Role of Capping Agent in Wet Synthesis of Nanoparticles

Gold Nanoclusters, Gold Nanoparticles, and Analytical Techniques for Their Characterization

Many reliable and reproducible methods exist for manufacturing gold nanoparticles with the desired and specific compositions, structures, arrangements, and physicochemical properties. In this report, we review the key principles guiding the formation and growth of nanoclusters, their evolution into nanoparticles, and the role and contribution of coatings. We describe a range of imaging methods for characterization of nanoparticles at atomic resolution and a range of spectroscopy methods for structural and physicochemical characterization of such nanoparticles. This chapter concludes with a short review of the emergent applications of nanoparticles in biosciences.

A Highly Reversible, Dendrite-Free Lithium Metal Anode Enabled by a Lithium-Fluoride-Enriched Interphase

Metallic lithium is the most competitive anode material for next-generation lithium (Li)-ion batteries. However, one of its major issues is Li dendrite growth and detachment, which not only causes safety issues, but also continuously consumes electrolyte and Li, leading to low coulombic efficiency (CE) and short cycle life for Li metal batteries. Herein, the Li dendrite growth of metallic lithium anode is suppressed by forming a lithium fluoride (LiF)-enriched solid electrolyte interphase (SEI) through the lithiation of surface-fluorinated mesocarbon microbeads (MCMB-F) anodes. The robust LiF-enriched SEI with high interfacial energy to Li metal effectively promotes planar growth of Li metal on the Li surface and meanwhile prevents its vertical penetration into the LiF-enriched SEI from forming Li dendrites. At a discharge capacity of 1.2 mAh cm^-2 , a high CE of >99.2% for Li plating/stripping in FEC-based electrolyte is achieved within 25 cycles. Coupling the pre-lithiated MCMB-F (Li@MCMB-F) anode with a commercial LiFePO₄ cathode at the positive/negative (P/N) capacity ratio of 1:1, the LiFePO₄ //Li@MCMB-F cells can be charged/discharged at a high areal capacity of 2.4 mAh cm^-2 for 110 times at a negligible capacity decay of 0.01% per cycle.

Colorimetric aggregation assay based on array of gold and silver nanoparticles for simultaneous analysis of aflatoxins, ochratoxin and zearalenone by using chemometric analysis and paper based analytical devices

A paper based sensor array is presented to discriminate and determine five mycotoxins classified into three categories, namely aflatoxins, ochratoxins and zearalenone. The gold and silver nanoparticles, synthesized by three different reducing or capping agents, were employed as sensing elements of the fabricated device. These nanoparticles were poured onto hydrophilic circular zones embedded on the hydrophobic substrate. The response of the assay is dependent on the aggregation of nanoparticles for interaction with mycotoxins. Due to aggregation, the gold and silver nanoparticles changed to purple and brown, respectively. Color changes provide unique colorimetric signatures conducive to recognizing the type of mycotoxin, identifying its chemical structure, and finding the fungi that produce it. The discrimination ability of the assay was investigated by both supervised (linear discriminate analysis) and unsupervised (principle component analysis and hierarchical cluster analysis) pattern recognition methods. The assay was applied to the point of need determination of aflatoxin B1, aflatoxin G1, aflatoxin M1, ochratoxin A and zearalenone with a detection limit of 2.7, 7.3, 2.1, 3.3 and 7.0 ng.mL^-1, respectively. The fabricated device has high potential of simultaneously determining the mycotoxins in pistachio, wheat, coffee and milk with the help of partial least square method. The root mean square errors for prediction of PLS model were 5.7, 5.2, 1.5, 7.2 and 2.9 for aflatoxin B1, aflatoxin G1, aflatoxin M1, ochratoxin A and zearalenone, respectively. Graphical abstractSchematic representation of paper based colorimetric sensor array based on gold and silver nanoparticles for both qualitative and quantitative analysis of aflatoxins, ochratoxin and zearalenone.

Hollow Silver Nanostructures: The Role of Capping Agents in Tailoring the Shape, Structure, and Plasmonic Properties

The shape- and structure-directing ability of capping agents, namely, acetic acid (AA) and folic acid (FA), has been analyzed in the synthesis of hollow plasmonic nanostructures via the nanoscale Kirkendall effect. FA was found to possess both shape-directing and structure-directing abilities when spherical solid Ag2O nanoparticles were transformed into hollow silver nanocubes (HAgNCs). In contrast, AA acted only as a structure-directing agent in the transformation from solid Ag2O nanospheres to hollow Ag nanospheres (HAgNSs). FA capping leads to enhanced plasmon tunability range from 535 to 640 nm in the hollow silver nanostructures. The size and shape of nanostructures were analyzed by high-resolution transmission electron microscopy (HRTEM). HRTEM revealed that the outer diameter of AA-capped HAgNSs is 50 ± 10 nm while edge-length for FA-capped HAgNCs is 100 ± 15 nm. The diameter of inner void space was found to be 30 ± 5 and 43 ± 5 nm for HAgNSs and HAgNCs, respectively. The phase purity of the hollow nanostructures was confirmed by X-ray diffraction and energy dispersive X-ray measurements. Due to unique structural and plasmonic features, FA-capped HAgNCs are well-suited for biomedical applications.

