Recyclable Surface-enhanced Raman Scattering Substrate Research Articles

Reuseable Fe3O4@PEI-DTC-Au@Ag magnetic nanocomposites: A versatile and sensitive SERS substrate for food safety assessment

A novel recyclable SERS substrate with magnetic manipulation capability and surface-enhanced Raman scattering (SERS) effect based on Fe3O4@PEI-DTC-Au@Ag (FPDAA) core-shell nanocomposites has been successfully prepared by engineered hydrothermal deposition and seed deposition techniques. The uniformity and SERS efficacy of these substrates, incorporating various Au@Ag core-shell nanocomposites with differing Ag shell thicknesses, were evaluated using 4-aminothiophenol (4-ATP) molecules. The optimal SERS substrate, Fe3O4@PEI-DTC-Au@Ag-3 (FPDAA-3), exhibited an enhancement factor (EF) of up to 1.121×106. This remarkable performance can be attributed to the synergistic effect between the magnetic plasmon of the Fe3O4 nanoparticles (NPs) core and the surface plasmonic resonance properties of Au@Ag core-shell nanocomposites, which create abundant interparticle hotspots within the FPDAA nanocomposites. Furthermore, the FPDAA-3 nanocomposite was employed as a SERS substrate for rapid thiram detection, achieving a minimum detectable concentration of 1×10−9 M. Notably, the relative standard deviation of SERS measurements from 50 randomly selected points was found to be less than 12.13 %, and the SERS spectra intensity showed minimal variation after 5 cycling tests, underscoring the excellent uniformity and recyclability of the FPDAA-3 substrate. The highly reusable and reliable FPDAA-3 nanocomposites enable direct on-site detection of thiram pesticide residues on fruit skins, thereby offering significant implications for food safety assessment and spectroscopic identification.

Au Nanoparticles Decorated CoP Nanowire Array: A Highly Sensitive, Anticorrosive, and Recyclable Surface-Enhanced Raman Scattering Substrate.

Metal-semiconductor composites are promising candidates for surface-enhanced Raman scattering (SERS) substrates, but their inert basal plane, poor active sites, and limited stability hamper their commercial prospects. Herein, we report a three-dimensional CoP nanowire array decorated with Au nanoparticles on carbon cloth (Au@CoP/CC) as a self-supporting flexible SERS substrate. The Au nanoparticles spontaneously grew on the surface of the CoP nanowire array to form efficient SERS hot spots by a redox reaction with HAuCl4 without any additional reducing agents. Such Au@CoP/CC substrate exhibited a limit of detection of 10-11 M using rhodamine 6G as a model dye with outstanding corrosion resistance ability even under extreme acid and alkali conditions, which is better than many recently reported Au-based SERS substrates. Finite-difference time-domain simulation results demonstrated that Au@CoP/CC can provide a high density of regions with intense local electric field enhancement. Moreover, Au@CoP/CC can degrade target organic dyes for the self-cleaning and reproduction of SERS-active substrates under visible light irradiation. This work provides a novel means of using the plasmonic metal-transition metal phosphide composites for high-performance SERS sensing and photodegradation.

Umbrella-frame silicon nanorod arrays decorated with Au nanoparticles as recyclable SERS substrates.

