Evaluating the mechanism of nucleation and growth of silver nanoparticles in a polymer membrane under continuous precursor supply: tuning of multiple to single nucleation pathway

Extracellular synthesis of silver nanoparticle using yeast extracts: antibacterial and seed priming applicationss

The evolution and rapid spread of multidrug-resistant (MDR) bacterial pathogens have become a major concern for human health and demand the development of alternative antimicrobial agents to combat this emergent threat. Conventional intracellular methods for producing metal nanoparticles (NPs) using whole-cell microorganisms have limitations, including binding of NPs to cellular components, potential product loss, and environmental contamination. In contrast, this study introduces a green, extracellular, and sustainable methodology for the bio-materialization of silver NPs (AgNPs) using renewable resource cell-free yeast extract. These extracts serve as a sustainable, biogenic route for both reducing the metal precursor and stabilizing the surface of AgNPs. This method offers several advantages such as cost-effectiveness, environment-friendliness, ease of synthesis, and scalability. HR-TEM imaging of the biosynthesized AgNPs revealed an isotropic growth route, resulting in an average size of about ~ 18 nm and shapes ranging from spherical to oval. Further characterization by FTIR and XPS results revealed various functional groups, including carboxyl, hydroxyl, and amide contribute to enhanced colloidal stability. AgNPs exhibited potent antibacterial activity against tested MDR strains, showing particularly high efficacy against Gram-negative bacteria. These findings suggest their potential role in developing alternative treatments to address the growing threat of antimicrobial resistance. Additionally, seed priming experiments demonstrated that pre-sowing treatment with AgNPs improves both the germination rate and survival of Sorghum jowar and Zea mays seedlings. KEY POINTS: •Yeast extract enables efficient, cost-effective, and eco-friendly AgNP synthesis. •Biosynthesized AgNPs showed strong antibacterial activity against MDR bacteria. •AgNPs boost seed germination and protect against seed-borne diseases.

Tamoxifen-Loaded Eudragit Nanoparticles: Quality by Design Approach for Optimization of Nanoparticles as Delivery System

Nanoparticles have numerous applications as drug carriers in drug delivery. The aim of the study was to produce tamoxifen nanoparticles with a defined size and higher encapsulation for efficient tissue uptake with controlled drug release. The quality by design approach was utilized to produce tamoxifen-loaded Eudragit nanoparticles by identifying the significant process variables using the nanoprecipitation method. The process variables (amount of drug, polymer, and surfactant) were altered to analyze the influence on particle size (PS), % encapsulation efficiency (EE). The results showed that the drug and polymer individually as well as collectively have an impact on PS, while the surfactant has no impact on the PS. The %EE was influenced by the surfactant individually and in interaction with the drug. The linear regression model was endorsed to fit the data showing high R2 values (PS, 0.9146, %EE, 0.9070) and low p values (PS, 0.0004, EE, 0.0005). The PS and EE were confirmed to be 178 nm and 90%, respectively. The nanoparticles were of spherical shape, as confirmed by SEM and TEM. The FTIR confirmed the absence of any incompatibility among the ingredients. The TGA confirmed that the NPs were thermally stable. The in vitro release predicted that the drug release followed Higuchi model.

Consideration of a new approach to clarify the mechanism formation of AgNPs, AgNCl and AgNPs@AgNCl synthesized by biological method

The biological methods are considered as environmental-eco-friendly methods for the silver nanocomposites mediation and are widely used in this context. However, the biological methods go along with the relevant limitations, for instance simultaneous synthesis of silver chlorides (AgNCl) type during the AgNPs mediation process. Therefore, the present research is coming to summarize several aspects in this context. Firstly, to present the possible promotion of the sustainable development using bioactive source (e.g. milk) as a source of two different available and new lactobacillus strains (Lactobacillus curvatus and Lactobacillus fermentum). Secondly, to show the ability of the respective isolates to be involved in mediation of various biosilver nanocomposites ((Bio)NCs) synthesis. Moreover, at this stage, for the first time, two (Bio)NCs mediation methods, called "direct method" and "modified method", have been developed, thus three types (AgNPs, AgNCl and AgNP@AgNCl) of nanocomposites mediated by two different Lactobacillus isolates take place. The interdisciplinary approach included using several spectroscopic, microscopic, spectrometric and thermogravimetric methods demonstrated that all six synthesized nanoparticles (three AgNPs, AgNCl and AgNP@AgNCl types from each source) consist of complex structure including both metallic silver core as well as organic surface deposits. The spectrometric technique allowed to identification of the organics branching surface, naturally secreted by the used Lactobacillus isolates during the inoculation step, suggesting the presence of amino-acids sequences which are direct connected with the reduction of silver ion to metal silver, and subsequently with the formation of coated (Bio)NCs and nucleation process. Moreover, based on the obtained results, the mediation mechanism of each (Bio)NCs has been proposed, suggesting that the formation of AgNPs, AgNCl and AgNP@AgNCl types occurs in different manners with faster synthesis firstly of AgNCl, then of the AgNPs type. No differences between the (Bio)NCs synthesized by two different Lactobacillus isolates have been noticed indicating no discrepancies between metabolites secreted by the respective sources.

