UV-Vis Sintering Process for Fabrication of Conductive Coatings Based on Ni-Ag Core-Shell Nanoparticles.

The UV-Vis sintering process was applied for the fabrication of conductive coatings composed of low-cost nickel-silver (Ni@Ag) nanoparticles (NPs) with core-shell structures. The metallic films were formed on a plastic substrate (polyethylene napthalate, PEN), which required their sintering at low temperatures to prevent the heat-sensitive polymer from destroying them. The UV-Vis sintering method, as a non-invasive method, allowed us to obtain metallic coatings with good conductivity at room temperature. In optimal sintering conditions, i.e., irradiation with a wavelength of 350-400 nm and time of 90 min, conductivity corresponding to about 30% of that of bulk nickel was obtained for the coatings based on Ni@Ag NPs.

Silver Shell Thickness-Dependent Conductivity of Coatings Based on Ni@Ag Core@shell Nanoparticles.

Introductions: Ink based on metallic nanoparticles has been widely used so far for the fabrication of electronic circuits and devices using printing technology. This study aimed at the analysis of the effect of the silver shell thickness of nickel@silver core@shell (Ni@Ag) nanoparticles (NPs) on the fabrication and conductive properties of deposited coatings. Methods: The process of the synthesis of Ni@Ag NPs with various silver shell thicknesses was developed. The physicochemical properties (size, stability against aggregation process) of synthesized Ni@Ag nanoparticles were analyzed. The films based on ink containing Ni@Ag NPs with different silver shell thicknesses were fabricated and sintered in a temperature range of 120-300 °C and at times from 15 to 90 min. The dependence of their conductive properties on the applied temperature and time as well as silver shell thickness was evaluated. Results: Ni NPs were coated with 10, 20, 30, 35, 45, and 55 nm silver shell thickness. The resistivity of coatings based on obtained NPs depends on the thickness of the Ag shell and the sintering temperature. After sintering at 300 °C, the highest decrease in its value (at an optimal sintering time of 60 min) from about 100 µΩ·cm to 9 µΩ·cm was observed when the thickness of the shell increased from 10 to 55 nm. At the lowest sintering temperature (120 °C) the highest conductivity (about 50% of that for bulk nickel) was obtained for films based on Ni@Ag NPs with 45 and 55 nm of the silver shell thickness. Discussions: The analysis of the resistivity of the sintered films showed that higher conductivity was obtained for the coatings formed from Ni@Ag NPs with the thicker Ag shell; moreover, thicker shells allowed a lowering of sintering temperature due to higher conductivity and a lower melting point of silver in comparison to nickel NPs.

Improving the Effect of Cancer Cells Irradiation with X-rays and High-Energy Protons Using Bimetallic Palladium-Platinum Nanoparticles with Various Nanostructures.

Nano-sized radiosensitizers can be used to increase the effectiveness of radiation-based anticancer therapies. In this study, bimetallic, ~30 nm palladium-platinum nanoparticles (PdPt NPs) with different nanostructures (random nano-alloy NPs and ordered core-shell NPs) were prepared. Scanning transmission electron microscopy (STEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDS), zeta potential measurements, and nanoparticle tracking analysis (NTA) were used to provide the physicochemical characteristics of PdPt NPs. Then, PdPt NPs were added to the cultures of colon cancer cells and normal colon epithelium cells in individually established non-toxic concentrations and irradiated with the non-harmful dose of X-rays/protons. Cell viability before and after PdPt NPs-(non) assisted X-ray/proton irradiation was evaluated by MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) assay. Flow cytometry was used to assess cell apoptosis. The results showed that PdPt NPs significantly enhanced the effect of irradiation on cancer cells. It was noticed that nano-alloy PdPt NPs possess better radiosensitizing properties compared to PtPd core-shell NPs, and the combined effect against cancer cells was c.a. 10% stronger for X-ray than for proton irradiation. Thus, the radio-enhancing features of differently structured PdPt NPs indicate their potential application for the improvement of the effectiveness of radiation-based anticancer therapies.

Effect of Oxalic Acid Treatment on Conductive Coatings Formed by Ni@Ag Core-Shell Nanoparticles.

Low-cost metallic nanoink based on nickel-silver core-shell nanoparticles (Ni@Ag NPs) was used for the formation of conductive metallic coatings with low sintering temperature, which can be successfully applied for replacement of currently used silver-based nanoinks in printed electronics. The effect of oxalic acid (OA) on the sintering temperature and conductivity of coatings formed by Ni@Ag NPs was evaluated. It was found that the addition of OA to the ink formulation and post-printing treatment of deposited films with this acid provided a noticeable decrease in the sintering temperature required for obtaining conductive patterns that is especially important for utilizing the polymeric substrates. The obtained resistivity of metallic coatings after sintering at temperature as low as 100 °C was found to be 30 µΩ·cm, only ~4 times higher compared to the resistivity of bulk Ni that is promising for future application of such materials for fabrication of low-cost flexible printed patterns.

