High-performance Surface-enhanced Raman Scattering Research Articles

Photoinduced Charge Transfer Empowers Ta4C3 and Nb4C3 MXenes with High SERS Performance.

This study introduces two-dimensional (2D) Ta4C3 and Nb4C3 MXenes as outstanding materials for surface-enhanced Raman scattering (SERS) sensing, marking a significant departure from traditional noble-metal substrates. These MXenes exhibit exceptional SERS capabilities, achieving enhancement factors around 105 and detection limits as low as 10-7 M for various analytes, including environmental pollutants and drugs. The core of their SERS functionality is attributed to the robust interfacial photoinduced charge-transfer interactions between the MXenes and the adsorbed molecules. This deep insight not only advances our understanding of MXene materials in SERS applications but also opens new avenues for developing highly sensitive and selective SERS sensors. The potential of Ta4C3 and Nb4C3 MXenes to revolutionize SERS technology underscores their importance in environmental monitoring, food safety, and beyond.

A durian-shaped multilayer core-shell SERS substrate for flow magnetic detection of pesticide residues on foods

A new type of durian-shaped Fe3O4@Au@Ag@Au (DFAAA) multilayer core-shell composite was prepared as an efficient surface-enhanced Raman scattering (SERS) substrate. The optimization process and SERS enhancement mechanism of the substrate were further explained with finite-difference time-domain simulation. The dense and uniform spiny array on the DFAAA surface had abundant “hot spots”, greatly improving sensitivity, uniformity and reproducibility, with a Raman enhancement factor of 3.01 × 107 and storage-life of 30 d. A “flow magnetic detection method” was proposed to realize rapid and flexible detection of pesticide residues on the surface of different foods including fish and apple. The limit of detection of malachite green and thiram on the fish and apple surfaces were 0.13 and 0.18 ng/cm2, respectively. With its high SERS performance and good magnetic, the DFAAA possessed great application prospects as a facile SERS substrate for rapid and non-destructive detection of trace pesticide residues on foods.

The Advanced Applications of 2D Materials in SERS

Surface-enhanced Raman scattering (SERS) as a label-free, non-contact, highly sensitive, and powerful technique has been widely applied in determining bio- and chemical molecules with fingerprint recognitions. 2-dimensional (2D) materials with layered structures, tunable optical properties, good chemical/physical stabilities, and strong charge–transfer interaction with molecules have attracted researchers’ interests. Two-D materials with a large and flat surface area, as well as good biocompatibility have been considered promising candidates in SERS and widely applied in chemical and bio-applications. It is well known that the noble metallic nanostructures with localized surface plasmon effects dominate the SERS performance. The combination of noble metallic nanostructure with 2D materials is becoming a new and attractive research domain. Until now, the SERS substrates combined with 2D materials, such as 2D graphene/metallic NPs, 2D materials@metallic core-shell structures, and metallic structure/2D materials/metallic structure are intensely studied. In this review, we introduce different kinds of fabrication strategies of 2D and 3D SERS substrates combing with 2D materials as well as their applications. We hope this review will help readers to figure out new ideas in designing and fabricating SERS substrates with high SERS performance that could enlarge the applicable domains of SERS.

Large Area Patterning of Highly Reproducible and Sensitive SERS Sensors Based on 10-nm Annular Gap Arrays.

Applicable surface-enhanced Raman scattering (SERS) active substrates typically require low-cost patterning methodology, high reproducibility, and a high enhancement factor (EF) over a large area. However, the lack of reproducible, reliable fabrication for large area SERS substrates in a low-cost manner remains a challenge. Here, a patterning method based on nanosphere lithography and adhesion lithography is reported that allows massively parallel fabrication of 10-nm annular gap arrays on large areas. The arrays exhibit excellent reproducibility and high SERS performance, with an EF of up to 107. An effective wearable SERS contact lens for glucose detection is further demonstrated. The technique described here extends the range of SERS-active substrates that can be fabricated over large areas, and holds exciting potential for SERS-based chemical and biomedical detection.

