Recent progressive preparations and applications of silver-based SERS substrates

Accepted Manuscript Recent progressive preparations and applications of the SERS substrates based on silver Qing Tong, Weijia Wang, Yining Fan, Lin Dong PII:

S0165-9936(18)30228-0

DOI:

10.1016/j.trac.2018.06.018

Reference:

TRAC 15189

To appear in:

Trends in Analytical Chemistry

Received Date: 23 May 2018 Revised Date:

25 June 2018

Accepted Date: 25 June 2018

Please cite this article as: Q. Tong, W. Wang, Y. Fan, L. Dong, Recent progressive preparations and applications of the SERS substrates based on silver, Trends in Analytical Chemistry (2018), doi: 10.1016/j.trac.2018.06.018. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

Recent progressive preparations and applications of the SERS substrates based on silver Qing Tong a, b, †, Weijia Wang a, †, Yining Fan a, b, *, Lin Dong a, * a

RI PT

Key Laboratory of Mesoscopic Chemistry of MOE, Jiangsu Key Laboratory of Vehicle Emissions Control, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China. b Nanjing University-Yangzhou Chemistry and Chemical Engineering Institute, Yangzhou, 211400, China. †

SC

These authors contributed equally to this work. E-mail addresses: [email protected] (Y. Fan), [email protected] (L. Dong)

M AN U

Abstract: In recent years, considerable interest has been focused on the development of novel surface-enhanced Raman spectroscopy (SERS) techniques. Previous studies have shown that the structures of the substrates are critical for taking advantage of strong Raman signal enhancement. This review summarizes the recent trends and developments of SERS substrates with various structures and their applications based on silver.

TE D

Keywords: SERS, Enhancement substrate, Silver, Preparation, Application

AC C

EP

Content 1. Introduction…………………………………………………………………………………....2 2. The different supports of SERS substrates…………………………………………………….2 2.1 Metal oxide………………………………………………………………………………..2 2.2 Graphene…………………………………………………………………………………..4 2.3 Silica……………………………………………………………………………………....5 2.4 Polymer…………………………………………………………………………………....5 2.5 Other……………………………………………………………………………………....6 3. The significant types and structures of different SERS substrates based on silver……………7 3.1 The core-shell structure substrates………………………………………………………...7 3.2 The three-dimensional (3D) substrates……………………………………………………9 3.3 The self-assembled substrates…………………………………………………………….11 3.4 The recyclable substrates…………………………………………………………………12 3.5 The magnetic substrates…………………………………………………………………..13 3.6 The array-like substrates………………………………………………………………….14 3.7 Other……………………………………………………………………………………...16 4. Conclusions…………………………………………………………………………………...17

ACCEPTED MANUSCRIPT Acknowledgments……………………………………………………………………………..20 References……………………………………………………………………………………..20

AC C

EP

TE D

M AN U

SC

RI PT

1 Introduction The Raman scattering effect was first explored by Raman in 1928; however, the natural Raman signal was very weak [1]. A strong Raman signal of pyridine was obtained via a Ag electrode by Fleischmen in the 1970s [2]. Then, Van Duyne and Creighton named this phenomenon surface-enhanced Raman spectroscopy (SERS) [3]. The enhancement factor (EF) of SERS can reach up to 1010-1011 on metallic surfaces [4]. Thus, there are many useful applications of SERS, such as in the detection of water pollution [5], detection of illegal and carcinogenic food additives [6], pesticide monitoring [7, 8], trace detection for organic substances, identification of explosives [9, 10], and biological and medical detection [4, 11-13]. The mechanisms of SERS can be divided into physical and chemical enhancement mechanisms [14]. The physical enhancement mechanism mainly describes how the localized surface plasmon resonance (SPR) on the surface of the noble metals and transition metals (such as Ag, Au, Cu, Pd, Co and Ni) could enhance the electromagnetic field [15-19]. The chemical enhancement mechanism describes the interaction between the compounds and enhancement substrate, which can be classified as the chemical-bonding, surface complex or photo-induced charge transfer. These two mechanisms may also have combined effects [18]. Previous studies have shown that the shape, morphology, space, assembly, and distance of the substrates may affect the SERS activity [17, 20]. The sharp corner of the metals will provide better enhancement for SERS detection [21, 22]. The metals used as the SERS substrates should also follow the size rule, which is that the size of the metal particles should be within a certain range; for example, Andreia Araújo et al. found that silver nanoparticles with a size of 60 nm could achieve the maximum SERS enhancement factor [23]. In addition, the preparation methods may affect the SERS activity of the silver colloidal nanoparticles [24]. Therefore, the structures of the substrate are very important to the properties for a certain metal. Recently, researchers have developed many kinds of SERS substrates with various structures, and their applications are also variable because of the structures. In this review, we summarize the SERS substrate development in recent years, focusing primarily on the SERS substrates based on silver. We also describe the preparations and applications of these substrates with different structures and properties. 2 The different supports of SERS substrates The supports are the basic parts of the SERS substrates structures, especially when the SERS substrates play facilitate other functions for the analytes. The most important supports are metal oxides, graphene, silica and polymers. 2.1 Metal oxide The applied metal oxides mainly include CuO, ZnO, TiO2, and Al2O3 [5, 15, 25-28]. The metal oxides can be easily prepared to different shapes with various morphologies, and the prepared metal oxides are stable under various conditions, which is the advantage of metal oxides. CuO is an important p-type semiconductor, and it has a narrow band gap of 1.21 eV, which is widely used in many application fields, such as for sensors and electronics devices [15]. Jayram et al. used Ag-decorated CuO as a SERS substrate and constructed the substrate as a thin film [15].

