SERS Performance Research Articles

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.

Constructing recyclable SERS platform based on peroxidase-like Cu2O/g-C3N4/Ag composites for sensitive sensing of fungicides

In this work, we proposed a straightforward self-assembly and in-situ deposition protocol to construct Cu2O/g-C3N4/Ag composites, which demonstrated peroxidase-like attribute and exceptional SERS activity. These composites proved to be an effective SERS analysis tool for detecting organic fungicides like malachite green (MG) and crystal violet (CV). Remarkably, they achieved detection limits as low as 10−9 M in DI water as well as fish pond water, and exhibited a strong linear correlation between logarithmic concentrations and SERS intensities (R2 ≥ 0.97). Beyond that, with the aid of hydrogen peroxide (H2O2), the peroxidase-like Cu2O/g-C3N4/Ag composites rapidly degraded MG and CV molecules within just 5 min. Furthermore, their practical reusability based on the peroxidase-like reaction was proved by high SERS performance across 5 detection cycles. These results emphasize the immense potential of Cu2O/g-C3N4/Ag in SERS-based trace fungicide detection and suggest future applications in ecological restoration through peroxidase-like reactions.

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.

Fabrication of TiN–Ag@Ag Composite Substrate with SERS Performance and Application in Ibuprofen Detection

Fabrication of TiN–Ag@Ag Composite Substrate with SERS Performance and Application in Ibuprofen Detection

Enhanced SERS performance of cavity-hosting silver dendrites grown over TiO2 nanotubes

Silver nanostructures, utilized as SERS substrates, consistently exhibit exceptional performance in detecting organic compounds through Raman spectroscopy, primarily due to the electromagnetic enhancement mechanism. This study explores an advanced SERS substrate composed of cavities formed by silver dendrites (Ag-Ds) on TiO2 nanotubes (TiO2-NT), demonstrating exceptional performance in detecting organic compounds through Raman spectroscopy. TiO2-NT acts as a template, guiding the nucleation and growth of Ag-D to create the cavity structures. The deposition time of silver significantly influences substrate performance in detecting Rhodamine 6G (R6G) and Ibuprofen (IB). It has been observed that an extended deposition time diminishes the enhancement factor. In contrast, a shorter deposition time yields notable enhancement due to the combined effects of electromagnetic and chemical enhancement mechanisms. An optimum deposition time limits dendrite growth, forming cavities where the electric field couples with multiple light reflections, further amplifying the SERS enhancement. The cavity-hosted Ag-D/TiO2-NT substrate achieves an impressive analytic SERS enhancement factor of up to 2 × 109, enabling the detection of R6G and IB at a low detection limit of 10-12 M.

Controlling the growth mode of Au depositing on Au nanobipyramids via ligand coverage for SERS enhancement

Gold deposition on Au nanoparticles is a common method to control the shape and further modify the properties of nanoparticles as their properties have a strong correlation with their nanostructures. For Au nanobipyramid (Au NBP), it has advantages such as the enhancement of electric field and a higher tunability in plasmon wavelength than the Au nanorod and thus owns a greater potential in shape control. In this paper, we demonstrate a scheme of depositing Au on the surface of Au NBP with the presence of a type of ligand 2-mercaptobenzoimidazole-5-carboxylic acid (MBIA) to synthesize Au NBP@Au dimers. The growth mode of Au depositing on Au NBP can be controlled by the coverage of MBIA. As the coverage is low, with a concentration of MBIA below 0.4 mM, the rough core–shell nanostructure is synthesized; However, as the coverage is high, with a concentration of MBIA over 0.8 mM, gold deposition may form islands on the surface of Au NBP. The SERS performance of Au depositing on Au NBP can also be enhanced by growth mode. For the rough-surface core–shell growth mode, the enhancement is more significant as the EF is improved from 3.5 × 105 to 1.06 × 106 than the islands-growing growth mode due to the coupling between core and shell. And our results show that with multiple types of nanosturctures easy to obtained by changing modified ligand coverage, the controlled growth has a great potential in the dimer design and SERS enhancement using Au NBP.