Surface-enhanced Raman scattering (SERS) is a powerful technique for detection and identification of trace amounts of molecules with high specificity. A variety of two- and three-dimensional (3D) SERS substrates have been developed. Among these SERS substrates, to further develop new morphology of 3D SERS-active substrate with robust SERS functionality is still desired and necessary. In this paper, what we believe to be a novel and effective SERS-active substrate based on large-scale 3D Si hierarchical nanoarrays in conjunction with homogeneous Au nanoparticles (AuNPs) was proposed. Its building block shaped like the umbrella-frame structure was fabricated by a simple and cost-effective top-down nanofabrication method. Such umbrella-frame structure achieved excellent SERS performance with high sensitivity and spatial uniformity. For R6G molecules, the detection limit can be as low as 10-14 M, with an enhancement factor of up to 107. The relative standard deviation can reach about 11% above 30 positions across an area of 100×100 μm2. This is mainly attributed to much more active-sites provided by the umbrella-frame structure for adsorption of target molecules and AuNPs, and sufficient 3D hotspots generated by the coupling between the SiNRs guided mode and AuNPs localized surface plasmon resonance (LSPR), as well as that between AuNPs LSPR. Especially by introducing the umbrella-ribs SiNRs and AuNPs, the light field can be greatly confined to the structure surface, creating strongly enhanced and even zero-gap fields in 3D space. Moreover, the proposed SERS-active substrate can be erased and reused multiple times by plasma cleaning and exhibits typically excellent recyclability and stability for robust SERS activity. The experimental results demonstrate the proposed substrate may serve as a promising SERS platform for trace detection of chemical and biological molecules.

CuO nanorods decorated gold nanostructures as an ultra-sensitive and recyclable SERS substrate

Conventional surface-enhanced Raman scattering (SERS) substrates require complicated fabrication techniques and precious nanometals to achieve high sensitivity and reproducibility. Furthermore, since SERS requires the adsorption of analytes on the substrate, the reusability of the substrate is still challenging. Herein, CuO nanorods decorated with gold nanostructure have been developed as a highly sensitive, recyclable, and cost-effective SERS substrate. For the fabrication, CuO nanorods were simply constructed on Cu wire by thermal oxidation at 500 °C. Then, Au nanostructures were decorated on the CuO nanorod's surface by UV photoreduction approach. The prepared Au–CuO substrate enabled the identification of methylene blue at a concentration as low as 0.1 pM. Furthermore, the SERS activity of Au–CuO substrate was still maintained at approximately 80% after 3 times recycling by illuminating the substrate with UV irradiation. The long-term surface stability of the substrate was also evaluated, and the decrease of SERS signal was only 4.7% after three days of exposing the substrate to the ambient environment.

Highly sensitive and recyclable surface-enhanced Raman scattering (SERS) substrates based on photocatalytic activity of ZnSe nanowires

The semiconductor-based SERS substrates have attracted considerable attention due to their unique optical and reusable biosensor applications. However, most substrates generally exhibit poor enhancement effects and are non-reusable, needing a complicated fabrication process. In the present study, novel recyclable SERS substrates were synthesized from ZnSe nanowires using chemical vapor deposition. SERS performance was enhanced via introducing the defects by adding Se dopant in the ZnSe and achieved the value of EF 6.92 × 107 for the Zn/Se ratio 1:1.2. The SERS efficiency of the fabricated ZnSe nanowire was probed by rhodamine 6 G (R6G) and methylene blue (MB), presenting excellent stability and reaching the sensitivity level of 10−11 M. The photocatalytic degradation of R6G molecules were experimentally investigated with Raman mapping tests using a visible light source to explore the recyclability of the SERS substrates. Our study demonstrates that the proposed ZnSe nanostructure possesses the capability to reuse up to 6 times with preserving strong SERS signal reproducibility. The bifunctional recyclable ZnSe substrate not only presents a novel method to truly enhance the SERS performance, photocatalytic behavior but is also considerable for food safety application.

TiO2 nanorod arrays decorated with Au nanoparticles as sensitive and recyclable SERS substrates

Surface enhanced Raman scattering (SERS) platforms with recyclability are highly required for the practical applications. In this work, TiO2 nanorod arrays decorated with Au particles (Au@TiO2 NRAs) are prepared by glancing angle deposition technology and subsequent gold sputtering. Au@TiO2 NRAs are demonstrated as sensitive SERS substrate while the optimal substrate with high reproducibility and stability is obtained. Illustrated by Frequency-domain finite element method (FEM), this excellent SERS performance can be attributed to the formation of high intensity hot spots located on the gap between Au nanoparticles. Moreover, the SERS substrates are extensively recyclable due to the well-known ability of TiO2 photocatalytic degradation of dye molecule under ultra-violet light.

