Three-Dimensionally Nanometallic Superstructure Synthesized via a Single-Particle Soft-Enveloping Strategy.

Three-dimensionally (3D) integrated metallic nanomaterials composed of two or more different types of nanostructures make up a class of advanced materials due to the multidimensional and synergistic effects between different components. However, designing and synthesizing intricate, well-defined metallic 3D nanomaterials remain great challenges. Here, a novel single-particle soft-enveloping strategy using a core-shell Au NP@mSiO2 particle as a template was proposed to synthesize 3D nanomaterials, namely, a Au nanoparticle@center-radial nanorod-Au-Pt nanoparticle (Au NP@NR-NP-Pt NP) superstructure. Taking advantage of the excellent plasmonic properties of Au NP@NR-NP by the synergistic plasmonic coupling of the outer Au NPs and inner Au nanorods, we can enhance the catalytic performance for 4-nitrophenol hydrogenation using Au NP@NR-NP-Pt NP as a photocatalyst with plasmon-excited hot electrons from Au NP@NR-NP under light irradiation, which is 2.76 times higher than in the dark. This process opens a door for the design of a new generation of 3D metallic nanomaterials for different fields.

Directly Self-Assembly of Aligned Ag NWs Films at the Air-Water Interface for the Detection of Pathogens in Artificial Breath Aerosols.

Exhaled aerosols from humans, containing various pathogens, are crucial for early disease diagnosis. However, the traditional pathogen detection methods, such as polymerase chain reaction, are often slow and cumbersome due to complex sampling and procedures. This study introduces a novel, direct, and label-free detection method for pathogens in respiratory aerosols, utilizing a highly aligned silver nanowire (Ag NW) film combined with a filter membrane (Ag NWs@filter) as a surface-enhanced Raman spectroscopy-active substrate. A large-scale, ordered silver nanowire film was developed through a simplified self-assembly process. This process eliminates the need for an organic phase and complex surface modifications of Ag NWs, which are common in other preparation methods. Subsequently, the fabricated Ag NWs@filter demonstrated its capability to continuously capture and efficiently preconcentrate pathogens from aerosols, achieving a remarkable detection limit of 3 × 103 CFU/mL, demonstrated using Escherichia coli (E. coli) as a model pathogen. Moreover, the classification between E. coli and Pseudomonas aeruginosa achieved an overall accuracy of 96.5% by the principal component analysis with linear discriminant analysis models. The success of this sensing strategy illustrates its potential in detecting and identifying a variety of biomarkers present in respiratory aerosols, marking a significant step forward in the field of pathogen detection.

Confined-Enhanced Raman Spectroscopy.

In 1997, the discovery of single molecule-surface enhanced Raman spectroscopy (SM-SERS) rekindled broad interests owing to its ultrahigh enhancement factor up to the 1014-1015 level. However, regretfully, the advantage of SM-SERS with an ultralow detection limit has not yet been fully utilized in commercialized applications. Here, we report a strategy, which we name confined-enhanced Raman spectroscopy, in which the overall Raman properties can be remarkably improved with in situ-formed active nanoshell on the surface of silver or gold nanoparticles. The nanoshell can confine and anchor molecules onto the surface of plasmonic nanoparticles and avoid desorption from hot spots so that the "on and off" blinking effect can be eliminated. It is the first time the single-molecule detection of analytes with super sensitivity, high stability, and reproducibility based on gold nanoparticles has been realized. In addition, this strategy is suitable for SERS detection in diverse molecule systems, including biomedical diagnosis, catalytic reaction, etc.

Remote Raman Detection of Trace Explosives by Laser Beam Focusing and Plasmonic Spray Enhancement Methods.

