Analytical Enhancement Factor Research Articles

Facile synthesis of Ag NPs@MgO nanosheets for quantitative SERS-based detection and removal of hazardous organic pollutants

Surface-enhanced Raman spectroscopy (SERS) is a highly precise and non-invasive analytical method known for its ability to detect vibrational signatures of minute analytes with exceptional sensitivity. However, the efficacy of SERS is subject to substrate properties, and current methodologies face challenges in attaining consistent, replicable, and stable substrates to regulate plasma hot spots across a wide spectral range. This study introduces a straightforward and economical approach that incorporates monodispersed silver nanoparticles onto 2-D porous magnesium oxide nanosheets (Ag@MgO-NSs) through an in-situ process. The resulting nanocomposite, Ag@MgO-NSs, demonstrates substantial SERS enhancement owing to its distinctive plasmonic resonance. The effectiveness of this nanocomposite is exemplified by depositing diverse environmental pollutants as analytes, such as antibiotic ciprofloxacin (CIP), organic dyes like rhodamine 6G (R6G) and methylene blue (MB), and nitrogen-rich pollutant like melamine (MLN), onto the proposed substrate. The proposed nanocomposite features a 2-D porous structure, resulting in a larger surface area and consequently providing numerous adsorption sites for analytes. Moreover, engineering the active sites of the nanocomposite results in a higher number of hotspots, leading to an enhanced performance. The nanocomposite outperforms, exhibiting superior detection capabilities for R6G, MB, and MLN at concentrations of 10-6 M and CIP at concentration of 10-5 M, with impressive uniformity, reproducibility, stability, and analytical enhancement factors (EF) of 6.3 x 104, 2 x 104, 2.73 x 104 and 1.8 x 104 respectively. This approach provides a direct and cost-effective method for the detection of a broad spectrum of environmental pollutants and food additives, presenting potential applications across diverse domains. The detected environmental pollutants and food additives are removed through both catalytic degradation (R6G and MB) and adsorption (CIP and MLN).

Silver Dendrite‐Coated Silicon Pyramid Substrate as Surface‐Enhanced Raman Scattering Probe for Detecting Glucose

Raman spectroscopy offers a rapid and nondestructive method for qualitatively and quantitatively analyzing the molecular structure of substances. Herein, a facile and cost‐effective approach for the preparation of three‐dimensional (3D) surface‐enhanced Raman scattering (SERS) substrates is proposed, in which pyramid structures are fabricated using silicon anisotropic wet etching and silver dendrites are decorated on these silicon pyramid (PSi) substrates by immersing them in a mixture of hydrofluoric acid and silver nitrate for several minutes. The 3D SERS substrates, based on PSi coated with Ag dendrites, reveal high‐performance SERS enhancement (with an analytical enhancement factor reaching 3.54 × 1010) and can detect rhodamine 6G (R6G) in the presence of chemical enhancer (lithium chloride) at low concentrations down to 10−11 m. For glucose detection, 2‐thienylboronic acid is employed to faciliate glucose attachment to the substrate surface, achieving a detection limit as low as 10−6 m. The substrate exhibits good repeatability with a relative standard deviation of 11.223%, as well as reusability and long‐term stability for detection. The results also highlight the excellent sensitivity of the PSi‐based SERS substrate, which is expected to be instrumental in biochemical analysis and holds significant potential for developing noninvasive glucose sensor for diabetic patients using saliva samples.

Capillary action-driven surface-enhanced Raman spectroscopy (SERS) for the identification of phthalocyanine blue in modern paintings based on the BPG spot test.

A method for the extraction and accumulation of Ag nanoparticles utilizing capillary action through a piece of triangular-shaped cotton paper is reported. This method allowed the integration of SERS and the BPG spot test, which are typically employed for examining pigments on paper or in books. Malachite green oxalate was used as the model material for investigating the extent of enhancement when SERS was applied. The dynamic behavior of the Ag nanoparticles was also studied. When the cotton paper was pre-treated with malachite green oxalate, Ag nanoparticles could be extracted and accumulated on the triangular top, resulting in a dramatic SERS improvement. When malachite green oxalate (at a concentration of 10-6 M) was applied using this method, a dramatic analytical enhancement factor of approximately 3000% was obtained. Finally, the method developed in this study was successfully applied to the analysis of pigments in paintings from a university collection. The findings revealed that phthalocyanine blue was a popular pigment used in numerous paintings during the 1950s.

