Surfactant-assisted, shape-controlled synthesis of gold nanocrystals

Colloidal Synthesis of Na2Fe2(SO4)3 Nanocrystals as the Cathode Toward High-Rate Capability and High-Energy Density Sodium-ion Batteries

Alluaudite-type Na2+2xFe2-x(SO4)3 (NFS) with high theoretical energy density is regarded as the promising cathode of sodium-ion batteries (SIBs), while practical rate and cyclic performances are still hindered by intrinsic poor conductivity. Here, a facile method is developed, collaborating high-boiling organic solvents assisted colloidal synthesis (HOS-CS) with sintering for tailoring Na2Fe2(SO4)3 nanocrystals decorated by conductive carbon network toward high-rate-capability cathode of SIBs. Impressively, the as-prepared Na2Fe2(SO4)3@MC provides 60.6 and 46.9 mAh g-1 of reversible capacities even at ultrahigh rates of 20 and 30 C, respectively, ranking the superior state among the current NFS-based cathode. More importantly, Na2Fe2(SO4)3@MC achieves 73% of capacity retention at 20 C after 500 cycles, highlighting its potential for application as a fast chargeable cathode. As a bonus, the full-cell configuration constructed with Na2Fe2(SO4)3@MC cathode and commercial hard carbon (HC) anode delivers 45.6 mAh g-1 at 10 C and 68.3 mAh g-1 of initial capacity with ≈79.4% of retention after 100 cycles at 2 C. Also, Na2Fe2(SO4)3@MC||HC full cell supplies as high as 140 Wh kg-1 of practical energy density. This work offers a novel approach to prepare NFS cathode for SIBs with both high energy density and fast-charging ability.

Gold nanowires-based sensor for quantification of H2O2 released by human airway epithelial cells

Hydrogen peroxide (H2O2) is a biomarker relevant for oxidative stress monitoring. Most chronic airway diseases are characterized by increased oxidative stress. To date, the main methods for the detection of this analyte are expensive and time-consuming laboratory techniques such as fluorometric and colorimetric assays. There is a growing interest in the development of electrochemical sensors for H2O2 detection due to their low cost, ease of use, sensitivity and rapid response. In this work, an electrochemical sensor based on gold nanowire arrays has been developed. Thanks to the catalytic activity of gold against hydrogen peroxide reduction and the high surface area of nanowires, this sensor allows the quantification of this analyte in a fast, efficient and selective way. The sensor was obtained by template electrodeposition and consists of gold nanowires about 5 μm high and with an average diameter of about 200 nm. The high active surface area of this electrode, about 7 times larger than a planar gold electrode, ensured a high sensitivity of the sensor (0.98 μA μM-1cm-2). The sensor allows the quantification of hydrogen peroxide in the range from 10 μM to 10 mM with a limit of detection of 3.2 μM. The sensor has excellent properties in terms of reproducibility, repeatability and selectivity. The sensor was validated by quantifying the hydrogen peroxide released by human airways A549 cells exposed or not to the pro-oxidant compound rotenone. The obtained results were validated by comparing them with those obtained by flow cytometry after staining the cells with the fluorescent superoxide-sensitive Mitosox Red probe giving a very good concordance.

Bridging colloidal and electrochemical syntheses of metal nanocrystals with seeded electrodeposition for tracking single nanocrystal growth

Metal nanocrystals (NCs) produced by colloidal synthesis have a variety of structural features, such as different planes, edges, and defects. Even from the best colloidal syntheses, these characteristics are distributed differently in each NC. This inherent heterogeneity can play a significant role in the properties displayed by NCs. This manuscript reports the use of electrochemistry to synthesize Au NCs in a system evaluated to track individual NC growth trajectories as a first step toward rapid identification of NCs with different structural features. Au nanocubes were prepared colloidally and deposited onto a glassy carbon electrode using either electrospray or an airbrush, resulting in well-spaced Au nanocubes. The Au nanocubes then served as seeds as gold salt was reduced to deposit metal at constant potential. Deposition at constant potential facilitates overgrowth on the Au nanocubes to achieve new NC shapes. The effects of applied potential, deposition time, precursor concentration, and capping agents on NC shape evolution were studied. The outcomes are correlated to results from traditional colloidal syntheses, providing a bridge between the two synthetic strategies. Moreover, scanning electron microscopy was used to image the same NCs before and after deposition, linking individual seed features to differences in deposition. This ability is anticipated to enable tracking of individual growth trajectories of NCs to elucidate sources of heterogeneity in NC syntheses.

