Starch-mediated shape-selective synthesis of Au nanoparticles with tunable longitudinal plasmon resonance

Microcrystalline Cellulose-Supported Gold Nanoparticle Catalysts for Homocoupling of Phenylboronic Acids

A solid-grinding strategy for the large-scale synthesis of solid microcrystalline cellulose (MCC)-supported gold nanoparticle (NP) catalysts without using solvents and a sophisticated purification technique is reported. In contrast to typical solution-based methods, the deposition of high loading of gold NPs with greater uniformity on native MCC polymers without chemical modifications was achieved rapidly by manual grinding. The Fourier transform infrared (FT-IR) study revealed that the abundant hydroxyl functional groups present on the MCC support could effectively hold tiny gold NPs through hydrogen bonding between the -OH groups of MCC and gold NPs, thereby making the MCC-supported gold NPs stable heterogeneous catalysts. Thus, the Au/MCC catalyst exhibits higher catalytic activity and selectivity toward homocoupling of phenylboronic acids into corresponding biphenyls in water under air. Compared to other solid-supported gold NP catalysts, the MCC-supported gold catalysts showed greater catalytic activity and selectivity in the homocoupling of phenylboronic acids. The kinetics study on the homocoupling reaction catalyzed by Au/MCC reveals that the catalysts possess much lower apparent activation energy than the reported gold catalysts. Thus, the present sustainable approach may inspire more studies on the design of renewable biopolymer matrix-supported gold NPs in a large scale for heterogeneous catalysis.

Green synthesis and characterization of gold-based anisotropic nanostructures using bimetallic nanoparticles as seeds

Nanostructured noble metals are of great interest because of their tunable optical and electronic properties. However, the green synthesis of anisotropic nanostructures with a defined geometry by the systematic nanoassembly of particles into specific shape, size, and crystallographic facets still faces major challenges. The present work aimed to establish an environmentally friendly methodology for synthesizing gold-based anisotropic nanostructures using starch-capped bimetallic silver/gold nanoparticles as seeds and hydrogen peroxide as a reducing agent.

Self-assembly in biobased nanocomposites for multifunctionality and improved performance

Concerns of petroleum dependence and environmental pollution prompt an urgent need for new sustainable approaches in developing polymeric products. Biobased polymers provide a potential solution, and biobased nanocomposites further enhance the performance and functionality of biobased polymers. Here we summarize the unique challenges and review recent progress in this field with an emphasis on self-assembly of inorganic nanoparticles. The conventional wisdom is to fully disperse nanoparticles in the polymer matrix to optimize the performance. However, self-assembly of the nanoparticles into clusters, networks, and layered structures provides an opportunity to address performance challenges and create new functionality in biobased polymers. We introduce basic assembly principles through both blending and in situ synthesis, and identify key technologies that benefit from the nanoparticle assembly in the polymer matrix. The fundamental forces and biobased polymer conformations are discussed in detail to correlate the nanoscale interactions and morphology with the macroscale properties. Different types of nanoparticles, their assembly structures and corresponding applications are surveyed. Through this review we hope to inspire the community to consider utilizing self-assembly to elevate functionality and performance of biobased materials. Development in this area sets the foundation for a new era of designing sustainable polymers in many applications including packaging, construction chemicals, adhesives, foams, coatings, personal care products, and advanced manufacturing.

Inkjet-printed paper-based electrochemical sensor with gold nano-ink for detection of glucose in blood serum

An inkjet-printed paper electrode with gold nanoparticle-ink as a non-enzymatic electrochemical sensor for detection of glucose in blood serum is reported.

