Surface-enhanced Raman Scattering Enhancement Factor Research Articles

Ag Nanoparticles Modified Sea Urchin-like W18O49 Microstructures for Sensitive Surface Enhanced Raman Spectroscopy Detection

Surface-enhanced Raman scattering (SERS) has gained significant attention in various fields, including biomedical diagnostics, environmental monitoring, and food safety. This technique offers many advantages such as label-free detection and the ability to detect analytes at low concentrations. In this study, we present a variety of tungsten oxide (W18O49) microstructures as solid SERS substrates using various solvents realized by a simple hydrothermal approach. Among them, the well-defined sea urchin-like W18O49 microstructures support greater light scattering and confinement to enhance the SERS signal when compared to other W18O49 structures. The surface of well-defined sea urchin-like W18O49 microstructures was then modified with uniformly distributed silver nanoparticles (Ag NPs). The combination of the unique morphology of the Ag and sea urchin-like W18O49 microstructures (W18O49@Ag) led to improved detection capabilities for analytes such as rhodamine 6G (R6G) and thiram molecules. The SERS enhancement factor (EF) of sea urchin-like W18O49@Ag microstructures was estimated to be as high as 1.53×106 with the lowest detectable concentrations of 1nM and 1μM for R6G and thiram, respectively. Thus, the well-defined sea urchin-like W18O49@Ag microstructures are excellent choice to replace the pure noble metal SERS substrates in the fields of rapid detection and trace analysis due to their high sensitivity, repeatability, and long-term stability.

Two-dimensional tellurium nanosheet: A novel sensitive and stable surface-enhanced Raman scattering substrate

Two-dimensional (2D) materials with merits such as low cost, high chemical inertness and tunable electronic structure have become favorable candidates for next generation of surface-enhanced Raman scattering (SERS) platforms. However, the SERS sensitivity of 2D materials still needs to be improved and the large-scale synthesis methods should be developed to meet the requirements of practical applications. In this work, we explored performances of a brand-new SERS substrate made of 2D Te nanosheets (NSs), which exhibited thickness-dependent SERS properties, with thinner nanosheets yielding stronger SERS intensity. Under optimized conditions, the limits of detection (LODs) reached the order of 10−9 M combining with SERS enhancement factors (EFs) as high as 105 for copper phthalocyanine (CuPc) and methylene blue (MB). This impressive SERS performance could be attributed to the strong interaction and photoinduced charge transfer (PICT) processes between 2D Te NSs and molecules. Benefiting from the appropriate positions of valence band (VB) and conduction band (CB), the 2D Te NSs showed significant Raman enhancement for various molecules. Furthermore, the 2D Te NSs exhibited good air-stability for up to ∼2 months. These outstanding performances establish 2D Te NSs as a favorable SERS detection material with enormous potential in practical applications.

A Surface Enhanced Raman Scattering (SERS) Sensing Method Enhanced by All-metal Metasurface

In this study, we developed a simple surface-enhanced Raman Scattering (SERS) composite substrate, composed of an all-metal metasurface and on-surface random distributing silver nanoparticles (AgNPs), to enhance the performance of SERS sensing. The metasurface is made up of gold (Au) nanopillars array on aluminum (Al), it can localize the electromagnetic field energy with a resonant absorption peak near the 630 nm wavelength, which contributes to the SERS performance of AgNPs deposited into the structure. The composite substrate can significantly improve the sensing performance, and the SERS Enhancement Factor (EF) reaches 2.81 × 106. The substrate also has good stability and reproducibility. The research is based on the combination of Localized Surface Plasmon Resonance (LSPR) and SERS effects, providing a method and idea for improving the sensitivity of SERS detection, and achieving the trace detection of Rhodamine 6G (R6G) and Thiram at 10−10 M, respectively.

