Protocol for synthesis of spherical silver nanoparticles with stable optical properties and characterization by transmission electron microscopy

The synthesis of metallic plasmonic nanoparticles (NPs) faces challenges in stability and reproducibility, especially with silver. Here, we present a protocol for tunable synthesis of spherical silver NPs (AgNPs) with stable optical properties. We describe steps for preparing solutions, morphological characterization of AgNPs by transmission electron microscopy, and testing stability. AgNPs exhibit enduring stability and compatibility with various pH values. Moreover, they can be functionalized for optical biosensing applications, offering versatility in nanomaterial applications.

Effects of Different Surfactant Charges on the Formation of Gold Nanoparticles by the LASiS Method

The laser ablation synthesis in solution (LASiS) method has been widely utilized due to its significant prospects in laser microprocessing of nanomaterials. In this study, the LASiS method with the addition of different surfactant charges (cationic CTAB, nonionic TX-100, and anionic SDS) was used to produce Au NPs. An Nd:YAG laser system at 532 nm excitation with some synthetic parameters, including different laser fluences, ablation times, and surfactant concentrations was performed. The obtained Au NPs were characterized by UV-Vis spectroscopy, transmission electron microscopy, and zeta potential analyzer. The Au NPs exhibited the maximum absorption peak at around 520 nm for all samples. The color of Au NPs was changed from red to reddish by increasing the laser fluence. The surfactant charges also played different roles in the Au NPs’ growth during the synthesis process. The average sizes of Au NPs were found to be 8.5 nm, 5.5 nm, and 15.5 nm with the medium containing CTAB, TX-100, and SDS, respectively. Besides, the different surfactant charges induced different performances to protect Au NPs from agglomeration. Overall, the SDS and CTAB surfactants exhibited higher stability of the Au NPs compared to the Au NPs with TX-100 surfactant.

Preparation of Gold Nanoplates Using Ortho Carbonyl Compounds as Capping Agents for Electrochemical Sensing of Lead Ions

In this study, gold nanoplates were synthesized using plant molecules (gallic acid) following a kinetic control mode. The growth of nanoplates is mainly due to the specific adsorption of capping agents on certain crystal facets. Through systematical characterizations, it is found that the distance between two oxygen atoms in ortho carbonyl compounds matches well with the lattice spacing of gold (111) facets exactly, which is beneficial to the formation of twin seeds and further the growth of plate-like gold nanoparticles. The gold nanoplates on glassy carbon electrode show a remarkably improved electrochemical sensing activity of lead ions compared to the bare glassy carbon electrode or spherical gold nanoparticle-modified electrode. The modified electrode is expected to be used in the detection of lead ion concentration in heavy metal wastewater.

A low cost and open access system for rapid synthesis of large volumes of gold and silver nanoparticles

Rapid synthesis of nanomaterials in scalable quantities is critical for accelerating the discovery and commercial translation of nanoscale-based technologies. The synthesis of metal nanogold and silver in volumes larger than 100 mL is not automatized and might require of the use of harsh conditions that in most cases is detrimental for the production of nanoparticles with reproducible size distributions. In this work, we present the development and optimization of an open-access low-cost NanoParticle Flow Synthesis System (NPFloSS) that allows for the rapid preparation of volumes of up to 1 L of gold and silver nanoparticle aqueous solutions.

Ampicillin-mediated functionalized gold nanoparticles against ampicillin-resistant bacteria: strategy, preparation and interaction studies

Antibiotic resistance is a highly challenging concern of infectious diseases, and it requires a rational approach to overcome. Through this work, we have synthesized ampicillin-capped gold nanoparticles (Amp-Au NPs) and studied its interaction with bacterial cells. In this process of synthesis, the primary amine group of ampicillin acts as both reducing as well as capping agent. In addition to synthesized gold nanoparticles, the β-lactam ring remains free to interact with bacteria. This approach not only utilizes the maximum efficiency of nanoparticles and antibiotics towards ampicillin sensitive bacterial cells but also proves to be effective against ampicillin resistance bacteria. Our results illustrate that the optimized system of Amp-Au NPs was formulated by taking 1.25 mM ampicillin and 10^-2 of gold ions concentration. UV-vis spectrum of gold nanoparticles and the presence of ampicillin were recorded at around 540 nm and 259 nm, respectively. Microscopic images indicate that particles are nearly spherical and are in size range between 25 and 50 nm. Moreover, formulated Amp-Au NPs show successful accumulation onto the surface of the bacterial cell as a result of which pores were formed into the bacterial membrane. The entry of nanoparticles into bacterial cells was validated through both atomic force microscopy and fluorescent microscopy. The adhesive properties of this coating material and its stability in various pH, i.e. pH 3, pH 7 and pH 10 conditions, could make them a good candidate in the prevention of biofilm formation. Amp-Au NPs show promising antimicrobial activity against ampicillin resistance Escherichia coli bacteria. Furthermore, antimicrobial studies indicate that the efficacy of Amp-Au NPs increased against both ampicillin sensitive and ampicillin resistance bacteria up to sixteen folds and four folds respectively.