Nanostructured Gold Coating for Prevention of Biofilm Development in Medical Devices

Bacterial biofilms on medical devices (MDs) can cause deadly infections due to their resistance to antibiotics. Technology to prevent this kind of complication is urgently needed because they impact not only patients' lives but also hospital budgets. In this article, the creation and testing of an easy-to-produce antibiofilm (more precisely antibiofouling) coating are described for the first time. This coating can be applied to catheters, prostheses, and other plastic pieces, even after they have been manufactured. Rapid and ecofriendly synthesis of nanostructured gold coating was done in situ in just 15 minutes. Complete characterization and microbiological analysis of its antibiofouling capacity are presented. The coating prevents biofilm formation of pathogenic clinical isolates and ATCC strains on MDs, possibly due to its complex nanostructured gold surface. If the next generation of MDs is coated with this kind of antibiofouling technology, biofilm-related infections could be dramatically reduced. Graphical Abstract [Figure: see text].

Tree gum-based renewable materials: Sustainable applications in nanotechnology, biomedical and environmental fields

The prospective uses of tree gum polysaccharides and their nanostructures in various aspects of food, water, energy, biotechnology, environment and medicine industries, have garnered a great deal of attention recently. In addition to extensive applications of tree gums in food, there are substantial non-food applications of these commercial gums, which have gained widespread attention due to their availability, structural diversity and remarkable properties as 'green' bio-based renewable materials. Tree gums are obtainable as natural polysaccharides from various tree genera possessing exceptional properties, including their renewable, biocompatible, biodegradable, and non-toxic nature and their ability to undergo easy chemical modifications. This review focuses on non-food applications of several important commercially available gums (arabic, karaya, tragacanth, ghatti and kondagogu) for the greener synthesis and stabilization of metal/metal oxide NPs, production of electrospun fibers, environmental bioremediation, bio-catalysis, biosensors, coordination complexes of metal-hydrogels, and for antimicrobial and biomedical applications. Furthermore, polysaccharides acquired from botanical, seaweed, animal, and microbial origins are briefly compared with the characteristics of tree gum exudates.

Synthesis of Colloidal Metal Nanocrystals: A Comprehensive Review on the Reductants

There is a growing interest in controlling the synthesis of colloidal metal nanocrystals and thus tailoring their properties toward various applications. In this context, choosing an appropriate combination of reagents (e.g., salt precursor, reductant, capping agent, and stabilizer) plays a pivotal role in enabling the synthesis of metal nanocrystals with diversified sizes, shapes, and structures. Here we present a comprehensive review that highlights one of the key reagents for the synthesis of metal nanocrystals via chemical reduction: the reductants. We start with a brief introduction to the compounds commonly employed as reductants in the colloidal synthesis of metal nanocrystals by showing their oxidation half-reactions and the corresponding oxidation potentials. Then we offer specific examples pertaining to the controlled synthesis of metal nanocrystals, followed by some fundamental aspects covering the general mechanisms of metal ion reduction based on the Marcus Theory. Afterwards, we present a case-by-case discussion on a wide variety of reductants, including their major properties, reduction mechanisms, and additional effects on the final products. We illustrate these aspects by selecting key examples from the literature and paying close attention to the underlying mechanism in each case. At the end, we conclude by summarizing the highlights of the review and providing some perspectives on future directions.

Starch-templated bio-synthesis of gold nanoflowers for in vitro antimicrobial and anticancer activities

We describe an in situ method of synthesizing highly branched gold nanoflower (AuNFs) using aqueous seed extract of Syzygium cumini (L.) Skeels as reductant in the presence of 0.3% starch. Surprisingly, when the same reaction was carried out in the absence of starch or with starch at a lower concentration (0.15%), instead of flower-like morphology quasi-spherical or polyhedral nanoparticles (AuNPs) are obtained. The nanomaterials were extensively characterized by HRTEM, FESEM, UV–Vis, FTIR, XRD, XPS and TGA analysis. The biological activities of the materials were investigated for antimicrobial activities against four bacterial strains that include one Gram positive (Staphylococcus aureus MTCC 121), two Gram negative (Escherichia coli MTCC 40 and Pseudomonas aeruginosa MTCC 4673) and one fungi (Candida albicans MTCC 227). The nanoparticles functioned as effective antimicrobial and anti-biofilm agents against all the strains under study. Controlled study revealed that, the AuNFs showed improved efficacy over conventional polyhedral AuNPs against all the microbes under study which might be attributed to the larger surface-to-volume ratio of the nanoflowers. The AuNFs also showed effective in vitro anticancer activity against a human liver cancer cell line (HepG2) with no significant cytotoxicity. Our data suggest that the AuNFs can significantly reduce the cancer cell growth with IC50 value of 20 µg mL−1.

