Gold Nanocrystals Research Articles

Faceted gold nanocrystal film over nanosphere for sensitive SERS distinction of fungicides by deep learning analysis

Metal film over nanosphere (MFON) as a classical SERS-active substrate has attracted numerous attention and applications due to its excellent sensitivity and signal uniformity. However, such MFON substrates prepared by metal deposition require strictly controlled experimental conditions with high cost to obtain high batch reproducibility. In addition, the precise adjustment of the metal particle fineness and crystal facet is hard to conduct, limiting the SERS signal for further improvement. In this work, we propose multifaceted Au nanocrystal over nanosphere (AuNCFON) structures based on a facile and robust interfacial assembly technique. Notably, the preparation method could reduce significant loss of metallic materials without the requirement of large-scale instrumentation, and allows precise control of the metal film thickness and the nanocrystal facet. Specifically, the size and facet of nanocrystals on PS spheres are systematically regulated and the Au dodecahedral films with {110} facet on PS arrays exhibit optimal SERS activity. The SERS intensity is amplified by an enhancement factor of 0.13 × 107 with excellent signal homogeneity and batch reproducibility. Finally, the sensitive and accurate distinction of similarly structured molecules including crystal violet and malachite green (fungicides) is demonstrated assisted by principal component analysis-partial least squares (PCA-PLS) algorithm. The AuNCFON SERS substrate combined with deep learning analysis has a broad application prospect in reliable identification of chemical pollutants.

Experimental and theoretical evidence for unprecedented strong interactions of gold atoms with boron on boron/sulfur-doped carbon surfaces.

The 16e square-planar bis-thiolato-Au(iii) complexes [AuIII(1,2-dicarba-closo-dodecarborane-1,2-dithiolato)2][NBu4] (Au-1) and [AuIII(4-methyl-1,2-benzenedithiolato)2][NBu4] (Au-2) have been synthesized and fully characterized. Au-1 and Au-2 were encapsulated in the symmetrical triblock copolymer poloxamer (Pluronic®) P123 containing blocks of poly(ethylene oxide) and poly(propylene oxide), giving micelles AuMs-1 and AuMs-2. High electron flux in scanning transmission electron microscopy (STEM) was used to generate single gold atoms and gold nanocrystals on B/S-doped graphitic surfaces, or S-doped amorphous carbon surfaces from AuMs-1 and AuMs-2, respectively. Electron energy loss spectroscopy (EELS) data suggested strong interactions of gold atoms/nanocrystals with boron in the B/S-doped graphitic matrix. Density-functional theory (DFT) calculations, also supported the experimental findings, pointing towards strong Au-B bonds, depending on the charge on the Au-(B-graphene) fragment and the presence of further defects in the graphene lattice.

Mineralized aggregates based on native protein phase transition for non-destructive diagnosis of seborrheic skin by surface-enhanced Raman spectroscopy.

The non-homeostasis of sebum secretion by the sebaceous glands in a complicated microenvironment dramatically impacts the skin health of many people in the world. However, the complexity and hydrophobicity of sebum mean a lack of diagnostic tools, which makes it challenging to determine the reason behind cortical imbalances. Herein, a biomimetic mineralized aggregates (PTL@Au and PTB@Au) strategy has been proposed, which could obtain molecular information about sebum by surface-enhanced Raman spectroscopy (SERS). The breaking of disulfide bonds leads to changes in hydrogen bonding, which transform the natural protein into amyloid-like phase transition protein with β-sheets. It provides sites for the nucleation and crystallization of gold nanocrystals to build mineralized aggregates. The mineralized aggregates show robust adhesion stability at the interfaces of different materials through hydrogen bonding and electrostatic interactions. The stabilization, hydrophobicity (contact angle: 134°), and optical transmission (75%) of the structure could result in superior SERS performance for sebum analysis. It should be noted that this enables the sebum detection of clinical samples while ensuring safety. Such generalized bionic mineralization construction and diagnosis methods also serve as an advanced paradigm for a range of biomedical applications.