Light-enhanced catalytic activity of stable and large gold nanoparticles in homocoupling reactions

Validating the direct photocatalytic activity of colloidal plasmonic nanoparticles is challenging due to their limited stability and needed support materials that can often contribute to the chemical reactions. Stable gold nanoparticles (AuNPs) with tunable sizes are prepared across porous polymer particles without any chemical bonds where the resulting composite particles exhibit intense surface plasmon resonances (SPRs) in the visible region. These composite particles are then tested as photocatalysts under a broadband solar-simulated light source to examine the contribution degree of photothermal heating and SPR coming from the incorporated AuNPs in the C-C bond forming homocoupling reaction. Generally, the thermal and photothermal heating are the main driving force to increase the reactivity of relatively smaller AuNPs (~ 44 nm in diameter) with a narrower SPR band. However, the SPR-induced catalytic activity is much greater for the composite particles containing larger AuNPs (~ 87 nm in diameter) with a broader SPR. As the polymer particle matrix does not influence the catalytic activity (e.g., inducing charge delocalization and/or separation), the unique SPR role of the colloidal AuNPs in the catalytic reaction is assessable under light irradiation. This study experimentally demonstrates the possibility of evaluating the direct contribution of SPRs to photocatalytic chemical reactions.

Formation and Growth of Atomic Scale Seeds of Au Nanoparticle in the Nanospace of an Organic Cage Molecule

Seed-mediated growth has been widely used to synthesize noble metal nanoparticles with controlled size and shape. Although it is becoming possible to directly observe the nucleation process of metal atoms at the single atom level by using transmission electron microscopy (TEM), it is challenging to control the formation and growth of seeds with only a few metal atoms in homogeneous solution systems. This work reports site-selective formation and growth of atomic scale seeds of the Au nanoparticle in a nanospace of an organic cage molecule. We synthesized a cage molecule with amines and phenols, which were found to both capture and reduce Au(III) ions to spontaneously form the atomic scale seeds containing Au(0) in the nanospace. The growth reaction of the atomic scale seeds afforded Au nanoparticles with an average diameter of 2.0±0.2 nm, which is in good agreement with the inner diameter of the cage molecule.

Stable CsPbBr3 Nanocrystals—Decorated Nanoporous Gold for Optoelectronic Applications

Halide perovskite colloidal nanocrystals have recently gained much attention thanks to their superior stability compared with their bulk counterpart and to their unique optical properties. In this paper, two systems combining nanocrystals and nanoporous gold are studied to create an optimal metal semiconductor heterojunction that can be used in photocatalysis and photovoltaic devices. The perovskite degradation phenomenon is observed when the nanoporous gold powder is mixed into the hexane suspension of nanocrystals, while the charge separation efficiency is increased by synthesizing the nanocrystals directly onto the gold porous structure. The analysis of the structural and optical properties evidences an energy transfer efficiency of 47%, along with the high structural stability of the hybrid system.

Salt-mediated, plasmonic field-field/field-lattice coupling-enhanced NIR-II photodynamic therapy using core-gap-shell gold nanopeanuts

Plasmonic field-field coupling-induced enhancement of the optical properties of dye molecules in the nanogaps among metal nanoparticle clusters and thin films has attracted significant attention especially in disease-related theranostic applications. However, it is very challenging to synthesize plasmonic core-gap-shell nanostructures with a well-controlled nanogap, uniform shape, and distances to maximize the plasmonic field-field coupling between the core and the shell. Herein, we synthesized Au@gap@AuAg nanopeanut-shaped core-gap-shell nanostructures (Au NPN) and tuned their optical absorption from near-infrared region-I (NIR-I) to near-infrared region-II (NIR-II) by filling their nanogap with a high dielectric NaCl_(aq) aqueous solution, which led to a dramatic redshift in the plasmonic absorption band by 320 nm from 660 to 980 nm and a 12.6-fold increase (at 1064 nm) in the extinction coefficient in the NIR region (1000-1300 nm). Upon filling the nanogap with NaCl_(aq) aqueous solution, the Au NPN6.5(NaCl) (i.e., ∼6.5 nm nanogap)-mediated NIR-II photodynamic therapy effect was dramatically enhanced, resulting in a much longer average lifespan of >55 days for the mice bearing a murine colon tumor and treated with Au NPN6.5(NaCl) plus 1064 nm light irradiation compared to the mice treated with Au NPN6.5 + 1064 nm light irradiation (without nanogap filled with dielectric NaCl_(aq), 40 d) and the doxorubicin-treated group (23 d). This study demonstrates a simple but effective method to tune and maximize the plasmonic field-field coupling between the metal shell and metal core of core-gap-shell nanostructures, the plasmonic field-lattice interactions, and biomedical applications for the treatment of tumors. Overall, our work presents a new way to enhance/maximize the plasmonic field-field and field-lattice coupling, and thus the performance/sensitivities in nanogap-based bioimaging, sensing, and theranostic nanomaterials and devices.