A Comprehensive Commentary of “Smart Design of High-Performance Surface Enhanced Raman Scattering Substrates”

Recently, our group published a review about surface enhanced Raman scattering (SERS) in SmartMat, which summarized the recent developments of noble metal and semiconductor SERS substrates, and then proposed the key factors for substrate design and future directions. The fundamental theories for SERS technique, i.e., the electromagnetic enhancement mechanism and chemical enhancement mechanism, and the design strategies for noble metal and semiconductor substrates are introduced detailed

Ag nanoparticle-modified porous nickel foam nanotemplate: An efficient surface-enhanced Raman scattering platform for the rapid detection of artemisinin

Because of the advantages of rapid sampling and real-time detection, the surface-enhanced Raman scattering (SERS) technique provides greater potential for ultrasensitive detection of active components in traditional Chinese medicine. In this paper, an ultrasensitive SERS detection system was successfully designed using controllable magnetron sputtering technology for the rapid and quantitative detection of artemisinin, a traditional Chinese medicine. Using nickel foam (NF) with a three-dimensional porous mesh structure as a template, Ag nanoparticle layers were sputtered on the NF surface by the magnetron sputtering technique to prepare Ag-NF-20 (the magnetron sputtering time was 20 min) SERS substrates with high SERS performance. According to the SERS signal response of the R6G molecule on the Ag-NF-20 substrate, this efficient SERS platform showed excellent Raman signals and enhanced performance and time-stability. The results suggested that owing to the abundant electromagnetic enhancement “hot spots” distributed on Ag-NF-20 nanostructures, an experimental enhancement factor value of 6.57 × 105 was obtained. The time-stability for 30 days in an atmospheric environment was also determined, which revealed that a minimum decrease of 2.6% in Raman signal intensity was recorded, indicating the excellent time-stability of the Ag-NF-20 substrate. Furthermore, when applying this in the detection of artemisinin, the limit of detection value for artemisinin was 1 × 10−4 ng/ml. Therefore, the Ag-NF-20 SERS substrate has great potential for trace detection of other active ingredients in traditional Chinese medicine and is expected to expand the detection of pharmacodynamic substances in clinical drugs.

Construction of black phosphorus nanosheets and Ag nanoparticles co-sensitized TiO2 nanorod arrays as high-performance SERS substrate and photocatalyst

In this study, high-performance surface-enhanced Raman scattering (SERS) substrates and photocatalysts based on TiO2 nanorod (TNR) arrays co-sensitized with black phosphorus (BP) nanosheets and Ag nanoparticles were successfully synthesized. The detection limit of the organic pollutant rhodamine 6G (R6G) on this novel SERS substrate was as low as 1.0 × 10−14 M. The calculated enhancement factor (EF) was as high as 3.81 × 105. These results prove the excellent SERS sensitivity of the BP/Ag/TNR substrate. Furthermore, a good uniformity of the signals was observed during the detection process. The relative standard deviation of the intensity of the Raman fingerprint peak of R6G at 1650 cm−1 was only 8.41%. Moreover, the BP/Ag/TNR substrate exhibited self-cleaning abilities through the photocatalytic degradation of the adsorbed R6G molecules. The BP/Ag/TNR substrate exhibited a maximum rate of 93.5% for the photocatalytic degradation of R6G. The corresponding photodegradation rate constant was 34.2 × 10−3 min−1, which was approximately 3.98 and 2.01 times higher than those of the TNR and Ag/TNR arrays. The improved SERS performance and excellent photocatalytic activity of the BP/Ag/TNR substrate was due to the formation of high-density hot spots, expansion of the optical capture abilities, and enhancement of the charge transfer properties.

Tunable and Highly Accessible Plasmonic Gap Nanostructures on Flexible Film as a High-Performance Surface-Enhanced Raman Scattering Sensor

Tunable and Highly Accessible Plasmonic Gap Nanostructures on Flexible Film as a High-Performance Surface-Enhanced Raman Scattering Sensor

Three-dimensional surface-enhanced Raman scattering substrates constructed by integrating template-assisted electrodeposition and post-growth of silver nanoparticles

Three-dimensional (3D) plasmonic nano-arrays can provide high surface-enhanced Raman scattering (SERS) sensitivity, good spectral uniformity and excellent reproducibility. However, it is still a challenge to develop a simple and efficient method for fabrication of 3D plasmonic nano-arrays with high SERS performance. Here we report a facile approach to construct ordered arrays of silver (Ag) nanoparticles-assembled spherical micro-cavities using polystyrene (PS) sphere template-assisted electrodeposition and post-growth. The electrodeposited small Ag nanoparticles grow into bigger stable nanoparticles during the post-growth process, which could significantly improve the SERS sensitivity. The Ag nanoparticles-assembled 3D micro-cavity array provides much more hotspots in the excitation laser beam-covered volume than the two-dimensional counterpart. The relative standard deviation (RSD) of 612 cm−1 peak of rhodamine 6G (R6G) was calculated to be 8%, and the RSD of the characteristic peak taken from substrates of different batches was less than 10%. The detectable lower concentration as low as 1 fM was achieved for an aqueous solution of R6G. Such SERS substrate also showed high sensitivity to thiram (fungicide) and paraquat (herbicide) in water with limits of detection of 0.067 nM and 2.5 nM respectively. Furthermore, it also demonstrated that SERS detection of pesticide residues on fruits can be realized, showing a potential application in rapid monitoring food safety.