Continuous flow synthesis and simulation-supported investigation of tunable plasmonic gold patchy nanoparticles.

Plasmonic nanoparticles have intriguing optical properties which make them suitable candidates for sensing or theranostic applications. Anisotropic patchy particles, where metal is locally deposited on the surface of a core particle, exhibit plasmon resonances that can be specifically adjusted for these applications. However, many existing synthesis routes are complex, yield too little material, or provide particles with limited optical tunability. In this work, we present a simple and scalable continuous flow synthesis of gold-on-polystyrene patchy particles with widely adjustable optical properties. By increasing the chloride concentration in the electroless deposition of gold, we slow down the redox reduction kinetics and obtain a dense patch morphology as well as a reduced nucleation rate. The latter is counteracted by introducing a low-level seeding approach where a small number of gold nanocrystals heterocoagulate with the core particles prior to patch growth. Seeding and patch growth are performed in a continuous flow set-up with two T-shaped milli-mixers. The resulting patchy particle samples exhibit a tunable dipolar plasmon peak between 600 nm and 1100 nm. We also investigate the structure-property relationship for our gold patchy particles using finite element method simulations. After identifying a suitable patch shape model, we elucidate the influence of individual geometric parameters on the optical properties and show that the relationship holds true for a large range of patch coverages. Finally, we apply the relationship to explain the time-dependent change in the optical properties of as-synthesized patches by correlating it with the patch shape transformation revealed by electron microscopy.

Amine oxide surfactant-mediated synthesis of plate-based gold nanocrystals with tunable surface wrinkles and their applications in the ethylene glycol oxidation reaction

Gold nanoplates with tunable surface wrinkles are prepared using an amine oxide surfactant, showing improved EGOR activity due to enriched uncoordinated active sites.

Molar excess of coordinating N-heterocyclic carbene ligands triggers kinetic digestion of gold nanocrystals.

There has been much interest in evaluating the strength of the coordination interactions between N-heterocyclic carbene (NHC) molecules and transition metal ions, nanocolloids and surfaces. We implement a top-down core digestion test of Au nanoparticles (AuNPs) triggered by incubation with a large molar excess of poly(ethylene glycol)-appended NHC molecules, where kinetic dislodging of surface atoms and formation of NHC-Au complexes progressively take place. We characterize the structure and chemical nature of the generated PEG-NHC-Au complexes using 1D and 2D 1H-13C NMR spectroscopy, supplemented with matrix assisted laser desorption/ionization mass spectrometry, and transmission electron microscopy. We further apply the same test using thiol-modified molecules and find that though etching can be measured the kinetics are substantially slower. We discuss our findings within the classic digestion of transition metal ores and colloids induced by interactions with sodium cyanide, which provides an insight into the strength of coordination between the strong σ-donating (soft Lewis base) NHC and Au surfaces (having a soft Lewis acid character), as compared to gold-to-gold covalent binding.

Evidence of brain target engagement in Parkinson’s disease and multiple sclerosis by the investigational nanomedicine, CNM-Au8, in the REPAIR phase 2 clinical trials