V2O5 nanoparticle films as a platform for plasmon-free surface-enhanced Raman spectroscopy

Metal-oxide nanomaterials represent a promising and inexpensive alternative to plasmonic metallic nanostructures currently used for surface-enhanced Raman scattering (SERS) spectroscopy. They profit from a chemical enhancing mechanism, i.e., charge transfer between the adsorbed molecule and the substrate. In this study, SERS-active nanostructured films based on vanadium pentoxide (V2O5) are produced by the combination of gas-phase synthesis of nanoparticles followed by their thermal annealing, i.e., using a fully solvent- and linker-free procedure. The SERS performance of V2O5 nanoparticle films was found to be strongly linked with porosity and the appropriate crystalline structure adjusted by annealing. A Raman spectroscopy and X-ray diffraction revealed that V2O5 crystalline nanoparticles are formed only after the annealing at temperatures equal to or higher than 300 °C. Such produced V2O5 nanoparticle films allow for sensitive and reproducible detection of organic dyes (methylene blue, rhodamine 6G and crystal violet), while their SERS enhancement (analytical enhancement factor close to 103) is significantly higher as compared with magnetron sputtered and annealed V2O5 thin films. Our study represents an important step in designing novel plasmon-free SERS-active platforms with the aim of improving their stability and spectral reproducibility compared to other non-plasmonic and plasmonic ones.

(Invited) Plasma-Synthesized Coupled Nanoplasmonic Gold for DNA Sersing

The facilitated electrochemical properties of plasma play a critical role in enhancing the synthesis and design of functional nanomaterials for the development of novel sensors. The targeted challenge is to customize and tailor functionality at multiple scales to improve detection device performance. In the realm of optoelectronics, plasmonic sensing is considered an efficient tool for investigating molecular properties, often accompanied by Raman, FTIR or Fluorescent spectroscopy. Specifically, Raman scattering, also known as SERS (surface-enhanced Raman scattering), is commonly used to probe analytes at a reduced scale using plasmonic enhancers. This technique is especially useful for rapidly and accurately investigating biologically relevant samples, such as DNA and RNA. DNA/RNA-related investigations are crucial in modern nanomedicine due to the progress made in bionanotechnology, DNA vaccines, and functional gene engineering. DNA, in particular, is highly valued by microbiologists because it contains information about the nature of bio-species. Currently, PCR-related methods dominate the field for molecular-sensitive DNA-level studies, but it is challenging to investigate using optical techniques like SERS. Despite its promise, SERS still requires technological and analytical improvements. A sophisticated plasmonic nanomaterial provides considerably improved photon scattering due to the strongly localized field confinement effect, resulting in better performance. In this report, a nanoplasmonic sensor was designed using a plasma-driven electrochemical reduction mechanism, achieved through an atmospheric pressure He-plasma jet setup operating at kHz frequency. The reactive oxidative species donated electrons via liquid-gas electrochemistry towards the Ar-delivered Au(3+)-containing microdroplets, resulting in microscaled aggregates composed of AuNPs obtained from the nebulized ionic gold liquid precursor. Due to the strong coupling between nanoparticles, a high analytical enhancement factor of about 107 was achieved, and the substrate enabled obtaining Raman fingerprints of bacterial DNA fragments (M. luteus and S. aureus, E. coli, J. lividum) at nanovolume sample quantities. Additionally, the main DNA molecular vibrational signatures associated with nucleobase motions were extracted from the collected spectra and used to reliably classify bacterial strains using statistical principal component analysis.[1] References[1] Shvalya, V., Vasudevan, A., Modic, M., Abutoama, M., Skubic, C., Nadižar, N., ... & Cvelbar, U. (2022). Bacterial DNA Recognition by SERS Active Plasma-Coupled Nanogold. Nano Letters.