Durable and flexible Ag-nanowire-embedded PDMS films for the recyclable swabbing detection of malachite green residue in fruits and fingerprints

Swab sampling for the trace surface-enhanced Raman scattering (SERS) analysis of an aromatic dye (e.g., malachite green, MG) residue in fruits as well as fingerprints is promising due to its practical utility and efficiency in food security and forensic science. However, the durability and recyclability of the SERS substrates pose an enormous challenge. In this study, a novel flexible film was constructed by embedding a commercial Ag nanowire suspension into a polydimethylsiloxane film (Ag NWs@PDMS), which simultaneously exhibits SERS activity, durability and recyclability. High SERS performance was still maintained, even against 20 times stretchability, corrosion by HNO3, destruction by ultrasonication and a broad working temperature of −20 ℃ to 80 ℃. Excellent recyclability for MG sensing was achieved in ten cycles. Ag NWs@PDMS was successfully used for the quantitative detection of MG in juices of fruits (such as apple and pear) by drop dripping, with a limit of detection of 10 nM and good anti-interference. Meanwhile, the sensitive detection of the MG residue (only 3 ng/cm2) on fruits was enabled by the on-site surface swabbing by recycling for five cycles. Portable detection of the MG residue was further achieved from the 10th fingerprint after successively touching a dye drop onto the functional film combined with a portable Raman spectrometer.

Mesoporous Au films assembled on flexible cellulose nanopaper as high-performance SERS substrates

The fabrication of nanoarchitectured mesoporous gold films on flexible cellulose nanofiber (CNF) paper is reported for high-performance surface-enhanced Raman scattering (SERS) substrates via an electrochemical deposition method using polymeric micelles. Silver nanowires (AgNWs) are coated onto 2,2,6,6-tetramethylpiperidine-1-oxy-oxidized CNF nanopaper (TEMPO-CNF), and the resulting AgNW@TEMPO-CNF substrate is used as a conductive electrode to guide the thickness-controllable electrodeposition of mesoporous Au. Interestingly, the electrodeposition of mesoporous Au on the AgNW@TEMPO-CNF nanopaper formed a dense network of anisotropic nanoscale creases and channels, whereas deposition on flat Au electrodes makes round mesopores. Numerical simulations performed on both types of structures show that these anisotropic mesopores create more hotspots per unit area than the round mesopore films. Importantly, the mAu@AgNW@TEMPO-CNF nanopaper enables the highly sensitive detection of rhodamine 6G at concentrations as low as 100 fM, with an enhancement factor of 8.72 × 1011 and excellent reproducibility. As a demonstration of their utility in practical chemical detection measurements, the SERS substrates are used to detect the pesticide thiram and a model gas, 2-naphthalenethiol; the detection limits were 10 fM and 1 ppb, respectively. SERS substrates composed of mAu@AgNW@TEMPO-CNF nanopaper may serve as an inexpensive, flexible, and stable chemical detection platform to sense both solution- and gas-phase analytes.

A low-cost 3D core-shell nanocomposite as ultrasensitive and stable surface enhanced Raman spectroscopy substrate

It is a great challenge to assemble low-cost and recyclable surface enhanced Raman scattering (SERS) substrates for sensitive detection towards target analytes. In this work, a 3D core-shell Cu2O@SiO2@zinc 2-methylimidazolate metal-organic frameworks@Ag nanocomposite (Cu2O@SiO2@ZIF-8@Ag) was facilely fabricated only with 0.5 wt.% Ag. The successful construction of the novel Cu2O-based SERS platform with special structure was confirmed by scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, and X-ray photoelectron spectroscopy. It showed that the nanocomposite can offer high-dispersion and small size Ag NPs implanted on the Cu2O@SiO2@ZIF-8, thus providing high-density hotspots. Importantly, the nanocomposite exhibited a highly sensitive and stable SERS response toward crystal violet (CV, a dose-related carcinogen) molecules. Especially, it can be detected as low as 1 × 10−19 M. The considerable SERS enhancement over the nanocomposite was owed to the special Ag and the powerful enrichment effect of the ZIF-8 shell sustained by the Cu2O@SiO2 core. Moreover, with the nanocomposite as the SERS substrate towards CV detection, the high SERS performance was still kept even after 15 cycles and even after placed in the air for 40 days. Additionally, a little silver and good selectivity were both significant for reliable quantitative detection in practical application.

