Detection Of Rhodamine 6G Research Articles

Enhanced SERS signal in the hybrid substrate through electronic modulation of CVD grown single-layer graphene

The ever-growing demand for sensitive and reliable detection of hazardous material in the food chain and trace detection of chemical entities in a variety of field attracted advanced Surface Enhanced Raman Spectroscopy (SERS) active materials such as graphene-based hybrid SERS. The graphene silver nanostructures (AgNS) based hybrid SERS substrates are explored to understand the critical role of pristine graphene grown by chemical vapor deposition (CVD) on SERS signal and its possible mechanism. A lithography-free fabrication process has been developed for growth of uniform array of AgNS with varying both particle sizes and inter-particle gaps. The optimal AgNS with average feature size ∼40 nm and average inter-particle spacing of ∼13 nm demonstrated the maximum SERS enhancement with rhodamine 6G (R6G). The single-layer graphene (SLG) grown by CVD with the aid of controlling the reaction geometry with growth under a free molecular regime leads to the highest quality graphene with I2D/IG ratio of ∼3.58 and ID/IG ratio of ∼0.154. The flow regime-controlled CVD-grown SLG integrated with AgNS and its SERS enhancement mechanism is explored for trace detection of R6G. The graphene with its ability to modulate the electronic structure and tune it relative to the highest occupied molecular orbital-lowest occupied molecular orbital (HOMO-LUMO) levels of R6G molecules resulted in improved SERS signal by about an order for graphene-AgNS hybrid structure as compared to bare AgNS. The obtained findings paved the way for the futuristic and reliable hybrid SERS substrate for trace-level detection of a wide range of chemical entities.

Eco-sustainable and flexible SERS platform based on waste cellulose decorated by Ag nanoparticles

This paper presents an innovative and environmentally friendly technology for the fabrication of low-cost SERS (Surface-Enhanced Raman Spectroscopy) sensors based on flexible substrates made of cellulose fibers reclaimed from waste. The substrates are decorated with nanostructured silver (Ag) thin films produced by pulsed laser deposition (PLD). In this process, the deposition conditions (laser fluence, gas pressure, target-substrate distance, deposition time, etc.) were optimized to enhance the SERS response. Different types of paper with different textures were tested, as it was also observed that the paper roughness significantly influences SERS efficiency. The samples were characterized using UV–Vis absorption spectroscopy, SEM microscopy, and surface profilometry to evaluate both the paper and the deposited films' morphologies. The SERS activity was assessed by detecting Rhodamine 6G in aqueous solutions drop-casted on the sensors, with concentrations ranging from 10−2 M to 10−10 M. Measurements were carried out using a handheld instrument equipped with dual excitation laser lines centered at 785 nm and 833 nm. The observed lower detection limit of 10−10 M was achieved across all paper types tested. These results demonstrate the potential of integrating smart, eco-friendly materials in the fabrication of chemical sensors for sustainable advancement in environmental monitoring and safety. The materials not only exhibit excellent sensing capabilities but also minimize ecological footprints through renewable sourcing and eco-friendly production processes. While the deposition protocol is well-established for other substrates, this study marks the first exploration of its use on biomass-derived substrates.

The Influence of Thickness and Spectral Properties of Green Color-Emitting Polymer Thin Films on Their Implementation in Wearable PLED Applications.

A systematic investigation of optical, electrochemical, photophysical, and electrooptical properties of printable green color-emitting polymer (poly(9,9-dioctylfluorene-alt-bithiophene)) (F8T2) and spiro-copolymer (SPG-01T) was conducted to explore their potentiality as an emissive layer for wearable polymer light-emitting diode (PLED) applications. We compared the two photoactive polymers in terms of their spectral characteristics and color purity, as these are the most critical factors for wearable lighting sources and optical sensors. Low-cost, solution-based methods and facile architecture were applied to produce rigid and flexible light-emitting devices with high luminance efficiencies. Emission bandwidths, color coordinates, operational characteristics, and luminance were also derived to evaluate the device's stability. The tuning of emission's spectral features by layer thickness variation was realized and was correlated with the interplay between H-aggregates and J-aggregates formations for both conjugated polymers. Finally, we applied the functional green light-emitting PLED devices based on the two studied materials for the detection of Rhodamine 6G. It was determined that the optical detection of the R6G photoluminescence is heavily influenced by the emission spectrum characteristics of the PLED and changes in the thickness of the active layer.

Atomic Basal Defect-Rich MoS2 by One-Step Synthesis and Mechanism Exploration.