Mesoporous Gold Nanostructures: Synthesis and Beyond

Mesoporous metal nanostructures have offered multiple advantages that cannot be realized elsewhere. These materials have been attracting more research attention in catalysis and electrocatalysis owing to their functional structures and compositions. Of the various mesoporous metals available, mesoporous gold (mesoAu) nanostructures are of special interest in surface-enhanced Raman scattering (SERS) and related applications because of their strong electromagnetic field (localized surface plasmon resonance). In the last few decades, various synthesis strategies have been developed to prepare mesoAu nanostructures with controllable morphologies that exhibit fascinating physicochemical properties and increase applications in SERS, catalysis, and electrocatalysis. In this Perspective, we systematically summarize recent advances in synthesis and applications of mesoAu nanostructures. Four synthesis strategies, including dealloying, nanocasting, electrochemical deposition, and intermediate template, are discussed in detail. Moreover, physicochemical properties and promising applications of mesoAu nanostructures are presented. Finally, we describe current challenges and give a general outlook to explore further directions in synthesis and applications of mesoAu nanostructures.

Classical and Nonclassical Nucleation and Growth Mechanisms for Nanoparticle Formation

All solid materials are created via nucleation. In this evolutionary process, nuclei form in solution or at interfaces and expand by monomeric growth, oriented attachment, and phase transformation. Nucleation determines the location and size of nuclei, whereas growth controls the size, shape, and aggregation of newly formed nanoparticles. These physical properties of nanoparticles can determine their functionalities, reactivities, and porosities, as well as their fate and transport. Recent advances in nanoscale analytical technologies allow in situ real-time observations, enabling us to uncover the molecular nature of nuclei and the critical controlling factors for nucleation and growth. Although a single theory cannot yet fully explain such evolving processes, we have started to better understand how both classical and nonclassical theories can work together, and we have begun to recognize the importance of connecting these theories. This review discusses the recent convergence of knowledge about the nucleation and the growth of nanoparticles. Expected final online publication date for the Annual Review of Physical Chemistry, Volume 73 is April 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Coupled catalytic dephosphorylation and complex phosphate ion-exchange in networked hierarchical lanthanum carbonate grafted asymmetric bio-composite membrane

The remediation of non-reactive phosphate pollutants in the aquatic system is essential for protecting the ecological niche. In this work, a highly robust protein nanoparticles networked rare-earth metal carbonate-grafted bio-composite membrane (abbreviated as REMC) was fabricated via chemical crosslinking of three-dimensional (3D) hierarchical lanthanum carbonate (mREM) and casein nanoparticles (CsNPs) for selective rejection of non-reactive phosphates. The main components of the REMC membrane are mREM and CsNPs, which were prepared via SDS/CTAB templated homogeneous precipitation and the coacervation/desolvation hybrid method, respectively. The active lanthanum ion (La³⁺) on the 3D spherulitic surface of mREM exhibited excellent phosphate adsorption capacity (maximum adsorption capacity was 358 mg.g^-1) across a wide pH range and in a multi-ionic environment. A series of batch testing and characterizations revealed that the active La³⁺ and dominating phosphate centers in the REMC membrane framework enable non-enzymatic phosphatase-like activity, cleaving the phosphate ester bond of organic phosphates and releasing free phosphate anions. These released phosphate ions are retained in the REMC membrane via an ion exchange mechanism, where they contribute to improved phosphate removal capacities. Furthermore, CsNPs have a dual function in the membrane, acting as a matrix in the REMC membrane framework and contributing to phosphate ion sequestrations in a synergistic manner. The catalysis of para-nitrophenyl phosphates (pNPP) to paranitrophenol (pNP) in a sequential dephosphorylation by REMC offers an estimate of reaction kinetics and elucidates the underlying mechanism of improved phosphate selectivity in a multi-ionic environment. Furthermore, phosphate specificity, homogeneous binding capacity, reusability, and visual observation of REMC membrane saturation binding direct it's useful economic, industrial applications in aqueous phosphate contaminant removal, which could be beneficial for the active recovery of the aquatic ecosystem.

Intraband Transition and Localized Surface Plasmon Resonance of Metal Chalcogenides Nanocrystals and their Dependence on Crystal Structure

Understanding the localized surface plasmon resonance (LSPR) and the intraband transition of semiconductor nanocrystals (NCs) has attracted considerable attention since it can provide the opportunity to investigate the boundary between...