Lab-On-Capillary Platform for On-Site Quantitative SERS Analysis of Surface Contaminants Based on Au@4-MBA@Ag Core–Shell Nanorods

A portable and highly reproducible lab-on-capillary surface-enhanced Raman scattering (SERS) platform was developed using a specially designed homemade device for rapid on-site SERS measurement. In particular, this platform was composed of a capillary with a tiny orifice, which allows an effective and lossless sample extraction, resulting in high SERS performance. The capillary-based plasmonic substrate was prepared by compactly assembling Au@Ag core-shell nanorods (NRs) embedded with the 4-mercaptobenzoic acid (4-MBA) molecule as an internal standard onto the inner wall of a capillary tube. The fabrication process is facile and convenient with no requirement for complicated procedures. The exclusively prepared nanoparticles were able to significantly improve the signal consistency and overcome the limitations of reliable quantitative SERS analysis compared with conventional methods. Importantly, it was found that this capillary-based substrate with higher sensitivity was essentially attributed to more valid nanoparticles in the effective laser excitation region derived from the unique structure of the capillary. Furthermore, the applicability of the Au@4-MBA@Ag nanorod-decorated capillary for the quantitative identification of fungicides (malachite green and crystal violet) on the shell was demonstrated. As a result, this proposed lab-on-capillary sensor holds promising practical potential for rapid on-site analysis, especially for various contaminants on an uneven surface.

Silver Nanostructures on Graphene Oxide as the Substrate for Surface-Enhanced Raman Scattering (SERS)

Nanosized surface-enhanced Raman scattering (SERS) substrates fabricated by the controlled growth of metal nanostructures on water-dispersed two-dimensional nanomaterials can open a new avenue for SERS analysis of liquid samples in biological fields. In this work, regular and uniform Ag nanostructures were grown on the surface of graphene oxide (GO) through a microwave-assisted hydrothermal method. Polyamidoamine (PAMAM) dendrimers were assembled on the surface of GO to form GO/PAMAM templates for growing Ag nanostructures, which are primarily comprised of Ag dimers and trimers. The prepared Ag/GO nanocomposites are highly dispersed and stable in aqueous solution and may be used as substrates for enhanced Raman detection of rhodamine 6 G (R6G) in aqueous solution. This special substrate provides high-performance SERS and suppresses R6G fluorescence in aqueous solution and is promising as a nanosized material for the enhanced Raman detection of liquid samples in biological diagnostics.

Three-Dimensional Hierarchical Reticular Nanostructure of Fulfora candelaria Wing Decorated by Ag Nanoislands as Practical SERS-Active Substrates.

Although surface-enhanced Raman scattering (SERS) technology has been widely explored nowadays in various fields, the fabrication of practical SERS-active substrates with prominent recognition ability for various analyte molecules is still defective. Natural Fulfora candelaria wing (FCW) with three-dimensional (3D) hierarchical reticular nanostructure was selected as a new bioscaffold for rough silver (Ag) nanoislands to be assembled on to prepare a practical SERS substrate (Ag/FCW substrate). By adjusting the sputtering time of metal Ag, the morphology of the substrates could be easily tuned to control the formation and distribution of “hot spots”. Three-dimensional finite-difference time-domain (3D-FDTD) simulation indicated that the excellent SERS performance under optimal morphology was ascribed to the local enhanced electric field in rough Ag surface and effective “hot spot” areas. The SERS measurement results show that the optimal Ag/FCW substrates had high SERS performance in terms of Raman signal sensitivity, reproducibility, uniformity and recognition ability for various analyte molecules. Coupled with flexibility of the biological substrates and the cost effectiveness, the sensitive SERS detection of varied analytes based on Ag/FCW substrates offered great potential for practical applications.

Achieving High-Performance Surface-Enhanced Raman Scattering through One-Step Thermal Treatment of Bulk MoS2

We present a strong Raman enhancement substrate through one-step thermal treatment of bulk MoS2. The substrate provides very efficient hot spots by using the rhodamine 6G (R6G) molecule as a probe. Raman and photoluminescence spectra of modified MoS2 reveal the detailed mechanism for enhancing Raman signal of R6G. It is found that both the substrate roughness and the slight chemical bond broken on the surface are the main driven forces to induce the surface enhanced Raman scattering (SERS) effects. The minimum detectable concentration of R6G on the most optimized thermally treated MoS2 can be as low as 10–8 M. This synthetic approach is facile, sensitive, and reliable, which shows great potential to be an excellent SERS substrate for biological and chemical detection.

Bimetallic Au/Ag Core-Shell Superstructures with Tunable Surface Plasmon Resonance in the Near-Infrared Region and High Performance Surface-Enhanced Raman Scattering.