Silver Nanoflowers as an Interfacial Liquid-State Surface Enhanced Raman Spectroscopy (SERS) Sensor for Water Pollution

Water pollution has created a critical threat to the environment.‎‎ A lot of research has been done ‎recently to use surface-enhanced Raman spectroscopy (SERS) to detect multiple pollutants in water. This study aims to use Ag colloid nanoflowers as liquid SERS enhancer. Tri sodium phosphate (Na3PO4) was investigated as a pollutant using liquid SERS ‎based on colloidal Ag ‎nanoflowers. The chemical method was used to synthesize nanoflowers from silver ‎ions. Atomic Force Microscope (AFM), Scanning Electron Microscope (SEM), and X-ray diffractometer (XRD) were employed to characterize the silver nanoflowers. This ‎nanoflowers SERS action in detecting Na3PO4 was reported and analyzed concerning both shape and size using a 532 ‎nm laser. We observed that the nanoflower's structure produced strong SERS signals. The increase in the SERS signal is related to ‎the deposition of Na3PO4 molecules in the aggregated silver nanostructure ‎in the solution. The concentration of Na3PO4 plays a main role in detection since the Raman ‎signal becomes stronger as the concentration increases. The highest phosphate analytical enhancement factor obtained for SERS in colloidal nanoflowers was 1.7×103 at 0.7×10-6 M which was the lowest concentration.

Laser-induced silver nanoparticles with HfO2 shell for melamine detection

Pure Ag nanoparticles (NPs) were synthesized on glass substrates by laser dewetting and then modified with hafnium dioxide (HfO2) by a sputtering process. The optical properties and melamine detection performance of the modified Ag NPs were investigated. The results showed that the Ag NPs produced in the laser dewetting process with accumulated unit volume energies of 0.2–3.67 kJ/mm3s had a size of 51–107 nm. Furthermore, the Ag NPs exhibited an optical absorption peak in the wavelength range of 429–495 nm. A strong Raman signal fingerprint peak was observed at 701 cm−1 in a 10−3 M melamine solution. The corresponding analytical enhancement factor (AEF) was 1.9 × 102. For the Ag@HfO2 NPs, localized surface plasmon resonance (LSPR) occurred at 584–800 nm, with an AEF of 2.3 × 104. The limit of detection for melamine using the Ag@HfO2 NPs was 10−5 M. Moreover, the Ag@HfO2 NPs showed a more stable Raman spectrum than the Ag NPs. Hence, the potential of the Ag@HfO2 NPs for melamine detection was confirmed.

Sensitive and high laser damage threshold substrates for surface-enhanced Raman scattering based on gold and silver nanoparticles.

Surface-enhanced Raman scattering (SERS) is a sensitive and fast technique for sensing applications such as chemical trace analysis. However, a successful, high-throughput practical implementation necessitates the availability of simple-to-use and economical SERS substrates. In this work, we present a robust, reproducible, flexible and yet cost-effective SERS substrate suited for the sensitive detection of analytes at near-infrared (NIR) excitation wavelengths. The fabrication is based on a simple dropcast deposition of silver or gold nanomaterials on an aluminium foil support, making the design suitable for mass production. The fabricated SERS substrates can withstand very high average Raman laser power of up to 400mW in the NIR wavelength range while maintaining a linear signal response of the analyte. This enables a combined high signal enhancement potential provided by (i) the field enhancement via the localized surface plasmon resonance introduced by the noble metal nanomaterials and (ii) additional enhancement proportional to an increase of the applicable Raman laser power without causing the thermal decomposition of the analyte. The application of the SERS substrates for the trace detection of melamine and rhodamine 6G is demonstrated, which shows limits of detection smaller than 0.1ppm and analytical enhancement factors on the order of 104 as compared to bare aluminium foil.