Influence of Pyramidal M20 (M = Cu, Ag and Au) Clusters on SERS and Noncovalent Interactions toward Tuberculosis Drug Pretomanid (PTD): DFT Study

The study of interaction and adsorption of drug molecules on the active surface of noble metal nanocluster is of particular interest due to effective change in the properties of the drug molecules. Surface-enhanced Raman scattering (SERS) theoretical calculations were performed to investigate the adsorption properties of pretomanid (PTD) on pyramidal [Formula: see text]/[Formula: see text]/[Formula: see text] metal clusters. The charge transfer process from the [Formula: see text] pyramids is revealed by MEP and electronic analysis. The frequencies of PTD are enhanced in the PTD–metal complexes due to the noticeable SERS effect, and the binding energies were calculated to be −36.2 kcal/mol, −46.3 kcal/mol and −43.6 kcal/mol with Ag, Au and Cu structures, respectively. For the PTD–metal clusters, there is an entire potential rearrangement due to adsorption process which is due to charge transfer and adsorptions as chemisorption. The polarizability variations are predicted in the order PTD–Au > PTD–Cu > PTD–Ag which contribute the SERS enhancement due to adsorption. Changes in thermodynamic parameters reveal that adsorption is exothermic and at the same time spontaneous with ordered interactions due to the negative values. There is a redshift for the ultraviolet–visible (UV–vis) absorption of PTD–metal complexes with a lowering intensity in comparison with that of PTD, more likely indicating a chemisorption process. SERS enhancement factors are remarkable due to adsorption of conformationally flexible PTD on metal clusters. The noncovalent interactions between PTD and the metal pyramids were also determined. The study provided key information on designing a molecular structure with a good pharmacological profile by calculating bioactivity and drug similarity parameters for bioactive drug molecules.

Aiming for Maximized and Reproducible Enhancements in the Obstacle Race of SERS.

Surface enhanced Raman scattering (SERS), since its discovery in the mid-1970s, has taken on many roles in the world of analytical measurement science. From identifying known and unknown chemicals in mixtures such as pharmaceutical and environmental samples to enabling qualitative and quantitative analysis of biomolecules and biomedical disease markers (or biomarkers), furthermore expanding to tracking nanostructures in vivo for medical diagnosis and therapy. This is because SERS combines the inherent power of Raman scattering capable of molecular species identification, topped with tremendous amplification in the Raman signal intensity when the molecule of interest is positioned near plasmonic nanostructures. The higher the SERS signal amplification, the lower the limit of detection (LOD) that could be achieved for the above applications. Therefore, improving SERS sensing efficiencies is vital. The signal reproducibility and SERS enhancement factor (EF) heavily rely on plasmonic nanostructure design, which has led to tremendous work in the field. But SERS signal and EF reproducibility remain key limitations for its wider market usability. This Review will scrutinize factors, some recognized and some often overlooked, that dictate the SERS signal and are of utmost importance to enable reproducible SERS EFs. Most of the factors pertain to colloidal labeled SERS. Some critically reviewed factors include the nanostructure's surface area as a limiting factor, SERS hot-spots including optimizing the SERS EF within the hot-spot volume and positioning labels, properties of label molecules governing molecule orientation in hot-spots, and resonance effects. A better understanding of these factors will enable improved optimization and control of the experimental SERS, enabling extremely sensitive LODs without overestimating the SERS EFs. These are crucial steps toward identification and reproducible quantification in SERS sensing.

Highly Controllable Fabrication of Gold Composite Nanostructures by Multiple Electroplating for High‐Performance Electrochemical and Raman Scattering Measurements

Morphology‐controlled nanostructures are important functional materials in multidisciplinary research fields, such as sensing, imaging, catalysis, and energy harvesting. However, existing nanofabrication methods have limitations in terms of controllability, diversity, cost, and efficiency. Here, a novel nanofabrication approach is proposed to construct Au nanostructures with high controllability, cost‐efficiency, and high‐performance sensing and energy harvesting. The fabrication incorporates electric field‐assisted hydrothermal growth of zinc oxide nanorods (ZnO NRs) with two‐step gold electroplating. The ZnO NRs serve as a dissolvable template during the electroplating formation of gold nanostructures for eventually synthesizing pure gold nanostructures on electrodes. The synthesized gold nanostructures take unique composite shape of nanospheres (hundreds of nanometers) covered with tinier nanostructures (tens of nanometers) like floccules, grains, lamellas, or rods, which are highly controlled by regulating electroplating parameters. The gold composite nanostructures provide high‐performance sensing and energy harvesting, such as enhanced electrochemical sensing interface (electric double‐layer impedance decrease up to 97.1%), excellent surface‐enhanced Raman scattering (SERS enhancement factor up to ), and preferable visible–near‐infrared light harvesting (absorptivity near to 90%). For the first time, the application of tumor cell photothermal therapy with nanostructured electrodes and in situ bimodal monitoring of single‐cell impedance and SERS‐based molecular expression during therapy is demonstrated.

