4-mercaptobenzoic Acid Research Articles

Construction and Application of Au NRs/4-MBA/PAM Ratiometric Surface-Enhanced Raman Scattering Substrate for Fish Veterinary Drug Residue Detection

Surface-enhanced Raman scattering (SERS) is widely used for trace detection of substances, and the key to this technology lies in the preparation of the substrate material. In this study, a composite SERS material of Au NRs/4-MBA/PAM was constructed and characterized to better immobilize the reference molecule 4-mercaptobenzoic acid (4-MBA). Electron transmission microscopy results demonstrated that the PAM film helps Au NRs to pack closely, enhancing the stability of the material structure and reducing the interference of external environmental factors on the response of 4-MBA, thus improving the accuracy of quantitative determination. Comparative experimental results with the Au NRs/4-MBA substrate showed that the relative standard deviations (RSDs) of the detection results for MG on different batches of Au NRs/4-MBA/PAM were less than 8.0%, and the RSDs of different points on the same material were less than 10.0%, indicating that the Au NRs/4-MBA/PAM has higher uniformity, better reproducibility, and higher sensitivity in detecting malachite green (MG). Applying this material in the recovery determination of fish extract showed that the recovery rates of MG were between 75.60% and 83.24%. Therefore, the Au NRs/4-MBA/PAM substrate can accurately detect and quantify veterinary drug residue in complex matrices such as food tissue.

Long Stability of Atomically Precise Red Emissive Copper Nanoclusters within the Gel and Their Use As a Potential Catalyst and Fluorescent Ink.

Herein, an amphiphile-based hydrogel (with 5% DMF) containing natural amino acid residue has been used to prepare and stabilize red-emitting CuNCs for several months. Though different methods have been attempted, amphiphile and 4-mercaptobenzoic acid (4-MBA)-containing hydrogels are pinpointed to be the base medium to stabilize this new Cu-cluster. From a MALDI-TOF MS analysis it was found that it is a Cu8-atom cluster stabilized by three 4-MBA ligands. Copper acetate monohydrate (Cu(CH3COO)2·H2O) has been used as a copper precursor, and l-ascorbic acid has been used as a reducing agent. FEG-TEM analysis shows that the Cu cluster has an average size of 2.83 nm. Interestingly, these clusters can be used as a fluorescent ink with a visibility of the solid state under a UV-lamp with an excitation of 365 nm. This envisaged applying these CuNCs for anticounterfeiting. These Cu-clusters show an excitation of 420 nm with an emission of 620 nm, as is evident from the fluorescence spectroscopic analysis. Based on our knowledge, this is the first example of making and consequently stabilizing Cu-clusters using hydrogel as a template for a few months. Moreover, these CuNCs can also be used as a catalyst for the reduction of nitro derivatives to their amine derivatives in aqueous medium.

An easily fabricated nanoporous Au membrane in drug detection with reusable functionality and high SERS performance.

Amethod for detecting methamphetamine (MET), ketamine (KET), and morphine (MOP) molecules is presentedusing a reusable substrate based on SERS. The SERS substrate was prepared by etching the Au/Ag alloy film to synthesize a nanoporous Au membrane (AuNPM). By optimizing the preparation conditions and using rhodamine 6G (R6G) as an analyte, the AuNPM exhibited good SERS performance with a limit of detection (LOD) of 10-9mol L-1. A competitive immunoassay category has been applied to the detection of MET, KET, and MOP. The MET, KET, and MOP antigens were functionalized on the surface of theAuNPM to specifically bind to the related drug antibodies. The Au nanoparticles (AuNPs) modified with 4-mercaptobenzoic acid (4-MBA) and antibodies against MET, KET, and MOP were used as nanotags. The 4-MBA served as the reporting molecule and drug antibodies were used to bind to free drug molecules in the target solution. The mixture of nanotags and target solution was dropped onto the antigen-modified AuNPM (antigen/AuNPM), and the free nanotags bind to the antigen/AuNPM. By comparing the SERS intensity of 4-MBA with the presence or absence of drug molecules, the drugs were qualitatively and quantitatively identified. Through this category, the LODs for detecting MET, KET, and MOP were 0.1, 1, and 1ngmL-1, respectively. This study proposes an effective method for constructing SERS-based detection of drug molecules with good potential for practical applications.