Two-dimensional molybdenum disulfide (2D MoS2) shows great promise as a surface-enhanced Raman scattering (SERS) substrate due to its strong exciton resonance. However, the inert basal plane limits the performance of SERS. In this work, a strategy is proposed for the one-step synthesis of atomically basal defect-rich MoS2. The study first reveals that NaCl plays a two-stage role in the growth process, where NaCl initially promotes the rapid growth of large MoS2 as previously reported, and then promotes the formation of atomic basal defects dominated by single sulfur vacancies. Additionally, spectral changes induced by modulation of experimental parameters and density function theory calculation show that defect generation occurs during cooling. Meanwhile, the ratio of to A1g in defect-rich MoS2 exhibits different variation trends compared with pristine MoS2 in power-dependent Raman, and the ratio increases with increasing basal defects. In SERS tests, the limit of detection for rhodamine 6G reached 10-9m, which is comparable to the performance of conventional noble metal SERS substrate. The activation strategy of the inert basal plane is applicable to other 2D transition metal dichalcogenides, and further has the potential to enhance performance in other domains, such as SERS and hydrogen evolution reactions.

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.

Hydrothermally in-situ grown MoS2 films over different conducting substrates as electrochemical-SERS biosensors

Detection of organic pollutants and biomolecules at very low concentrations is a great challenge for protecting the environment and diagnosis of human health. Noble metal nanomaterials have been employed as active surface-enhanced Raman spectroscopy (SERS) substrates for such detection but suffer with high cost. The two-dimensional (2D) transition-metal dichalcogenides (TMDs) can be used as cost-effective alternative SERS substrates for the detection of organic impurities and biomolecules. Here, we report the hydrothermally synthesized in-situ grown MoS2 films over conducting carbon paper (CCP) and fluorine-doped tin oxide (FTO) coated glass and used them as SERS substrates for the detection of Rhodamine 6G (R6G), vitamin B12 and bilirubin. We observe that hydrothermally in-situ grown MoS2 film over FTO coated glass (MoS2-FTO) shows a better SERS detection limit for studied analytes compared to the in-situ grown MoS2 film over conducting carbon paper (MoS2-CCP). We observe the detection of R6G, vitamin B12, and bilirubin with maximum enhancement factors of 2.42 × 106, 4.18 × 102, and 2.78 × 106, respectively, using MoS2-FTO as SERS substrate. Furthermore, we demonstrate the electrochemical-SERS (EC-SERS) activity of prepared SERS substrates. The MoS2-FTO shows a better EC-SERS signal as compared to MoS2-CCP due to the high conductivity (maximum charge transfer at oxidation potential), strong chemical adsorption, change of orientation, and density of the molecules on the surface of the substrate.

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.

Suppression of coffee rings by controllable nanoparticle enrichment through superhydrophobicity-enabled dynamic evaporation

Coffee rings formed by evaporation of analyte-containing droplets are widely observed in micropatterning, bio-arrays, and trace detection. The coffee-ring effect caused by contact line pinning significantly affects the detection uniformity and sensitivity. Here, we propose a simple and operable method to effectively suppress coffee rings through controllable nanoparticles aggregation by superhydrophobicity-enabled dynamic evaporation. The gold nanoparticles (AuNPs) deposition footprint formed after dynamic evaporation on an integrated superhydrophobic surface was reduced by ∼3 orders of magnitude compared to that of non-interventional evaporation. Detailed experiments, numerical simulations, and theoretical studies have revealed that substrate wettability, temperature and droplet motion behaviors play significant roles in suppressing coffee-ring effect. More critically, based on the force mechanism of AuNPs at the interface/contact line, universal mathematical models and regime maps were established to classify the different deposition modes for AuNPs under different evaporation conditions by introducing dimensionless parameter G, revealing the enrichment mechanism of AuNPs in droplets under superhydrophobicity-enabled dynamic evaporation. The accuracy of the theoretical model and enrichment mechanism was demonstrated through the single-molecule detection of rhodamine 6G with excellent sensitivity (10–17 M, enhancement factor ∼1013) and perfect uniformity (relative standard deviation ∼5.57 %), which provides a valuable guide for research and applications of nanoparticle aggregation.

Non-invasive detection of systemic lupus erythematosus using SERS serum detection technology and deep learning algorithms

Systemic lupus erythematosus (SLE) is an autoimmune disease with multiple symptoms, and its rapid screening is the research focus of surface-enhanced Raman scattering (SERS) technology. In this study, gold@silver-porous silicon (Au@Ag-PSi) composite substrates were synthesized by electrochemical etching and in-situ reduction methods, which showed excellent sensitivity and accuracy in the detection of rhodamine 6G (R6G) and serum from SLE patients. SERS technology was combined with deep learning algorithms to model serum features using selected CNN, AlexNet, and RF models. 92 % accuracy was achieved in classifying SLE patients by CNN models, and the reliability of these models in accurately identifying sera was verified by ROC curve analysis. This study highlights the great potential of Au@Ag-PSi substrate in SERS detection and introduces a novel deep learning approach for SERS for accurate screening of SLE. The proposed method and composite substrate provide significant value for rapid, accurate, and noninvasive SLE screening and provide insights into SERS-based diagnostic techniques.