Rapid capture and quantification of food-borne spores based on the double-enhanced Fe3O4@PEI@Ag@PEI core-shell structure SERS sensor

To realize rapid capture and quantification of food-borne spores and prevent their potential harm, Fe3O4@PEI@Ag@PEI core-shell structure nanoparticles were combined with flower-like AgNPs for double enhancement and efficient capture of spores. The developed sensor showed excellent reproducibility and SERS enhancement factor (AEF) is 4.6 × 104. Orthogonal partial least-squares discrimination analysis and linear discriminant analysis accurately identified the three spores (Bacillus subtilis, Bacillus cereus, and Clostridium perfringens), and the qualitative identification accuracy of linear discriminant analysis was 100 %. Efficient enrichment of B. subtilis spores was realized within 5 min, with a detection limit of 3 cfu/mL. Spiked tests revealed that this sensor was effective in detecting spores in milk, orange juice, and water samples, with recovery ratio of 95.2−103.9 % and relative standard deviation of 3.1−7.7 %. Thus, the developed sensor was accurate and reliable, and could achieve rapid identification and quantitative detection of food-borne spores.

Controllable preparation of Ti3C2Tx/Ag composite as SERS substrate for ultrasensitive detection of 4-nitrobenzenethiol

Currently, metal carbonitride (MXene) has been identified as a hot research topic in the research area of surface-enhanced Raman scattering (SERS). In this study, Ti3C2Tx/Ag composite was fabricated as SERS substrate with different Ag contents. The fabricated Ti3C2Tx/Ag composites show good SERS behavior by detecting 4-Nitrobenzenethiol (4-NBT) probe molecules. Through calculation, the SERS enhancement factor (EF) of the Ti3C2Tx/Ag substrate was as high as 4.15 × 106. It is worth noting that the detection limit of 4-NBT probe molecules can be achieved ultralow concentration of 10−11 M. In this system, electromagnetic enhancement mechanism and chemical enhancement mechanism have synergistic effects on SERS phenomenon. Meanwhile, the Ti3C2Tx/Ag composite substrate exhibited good SERS reproducibility. In addition, the SERS detection signal hardly changed after 6 months of natural standing, and the substrate showed good stability. This work suggests that the Ti3C2Tx/Ag substrate could be used as a sensitivity SERS sensor for practical application, and could be applied in the field of environmental monitoring.

Silver nanoparticle decorated graphene-based SERS electrode towards procalcitonin detection

Monitoring procalcitonin levels (PCT) is critical for early diagnosis of sepsis, chronic disease, COVID-19 and other time-dependent pathologic cases. In this work, silver nanoparticles (AgNps) doped graphene-based Surface-enhanced Raman scattering (SERS) electrode was demonstrated for the first time to rapid detection of PCT biomarkers. An excellent combination of AgNps and single-layer graphene (SLG) was achieved, resulting in effective SERS enhancement. Due to the smooth and large surface area of SLG, many antibody molecules bind to the surface of SERS electrode and interact with PCT protein. The SERS enhancement factors (EFs) for R6G and PCT protein molecules were calculated to be 1012 and 1.6 × 109, respectively. The limits of detection (LODs) for R6G and PCT protein molecules were reported to be 10−13 M and 4 ngmL−1, respectively. These high EFs and lower LODs indicate that the fabricated AgNp/Gr@ ITO SERS electrodes have perfect SERS performance. SERS studies showed that there is a perfect interaction between PCT protein and AgNps and SLG, which leads to the enhancement of electromagnetic mechanism (EM) and chemical mechanism (CM) in the fabricated SERS materials. The developed eco-friendly SERS platform can provide reliable and sensitive test results, faster analysis compared to conventional biosensors, mobile applications and cost-effective clinical management.