Unravelling structural insights into ligand-induced photoluminescence mechanisms of sulfur dots.

Sulfur dots (S-QDs) hold promise as a new category of metal-free, luminescent nanomaterials, yet their practical application faces challenges primarily due to a limited understanding of their structure and its impact on their optical properties. Herein, by employing a spectrum of aliphatic and aromatic ligands, we identify the surface structure and composition of S-QDs while delineating the pivotal role of ligands in inducing photoluminescence. Thiol-functionalized ligands, such as 4-mercapto benzoic acid and glutathione, notably promote the formation of both green and blue luminescent S-QDs, boosting a high quantum yield of up to 56%. Further investigation on the synthesis of S-QDs with 4-mercapto benzoic acid unveils the dual role of H2O2: etching sulfur powder and oxidizing the -SH group to -SO2H. These oxidized ligands passivate the S-QD surface through hydrogen bonding. Electrospray ionization mass spectrometry analysis unveils the presence of distinct sulfur species such as [S4(C6H5SO2H)4(H2O)2H]+ and [S6(C6H5SO2H)6(H2O)3H]+, while XPS analysis confirms the existence of zerovalent sulfur and oxidized sulfur species including SO32- and SO42-. Further detailed spectroscopic examination demonstrates that S-QDs predominantly exist as aggregated entities, with the emission wavelength correlating with the degree of aggregation. The absence of photoluminescence in aggregations devoid of ligands underscores the critical role of ligands in the photoluminescence genesis of S-QDs.

Au25 Cluster-Based Atomically Precise Coordination Frameworks and Emission Engineering through Lattice Symmetry.

The atomically precise metal nanoclusters (NCs) have attracted significant attention due to their superatomic behavior originating from the quantum confinement effect. This behavior makes these materials suitable for various photoluminescence-based applications, including chemical sensing, bioimaging, and phototherapy, owing to their intriguing optical properties. Especially, the manipulation of inter- or intracluster interaction through cluster-assembled materials (CAMs) presents significant pathways for modifying the photophysical properties of NCs. Herein, two distinct CAMs, Au25-Zn-Hex and Au25-Zn-Rod, were synthesized via forming a coordination bond between [Au25(p-HMBA)18]- (p-H2MBA = 4-mercaptobenzoic acid) and Zn2+. Au25-Zn-Rod exhibited a 6-fold higher luminescence intensity in the near-infrared region compared to Au25-Zn-Hex, attributed to synergistic inter- and intracluster interactions that induce exciton delocalization and structure rigidification at the atomic scale. This study highlights the potential of diverse lattice symmetries in cluster-based frameworks for tuning the photophysical properties, contributing to a deeper understanding of the structure-property relationship in Au NCs.

Au-modified metal-organic framework photonic heterostructure as a SERS sensor for enrichment and detection of trace organic dyes and pesticides

Surface enhanced Raman scattering (SERS) sensors with excellent sensitivity, stability and repeatability are essential for the ultrasensitive analysis of trace targets. In this study, a SERS sensor was developed using a photonic heterostructure composed of Au nanoparticles (AuNPs) & Zeolitic Imidazolate Framework-8 photonic crystals (ZIF-8 PCs). The sensor aims to enrich and detect organic dyes and pesticides, with enhanced detection capabilities achieved through adjustments in AuNPs content and the band-edge effects of ZIF-8 PCs. The sensor exhibited excellent performances in detecting 4-mercaptobenzoic acid. The detection limit was 1 × 10–12 mol·L−1, with a relative standard deviation of 5.0 % and the enhancement factor of 1.439 × 1011. Furthermore, the self-enrichment function of the sensor was verified through molecular dynamics simulations. This validation enabled the SERS sensor to be effectively utilized for the analysis of Rhodamine 6 G (R6G), methylene blue (MB), Thiabendazole (TBZ) and Parathion-methyl (PTM) without complex pretreatment. The detection limits achieved were 1 × 10–12 for R6G and MB, and 1 × 10–11 mol·L−1 for TBZ and PTM, respectively. This study presented an effective strategy for constructing high-performance SERS sensors, elucidated the mechanism of analyte enrichment and achieved the detection of samples in natural lake water, which offers a new option for on-site monitoring of contaminants with a portable Raman spectroscopy.