Remote Raman spectroscopy is a technique that can detect and identify different target molecules through Raman vibrational modes from a remote distance. However, the current remote Raman technique is restricted by poor detection sensitivity, and it is still extremely challenging for trace explosive detection. Here, in order to achieve trace explosive detection from a remote distance, we innovatively propose two enhanced Raman spectroscopy methods by using a plasmonic spray and a laser beam focusing/Raman signal collecting instrument. In brief, a facile convex lens can converge the laser beam and collect Raman scattering signals, and a plasmonic spray can be used for surface-enhanced Raman scattering. Under the combination of the above enhancement methods, we achieve remote Raman detection of a variety of trace explosives with a concentration of ∼1 µg/cm2 from a distance of 30 m. These novel methods demonstrate a simple approach that significantly improves the capability of remote detection of trace chemicals for further applications.

Light modulation based on the enhanced Kerr effect in molybdenum disulfide nanostructures with curved features.

A novel type of molybdenum disulfide (MoS2) nanoparticles (NPs) was chemically synthesized, which possessed curved features with three-dimensional (3D) freedom compared with planar two-dimensional (2D) materials. Due to the introduction of curved features, the synthesized NPs exhibited a strongly enhanced nonlinear refractive index (n2 ∼ 10-5 cm-2 W-1) and third-order susceptibility (χ(3) ∼ 10-7 esu), which were experimentally verified by the spatial self-phase modulation effect in the visible wavelength range. Both the nonlinear parameters were two orders of magnitude higher than their planar MoS2 nanostructure counterparts. In addition, the relative change of the effective nonlinear refractive index Δn2/n2 was found to be distinctly dependent on the intensity of the applied electromagnetic field. Moreover, an all-optical modulation was experimentally realized based on the spatial cross-phase modulation effect. Our results demonstrate planar MoS2 materials with 3D features as potential candidates for next generation all-optical applications and open a substantial approach for the design of efficient nanomaterials with favorable optical nonlinearity.

Solution-Based SERS Detection of Weak Surficial Affinity Molecules Using Cysteamine-Modified Au Bipyramids.

To achieve ultrasensitive detection of trace targets through solution-based surface-enhanced Raman spectroscopy (SERS), direct adsorption of the target molecules on a SERS-active surface is vital. In this work, cetyltrimethylammonium bromide (CTAB)-capped gold nano-bipyramids (Au BPs) with different aspect ratios (ARs) are prepared and the surface is successfully modified by a simple ligand exchange method. Cysteamine-capped gold nano-bipyramids (cyst-Au BPs) are obtained by means of replacement of CTAB by cysteamine using Au-S covalent bonding and applied in the solution-based SERS detection of different pigment molecules, which always have weak affinity to the gold surface. The hydrogen bonding between the pigment molecule and cysteamine causes the aggregation of Au BPs to generate local electromagnetic field enhancement. The influence of the AR and concentration of Au BPs on SERS properties is investigated. The SERS detection of weak-affinity molecules to an extremely low limit shows that the cyst-Au BPs are highly sensitive compared to CTAB-capped Au BPs. The limit of detection (LOD) of allura red as low as 0.1 ppb and that of sunset yellow as low as 1 ppb show that the proposed strategy has many advantages due to its simplicity and fast and rapid detection for the sensitivity analysis of weak-affinity molecules.

Facile Surface Modification of Mesoporous Au Nanoparticles for Highly Sensitive SERS Detection.

The stability, dispersity, and surface chemical properties of colloidal nanoparticles are crucial for the reliable and desired chemical sensing in various applications. Here, we report an effective strategy to engineer the surface properties of mesoporous Au nanoparticles (meso-Au NPs) via PVP ligand modification, template removal, and surface purification. Monodispersed 3D meso-Au NPs with well-defined sizes and shapes were obtained using a general soft-enveloping strategy. During surface modification, the addition of PVP ligands and the concentration of HF solutions play key roles in the stability, shape, and size distributions of ordered Au networks. In order to obtain an improved sensing performance, the morphologies of meso-Au NPs were optimized with smaller mesopore size, and NaBH4 solution was used to efficiently remove the adsorbed PVP ligands. Due to the characteristics of high-density porosities and large surface area, the purified meso-Au NPs could be a kind of promising plasmonic-enhanced nanomaterial and provide abundant "hot spots." Combined with the enrichment effect using a slippery liquid-infused porous surface, the lowest detection limits of crystal violet molecule could be down to 0.1 pM, demonstrating an excellent SERS sensitivity. Moreover, a realistic illegal drug containing aspirin could be sensitively detected with a limit of 2.8 × 10-6 M, showing great potential for practical molecular sensing and applications.