Strongly coupled Raman scattering enhancement revealed by scattering-type scanning near-field optical microscopy

Abstract Recent advances in near-field technology with an ultrahigh spatial resolution breaking optical diffraction limit, make it possible to further identify surface-enhanced Raman scattering (SERS) enhancement theories, and to monitor the SERS substrates. Here we verify the electromagnetic enhancement mechanism for SERS with a close-up view, using scattering-type scanning near-field optical microscopy. The array of metal-insulator-metal (MIM) subwavelength structures is studied, in which the field enhancement comes from the strong coupling between gap plasmon polariton and surface plasmon polariton modes. The near-field optical measurements reveal that SERS enhancement factor (EF) varies from one MIM subwavelength unit to another in a finite array. Besides the enhancement of isolated unit, the loss exchange phenomenon in strong coupling with a large Rabi splitting can give rise to an additional enhancement of more than 2 orders of magnitude in periodic arrays and close to 3 orders of magnitude in finite arrays. The SERS EF of the array composed of only 5 units is demonstrated to yield the best SERS performance. Our near-field optical measurements show evidence that finite-size structures embodied with strong coupling effect are a key way to develop practical high-performance SERS substrates.

High-sensitivity and throughput optical fiber SERS probes based on laser-induced fractional reaction method

Surface-enhanced Raman scattering (SERS) is widely used in many fields, such as biosensors, medical diagnostics, materials science, and food security. Here, we report a low-cost, high-throughput laser-induced fractional reaction method for optical fiber SERS probes. Under laser irradiation, the local thermal effect and the electromagnetic interaction between nanoparticles effectively contribute to the formation and growth of silver nanoparticles on the optical fiber facet. Sodium dodecyl sulfate (SDS) solution with a concentration of 2 mM is employed as a surfactant to control the shape and size of the silver nanoparticles. A detection limit of 1.0 × 10−11 M for R6G is achieved, which is, as far as we know, the highest sensitivity that laser-induced fabricated optical fiber SERS probes have achieved. The SERS enhancement factors (EFs) are calculated to be 6.795 × 1011. The SERS intensity of R6G at peaks of 621 cm−1, 1281 cm−1, and 1359 cm−1 are measured with probes fabricated under the same condition, and showed perfect repeatability with an RSD of less than 4.5%. This new method shows effectively in fabricating optical fiber SERS probes with high sensitivity and good repeatability.

Rational design of wettability-patterned microchips for high-performance attomolar surface-enhanced Raman detection

Recent progress in wettability-patterned microchips has facilitated the development of ultra-trace detection in multiple biomedical and food safety fields. The existence of a superhydrophilic trap can realize targeted deposition of the analyte. However, the wetting transition from the Cassie-Baxter state to the Wenzel state usually occurs during evaporation and leads to a larger deposition footprint, which has a strong impact on the detection sensitivity and uniformity. In this paper, we report an integrated design, fabrication, and evaporation strategy to avoid the transition for high-performance attomolar surface-enhanced Raman scattering (SERS) detection. An improved force balance model was proposed to design the microstructures of wettability-patterned microchips, which were fabricated by nanosecond laser direct writing and surface fluorination. The microchips were composed of superhydrophobic micro-grooves and superhydrophilic traps, by which the targeted deposition of Au nanoparticles and rhodamine 6G (R6G) onto a minimal area of ∼70 × 70 μm2 was realized after a two-step heated evaporation. Accordingly, the detection limit was down to the attomolar level (5 × 10−18 M) with SERS enhancement factors (EFs) exceeding 1010. More importantly, the Raman signals showed good uniformity (RSD of 11.5%) for the concentration of 2 × 10−17 M. A good linear relationship was obtained in the quantitative concentration range of 10−12 M to 5 × 10−18 M with a high correlation coefficient (R2) of 0.996. These wettability-patterned microchips exhibit high performance (that is, both good sensitivity and good uniformity) in the detection of ultra-trace molecules in aqueous solutions, avoiding the need for expensive equipment and considerable skill in operations. The proposed strategy could also be applied to other microfluidic devices for rapid and simple analyte pre-concentration.

Generalization of Self-Assembly Toward Differently Shaped Colloidal Nanoparticles for Plasmonic Superlattices.

Periodic superlattices of noble metal nanoparticles have demonstrated superior plasmonic properties compared to randomly distributed plasmonic arrangements due to near-field coupling and constructive far-field interference. Here, a chemically driven, templated self-assembly process of colloidal gold nanoparticles is investigated and optimized, and the technology is extended toward a generalized assembly process for variously shaped particles, such as spheres, rods, and triangles. The process yields periodic superlattices of homogenous nanoparticle clusters on a centimeter scale. Electromagnetically simulated absorption spectra and corresponding experimental extinction measurements demonstrate excellent agreement in the far-field for all particle types and different lattice periods. The electromagnetic simulations reveal the specific nano-cluster near-field behavior, predicting the experimental findings provided by surface-enhanced Raman scatteringmeasurements. It turns out that periodic arrays of spherical nanoparticles produce higher surface-enhancedRamanscatteringenhancement factors than particles with less symmetry as a result of very well-defined stronghotspots.