Parallel Plate Capacitor Model at the Nanoscale for Stable and Gigantic SERS Activity of the 4-MBA@R-AuNP-4-MBA@R-AuNP System.

Selective use of ingredients out of a specific natural product (e.g., fruit, leaf, flower, or honey extract) or their mixture (e.g., bacteria, viruses, fungi, plants, etc.) by smart manipulation of precursors and reaction conditions to synthesize nanoparticles can provide us a low-cost, environmentally friendly route for their industrial-scale production. The presence of more than one active ligand (sourced natural product extract) on the surface not only makes them the most stable (electrostatically) and monodispersed (controlled kinetics) but also devoid of any external ligand-assisted aggregation. This empowered us to modify the surface of the nanoparticles in a monolayered fashion or to couple between nanoparticles through a ligand-assisted chemical coupling pathway to avoid their aggregation and hence to keep their nanoscale property intact. A metal-to-ligand charge transfer (MLCT) trajectory combined with electromagnetic field-induced coherent capacitive coupling between two nanoparticles was introduced to explain the gigantic Raman enhancement observed from these nanoparticles. As a model system, we have synthesized the nanoparticles from rose extract as the active ligand ingredient source for 2-phenyl ethanol, linalool, citronellol, nerol, geraniol, pyrogallol (C6H3(OH)3), and quercetin (3,3',4',5,7-pentahydroxyflavone) and the surface of the synthesized nanoparticles has been modified by 4-mercaptobenzoic acid (4-MBA) acting as a Raman tag. The obtained structural and spectroscopic data correlate well between our numerical and density functional theory (DFT)-based calculations to justify their gigantic SERS activity, which may lead us to propose an unexplored coherent capacitive coupling-based Raman enhancement mechanism.

Exploring the charge transfer enhancement mechanism in selective SERS detection with Mo1−xWxS2@Ag2S nanosheets

In order to solve the problem of poor sensitivity and selectivity of conventional SERS substrates, we synthesized Mo1−xWxS2@Ag2S nanosheets in this paper by a two-step hydrothermal method. The structure and morphology of the synthesized Mo1−xWxS2@Ag2S nanosheets were characterized by XRD and SEM,respectively. The results show that the Mo1−xWxS2@Ag2S nanosheet has an irregular layered structure. Further, the SERS properties of Mo1−xWxS2@Ag2S nanosheets were tested by using rhodamine 6G (R6G), crystalline violet (CV), and 4-mercaptobenzoic acid (4-MBA) as probe molecules, respectively. The test results demonstrated that the nanosheets were specific to R6G and CV probe molecules, and the mechanism of selectivity was due to CT enhancement. In addition, Mo1−xWxS2@Ag2S exhibits ultrahigh sensitivity in R6G and CV, with the corresponding detection limit of both reached 10−8 M. And linear fitting of the peak intensities was carried out, with the R2 coefficient of 0.981 and 0.951, respectively. Finally, the relative standard deviations (RSDs) of this Mo1-xWxS2@Ag2S nanosheets was obtained to be 8.56 % by test 1 × 10−4 M R6G at the characteristic peak 613 cm−1, which represents excellent detection repeatability. The Mo1−xWxS2@Ag2S nanosheets are rich in edge-active sites favorable for charge transfer, which can enhance the SERS signals of the target molecules better. Besides, the Raman detection of the surface of Mo1−xWxS2@Ag2S nanosheets using nitrofurantoin (NFT) also reached a detection limit of 10−8 M. Mo1−xWxS2@Ag2S nanosheets substrates can find applications in medicine and provide new strategies for improving the SERS performance.

Geometric and Electronic Structure Modulation to Optimize the Charge Transfer of TiO2 for Ultrasensitive and Stable SERS Sensing.