Investigation on (Zn) doping and anionic surfactant (SDS) effect on SnO2 nanostructures for enhanced photocatalytic RhB dye degradation

Herein we reported the effect of doping and addition of surfactant on SnO₂ nanostructures for enhanced photocatalytic activity. Pristine SnO₂, Zn-SnO₂ and SDS-(Zn-SnO₂) was prepared via simple co-precipitation method and the product was annealed at 600 °C to obtain a clear phase. The structural, optical, vibrational, morphological characteristics of the synthesized SnO₂, Zn-SnO₂ and SDS-(Zn-SnO₂) product were investigated. SnO₂, Zn-SnO₂ and SDS-(Zn-SnO₂) possess crystallite size of 20 nm, 19 nm and 18 nm correspondingly with tetragonal structure and high purity. The metal oxygen vibrations were present in FT-IR spectra. The obtained bandgap energies of SnO₂, Zn-SnO₂ and SDS-(Zn-SnO₂) were 3.58 eV, 3.51 eV and 2.81 eV due to the effect of dopant and surfactant. This narrowing of bandgap helped in the photocatalytic activity. The morphology of the pristine sample showed poor growth of nanostructures with high level of agglomeration which was effectively reduced for other two samples. Product photocatalytic action was tested beneath visible light of 300 W. SDS-(Zn-SnO₂) nanostructure efficiency showed 90% degradation of RhB dye which is 2.5 times higher than pristine sample. Narrow bandgap, crystallite size, better growth of nanostructures paved the way for SDS-(Zn-SnO₂) to degrade the toxic pollutant. The superior performance and individuality of SDS-(Zn-SnO₂) will makes it a potential competitor on reducing toxic pollutants from wastewater in future research.

Single-parameter-tuned synthesis for shape-controlled gold nanocrystals stimulated by iron carbonyl

Shape-controlled synthesis is essential for functional nanomaterials, allowing deeper insights intothe relationship between the structures and the catalytic properties. Synthesis of nanocrystals with particular morphologies are usually studied independently among various synthetic methods, those underline that different surface capping ligands or shape-directing agents bring about disparate shapes. However, a single quantitative parameter method is still lacking to realize precise control of well-defined morphology nanocrystals, especially anisotropic structures, which is essential to understanding the growth process of nanocrystals. Herein, we proposed a single-parameter-tuned synthesis strategy for preparation of shape-controlled gold nanocrystals by regulating the amount of iron carbonyl, by which we produced highly monodisperse Au nanocrystals with various shapes in organic phase including nanoplates (diameter of 16.02 ± 1.13 nm and thickness of 5.35 ± 0.58 nm), nanorods (length of 37.53 ± 3.73 nm and width of 5.26 ± 0.37 nm) and nanospheres (diameter of 8.26 ± 0.38 nm). The single-parameter-tuned method reveals the dual roles of iron carbonyl for controlling the shapes of gold nanocrystals including reductant and oxidative etchant and empowers versatility in synthetic methodology for other noble metals. Moreover, catalytic activity shifting in shapes of nanocrystals was revealed based on the reduction of 4-nitrophenol, showing that the as-synthesized Au nanoplates displayed the enhanced catalytic performance with the lowest activation energy. Our work provides a brand-new pathway for shape-controlled synthesis of noble-metal nanocrystals and has a strong practical value in application fields.

Nanomaterial Shape Influence on Cell Behavior

Nanomaterials are proven to affect the biological activity of mammalian and microbial cells profoundly. Despite this fact, only surface chemistry, charge, and area are often linked to these phenomena. Moreover, most attention in this field is directed exclusively at nanomaterial cytotoxicity. At the same time, there is a large body of studies showing the influence of nanomaterials on cellular metabolism, proliferation, differentiation, reprogramming, gene transfer, and many other processes. Furthermore, it has been revealed that in all these cases, the shape of the nanomaterial plays a crucial role. In this paper, the mechanisms of nanomaterials shape control, approaches toward its synthesis, and the influence of nanomaterial shape on various biological activities of mammalian and microbial cells, such as proliferation, differentiation, and metabolism, as well as the prospects of this emerging field, are reviewed.

Stabilization of Size-Controlled BaTiO3 Nanocubes via Precise Solvothermal Crystal Growth and Their Anomalous Surface Compositional Reconstruction