Facile fabrication of adjustable Al/C3N4/Agx nano-micro composites for sensitive SERS detection

In this paper, the aluminum/graphitic‑carbon nitride (Al/C3N4) loaded with various sizes of prismatic Ag nanoparticles (AgNPs) was facilely prepared. By means of XRD, XPS, Raman and fluorescence spectroscopy, it was demonstrated that strong interaction between Al/C3N4 and various sizes of prismatic AgNPs can be achieved, which was beneficial for the uniform distribution of AgNPs on surfaces of Al/C3N4. Interestingly, the change trend of AgNPs' size in Al/C3N4/Agx exhibited a distinct “W-shaped” with the increase of reduction time. Also, as the changing size of prismatic AgNPs, the surface-enhanced Raman scattering (SERS) intensity of brilliant blue on Al/C3N4/Agx showed the “M-shaped” based on the bands at 1166 cm−1, 1242 cm−1, 1580 cm−1, and 1606 cm−1. Moreover, the SERS spectra of brilliant blue and relative SERS intensities were hardly changed on the Al/C3N4/Ag168 substrate for 45 days or after seven recycles. In addition, brilliant blue, crystal violet and 4-aminothiophenol with low concentration can also be detected, which indicated that the Al/C3N4/Agx as a recyclable SERS substrate not only presented a continuous stability but also kept high sensitivity for detection of environmental pollutants.

Ultrasensitive and recyclable superstructure of Au[sbnd]SiO2@Ag wire for surface-enhanced Raman scattering detection of thiocyanate in urine and human serum

Thiocyanate level in the human system can serve as a biomarker to distinguish smokers from non-smokers. Thiocyanate is a potential goitrogen, thus an accurate determination may help to identify lactating mothers with high thiocyanate dosage, thereby preventing the transport of excess SCN− to infants. Surface-enhanced Raman spectroscopy has become a versatile and reliable technique to detect SCN− in different media. However, the conventional surface-enhanced Raman scattering (SERS) substrates used to detect SCN− are often discarded after use. The frequent disposal of such metal nanoparticles is detrimental to the environment and makes the SERS-based detection of SCN− uneconomical. In this study, we present fabrication of a new, ultrasensitive and recyclable SERS substrate, based on an AuSiO2@Ag wire (W) superstructure, to detect SCN− in different media. The hierarchical AuSiO2@AgW substrate was obtained by forming nano-sized patches of SiO2 on micron-sized AgW and anchoring 30 nm-sized gold nanoparticles on the patches with mercaptopropyltrimethoxysilane. This ultrasensitive substrate could detect SCN− at a low concentration of 0.001 μM in water, and 0.01 μM in urine and human serum. In addition, a facile procedure to regenerate and recycle the SCN− bound AuSiO2@AgW platform in different media has been demonstrated. The insight gained in the present study can serve as a promising and powerful method for fabrication of active and recyclable substrates for SERS-based detection of SCN−.

Parameter optimization for Ag-coated TiO2 nanotube arrays as recyclable SERS substrates

The Ag-coated titanium dioxide nanotube arrays (Ag-coated TNTs) are obtained via the deposition of Ag nanoparticles on the two-step anodized TNTs. The wall thickness of TNTs is modulated via finite difference time domain simulation to get the favorable electromagnetic field for surface enhanced Raman scattering (SERS). Ag-coated TNTs with optimal wall thickness of 20 nm were employed as the SERS substrates to detect 2-mercaptobenzoxazole, which show superior detection sensitivity and uniformity. In addition, due to the photocatalysis of TNTs, the SERS substrates could clean themselves and be repeatedly used by photo-degradation of target molecules under the ultra-violet irradiation. The Ag-coated TNTs are a kind of bifunctional SERS substrates which can produce high-quality SERS signals and reuse to reduce the cost.