Exploring the relationship between semiconductor structure and surface-enhanced Raman scattering (SERS) activity was essential for the development of ultrasensitive SERS substrates. Herein, we report an ytterbium atomic doping strategy to render TiO2 (Yb-TiO2) highly SERS sensitive superior to pure TiO2, with a detection limit as low as 1 × 10-9 M for 4-mercaptobenzoic acid. First-principles density functional theory calculations reveal that ytterbium doping leads to high electrostatic properties, allowing for significant charge transfer from molecules to semiconductors. Theoretical and experimental results indicate that Yb-TiO2 has a smaller band gap and higher density of states, which effectively enhance charge transfer between molecules and substrates, resulting in significant SERS activity. More importantly, Yb-TiO2 was particularly stable in air and acid solution and can be used for trace molecule detection in extreme environments. We demonstrate a promising approach to construct ultrasensitive SERS by optimizing the electronic structure induced by geometric structures.

Efficiently shape-selective synthesis of single crystal silver nanocube with the combination of HNO3/NaCl and reaction time for developing surface enhanced Raman scattering (SERS) substrate

Shape control of noble nanomaterials has garnered significant attention in the past decade because niche applications rely on the relationship between the nanoparticle morphology and optical properties. Although many chemical methods have been reported, there is still a need for improvement in terms of uniformity, yields, and synthesis scale. This work exploited the novel modification approach based on the polyol method to control synthesis to obtain a high amount of single-crystal silver nanocubes (AgNCs) with relatively homogeneous sizes and edge lengths of approximately 100 nm. Furthermore, we have discovered the high effectiveness of controlling temperature conditions to examine the conversion from silver nanocubes to tetrahedron nanoparticles, which had been rarely studied before. These as-prepared AgNCs colloidal solutions were further used to develop the SERS substrate on the glass slide through the facile drop cast method. Additionally, through synthesis using ethylene glycol and redispersed in the ethanol solvent, the obtained AgNCs have a high probability coverage on the glass slide once natural evaporation technique to achieve a remarkable amplification effect and reproducibility behavior. It was explored that these substrates could significantly enhance the Raman signal of 4-mercaptobenzoic acid (4-MBA), which is utilized as the probe molecule to assess the SERS behaviors. The enhancement factor (EF) of the SERS substrates prepared using AgNCs was approximately 3.6 × 106. The presence of 4-MBA could be detected with AgNCs in concentrations ranging from 0.01 to 10 mM, with a limit of detection (LOD) of 8.40 μM and a limit of quantification (LOQ) of 25.46 μM. Through analyzing over 20 different spots on various AgNC substrates, synthesized with similar methods and conditions, the Raman signals of 4-MBA were almost unchanged, with a relative standard deviation (RSD) value of 5.81%, indicating that the SERS signal produced by AgNC substrates was highly reproducible. Based on the results, the SERS nanosubstrates developed with AgNCs could potentially be used to detect trace amounts of other harmful organic compounds.

Flexible plasmonic microneedle array-based SERS sensor for pH monitoring of skin interstitial fluid

Interstitial fluid (ISF) is a prevalent accessible and information-rich biofluid, and monitoring pH level of interstitial fluid plays a crucial role in the physiological health assessment. However, facile extraction of ISF and sensitive detection of pH is still a great challenge. Herein, a flexible plasmonic microneedle array (PMNA)-based SERS sensor was developed for facile and sensitive pH monitoring of skin ISF. The flexible microneedle arrays were fabricated by norland optical adhesive 65 (NOA65), and coated with pH-sensitive 4-Mercaptobenzoic acid (4-MBA)-labeled silver nanoparticles (Ag NPs) by electrostatic assembly. The proposed flexible PMNA-based SERS sensor has a good linear response in the pH range of 5 to 9 which covers the normal pH level in skin interstitial fluid. The ISF extracted from porcine skin was chosen as the test model, and the pH levels detected by the PMNA-based SERS sensors were well consistent with the theoretical results. Besides, the proposed flexible SERS sensors show good mechanical robustness, sensing stability, and biocompatibility before and after skin insertion, which can be a potential analytical tool for practical detection of pH levels in ISF and provide technical support for SERS-based wearable biosensing.