Crystal growth of barium titanate (BaTiO₃) using a wet chemical reaction was investigated at various temperatures. BaTiO₃ nanoparticles were obtained at an energy-efficient temperature of 80 °C. However, BaTiO₃ nanocubes with a preferred size and shape could be synthesized using a solvothermal method at 200 °C via a reaction involving titanium tetraisopropoxide [(CH₃)₂CHO]₄Ti for nucleation and fine titanium oxide (TiO₂) nanoparticles for crystal growth. The BaTiO₃ nanocubes showed a high degree of dispersion without the use of dispersants or surfactants. The morphology of BaTiO₃ was found to depend on the reaction medium. The size of the BaTiO₃ particles obtained using water as the reaction medium was the largest among the particles synthesized using various reaction media. In the case of alcohol reaction media, the BaTiO₃ particle size increased in the order methanol, ethanol, 1-propanol, 1-butanol, and 1-pentanol. Furthermore, BaTiO₃ powder obtained using alcohol reaction media resulted in cubic shapes as opposed to the round shapes obtained when water was used as the medium. We found that the optimal condition for the synthesis of BaTiO₃ nanocubes involved the use of 1-butanol as the reaction medium, resulting in an average particle size of 52 nm, which is the average distance of the cubes measured diagonally from corner to corner, and gives an average side length of 37 nm, and a tetragonal crystal system as evidenced by the powder X-ray diffraction pattern obtained using high-energy synchrotron X-rays. The origin of the spontaneous polarization of the BaTiO₃ tetragonal crystal structure was clarified by a pair distribution function analysis. In addition, surface reconstruction of BaTiO₃ nanocubes led to an outermost surface comprising two layers of Ti columns.

Systematic Incorporation of Gold Nanoparticles onto Mesoporous Titanium Oxide Particles for Green Catalysts

This report describes the systematic incorporation of gold nanoparticles (AuNPs) onto mesoporous TiO2 (MPT) particles without strong attractive forces to efficiently serve as reactive and recyclable catalysts in the homocoupling of arylboronic acid in green reaction conditions. Unlike using nonporous TiO2 particles and conventional SiO2 particles as supporting materials, the employment of MPT particles significantly improves the loading efficiency of AuNPs. The incorporated AuNPs are less than 10 nm in diameter, regardless of the amount of applied gold ions, and their surfaces, free from any modifiers, act as highly reactive catalytic sites to notably improve the yields in the homocoupling reaction. The overall physical properties of the AuNPs integrated onto the MPT particles are thoroughly examined as functions of the gold content, and their catalytic functions, including the rate of reaction, activation energy, and recyclability, are also evaluated. While the rate of reaction slightly increases with the improved loading efficiency of AuNPs, the apparent activation energies do not clearly show any correlation with the size or distribution of the AuNPs under our reaction conditions. Understanding the formation of these types of composite particles and their catalytic functions could lead to the development of highly practical, quasi-homogeneous catalysts in environmentally friendly reaction conditions.

Spin-Orbit Coupling Effects in Au 4f Core-Level Electronic Structures in Supported Low-Dimensional Gold Nanoparticles

Despite their many advantages, issues remain unresolved over the variability in catalytic activities in supported gold nanoparticle (AuNP)-based catalysts, which requires precise characterization to unravel the presence of any fine features. Herein, upon analyzing the Au 4f core-level spin-orbit components in many as-synthesized AuNP-based catalysts, we observed that like deviations in the Au 4f7/2 binding energy positions, both the Au 4f7/2-to-Au 4f5/2 peak intensity and linewidth ratios varied largely from the standard statistical bulk reference values. These deviations were observed in all the as-synthesized supported AuNPs irrespective of different synthesis conditions, variations in size, shape or morphology of the gold nanoparticles, and different support materials. On the other hand, the spin-orbit-splitting values remained almost unchanged and did not show any appreciable deviations from the atomic or bulk standard gold values. These deviations could originate due to alterations in the electronic band structures in the supported AuNPs and might be present in other NP-based catalyst systems as well, which could be the subject of future research interest.

Nanometal Thermocatalysts: Transformations, Deactivation, and Mitigation

Nanometals have been proven to be efficient thermocatalysts in the last decades. Their enhanced catalytic activity and tunable functionalities make them intriguing candidates for a wide range of catalytic applications, such as gaseous reactions and compound synthesis/decomposition. On the other hand, the enhanced specific surface energy and reactivity of nanometals can lead to configuration transformation and thus catalytic deactivation during the synthesis and catalysis, which largely undermines the activity and service time, thereby calling for urgent research effort to understand the deactivating mechanisms and develop efficient mitigating methods. Herein, the recent progress in understanding the configuration transformation-induced catalytic deactivation within nanometals is reviewed. The major pathways of configuration transformations, and their kinetics controlled by the environmental factors are presented. The approaches toward mitigating the transformation-induced deactivation are also presented. Finally, a perspective on the future academic approaches toward in-depth understanding of the kinetics of the deactivation of nanometals is proposed.