ACCEPTED MANUSCRIPT

M AN U

SC

RI PT

The silver was deposited onto the surface of CuO via a thermal evaporation method, and the nanoflower-like hot spot was deposited on the film. Using this substrate, the detection limit of rhodamine 6G (R6G) could be lowered to 10-10 mol L-1 [15]. Rao et al.[29] synthesized a Cu-Ag bimetal thin film on the polyvinyl alcohol (PVA) surface in which the PVA surface was covered by the Cu(NO3)2 and obtained CuO under heating; then, the CuO was transformed to Cu by hydrazine. After this treatment, AgNO3 was coated on the Cu/PVA surface, and then a Cu-AgNP-embedded polymer thin film was constructed [29]. This film provided an EF of 107-108 for the analytes, achieving subpicomolar limits of detection (Fig. 1). ZnO is one of the significant photocatalysts because of its properties: wide band-gap energy, high stability, low cost and simple preparation [30]. Macias-Montero et al.[31] synthesized Ag@ZnO supported nanorods (NRs) followed by plasma-enhanced chemical vapor deposition (PECVD) and UV laser treatment (193 nm) (Fig. 2), which can improve the stability of the SERS substrate.[31] There are also many other reports on the use of ZnO as the substrate support, which shows the wide applicability of ZnO. For example, Koleva et al.[32] used the two-step laser method to prepare the mosaic Ag-ZnO SERS substrate. To obtain higher SERS activity than that of pure Ag, Chen et al.[17] used SnCl2 to reduce [Ag(NH3)2]+ and achieve the dispersion of the Ag nanoparticles (AgNPs) on the surface of ZnO/SiO2 microspheres. A polarization-induced local electromagnetic field can be created by the metal-semiconductor heterojunctions in this system. On the other hand, the controllability of metal oxides is also very good. The structures of the support can be controlled through different conditions. Ma et al.[27] synthesized Ag@Al2O3 SERS substrate by the atomic layer deposition (ALD) method with trimethylaluminum. The pinholes over the Al2O3 shells could be controlled to obtain sensitive SERS performance with different pinhole rates, and their structures and SERS efficiency at temperatures higher than 250 °C melting point.

TE D

could be preserved on the substrates by coating protective Al2O3 layers over Ag NRs to modify the

AC C

EP

In addition, the catalytic property of the metal oxides can be applied with their SERS activity. Yong Zhao et al.[33] deposited AgNPs on the surface of electrospun TiO2 nanofelt. The target molecule (R6G, 4-aminothiophenol) on these deposited AgNPs can be cleaned by UV irradiation in O2-saturated water based on the photodegradation properties of anatase-phase TiO2.[33] The TiO2-Ag porous nanocomposites can be used to detect organic pollutants in water, especially dyes such as R6G.[5]

Fig. 1 The synthesis procedure of the Cu-AgNPs-embedded polymer thin film {Reprinted with permission from [29], © 2017, American Chemical Society}.

RI PT

ACCEPTED MANUSCRIPT

SC

Fig. 2 The synthesis procedure of the Ag@ZnO supported nanorods {Reprinted with permission from [29], © 2015, American Chemical Society}.

AC C

EP

TE D

M AN U

2.2 Graphene Graphene is also widely used as a support [34]. Sometimes metal oxide may be combined with graphene as a support. Ko et al.[30] used arginine to reduce AgNO3 via the microwave-assisted green method to build Ag/ZnO/reduced graphene oxide nanocomposite as a SERS substrate with both bactericidal properties and SERS activity. Hiany Mehl et al. [35] prepared reduced graphene oxide (rGO)/AgNPs directly at the liquid-liquid interface of water and toluene, which provided good SERS enhancement to the 4-aminothiophenol molecule (1×10-7 mol L-1). The stability of the graphene is very good because of its conjugated system. If stable graphene can be combined with the supports, the stability of the SERS substrate may be improved. The AgNPs were deposited on the surface of pyramidal silicon (PSi), and graphene oxide (GO) was coated on the AgNPs by a spin-coating method (Fig. 3) [36]. The uniform GO film can protect the AgNPs from oxidation and give the hybrid system with good stability and a long lifetime, providing excellent SERS activity. For example, this approach can detect R6G concentrations as low as 10-12 mol L-1. Jiang et al. [37] also prepared the MoS2@AgNPs@pyramidal silicon structure SERS substrate, which is a very sensitive, uniform and reproducible SERS substrate. This substrate is also very stable with R6G tested as the probe molecule. Thus, GO can also increase the homogeneity of the SERS substrate. Hsu et al. [38] utilized microwave irradiation to synthesize the AgNPs/rGO. Microwave irradiation is a simple, rapid and green method, and the enhancement factor of the synthesized Ag/rGO can reach up to 1.27×1010 for the 4-aminothiophenol molecule. The surface of GO can be decorated, and if the analytes can be linked on the surface, the sensitivity of the SERS substrate can also be improved. Pham et al. [39] prepared a composite in which 4-mercaptophenyl boronic acid (4-MPBA) was coated on the surface of AgNP-embedded silica-coated graphene oxide by a self-assembly method, denoted GO@SiO2@AgNPs@MPBA, which can be used for detecting glucose, and binding glucose on the 4-MPBA-incorporated GO@SiO2@AgNPs increased the SERS signals.