Detection of water pollutants using super-hydrophobic porous silicon-based SERS substrates.

Super hydrophobic porous silicon surface is prepared using a wet chemical synthesis route. Scanning electron microscopic investigation confirms a correlation between pore size and reaction time. SERS substrates are prepared by silver nanoparticle deposition on porous silicon surface. They exhibit excellent characteristics in terms of sensitivity, reproducibility, stability, and uniformity. They could detect rhodamine 6G in femtomolar range with SERS enhancement factor of ~ 6.1 × 1012, which is best ever reported for these substrates. Molecule-specific sensing of water pollutants such as methylene blue, glyphosate, andchlorpyrifos, is demonstrated for concentrations well below their permissible limits along with excellent enhancement factors. Porous silicon substrate functionalized with Ag nanoparticles demonstrates to be a promising candidate for low-cost, long-life, reliable sensors for environmental conservation applications.

A Wettability Contrast SERS Droplet Assay for Multiplexed Analyte Detection.

Droplet assay platforms have emerged as a significant methodology, providing distinct advantages such as sample compartmentalization, high throughput, and minimal analyte consumption. However, inherent complexities, especially in multiplexed detection, remain a challenge. We demonstrate a novel strategy to fabricate a plasmonic droplet assay platform (PDAP) for multiplexed analyte detection, enabling surface-enhanced Raman spectroscopy (SERS). PDAP efficiently splits a microliter droplet into submicroliter to nanoliter droplets under gravity-driven flow by wettability contrast between two distinct regions. The desired hydrophobicity and adhesive contrast between the silicone oil-grafted nonadhesive hydrophilic zone with gold nanoparticles is attained through (3-aminopropyl) triethoxysilane (APTES) functionalization of gold nanoparticles (AuNPs) using a scotch-tape mask. The wettability contrast surface facilitates the splitting of aqueous droplets with various surface tensions (ranging from 39.08 to 72 mN/m) into ultralow volumes of nanoliters. The developed PDAP was used for the multiplexed detection of Rhodamine 6G (Rh6G) and Crystal Violet (CV) dyes. The limit of detection for 120 nL droplet using PDAP was found to be 134 pM and 10.1 nM for Rh6G and CV, respectively. These results align with those from previously reported platforms, highlighting the comparable sensitivity of the developed PDAP. We have also demonstrated the competence of PDAP by testing adulterant spiked milk and obtained very good sensitivity. Thus, PDAP has the potential to be used for the multiplexed screening of food adulterants.

Unlocking the power of nano Petals: Magnifying Rhodamine 6G detection sensitivity in SERS

The escalating prevalence of hazardous, chromatic dye pollutants necessitates the implementation of a discerning and expeditious detection methodology. This investigation responds to this imperative by introducing silver-coated nickel oxide (Ag@NiO) nanostructured thin films as efficacious substrates for Surface-Enhanced Raman Spectroscopy (SERS). Interrogating the exceptional enhancement capabilities of Ag@NiO nano petals and unraveling the underlying mechanisms governing their formation, the study provides valuable insights into the optimization of SERS substrate fabrication. X-ray diffraction (XRD) analysis affirms the presence of a Face-Centered Cubic (FCC) structure within NiO, accompanied by an average crystallite size ranging from 38 to 53 nm. Scanning electron microscopy (FESEM) images unveil petal-like morphologies with widths fluctuating between 36 and 48 nm. Energy-dispersive X-ray (EDX) analysis validates the elemental composition, while UV–visible spectrum analysis delineates a band gap energy (Eg) spectrum spanning from 3.23 to 3.43 eV. Of particular significance is the showcase of Ag@NiO nano petals' astounding enhancement factor, reaching an impressive 3.2 x 107 for Rhodamine 6G (R6G). This enables detection at an extraordinary limit of 10-7 mol/L. These discernments not only propel advancements in SERS substrate engineering but also harbor implications for the meticulous analysis of R6G dye and other environmental pollutants, thereby enriching the arsenal of chemical sensing and environmental monitoring methodologies.

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.

Benchtop Fabricated Nano-Roughened Microstructured Electrodes for Electrochemical and Surface-Enhanced Raman Scattering Sensing.