Effect of ultrasonic irradiation power on sonochemical synthesis of gold nanoparticles

In this work, optimized size distribution and optical properties in the colloidal synthesis of gold nanoparticles (GNPs) were obtained using a proposed ultrasonic irradiation assisted Turkevich-Frens method. The effect of three nominal ultrasound (20 kHz) irradiation powers: 60, 150, and 210 W have been analyzed as size and shape control parameters. The GNPs colloidal solutions were obtained from chloroauric acid (HAuCl₄) and trisodium citrate (C₆H₅Na₃O₇·2H₂O) under continuous irradiation for 1 h without any additional heat or stirring. The surface plasmon resonance (SPR) was monitored in the UV-Vis spectra every 10 min to found the optimal time for localized SPR wavelength (λ_LSPR), and the 210 sample procedure has reduced the λ_LSPR localization at 20 min, while 150 and 60 samples have showed λ_LSPR at 60 min. The nucleation and growth of GNPs showed changes in shape and size distribution associated with physical (cavitation, temperature) and chemical (radical generation, pH) conditions in the aqueous solution. The results showed quasi-spherical GNPs as pentakis dodecahedron (λ_LSPR = 560 nm), triakis icosahedron (λ_LSPR = 535 nm), and tetrakis hexahedron (λ_LSPR = 525 nm) in a size range from 12 to 16 nm. Chemical effects of ultrasound irradiation were suggested in the disproportionation process, electrons of AuCl₂^- are rapidly exchanged through the gold surface. After AuCl₄^- and Cl^- were desorbed, a tetrachloroaurate complex was recycled for the two-electron reduction by citrate, aurophilic interaction between complexes AuCl₂^-, electrons exchange, and gold seeds, the deposition of new gold atoms on the surface promoting the growth of GNPs. These mechanisms are enhanced by the effects of ultrasound, such as cavitation and transmitted energy into the solution. These results show that the plasmonic response from the reported GNPs can be tuned using a simple methodology with minimum infrastructure requirements. Moreover, the production method could be easily scalable to meet industrial manufacturing needs.

Colorimetric detection of glucose based on the binding specificity of a synthetic cyclic peptide

A novel colorimetric sensing method for glucose was developed based on the catalytic activity of Au nanoparticles (NPs) and a synthetic cyclic peptide that specifically binds with glucose. It is the first time that a cyclic peptide was used as a recognition element for glucose sensing. In the absence of glucose, the monolayers of cyclic peptide on the Au NP surfaces interfered little with the adsorption of 4-nitrophenol, and the Au NPs catalyze the reduction of bright yellow 4-nitrophenol to colorless 4-aminophenol in the presence of NaBH4. Added glucose was preferentially bound by the cyclic peptides and impeded the adsorption of 4-nitrophenol. Therefore, the color of the solution presented varying shades of yellow depending on the concentration of glucose. The method had a short response time of 10 min and demonstrated a linear response over a range of glucose concentrations from 0.1 mM to 20 mM, with a lower limit of detection of 0.04 mM. Meanwhile, it also provided results readily observable by the naked eye. The method was successfully applied for the detection of glucose in spiked food samples (Chinese cabbage, pear, and wheat flour) and spiked rabbit blood, and a good recovery rate of 88.04-103.28% and 94.27-101.53% was obtained, respectively.

Synthesis of 3D Dendritic Gold Nanostructures Assisted by a Templated Growth Process: Application to the Detection of Traces of Molecules

Complex architectures like 3D gold dendritic nanostructures were synthesized by an in situ templated growth method using a thin film of a block copolymer [polystyrene-b-poly(4-vinylpyridine)] deposited onto silicon substrates. The overall study has demonstrated the strong link between the morphology, size, and distribution of the structures and the synthetic physicochemical parameters, such as pH, reaction temperature, concentration, and nature of reactants. A nonequilibirum state of the medium has been required to create a fractal growth of the gold structures onto a prepatterned gold-seeded surface and has led to a better control of the structures' surface coverage rate. Those as-prepared nanodendrites have also exhibited high electrocatalytic activity toward a significant enhancement factor, as well as important sensitivity, thanks to tip effects. The electrochemical experiment results have demonstrated efficient adsorption and quantification of very low traces of specific molecules like glutathione or hexadecanethiol.

Intratumoral generation of photothermal gold nanoparticles through a vectorized biomineralization of ionic gold

Various cancer cells have been demonstrated to have the capacity to form plasmonic gold nanoparticles when chloroauric acid is introduced to their cellular microenvironment. But their biomedical applications are limited, particularly considering the millimolar concentrations and longer incubation period of ionic gold. Here, we describe a simplistic method of intracellular biomineralization to produce plasmonic gold nanoparticles at micromolar concentrations within 30 min of application utilizing polyethylene glycol as delivery vector for ionic gold. We have characterized this process for intracellular gold nanoparticle formation, which progressively accumulates proteins as the ionic gold clusters migrate to the nucleus. This nano-vectorized application of ionic gold emphasizes its potential biomedical opportunities while reducing the quantity of ionic gold and required incubation time. To demonstrate its biomedical potential, we further induce in-situ biosynthesis of gold nanoparticles within MCF7 tumor mouse xenografts which is followed by its photothermal remediation.