Advances in Lipid and Metal Nanoparticles for Antimicrobial Peptide Delivery

Antimicrobial peptides (AMPs) have been described as excellent candidates to overcome antibiotic resistance. Frequently, AMPs exhibit a wide therapeutic window, with low cytotoxicity and broad-spectrum antimicrobial activity against a variety of pathogens. In addition, some AMPs are also able to modulate the immune response, decreasing potential harmful effects such as sepsis. Despite these benefits, only a few formulations have successfully reached clinics. A common flaw in the druggability of AMPs is their poor pharmacokinetics, common to several peptide drugs, as they may be degraded by a myriad of proteases inside the organism. The combination of AMPs with carrier nanoparticles to improve delivery may enhance their half-life, decreasing the dosage and thus, reducing production costs and eventual toxicity. Here, we present the most recent advances in lipid and metal nanodevices for AMP delivery, with a special focus on metal nanoparticles and liposome formulations.

Susceptibility of microbial cells to the modified PIP2-binding sequence of gelsolin anchored on the surface of magnetic nanoparticles

BACKGROUND

Magnetic nanoparticles (MNPs) are characterized by unique physicochemical and biological properties that allow their employment as highly biocompatible drug carriers. Gelsolin (GSN) is a multifunctional actin-binding protein involved in cytoskeleton remodeling and free circulating actin sequestering. It was reported that a gelsolin derived phosphoinositide binding domain GSN 160-169, (PBP10 peptide) coupled with rhodamine B, exerts strong bactericidal activity.

RESULTS

In this study, we synthesized a new antibacterial and antifungal nanosystem composed of MNPs and a PBP10 peptide attached to the surface. The physicochemical properties of these nanosystems were analyzed by spectroscopy, calorimetry, electron microscopy, and X-ray studies. Using luminescence based techniques and a standard killing assay against representative strains of Gram-positive (Staphylococcus aureus MRSA Xen 30) and Gram-negative (Pseudomonas aeruginosa Xen 5) bacteria and against fungal cells (Candida spp.) we demonstrated that magnetic nanoparticles significantly enhance the effect of PBP10 peptides through a membrane-based mode of action, involving attachment and interaction with cell wall components, disruption of microbial membrane and increased uptake of peptide. Our results also indicate that treatment of both planktonic and biofilm forms of pathogens by PBP10-based nanosystems is more effective than therapy with either of these agents alone.

CONCLUSIONS

The results show that magnetic nanoparticles enhance the antimicrobial activity of the phosphoinositide-binding domain of gelsolin, modulate its mode of action and strengthen the idea of its employment for developing the new treatment methods of infections.

Magnetic Functionalized Nanoparticles for Biomedical, Drug Delivery and Imaging Applications

Medicine is constantly looking for new and improved treatments for diseases, which need to have a high efficacy and be cost-effective, creating a large demand on scientific research to discover such new treatments. One important aspect of any treatment is the ability to be able to target only the illness and not cause harm to another healthy part of the body. For this reason, metallic nanoparticles have been and are currently being extensively researched for their possible medical uses, including medical imaging, antibacterial and antiviral applications. Superparamagnetic metal nanoparticles possess properties that allow them to be directed around the body with a magnetic field or directed to a magnetic implant, which opens up the potential to conjugate various bio-cargos to the nanoparticles that could then be directed for treatment in the body. Here we report on some of the current bio-medical applications of various metal nanoparticles, including single metal nanoparticles, functionalized metal nanoparticles, and core-shell metal nanoparticles using a core of Fe₃O₄ as well as synthesis methods of these core-shell nanoparticles.