Development of Fe3O4/DEX/PDA@Au(Raman reporters)@Au-MPBA nanocomposites based multi-hotspot SERS probe for ultrasensitive, reliable, and quantitative detection of glucose in sweat

Glucose is a key biomarker of diabetes, and effective glucose monitoring methods are crucial to the prevention and management of diabetes. Therefore, in this paper, Fe3O4/DEX/PDA@Au (Raman reporters) @Au nanocomposites were synthetized that with DTNB (5,5′-dithiobis(2-nitrobenzoic)), MMTA (2-mercapto-4-methyl-5-thiazole acetic acid), MBA (4-mercaptobenzoic acid) and 4-Mpy(4-Mercaptopyridine) were used separately as Raman reporters. Fe3O4 and PDA (Polymerized dopamine) could supply more high surface area of active sites and high SERS (Surface-Enhanced Raman Scattering) substrate, which has high stability and reproducibility. Dextran coating is an effective way to prepare biocompatible materials TEM, XRD, TG and VSM were used to analyze the size, morphology and magnetic properties of the nanocomposites. Fe3O4/DEX/PDA@Au(Raman reporters)@Au that integrates a multi-hotspot structure and magnetic separation techniques were studied the enhancement effect of Raman spectra, and glucose solutions with different concentrations were tested. Furthermore, the optimal Fe3O4/DEX/PDA@Au(Raman reporters)@Au nanocomposites were supplied as SERS substrates for detection of glucose accurately and quickly in sweat. SERS signal intensity is linearly correlated with glucose concentration within the measurement range of 5 × 10-3 to 10 mM, and the minimum detectable concentration is 5 µM. The Fe3O4/DEX/PDA@Au(Raman reporters)@Au nanocomposites exhibit high reliability, specificity and repeatability of the strategy were then verified by practical detection of sweat.

Developing an off-on fluorescence sensor based on red copper nanoclusters wrapped by sulfhydryl and polymer double ligands for sensitive detection of N-acetyl-L-cysteine

N-acetyl-L-cysteine (NAC) as a class of thiols is commonly used in the treatment of lung diseases, detoxification and prevention of liver damage. In this paper, 4-mercaptobenzoic acid (4-MBA) coated and polyvinylpyrrolidone (PVP) attached copper nanoclusters (4-MBA@PVP-CuNCs) were successfully synthesized using a simple one-pot method with an absolute quantum yield of 10.98 %, and its synthetic conditions (like effects of single/double ligands and temperature) were studied intensively. Then Hg2+ could quench the fluorescence of the 4-MBA@PVP-CuNCs and its fluorescence was restored with the addition of NAC. Based on the above principles, an off–on switching system was established to detect NAC. That is, the 4-MBA@PVP-CuNCs-Hg probe was prepared by adding Hg2+ to switch off the fluorescence of the CuNCs by static quenching, and then NAC was added to switch on the fluorescence of the probe based on the chelation of NAC and Hg2+. Moreover, the effects of metal ion types and mercury ion doses for the probe construction were also further discussed. The method showed excellent linearity in the range of 0.05–1.25 µM and low detection limit of 16 nM. Meanwhile, good recoveries in real urine, tablets and pellets were observed, which proved the reliability of the method and provided a convenient, fast and sensitive method for NAC detection.

Optimizing the SERS activity of PS@Ag/Au chips for quantitative analysis of carcinoembryonic antigen

Tumor markers play an important role in the diagnosis, treatment, and monitoring of tumors. Carcinoembryonic antigen (CEA) is a breast and rectal cancer biomarker that plays a crucial role in the early detection of cancer. Therefore, designing a suitable and ultrasensitive method for CEA analysis is very important. In this study, we demonstrated the high surface-enhanced Raman scattering (SERS) performance, high reproducibility, and good biocompatibility of a polystyrene (PS)@Ag/Au chip. This chip was produced layer-by-layer by magnetron sputtering to generate abundant “hotspots” between the Ag and Au layers covering the PS microspheres. Interestingly, the thickness of the Au layer was easily controlled to the appropriate value. When 4-mercaptobenzoic acid (MBA) was used as a probe molecule to explore the SERS activity of the chip, the enhancement factor (EF) reached 1.12×108, with a relative standard deviation of 3.059 %. A chip labeled with 5,5’-dithiobis(succinimidyl-2-nitrobenzoic acid) (DSNB) was used for CEA immunological recognition. With a linear range of 0–10,000 ng/mL, the limit of detection (LOD) was 0.0229 ng/mL. The standard recovery of CEA in fetal bovine serum (FBS) was between 84.90 % and 103.1 %. This chip is expected to be a novel tool in the field of cancer detection.