BackgroundImpaired brain energy metabolism has been observed in many neurodegenerative diseases, including Parkinson’s disease (PD) and multiple sclerosis (MS). In both diseases, mitochondrial dysfunction and energetic impairment can lead to neuronal dysfunction and death. CNM-Au8® is a suspension of faceted, clean-surfaced gold nanocrystals that catalytically improves energetic metabolism in CNS cells, supporting neuroprotection and remyelination as demonstrated in multiple independent preclinical models. The objective of the Phase 2 REPAIR-MS and REPAIR-PD clinical trials was to investigate the effects of CNM-Au8, administered orally once daily for twelve or more weeks, on brain phosphorous-containing energy metabolite levels in participants with diagnoses of relapsing MS or idiopathic PD, respectively.ResultsBrain metabolites were measured using 7-Tesla 31P-MRS in two disease cohorts, 11 participants with stable relapsing MS and 13 participants with PD (n = 24 evaluable post-baseline scans). Compared to pre-treatment baseline, the mean NAD+/NADH ratio in the brain, a measure of energetic capacity, was significantly increased by 10.4% after 12 + weeks of treatment with CNM-Au8 (0.584 units, SD: 1.3; p = 0.037, paired t-test) in prespecified analyses of the combined treatment cohorts. Each disease cohort concordantly demonstrated increases in the NAD+/NADH ratio but did not reach significance individually (p = 0.11 and p = 0.14, PD and MS cohorts, respectively). Significant treatment effects were also observed for secondary and exploratory imaging outcomes, including β-ATP and phosphorylation potential across both cohorts.ConclusionsOur results demonstrate brain target engagement of CNM-Au8 as a direct modulator of brain energy metabolism, and support the further investigation of CNM-Au8 as a potential disease modifying drug for PD and MS.

Nanoparticle Size Influences the Self-Assembly of Gold Nanorods Using Flexible Streptavidin-Biotin Linkages.

The self-assembly of colloidal nanocrystals remains of robust interest due to its potential in creating hierarchical nanomaterials that have advanced function. For gold nanocrystals, junctions between nanoparticles yield large enhancements in local electric fields under resonant illumination, which is suitable for surface-enhanced spectroscopies for molecular sensors. Gold nanorods can provide such plasmonic fields at near-infrared wavelengths of light for longitudinal excitation. Through the use of careful concentration and stoichiometric control, a method is reported herein for selective biotinylation of the ends of gold nanorods for simple, consistent, and high-yielding self-assembly upon addition of the biotin-binding protein streptavidin. This method was applied to four different sized nanorods of similar aspect ratio and analyzed through UV-vis spectroscopy for qualitative confirmation of self-assembly and transmission electron microscopy to determine the degree of self-assembly in end-linked nanorods. The yield of end-linked assemblies approaches 90% for the largest nanorods and approaches 0% for the smallest nanorods. The number of nanorods linked in one chain also increases with an increased nanoparticle size. The results support the notion that the lower ligand density at the ends of the larger nanorods yields preferential substitution reactions at those ends and hence preferential end-to-end assembly, while the smallest nanorods have a relatively uniform ligand density across their surfaces, leading to spatially random substitution reactions.

In situ tuning and investigating the growth process of size controllable gold nanoparticles and statistical size prediction analysis

A critical understanding of the formation and growth process of gold nanoparticles (GNPs) is crucial, in order to synthesize monodisperse gold nanocrystals of controllable size and shape in a predictable way. GNPs of different shapes and sizes can be produced by altering different physicochemical reaction conditions, such as pH, temperature, and the ratio of reactants. The significant variations in the morphological features of GNPs can be monitored in situ in a time-dependent manner by using UV–visible spectroscopy. In this study, we have synthesized seedless GNPs by reduction of HAuCl4 by using various molar ratios of HEPES and Na2HPO4. The shape and the geometry of the gold nanostructures were optimized by varying the pH (5, 7, and 9) of the HEPES, molar concentrations of disodium phosphate to HAuCl4, and reaction temperatures (20 °C, 40 °C, and 60 °C). The changes in the color of the reaction mixtures over time were recorded in situ in terms of the absorbance of the UV–visible light to tune and investigate the growth process of gold nanostructures. Transmission electron microscopic (TEM) images indicated that the gold nanostructures are anisotropic, stable, and exist in the size range of < 1–100 nm. The present study also confirms that the change in the color of nanostructure reaction mixtures is a function of the surface plasmon resonance bands under the influence of physicochemical reaction conditions and corroborates with the size and shape of nano-gold. Physicochemical parameters such as temperature, pH, and the molar concentration of the reactants act synergistically to influence the growth, molecular mechanics, and reaction thermodynamics that aid to affect the particle size, shape, and surface corona of the GNPs. By tracking the growth process, we can confirm that the nucleation, growth process, size, and shape of the gold nanostructures depend on the HEPES free radicals and phosphate ions which cluster to form polymeric chains on the gold nanocore. The present study's findings explain the growth process of the GNPs of various colors that can be observed by the naked eye and have promising applications, for example in the development of the biosensing rapid lateral flow immunoassays (LFIA) for the detection of mycotoxins in food samples.