Due to the larger surface area and the synergistic effects between two noble metals, the bimetallic superstructures exhibit enhanced distinctive optical, catalytic, and photothermal performances and surface-enhanced Raman scattering (SERS) "hot-spot" effect, and thus have attracted great interest in various applications. Compared with the common Pd, Pt hierarchical structures coated onto Au nanoparticles (NPs), easily synthesized via fast autocatalytic surface growth arising from intrinsic properties of Pd and Pt metals, precisely controlling the hierarchical Ag growth onto Au NPs is rarely reported. In our present study, the reducing agent dopamine dithiocarbamate (DDTC) was covalently capped onto the first metal core (Au) to delicately control the growth model of the second metal (Ag). This results in heterogeneous nucleation and growth of Ag precursor on the surface of Au nanorods (NRs), and further formation of cornlike bimetallic Au/Ag core-shell superstructures, which usually cannot be achieved from traditional epitaxial growth. The thickness of the hierarchical Ag shell was finely tuned in a size range from 8 to 22 nm by simply varying the amount of the ratio between Ag ions and DDTC capped on Au NR core. The tunable Ag shell leads to anisotropic bimetallic Au/Ag core-shell superstructures, displaying two distinctive plasmonic resonances in the near-infrared region (NIR). In particular, the longitudinal surface plasmon resonance exhibits a broadly tunable range from 840 to 1277 nm. Additionally, the rich hot spots from obtained Au/Ag superstructures significantly enhance the SERS performance.

Templated Growth of Surface Enhanced Raman Scattering-Active Branched Gold Nanoparticles within Radial Mesoporous Silica Shells.

Noble metal nanoparticles are widely used as probes or substrates for surface enhanced Raman scattering (SERS), due to their characteristic plasmon resonances in the visible and near-IR spectral ranges. Aiming at obtaining a versatile system with high SERS performance, we developed the synthesis of quasi-monodisperse, nonaggregated gold nanoparticles protected by radial mesoporous silica shells. The radial mesoporous channels were used as templates for the growth of gold tips branching out from the cores, thereby improving the plasmonic performance of the particles while favoring the localization of analyte molecules at high electric field regions: close to the tips, inside the pores. The method, which additionally provides control over tip length, was successfully applied to gold nanoparticles with various shapes, leading to materials with highly efficient SERS performance. The obtained nanoparticles are stable in ethanol and water upon thermal consolidation and can be safely stored as a powder.

Homogeneous large-scale crystalline nanoparticle-covered substrate with high SERS performance

This article details the surface-enhanced Raman scattering (SERS) performance of plasmonic substrates fabricated by a physical metal evaporation technique that uses no precursor or intermediate coating. We outline a cost-effective nanofabrication protocol that uses common laboratory equipment to produce homogeneously covered crystalline nanoparticle substrates. Our fabrication yields a homogeneous SERS response over the whole surface. The platform is tested with methylene blue diluted at various concentrations to estimate the sensitivity, homogeneity, and reproducibility of the process. The capacity of the substrates is also confirmed with spectroscopic investigations of human microsomal cytochrome b5.

3D silver nanoparticles decorated zinc oxide/silicon heterostructured nanomace arrays as high-performance surface-enhanced Raman scattering substrates.

Three-dimensional (3D) hierarchical nanostructures have been considered as one of the most promising surface-enhanced Raman spectroscopy (SERS) substrates because of the ordered arrangement of high-density hotspots along the third dimension direction. Herein, we reported a unique 3D nanostructure for SERS detection based on silver nanoparticles (AgNPs) decorated zinc oxide/silicon (ZnO/Si) heterostructured nanomace arrays. They were prepared by two steps: (1) Si nanoneedles were grafted onto ZnO nanorod arrays via a catalyst-assisted vapor-liquid-solid (VLS) growth mechanism. (2) AgNPs were rapidly immobilized on the surface of nanomaces by a facile galvanic displacement reaction. The fabricated substrates were employed to detect rhodamine 6G (R6G) with a detection limit down to 10(-16) M, and exhibited a high-enhanced performance (enhancement factor (EF) as high as 8.7 × 10(7)). To illustrate the potential value of the prepared substrates, the different concentrations of melamine aqueous solution (from 10(-4) to 10(-10) M) were detected, and a quantitative relationship between the SERS spectrum intensity and the melamine concentration had been established. In addition, the measure of melamine residual in pure milk was carried out successfully, and the results indicated that the prepared 3D nanomace substrates had great potential in food inspection, environment protection, and a few other technologically important fields.