Tailoring a material's surface with hierarchical structures from the micro- to the nanoscale is key for fabricating highly sensitive detection platforms. To achieve this, the fabrication method should be simple, inexpensive, and yield materials with a high density of surface features. Here, using benchtop fabrication techniques, gold surfaces with hierarchically structured roughness are generated for sensing applications. Hierarchical gold electrodes are prepared on pre-stressed polystyrene substrates via electroless deposition and amperometric pulsing. Electrodes fabricated using 1mm H[AuCl₄] and roughened with 80 pulses revealed the highest electroactive surface area. These electrodes are used for enzyme-free detection of glucose in the presence of bovine serum albumin and achieved a limit of detection of 0.36mm, below glucose concentrations in human blood. The surfaces nanoroughened with 100 pulses also showed excellent surface-enhanced Raman scattering (SERS) response for the detection of rhodamine 6G, with an enhancement factor of ≈2×106 compared to detection in solution, and for the detection of a self-assembled monolayer of thiophenol, with an enhancement factor of ≈30 compared to the response from microstructured gold surfaces. It is envisioned that the simplicity and low fabrication cost of these gold-roughened structures will expedite the development of electrochemical and SERS sensing devices.

Highly ordered TiO2 Nanotubes decorated with plasmonic silver nanoparticles (TiO2/Ag) for ultra-sensitive SERS detection of textile dye contaminant Rhodamine 6 G

We report a susceptible, ultrafast, molecular fingerprint-specific detection tool of analytes at an extreme trace concentration using surface-enhanced Raman spectroscopy (SERS). Highly ordered TiO2 Nanotubes (NT) modified with plasmonic Ag nanoparticles (Ag) are fabricated by wet chemical strategy. TiO2/Ag nanostructures could benefit the SERS mechanism arising from the effects of both the charge transfer process within TiO2/Ag/analyte and the enhancement in the electromagnetic field by the twining of plasmonic Ag nanoparticles with the construction of semiconductor/plasmonic bi-component system (TiO2/Ag). To achieve a better density of Ag NPs on TiO2 nanotubes, the photoinduction process irradiation time was varied from 10 min to 40 min. The prepared bicomponent SERS system was validated for its structural and morphological properties. SERS optimization studies were analyzed with the probe molecule Rhodamine 6 G (R6G) with an initial concentration of 10−6M. The highest SERS enhancement was notified with TiO2/Ag20 min for R6G sensing. The fabricated optical sensor reproducibility in signal detection was scrutinized with Raman mapping studies and statistically validated by low RSD values of 9.8%. Furthermore, their detectability was gauged with low concentration detection of R6G down to Pico-molar levels (10−12M). Synergistic effects of both CT and EM contributed to SERS enhancement to trace and detected pico-levels of R6G by the fabricated bicomponent semiconductor/ plasmonic heterostructure system (TiO2/Ag 20 min).

Sandwich-like CuNPs@AgNPs@PSB SERS substrates for sensitive detection of R6G and Forchlorfenuron

The development of a highly sensitive, synthetically simple and economical SERS substrate is technically very important. A fast, economical, sensitive and reproducible CuNPs@AgNPs@ Porous silicon Bragg reflector (PSB) SERS substrate was prepared by electrochemical etching and in situ reduction method. The developed CuNPs@AgNPs@PSB has a large specific surface area and abundant “hot spot” region, which makes the SERS performance excellent. Meanwhile, the successful synthesis of CuNPs@AgNPs can not only modulate the plasmon resonance properties of nanoparticles, but also effectively prolong the time stability of Cu nanoparticles. The basic performance of the substrate was evaluated using rhodamine 6G (R6G). (Detection limit reached 10−15 M, R2 = 0.9882, RSD = 5.3 %) The detection limit of Forchlorfenuron was 10 μg/L. The standard curve with a regression coefficient of 0.979 was established in the low concentration range of 10 μg/L −100 μg/L. This indicates that the prepared substrates can accomplish the detection of pesticide residues in the low concentration range. The prepared high-performance and high-sensitivity SERS substrate have a very promising application in detection technology.

Deposition of alternative plasmonic ZrHfN thin films via closed-field dual-cathode DC unbalanced magnetron sputtering for enhanced SEF substrate applications

We present the preparation of zirconium hafnium nitride thin films as an alternative plasmonic sensing material. The ZrHfN thin films were deposited by closed-field dual-cathode DC unbalanced magnetron sputtering without an external substrate heating/biasing. A comprehensive investigation into the effect of zirconium sputtering current on the physical structural, and chemical compositions was systematically characterized by grazing-incidence X-ray diffraction, transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy. Our results indicate that the optimal ZrHfN thin films deposited at 500 mA-IZr exhibit good crystallinity and high surface roughness, which presents excellent surface-enhanced fluorescent substrate performance for detecting rhodamine 6G at a limit of detection of 5.99 × 10−8 M, an enhancement factor of 15.62 ± 0.79-fold and displaying reusability through 25 cycles. These findings suggest promising prospects for developing ZrHfN-based SEF sensor chips for diverse applications in the future.