Designing of a functional paper-tip substrate for sensitive surface-enhanced Raman spectroscopy (SERS) detection

A simple and flexible fabrication method of paper SERS substrate was developed by nanoparticles (NPs) droplet self-assembly at the paper tip with a temperature gradient (PTTG). We turned the drawback of the coffee ring effect into an effective way of preparing paper SERS substrate. When the NPs droplets were continuously dripped onto the PTTG, NPs were densely and uniformly distributed at the paper-tip front based on the combination of gravity and the coffee ring effect, which could achieve 91.2-fold improvement of SERS performance compared to a flat filter paper. Meanwhile, the analytes could also be enriched at the paper-tip front, which could achieve 9.3-fold signal enhancement compared to the paper-tip tail. Thus, the PTTG realized an excellent signal amplification for SERS detection. The paper-tip SERS substrate combined with a portable Raman spectrometer yielded an excellent analytical enhancement factor of 1.15 × 105 with the detection limit of 10 nM Rhodamine 6G (R6G). The whole fabrication procedure was completed within 2 h, and the paper-tip substrate showed a satisfactory substrate-to-substrate reproducibility with a relative standard deviation (RSD) of 5.13% (n = 10). It was successfully applied for quantitatively detecting real samples of oxytetracycline and malachite green with recoveries of 83.84–105.25% (n = 3). Meanwhile, we further evaluated the SERS performance of the PTTG using a laboratory-based Raman spectrometer, and it could realize the detection as low as 10 pM R6G. The proposed paper-tip substrate would offer a promising potential application for the on-site SERS analysis of food safety and environmental health.

Au nanoparticles-coated TiO2 SERS active substrate studies-based on plasmonic photonic interference coupling

In this work, gold nanoparticles coated titanium dioxide surface-enhanced Raman scattering (SERS) substrates were fabricated and tested. Amorphous titanium dioxide nanotubes with different geometry were prepared by anodization and subsequent spin-coating of gold nanoparticles is done. SERS signal enhancement for the effective detection of rhodamine 6G molecules is studied using these substrates. SERS enhancement factor of the substrates was dependent on the geometry of nanotubes and plasmonic photonic interference coupling (P-PIC). Analytical SERS enhancement factor of the substrates was estimated with respect to reference materials.

Exploring the surface-enhanced Raman scattering (SERS) activity of gold nanostructures embedded around nanogaps at wafer scale: Simulations and experiments

A unique way of converting free space light into a local electromagnetic field in small spaces is via metallic nanostructuring. In this work fabrication, experimental characterization and simulation of surface-enhanced Raman scattering (SERS) active specimens based on Au nanostructures are discussed. We used displacement Talbot lithography (DTL) to fabricate silicon nano-wedge substrates with Au nanostructures embedded around their apices. After the ion beam etching process, a nanogap is introduced between two Au nanostructures templated over nano-wedges, yielding specimens with SERS characteristics. The Au nanostructures and the nanogaps have symmetric and asymmetric configurations with respect to the wedges. With this nanofabrication method, various wafer-scale specimens were fabricated with highly controllable nanogaps with a size in the order of 6 nm for symmetric gaps and 8 nm for asymmetric gaps. SERS characteristics of these specimens were analyzed experimentally by calculating their analytical enhancement factor (AEF). According to finite-difference time-domain (FDTD) simulations, the Raman enhancement arises at the narrow gap due to plasmonic resonances, yielding a maximum AEF of 6.9 × 106. The results highlight the SERS activity of the nanostructures and ultimately comply with reliable substrates for practical applications.

Atomic layer deposition assisted fabrication of insertable silver dendrites-based SERS substrates with high adhesion

Considerable efforts have been dedicated to the development of low-cost and highly sensitive surface-enhanced Raman spectroscopy (SERS) substrates, which have found applications in numerous fields. However, the critical factors of adhesion and stability have been insufficiently addressed. Such as Ag dendrites (Ag D) have been recognized for their cost-effectiveness and superior efficiency as SERS substrates, nonetheless, the issue of weak adhesion to the substrate has remained a challenge. Herein, a novel strategy to fabricate a Planar Ag dendrites-based SERS substrate with high adhesion is reported, that employs a combination of atomic layer deposition, roll milling, and chemical etching. The resulting Planar Ag dendrites show excellent adhesion, with a surface stripping force 18 times greater than that of pristine Ag dendrites, allowing for prolonged ultrasonic cleaning. Moreover, the substrate can be used as an insertable SERS sensor to obtain spectral information inside apples due to its excellent adhesion. The proposed design achieves high SERS sensitivity, with a limit of detection of 10-9 M and an analytical enhancement factor of 1.5 × 108 for R6G. Overall, this work provides a valuable reference for improving the adhesion of noble metal nanostructures on supporting substrates, offering a reliable SERS substrate for practical applications.