Shape-Controlled Hierarchical Flowerlike Au Nanostructure Microarrays by Electrochemical Growth for Surface-Enhanced Raman Spectroscopy Application.

How to fabricate Au nanostructures conveniently on microstructured/nanostructured arrays surface with low cost has become a crucial and urgent challenge. In this study, we demonstrate hierarchical flowerlike Au nanostructures with rich nanothorns (HF-AuNTs) through one-step electrochemical deposition. The morphology of the HF-AuNTs is easily manipulated by controlling the applied potential or precursor solution concentration of electrodeposition. The as-prepared HF-AuNTs possessing unique local morphology of thin petals and dense thorns are further applied in the Si micropit arrays to acquire HF-AuNTs microarrays. As an initial detection, these HF-AuNTs microarrays exhibit a fascinating surface-enhanced Raman spectroscopy consistency (relative standard deviation is 7.17%) and sensitivity with the limitation of crystal violet reaching to 10-10 M, and Rhodamine 6G reaching to 10-11 M. The HF-AuNTs microarrays with well-defined shape and elaborate structure may be applicated in SERS substrates, superhydrophobic materials, and so on.

Ratiometric Sensing of Polycyclic Aromatic Hydrocarbons Using Capturing Ligand Functionalized Mesoporous Au Nanoparticles as a Surface-Enhanced Raman Scattering Substrate.

The absorption behavior between plasmonic nanostructures and a target molecule plays key roles in effective surface-enhanced Raman scattering (SERS) detection. However, for analytes with low surface affinity to the metallic surface, e.g., polycyclic aromatic hydrocarbons (PAHs), it remains challenging to observe the enhanced Raman signal. In this work, we reported a ratiometric SERS strategy for sensitive PAH detection through the surface functionalization of 3D ordered mesoporous Au nanoparticles (meso-Au NPs). By employing mono-6-thio-ß-cyclodextrin (HS-ß-CD) as capture ligands, the hydrophobic molecules, e.g., anthracene, could be effectively absorbed on the meso-Au NP surface via a host-guest interaction. Besides, a hydrophobic slippery surface is used as a concentrator to deliver and enrich the Au/analyte droplets into a small area. Consequently, the detection limits of anthracene and naphthalene are down to 1 and 10 ppb. The improved SERS enhancement is mainly ascribed to the host-guest effect of HS-ß-CD ligands, large surface area and high-density of sub-10 nm mesopores of Au networks, as well as the enrichment effect of hydrophobic slippery surface. Moreover, the HS-ß-CD (480 cm-1 band) could serve as an internal standard, leading to the ratiometric determination of anthracene ranging from 1 ppm to 1 ppb. The proposed surface modification strategy in combination with the hydrophobic slippery surface shows great potential for active capture and trace detection of persistent organic pollutants in real-world SERS applications.

Hydrophobic Slippery Surface-Based Surface-Enhanced Raman Spectroscopy Platform for Ultrasensitive Detection in Food Safety Applications.