Structural Elucidation and Ultrasensitive Analyses of Volatile Organic Compounds by Paper-Based Nano-Optoelectronic Noses

Paper-based optoelectronic noses (OENs) are being developed based on printing of organic and organometallic reagents on hydrophilic substrates that can visualize the odor of volatiles. In this work, we report for the first time the use of nanoparticles for fabrication of novel paper-based OENs, which represent much higher sensitivity and produce simple but discriminant colorimetric signature of volatile metabolomes. This nano-optoelectronic nose (NOEN) system, which is fabricated by dropping of gold and silver nanoparticles (each synthesized by 8 chemical species) on the paper, gives obvious colorimetric signatures for chemicals having individual or combined functional groups. Owning to their ultrasensitivity, these simple devices need very small amounts of analytes. These devices could detect and discriminate 45 volatile organic compounds in 9 chemical families including phenols, alchohols, ketones, aldehydes, amines, acids, esters, arenes, and hydrocarbons. In addition to excellent discrimination ability, this NOEN sensor shows ultrahigh sensitivity such that could determine volatile compounds with detection limits around or lower than 10 ppb. Moreover, it can be combined with multivariate calibration methods for quantitative analysis of a metabolite in a complex mixture.

Cu/Cu2O Nanoparticles Supported on a Phenol-Pyridyl COF as a Heterogeneous Catalyst for the Synthesis of Unsymmetrical Diynes via Glaser-Hay Coupling

Covalent organic frameworks (COFs) are a new class of porous crystalline polymers with a modular construct that favors functionalization. COF pores can be used to grow nanoparticles (nPs) with dramatic size reduction, stabilize them as dispersions, and provide excellent nP access. Embedding substrate binding sites in COFs can generate host-guest synergy, leading to enhanced catalytic activity. In this report, Cu/Cu₂O nPs (2-3 nm) are grown on a COF, which is built by linking a phenolic trialdehyde and a triamine through Schiff bonds. Their micropores restrict the nP to exceptionally small sizes (∼2-3 nm), and the pore walls decorated with strategically positioned hydrogen-bonding phenolic groups anchor the substrates via hydrogen-bonding, whereas the basic pyridyl sites serve as cationic species to stabilize the [Cu_clusterCl₂]^2- type reactive intermediates. This composite catalyst shows high activity for Glaser-Hay heterocoupling reactions, an essential 1,3-diyne yielding reaction with widespread applicability in organic synthesis and material science. Despite their broad successes in homocoupled products, preparation of unsymmetrical 1,3-diynes is challenging due to poor selectivity. Here, our COF-based Cu catalyst shows elevated selectivity toward heterocoupling product(s) (Cu nP loading 0.0992 mol %; turn over frequency: ∼45-50; turn over number: ∼175-190). The reversible redox activity at the Cu centers has been demonstrated by carrying out X-ray photoelectron spectroscopy on the frozen reactions, whereas the crucial interactions between the substrates and the binding sites in their optimized configurations have been modeled using density functional theory methods. This report emphasizes the utility of COFs in developing a heterogeneous catalyst for a truly challenging organic heterocoupling reaction.

Synthesis of Calixarene-Capped Silver Nanoparticles for Colorimetric and Amperometric Detection of Mercury (HgII, Hg0)

Calixarene-functionalized water dispersible silver nanoparticles have been synthesized and characterized on the basis of UV-vis, IR, X-ray diffraction, and high-resolution transmission electron microscopy analysis, and their sensing properties toward metal ions have been investigated. They selectively detect Hg2+ and Hg0 in solution and vapor phases, respectively, with distinct color change. Interference study with mixture of metal ions revealed no interference from any other metal ions used in this study. Their mechanism of detection involved Hg2+-aided displacement of calixarene moiety from the surface of the functionalized nanoparticles, followed by the formation of Ag-Hg amalgam due to interaction of Hg2+ with Ag0 and also the formation of assembly of Ag0 nanoparticles by dipole-dipole interaction of the bare-surfaced nanoparticles. Electrochemical study revealed that with the aid of functionalized nanoparticles, Hg2+ can be detected amperometrically with high sensitivity. The detection limits obtained for Hg2+ by UV-vis study and amperometry are 0.5 nM (0.1 ppb) and 10 nM (2 ppb), respectively. The new material has been used to detect Hg2+ in aqueous real sample and Hg0 in soil sample.

Fe-TiO2 Nanoparticles Synthesized by Green Chemistry for Potential Application in Waste Water Photocatalytic Treatment