Preparation of Ag nanoparticles using hydrogen peroxide as a reducing agent

The particle growth mechanism and antibacterial property of Ag nanoparticles prepared by H₂O₂ reduction was firstly discussed.

Green synthesis and characterisation of platinum nanoparticles using quail egg yolk

Nanotechnology is extensively used in all parts today. Therefore, nano synthesis is also significant in all explored areas. The results of studies conducted have revealed that nanoparticle synthesis is performed by using both chemical and physical methods. It is well known that these syntheses are carried out at high charge, pressure and temperature in harsh environments. Therefore, this study investigated green synthesis method that sustains more mild conditions. In this study, quail egg yolk having high vitamin and protein content was prepared for green synthesis reaction and used for the synthesis of platinum nanoparticles in the reaction medium. Reaction situations were optimised as a function of pH, temperature, time and concentration by using quail egg yolk. The results showed that the highest platinum nanoparticles were synthesised at 20°C and pH6.0 for 4h. Also, optimal concentration of metal ions was established as 0.5mM. The synthesised platinum nanoparticles were characterised by using UV spectrum, X-ray diffraction and scanning electron microscope.

Biomimetic and Bioinspired Synthesis of Nanomaterials/Nanostructures

In recent years, due to its unparalleled advantages, the biomimetic and bioinspired synthesis of nanomaterials/nanostructures has drawn increasing interest and attention. Generally, biomimetic synthesis can be conducted either by mimicking the functions of natural materials/structures or by mimicking the biological processes that organisms employ to produce substances or materials. Biomimetic synthesis is therefore divided here into "functional biomimetic synthesis" and "process biomimetic synthesis". Process biomimetic synthesis is the focus of this review. First, the above two terms are defined and their relationship is discussed. Next different levels of biological processes that can be used for process biomimetic synthesis are compiled. Then the current progress of process biomimetic synthesis is systematically summarized and reviewed from the following five perspectives: i) elementary biomimetic system via biomass templates, ii) high-level biomimetic system via soft/hard-combined films, iii) intelligent biomimetic systems via liquid membranes, iv) living-organism biomimetic systems, and v) macromolecular bioinspired systems. Moreover, for these five biomimetic systems, the synthesis procedures, basic principles, and relationships are discussed, and the challenges that are encountered and directions for further development are considered.

Reversible encapsulation of silver nanoparticles into the helix of amylose (water soluble starch)

Natural biodegradable polymeric starch capped Ag-nanoparticles (AgNPs) were prepared by using extract of Dioscorea deltoidea in the presence of starch.

Insights into biogenic and chemical production of inorganic nanomaterials and nanostructures