Plasma-Made Nanogold for DNA Sensing with SERS

Facilitated electrochemical properties of plasma are crucial for improving functional nanomaterials synthesis and design for novel sensor development. Controlled customization and functionality tailoring at multiscale is the targeted challenge for better detection devices performance. In the modern era of optoelectronics, among various probing approaches, plasmonic sensing accompanied by Raman, FTIR or Fluorescent spectroscopy is considered a tool for the efficient investigation of molecular properties. In particular, Raman scattering is often called SERS (surface-enhanced Raman scattering) due to plasmonic enhancers, which are used to improve the probing of analytes at a reduced scale. This feature is extremely useful for biologically relevant analytical tasks when samples alike DNA and similar need to be investigated fast and accurately. DNA/RNA-related investigations are highly important in modern nanomedicine due to the solid progress of bionanotechnology, DNA vaccines, and functional gene engineering. DNA is the most valued substance for microbiologists because it contains information about bio-species' nature.[1] Currently, the number of molecular-sensitive methods for DNA-level study is quite limited, among which PCR (polymer chain reaction) related methods dominate the field. However, it is challenging to investigate it with optical techniques like SERS. Despite being promising, SERS is still under technological and analytical improvement. Better performance comes with sophisticated plasmonic nanomaterials, which provide considerably improved photon scattering due to the strongly localized field confinement effect.[2] In the current report, a well-performing nanoplasmonic sensor was designed using a plasma-driven electrochemical reduction mechanism. Exploiting atmospheric pressure He-plasma jet setup operating kHz frequency, the reactive oxidative species donated electrons via liquid-gas electrochemistry towards the Ar-delivered Au(3+)-containing microdroplets. Through this method, microscaled aggregates composed of AuNPs were obtained from the nebulized ionic gold liquid precursor. Due to the strong coupling between nanoparticles, a high analytical enhancement factor of about 107 was achieved and the substrate allowed to obtain Raman fingerprints of bacterial DNA fragments (M. luteus and S. aureus, E. coli, J. lividum) at nanovolume sample quantities. In addition, main DNA molecular vibrational signatures associated with nucleobase motions were extracted from spectra collected and used to classify the bacterial strains reliably by employing statistical principal component analysis.

Coconcentration/Colocation Effects of Quasi Fabry–Pérot Cavity Structure with Anti‐Interference Feature on Light and Analytes: Accurate Raman Detection of Hg2+ under Diverse Real Environments

AbstractA quasi Fabry–Pérot (F–P) cavity structure of zinc oxide/sliver nanowires coated with zeolitic imidazolate framework‐8 (ZnO/Ag NWs/ZIF‐8) is designed to precisely guide target analytes into the hotspot zones while hindering the entry of various potential interferents during Raman detection. Owing to the triple synergistic effect of the ZIF‐8 dielectric F–P cavity, ZIF‐8 microsponge, and backward light scattering caused by the ZnO/Ag NW tip, the structure of ZnO/Ag NWs/ZIF‐8 is verified to have unique coconcentration and colocation effects on light and analytes. The molecular sieving effect of the ZIF‐8 layer and the selectivity of the premodified reporter probe on ZnO/Ag NWs endow the ZnO/Ag NWs/ZIF‐8 with an important anti‐interference feature for diverse interferents in practical Raman detection of heavy‐metal ions. The analytical enhancement factor of ZnO/Ag NWs/ZIF‐8 is as high as 3.97 × 106, with a limit of detection for Hg2+ reaching 10−10 M; and the relative standard deviation is only 6.03%. The structure directly and successfully attains accurate Raman detection of diverse real samples containing Hg2+, without an additional pre‐extraction process. This research provides a novel way of improving Raman detection reliability under real scenarios and is a new attempt to precisely manipulate light and analytes by controlling the dielectric.

Application of Anodic Titanium Oxide Modified with Silver Nanoparticles as a Substrate for Surface-Enhanced Raman Spectroscopy.