MoⅣ boosted carrier density of MoO3-X for surface-enhanced Raman spectroscopy

Molybdenum oxides (MoO3-X) with the same surface plasmon resonance (SPR) effect as Au/Ag, and occupies an irreplaceable value in SERS detections. MoO3-X SERS substrates with oxygen-rich defects tend to show better SERS performance, but the preparation and characterization of tunable O defects remain challenging. It cannot be ignored that the oxidation state of metal cations is also influenced by O defects. Here, a series of MoO3-X SERS sensors with regulable Mo valence state were fabricated using magnetron sputtering technology. By changing the Mo sputtering power and the O2/Ar2 ratio, the Mo/O element ratio of the substrate can be easily regulated to readjust the O defects. The X-ray Photoelectron Spectroscopy (XPS) and Raman spectra were performed to investigate the change and related relationship between Mo mixed valence state and SERS sensitivity. The abundant incompletely coordinated electrons produced by low valence MoⅣ act as free carriers, increasing the free carrier density of MoO3-X substrates, which is beneficial for the SERS effect. It has also been proven by Hall effect measurement. The SERS measurement shows that the enhancement factor (EF) reached 3.70 × 105, which is exceedingly close to Au/Ag. The MoO2.5 substrate also exhibited a repeatable and consistent response, high stability, and repeatability, which proves the splendid application potential in complex environments.

Enhanced SERS performance of Ag nanoparticles using hybrid dewetting process for melamine detection

A thermal evaporation system was used to deposit Ag thin films on glass substrates. The films were dewetted using both a regular laser irradiation approach and a hybrid dewetting process that involved laser irradiation followed by Ag thermal deposition. The study would evaluate and compare the optical characteristics and efficiency in melamine detection within these dewetted films. In the traditional dewetting process, as the laser power increased from 15 to 25 W, the nanoparticles (NPs) size decreased from 162 to 125 nm. Furthermore, an evident optical absorption peak range of 540–600 nm was also observed. Through the hybrid dewetting process, a mixture of small NPs (20 nm) and larger NPs (142–167 nm) were formed. It resulted in two distinct Surface Plasmon Resonance (SPR) peaks at 460 nm and 660 nm, respectively. Notably, a strong Raman peak at 701 cm−1 emerged when a melamine aqueous solution was placed on the hybrid dewetted surface. Comparing the two methods, the hybrid dewetted sample exhibited enhanced fingerprint peak intensity and a higher analytical enhancement factor (AEF). When operating at laser power of 25 W and a scanning speed of 100 mm/s, the maximum AEF value reached 1.9 × 105. The limit of detection for melamine solution in the hybrid dewetted sample was established at 10−7 M. Hence, the hybrid dewetting process is a potential method to produce the mixed-sized nanoparticles for diverse applications.

Shell thickness-dependent Au@Ag nanoparticles for surface-enhanced Raman scattering detection of pollutants

A series of Au@Ag core–shell nanocomposites with varying Ag shell thickness were prepared as potential SERS substrates via chemical reduction method. Rhodamine 6G, crystal violet, and thiram were selected as probes for SERS substrate optimization and sensitivity testing of nanocomposites. According to the results, the Au surface was uniformly coated with a ∼3–12 nm thick Ag layer, exhibiting the even particle size distribution. The above nanocomposites demonstrated an extremely high detection limit for Rhodamine 6G (up to 10−11 M) within a sensitivity range of 10−5 to 10−11 M. At the same time, the detection limits for crystal violet and thiram were 10−10 M and 10−9 M, respectively. Moreover, the SERS performance remained basically unchanged after 30-day storage, indicating good stability and uniformity of Au@Ag substrates. Thus, the proposed Au@Ag nanocomposites have a great application potential for the detection of low-concentration pollutants in the environment along with the prolonged in-use stability.

Selenium-Doped Seeded Growth of Truncated Octahedral Gold Nanocrystals with Surface Concavities for Surface-Enhanced Raman Spectroscopy.

Concave nanocrystals stand out as a testament to the importance of the nanoscale morphology in dictating the functional properties of materials. In this report, we introduce a facile synthesis method for producing gold (Au) nanocrystals with a truncated octahedral morphology that features surface concavities (Au CNTOs). The incorporation of selenium (Se) doping into the truncated octahedral Au seeds was essential for their enlargement and the formation of concave structures. By simply adjusting the quantity of seeds, we could control the size of the nanocrystals while maintaining their distinctive morphology and surface concavity. The formation mechanism suggests that Se doping likely passivates the side faces, thereby slowing growth and promoting atomic deposition at the edges and corners. The resulting Se-doped Au CNTOs exhibited strong localized surface plasmon resonance (LSPR) absorptions in the visible spectrum and the SERS performance of their assemblies was demonstrated through crystal violet detection, reaching enhancement factors around 105. This study presents an innovative approach to synthesizing concave Au nanocrystals through the incorporation of selenium during a seeded growth process, offering insights into the strategic design of plasmonic nanostructures.