SC

RI PT

ACCEPTED MANUSCRIPT

M AN U

Fig. 3 The synthesis procedure of GO-AgNPs-PSi substrate {Reproduced with permission from [36], ©2016, Elsevier}.

AC C

EP

TE D

2.3 Silica Silica is also a typical kind of support applied in many conditions [39, 40]. The most important advantage of silica is to prevent aggregation by coating the SERS-active points and separating them to obtain a much better SERS effect. A uniform and hybrid silica-3-aminopropyltriethoxysilane (APTES) coating on the surface of glass was established by Pilipavicius et al. [41] via a sol-gel process; then, different sizes of Ag nanoprisms were deposited on surface of the silica coating, which indicated that the individual particles are better for SERS than the aggregated particles. The silica coating can also improve the SERS stability of the substrates. Long et al.[42] synthesized mesoporous silica coated AgNPs as SERS hot spots, the shell of which is approximately 15 nm. In this method, the relative standard deviation of SERS intensity is lower than 20%, and the method also provides substantial SERS activity, with a detection limit as low as 10-8 mol L-1, as well as excellent SERS stability[42]. Porous silicon (pSi) was prepared by Mikac et al. [43] via an anodisation technique. The authors coated Ag clusters on the surface of pSi by dipping the pSi into AgNO3 solutions. This substrate has shown a great SERS effect for R6G, and the detection limit is as low as than 10-9 mol L-1. 2.4 Polymer Polymer is another important support in the SERS substrate field, and electrospinning is a convenient and efficient technique to build polymer substrates [44]. The polymer can be treated to a certain formation, such as fibers, which can disperse the SERS hot spots, such as the AgNPs, on the polymers well. AgNP-embedded PVA nanofibers were built by Zhang et al. [45] via an electrospinning method. The AgNPs were evenly dispersed in PVA solution. AgNP-embedded PVA can be obtained after the electrospinning process, and it can act as the SERS substrate and an antimicrobial agent. For example, AgNP-embedded PVA has a high SERS sensitivity to 4-mercaptophenol (4-MPh) molecules and robust antibacterial activities against gram-positive

ACCEPTED MANUSCRIPT

RI PT

Staphylococcus aureus (S. aureus) and gram-negative Escherichia coli (E. coli) microorganisms[45]. Chao et al. [20] used the templates to build the polystyrene/silica (PS/SiO2) nanocomposite microspheres by an in situ sol-gel method via the hydrolysis of tetraethyl orthosilicate (TEOS) in alkali solution. The microspheres were dispersed into the AgNO3 solution, and diethanolamine was added into the mixture to obtain the PS/SiO2/Ag nanocomposites. The electrospun nanofibers can also be used to deposit the AgNPs. The SERS effect can be determined by the size and the density of the AgNPs on the surface. Amarjargal et al. [46] used ethylene glycol to reduce the Ag+ to Ag0 and as a growth medium for AgNPs well-dispersed on the electrospun polyurethane (PU) fibers, which is a simple, safe and cost-effective method.

AC C

EP

TE D

M AN U

SC

2.5 Other In addition to the materials described above, many other materials are used as supports. The simplest support is glass. The typical method is to link the SERS hot spots onto the glass surface. Bu et al. [47] prepared a uniform and densely packed Ag and Au on the glass surface. They used citrate to reduce HAuCl4 and AgNO3 to synthesize AuNPs and AgNPs, respectively. The nanoparticles were cross-linked to the glass surface with the help of the amine termination of 3-aminopropyltrimethoxysilane (APTMS), which has a high sensitivity and can detect the power-law linearity of Raman intensity with probe (o-chlorothiophenol) concentrations from 10-7 mol L-1 to 10-4 mol L-1. The AuNPs have higher stability, while the AgNPs have higher SERS activity. ITO glass has electrical conductivity that is different from that of traditional glass, and the preparation of the SERS substrates can be applied into the electrochemistry field. Cheng et al.[48] used the electrodeposition method to deposit a hollowed Ag nanostructure onto the surface of ITO glass in a three-electrode system. The ITO-rGO/AgNPs nanocomposites were built by Wang et al. [49] via a chronoamperometry electrodeposition method, and the detection limit of the ITOrGO/AgNPs nanocomposites for R6G was significantly reduced to as low as 10-11 mol L-1, with a Raman enhancement factor up to 5.9×108. Additionally, plant seeds can be treated as a support, which takes advantage of their porosity to improve the SERS sensitivity. Zhou et al.[50] used NaBH4 to reduce AgNO3 in aqueous solutions, and basil seeds were immersed in the AgNO3 aqueous solutions. The AgNPs were deposited on the surfaces of basil seeds (Fig. 4). The porous basil seeds can absorb the analytes and have a preconcentrating effect. The resultant product is also exposed to a strong plasmonic field and can be used to detect toxic molecules. For example, the detected limit of methyl parathion in juice is up to 10-7 mol L-1, and it can also rapidly detect 10-6 mol L-1 melamine in milk.