The formation of nanostructured anodic titanium oxide (ATO) layers was explored on pure titanium by conventional anodizing under two different operating conditions to form nanotube and nanopore morphologies. The ATO layers were successfully developed and showed optimal structural integrity after the annealing process conducted in the air atmosphere at 450 °C. The ATO nanopore film was thinner (1.2 +/- 0.3 μm) than the ATO nanotube layer (3.3 +/- 0.6 μm). Differences in internal pore diameter were also noticeable, i.e., 88 +/- 9 nm and 64 +/- 7 nm for ATO nanopore and nanotube morphology, respectively. The silver deposition on ATO was successfully carried out on both ATO morphologies by silver electrodeposition and Ag colloid deposition. The most homogeneous silver deposit was prepared by Ag electrodeposition on the ATO nanopores. Therefore, these samples were selected as potential surface-enhanced Raman spectroscopy (SERS) substrate, and evaluation using pyridine (aq.) as a testing analyte was conducted. The results revealed that the most intense SERS signal was registered for nanopore ATO/Ag substrate obtained by electrodeposition of silver on ATO by 2.5 min at 1 V from 0.05M AgNO3 (aq.) (analytical enhancement factor, AEF ~5.3 × 104) and 0.025 M AgNO3 (aq.) (AEF ~2.7 × 102). The current findings reveal a low-complexity and inexpensive synthesis of efficient SERS substrates, which allows modification of the substrate morphology by selecting the parameters of the synthesis process.

Nanosphere Lithography-Enabled Hybrid Ag-Cu Surface-Enhanced Raman Spectroscopy Substrates with Enhanced Absorption of Excitation Light.

We demonstrated a low-cost, highly sensitive hybrid Ag-Cu substrate with enhanced absorption for the excitation laser beam via the nanosphere lithography technique. The hybrid Ag-Cu surface-enhanced Raman spectroscopy (SERS) substrate consists of a Cu nanoarray covered with Ag nanoparticles. The geometry of the deposited Cu nanoarray is precisely determined through a self-assembly nanosphere etching process, resulting in optimized absorption for the excitation laser beam. Further Raman enhancement is achieved by incorporating plasmonic hotspots formed by dense Ag nanoparticles, grown by immersing the prepared Cu nanoarray in a silver nitrate solution. The structural design enables analytical enhancement factor of hybrid Ag-Cu SERS substrates of 1.13 × 105. The Ag-Cu SERS substrates exhibit a highly sensitive and reproducible SERS activity, with a low detection limit of 10-13 M for Rhodamine 6G detection and 10-9 M for 4,4'-Bipyridine. Our strategy could pave an effective and promising approach for SERS-based rapid detection in biosensors, environmental monitoring and food safety.

Manifold enhancement in the near-field and SERS efficiency of all-sputter grown Ag-nanoparticles on Al-film based mirror structures

Gap mode plasmonic coupling of noble metal nanoparticles with metal films makes them ideal candidates for manifold improvement in the surface-enhanced Raman scattering (SERS) efficacy via strong near-field enhancement in their gap realized by deposition of sandwiched dielectric spacer layers. This report presents an all-sputtering grown SERS substrate based on gap mode plasmonic coupling of Ag-NPs with Al films separated with thin dielectric overlayers of AlOx or polytetrafluoroethylene (PTFE). A remarkably high Analytical enhancement factor (as high as 3.7 × 109) with manifold SERS enhancement (as high as 26 times) is obtained with a limit of detection up to 10−13 M concentration of CV dye. Growth of thin dielectric over layer remains conformal on randomly orientated hillocks-like Al nanocrystallites (NCs) on Si substrates. Reflection studies show the broadband absorption of gap plasmon mode coupled Ag nanoparticles (NPs) and Al films. An optical model constructed using generalized oscillator model with the help of Lorentz and Tauc-Lorentz oscillators which reveals the localized surface plasmon resonance (LSPR) of Ag-NPs is strongly enhanced after gap mode plasmonic coupling (GMPC) in Ag-NPs and Al film based nanoparticles-on-mirror (NPoM) system. Finite difference time domain (FDTD) simulations validate the experimental findings that NPoM structure results in GMPC between Ag-NPs and underlying Al films. This study paves a way towards NPoM-based manifold enhancement in SERS-based detection efficacy of ultralow concentration of complex molecules.