Stability issues and approaches to stabilised nanoparticles based drug delivery system

Nanoparticles form the fundamental building blocks for many exciting applications in various scientific disciplines due to its unique features such as large surface to mass ratio, targeting potential, ability to adsorbed and carry other compound which makes them suitable for biomedical applications. However, the problem of the large-scale synthesis of nanoparticles remains challenging due to physical instability associated with nanoparticles which lead to generation of aggregates particles with high polydispersity index (PDI) indicating low particle homogeneity and eventually loss of their special nanoscale properties. The stabilisation concept can be generated by repulsive electrostatic force, which nanoparticles experience, when they are surrounded by a double layer of electric charges. Selection of proper stabiliser will govern the stability of NPs and ultimately development of optimised drug delivery system. This review summarises mechanism of physical instability issues likely to be encountered during the development of nanoformulations. It also discusses potential stabilising agents used so far and their mechanism in achieving stable nanosystems.

Colorimetric immunosensor for determination of prostate specific antigen using surface plasmon resonance band of colloidal triangular shape gold nanoparticles

In this work, we demonstrated the development of a colorimetric immunosensor using surface plasmon resonance band of gold nanoparticles for the detection of prostate specific antigen (PSA). To develop this biosensing tool, triangular gold nanoparticles (AuNPs) were synthesized using Tween-20 as a nonionic surfactant and then, conjugated with PSA capture antibody (Ab₁-AuNPs). When exposed to Ab₁-AuNPs, PSA antigens were found to be successfully captured by nanosystem (PSA)-Ab₁-AuNPs. Next, (PSA)-Ab₁-AuNPs were incubated with second PSA antibody (2)-decorated magnetite (Fe₃O₄-Ab₂) and separated by an external magnetic force to leave Ab₁-AuNPs in the supernatant solution to be directly analyzed using UV-Vis spectroscopy. It was found that the absorption intensity was directly proportional to the PSA concentration. As a result, the linear range for PSA detection was found to be 0.01-20 ng mL^-1 with a detection limit of 0.009 ng mL^-1. Because of significant stability of the prepared Ab₁-AuNPs and excellent selectivity to the PSA antigen, this simple and sensitive sensing system is proposed to be potentially effective in the fast and real-time analysis of clinical samples from prostate cancer patients. We believe that the simple platform of this immunosensor to be useful in the development of future point-of-care sensing tools, working on the quantification of biomarkers in a drop of blood.

Detergent-modified catalytic and enzymomimetic activity of silver and palladium nanoparticles biotemplated by Pyrococcus furiosus ferritin

Palladium and silver nanoparticles (NPs) anchored at the outer surface of ferritin form stable suspension of non-coated particles that possess several catalytic and enzymomimetic activities. These activities are strongly affected by detergents that significantly influence the reaction efficiency and specificity. Reductive dehalogenation of various azo dye substrates shows strong differences in reactivity for each substrate-detergent pair. Reductive dehalogenation is negatively influenced by cationic detergents while catalytic depropargylation is severely impaired by polyethylene oxide containing detergents that is an important finding in respect to potential biorthogonal applications. Moreover, Suzuki-Miyaura reaction is promoted by polyethylene oxide containing detergents but some of them also facilitate dehalogenation. Enzymomimetic peroxidase activity of silver NPs can be detected only in presence of sodium dodecyl sulfate (SDS) while peroxidase activity of palladium NPs is enhanced by SDS and sodium deoxycholate.