Metallic core-shell nanoparticles for conductive coatings and printing.

The review is focused on bimetallic nanoparticles composed of a core formed by low-cost metal having high electrical conductivity, such as Cu and Ni, and a protective shell composed of stable to oxidation noble metal such as Ag or Au. We present the chemical and physical approaches for synthesis of such particles, as well as the combination of the two, the stability to oxidation of core-shell nanoparticles at various conditions, and the formulation of conductive compositions and their application in conductive coatings and printed electronics.

Gold-Decorated Platinum and Palladium Nanoparticles as Modern Nanocomplexes to Improve the Effectiveness of Simulated Anticancer Proton Therapy.

Noble metal nanoparticles, such as gold (Au NPs), platinum (Pt NPs), or palladium (Pd NPs), due to their highly developed surface, stability, and radiosensitizing properties, can be applied to support proton therapy (PT) of cancer. In this paper, we investigated the potential of bimetallic, c.a. 30 nm PtAu and PdAu nanocomplexes, synthesized by the green chemistry method and not used previously as radiosensitizers, to enhance the effect of colorectal cancer PT in vitro. The obtained nanomaterials were characterized by scanning transmission electron microscopy (STEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDS), UV-Vis spectroscopy, and zeta potential measurements. The effect of PtAu and PdAu NPs in PT was investigated on colon cancer cell lines (SW480, SW620, and HCT116), as well as normal colon epithelium cell line (FHC). These cells were cultured with both types of NPs and then irradiated by proton beam with a total dose of 15 Gy. The results of the MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) test showed that the NPs-assisted PT resulted in a better anticancer effect than PT used alone; however, there was no significant difference in the radiosensitizing properties between tested nanocomplexes. The MTS results were further verified by defining the cell death as apoptosis (Annexin V binding assay). Furthermore, the data showed that such a treatment was more selective for cancer cells, as normal cell viability was only slightly affected.

Varied-shaped gold nanoparticles with nanogram killing efficiency as potential antimicrobial surface coatings for the medical devices.

Medical device-associated infections are a serious medical threat, particularly for patients with impaired mobility and/or advanced age. Despite a variety of antimicrobial coatings for medical devices being explored to date, only a limited number have been introduced for clinical use. Research into new bactericidal agents with the ability to eradicate pathogens, limit biofilm formation, and exhibit satisfactory biocompatibility, is therefore necessary and urgent. In this study, a series of varied-morphology gold nanoparticles in shapes of rods, peanuts, stars and spherical-like, porous ones with potent antibacterial activity were synthesized and thoroughly tested against spectrum of Candida albicans, Pseudomonas aeruginosa, Staphylococcus aureus clinical strains, as well as spectrum of uropathogenic Escherichia coli isolates. The optimization of gold nanoparticles synthesis allowed to develop nanomaterials, which are proved to be significantly more potent against tested microbes compared with the gold nanoformulations reported to date. Notably, their antimicrobial spectrum includes strains with different drug resistance mechanisms. Facile and cost-efficient synthesis of gold nanoparticles, remarkable bactericidal efficiency at nanogram doses, and low toxicity, underline their potential for development as a new coatings, as indicated by the example of urological catheters. The presented research fills a gap in microbial studies of non-spherical gold nanoparticles for the development of antimicrobial coatings targeting multidrug-resistant pathogens responsible for device-associated nosocomial infections.

Polydispersity vs. Monodispersity. How the Properties of Ni-Ag Core-Shell Nanoparticles Affect the Conductivity of Ink Coatings.

The effect of polydispersity of nickel-silver core-shell nanoparticles (Ni-Ag NPs) on the conductivity of ink coatings was studied. Ni-Ag NPs of various average diameters (100, 220, and 420 nm) were synthesized and utilized for the preparation of conductive inks composed of monodisperse NPs and their polydisperse mixtures. The shell thickness of synthesized Ni-Ag NPs was found to be in the range of 10-20 nm and to provide stability of a core metal to oxidation for at least 6 months. The conductivity of metallic films formed by inks with monodisperse Ni-Ag NPs was compared with those formed by polydisperse inks. In all cases, the optimal conditions for the formation of conductive patterns (weight ratio of monodisperse NPs for polydisperse composition, the concentration of the wetting agent, sintering temperature, and duration) were determined. It was found that metallic films formed by polydisperse ink containing 100, 220, and 420 nm Ni-Ag NPs with a mass ratio of 1:1.5:0.5, respectively, are characterized by the lowest resistivity, 10.9 µΩ·cm, after their thermal post-coating sintering at 300 °C for 30 min that is only 1.6 higher than that of bulk nickel.

Application of metallic inks based on nickel-silver core-shell nanoparticles for fabrication of conductive films.

