Effect of AgNO3 addition rate on aspect ratio of CuCl2–mediated synthesized silver nanowires using response surface methodology

Nanoformulation approach for improved stability and efficiency of lactoperoxidase

Lactoperoxidase is a glycosylated protein with a molecular mass of 78 kDa, which being excreted in several mammalian secretions. Lactoperoxidase is included in many biological processes and well-known to have biocidal actions, attending as active antibiotics and antiviral agents. This wide-spectrum of biocidal activities mediates via a definite inhibitory system named lactoperoxidase system which acts a potent role in the innate immune response since its activity is not restricted by the antimicrobial effect, but might act a significant role in the hydrolysis of many toxins like aflatoxin. Hence with the current progresses in technology, nanoparticles can offer chances as an active candidate that might be utilized for stabilizing and potentiating the activity of LPO for use in several applications. Due to the variability functions of LPO, this enzyme considers an active target to be encapsulated or coated to NPs for developing novel nanocombinations with controlled surface characteristics. The development of approaches which might enhance conformational stabilization for several weeks of LPO via nanoformulation could improve the biopharmaceutical applicability of this bioactive ingredient. Nanoformulation of LPO enhances novel functions that can be useful in many biotechnological applications like food industry, cosmetic and pharmaceutical applications or to deliver and encapsulate bioactive components.

Ultra-Uniform and Very Thin Ag Nanowires Synthesized via the Synergy of Cl-, Br- and Fe3+ for Transparent Conductive Films

The properties and applications of Ag nanowires (AgNWs) are closely related to their morphology and composition. Therefore, controlling the growth process of AgNWs is of great significance for technological applications and fundamental research. Here, silver nanowires (AgNWs) were synthesized via a typical polyol method with the synergistic effect of Cl⁻, Br⁻, and Fe³⁺ mediated agents. The synergistic impact of these mediated agents was investigated intensively, revealing that trace Fe³⁺ ions provided selective etching and hindered the strong etching effect from Cl⁻ and Br⁻ ions. Controlling this synergy allowed the obtainment of highly uniform AgNWs with sub-30 nm diameter and an aspect ratio of over 3000. Transparent conductive films (TCFs) based on these AgNWs without any post-treatment showed a very low sheet resistance of 4.7 Ω sq⁻¹, a low haze of 1.08% at a high optical transmittance of 95.2% (at 550 nm), and a high figure of merit (FOM) of 1210. TCFs exhibited a robust electrical performance with almost unchanged resistance after 2500 bending cycles. These excellent high-performance characteristics demonstrate the enormous potential of our AgNWs in the field of flexible and transparent materials.

Synthesis and Applications of Silver Nanowires for Transparent Conductive Films

Flexible transparent conductive electrodes (TCEs) are widely applied in flexible electronic devices. Among these electrodes, silver (Ag) nanowires (NWs) have gained considerable interests due to their excellent electrical and optical performances. Ag NWs with a one-dimensional nanostructure have unique characteristics from those of bulk Ag. In past 10 years, researchers have proposed various synthesis methods of Ag NWs, such as ultraviolet irradiation, template method, polyol method, etc. These methods are discussed and summarized in this review, and we conclude that the advantages of the polyol method are the most obvious. This review also provides a more comprehensive description of the polyol method for the synthesis of Ag NWs, and the synthetic factors including AgNO3 concentration, addition of other metal salts and polyvinyl pyrrolidone are thoroughly elaborated. Furthermore, several problems in the fabrication of Ag NWs-based TCEs and related devices are reviewed. The prospects for applications of Ag NWs-based TCE in solar cells, electroluminescence, electrochromic devices, flexible energy storage equipment, thin-film heaters and stretchable devices are discussed and summarized in detail.

Synthesis and modelling of the mechanical properties of Ag, Au and Cu nanowires

The recent interest to nanotechnology aims not only at device miniaturisation, but also at understanding the effects of quantised structure in materials of reduced dimensions, which exhibit different properties from their bulk counterparts. In particular, quantised metal nanowires made of silver, gold or copper have attracted much attention owing to their unique intrinsic and extrinsic length-dependent mechanical properties. Here we review the current state of art and developments in these nanowires from synthesis to mechanical properties, which make them leading contenders for next-generation nanoelectromechanical systems. We also present theories of interatomic interaction in metallic nanowires, as well as challenges in their synthesis and simulation.

An eco-friendly water-assisted polyol method to enhance the aspect ratio of silver nanowires

With water as an eco-friendly heterogeneous nucleation accelerator, silver nanowires (Ag NWs) have been successfully prepared with a high aspect ratio (>1600). The Ag NW-based film exhibits a low sheet resistance of 8.1 Ω sq⁻¹ with a transparency of 81.9% at 550 nm, showing the potential application of electrode materials in polymer solar cells.