CVD grown bi-layer MoS2 as SERS substrate: Nanomolar detection of R6G and temperature response

The two-dimensional bi-layer MoS2 is less investigated as compared to monolayer and few-layer (4–6 layers) MoS2 for fundamental aspects and applications such as photodetectors, transistors, etc. In the present work, we prepare triangular-shaped bi-layer MoS2 over SiO2/Si substrate via chemical vapour deposition (CVD) technique for surface enhanced Raman scattering (SERS) based detection of Rhodamine 6G (R6G). We perform density functional theory calculations and spectroscopy studies to investigate the semiconducting feature of bi-layer MoS2. We demonstrate the nanomolar concentration (10-9 M) limit for R6G detection at room temperature using pristine bi-layer MoS2 as SERS substrate. Further, we also examine the cryogenic response of the SERS detection of R6G with bi-layer MoS2 for the first time. The high detection limit of CVD-grown bi-layer MoS2 is ascribed to the charge transfer enabled via vibronic coupling between MoS2 and R6G molecules. This study paves the way for cryogenic-based SERS sensing.

A facile paper-based chromatography coupled Au nanodendrite on nickel foam for application in separation and SERS measurement

A simple paper-based chromatography coupling with nickel foam decorated Au nanodendrite (PP-AuND/NiF) was fabricated for simultaneous separation and surface-enhanced Raman scattering (SERS) detection of Rhodamine-6G (R6G) from a mixture of analytes. The three-dimensional porous nickel foam (NiF) was employed as a sampling diffusion platform, and AuND with a high surface active area beneficial for SERS efficiency was electro-deposited directly onto the NiF frame. The structure of AuND/NiF was characterized by X-ray diffraction and scanning electron microscopy. The AuND/NiF could detect R6G at 0.1 nM, and the enhancement factor was 1.84 x 106. The AuND/NiF was durable, with a slight signal decrease after 6 m of drop-testing. Also, upon three days of exposure to ambient air, the signal droped only 3.35 %. Subsequently, the PP-AuND/NiF was constructed by directly situating AuND/NiF on a paper strip, serving as a sample in and out to AuND/NiF. A mixture of two SERS active compounds, namely 2-Naphthalenethiol (2-NpSH) and Rhodamine 6G (R6G), was prepared in ethanol: water (1:1) solution to evaluate PP-AuND/NiF separation capability. Raman measurements along different distances of AuND/NiF were performed, and the signal of 2-NpSH was dismissed after 3.0 mm, while R6G’s signals were observed throughout AuND/NiF. In general, the PP-AuND/NiF demonstrated effective separation and SERS measurement of analytes in a mixture, which could be applicable for more complex samples in the future, especially in clinical analysis.

Fabrication of Superhydrophobic–Hydrophilic Patterned Cu@Ag Composite SERS Substrate via Femtosecond Laser

Ultralow concentration molecular detection is critical in various fields, e.g., food safety, environmental monitoring, and disease diagnosis. Highly sensitive surface-enhanced Raman scattering (SERS) based on ultra-wettable surfaces has attracted attention due to its unique ability to detect trace molecules. However, the complexity and cost associated with the preparation of traditional SERS substrates restrict their practical application. Thus, an efficient SERS substrate preparation with high sensitivity, a simplified process, and controllable cost is required. In this study, a superhydrophobic–hydrophilic patterned Cu@Ag composite SERS substrate was fabricated using femtosecond laser processing technology combined with silver plating and surface modification treatment. By inducing periodic stripe structures through femtosecond laser processing, the developed substrate achieves uniform distribution hotspots. Using the surface wettability difference, the object to be measured can be confined in the hydrophilic region and the edge of the hydrophilic region, where the analyte is enriched by the coffee ring effect, can be quickly located by surface morphology difference of micro-nanostructures; thus, greatly improving detection efficiency. The fabricated SERS substrate can detect Rhodamine 6G (R6G) at an extraordinarily low concentration of 10−15 mol/L, corresponding to an enhancement factor of 1.53 × 108. This substrate has an ultralow detection limit, incurs low processing costs and is simple to prepare; thus, the substrate has significant application potential in the trace analysis field.