Additional Important Considerations in Surface-Enhanced Raman Scattering Enhancement Factor Measurements

Despite considerable progress, the issues for precise evaluation of the surface-enhanced Raman scattering (SERS) substrate enhancement factor (EF) have not yet been completely solved until now. Herein, we verify that key aspects of probe molecules including initial concentration, footprint, and diffusion kinetics need to be taken into account for the experimental SERS EF measurement. The three factors collectively affect the surface coverage and thereby the determination of the number of probe molecules on the SERS substrate. We recommend that the measurement of the SERS EFs should be performed with complete surface coverage of probe molecules at steady-state equilibrium using relatively high initial concentrations. It has been demonstrated for the first time that the SERS EFs are independent of the initial concentration of probe molecules when exceeding the threshold initial concentration for complete surface coverage. This study highlights the importance of probe molecules in terms of diffusion kinetics and surface coverage for the accurate determination of the SERS EFs, which has yet to be addressed in the literature.

π-Conjugated Small Organic Molecule-Modified 2D MoS2 with a Charge-Localization Effect Enabling Direct and Sensitive SERS Detection

Organic semiconductors have been discovered to exhibit impressive surface-enhanced Raman scattering (SERS) activity recently. However, owing to the underdeveloped candidate materials and relatively low SERS sensitivity, practical application of SERS detection based on organic materials is still a challenge. Herein, we explored ways to further enhance the SERS sensitivity of π-conjugated fluorinated 7,7,8,8-tetracyanoquinodimethane derivatives (FnTCNQ, n = 2, 4) by utilizing the charge-localization effect induced by two-dimensional (2D) MoS2 flakes. A strong Raman signal enhancement in SERS has been realized via an organic/2D heterostructure constructed by FnTCNQ nanostructures grown on a 2D MoS2 flake. Moreover, F2TCNQ and F4TCNQ show different SESR sensitivities due to different numbers of cyano groups leading to different charge transfer (CT) directions. The SERS enhancement factor (EF) of methylene blue (MB) molecules on the optimal F4TCNQ/MoS2 nanocomposite substrate can reach as high as 2.531 × 106, and the concentration of the limit of detection (LOD) is as low as 10-10 M. The SERS results for MB, rhodamine 6G (R6G), and 4-aminothiophenol (4-ATP) molecules demonstrate that high versatility, low cost, good stability, and easy preparation will make the FnTCNQ/MoS2 SERS platform promising for the detection of trace molecules. The studies on the complex microscopic interaction of organic/2D composite nanomaterials will provide some novel insights into improved SERS performance and mechanisms.

Au/Ag SERS active substrate for broader wavelength excitation

Self-organized Ag nanoparticles arrays capped with Au layer are produced by depositing Ag nanoparticles on ion beam produced ripple patterned Si substrate followed by Au deposition. Au/Ag combination of nanoparticles shows intermediate plasmonic properties of Ag and Au nanoparticles by overcoming the associated drawbacks. Such combination redshifts the Localized Surface Plasmon Resonance (LSPR) compared to pure Ag and makes them suitable to excite the surface plasmon by both 532 nm and 785 nm laser for a wider range SERS application. The optimized Au deposition decreases the interparticle gap and elongates the nanoparticles along the ripple direction and makes a larger redshift in the LSPR. FDTD simulation also revealed that the electric field enhancement is higher along the ripple direction for both exciting lasers and shows that the LSPR of the combined Au/Ag system is shifted towards 785 nm. The limit of detection of Crystal Violet using the optimized Au/Ag substrate is found to be 10−10 M for 532 nm laser and 10−8 M for 785 nm laser, respectively. The substrate shows good spatial uniformity with a relative standard deviation of less than 10% with SERS enhancement factors in the order of 104-105 for both lasers. These studies suggest that the as-prepared substrate is a promising candidate for detecting molecules sensitive to different wavelengths of laser excitation.

