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.

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.

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.

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.

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.

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.

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.

Ultra-rapid and highly efficient enrichment of organic pollutants via magnetic mesoporous nanosponge for ultrasensitive nanosensors.

Currently, owing to the single-molecule-level sensitivity and highly informative spectroscopic characteristics, surface-enhanced Raman scattering (SERS) is regarded as the most direct and effective detection technique. However, SERS still faces several challenges in its practical applications, such as the complex matrix interferences, and low sensitivity to the molecules of intrinsic small cross-sections or weak affinity to the surface of metals. Here, we show an enrichment-typed sensing strategy with both excellent selectivity and ultrahigh detection sensitivity based on a powerful porous composite material, called mesoporous nanosponge. The nanosponge consists of porous ß-cyclodextrin polymers immobilized with magnetic NPs, demonstrating remarkable capability of effective and fast removal of organic micropollutants, e.g., ~90% removal efficiency within ~1 min, and an enrichment factor up to ~103. By means of this current enrichment strategy, the limit of detection for typical organic pollutants can be significantly improved by 2~3 orders of magnitude. Consequently, the current enrichment strategy is proved to be applicable in a variety of fields for portable and fast detection, such as Raman and fluorescent sensing.

Switchable Binding Energy of Ionic Compounds and Application in Customizable Ligand Exchange for Colloid Nanocrystals.

The ability to engineer the surface ligands or adsorbed molecules on colloid nanocrystals (NCs) is important for various applications, as the physical and chemical properties are strongly affected by the surface chemistry. Here, we develop a facile and generalized ionic compound-mediated ligand-exchange strategy based on density functional theory calculations, in which the ionic compounds possess switchable bonding energy when they transfer between the ionized state and the non-ionized state, hence catalyzing the ligand-exchange process. By using an organic acid as the intermediate ligand, ligands such as oleylamine, butylamine, polyvinylpyrrolidone, and poly(vinyl alcohol) can be freely exchanged on the surface of Au NCs. Benefiting from this unique ligand-exchange strategy, the ligands with strong bonding energy can be replaced by weak ones, which is hard to realize in traditional ligand-exchange processes. The ionic compound-mediated ligand exchange is further utilized to improve the catalytic properties of Au NCs, facilitate the loading of nanoparticles on substrates, and tailor the growth of colloid NCs. These results indicate that the mechanism of switchable bonding energy can be significantly expanded to manipulate the surface property and functionalization of NCs that have applications in a wide range of chemical and biomedical fields.

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.

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.

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.

Buoyant particulate strategy for few-to-single particle-based plasmonic enhanced nanosensors.

Detecting matter at a single-molecule level is the ultimate target in many branches of study. Nanosensors based on plasmonics have garnered significant interest owing to their ultrahigh sensitivity even at single-molecule level. However, currently, plasmonic-enhanced nanosensors have not achieved excellent performances in practical applications and their detection at femtomolar or attomolar concentrations remains highly challenging. Here we show a plasmonic sensing strategy, called buoyant plasmonic-particulate-based few-to-single particle-nanosensors. Large-sized floating particles combined with a slippery surface may prevent the coffee-ring effect and enhance the spatial enrichment capability of the analyte in plasmonic sensitive sites via the aggregation and lifting effect. Dimer and single particle-nanosensors demonstrate an enhanced surface-enhanced Raman spectroscopy (SERS) and a high fluorescence sensitivity with an enrichment factor up to an order of ∼104 and the limit of detection of CV molecules down to femto- or attomolar levels. The current buoyant particulate strategy can be exploited in a wide range of plasmonic enhanced sensing applications for a cost-effective, simple, fast, flexible, and portable detection.

Curved 2D WS2 nanostructures: nanocasting and silent phonon mode.

Layered two-dimensional (2D) materials and their heterostructures possess excellent optoelectronic properties due to their unique planar features. However, planar structures can only selectively support the fundamental optical modes, which is averse to fully exploit the potential of the 2D materials. Here, a novel type of tungsten disulfide (WS2) nanoparticle (NP) with a uniform size and morphology and highly ordered WS2 supercrystals (SCs) are synthesized by a nanocasting process using ordered mesoporous silica as a template. Due to the curved feature of individual nanostructures, their Raman signals show complex dependence behavior on the excitation wavelength, excitation power and temperature. Significantly, the silent phonon mode becomes Raman active due to the curvature of the interlaced WS2 layers. We believe that curved features will greatly enrich the optoelectronic applications of 2D materials.

"Burning Lamp"-like Robust Molecular Enrichment for Ultrasensitive Plasmonic Nanosensors.

Enriching and locating target analytes into specific "hot spots" are vital for ultrasensitive molecular identification and detection using plasmonic-based techniques. Inspired by mass transportation in lamp wicks, we develop an effective enrichment strategy for highly diluted analytes in which analytes and Au nanoparticles are transported via a solution microflow under the capillarity driving force of glass fiber papers to a heated region. After evaporation, a large volume of a solution containing analytes and Au nanoparticles is condensed into a very limited area, and thus, analyte molecules are effectively enriched and located into surface-enhanced Raman scattering (SERS) hot spots. Using this enrichment strategy, the sensitivity and detection limits of SERS are remarkably improved. Detection levels of crystal violet and anthracene are down to 10-16 and 10-10 M, respectively. This enrichment strategy is very robust and easy to implement, and it can potentially be exploited in various plasmonic-based molecular detection and identification techniques.

Mesoporous gold nanoparticles for photothermal controlled anticancer drug delivery.

Aim: To realize the transit and release of cancer drug exactly as well as high drug loading ratio, we reported a biocompatible and temperature responsive controlled drug delivery system based on 3D mesoporous structured Au networks. Materials & methods: Here, we filled the hollow interiors of Au networks with a phase-change material so that the drug release was easily regulated by controlling the temperature only. Results: Thanks to the high near-infrared reflectance absorbance and mesoporous structure, the Au-PEG + lauric acid/doxorubicin system showed a strong photothermal conversion efficiency, high drug-loading ratio (54.2% for doxorubicin) and controlled drug release. Conclusion: This system revealed great advantages in photothermal therapy and chemotherapy, offering an obvious synergistic effect in cancer treatment.

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.

[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.