Conductive inks based on nickel nanoparticles (NPs) have attracted much attention as a low-cost replacement for the currently used silver and gold inks, for fabrication of printed electronic circuits and devices. Nickel NPs as a component of conductive inks should be stable against oxidation process at all stages of preparation of conductive patterns: ink formulation and storage, printing, and post-printing treatment. In the present study, the oxidation resistance of the Ag layer and the conductive properties of the Ni core allowed the use of nickel-silver core-shell (Ni@Ag) NPs as the component of conductive ink. Thick films composed of Ni-Ag core-shell NPs were deposited on a glass substrate and then sintered at temperatures ranging from 250 °C-370 °C. The conductivity of Ni@Ag coatings after sintering at 350 °C reached 11% of that for a bulk nickel.

The optimization of methods of synthesis of nickel-silver core-shell nanoparticles for conductive materials.

Nickel-silver core-shell (Ni@Ag) nanoparticles (NPs) were formed in a two-step process: (1) the formation of a dispersion of Ni NPs; and (2) the transmetalation (galvanic displacement) reaction, where the surface of the Ni NPs acted as the reducing agent of Ag ions. Ni NPs were synthesized by the 'wet' chemical method, i.e., by the reduction of metal ions by using NaBH4 as the reducing agent. The influence of the concentration of polymeric stabilizer, reducing agent and Ag precursor on the properties of synthesized NPs was evaluated. In the optimal condition of synthesis, Ni@Ag NPs with about 50 and 210 nm-diameter Ni core coated with a thin (∼10-20 nm) Ag shell, were obtained. Finally, the stability of the synthesized spherical-shaped Ni@Ag NPs was tested and the results indicate long-term stability against aggregation and Ni oxidation. Thus, the resulting NPs are promising candidates for application in electronic devices, e.g., as components of conductive inks or pastes.

Design and assembly of ternary Pt/Re/SnO2 NPs by controlling the zeta potential of individual Pt, Re, and SnO2 NPs.

In this study Pt, Re, and SnO2 nanoparticles (NPs) were combined in a controlled manner into binary and ternary combinations for a possible application for ethanol oxidation. For this purpose, zeta potentials as a function of the pH of the individual NPs solutions were measured. In order to successfully combine the NPs into Pt/SnO2 and Re/SnO2 NPs, the solutions were mixed together at a pH guaranteeing opposite zeta potentials of the metal and oxide NPs. The individually synthesized NPs and their binary/ternary combinations were characterized by Fourier transform infrared spectroscopy (FTIR) and scanning transmission electron microscopy (STEM) combined with energy dispersive X-ray spectroscopy (EDS) analysis. FTIR and XPS spectroscopy showed that the individually synthesized Pt and Re NPs are metallic and the Sn component was oxidized to SnO2. STEM showed that all NPs are well crystallized and the sizes of the Pt, Re, and SnO2 NPs were 2.2, 1.0, and 3.4 nm, respectively. Moreover, EDS analysis confirmed the successful formation of binary Pt/SnO2 and Re/SnO2 NP, as well as ternary Pt/Re/SnO2 NP combinations. This study shows that by controlling the zeta potential of individual metal and oxide NPs, it is possible to assemble them into binary and ternary combinations. Graphical abstractᅟ.

Evaporation of Nanosuspensions on Substrates with Different Hydrophobicity.

Liquid drop evaporation on surfaces is present in many industrial and medical applications, e.g., printed electronics, spraying of pesticides, DNA mapping, etc. Despite this strong interest, a theoretical description of the dynamic of the evaporation of complex liquid mixtures and nanosuspensions is still lacking. Indeed, one of the aspects that have not been included in the current theoretical descriptions is the competition between the kinetics of evaporation and the adsorption of surfactants and/or particles at the liquid/vapor and liquid/solid interfaces. Materials formed by an electrically isolating solid on which a patterned conducting layer was formed by the deposits left after drop evaporation have been considered as very promising for building electrical circuits on flexible plastic substrates. In this work, we have done an exhaustive study of the evaporation of nanosuspensions of latex and hydrophobized silver nanoparticles on four substrates of different hydrophobicity. The advancing and receding contact angles as well as the time dependence of the volume of the droplets have been measured over a broad range of particle concentrations. Also, mixtures of silver particles and a surfactant, commonly used in industrial printing, have been examined. Furthermore, the adsorption kinetics at both the air/liquid and solid/liquid interfaces have been measured. Whereas the latex particles do not adsorb at the solid/liquid and only slightly reduce the surface tension, the silver particles strongly adsorb at both interfaces. The experimental results of the evaporation process were compared with the predictions of the theory of Semenov et al. (Evaporation of Sessile Water Droplets: Universal Behavior in the Presence of Contact Angle Hysteresis. Colloids Surf. Physicochem. Eng. Asp. 2011, 391 (1-3), 135-144) and showed surprisingly good agreement despite that the theory was developed for pure liquids. The morphology of the deposits left by the droplets after total evaporation was studied by scanning electronic microscopy, and the effects of the substrate, the particle nature, and their concentrations on these patterns are discussed.