Size- and Shape-Controlled Synthesis of Calcium Silicate Particles Enables Self-Assembly and Enhanced Mechanical and Durability Properties

Calcium silicate (CS)-based materials are ubiquitous in diverse industries ranging from cementitious materials to bone tissue engineering and drug delivery. As a symbolic example, concrete is the most widely used synthetic material on the planet. This large consumption entails significant negative environmental footprint, which calls for innovative strategies to develop greener concrete with improved properties (to do more with less). Herein, we focus on the physicochemical properties of novel spherical calcium silicate particles with an extremely narrow size distribution and report their promising potential as fundamental building blocks. We demonstrate a scalable size- and shape-controlled synthesis protocol to yield highly spherical CS submicron particles, leading to favorable aggregation mechanisms and thus self-assembly of the bulk ensemble. This optimized kinetics-controlled synthesis is governed by suitable stoichiometric ratio of calcium over silicon, type and concentration of the surfactant, and molar ratio of the alkaline solution. Our extensive nano/micro/macro-characterization results show that the bulk ensemble exhibits many superior properties, such as improved strength, toughness, ductility, and durability, paving the path for bottom-up science-based engineering of concrete.

A plasmonic nanosensor for lipase activity based on enzyme-controlled gold nanoparticles growth in situ

A plasmonic nanosensor for lipase activity was developed based on one-pot nanoparticle growth. Tween 80 was selected not only as the substrate for lipase recognition but also as the reducing and stabilizing agent for the sensor fabrication. The different molecular groups in Tween 80 could have different roles in the fabrication procedure; the H2O2 produced by the autoxidation of the ethylene oxide subunits in Tween 80 could reduce the AuCl4(-) ions to Au atoms, meanwhile, the lipase could hydrolyze its carboxyl ester bond, which could, in turn, control the rate of nucleation of the gold nanoparticles (AuNPs) and tailor the localized surface plasmon resonance (LSPR) of the AuNP transducers. The color changes, which depend on the absence or presence of the lipase, could be used to sense the lipase activity. A linear response ranging from 0.025 to 4 mg mL(-1) and a detection limit of the lipase as low as 3.47 μg mL(-1) were achieved. This strategy circumvents the problems encountered by general enzyme assays that require sophisticated instruments and complicated assembling steps. The methodology can benefit the assays of heterogeneous-catalyzed enzymes.

Colorimetric assay for heterogeneous-catalyzed lipase activity: enzyme-regulated gold nanoparticle aggregation

Lipase is a neglected enzyme in the field of gold nanoparticle-based enzyme assays. This paper reports a novel colorimetric probe to rapidly visualize lipase activities by using Tween 20 functioned GNPs (Tween 20-GNPs) as a reporter. The present strategy hence could overcome the limitations caused by the heterogeneous interface in lipase assay. Catalytic hydrolytic cleavage of the ester bond in Tween 20-GNPs by lipase will trigger the rapid aggregation of GNPs at a high salt solution. The color change from red to purple could be used to sense the activity of lipase. The detection limit (3σ) is as low as 2.8 × 10-2 mg/mL. A preliminary enzyme activity screening was carried out for seven commercially purchased lipase samples. It also has been successfully applied to detecting lipase in fermentation broth of Bacillus subtilis without any pretreatment.

Facile synthesis of silver submicrospheres and their applications

Silver submicrospheres fabricated under an ambient condition can catalyze the reduction of 4-nitrophenol and improve significantly the Raman signal of crystal violet as surface-enhanced Raman scattering (SERS) substrate.

Phage based green chemistry for gold ion reduction and gold retrieval

The gold mining industry has taken its toll on the environment, triggering the development of more environmentally benign processes to alleviate the waste load release. Here, we demonstrate the use of bacteriophages (phages) for biosorption and bioreduction of gold ions from aqueous solution, which potentially can be applied to remediate gold ions from gold mining waste effluent. Phage has shown a remarkably efficient sorption of gold ions with a maximum gold adsorption capacity of 571 mg gold/g dry weight phage. The product of this phage mediated process is gold nanocrystals with the size of 30-630 nm. Biosorption and bioreduction processes are mediated by the ionic and covalent interaction between gold ions and the reducing groups on the phage protein coat. The strategy offers a simple, ecofriendly and feasible option to recover of gold ions to form readily recoverable products of gold nanoparticles within 24 h.