Silver nanowires with a high aspect ratio over 1600 were realized through a water-assisted polyol method.

Modified Finke-Watzky mechanisms for the two-step nucleation and growth of silver nanoparticles

In this work, a new modification was made on the Finke-Watzky mechanism for investigating the nucleation and growth steps in the synthesis of silver nanoparticles (AgNPs). UV-vis spectrophotometry and transmission electron microscopy evaluations proved that the former linear form of Finke-Watzky mechanism is not efficient for describing the nucleation and growth steps of AgNPs synthesis. In this manner, the Finke-Watzky mechanism was modified by considering a reversible pseudo first-order reaction for nucleation step. In addition, no assumptions were made in mathematical calculations related to the rate law which were previously adapted by the researchers in this field; i.e. [A]₀ > [A] and k ₂[A] ≫ k ₁. These considerations led to the development of a kinetic model that is more closely related to what really occurs within the synthesis system. Kinetics data were obtained in a well-known synthesis process of AgNPs namely as sodium borohydride reduction. Furthermore, it was elucidated that polyvinylpyrrolidone (PVP) retards both the nucleation and growth steps resulting in the isotropic growth of seeds; this effect subtly provides a tunable synthesis process for achieving desired size of AgNPs. Moreover, Fourier-transform infrared spectroscopy revealed that the nitrogen atoms present in the PVP molecules are responsible for the interaction of PVP with AgNPs.

Immobilization of lactoperoxidase on graphene oxide nanosheets with improved activity and stability

OBJECTIVES

The purpose of this study was to develop a facile and efficient method to enhance the stability and activity of lactoperoxidase (LPO) by using its immobilization on graphene oxide nanosheets (GO-NS).

METHODS

Following the LPO purification from bovine whey, it was immobilized onto functionalized GO-NS using glutaraldehyde as cross-linker. Kinetic properties and stability of free and immobilized LPO were investigated.

RESULTS

LPO was purified 59.13 fold with a specific activity of 5.78 U/mg protein. The successful immobilization of LPO on functionalized GO-NS was confirmed by using dynamic light scattering (DLS) and Fourier transform infrared spectroscopy (FT-IR). The overall results showed that the stability of the immobilized LPO was considerably improved compared to free LPO. Apparent K_m and V_max of LPO also indicated that the immobilized enzyme had greater affinity to the substrate than the native enzyme.

CONCLUSIONS

Graphene oxide nanosheets are effective means for immobilization of LPO.

Colorimetric determination of Timolol concentration based on localized surface plasmon resonance of silver nanoparticles

In this work, a rapid and simple colorimetric method based on the surface plasmon resonance of silver nanoparticles (AgNPs) was developed for the detection of the drug Timolol. The method used is based on the interaction of Timolol with the surface of the as-synthesized AgNPs, which promotes aggregation of the nanoparticles. This aggregation exploits the surface plasmon resonance through the electric dipole-dipole interaction and coupling among the agglomerated particles, hence bringing forth distinctive changes in the spectra as well as the color of colloidal silver. UV-vis spectrophotometery was used to monitor the changes of the localized surface plasmon resonance of AgNPs at wavelengths of 400 and 550 nm. The developed colorimetric sensor has a wide dynamic range of 1.0 × 10(-7) M-1.0 × 10(-3) M for detection of Timolol with a low detection limit of 1.2 × 10(-6) M. The proposed method was successfully applied for the determination of Timolol concentration in ophthalmic eye-drop solution with a response time lower than 40 s.

High Rate Performance Nanocomposite Electrode of Mesoporous Manganese Dioxide/Silver Nanowires in KI Electrolytes

In recent years, manganese dioxide has become a research hotspot as an electrode material because of its low price. However, it has also become an obstacle to industrialization due to its low ratio of capacitance and the low rate performance which is caused by the poor electrical conductivity. In this study, a KI solution with electrochemical activity was innovatively applied to the electrolyte, and we systematically investigated the rate performance of the mesoporous manganese dioxide and the composite electrode with silver nanowires in supercapacitors. The results showed that when mesoporous manganese dioxide and mesoporous manganese dioxide/silver nanowires composite were used as electrodes, the strength of the current was amplified five times (from 0.1 to 0.5 A/g), the remaining rates of specific capacitance were 95% (from 205.5 down to 197.1 F/g) and 92% (from 208.1 down to 191.7 F/g) in the KI electrolyte, and the rate performance was much higher than which in an Na₂SO₄ electrolyte with a remaining rate of 25% (from 200.3 down to 49.1 F/g) and 60% (from 187.2 down to 113.1 F/g). The morphology and detail structure were investigated by Scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectrometry and Nitrogen adsorption-desorption isotherms. The electrochemical performance was assessed by cyclic voltammograms, galvanostatic charge/discharge and electrochemical impedance spectroscopy.