Competitive Nucleation Mechanism for CsPbBr3 Perovskite Nanoplatelet Growth

We analyze nucleation-controlled nanocrystal growth in a solution containing surface-binding molecular ligands, which can also nucleate compact layers on the crystal surfaces. We show that, if the critical nucleus size for ligands is larger and the nucleation barrier is lower than those for crystal atoms, the ligands nucleate faster than the atoms on relatively wide crystal facets but much slower, if at all, on narrow facets. Such competitive nucleation of ligands and atoms results in ligands covering predominantly wider facets, thus excluding them from the growth process, and acts as a selection mechanism for the growth of crystals with narrower facets, the so-called nanoplatelets. The theory is confirmed by Monte Carlo simulations and validated experimentally for CsPbBr₃ nanoplatelets grown from solution. We find that the anisotropic crystal growth is controlled by the growth temperature and the strength of surface bonding for the passivating molecular ligands.

Reverse Coarsening and the Control of Particle Size Distribution through Surfactant

The minimization of surface area, as a result of the minimization of (positive) surface energy, is a well-known driving force behind the spontaneous broadening of (nano) particle size distribution. We show that surfactant molecules binding to particle surfaces effectively decrease the surface energy and may change its sign. In this case, contrary to the expected broadening behavior, a minimum of free energy is achieved at the maximum surface area for all particles, i.e., when the particles are identical. Numerical simulations based on the classical Lifshitz–Slyozov–Wagner theory with surfactant-induced surface energy renormalization confirm the collapse of the particle size distribution. As the particle size evolution is much slower than particle nucleation and growth, the manipulation of surface energy with in-situ replacement of surfactant molecules provides a method for controlling particle size distribution with great potential for creating mono-disperse nanoparticles, a key goal of nanotechnology.

Lamellar nanoporous gold thin films with tunable porosity for ultrasensitive SERS detection in liquid and gas phase

Lamellar nanoporous gold thin films, constituted of a stack of very thin layers of porous gold, are synthesized by chemical etching from a stack of successively deposited nanolayers of copper and gold. The gold ligament size, the pore size and the distance between lamellas are tunable in the few tens nanometer range by controlling the initial thickness of the layers and the etching time. The SERS activity of these lamellar porous gold films is characterized by their SERS responses after adsorption of probe bipyridine and naphtalenethiol molecules. The SERS signal is investigated as a function of the bipyridine concentration from 10^-14 mol L^-1 to 10^-3 mol L^-1. The higher SERS response corresponds to an experimental detection limit down to 10^-12 mol L^-1. These performance is mainly attributed to the specific nanoporous gold architecture and the larger accessible surface to volume ratio. The lamellar nanoporous gold substrate is explored for sensitive SERS detection of dimethyl methylphosphonate (DMMP), a surrogate molecule of the highly toxic G-series nerve agents. The resultant nanostructure facilitates the diffusion of target molecules through the nanopores and their localization at the enhancing metallic surface leading to the unequivocal Raman signature of DMMP at a concentration of 5 parts per million.

Multilayer capsules encapsulating nimbin and doxorubicin for cancer chemo-photothermal therapy

Layer-by-layer (LbL) assembled poly(allylamine hydrochloride) (PAH) and poly(methacrylic acid) (PMA) microcapsules were designed to incorporate gold nanorods (NRs) and co-encapsulate and release two drugs for cancer therapy. Calcium carbonate (CaCO₃) microparticles modified with preformed NRs were used as sacrificial templates for the fabrication of hollow PAH/PMA/NR capsules incorporated with NRs. The hollow capsules were found to be 4.5 ± 0.5 µm in size and appeared with uniformly distributed NRs in the interior of the capsules. The morphology of the capsules transformed from pore free continuous structure to porous structure under laser light irradiation at 808 nm and 0.5 W cm^-2. The encapsulation experiments showed that the hydrophilic drug (doxorubicin hydrochloride, Dox) was encapsulated in the interior of the capsules while the hydrophobic drug (nimbin, NB) was entrapped in the porous polymeric network of the layer components. The encapsulation efficiency was found to be 30% for both Dox and NB. The release experiments showed an initial burst release followed by sustained release up to 3 h. Notably, the release was completed within 30 min under NIR irradiation at 808 nm. The estimated IC₅₀ values against THP-1 cells were 75 and 1.8 µM for NB and Dox, respectively. The dual drug loaded capsules showed excellent anticancer activity against THP-1 cells under NIR light exposure in in-vitro experiments. Thus, such remotely addressable dual-drug loaded capsules with the provision for encapsulation of natural drugs demonstrate high potential for use as theranostics in cancer therapy.