Improved Thermal Stability of Graphene-Veiled Noble Metal Nanoarrays as Recyclable SERS Substrates.

The ability to enhance the heat resistance of noble metals is vital to many industrial and academic applications. Because of its exceptional thermal properties, graphene was used to enhance the thermal stability of noble metals. Monolayer graphene-covered noble metal triangular nanoarrays (TNAs) showed excellent heat resistance, which could maintain their original triangular nanoarrays at high temperatures, whereas bare noble metal TNAs all agglomerate into spherical nanoparticles. On the basis of this mechanism, we obtained a universal recyclable surface-enhanced Raman scattering (SERS) substrate; after 16 cycles, the SERS substrate still worked well. The improvement of the heat resistance of noble metals by graphene has a great significance to the working reliability and service life of electronic devices and the single-use problem of traditional SERS substrates.

Fabrication of Au-Decorated 3D ZnO Nanostructures as Recyclable SERS Substrates

Highly roughened Au-decorated 3D ZnO nano-structures were prepared using a combination of prism holographic lithography and atomic layer deposition techniques. Prism holographic lithography is a simple and rapid method for fabricating ordered 3D nanostructures using the optical interference effects of multiple beams derived from a specially designed prism. Highly ordered reproducible surface-enhanced Raman scattering (SERS) substrates are needed for the reliable calibration of target analyte concentrations. A high density of Au nanoparticles separated by nanoscale gaps was generated on the Au-coated ZnO inverse structures. The nanogaps may function as strong hot spots for highly sensitive SERS-based chemical/biological sensors. The optimized SERS intensity from the prepared Au-coated 3D ZnO inverse structures was 20 times the intensity obtained from an Au-coated flat glass control substrate. The surfaces could be reused after the photocatalytic degradation and removal of adsorbates in the presence of ZnO. The Au-coated 3D ZnO structures described here offer an alternative to traditional single-use SERS substrates.

Rational Design of α-Fe2O3/Reduced Graphene Oxide Composites: Rapid Detection and Effective Removal of Organic Pollutants.

α-Fe2O3/reduced graphene oxide (α-Fe2O3/rGO) composites are rationally designed and prepared to integrate organic pollutants detection and their photocatalytic degradation. Specifically, the composites are used as the substrate for surface-enhanced Raman scattering (SERS) to detect rhodamine 6G (R6G). Repeatable strong SERS signals could be obtained with R6G concentration as low as 10(-5) M. In addition, the substrate exhibits self-cleaning properties under solar irradiation. Compared with pure α-Fe2O3 and α-Fe2O3/rGO mechanical mixtures, the α-Fe2O3/rGO composites show much higher photocatalytic activity and much greater Raman enhancement factor. After 10 cycling measurements, the photodegradation rate of R6G could be maintained at 90.5%, indicating high stability of the photocatalyst. This study suggests that the α-Fe2O3/rGO composites would serve both as recyclable SERS substrate and as excellent visible light photocatalyst.

Using Ag-embedded TiO2 nanotubes array as recyclable SERS substrate

A simple strategy for synthesizing Ag-loaded TiO2 nanotube film for use as multifunctional photocatalyst and recyclable surface-enhanced Raman scattering (SERS) substrate is introduced. Highly aligned TiO2 nanotube arrays (TNTA) prepared via electrochemical anodization were used as a 3D rough host for silver nanoparticles. Ag deposits were sputtered in a vacuum, and it was found that their morphologies were mainly influenced by the diameters of nanotubes and the UV irradiation induced aging process, especially the self-migration of silver along the tubular wall. SERS and the self-cleaning effect were observed using Rhodamine 6G (R6G) as the probe molecule. The results showed that narrow nanotube and silver nanoparticles embedment contributed significantly to both the phenomenal SERS and recyclability.