The synthesis of inorganic nanomaterials and nanostructures by the means of diverse physical, chemical, and biological principles has been developed in recent decades. The nanoscale materials and structures creation continue to be an active area of researches due to the exciting properties of the resulting nanomaterials and their innovative applications. Despite physical and chemical approaches which have been used for a long time to produce nanomaterials, biological resources as green candidates that can replace old production methods have been focused in recent years to generate various inorganic nanoparticles (NPs) or other nanoscale structures. Cost-effective, eco-friendly, energy efficient, and nontoxic produced nanomaterials using diverse biological entities have been received increasing attention in the last two decades in contrast to physical and chemical methods owe using toxic solvents, generate unwanted by-products, and high energy consumption which restrict the popularity of these ways employed in nanometric science and engineering. In this review, the biosynthesis of gold, silver, gold-silver alloy, magnetic, semiconductor nanocrystals, silica, zirconia, titania, palladium, bismuth, selenium, antimony sulfide, and platinum NPs, using bacteria, actinomycetes, fungi, yeasts, plant extracts and also informational bio-macromolecules including proteins, polypeptides, DNA, and RNA have been reported extensively to mention the current status of the biological inorganic nanomaterial production. In other hand, two well-known wet chemical techniques, namely chemical reduction and sol-gel methods, used to produce various types of nanocrystalline powders, metal oxides, and hybrid organic-inorganic nanomaterials have presented.

Biopolymer-activated graphitic carbon nitride towards a sustainable photocathode material

Photoelectrochemical (PEC) conversion of solar light into chemical fuels is one of the most promising solutions to the challenge of sustainable energy. Graphitic carbon (IV) nitride polymer (g-CN) is an interesting sustainable photocathode material due to low-cost, visible-light sensitivity, and chemical stability up to 500 °C in air. However, grain boundary effects and limited active sites greatly hamper g-CN activity. Here, we demonstrate biopolymer-activation of g-CN through simultaneous soft-templating of a sponge-like structure and incorporation of active carbon-dopant sites. This facile approach results in an almost 300% increase in the cathodic PEC activity of g-CN under simulated solar-irradiation.

Green chemistry approach for the synthesis and stabilization of biocompatible gold nanoparticles and their potential applications in cancer therapy

The biological approach to synthesis of AuNPs is eco-friendly and an ideal method to develop environmentally sustainable nanoparticles alternative to existing methods. We have developed a simple, fast, clean, efficient, low-cost and eco-friendly single-step green chemistry approach for the synthesis of biocompatible gold nanoparticles (AuNPs) from chloroauric acid (HAuCl(4)) using a water extract of Eclipta Alba leaves at room temperature. The AuNPs using Eclipta extract have been formed in very short time, even in less than 10 min. The as-synthesized AuNPs were thoroughly characterized by several physico-chemical techniques. The in vitro stability of as-synthesized AuNPs was studied in different buffer solutions. A plausible mechanism for the synthesis of AuNPs by Eclipta extract has been discussed. The biocompatibility of AuNPs was observed by in vitro cell culture assays. Finally, we have designed and developed a AuNPs-based drug delivery system (DDS) (Au-DOX) containing doxorubicin (DOX), a FDA approved anticancer drug. Administration of this DDS to breast cancer cells (MCF-7 and MDA-MB-231) shows significant inhibition of breast cancer cell proliferation compared to pristine doxorubicin. Therefore we strongly believe that the use of Eclipta Alba offers large-scale production of biocompatible AuNPs that can be used as a delivery vehicle for the treatment of cancer diseases.

Rapid seeded growth of monodisperse, quasi-spherical, citrate-stabilized gold nanoparticles via H2O2 reduction

In this report, we demonstrate a rapid and simple seeded growth method for synthesizing monodisperse, quasi-spherical, citrate-stabilized Au nanoparticles (Au NPs) via H(2)O(2) reduction of HAuCl(4). Au NPs with diameter ranging from 30 to 230 nm can be synthesized by simply adding 12 nm citrate stabilized Au NP seeds to an aqueous solution of H(2)O(2) and HAuCl(4) under ambient conditions. The diameter of the resulting Au NPs can be quantitatively controlled by the molar ratio of HAuCl(4) to the Au seeds. The standard deviation of the Au NP sizes is less than 10%, and the ellipticity (ratio of major to minor axes) of the NPs is less than 1.1. Compared to existing ones, the present seeded growth approach is implemented within 1 min under ambient condition, and no unfavorable additives are involved because H(2)O(2) can readily decompose into H(2)O during storage or via boiling.