RI PT

ACCEPTED MANUSCRIPT

Fig. 4 The synthesis procedure of the AgNPs@basil-seed network {Reproduced with permission from [50], ©2015, Elsevier}.

AC C

EP

TE D

M AN U

SC

Ag, Au and Cu have the high SERS activity when they work together as a substrate[16]. Zhang et al. [51] prepared bimetallic Ag-Au composites by floating a commercial Ag-Au alloy on an HAuCl4 solution. The authors then removed AgCl with a saturated NaCl solution. The nanogaps, sharp edges and corners of the samples provide enhanced local surface plasmon fields and electromagnetic coupling, which increases the SERS activity. Hu et al. [16] fabricated the Ag-Cu substrates by immersing the Cu foils into the AgNO3 solution, which involved a replacement reaction, and the approach was very simple and affordable. Jiang et al. [52] reported that they dispersed AgNPs with single atomic layer graphitic-C3N4 (S-g-C3N4), which had great SERS performance, while the AgNPs were unlikely to be oxidized. The EF for the crystal violet (CV) probe molecule can be up to 2.1×109. The Au-Ag alloy particles inlaid AgCl membranes prepared by Cao et al. [53] have SERS-monitored catalytic properties, demonstrated by reactions with 4-nitrophenol (4-NP) and R6G, which can be applied in catalytic and sensing devices (Fig. 5).

Fig. 5 The applications of the Au-Ag alloy particles inlaid AgCl membranes {Reprinted with permission from [53], © 2015, American Chemical Society}.

ACCEPTED MANUSCRIPT

RI PT

3 The significant types and structures of different SERS substrates based on silver The topology structures of the substrates can significantly affect the EF of SERS. For example, the sharp edges of silver are hot spots with high field amplitudes [21]. There are many structures for nano- and micro-materials, for example, hollow spheres and microspheres.[54, 55] There have been many types and structures of the SERS substrates developed in recent years, such as core-shell structures, three-dimensional (3D) structures, and array-like structures. In this section, the preparation and significant structures of the various SERS substrates based on silver will be classified and discussed.

AC C

EP

TE D

M AN U

SC

3.1 The core-shell structure substrates The core-shell structure is popular and classic in the SERS substrate field [56-62], and the Au-Ag core-shell structure is the most widely applied [63-67]. The most important aim of this type is to increase the sensitivity of SERS detection, and the methods differ. Jin et al. [68] built Ag-Au-Ag nanostructures in which the AuNPs were put on the surface of the AgNPs, and the sizes of the AuNPs and the AgNPs were 2.5-6 nm and 50-100 nm, respectively. A nanogap between the two metals can be formed, and the incident electromagnetic field can be concentrated into a small space to improve the SERS enhancement. A Ag-nanocube@Au-nanospheres core@satellites SERS substrate was reported by Huang et al.[69]. Au-nanospheres were synthesized by reducing the auric chloride acid via trisodium citrate, and Ag-nanocubes were synthesized by the modified polyol reduction of silver ions method in the presence of Cl-. Hot spots can be formed at the sharp edges of the Ag-nanocubes and the gaps between the Au-nanospheres and the Ag-nanocubes, providing high SERS activity. Another advantage of the core-shell structure is that the shell can be decorated more easily than the pure SERS hot spot and that the analytes can be adsorbed and enriched on the decorated surface of the substrate. Zeng et al. [70] synthesized Au@Ag core-shell nanoparticles with HAuCl4, AgNO3, sodium citrate and ascorbic acid. The monolayer 2, 5-dimercapto-1, 3, 4-thiadiazole (DMcT) was coated on the surface of the particles, and the nitrogen atoms of this bidentate ligand can strongly coordinate Hg2+. Thus, this substrate provided a much higher SERS factor result than that without the monolayer because of the coordination effect. The detected concentration of Hg2+ can be as low as 1.0×10-11 mol L-1, and it is a label-free method, which has great sensitivity and selectivity for detecting Hg2+ ions. The hollow sea urchin-like TiO2@AgNPs SERS substrates were prepared by Zhou et al. [56] to test Cr(VI) detection by coordinating with the glutathione coating on the nanoparticles, and the detection limit of Cr(VI) is ca. 1.45×10-9 mol L-1. The core-shell structure substrates follow the size rule, and the thickness of the shell is related to the SERS effect. Khurana et al. [71] varied the volume of HAuCl4 solution added to control the Au shell thickness of the Agcore-Aushell bimetallic nanocomposites, and crystal violet was used as a probe molecule to test the SERS activity of each thickness. They found that 30 nm of a Ag core with 8 nm of a Au nanoshell had the best SERS activity for crystal violet. Nguyen et al. [72] found that ~1.4 nm silica layer coated on Ag nanocubes in the Ag@SiO2 nanocube structures had the best SERS activity. The “pillar-cap”-shaped Ag/SiO2 multilayer arrays were prepared by Wang et al. [73]. The [Ag 30 nm/SiO2 5 nm]n (n=1-4) multilayer nanostructure was synthesized by sputtering Ag and SiO2 targets; the size could be modulated by annealing, and the nanostructure