TiO2 nanofilms for surface-enhanced Raman scattering analysis of urea

In this study, titanium dioxide (TiO2) nanofilms with nanoparticle structure were grown in situ on metallic aluminum (Al) sheets using a simple sol-hydrothermal method. Al sheets were chosen because they can form Schottky junctions with TiO2 during the calcination process, thus achieving a tight bonding between the nanoparticles and the solid substrate, which cannot be achieved with conventional glass substrates. The substrates synthesized with different contents of titanium butoxide [Ti(OBu)4] were investigated using 4-mercaptobenzoic acid as a probe molecule, and the results showed that the substrate with 9 % of the total volume of Ti(OBu)4 had the highest surface-enhanced Raman scattering (SERS) performance. As a low-cost SERS substrate that is simple to synthesize, it has excellent signal reproducibility, with a relative standard deviation of 4.51 % for the same substrate and 6.43 % for different batches of synthesized substrates. Meanwhile, the same batch of substrate can be stored at room temperature for at least 20 weeks and still maintain stable SERS signals. In addition, the synthetic substrate was used to quantitatively detect urea with a detection limit of 4.23 × 10−3 mol/L, which is comparable to the application of noble metal substrates. The feasibility of this method was verified in human urine, and the results were consistent with the clinical results, indicating that this method has great potential for clinical application.

A novel three-dimensional porous Ag/TiO2 hybrid aerogels with high dense hot spot as effective SERS substrate for ultrasensitive detection

This research focuses on preparing a series of new TiO2/Ag hybrid aerogels with varying TiO2 contents, and demonstrates their application as ultrasensitive SERS substrates. The synthesized TiO2/Ag hybrid aerogels exhibited excellent SERS behavior when detecting 4-Mercaptobenzoic acid (4-MBA), and the calculated SERS enhancement factor (EF) was 6.34 × 106. 3D structured aerogels can create more hot spots and adsorption sites, and multiple interband chemical transfer (CT) pathways emerged and enhanced CT efficiency because of the large number of surface oxygen vacancies of meso-TiO2 NPs. Therefore, the synergy of electromagnetic field enhancement and chemical enhancement leads to SERS enhancement. In addition, the composite SERS substrate has high sensitivity, and the detection limit of adsorbed 4-MBA probe molecules reaches 10-11 M. Furthermore, the TiO2/Ag hybrid aerogels demonstrate good reproducibility with minimal standard deviation in terms of SERS signals. In addition, even after standing for 6 months, there is almost no attenuation in the SERS signal intensity, which highlights the excellent stability of this substrate. Therefore, these highly sensitive TiO2/Ag hybrid aerogels SERS substrates have important practical value in environmental monitoring, medical inspection and food supervision.

Single Crystal to Single Crystal Transformation of Porous Materials Based on Zinc Nodes and Mercaptobenzoic Acid.

Porous coordination polymers (PCPs) are an excellent class of porous crystalline materials with tunable properties and intriguing potential applications spanning multiple disciplines. In this work, we report the synthesis and characterization of a PCP (HI-103) based on 4,4'-dithiodibenzoic acid ligand and zinc nitrate with two DMF molecules residing in the porous network. The stability of the porous network was analyzed by heating the compound at 60.0 °C for two days, and the structural analysis revealed a new PCP (HI-104) was formed with one of the DMF molecules, indicating a single-crystal to single-crystal (SCSC) transformation. The solvent molecules were completely removed by extensive drying (HI-103-dry), and the integrity of the porous network was verified by powder X-ray diffraction (PXRD) and thermogravimetric analysis. The reversibility of SCSC transformation was confirmed by treating HI-103-dry with DMF molecules, resulting in HI-103 after five days. The adsorption studies of HI-103-dry with other solvents revealed that SCSC transformation was not observed for DMA and DEA, but some structural changes were observed in the presence of DMSO. The adsorption studies performed in the presence of an equimolar mixture of DMF, DMA, and DMA indicated that HI-103-dry could selectively adsorb DMF molecules from the analogous mixture.

