Nucleation and growth kinetics of silver nanoparticles prepared by glutamic acid in micellar media

Silk Protein Paper with In Situ Synthesized Silver Nanoparticles

Silver nanoparticles (AgNPs) are in situ synthesized for the first time on microfibrillated silk (MFS) exfoliated from domesticated Philosamia cynthia ricini (eri) and Bombyx mori (mulberry) silkworm silk fibers. The process is rapid (hours time), does not rely on harmful chemicals, and produces robust and flexible AgNPs coated MFS (MFS-AgNPs) protein papers with excellent handling properties. None of these can be achieved by approaches used in the past to fabricate AgNPs silk systems. MFS bonds the AgNPs strongly, providing good support and stabilization for the NPs, leading to strong wash fastness. The mechanical properties of the MFS-AgNPs papers largely do not change compared to the MFS papers without nanoparticles, except for some higher concentration of AgNPs in the case of mulberry silk. The improved tensile properties of eri silk papers with or without AgNPs compared to mulberry silk papers can be attributed to the higher degree of fibrillation achieved in eri silk and its inherent higher ductility. MFS-AgNPs from eri silk also exhibit strong antibacterial activity. This study provides the basis for the development of smart protein papers based on silk fiber and functional nanomaterials.

Following the Formation of Silver Nanoparticles Using In Situ X-ray Absorption Spectroscopy

The formation of silver and Au@Ag core@shell nanoparticles via reduction of AgNO₃ by trisodium citrate was followed using in situ X-ray absorption near-edge structure (XANES) spectroscopy and time-resolved UV-visible (UV-vis) spectroscopy. The XANES data were analyzed through linear combination fitting, and the reaction kinetics were found to be consistent with first-order behavior with respect to silver cations. For the Au@Ag nanoparticles, the UV-vis data of a lab-scale reaction showed a gradual shift in dominance between the gold- and silver-localized surface plasmon absorbance bands. Notably, throughout much of the reaction, distinct gold and silver contributions to the UV-vis spectra were observed; however, in the final product, the contributions were not distinct.

In situ assembly of Ag nanoparticles (AgNPs) on porous silkworm cocoon-based wound film: enhanced antimicrobial and wound healing activity

Preventing wound infection and retaining an appropriate level of moisture around wounds represent the most critical issues in wound treatment. Towards these ends, special focus has been placed on Bombyx mori cocoons because the protective function of the silkworm cocoon resembles the manner in which the skin protects the human body. We have designed a facile technique to develop a novel silkworm cocoon-based wound film (SCWF) wound dressing utilizing a CaCl₂-ethanol-H₂O solution. To improve the anti-bacterial performance of SCWF, we have incorporated the ability of silk sericin to act as a reducing agent for the conversion of Ag⁺ to Ag, yielding nanoparticles (AgNPs) linked together by peptide bonds of silkworm cocoon wound film (SCWF-AgNPs). SCWF-AgNP dressing exhibited excellent biocompatibility, anti-bacterial performance, and good extensibility. Furthermore, in vivo experiments indicated that SCWF-AgNP dressing was able to significantly accelerate the healing rate of infected wounds in New Zealand White rabbits and histological examination revealed that it aided in the successful reconstruction of intact and thickened epidermis during 14 days of healing of impaired wound tissue. These results demonstrate that the present approach might shed new light on the design of anti-bacterial materials such as SCWF-AgNPs with promising applications in wound dressing.

Kinetics for an Optimized Biosynthesis of Silver Nanoparticles Using Alfalfa Extracts

In recent years, great efforts have been directed to provide eco-friendly methods for nanoparticles (NPs) synthesis. In this endeavor, it is desired that polydispersity be as narrow as possible and that the chemical and physical properties can be controlled. In this work, silver nanoparticles (SNPs) were obtained by means of (a) a green approach (biosynthesis) using alfalfa extracts; and (b) a thermal decomposition method in organic media. As per biosynthesis, pH, initial concentration of precursor (Ag+) and extraction solvent of plant metabolites were varied in order to identify the conditions where SNP polydispersity presented a best value. When these conditions were determined, the reaction kinetics was evaluated. The rate constant and order of reaction were 7.33×10−6 L3.6/mol3.6 s, and 4.6, respectively. Also, in the biosynthesis, it was found that the size and the degree of polydispersity depend on initial concentration of precursor and the type of extractant. Thermal decomposition was performed using silver oleate as precursor in order to compare characteristics of the NPs obtained by both biosynthesis and the chemical method. According to our results, SNPs obtained through thermal decomposition showed a lower polydispersity and higher degree of crystallinity than those obtained using biosynthesis. However, the green method eliminates the use of toxic compounds, which is extremely important if these particles are intended for biomedical purposes. In addition, this is a less expensive method as compared to other chemical methods. To our knowledge, this is one of the few reports analyzing the reaction kinetics, which is extremely important if scale-up is intended.

Effects of Surfactants on the Rate of Chemical Reactions

Surfactants are self-assembled compounds that depend on their structure and electric charge can interact as monomer or micelle with other compounds (substrates). These interactions which may catalyze or inhibit the reaction rates are studied with pseudophase, cooperativity, and stoichiometric (classical) models. In this review, we discuss applying these models to study surfactant-substrate interactions and their effects on Diels-Alder, redox, photochemical, decomposition, enzymatic, isomerization, ligand exchange, radical, and nucleophilic reactions.

Preparation of bimetallic nanoparticles using a facile green synthesis method and their application

A straightforward, economically viable, and green approach for the synthesis of well-stabilized Au/Ag bimetallic nanoparticles is described; this method uses nontoxic and renewable degraded pueraria starch (DPS) as a matrix and mild reaction conditions. The DPS acted as both a reducing agent and a capping agent for the bimetallic nanoparticles. Au/Ag bimetallic nanoparticles were successfully grown within the DPS matrixes, and the bimetallic structures were characterized using various methods, including high-resolution transmission electron microscopy, energy-dispersive X-ray, and X-ray diffraction. Moreover, it was shown that these DPS-capped Au/Ag bimetallic nanoparticles could function as catalysts for the reduction of 4-nitrophenol in the presence of NaBH4 and were more effective than Au or Ag monometallic nanoparticles.