Facile preparation of highly uniform type 3 resistant starch nanoparticles

Resistant starch (RS) has emerged as a promising functional food ingredient. To improve the textural and sensory characteristics of RS, there need to be an effective approach to produce RS with well-defined size and shape. Here, we present a facile approach for the synthesis of highly uniform resistant starch nanoparticles (RSNP) based on recrystallization of short-chain glucan (SCG) originated from debranched starch. We found that the ratio of SCG to partially debranched amylopectin was a key parameter in regulating the morphology, size, and crystallinity of the nanoparticles, which enable us to prepare highly uniform RSNP with an average diameter of around 150 nm, while showing a good colloidal stability over a broad range of pH (2-10). Moreover, the in-vitro digestibility and RS content of RSNP was not affected over the ten successive cycles of assembly and disassembly, which would provide useful insights for the development of RS-based functional food ingredients.

An Algorithmic Approach Based on Data Trees and Genetic Algorithms to Understanding Charged and Neutral Metal Nanocluster Growth

Metal nanocluster growth pathways are challenging to study due to the number of possible species involved and the branching nature of possible mechanisms. We present a data tree-based approach to mapping these reaction pathways based on structures and energies obtained from Density Functional Theory (DFT) computations and including positive, negative, and neutral clusters in a continuum solvent of water. We also develop a genetic algorithm to study the relative stability of the clusters, which we combine with the data tree method to determine the effects that favorable decomposition reactions have on the reaction pathways. Introducing data tree pruning based on the exothermicity of each reaction, and including the first and second most important paths for each cluster up to five atoms including positive, neutral, and negative clusters, is then implemented to determine the cluster growth paths. These most favorable Ag-Ag reaction pathways are in agreement with more limited prior theoretical and experimental results, but they provide more systematic results that include predictions about the importance of clusters not previously identified. A key feature of the data tree approach is that it provides a comprehensive sampling of possible clusters, but without needing to generate the entire reaction tree. Additionally, the data tree-based approach allows for flexibility in the analysis based on restricting reactant charge or size, selecting a starting species to mimic an experimental precursor, and choosing a maximum allowable final cluster size or charge of interest.

Antibacterial, antifungal, antiviral, and photocatalytic activities of TiO2 nanoparticles, nanocomposites, and bio-nanocomposites: Recent advances and challenges

The applications of nanomaterials specifically metal and metal nanoparticles in various medical and industrial fields have been due to their unique properties compared to bulk materials. A combination of pharmacology and nanotechnology has helped the production of novel antimicrobial agents to control resistant microorganisms of bacteria and fungi. The properties of metal nanoparticles and metal oxides such as titanium dioxide (TiO2), zinc oxide (ZnO), silver (Ag), and copper (Cu) are well known as efficient antimicrobial agents. In particular, TiO2 nanoparticles have been considered as an attractive antimicrobial compound due to their photocatalytic intrinsic and their stable, non-toxic, inexpensive, and safe physicochemical properties. Therefore, in this review, recent advances and challenges of antibacterial, antifungal, antiviral, and photocatalytic activities of TiO2 nanoparticles, nanocomposites, and bio-nanocomposites are presented to help future studies.

Insight into nanocrystal synthesis: from precursor decomposition to combustion

Nanotechnology-based synthesis of nanoscale materials has appealed to the attention of scientists in the modern scientific community. In the bottom-up approach, atoms start to aggregate/agglomerate and form nuclei within the minimum and maximum supersaturation range. Once nuclei are generated above the critical-free energy/radius, the growth is initiated by obeying the LaMar model with a slight extra simple growth by diffusion advancement. The in situ real-time liquid phase analysis using STEM, AFM, and XAS techniques is used to control precursor decomposition to the nanocrystal formation process and should be a non-stoppable technique. Solution combustion synthesis (SCS) is a time-/energy-efficient self-sustained process that produces mass-/ion transport active porous materials. SCS also permits the synthesis of evenly distributed-doped and hybrid-nanomaterials, which are beneficial in tuning crucial properties of the materials. The growth and development of nanocrystals, dehydrating the sol in the presence of a surfactant or/and fuel results in combustion once it arrives at the ignition temperature. Besides, the kinetic and thermodynamics controlled architecture-directing agent-assisted SCS offers colloidal nanocrystal framework formation, which is currently highly applicable for energy devices. This short review provides insightful information that adds to the existing nanocrystal synthesis process and solution combustion synthesis and recommends future directions in the field.

The LaMar model visualizes the process of nanocrystal formation. The solution combustion synthesis approach is a noble methodology resulting in highly stable and ordered porous nanomaterials.