Facile modification method for the controlled synthesis of dumbbell-like gold nanoparticles (AuNDBs) for application in detecting glucose using the SERS method

Dumbbell-like nanoparticles, previously known for their excellent light absorption and dispersion, have diverse applications, especially in SERS. Herein, we have explored a fast and novel controlled synthesis approach to achieve a high formation of AuNDBs. Precise control of precursor amounts and seed addition order halted seed growth at the AuNDB formation stage, preventing further elongation into rod-like structures. The AuNDBs were functionalized with 4-mercaptobenzoic acid (4-MBA) to create SERS nanosubstrates and deposited on the glass slide through 3-mercaptopropyl (dimethoxy)methylsilane by the spin-coating technique. The detection of d-glucose was achieved by measuring the signal decrease of the 4-MBA Raman probe molecules on the nanosubstrates at different trace concentrations of the analyte. These novel SERS substrates have the potential to provide an enhancement factor (EF) of 2.41 × 107 and a limit of detection (LOD) as low as 1.17 nmol/L. The electromagnetic field distribution of AuNDBs with many arrangements surrounded by air and d-glucose solutions was also determined by using the finite-difference time-domain technique (FDTD). The FDTD results confirmed that d-glucose on the SERS substrates caused the local electromagnetic field to degrade, resulting in the degree of the Raman signal. Our findings suggest that dumbbell-shaped SERS substrates can effectively detect very low levels of glucose, making them ideal for designing novel anisotropic nanoparticle-functionalized surfaces with ease.

Development of tri-mode lateral flow immunoassay based on tailored porous gold nanoflower for sensitive detection of aflatoxin B1

Aflatoxin B1 (AFB1) is regarded as the most toxic mycotoxin and a proven human carcinogen. The development of detection assays for AFB1 is important for human health and environmental protection. In this study, the hollow porous gold nanoflower (HPGN) was synthesized to achieve colorimetric and photothermal performance. Especially, the HPGN exhibited excellent surface-enhanced Raman scattering (SERS) performance by loading with 4-mercaptobenzoic acid (4-MBA), thus SERS determination of AFB1 could be achieved. Compared with gold nanoparticles (AuNPs), the HPGN possessed unique morphology and excellent properties, providing the basis for sensitive and selective AFB1 detection. Under the optimized experimental conditions, the limits of detection (LODs) of lateral flow immunoassay (LFIA) for AFB1 through colorimetric, photothermal and SERS modes were 0.09 ng/mL, 0.09 ng/mL and 0.05 ng/mL, respectively. The tri-mode detection strategy provided a novel concept for immunosensing of mycotoxins or other small molecules.

Magnesium Nanoparticles for Surface-Enhanced Raman Scattering and Plasmon-Driven Catalysis.

Nanostructures of some metals can sustain localized surface plasmon resonances, collective oscillations of free electrons excited by incident light. This effect results in wavelength-dependent absorption and scattering, enhancement of the incident electric field at the metal surface, and generation of hot carriers as a decay product. The enhanced electric field can be utilized to amplify the spectroscopic signal in surface-enhanced Raman scattering (SERS), while hot carriers can be exploited for catalytic applications. In recent years, cheaper and more earth abundant alternatives to traditional plasmonic Au and Ag have gained growing attention. Here, we demonstrate the ability of plasmonic Mg nanoparticles to enhance Raman scattering and drive chemical transformations upon laser irradiation. The plasmonic properties of Mg nanoparticles are characterized at the bulk and single particle level by optical spectroscopy and scanning transmission electron microscopy coupled with electron energy-loss spectroscopy and supported by numerical simulations. SERS enhancement factors of ∼102 at 532 and 633 nm are obtained using 4-mercaptobenzoic acid and 4-nitrobenzenethiol. Furthermore, the reductive coupling of 4-nitrobenzenethiol to 4,4'-dimercaptoazobenzene is observed on the surface of Mg nanoparticles under 532 nm excitation in the absence of reducing agents, indicating a plasmon-driven catalytic process. Once decorated with Pd, Mg nanostructures display an enhancement factor of 103 along with an increase in the rate of catalytic coupling. The results of this study demonstrate the successful application of plasmonic Mg nanoparticles in sensing and plasmon-enhanced catalysis.