Collecting highly diluted target analytes into specific hot spot regions is vital for ultrasensitive surface-enhanced Raman spectroscopy (SERS) applications. In this work, a hydrophobic slippery platform was employed as a concentrator to construct colloidal SERS-active substrates regardless of the diffusion limits during droplet evaporation. Within only 140 s, sufficient absorption between the analytes and colloidal Au nanoparticles (Au NPs) was observed by fluorescence imaging. This effect resulted in excellent SERS sensitivity and stability. Compared with the common metal colloid-based SERS substrates, e.g., drying on a silicon wafer or detection in colloidal solutions, this preconcentrated method showed lower detection limits and the lowest detection concentration of crystal violet molecule down to 10-12 M with a portable Raman spectrometer. Such high signal enhancement was mainly ascribed to the condensation effect of Au colloids/analytes on the hydrophobic slippery substrate, by which almost all probe molecules were guided into the "hot spot" regions of aggregated Au NPs. Using the SERS platform, various illegal additives in realistic food and health-care products, for example, malachite green (1 ppb) added in fish and morphine (0.1 ppm) added in a chafing dish, could be sensitively detected. Therefore, our protocol is a general SERS platform that may provide a simple, fast, and cost-effective approach for trace molecular sensing.

Designing Novel Nonsymmetric Ag/AgI Nanoplates for Superior Photocatalytic Activity.

Precisely engineering the decoration of metal nanoparticles on the special surface of semiconductor represents a promising strategy to design efficient metal-semiconductor heterostructured photocatalysts. This study demonstrates a versatile soft-template method to fabricate a novel nonsymmetrical heterostructured Ag/AgI nanoplate, in which only one side surface of the nanoplate is covered with uniform 2D Ag nanoweb. Compared with symmetrical heterostructure, the nonsymmetrical heterostructure may further facilitate the separation of photogenerated electron-hole pairs and shows a greatly enhanced photocatalytic activity. This study may open up a new way to improve the photocatalytic property by synthesizing nonsymmetrical metal-semiconductor composites.

In Situ Probing of the Particle-Mediated Mechanism of WO3 -Networked Structures Grown inside Confined Mesoporous Channels.

Nanocasting, using ordered mesoporous silica or carbon as a hard template, has enormous potential for preparing novel mesoporous materials with new structures and compositions. Although a variety of mesoporous materials have been synthesized in recent years, the growth mechanism of nanostructures in a confined space, such as mesoporous channels, is not well understood, which hampers the controlled synthesis and further application of mesoporous materials. Here, the nucleation and growth of WO3 -networked mesostructures within an ordered mesoporous matrix, using an in situ transmission electron microscopy heating technique and in situ synchrotron small-angle X-ray scattering spectroscopy, are probed. It is found that the formation of WO3 mesostructures involves a particle-mediated transformation and coalescence mechanism. The liquid-like particle-mediated aggregation and mesoscale transformation process can occur in ≈10 nm confined mesoporous channels, which is completely unexpected. The detailed mechanistic study will be of great help for experimental design and to exploit a variety of mesoporous materials for diverse applications, such as catalysis, absorption, separation, energy storage, biomedicine, and nanooptics.

Insight of holey-graphene in the enhancing of electrocatalytic activity as supporting material.

An ideal supporting material improves both activity and durability of noble metal nanoparticles in electrocatalytic reactions. Graphene possesses a high transport rate of electrons in-plane, a low cost, and stability, but, the restacking of graphene layers trap noble metal nanoparticles and make them inaccessible to reactants and results in reduced catalytic activity. Here, holey-graphene as the supporting materials for Pt nanoparticle catalysts is deeply investigated in the electrocatalytic reaction of methanol oxidation. The holey-graphene can be scalable to synthesize using our simple method described herein. The holes on the holey-graphene layer promote the access of reactants with Pt nanoparticle catalysts compared with carbon black and graphene when used as supporting materials. Density functional theory calculations and molecule dynamic simulation further explain the function of holey-graphene in the promotion of electrocatalytic activity. Holey-graphene may open extraordinary possibilities as a supporting material for electrocatalysts.

[Metabonomics study on hepatoprotective effect of Schisandrae Chinensis Fructus based on UPLC-Q-TOF-MS].