Construction of an efficient molecular enrichment and magnetic separation flow with Fe3O4@Ag@COF for ratiometric SERS detection of methamidophos

As a typical organophosphorus pesticide widely utilized in agricultural production with its residue as enormous threat to human health and environment, methamidophos (MTD) has gained increasing attention in recent years, so, it is necessary to develop an effective strategy to detect MTD from complex matrix. Here, an efficient molecular enrichment and magnetic separation flow was constructed through Fe3O4@Ag@COF (covalent organic framework) for ratiometric SERS detection of MTD. Specifically, Fe3O4@Ag@COF is shown to have a high-density hot-spot region and optimal SERS performance by adjusting the particle size and addition volume of Fe3O4@Ag. COF endows Fe3O4@Ag@COF with a platform for enriching MTD molecules and isolating impurities, allowing the separation of Fe3O4@Ag@COF with MTD molecules from complex matrix by magnetism. More importantly, due to its natural core–shell structure, the Raman peaks of COF can be employed as an internal standard for ratiometric SERS sensing, thereby increasing its analysis accuracy and reliability. Under the optimal extraction method and solvent conditions, the developed detection flow exhibited a wide linear range from 10-4 M to 10-9 M and a low MTD detection limit of 8.3 × 10-5 mg/kg. Furthermore, the SERS sensor had excellent reproducibility and long-term stability with a low relative standard deviation (RSD). In practical application, this detection flow was tested for quantifying trace MTD in green tea samples, with recoveries of 89.54 % to 101.89 % and RSDs below 5 % (n = 5), comparable to the performance of gas chromatography mass spectrometry (GC–MS).

SERS Detection of Trace Carcinogenic Aromatic Amines Based on Amorphous MoO3 Monolayers.

Aromatic amines are important commercial chemicals, but their carcinogenicity poses a threat to humans and other organisms, making their rapid quantitative detection increasingly urgent. Here, amorphous MoO3 (a-MoO3) monolayers with localized surface plasmon resonance (LSPR) effect in the visible region are designed for the trace detection of carcinogenic aromatic amine molecules. The hot-electron fast decay component of a-MoO3 decreases from 301 fs to 150 fs after absorption with methyl orange (MO) molecules, indicating the plasmon-induced hot-electron transfer (PIHET) process from a-MoO3 to MO. Therefore, a-MoO3 monolayers present high SERS performance due to the synergistic effect of electromagnetic enhancement (EM) and PIHET, proposing the EM-PIHET synergistic mechanism in a-MoO3. In addition, a-MoO3 possesses higher electron delocalization and electronic state density than crystal MoO3 (c-MoO3), which is conducive to the PIHET. The limit of detection (LOD) for o-aminoazotoluene (o-AAT) is 10-9 M with good uniformity, acid resistance, and thermal stability. In this work, trace detection and identification of various carcinogenic aromatic amines based on a-MoO3 monolayers is realized, which is of great significance for reducing cancer infection rates.

SERS Detection of Trace Carcinogenic Aromatic Amines Based on Amorphous MoO3 Monolayers

AbstractAromatic amines are important commercial chemicals, but their carcinogenicity poses a threat to humans and other organisms, making their rapid quantitative detection increasingly urgent. Here, amorphous MoO3 (a‐MoO3) monolayers with localized surface plasmon resonance (LSPR) effect in the visible region are designed for the trace detection of carcinogenic aromatic amine molecules. The hot‐electron fast decay component of a‐MoO3 decreases from 301 fs to 150 fs after absorption with methyl orange (MO) molecules, indicating the plasmon‐induced hot‐electron transfer (PIHET) process from a‐MoO3 to MO. Therefore, a‐MoO3 monolayers present high SERS performance due to the synergistic effect of electromagnetic enhancement (EM) and PIHET, proposing the EM‐PIHET synergistic mechanism in a‐MoO3. In addition, a‐MoO3 possesses higher electron delocalization and electronic state density than crystal MoO3 (c‐MoO3), which is conducive to the PIHET. The limit of detection (LOD) for o‐aminoazotoluene (o‐AAT) is 10−9 M with good uniformity, acid resistance, and thermal stability. In this work, trace detection and identification of various carcinogenic aromatic amines based on a‐MoO3 monolayers is realized, which is of great significance for reducing cancer infection rates.