Selective Self-assembly of Gold Nanocrystals Using Complementary Leucine Zipper Peptides

Abstract A heterodimeric leucine zipper (Lz)–based peptide hybrid was utilized as a molecular adhesive to bind two types of gold nanocrystals with different shapes. An acidic leucine zipper (LzE) and a basic leucine zipper (LzK) peptides with terminal cysteine are respectively adsorbed to the surface of spherical gold nanoparticles (LzE–Au NPs) and gold nanocubes (LzK–Au NCs). Transmission electron microscope (TEM) observation and visible (Vis) absorption spectroscopy revealed that LzE–Au NPs and LzK–Au NCs are selectively self-assembled in water. The dynamic self-assembly behavior is also confirmed by in-situ fluorescence resonance energy transfer between fluorescence dyes connected to LzE and LzK peptides and other control experiments.

Imaging-Guided Antibacterial Based on Gold Nanocrystals and Assemblies.

Bacterial infection becomes a severe threat to human life and health worldwide. Antibiotics with the ability to resist pathogenic bacteria are therefore widely used, but the misuse or abuse of antibiotics can generate multidrug-resistant bacteria or resistant biofilms. Advanced antibacterial technologies are needed to counter the rapid emergence of drug-resistant bacteria. With the excellent optical properties, engineerable surface chemistry, neglectable biotoxicity, gold nanocrystals are particularly attractive in biomedicine for cancer therapy and antibacterial therapy, as well as nanoprobes for bioimaging and disease diagnosis. In this perspective, gold nanocrystal-based antibacterial performance and deep-tissue imaging are summarized, including near-infrared-light excited photoacoustic imaging and fluorescence imaging through deep tissue infections. On the basis of integrating "imaging-therapy-targeting" in single nanotheranostic, the current challenges of imaging-guided antibacterial and therapy based on gold nanocrystals are discussed, and some insights are provided into the gold nanocrystal-based nanoplatform that integrates antibacterial activity and therapy. This perspective is expected to provide comprehensive guidance for diagnosing and combating bacterial infections based on gold nanostructures.

Diffracted X-ray Tracking for Observing the Internal Motions of Individual Protein Molecules and Its Extended Methodologies.

In 1998, the diffracted X-ray tracking (DXT) method pioneered the attainment of molecular dynamics measurements within individual molecules. This breakthrough revolutionized the field by enabling unprecedented insights into the complex workings of molecular systems. Similar to the single-molecule fluorescence labeling technique used in the visible range, DXT uses a labeling method and a pink beam to closely track the diffraction pattern emitted from the labeled gold nanocrystals. Moreover, by utilizing X-rays with extremely short wavelengths, DXT has achieved unparalleled accuracy and sensitivity, exceeding initial expectations. As a result, this remarkable advance has facilitated the search for internal dynamics within many protein molecules. DXT has recently achieved remarkable success in elucidating the internal dynamics of membrane proteins in living cell membranes. This breakthrough has not only expanded our knowledge of these important biomolecules but also has immense potential to advance our understanding of cellular processes in their native environment.