To investigate the hepatoprotective effect of Schisandrae Chinensis Fructus (SCF) on CCl4-induced liver injury, observe its effect on serum metabolites, explore its scientific connotation in liver preservation and find the biomarkers for hepatoprotective effect of SCF. Liver injury model was established by using CCl4. The pathological sections of liver tissues were observed and the contents of alanine transaminase (ALT) and aspartate transaminase (AST) in serum were determined. The metabolic skills were adopted based on ultra performance liquid chromatography time-of-flight mass spectrometry (UPLC-Q-TOF-MS), principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) for screening and identification of biomarkers related to liver injury. The results showed the metabolites in blank group, model group and administration group could be easily distinguished, 50 differential compounds were identified and 7 possible metabolic pathways of liver protection were enriched. In this experiment, the hepatoprotective effect of SCF was verified, and the related metabolic pathways such as amino acid metabolism, vitamin metabolism and glycerophospholipid metabolism were discussed.

Evaluation of Raman spectroscopy for diagnosing EGFR mutation status in lung adenocarcinoma.

Somatic mutations in the epidermal growth factor receptor (EGFR) gene were associated with sensitivity to small molecule tyrosine kinase inhibitors for patients with lung adenocarcinomas. In this research, EGFR mutation status was analyzed by DNA sequencing in 153 lung adenocarcinoma tissues. Of these, 75 samples carried EGFR mutations, including 29 with E19del mutation, 33 with L858R mutation, 7 with T790M mutation, and 6 with multiple mutations. Then, 30 samples including 10 with wild type (wt)-EGFR, 10 with L858R and 10 with E19del mutations were selected for Raman and immunohistochemistry (IHC) analyses. After removing the spectra from normal and non-mutated regions, 441 spectra were found appropriate for Raman analysis: 149 from wt-EGFR, 135 from L858R and 157 from E19del mutations. The Raman peaks at 675, 1107, 1127 and 1582 cm(-1) were significantly increased in wt-EGFR tissues which can be attributed to specific amino acids and DNA. The Raman peaks at 1085, 1175 and 1632 cm(-1) assigned to arginine were slightly increased in L858R tissues. The overall intensity of E19del tissues was weaker than others due to exon 19 deletion that removes residues 746-750 of the expressed protein. Principal component analysis (PCA) and support vector machine (SVM) were applied for final prediction. The PCA/SVM algorithm yielded an overall accuracy of 87.8% for diagnosing L858R or E19del from wt-EGFR tissues. Finally, RS provides a simple, rapid and low-cost procedure based upon the molecular signatures for predicting EGFR mutation status.

Effective enrichment of trace exosomes for the label-free SERS detection via low-cost thermophoretic profiling.

Exosome-based liquid biopsies possess great potential in monitoring cancer development However, current exosome detection biosensors require large exosome volumes, showing the weak detection sensitivity. Besides, these methods pay little attention to in situ analysis of exosomes, hence limiting the provision of more accurate clinically-relevant information. Herein, we develop an innovative label-free biosensor combining the low-cost thermophoretic enrichment method with the surface-enhanced Raman spectroscopy (SERS) detection. Based on the thermophoretic enrichment strategy, exosomes and gold nanoparticles can be enriched together into a small area with a scale of 500 µm within 10 min. The Raman signals of various exosomes derived from normal, cancerous cell lines and human serum are dynamically monitored in situ, with the limit of detection of 102-103 particles per microliter, presenting higher sensitivity compared with the similar label-free SERS detection. The spectral data set of different exosomes is applied to train for multivariate classification of cell types and to estimate how the normal exosome data resemble cancer cell exosome. The reliable classification and identification of different exosomes can be realized. The current biosensor is convenient, low-cost and requires small exosome volumes (∼3 µL), and if validated in larger cohorts may contribute to the tumor prediction and diagnosis.