Fast and scalable fabrication of Ag/TiO2 nanostructured substrates for enhanced plasmonic sensing and photocatalytic applications

Here we propose a fast and scalable (up to 3 min for 6 × 1 cm size substrate) innovative approach to fabricate coral-shaped TiO2 nanostructured substrates based on thermal oxidation of titanium foil followed by deposition of Ag nanoparticles for bifunctional sensing and photocatalysis. Comprehensive studies on the morphology, crystal structure, stoichiometry, optical, and electronic properties of these nanostructures reveal the formation of a Schottky barrier at the Ag/TiO2 interface. This interface alters the electronic structure of the Ag/TiO2 nanosystem, retaining the plasmonic properties of Ag nanoparticles while enhancing their catalytic activity. The SERS performance and photocatalytic activity of Ag/TiO2 nanostructures are demonstrated by the test analyte Rhodamine 6G detection down to concentrations of 10-12 M and acceleration of its degradation under simulated sunlight by 5.8 times. Tests with tetracycline water solutions indicate a nanomolar detection limit and 4.4-fold increase in degradation rate. The proposed Ag/TiO2 nanostructures are prospective for creation of low-cost bifunctional platforms for the sensitive detection of organic residues in water as well as their fast neutralization under solar light.

A novel Fe2O3@CeO2 heterojunction substrate with high surface‐enhanced Raman scattering performance

AbstractSurface‐enhanced Raman scattering (SERS) has been applied in many fields due to its advantages of fast and nondestructive detection. For semiconductors, the large‐scale electron‐hole pair separation of heterojunction is conducive to efficient charge transfer, which is a promising SERS substrate. Here, we designed a Fe2O3@CeO2 heterojunction substrate by hydrothermal method and explored its enhancement mechanism in detail. α‐Fe2O3 is a promising semiconductor with a narrow bandgap, and CeO2 has adequate oxygen vacancies on the surface. Combing α‐Fe2O3 and CeO2 into a shell‐core structure, Fe2O3@CeO2 heterojunction presents higher SERS performance than pure Fe2O3 and CeO2 for methyl orange (MO) molecule with a limit of detection (LOD) of 5 × 10−8 mol/L. Under the excitation of 514 nm, Fe2O3 can produce an effective exciton resonance due to its narrow bandgap (2.01 eV). The oxygen vacancy in CeO2 acts as the active site to promote the adsorption of molecules and facilitate the photo‐induced charge transfer (PICT) between the substrate and MO molecules. Therefore, the high SERS performance of Fe2O3@CeO2 heterojunction is achieved due to the coupling effect of excitons resonance, molecular resonance, and PICT resonance. It is found that Fe2O3@CeO2 has good SERS performance and stability to organic pesticides, especially metamitron (LOD = 5 × 10−9 mol/L). This work combines the advantages of Fe2O3 being prone to producing photoelectrons and abundant oxygen vacancies of CeO2, providing a reference for designing semiconductor SERS.

EM and CT synergistic SERS enhancement in Si/TiO2/Ag heterostructures via local interfacial effect

The Si/TiO2/Ag heterostructures with high SERS sensitivity were prepared by sol–gel and electrochemical self-assembly. The electromagnetic (EM) and charge transferring (CT) synergistic mechanism for SERS enhancement was explored by FDTD. The “localized interfacial effect (LIE)” of metal–semiconductor heterostructures can result in the CT between them and the charge carriers’ redistribution, which can facilitate the probe molecules’ adsorption and generate the 3D volume-enhancement of electromagnetic fields, therefore improve the SERS performance effectively. Furthermore, the morphology of Ag was flexibly regulated by changing the applied voltage, and the optimal SERS performance was achieved. With the R6G as a probe molecule, the ultra-low concentration of 10-13 M can be detected. The EF is estimated to be about 1.75 × 1011, and the RSD is about 4.3 %. The photocatalytic effect of Si/TiO2/Ag heterostructure can realize the SERS substrates’ UV self-cleaning and recyclable use with high stability.