Controlled synthesis of gold nanorods and integrated with titanium dioxide for enhancing visible light‐driven antioxidant activity

AbstractIn this work, gold nanorods (AuNRs) with well‐controlled aspect ratios were prepared using a modified seed‐growth method and covered by TiO2 layers through the hydrothermal reaction to improve stability. Integrating TiO2 with plasmonic rod‐like gold nanoparticles could enhance their photo activity by the local surface plasmon resonance (LSPR) effect. AuNRs aspect ratios were controlled by varying the amount of seed solution, reducing agents, surfactant (CTAB), and titanium (IV) but oxide. The optical properties of formed AuNRs can be tuned in the spectral range from 400 to 900 nm by adjusting the ratio between seed solution and reducing agent concentration. Besides, the absorption of the UV‐light function of TiO2 and the antioxidant properties of gold nanoparticles were also integrated to prepare a kind of multifunctional material. The obtained AuNRs/TiO2 were then determined by ultraviolet‐visible spectroscopy (UV‐Vis), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high‐resolution transmission electron microscopy (HR‐TEM), selected area electron diffraction (SAED), and energy‐dispersive X‐ray spectroscopy (EDS). Microscopic images (TEM, SEM) revealed that the average particle size of the AuNRs decorated in the titanium dioxide ranged from 20 to 60 nm, depending on the experimental parameters. Furthermore, HRTEM, EDS, and SAED results provided more precise information insight into the formed gold nanocrystals. The AuNRs/TiO2 exhibited superior antioxidant activity by reducing free 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) radicals at different concentrations. The results indicated that AuNRs/TiO2 improves antioxidant and optical absorption activities. The antioxidation effect was proved more excellent than solely used of spherical, rod‐liked gold nanoparticles or TiO2 nanoparticles. This novel design of AuNRs/TiO2 may open a new avenue for facilitating multifunctional nanoparticles in cosmetic applications.

Analysis of the Structural Dynamics of Proteins in the Ligand-Unbound and -Bound States by Diffracted X-ray Tracking.

Although many protein structures have been determined at atomic resolution, the majority of them are static and represent only the most stable or averaged structures in solution. When a protein binds to its ligand, it usually undergoes fluctuation and changes its conformation. One attractive method for obtaining an accurate view of proteins in solution, which is required for applications such as the rational design of proteins and structure-based drug design, is diffracted X-ray tracking (DXT). DXT can detect the protein structural dynamics on a timeline via gold nanocrystals attached to the protein. Here, the structure dynamics of single-chain Fv antibodies, helix bundle-forming de novo designed proteins, and DNA-binding proteins in both ligand-unbound and ligand-bound states were analyzed using the DXT method. The resultant mean square angular displacements (MSD) curves in both the tilting and twisting directions clearly demonstrated that structural fluctuations were suppressed upon ligand binding, and the binding energies determined using the angular diffusion coefficients from the MSD agreed well with the binding thermodynamics determined using isothermal titration calorimetry. In addition, the size of gold nanocrystals is discussed, which is one of the technical concerns of DXT.

How do gold-nanocrystal surface facets affect their electrocatalytic activities and the benzocaine-oxidation mechanism?

Here we unveil the effect of gold (Au) nanocrystals with different surface facets on electrocatalytic sensing activities using benzocaine as an analyte. To this end, we performed cyclic voltammetry, differential pulse voltammetry, and in-situ Raman spectroelectrochemical experiments by employing Au nanocrystals with different exposed surface facets as electrocatalytic sensors for benzocaine. The experiments were complemented by density-functional calculations, where the rhombic dodecahedra nanocrystals, enclosed by {110} facets, showed stronger interaction energy with benzocaine, followed by cubes ({100} facets) and octahedra ({111} facets). Results from in-situ Raman spectroelectrochemical measurements have also demonstrated that the benzocaine adsorption displayed a facet-dependent behavior, which supports that the analyte can be strongly adsorbed on the Au{110} facets in comparison to {100} and {111} counterparts. In this case, we propose an oxidative mechanism of the benzocaine reaction, in which benzocaine may be electrochemically adsorbed at Au nanocrystals through the –NH2 groups. After that, this –NH(Au) group is oxidized to –NO and, further to –NO2, in which different profiles were observed as a function of the Au nanocrystal facets. The effect of these facets was also observed in the oxygen reduction reaction; the rhombic dodecahedra presented a potential reduction of 200 mV, and a current increased by more than twenty times relative to the values of a commercial Au electrode (bulk). Indeed, our findings provide a deeper understanding of facet-dependent electrooxidation activity, mechanisms, and electrocatalytic detection of organic compounds.