Morphology-regulated core–shell Ag@Au NPs for rapid SERS detection of 1-amino-hydantoin (AHD) in crayfish

ABSTRACT Gold-coated silver core–shell nanoparticles (Ag@Au NPs) have been widely used for SERS analysis due to plasmon resonance performances. However, it is a great challenge to fabricate Ag@Au core–shell structures with specified morphology. In this paper, the size and shape of Ag NPs (core) were precisely controlled by a seed-mediated approach, and then the gold shell was completely coated on under the strong reduction of ascorbic acid, resulting in Ag@Au NPs with highly regulated morphology. The obtained Ag@Au NPs achieved a similar or even better SERS enhancement factor (EF) (up to 5.7 × 107) compared to Ag NPs, but significantly higher stability. For the rapid SERS detection of nitrofurantoin metabolite AHD, a limit of detection (LOD) as low as 1 × 10−10 M and a wide linear range from 1 × 10−4 to 1 × 10−8 M were obtained. Furthermore, recoveries for crayfish samples were from 90.5% to 108%, indicating a good performance of the presented method in real sample detection.

Seed-mediated growth of highly concentrated silver nanoparticles on a flexible substrate for applications in SERS-based trace detection

In this work, we demonstrate a seeded approach for in-situ growth of Ag nanostructures directly on filter paper. Multiple growth steps were used to increase the size of Ag NPs grown from Au seeds. Essentially, this procedure generated a high density of NPs on filter paper which in turn provided high enhancement of Raman signals. We have seen a marked increase in the SERS enhancement factor with each growth step. Moreover, the relative standard deviation (RSD) values decreased with each growth step, indicating the relatively uniform distribution of NPs on the substrate. With four growth steps, we were able to achieve an EF of 9.28 × 104 with RSD values of 14%. In particular, the detection limit of 10 nM for CV has been achieved by both solution drying and swabbing. Moreover, swab detection of explosive material ammonium nitrate down to 100 µM has also been demonstrated.

Quasi‐3D‐Structured Surface‐Enhanced Raman Scattering Substrates Based on Silver Nanoparticles/Mesoporous Silicon Hybrid

The surface‐enhanced Raman scattering (SERS) is a powerful spectroscopic technique for ultrasensitive and selective biochemical detection due to its capability of providing the “fingerprint” of information of molecular structures at low concentrations. Herein, mesoporous silicon (MPSi)‐based nanocomposites containing silver nanoparticles (AgNPs) provide novel efficient substrates for the detection of molecules. The quasi‐3D‐structured SERS substrate is formed by introducing Ag into the MPSi hollow column‐shaped nanostructure. This SERS substrate uniquely combines the ability of metal surfaces to amplify Raman scattering signals with an enlarged surface area and the increasing light–matter interaction duration that generates large SERS signals for the detection of chemicals. The proposed SERS substrate is verified by detecting orange methylene in solutions at ultralow concentration in the range of 10−11–10−6 m with a linear‐dependent coefficient of R2 = 0.99922 and the SERS enhancement factor is achieved up to 1010. Moreover, the proposed platform can detect diphenylamine with ultralow concentration of 10−10 m and reliable reproducibility with an average relative stand deviation of 6.3%. The ability for MPSi substrate to detect target molecules at low concentrations helps pave a way to develop the detection tool for integrated, on‐chip devices.

Surface-enhanced Raman Scattering of Au–Ag bimetallic nanopillars fabricated using surface-plasmon lithography

Arrays of gold–silver (Au–Ag) bimetallic nanopillars were fabricated by a newly developed surface-plasmon lithography (SPL) and their enhancement properties as surface-enhanced Raman scattering (SERS) substrates have been studied. We demonstrated that the SPL is a low-cost and high efficiency method for the fabrication of SERS substrates with both high sensitivity and reproducibility. The nanopillars showed a good response in the detection of methylene blue molecules at a low concentration of 1.0 × 10–11 mol· l−1. The SERS enhancement factors (EFs) are on the orders of 107 and the relative standard deviation of SERS intensity is <8% over an area of 50 μm × 50 μm. The EFs increase fast with the height increasing from 200 to 530 nm, then increase slowly when further increase the height of the nanopillars to 1100 nm. In addition, the Au–Ag bimetallic coating has shown much higher SERS enhancement than the coatings of either the pure Au or Ag. The excellent SERS enhancement and reproducibility of the Au–Ag coated nanopillars indicated that the fabricated SERS substrates can be used for the detection of biochemical molecules at trace level and the SPL is a promising method for fabrication of SERS substrates.