Self‐Assembled Hierarchical Nanostructures: Toward Engineered SERS‐Active Platforms

AbstractThe creation of SERS‐active substrates is investigated by self‐assembling hierarchical structures of plasmonic‐assisted nanospheres (HSNs). The hierarchical architecture exploits the advantages of the well‐known ordered configuration of a hexagonally closed‐packed array (CPA) of nanospheres. A further layer of upper nanospheres is used to provide regular and intense surface hotspots, located at the nanogaps between neighboring nanospheres. Numerical analysis is carried out to predict the SERS performances and to identify the more promising configurations, by offering design criteria and a physical insight on the conditions affecting the SERS response of the self‐assembled substrates. Two alternative self‐assembly fabrication methods have been pursued to realize HSNs, namely co‐deposition and sequential deposition. Morphological analysis revealed the formation of well‐ordered hierarchical structures with different ratios between the diameters of the bottom and upper nanospheres. Experimental analysis of the SERS response demonstrates that HSNs can work as cost‐effective SERS substrates with superior performances with respect to the simpler single‐layer CPA configurations.

Fabricating periodic sandwich SERS structure in detecting SARS-CoV-2 S protein with high-performance

This study reported a sandwich SERS structure in detecting SARS-CoV-2 spike protein (SARS-CoV-2 S protein) with high performance. The periodic Ag nanoarrays (AgNAs) functionalized with angiotensin-converting enzyme 2 (ACE2) were utilized as the bottom structure to specifically bound to the SARS-CoV-2 S protein. A complex of SARS-CoV-2 S protein antibody and 4-mercaptobenzoic acid (4-Mba) modified Au nanoparticles (AuNPs@4-Mba@Antibody) were used as nanotags and top SERS enhancing structures. By utilized the “hot spots” in parallel and perpendicular directions, the SERS signals of the 4-Mba as reporters were largely enhanced. By modulated the diameters and the heights of the AgNAs, the SERS performance of the sandwich structures was optimized by using R6G as a stand analyst with limits of detection (LOD) of 1 × 10−9 M. By applied the optimized sandwich structures in detecting SARS-CoV-2 S protein in phosphate buffered saline (PBS) and pharyngeal swabs solution (PSS), the proposed sandwich structure illustrates a high performance, and the LODs were 0.1 fg mL−1 and 1 fg mL−1, respectively. This study presented an efficient way to construct a sandwich SERS structure in directly detecting SARS-CoV-2 S protein and this method illustrates a good potential in viral detection.

A tailored dual core-shell magnetic SERS substrate with precise shell-thickness control for trace organophosphorus pesticides residues detection

For addressing the challenges of strong affinity SERS substrate to organophosphorus pesticides (OPs), herein, a rapid water-assisted layer-by-layer heteronuclear growth method was investigated to grow uniform UiO-66 shell with controllable thickness outside the magnetic core and provide abundant defect sites for OPs adsorption. By further assembling the tailored Au@Ag, a highly sensitive SERS substrate Fe3O4-COOH@UiO-66/Au@Ag (FCUAA) was synthesized with a SERS enhancement factor of 2.11 × 107. The substrate's suitability for the actual vegetable samples (cowpeas and peppers) was confirmed under both destructive and non-destructive detection conditions, showing a strong SERS response to fenthion and triazophos, with limits of detection of 1.21 × 10-5 and 2.96 × 10-3 mg/kg in the vegetables under destructive conditions, and 0.13 and 1.39 ng/cm2 for non-destructive detection, respectively. The FCUAA substrate had high SERS performance, effective adsorption capability for OPs, and demonstrated good applicability, thus exhibiting great potential for rapid detection of trace OPs residues in the food industry.

Rapid determination of thiram in lake water using Au/Fe3O4 nanoparticles decorated MOF-867 as efficient surface-enhanced Raman scattering substrate

Rapid determination of pesticide residues in water is of vital importance for human health. However, rapid, reliable, and highly sensitive detection of pesticide residues in water environments remains a challenging issue. In this paper, we prepare Fe3O4/MOF-867 composites using the hot solvent method, and Au+ is reduced to Au NPs by the reducing agent and attached to the film of Fe3O4/MOF-867 composites by the addition of APTES as a linker to synthesize the Au/Fe3O4/MOF-867 SERS substrates. Then, we change the Fe3O4 content and the concentration of the reducing agent to obtain the optimal substrate. The substrate has a detection capability of up to 10−9 M for probe molecule R6G and the RSD is less than 5%, which demonstrates that the substrate has excellent SERS effect and reproducibility. In addition, the Au/Fe3O4/MOF-867 SERS substrates have been applied for the determination of thiram in lake water samples, with its limit of detection (LOD) up to 3.8 × 10−10 M. The Au/Fe3O4/MOF-867 SERS substrates can quickly and efficiently collect target analytes by magnetic enrichment, have high SERS performance, and have great potential for the rapid and sensitive detection of pesticide residues and other pollutants in the environment.