General in Colloidal Nanoparticles

It is almost impossible to fabricate size-controlled nanomaterials without full understanding about nanoscience, because nanomaterials sometimes suddenly grow up and precipitated, meanwhile other nanomaterials are disappeared during fabrication process. With this reason, it is necessary to understand the principle theories about nanoscience for fabrication of "well-defined" nanoparticles. This chapter explains basic theories about nanomaterials. And based on the theory, methods for controlling the size of nanoparticles and preventing the aggregation after fabrication are described.

Probing Kinetics and Mechanism of Formation of Mixed Metallic Nanoparticles in a Polymer Membrane by Galvanic Replacement between Two Immiscible Metals: Case Study of Nickel/Silver Nanoparticle Synthesis

Galvanic replacement between metals has received notable research interest for the synthesis of heterometallic nanostructures. The growth pattern of the nanostructures depends on several factors such as extent of lattice mismatch, adhesive interaction between the metals, cohesive forces of the individual metals, etc. Due to the difficulties in probing ultrafast kinetics of the galvanic replacement reaction and particle growth in solution, real-time mechanistic investigations are often limited. As a result, the growth mechanism of one metal on the surface of another metal at the nanoscale is poorly understood so far. In the present work, we could successfully probe the galvanic replacement of silver ions with nickel nanoparticles, stabilized in a polymer membrane, using two complementary methods, namely, small-angle X-ray scattering (SAXS) and radiolabeling, and the results are supported by density functional theory (DFT) computations. The silver-nickel system has been chosen for the present investigation because of the high degree of bulk immiscibility caused by the large lattice mismatch (15.9%) and the weak adhesive interaction, which makes it a perfect model system for immiscible metal pairs. Membrane, as a host medium, plays a crucial role in retarding the kinetics of atomic and particle rearrangements (nucleation and growth) due to slower mobility of the atoms (monomers) and particles within the polymer network. This allowed us to examine the real-time concentration of silver monomers during galvanic replacement of silver ions with nickel nanoparticles and evolution of Ni/Ag nanoparticles. From combined experiment and DFT computations, it has been demonstrated, for the first time to the best of our knowledge, that the majority of silver atoms, which are produced on the nickel nanoparticle surface by galvanic reactions, do not form traditional core-shell nanostructures with nickel and undergo a self-governing sequential nucleation and growth of silver nanoparticles via formation of intermediate prenucleation silver clusters, leading to the formation of mixed metallic nanoparticles in the membrane. The surface of NiNPs has a heterogeneous effect on the silver nucleation pathway, which is evident from the reduced critical free energy barrier of nucleation (ΔG_crit). The present work establishes an original mechanistic pathway based on a sequential nucleation model for formation of mixed metallic nanoparticles by the galvanic replacement route, which opens up future possibilities for size-controlled synthesis in mixed systems.

Silver nanoparticles: Synthesis, medical applications and biosafety

Silver nanoparticles (AgNPs) have been one of the most attractive nanomaterials in biomedicine due to their unique physicochemical properties. In this paper, we review the state-of-the-art advances of AgNPs in the synthesis methods, medical applications and biosafety of AgNPs. The synthesis methods of AgNPs include physical, chemical and biological routes. AgNPs are mainly used for antimicrobial and anticancer therapy, and also applied in the promotion of wound repair and bone healing, or as the vaccine adjuvant, anti-diabetic agent and biosensors. This review also summarizes the biological action mechanisms of AgNPs, which mainly involve the release of silver ions (Ag+), generation of reactive oxygen species (ROS), destruction of membrane structure. Despite these therapeutic benefits, their biological safety problems such as potential toxicity on cells, tissue, and organs should be paid enough attention. Besides, we briefly introduce a new type of Ag particles smaller than AgNPs, silver Ångstrom (Å, 1 Å = 0.1 nm) particles (AgÅPs), which exhibit better biological activity and lower toxicity compared with AgNPs. Finally, we conclude the current challenges and point out the future development direction of AgNPs.

A study on graphene composites for peripheral nerve injury repair under electrical stimulation

Electrical stimulation (ES) provides an effective alternative to peripheral nerve repair via conductive scaffolds. The aim of the present study is to investigate a graphene (GR)/thermoplastic polyurethane (TPU) composite for the repair of peripheral nerve injury under ES. To this end, conductive composite membranes were fabricated by blending GR (2, 4 and 6 wt%) with TPU. GR maintains its own structure in the composite and enhances the mechanical and electrical properties of the composite. The composites with excellent biocompatibility had a hemolysis rate of less than 5%. As a result, the 4GR–TPU (4 wt% GR) sample with enhanced mechanical properties possessed the highest conductivity value of 33.45 ± 0.78 S m⁻¹. Compared with the non-conductive sample, 4GR–TPU was favorable for the viability of Schwann cells (SCs) under ES. When different voltages of ES were applied, a direct current of 10 mV was more suitable for the growth and proliferation of SCs. This study provides beneficial information for peripheral nerve repair via ES.

Electrical stimulation (ES) provides an effective alternative to peripheral nerve repair via conductive scaffolds.