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

provided many hot spots for SERS. The Au-Ag hollow nanostructures prepared by Jiji et al. [64] also had good SERS activity, and the Raman enhancement factor could be controlled by adjusting the size of the cavities. The maximum SERS effect could be obtained by adding 1 mL of HAuCl4 into their system. Wang et al.[74] developed a green synthesis method to prepare the gold core silver shell SERS substrate. They used the epigallocatechin gallate (EGCG) extract from tea leaves to reduce and obtain AgNPs at room temperature, and the Au@Ag structure size could be tuned by adjusting the number of AgNP seeds. Thus, the size rule is important to the SERS activity. In addition to the Au-Ag structure, there are many other kinds of core-shell structure substrates. These substrates have various functions when created via different methods to achieve a variety of structures, and high SERS sensitivity has been achieved.[71-73] Zhao et al. [67] prepared a SERS substrate by reducing AgNO3 to Ag on the surface of a liposome, and Au could also be dispersed on the surface. Then, doxorubicin (DOX) molecules were loaded onto the composites, resulting in a structure that combined SERS enhancement and drug delivery. The drug release could be controlled by near-infrared laser irradiation and monitored drug molecules via SERS and fluorescence signals during the release procedure (Fig. 6). Ag2O@Ag core-shell structures on the surface of PMMA were prepared by Li et al. [75] to make a flexible SERS substrate, where the Ag2O was fabricated by laser irradiation in atmosphere. The Ag2O@Ag/PMMA hybrids have excellent SERS activity. The detection limit of R6G can be as low as 10-11 mol L-1, and the real-time and in situ detection concentration of chlorpyrifos on cucumber and apple peels can be as low as 10-7 mol L-1. Kang et al.[76] built Ag@Al2O3 nanobowl arrays as SERS substrates via ion beam etching and Ag coating, and the structures were on the surface of a Si substrate. The hot spots had a high density and were located at the metallic rim. Pal et al.[77] prepared a bimetal Ag-Cu film via a thermal evaporation method, and the SERS activity was also very high, with good biomolecule detection sensitivity. Ban et al.[14] synthesized a TiN-Ag double-shell hollow nanosphere SERS substrate with polystyrene nanospheres as a template, which was followed by magnetron sputtering deposition to build Ag and TiN layers. This kind of SERS substrate has the properties such as excellent thermal and chemical stabilities, and the substrate combines physical and chemical enhancement mechanisms to yield high SERS activity. Alula et al. [78] directly deposited AgNPs on the surface of bacteria by the silver mirror reaction, and Mycobacterium smegmatis could be evaluated. The porous silver coating fibers synthesized by Liu et al. [79] could detect triphenyltin chloride with a detection limit of 0.2 ppb combined with the solid-phase microextraction method. Rough-surface Au@Ag core-shell nanoparticles with high sensitivity were prepared by Fu et al. [59] and used in SERS immunochromatographic sensors to detect the haemoglobin and the Cd2+ ion, which can be used in clinical diagnosis and environmental pollution monitoring. 3.2 The three-dimensional (3D) substrates The 3D SERS substrate is also a significant form in the SERS substrates [80]. The 3D structure can increase the surface area [81] and contains more hot spots. The preparation of this kind of substrate is rapid and affordable. ZnO nanorods coated on the carbon fibers were synthesized by Huang et al. [81] via a hydrothermal method by methenamine and zinc acetate hexahydrate. Afterwards, ZnO/carbon fiber nanostructures were immersed in a AgNO3 solution; then, Ag+ was reduced by NaBH4. This kind of substrate is used to detect organic pollutants. The

ACCEPTED MANUSCRIPT

TE D

M AN U

SC

RI PT

substrate is very sensitive, and the detection limit of phenol red can reach as low as 1×10-9 mol L-1, with an enhancement factor of 3.18×109. ZnO-decorated AgNPs also have a self-cleaning function via UV irradiation to photocatalytically degrade analytic molecules. TiO2 supported the AgNP SERS substrate synthesized by Dai et al. [82], which had a good SERS effect and UV-cleaning properties. The AgNP-deposited paper strip prepared by Li et al.[83] also obtained a 3D structure and great SERS activity. The authors treated cellulose paper by oxidation with NaIO4 and LiCl solution to generate aldehyde groups on the surface of the paper. Then, the oxidized paper was immersed in Tollen’s reagent, and the silver mirror reaction was performed on the surface of the oxidized paper. Afterwards, the AgNPs could be deposited on the paper, which represents a very inexpensive and sensitive approach. With this substrate, the detection limit for R6G was as low as 10-11 mol L-1.

Fig. 6 The synthesis procedure and the application of the liposome @Ag/Au nanocomposite {Reproduced with permission from [67], ©2017, Elsevier}.

AC C

EP

The 3D structure can also improve the density of the SERS activity sites. Li et al.[84] utilized molding polyacrylonitrile (PAN) nanohump films to fabricate AgNP-decorated PAN nanohumps by sputtering AgNPs onto the PAN films (Fig. 7). This substrate is flexible and reliable, and the density of AgNPs on the sidewalls of the PAN nanohump could be increased by the sputtering process, which improved the SERS activity. The detection limit of trinitrotoluene is 10-12 mol L-1, and this kind of SERS substrate can be used for trace detection of methyl parathion on fruit surfaces. The substrate can be utilized in the field for rapid safety inspection and environmental protection.

ACCEPTED MANUSCRIPT Fig. 7 The fabrication method of AgNPs/PAN nanohump {Reprinted with permission from [84], ©2015, John Wiley & Sons, Ltd}.