Noncanonical Condensation of Nucleic Acid Chains by Hydrophobic Gold Nanocrystals.

Nucleic acid condensates are essential for various biological processes and have numerous applications in nucleic acid nanotechnology, gene therapy, and mRNA vaccines. However, unlike the in vivo condensation that is dependent on motor proteins, the in vitro condensation efficiency remains to be improved. Here, we proposed a hydrophobic interaction-driven mechanism for condensing long nucleic acid chains using atomically precise hydrophobic gold nanoclusters (Au NCs). We found that hydrophobic Au NCs could condense long single-stranded DNA or RNA to form composites of spherical nanostructures, which further assembled into bead-shaped suprastructures in the presence of excessive Au NCs. Thus, suprastructures displayed gel-like behaviors, and Au NCs could diffuse freely inside the condensates, which resemble the collective motions of condensin complexes inside chromosomes. The dynamic hydrophobic interactions between Au NCs and bases allow for the reversible release of nucleic acids in the presence of mild triggering agents. Our method represents a significant advancement toward the development of more efficient and versatile nucleic acid condensation techniques.

Real-Time Observation of Capsaicin-Induced Intracellular Domain Dynamics of TRPV1 Using the Diffracted X-ray Tracking Method.

The transient receptor potential vanilloid type 1 (TRPV1) is a multimodal receptor which responds to various stimuli, including capsaicin, protons, and heat. Recent advances in cryo-electron microscopy have revealed the structures of TRPV1. However, due to the large size of TRPV1 and its structural complexity, the detailed process of channel gating has not been well documented. In this study, we applied the diffracted X-ray tracking (DXT) technique to analyze the intracellular domain dynamics of the TRPV1 protein. DXT enables the capture of intramolecular motion through the analysis of trajectories of Laue spots generated from attached gold nanocrystals. Diffraction data were recorded at two different frame rates: 100 μs/frame and 12.5 ms/frame. The data from the 100 μs/frame recording were further divided into two groups based on the moving speed, using the lifetime filtering technique, and they were analyzed separately. Capsaicin increased the slope angle of the MSD curve of the C-terminus in 100 μs/frame recording, which accompanied a shifting of the rotational bias toward the counterclockwise direction, as viewed from the cytoplasmic side. This capsaicin-induced fluctuation was not observed in the 12.5 ms/frame recording, indicating that it is a high-frequency fluctuation. An intrinsiccounterclockwise twisting motion was observed in various speed components at the N-terminus, regardless of the capsaicin administration. Additionally, the competitive inhibitor AMG9810 induced a clockwise twisting motion, which is the opposite direction to capsaicin. These findings contribute to our understanding of the activation mechanisms of the TRPV1 channel.

Zirconium-Directed Supramolecular Self-Assembly of Coenzyme A@GNCs with Enhanced Phosphorescence for Developing Ultrasensitive Tracer Probe of Dipicolinic Acid, a Biomarker of Bacterial Spores.

Luminescent gold nanoclusters (GNCs) are a class of attractive quantum-sized nanomaterials bridging the gap between organogold complexes and gold nanocrystals. They typically have a core-shell structure consisting of a Au(I)-organoligand shell-encapsulated few-atom Au(0) core. Their luminescent properties are greatly affected by their Au(I)-organoligand shell, which also supports the aggregation-induced emission (AIE) effect. However, so far, the luminescent Au nanoclusters encapsulated with the organoligands containing phosphoryl moiety have rarely been reported, not to mention their AIE. In this study, coenzyme A (CoA), an adenosine diphosphate (ADP) analogue that is composed of a bulky 5-phosphoribonucleotide adenosine moiety connected to a long branch of vitamin B5 (pantetheine) via a diphosphate ester linkage and ubiquitous in all living organisms, has been used to synthesize phosphorescent GNCs for the first time. Interestingly, the synthesized phosphorescent CoA@GNCs could be further induced to generate AIE via the PO32- and Zr4+ interactions, and the observed AIE was found to be highly specific to Zr4+ ions. In addition, the enhanced phosphorescent emission could be quickly turned down by dipicolinic acid (DPA), a universal and specific component and also a biomarker of bacterial spores. Therefore, a Zr4+-CoA@GNCs-based DPA biosensor for quick, facile, and highly sensitive detection of possible spore contamination has been developed, showing a linear concentration range from 0.5 to 20 μM with a limit of detection of 10 nM. This study has demonstrated a promising future for various organic molecules containing phosphoryl moiety for the preparation of AIE-active metal nanoclusters.