Ag Nanorods Coated with Ultrathin TiO2 Shells as Stable and Recyclable SERS Substrates.

TiO2-coated Ag nanorods (Ag@TiO2 NRs) have been fabricated as multifunctional surface-enhanced Raman scattering (SERS) substrates. Uniform TiO2 shells could sufficiently protect the internal Ag NRs against oxidation and sulfuration, thus the temporal stability of SERS substrates was markedly improved. Meanwhile, due to the synergetic effect between crystalline TiO2 and Ag, the nanocomposites could clean themselves via photocatalytic degradation of the adsorbed molecules under ultraviolet irradiation and water dilution, making the SERS substrates renewable. Such Ag@TiO2 NRs were shown to serve as outstanding SERS sensors featuring high sensitivity, superior stability and recyclability.

Reproducible and recyclable SERS substrates: Flower-like Ag structures with concave surfaces formed by electrodeposition

Direct synthesis of three-dimensional Ag structures on solid substrates for the purposes of producing reproducible and recyclable surface-enhanced Raman scattering (SERS) applications remains challenging. In this work, flower-like Ag structures with concave surfaces (FACS) were successfully electrodeposited onto ITO glass using the double-potentiostatic method. The FACS, with an enhancement factor of the order of 108, exhibited a SERS signal intensity 3.3 times stronger than that measured from Ag nanostructures without concave surfaces. A cleaning procedure involving lengthy immersion of the sample in ethanol and KNO3 was proposed to recycle the substrate and confirmed by using rhodamine 6G, adenine, and 4-aminothiophenol as target molecules. The findings can help to advance the practical applications of Ag nanostructure-based SERS substrates.

Zinc oxide/silver nanoarrays as reusable SERS substrates with controllable ‘hot-spots’ for highly reproducible molecular sensing

HypothesisThe reproducible surface enhanced Raman scattering (SERS)-based sensing of an analyte relies on high quality SERS substrates that offer uniformity over large areas. Uniform ZnO nanoarrays are expected to offer an appropriate platform for SERS sensing. Moreover, since ZnO has good photocatalytic properties, controllable decoration of silver nanoparticles on ZnO nanoarrays may offer an additional opportunity to clean up SERS substrates after each sensing event. ExperimentsThis study employs a facile soft chemical synthesis strategy to fabricate Raman-active and recyclable ZnO/Ag nanorod arrays as reproducible SERS substrates. Arrays of ZnO nanorods were synthesized using hydrothermal method, which was followed by controllable decoration of ZnO with silver nanoparticles (AgNPs) using an electroless plating technique. FindingsThe uniform density of SERS-active ‘hot-spots’ on ZnO nanoarrays could be controlled on a large 1×1cm2 substrate. These ZnO/Ag nanoarrays showed high reproducibility (0.132 RSD) towards acquiring SERS spectra of rhodamine B (RB) at 30 random locations on a single substrate. The photocatalytic nature of ZnO/Ag semiconductor/metal hybrid endowed these substrates with reusability characteristics. By controlling metal loading on a semiconductor surface, photocatalytic activity and high SERS performance can be integrated within a single package to obtain high quality, reproducible, stable and recyclable SERS substrates.

High-adhesive superhydrophobic 3D nanostructured silver films applied as sensitive, long-lived, reproducible and recyclable SERS substrates.

Silver films with different morphologies were chemically deposited by controlling the bath composition. It is found that the wettability and surface enhanced Raman scattering (SERS) properties were closely connected with the surface morphology. Due to the perfect 3D morphology and the 3D electromagnetic field enhanced by three types of nanogaps distributed uniformly, the 3D microball/nanosheet (MN) silver film shows better SERS properties than those of 2D nanosheets (NSs) and nanoparticles (NPs). The MN silver film showed high adhesive superhydrophobic properties after an oxidation process without any functionalization. It can hold the liquid droplet and trace the target molecules in a rather small volume. The SERS properties of the oxidized MN substrate were enhanced remarkably compared to those of the freshly prepared substrate because of the concentrating effect of the superhydrophobicity. The as-prepared 3D MN silver substrate has also exhibited good performances in reproducibility and reutilization which makes it a promising substrate for molecule tracing.