Rapid and ultrasensitive solution-based SERS detection of drug additives in aquaculture by using polystyrene sulfonate modified gold nanobipyramids.

In recent years, surface-enhanced Raman spectroscopy (SERS) has been widely used in various fields for the rapid detection of trace-level molecular targets. In this study, we have developed a simple and effective solution-based SERS protocol to improve the activity for the detection of cationic dye molecules in aquaculture. The polystyrene sulfonate functionalized gold nanobipyramids (PSS-Au BPs) were synthesized from the cetyltrimethylammonium bromide (CTAB) reaction system followed by the ligand exchange process. The halide ions-induced aggregation of PSS-Au BPs was carried out by using four type of different salts such as NaCl, NaBr, MgCl2 and MgSO4 to investigate their influence on the SERS activity. The results demonstrate that the ionic strength of the solution has an important impact on the colloidal stability and SERS activity. The PSS-Au BPs show an improved SERS sensitivity at lower concentrations of the aggregating agents in solution-based SERS by detecting the crystal violet (CV) molecules with a limit of detection (LOD) to 3.28 × 10-11 M. Furthermore, to demonstrate the generality of our proposed strategy, trace amounts of three more dyes such as malachite green (MG), methylene blue (MB), and rhodamine 6G (R-6G), as well as other molecules such as thiram and bisphenol-S were also detected. This protocol not only provides a method for rapid on-site detection of trace-level molecules but can also be applied to other SERS-based analysis.

Gold mesoflower arrays with sub-10 nm intraparticle gaps for highly sensitive and repeatable surface enhanced Raman spectroscopy.

Self-assembling Au mesoflower arrays are prepared using a polymethylmethacrylate (PMMA) template on an iron substrate via a combined top-down/bottom-up nanofabrication strategy. The PMMA template with the holes around 300-500 nm in diameter is first fabricated by using polymer blend lithography on iron substrates, and the highly homogeneous Au mesoflower arrays with less than 10 nm intraparticle gaps are subsequently obtained by an in situ galvanic reaction between HAuCl4 solution and the iron substrate under optimal stirring of the solution as well as reaction time. Owing to the unique mesostructures and uniformity, Raman measurements show that the gold mesoflower arrays obtained demonstrated a strong and reproducible surface enhanced Raman scattering (SERS) enhancement on the order of ∼10(7)-10(8). The development of a SERS substrate based on the Au mesoflowers with high spatial density of hot spots, relatively low cost and facial synthesis provides a novel strategy for applications in chemical and biomolecular sensing.

Mesocrystals: syntheses in metals and applications.

Self-assembly of nanoparticles has emerged as a powerful technique to integrate nanoparticles into well-defined ensembles with collective properties that are different from those of individual nanoparticles and bulk materials with the same chemical composition. Compared with the classical ion/molecule-mediated crystal growth, particle-mediated crystallographically ordered self-assembly is considered as "non-classical crystallization" and the resultant product is termed a "mesocrystal". In this tutorial review, we begin by summarizing the progresses of this field during last decade. Secondly, we outline developments in related fields such as grain rotation and oriented attachment as well as mesocrystals. Thridly, the recent progress in the syntheses of mesocrystals particularly in metals, and the related properties are introduced. Finally, some of the current open questions are discussed.

Casted MoS2 nanostructures and their Raman properties.

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have been widely investigated for optoelectronic applications. Here, by employing the nanocasting method, molybdenum disulfide (MoS2) nanostructures, including supercrystals, nanoparticles and nanowires, are synthesized with curved features by changing the precursor concentration and template types. The Raman properties of different MoS2 nanostructures are investigated by varying the laser power under both resonant and non-resonant excitations. The defect disorder induced LA(M) mode and other silent Raman modes in planar 2D materials are clearly observed under the resonant excitation. We believe that the varying optical properties of TMDC nanostructures will greatly broaden the optoelectronic applications of 2D materials.