Electrochemical detection of isocarbophos in apple and cabbage with Ti3C2TX/arginine and serine-functionalized graphene quantum dot@gold nanostar aerogel and target cycle dual signal amplification

The paper reports one strategy for synthesis of Ti3C2TX/arginine and serine-functionalized graphene quantum dot@Au nanostar aerogel (Ti3C2TX/RS-GQD@Au). Positively charged RS-GQDs bound with negatively charged Ti3C2TX sheets to form Ti3C2TX aerogel. Then, HAuCl4 was in situ reduced with ascorbic acid in the presence of L-glutathione to form gold nanostars on Ti3C2TX sheets. The resulting Ti3C2TX/RS-GQD@Au shows one three-dimensional structure. The gold nanostars were homogeneously dispersed on Ti3C2TX sheets. Introduction of RS-GQD realizes construction of Schottky heterojunction. The presence of L-glutathione triggers an asymmetric structural evolution of gold nanocrystals and leads to more exposed high-index crystal facets. Unique structure achieves to high conductivity, structural stability and catalytic activity. Ti3C2TX/RS-GQD@Au was used for construction of electrochemical sensor for detection of isocarbophos coupled with target cycle amplification. The peak current at 0.27 V linearly increases with the increase of isocarbophos concentration between 1 × 10−11 and 8 × 10−16 M with 2.9 × 10−16 M of detection limit (S/N = 3). The analytical method provide advantage of sensitivity and specificity for detection of isocarbophos in apple and cabbage.

Gram-Scale Continuous Flow Synthesis of Silver-on-Silica Patchy Nanoparticles with Widely Tunable Resonances for Plasmonics Applications

Extensive research has been conducted on colloids that incorporate nanostructured noble metals, motivated in particular by their highly tunable optical properties. However, the lack of approaches that offer reproducibility, tunability, and scalable production is limiting their exploitation in many application areas. Here, we present an innovative process for the controlled formation of silver patches on silica nanospheres using gold nanocrystal seeds. The synthesis of the seeds and their attachment in very small numbers to the silica spheres is achieved without employing any surfactants, stabilizers, or linker molecules. Using advanced transmission electron microscopy techniques, we show that electroless deposition of nanostructured silver occurs at the introduced seeds and leads to a central protrusion from the metal patches not observed in earlier, seed-free work. We demonstrate that both seeding and growth processes can be achieved in millimixer flow reactors. With this simple and scalable approach, we provide compelling evidence for the use of seeds in producing targeted morphology and function. Specifically, patch size and optical properties can be tailored in a predictive manner by adjusting the density of seeds on the silica nanospheres as well as reagent concentrations during growth. As a result, our process can be used to obtain colloidal dispersions with localized surface plasmon resonance peaks anywhere in the range 400 to nearly 1300 nm. We confirm the scalability of our method by operating the growth process for around 70 min. Apart from changes in the first few minutes, the product properties remained rather stable and over a gram of high quality silver patch-coated silica could be recovered. Our approach opens up exciting new avenues for plasmonics applications, which typically require large amounts of nanoparticles with specifically designed optical properties. These include color and IR pigments, photocatalysts, and as light management components in optoelectronic devices like photovoltaic cells.