Facile one-step synthesis of Ag@Fe3O4 core–shell nanospheres for reproducible SERS substrates

A facile approach has been developed to synthesize Ag@Fe3O4 core–shell nanospheres, in which the Ag nanoparticle core was well wrapped by a permeable Fe3O4 shell. An in situ reduction of AgNO3 and Fe(NO3)3 was the basis of this one-step method with ethylene glycol as the reducing agent. The as-obtained Ag@Fe3O4 nanospheres were a highly efficient surface-enhanced Raman scattering (SERS) substrate; high reproducibility, stability, and reusability were obtained by employing 4-aminothiophenol (4-ATP) and rhodamine 6G (R6G) as the Raman probe molecules. It was revealed that the SERS signals of 4-ATP and R6G on the Ag@Fe3O4 nanospheres were much stronger than those on the pure Ag nanoparticles, demonstrating that the magnetic enrichment procedures can improve SERS detection sensitivity efficiently. A highly efficient and recyclable SERS substrate was produced by the new model system that has potential applications in chemical and biomolecular assays.

Reusable plasmonic substrates fabricated by interference lithography: a platform for systematic sensing studies

Surface‐enhanced Raman scattering (SERS) has become increasingly popular in the scientific and industrial communities because of its analytical capabilities and potential to study fundamentals in plasmonics. Although under certain conditions extremely high sensitivity is possible, the practical use of SERS is frequently limited by instability and poor reproducibility of the enhancement factor. For analytical applications or for comparative measurements to enable the distinction between electromagnetic and chemical enhancement, the development of standardized and recyclable SERS substrates, having uniform and persistent performance, is proposed. To this end, we have fabricated periodic nanoslit arrays using extreme ultraviolet lithography that provide average large (2*106) and homogeneous SERS enhancement factors with a spot‐to‐spot variability of less than 3%. In addition, they are reusable without any degradation or loss of enhancement. The fabrication of such arrays consists of two steps only, lithographic patterning followed by metal evaporation. Both processes may be performed over areas of several square mm on any planar substrate. The sensor capabilities were demonstrated by substrates with monomolecular films of several different thiols. The concept of reusable SERS substrates may open a powerful platform within an analytical tool and in particular for systematic SERS studies for the investigation of fundamental parameters such as chemical enhancement, surface selection rules, and molecular alignment. Copyright © 2012 John Wiley & Sons, Ltd.

Functional hybrid nickel nanostructures as recyclable SERS substrates: detection of explosives and biowarfare agents

We present the synthesis of highly anisotropic nickel nanowires (NWs) and large area, free-standing carpets extending over cm(2) area by simple solution phase chemistry. The materials can be post-synthetically manipulated to produce hybrid tubes, wires, and carpets by galvanic exchange reactions with Au(3+), Ag(+), Pt(2+), and Pd(2+). All of these structures, especially the hybrid carpets and tubes, have been prepared in bulk and are surface enhanced Raman scattering (SERS) active substrates. Molecules of relevance such as dipicolinic acid (constituting 5-15% of the dry weight of bacterial spores of Bacillus anthracis), dinitrotoluene, hexahydro-1,3,5-triazine (RDX), and trinitrotoluene at nanomolar concentrations have been detected. An enhancement factor of ∼10(10) was observed for the Ni-Au nanocarpet. The reusability of the Ni-Au nanocarpet for SERS applications was tested 5 times without affecting the sensitivity. The reusability and sensitivity over large area have been demonstrated by Raman microscopy. Our method provides an easy and cost effective way to produce recyclable, large area, SERS active substrates with high sensitivity and reproducibility which can overcome the limitation of one-time use of traditional SERS substrates.