A sunlight-induced rapid synthesis of silver nanoparticles using sodium salt of N-cholyl amino acids and its antimicrobial applications

Aqueous solution containing two additives, silver nitrate (AgNO(3)) and sodium salt of N-cholyl amino acid were irradiated by sunlight for the synthesis of spherical shaped AgNPs without the need for an additional stabilizer or capping agent. Variations of N-cholyl amino acid concentration provided good control over the morphology of the AgNPs, while the carboxylate group of bile salt reduced the Ag(+) ions and the amide group binds strongly to the surface of the NPs. The optical properties, morphology of the AgNPs were characterized by UV-visible, transmission electron microscopy (TEM) and dynamic light scattering (DLS) studies. The interaction of N-cholyl amino acid on the AgNPs surface was studied using cyclic voltammetry and FT-IR techniques. The reduction process was completed within 5 min and the synthesized AgNPs were stable for more than 6 months. The possible mechanism of N-cholyl amino acid on the reduction and stabilization of AgNPs is also discussed. The antimicrobial activity of N-cholyl amino acid capped AgNPs against Escherichia coli, Staphylococcus aureus and Pseudomonas aeroginosa using Mueller Hinton broth and the antifungal activity against Candida albicans, Candida krusei and Candida tropicalis using RPMI broth were determined by MIC studies as per CLSI guidelines.

Shape-tailoring and catalytic function of anisotropic gold nanostructures

We report a facile, one-pot, shape-selective synthesis of gold nanoparticles in high yield by the reaction of an aqueous potassium tetrachloroaurate(III) solution with a commercially available detergent. We prove that a commercial detergent can act as a reducing as well as stabilizing agent for the synthesis of differently shaped gold nanoparticles in an aqueous solution at an ambient condition. It is noteworthy that the gold nanoparticles with different shapes can be prepared by simply changing the reaction conditions. It is considered that a slow reduction of the gold ions along with shape-directed effects of the components of the detergent plays a vital function in the formation of the gold nanostructures. Further, the as-prepared gold nanoparticles showed the catalytic activity for the reduction reaction of 4-nitrophenol in the presence of sodium borohydride at room temperature.

Shape-tailoring of gold nanostructures: can a detergent act as the reducing or protecting agent?

A commercially available detergent was found to be an effective reducing as well as stabilizing agent for the synthesis of differently shaped gold nanoparticles in an aqueous solution at an ambient condition and the as-prepared gold nanoparticles behave as an efficient catalyst for the reduction reaction of 4-nitrophenol at room temperature.

Alginate stabilized silver nanocube-Rh6G composite as a highly selective mercury sensor in aqueous solution

Alginate-stabilized silver nanocubes are synthesized via a reduction method and are characterized by UV-Vis and fluorescence spectroscopies, SEM, AFM and HRTEM analyses. A silver nanocubes (Ag NCbs) based sensor for detecting Hg2+ ions in aqueous solution has been developed using Rh6G as an external spectroscopic probe. Using this system, Hg2+ ions (as low as 1×10(-10) mol L(-1)) are recognized in aqueous media via a colorimetric method with very high selectivity and sensitivity over other metal ions namely Fe2+, Zn2+, Pb2+, Cu2+, Sn2+, Cd2+, Ni2+, and Co2+.

Biopolymer-protected CdSe nanoparticles

A synthetic procedure for the encapsulation of cadmium selenide (CdSe) nanoparticles in a sago starch matrix is introduced. The nanocomposite was investigated using structural, spectroscopic, and thermal methods. TEM micrographs of the nanocomposite showed spherical CdSe particles of 4-5 nm in size coated with a biopolymer layer. The absorption edges of both the aqueous solution and the thin film of the CdSe-starch nanocomposite were shifted toward lower wavelengths in comparison to the value of the bulk semiconductor. Infrared measurements revealed that the interaction of CdSe nanoparticles and starch chains takes place via OH groups. Although the onset of the temperature of decomposition of CdSe-starch nanocomposite is lower than that of the pure matrix, thermogravimetric analysis also showed that introduction of CdSe nanoparticles significantly reduced starch degradation rate leading to high residual mass at the end of the degradation process.