M AN U

SC

RI PT

With some substrate structures, the 3D-structure substrate can be combined with other modern analytical methods, such as microfluidic devices. Xie et al.[85] reported an in situ method to deposit Ag on the surface of ZnO nanorods in microfluidic devices. The authors pumped a Zn(NO3)2 precursor into the microfluidic channel, and a laser (405 nm) was focused on the target area. The ZnO nanorods could grow on a gold substrate that was thermally evaporated onto a glass surface. Afterwards, a AgNO3 solution was injected into the microfluidic channel to replace the ZnO precursor, and the laser was focused on the area of ZnO nanorods; then, the AgNPs could be deposited on the surface of ZnO nanorods. This combination of SERS and microfluidic technology can be applied in the biological, biochemical, and biomedical fields. The SERS enhancement factor of the in situ fabricated 3D Ag@ZnO nanorods substrates in the microfluidic devices is up to 2×106, and it can also detect biomolecules in the liquid state and can test the surface chemical fingerprint of living cells. The overlay 3D structure substrate may combine the different advantages of each part and have higher SERS activity. Zhao et al. [86] combined Ag, Au and graphene to build a hybrid system. Monolayer graphene was placed between the AuNPs and Ag nanohole layers, which resembled a sandwich structure (Fig. 8). This structure integrated the advantages of the high SERS effect of Ag, the stability of Au and the flexibility and biological compatibility of the graphene. The sandwich structure between the Ag nanohole arrays and AuNPs and graphene had outstanding SERS activity with a 10-13 mol L-1 detection limit for R6G molecules.

AC C

EP

TE D

3.3 The self-assembled substrates The self-assembly method is very fast and allows easy preparation of an ordered structure, which increases the density of the SERS hot spots and improves the enhancement [6, 87]. Such a structure may be prepared by taking advantage of the polarity of the solvents. Leiterer et al.[6] synthesized a self-assembled monolayer (SAM) of AgNPs coated by dodecanethiol. The authors purified the dodecanethiol-coated AgNPs that were prepared by adding the dodecanethiol into hexane and shaking vigorously while adding methanol to the hexane system. As a result, they utilized the difference in the coated AgNP solubility in hexane and the methanol-hexane mixture. The AgNP SAM SERS substrates were synthesized by adding dropwise the hexane solution of AgNPs to methanol, and the SAMs could be formed at the liquid-air interface. The clear identification of the dye Sudan III by this substrate can be down to 10-5 mol L-1 concentration. Slekiene et al.[88] deposited lipid molecule self-assembled layers on the Au and Ag substrates, and the lipid on the substrate could be detected; with this approach, C-H stretching SERS signals of the lipid layer can be detected with high resolution. The self-assembly can also follow the photosensitive sol-gel and electrochemical reaction methods. Dendrite Ag arrays were fabricated by Huang et al. [87], utilizing a photosensitive sol-gel method to build a ZrO2 pattern and a electrochemical reaction self-assembly method to deposit Ag on the substrate (Fig. 9). This approach was utilized to detect R6G, and the detection limit concentration was as low as 10-13 mol L-1.

SC

RI PT

ACCEPTED MANUSCRIPT

M AN U

Fig. 8 The synthesis and the structure of The AuNPs/Grathene/Ag nanohole SERS substrate {Reproduced with permission from [86], ©2016, Royal Society of Chemistry}.

AC C

EP

TE D

3.4 The recyclable substrates Generally, recyclable substrates are mainly based on the core-shell structure and realized by washing, thermo release and photocatalytic degradation. Obviously, the outstanding advantage of recyclable substrates is that they are easy to reuse. Ouyang et al.[89] reported a graphene-Ag array SERS substrate to test DNA compounds, and the substrate has reusability (Fig. 10). The AgNPs were covered by a graphene layer, and the target DNA captured on the AuNPs had no chemical interaction with graphene; therefore, the target DNA could be washed easily. The substrate has high reproducibility and high SERS activity, and the detection limit of methylated DNA is as low as 1.8×10-12 mol L-1. The detection of DNA extracted from cells was also successful. A polyaniline@AgNPs SERS substrate was prepared by Mondal et al. [90] by depositing AgNPs on a high-aspect-ratio polyaniline fiber; the population of AgNPs on the fiber could be adjusted by the molar concentration of AgNO3. The analytes on the substrate could be washed off, and the substrate was recyclable and useful for detecting several analyte molecules. The substrate not only has recyclability for the detection of analyte molecules but also can carry out the trace detection of 4-mercaptobenzoic acid and R6G with a detection limit down to nanomolar levels; the substrate has excellent recyclability with these compounds as well.[90] Ma et al.[91] reported on Ag nanorods@HfO2 SERS substrates, which were recyclable and could achieve real-time detection. Ag nanorods were deposited on the Si films by the glancing angle deposition (GLAD) technique, and the HfO2 layers were coated on the Ag nanorods by an atomic layer deposition (ALD) method. Because of the high melting point of HfO2, the Ag nanorods@HfO2 SERS substrates exhibited excellent thermostability, and the probe molecule methylene blue could be released by heating the substrate. The SERS substrates can be reused again in “detection-heating” cycles. The substrate can be utilized for the real-time, continuous monitoring of vapor-phase samples under ultralow concentrations based on “detection-heating” cycles. The samples are in the aqueous and gaseous states and can be detected with high sensitivity, efficiency and stability.