Anatase TiO2 nanoparticles doped with iron ions have been synthesized via the green chemistry method using aqueous extract of lemongrass (Cymbopogon citratus) obtained from Soxhlet extraction and doped by wet impregnation. The TiO2 anatase phase has been doped with Fe3+ (0.05, 0.075, and 0.1 Fe3+ : Ti molar ratio) at 550°C and 350°C, respectively. The scanning electron microscopy with energy-dispersive X-ray (SEM-EDS) shows nanoparticle clusters and efficiencies of impregnations between 66.5 and 58.4% depending on the theoretical dopant amount. The electron transmission microscopy (TEM) reveals final particle sizes ranging between 7 and 26 nm depending on the presence or not of the dopant. The cathodoluminescence (CL) and photoluminescence (PL) studies of the doped and undoped nanoparticles show a luminescence signal attributed to surface oxygen vacancies (visible CL emission 380–700 nm and PL emission 350–800 nm); additionally, a decrease in emission intensity is observed due the inhibition of the recombination of the photogenerated electron-holes pairs; moreover, nanopowders were analyzed by UV-Vis spectrophotometry of diffuse reflectance, and the absorption edge of the Fe-TiO2 in comparison to undoped TiO2 is extended greatly toward the visible light. The six bands (A1g + 2B1g + 3Eg) found by Raman spectroscopy and the x-ray diffraction pattern (XRD) confirm that synthesized TiO2 is only anatase phase, which is commonly used as a catalyst in waste water treatment, specifically in heterogeneous photocatalytic processes.

Green synthesis of metal oxide nanostructures using naturally occurring compounds for energy, environmental, and bio-related applications

This review summarizes the synthesis and functional applications of metal oxide nanostructures synthesized using plant-derived phytochemicals for energy, environmental, and biomedical applications.

Gradient of zinc content in core–shell zinc ferrite nanoparticles – precise study on composition and magnetic properties

Structure, magnetic properties and chemical composition of synthesized zinc ferrite nanoparticles were characterized by a broad spectrum of methods.

An optoelectronic tongue based on an array of gold and silver nanoparticles for analysis of natural, synthetic and biological antioxidants

A colorimetric array, which can discriminate 20 food antioxidants of natural, synthetic and biological groups, is described. It consists of gold and silver nanoparticles that were synthesized using six different reducing and/or capping agents. The function of the array relies on the interaction of the antioxidants with the nanoparticles which causes aggregation or morphological changes. This, in turn, causes a change in the sensors' colors. The array produces a unique combination of colors for each antioxidant. The resulting colorations are determined by recording the absorbances of the arrays at wavelengths of 405, 450, 490 and 630 nm, or by capturing the images with a digital camera. The discriminatory ability of the array is investigated by principle component analysis and hierarchical cluster analysis. The method was applied to quantitative assay of gallic acid, caffeic acid, catechin, dopamine, citric acid, butylated hydroxytoluene and ascorbic acid. The respective limits of detection are 4.2, 13, 53, 6.9, 47, 3.5 and 43 nM, respectively. The simultaneous determination of 5 different antioxidants is achieved utilizing partial least square regression. The root mean square errors for prediction of the test set are 0.0650, 0.0782, 0.811, 0.0206 and 0.135 nM for gallic acid, catechin, butylated hydroxytoluene, dopamine, and ascorbic acid, respectively. This method demonstrates excellent potential for analysis of antioxidants in beverages such as tea and lemon juice. Graphical abstract Schematic of a method for the simultaneous determination of several antioxidants based on changes in the color of gold and silver nanoparticles. The antioxidants cause aggregation and/or morphological changes which can be detected by using both image analysis or by colorimetry.

Kinetic investigation for the catalytic reduction of nitrophenol using ionic liquid stabilized gold nanoparticles

We demonstrate the synthesis of gold nanoparticles (AuNP) stabilized by 1-butyl-3-hexadecyl imidazolium bromide (Au@[C₄C₁₆Im]Br) and their use as a catalyst for the reduction of nitrophenol. The AuNPs show excellent stability in presence of [C₄C₁₆Im]Br ionic liquids for the reduction of 4-nitrophenol and 2-nitrophenol using NaBH₄ as a reducing agent. The detailed kinetics for the reduction of 4-nitrophenol and 2-nitrophenol were investigated and the catalytic activity of Au@[C₄C₁₆Im]Br was evaluated. The pseudo first-order rate constant (k_app) values for 4-nitrophenol was observed to be greater than that of 2-nitrophenol and explained on the basis of hydrogen bonding present in 2-nitrophenol. Au@[C₄C₁₆Im]Br showed good separability and reusability and hence, it can be used for the complete reduction of nitrophenols in multiple cycles. The Langmuir–Hinshelwood reaction mechanism is elucidated for reduction of 4-nitrophenol by Au@[C₄C₁₆Im]Br nanocatalyst on the basis of the k_app values. The thermodynamic activation parameters such as activation energy, enthalpy of activation and entropy of activation were determined and explained using the temperature dependent kinetics for the reduction of nitrophenol using Au@[C₄C₁₆Im]Br. The above results reveal that the Au@[C₄C₁₆Im]Br nanocatalyst demonstrates excellent catalytic performance for the reduction of nitrophenol by NaBH₄ at room temperature.

Catalytic reduction of nitrophenol using ionic liquid stabilized AuNPs.