The extraction of gold nanoparticles from oat and wheat biomasses using sodium citrate and cetyltrimethylammonium bromide, studied by x-ray absorption spectroscopy, high-resolution transmission electron microscopy, and UV-visible spectroscopy

Gold (Au) nanoparticles can be produced through the interaction of Au(III) ions with oat and wheat biomasses. This paper describes a procedure to recover gold nanoparticles from oat and wheat biomasses using cetyltrimethylammonium bromide or sodium citrate. Extracts were analyzed using UV-visible spectroscopy, high-resolution transmission electron microscopy (HRTEM), and x-ray absorption spectroscopy. The HRTEM data demonstrated that smaller nanoparticles are extracted first, followed by larger nanoparticles. In the fourth extraction, coating of chelating agents is visible on the extracted nanoparticles.

Probing Au nanoparticle uptake by enzyme following the digestion of a starch-Au-nanoparticle composite

In this letter, we report on the digestion of starch, when present as a composite with Au nanoparticles (NPs), by alpha-amylase. It has been observed that the rate of digestion of free starch and that in the composite were identical. Also, the well-established iodine test could be carried out to investigate the kinetics in the presence of Au NPs. The investigations revealed that following the digestion of starch in the composite the NPs were released and subsequently attached to the enzyme only and not to the degraded products of starch. Also, the enzyme attached to NPs, following digestion, retained its catalytic activity. The particle sizes of the NPs were not affected in the process because no agglomeration was observed. Experimental observations indicated the possibility of oriented attachment of alpha-amylase to the NPs in comparison to amyloglucosidase, another digestive enzyme. Finally, we observed a change in the surface plasmon resonance (SPR) of the NPs following the digestion of starch in the composite, and thus we could demonstrate that the SPR of the NPs could be used as a direct probe for monitoring the digestion of the composite by the enzyme.

Preparation and properties of nano-sized Ag and Ag2S particles in biopolymer matrix

Silver (Ag) and silver sulfide (Ag(2)S) nanoparticles were synthesized in a sago starch matrix. The resulting nanocomposites were investigated using structural, optical and thermal methods. XRD spectra of the nanocomposites confirmed the presence of nanostructured silver (cubic phase) and silver sulfide (monoclinic phase) in the matrix. TEM micrographs showed that the nanoparticles are mostly spherical in shape. Analyzes of the optical properties of the silver nanocomposite aqueous dispersions/solutions of various concentrations were carried out. The results and the theoretical considerations suggested that at high concentrations there is a release of silver nanoparticles from the composite in the water environment. Further dilution produces homogeneous solution in which silver nanoparticles are capped with starch macromolecules. TGA analysis revealed reduced thermal stability of the nanocomposites with respect to pure starch matrix.

Biofabrication with Chitosan

The traditional motivation for integrating biological components into microfabricated devices has been to create biosensors that meld the molecular recognition capabilities of biology with the signal processing capabilities of electronic devices. However, a different motivation is emerging; biological components are being explored to radically change how fabrication is achieved at the micro- and nanoscales. Here we review biofabrication, the use of biological materials for fabrication, and focus on three specific biofabrication approaches: directed assembly, where localized external stimuli are employed to guide assembly; enzymatic assembly, where selective biocatalysts are enlisted to build macromolecular structure; and self-assembly, where information internal to the biological material guides its own assembly. Also reviewed are recent results with the aminopolysaccharide chitosan, a material that offers a combination of properties uniquely suited for biofabrication. In particular, chitosan can be directed to assemble in response to locally applied electrical signals, and the chitosan backbone provides sites that can be employed for the assembly of proteins, nucleic acids, and virus particles.