Large‐Area Gold‐Coated Polyamide Nanopillar Arrays Consisting of Secondary Lamellar Structures and Sub‐10‐nm Gaps for Ultrasensitive SERS Detection

AbstractLarge‐area gold‐coated polyamide 66 (PA66) nanopillar (PA66NP@Au) arrays consisting of secondary lamellar structures and sub‐10–nm gaps are fabricated for surface‐enhanced Raman spectroscopy (SERS) using ultrathin anodized aluminum oxide (AAO) template, solution‐phase growth of PA66 lamellae, and Au sputtering. Such closely packed PA66NP@Au arrays with high density of electromagnetic field enhancement (“hot spots”) on large area exhibit high SERS sensitivity for detection of rhodamine 6g (R6G) molecules with concentration down to 10−14 m and a large Raman analytical enhancement factor (AEF) of ≈1010. Furthermore, the as‐fabricated PA66NP@Au arrays provide highly sensitive Raman signals in detection of a commonly pesticide residue, carbendazim with a limit of detection (LOD) of 0.05 mg L−1 (0.05 ppm), which is lower than that of maximum residue limit of 0.2 ppm allowed in Europe Union. The as‐fabricated PA66NP@Au arrays are promising for highly sensitive and uniform SERS detection.

Unique high-performance metal-nanoparticle-free SERS substrate with rapid-fabricated hybrid 3D-Nano-Micro-Cavities anodic alumina for label-free detection

Conventional surface-enhanced Raman scattering (SERS) substrates were usually nanofabricated by coating Ag or Au metal nano particles (MNPs) to modify the surface. However, the complex and time-consuming nanofabrication prevents those good-performance substrates from the practical applications together with the instability of MNPs as a challenge. Here, a unique Roughened-Surface-with-hybrid-3D-Nano-Micro-Cavities (RS3DNMC) SERS substrate free of MNPs is proposed for high-performance enhancement using facile and rapid electrochemically micromachining aluminum foil to form randomly-distributed 3D over-etched cavities of 1 ∼ 2 μm in diameter embedded with the nanopores of anodized aluminum oxide (AAO). The metal-film-coated AAO with RS3DNMC structure creates great SERS enhancement because of two mechanisms from the significantly reduced reflectance for increasing the photonic-scattering-and-multi-reflection and the more peripheral-and-gap hotspots of 3D-nano-micro-cavities compared to the 2D flat surface. Our SERS substrate merits a high analytical enhancement factor (AEF) of 1.15x106 and a low limit of detection (LOD) of 1x10-10 M for methylene blue (MB) with a good uniformity of 9.64% relative standard deviation (RSD) in a large area of 2.25 cm2. The melamine widely remained in human body and environment was detected at LOD of 0.05 ppm that is much lower than WHO-recommended criteria (1 ppm).

Efficient and reliable detection of rhodamine B using SERS from silver-decorated photonic crystal silicon nanoscale pores

Porous silicon photonic crystal (PSi PhC) decorated with silver nanoparticles (AgNPs) is shown to provide a new substrate for the improvement of SERS. AgNPs are obtained through immersion of PSi PhC samples in AgNO3 solutions and successive thermal annealing. The nanocomposite material generated by adding AgNPs inside the silicon nanoscale pores, integrates the ability of metal surfaces to amplify Raman scattering signals and an enlarged surface area. Besides, PhC structure formed by multilayer PSi increases interaction time of light and matter of the multilayer structure. The experimental results show that the AgNPs-decorated PSi PhC has the largest Raman intensity in comparison with other SERS substrates based on Si. The enhancement of Raman signals also reduces the threshold of the detection down to below 10-10 M. The analytical enhancement factor of AgNPs/PSi PhC SERS substrate for the detection of Rhodamine B (RhB) reaches 1010. This proposed AgNPs/PSi PhC SERS substrate could serve as a potential candidate for detecting RhB in foodstuffs at very low concentrations.