RI PT

ACCEPTED MANUSCRIPT

SC

Fig. 9 The synthesis of the self-assembled dendrite Ag arrays {Reproduced with permission from [87], ©2016, Elsevier}.

AC C

EP

TE D

M AN U

Photocatalytic degradation may degrade the organic molecules under UV radiation with TiO2 as a support, and the existence of Ag could slow down the recombination of the photo-excited electrons and holes as well as improve the quantum efficiency of TiO2 [92-94]. Chong et al.[92] reported on AgNP-modified TiO2 nanotubes, and R6G could be photocatalytically degraded by UV radiation. The TiO2 nanotubes were synthesized by the anodization methods, and the AgNPs were immobilized on the TiO2 nanotubes under UV radiation (254 nm) in AgNO3/ methanolic solution. The R6G molecules on the substrate had high SERS activity based on the effect of AgNPs, and R6G could be degraded by UV radiation in response to the high photocatalytic activity of TiO2 nanotubes; the substrate had high recyclability as well.[92] This substrate has great SERS performance with a detection limit of R6G as low as 10-8 mol L-1. The SERS substrate also has photocatalytic activity. Furthermore, the substrate can not only can be used as a recyclable SERS substrate but can also be used to study and monitor in situ the surface photodegradation processes of organic molecules. A 3D AgNP-decorated TiO2 nanorod SERS substrate was prepared by Fang et al.[95] The TiO2 nanorods were synthesized by a hydrothermal method, and the AgNPs were deposited on the TiO2 nanorods by a chemical reduction impregnation method, reducing the AgNO3 with NaBH4. The detection limit for R6G is 10-7 mol L-1, and small molecules, such as R6G, methyl orange, Congo red, and methylene blue, can be rapidly removed from the substrates after exposure to visible light as a result of the photocatalytic activity of TiO2, which also enables recycling of the substrate.

RI PT

ACCEPTED MANUSCRIPT

SC

Fig. 10 The structure and the detection method of graphene-Ag array SERS substrate {Reproduced with permission from [89], ©2016, Elsevier}.

AC C

EP

TE D

M AN U

3.5 The magnetic substrates The typical advantage of magnetic substrates is that they are easy to separate. Liu et al.[96] prepared a Ag-coated Fe3O4@polystyrene (PS) core-shell structure as the SERS substrate. The PS was coated on the Fe3O4 core, and AgNPs were deposited on the PS shell. Because of the magnetic Fe3O4 core, the SERS substrates could be separated easily and used repeatedly at least three times[96]. Cube-like Fe3O4@SiO2@Ag (FSA) nanocomposites were successfully synthesized via a layer-by-layer procedure reported by Li et al. [97]. The nanocomposite showed great SERS activity and was used to detect thiram, one dithiocarbamate fungicide that has been widely used in agriculture. The detection limit was approximately 1×10-6 mol L-1 (0.24 ppm), which is lower than the maximal residue limit of 7 ppm in fruit prescribed by the US Environmental Protection Agency. Liu et al. [98] also successfully fabricated a multifunctional magnetic graphene SERS substrate via layer-by-layer assembly of silver and graphene oxide (GO) nanoparticles (NPs) on the magnetic ferroferric oxide particles (Fe3O4@GO@Ag), and the authors proposed a new method called the surface magnetic solid-phase extraction (SMSPE) technique. Shen et al. [99] investigated Fe3O4@TiO2@Ag-Au microspheres (MS) synthesized by grafting Ag nanoparticles onto 3-aminopropyltrimethoxysilane (APTMS)-modified Fe3O4@TiO2MS, which significantly increased the effect of the “hot spot” and offered stronger electromagnetic field enhancements. This substrate showed good magnetic and photocatalytic performance, and it had great potential for a multifunctional platform for simultaneous catalysis and in situ reaction monitoring. Additionally, a multifunctional nanotube-like Fe3O4/PANI/CDs/Ag hybrid was developed by Yan et al via a sol-gel method and in situ polymerization [100](Fig. 11). The Fe3O4 NTs/PANI/Ag hybrids achieved sensitive SERS signals, and the introduction of carbon dots (CDs) endowed good dispersion and stable photoluminescence (PL). The hybrid system photocatalytic properties, multicolored fluorescence and SERS sensitivity are promising features for hybrid applications in wastewater treatment, photocatalysis, biomedicine and environmental analysis.

RI PT

ACCEPTED MANUSCRIPT

SC

Fig. 11 Schematic representation of synthesis route of the Fe3O4 NTs/PANI/CDs/Ag hybrids {Reproduced with permission from [100], ©2015, Elsevier}.