Facile morphology control of gold(0) structures from aurophilic assemblies

Different gold microstructures have been synthesized by using supramolecular gold(i) organometallic compounds as templates and Ag nanoparticles as reducing agents. The use of fibers resulting from supramolecular assemblies of neutral gold(i) compounds gives rise to the formation of microrods. The use of supramolecular assemblies from ionic molecules results in spherical or square-based prism gold microstructures, depending on the shape of the supramolecular gold(i) precursor assembly. In addition to temperature and reaction time, solvents exert a strong influence on the formation and morphology of gold structures, as borne out by the example that well-defined star-like morphologies have been obtained in chloroform.

Fabrication of single-crystalline gold nanowires on cellulose nanofibers

Cellulose nanofibers (CNF) are promising nanomaterials for functional inks and printed sensors, although the potential applications are currently limited by the available functionalization methods. This work outlines a convenient method to grow a novel and highly conductive network of single-crystalline gold nanowires (AuNW) on CNF for use in conductive inks and printed sensors. The CNF are able to reduce Au (III) precursors to Au (0) monomers and generate nucleation sites for the subsequent monomer-by-monomer growth of Au nanocrystals; sodium citrate is used to control the reduction kinetics and the crystal growth. The growth of these AuNW/CNF materials is a three-step process of redox reaction, isotropic nucleation and anisotropic crystallization: the morphology and crystal structure of Au nanocrystals on CNF can be controlled by adjusting the reaction temperature and concentrations of citrate and CNF. The AuNW/CNF materials obtained have been formulated into highly conductive and atmospherically stable inks for use in either directly writing or screen printing. We have demonstrated AuNW/CNF-printed sensors with highly controllable electrical conductivity as well as excellent stability against rinsing and immersion by water and ethanol.

Continuous manufacturing of silver nanoparticles between 5 and 80 nm with rapid online optical size and shape evaluation

Flexible manufacturing technology of nanoparticles with sizes between 5 and 80 nm. This unique size flexibility is enabled by coupling rapid online spectroscopy and a mathematical Mie theory-based algorithm for size and shape evaluation.

Controllable synthesis of hierarchical Au/PdAg heterostructures consisting of nanosheets on nanorods with plasmon-enhanced electrocatalytic properties

Hierarchical Au/PdAg heterostructures consisting of PdAg nanosheets epitaxially grown on Au nanorods are synthesized in the presence of mixed surfactants and exhibit remarkable plasmon-enhanced electrocatalytic activity toward hydrogen evolution.

Toward greener methods of producing branched metal nanostructures

This review highlights the use of biogenic resources (i.e., plant extracts, microorganisms, and biomolecules) as green reagents for the production of technologically promising branched metal nanomaterials.

Ionic Liquid-Modulated Synthesis of Porous Worm-Like Gold with Strong SERS Response and Superior Catalytic Activities

Porous gold with well-defined shape and size have aroused extensive research enthusiasm due to their prominent properties in various applications. However, it is still a great challenge to explore a simple, green, and low-cost route to fabricate porous gold with a “clean” surface. In this work, porous worm-like Au has been easily synthesized in a one-step procedure from aqueous solution at room temperature under the action of ionic liquid tetrapropylammonium glycine ([N₃₃₃₃][Gly]). It is shown that the as-prepared porous worm-like Au has the length from 0.3 to 0.6 μm and the width of approximately 100–150 nm, and it is composed of lots of small nanoparticles about 6–12 nm in diameter. With rhodamine 6G (R6G) as a probe molecule, porous worm-like Au displays remarkable surface enhanced Raman scattering (SERS) sensitivity (detection limit is lower than 10⁻¹³ M), and extremely high reproducibility (average relative standard deviations is less than 2%). At the same time, owing to significantly high specific surface area, various pore sizes and plenty of crystal defects, porous worm-like Au also exhibits excellent catalytic performance in the reduction of nitroaromatics, such as p-nitrophenol and p-nitroaniline, which can be completely converted within only 100 s and 150 s, respectively. It is expected that the as-prepared porous worm-like Au with porous and self-supported structures will also present the encouraging advances in electrocatalysis, sensing, and many others.

Gold nanorods: from anisotropy to opportunity. An evolution update

Gold nanoparticles have drawn attention to nanomedicine for many years due to their physicochemical properties, which include: good stability; biocompatibility; easy surface chemistry and superior magnetic; and last, electronic properties. All of these properties distinguish gold nanoparticles as advantageous carriers to be exploited. The challenge to develop new gold nanostructures has led to anisotropy, a new property to exploit for various medical applications: diagnostic and imaging strategies as well as therapeutic options. Gold nanorods are the most studied anisotropic gold nanoparticles because of the presence of two absorption peaks according to their longitudinal and transversal plasmon resonances. The longitudinal surface plasmonic resonance can provide the absorption in the near-infrared region and this is an important aspect of using gold nanorods for medical purposes.