. This method was used with aqueous solutions (5–10 mM) of four organic compounds (phenanthroline, Congo Red, crystal violet and rhodamine 6G) at 55 °C, a temperature at which the gallium is molten. Irradiation with ultrasonic energy for ca. 3 min dispersed the molten gallium into microscopic spheres, which were found to contain various amounts of these organic compounds. Immersion of the isolated spheres in pure water results in slow leaching of some of the above compounds.

Micro- and nano-spheres of low melting point metals and alloys, formed by ultrasonic cavitation

Metals and alloys of low melting points (<430 °C) can be melted in hot silicone oil to form two immiscible liquids. Irradiation of the system with ultrasonic energy induces acoustic cavitation in the oil, which disperses the molten metals into microspheres that solidify rapidly upon cooling. This method has been applied to seven pure metals (Ga, In, Sn, Bi, Pb, Zn, Hg) and two eutectic alloys of gold (Au-Ge and Au-Si). The morphology and composition of the resulting microspheres were examined by SEM and EDS. Eutectic Au-Si formed also crystalline Au nanoparticles, which were separated and studied by HRTEM.

A hydrothermal reaction of an aqueous solution of BSA yields highly fluorescent N doped C-dots used for imaging of live mammalian cells

In the current study, we present a new and facile synthesis of N doped C-dots (N@C-dots) by hydrothermally reacting an aqueous solution of Bovine Serum Albumin (BSA). The as-prepared quantum dots (QDs) exhibited high quantum yield (44%), high photostability, colloidal stability, and high functionalization efficiency. In addition to their low cost, the N@C-dots have demonstrated a non-toxic and long-lasting effect when applied for imaging human cells (human osteosarcoma U2OS cells). Importantly, with high physiological stability, excellent biocompatibility, and homogenous distribution, the N@C-dot suspension was exploited for high quality cell imaging and to model the biological effects at the nuclear level. Moreover, the water-soluble N@C-dots are nontoxic to the selected cell line in our preliminary evaluation.

Chiral imprinting in molten gallium

Chiral imprinting in molten gallium can be attained by ultrasonic irradiation of molten Ga overlayed by an aqueous solution of D- or L-tryptophan. The products are micro/nanoparticles of Ga encapsulating molecules of one of the enantiomers. After leaching of the enantiomer in pure water, molecular templates are left on the surface of the gallium particles, enabling the entrapment of the specific enantiomer from a solution of the racemate and yielding an enantiomeric excess of 6–12%. The extent of the enantiomeric excess was determined using polarimetry, Chiral HPLC and circular dichroism measurements.

Formation of particles of bismuth-based binary alloys and intermetallic compounds by ultrasonic cavitation

This work describes the interactions of molten bismuth with other low-melting point metals (Sn, In, Ga and Zn) under sonication. Binary combinations of bismuth and one of these metals were melted together in hot silicone oil and irradiated with ultrasonic energy to form micro/nano alloy particles. The morphology, composition and crystal structure of these particles were analyzed. It was found that bismuth forms metal matrix composites with tin and zinc, intermetallic compounds with indium and an alloy with gallium. We also followed the structural changes in the system by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and electron microscopy.

Formation of metal microspheres by ultrasonic cavitation

A new physical method is described for the preparation of metal microspheres by ultrasonic cavitation of low-melting point metals (

Sonochemically-fabricated Ga@C-dots@Ga nanoparticle-aided neural growth

In this paper, we report the fabrication of an antibacterial material, Ga-doped C-dots on Ga nanoparticles (Ga@C-dots@Ga NPs), which is deposited on a glass substrate for neural growth. A one-step sonochemical process is applied for the simultaneous fabrication and coating of Ga@C-dots@Ga NPs using PEG 400 and molten gallium. The physical and chemical characteristics of the synthesized materials were studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), fluorescence analysis, dynamic light scattering (DLS) and other techniques. SH-SY5Y cells were plated on the substrates. The effect of the Ga@C-dots@Ga NPs on the development of neurites during the initiation and elongation growth phases was studied and compared with C-dots, Ga@C-dots and Ga NPs. Our research focuses on the influence of the physical and chemical properties of composites on neurite growth. We observed that cells grown on a Ga@C-dots@Ga-coated substrate exhibit a 97% increase in the number of branches originating from the soma. We found that surface modification and particle morphology play a significant role in the neural growth.

Dispersion of Polymers in Metallic Gallium

This work examines the concept of dispersing polymers in metals. Herein, this was mainly studied with molten gallium, in which 5-18 wt % of various short-chain polymers were incorporated and mixed. The nature of the solidified products was examined by using X-ray diffraction, electron microscopy, UV/Vis, differential scanning calorimetry, and thermal gravimetric analyses. It was found that some polymers can be dispersed as small domains within molten metals to form a heterogeneous solid. The ability to dope Ga with large polymers opens a new avenue to electronic materials.

Formation of metallic silver and copper in non-aqueous media by ultrasonic radiation

Concentrated suspensions of silver and copper salts in silicone oil were heated to 200 °C and irradiated with ultrasonic energy for different time durations. Characterization of the products was done using X-ray powder diffraction. In most cases, metallic Ag or Cu were obtained, together with their oxide forms Ag2O and Cu2O. The salts, used as precursors, do not dissolve in silicone oil but rather form a heterogeneous system, and we assume that local heating, caused by the acoustic cavitation, enhanced their thermal decomposition and the formation of metallic particles. It was found that the presence of silver particles enhances the formation of metallic copper. This phenomenon was observed in the experiment with the acetate salts mixture.