AC C

EP

TE D

M AN U

3.6 The array-like substrates The surface topography of noble metal particles is a significant factor in tailoring SERS properties, and there have been many efforts to improve the morphology of SERS substrates. A novel method to fabricate Ag nanoparticles clad with parylene C for high-stability microfluidic SERS biochemical sensing applications was reported by Tang et al. [101]. Ag nanoparticles were fabricated on Si wafers by simply using the sputtering and thermal vacuum annealing processes. Parylene was used for the cladding layer, and it was deposited on the substrate through a room-temperature chemical vapor deposition process. The parylene enhanced the Raman spectrum intensity by forming the hot spot structure between the nanoparticles. The cladding technology can be used on different micro and nanostructures, especially for biochemical applications, such as detecting environmental pollution by toxic heavy metals, quantifying ascorbic acid in human blood, and sensing bio/chemical molecules in food. Another SERS-active chip that operates by integrating silver dendrites with a copper substrate through a one-step process was explored by Gu et al. [102]. The structures of dendrites were prepared and controlled by an AgNO3/PVP aqueous system, and the synthesized chip displayed a high thermal stability and good reproducibility. A potential application of the SERS-active chip is in the detection of fluoranthene at a low concentration of 4.5 × 10−10 mol L-1, and the convenient and high-yield method would be a promising approach for rapid detection under field conditions. A fine nanopore array with sub-10 nm pore sizes has been successfully fabricated by Ma et al. [103]. First, they utilized 3D ordered mesoporous silica, EP-FDU-12, as hard templates, synthesizing large-sized 2D Ag NP supercrystals. The plasmonic Ag supercrystals composed NP building units that were approximately 22 nm in size with uniform nanogaps of ≈3 nm. Then, the authors used a chemical etching process with HNO3 aqueous solution to form a “nanopore-in-nanogap” hybrid plasmon mode. This novel hybrid plasmon mode generates an additional enhanced electromagnetic coupling effect and results in ≈10× magnification of the SERS signal. Some interesting models are based on examples in nature. Wang et al. [104] proposed a gecko-inspired nanotentacle surface-enhanced Raman spectroscopy (G-SERS) platform for the first time, which was inspired by the properties of gecko toe pads. The G-SERS platform was obtained from seeding deposition of AgNPs on a 3D PDMS nanotentacle array and provided excellent SERS activity (Fig. 12). 4-mercaptobenzoic acid (4-MBA) could still be clearly

ACCEPTED MANUSCRIPT

TE D

M AN U

SC

RI PT

identified, even at a low concentration of 10−12 mol L-1. The low cost and convenient storage of the G-SERS platform makes it easy to meet the demands of practical applications, such as rapid, efficient microarea sampling and simultaneous detection. G-SERS is expected to find potential applications in the food industry and environmental field. Tang et al. [105] also reported on hexagonally arranged urchin-like Ag-HS arrays, which have been fabricated via an AAO template-assisted approach and show excellent SERS performance. The urchin-like Ag-HS arrays could identify 10−7 mol L-1 dibutyl phthalate (a member of the plasticizers family) and 1.5 × 10−5 mol L-1 PCB-77 (a member of a notorious class of pollutants), showing great potential of the arrays as effective SERS substrates for the rapid detection and monitoring of trace organic pollutants. There are many other arranged arrays, such as the Ag nanopillar [106], Ag-NPs/Si [107], Ag-decorated Si nanocone arrays [108], single-crystalline TiO2 nanosheet (TNS) arrays decorated with Ag nanoparticles (TNS/Ag) [109], LAS-SERS substrates [110], Ag nanocavity arrays [111], Ag-Zn(OH)F networks [112], and Ag nanorod arrays [113]. All the arrays have high reproducibility and uniformity as well as good SERS activity.

AC C

EP

Fig. 12 Schematic demonstration of preparation of GSERS substrate and SERS measurement {Reprinted with permission from [104], © 2017, American Chemical Society}.

3.7 Other In addition to the above, there are many other structures of SERS substrates [114-139], such as different Ag nanostructure substrates [116, 128-130, 135-139], flower-like Ag substrates [115, 118, 120, 126], and Ag hemispheroid substrates [117].

Shin et al. [132] developed a novel droplet-based SERS sensor for real-time SERS monitoring based on a superhydrophobic SERS-active Ag dendritic substrate. This substrate was obtained through a galvanic displacement reaction between Cu and Ag, and water-repellent properties were achieved using a 1H,1H,2H,2H-perfluorodecanethiol (PFDT) coating. The optimal galvanic reaction time and height of the droplet stopper were discussed, and the optimized droplet-based real-time SERS sensor showed high resistance to surface contaminants. The sensor can control and detect rhodamine 6G, Nile blue A, and malachite green without spectral interference. Large-area membranes of plasmonic Ag-nanocubes (Ag-NCs) embedded in cellulose

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

acetate (CA) microspheres (MSs) (denoted Ag-NCs@CA-MSs) were prepared by an electrospray technique [137]. The Ag-NCs@CA-MS membranes could efficiently adsorb molecules in aqueous solution owing to the excellent hydrophilicity of CA. The membranes can detect p-aminothiophenol (a probe molecule) and methyl parathion (a toxic pesticide) with concentrations as low as 10-9 mol L-1 and 10-7 mol L-1, respectively, demonstrating potential for quantitative SERS-based analysis of organic pollutants in aqueous solution. Kumar et al. [130] demonstrated a simple and facile method to fabricate a highly sensitive, flexible and robust SERS active substrate. The novel SERS substrate was fabricated by embedding Ag nanorods into the polydimethylsiloxane (PDMS) polymer, and the AgNR-embedded SERS substrates exhibited a high sensitivity and excellent reproducibility for analyte detection. This substrate can directly extract trace levels (∼10−9 g/cm2) of thiram pesticide directly from fruit peels via a simple “paste and peel off” method. Zhang et al. [139] developed an innovative strategy to ultrasensitively detect SERS weak-intensity molecules by employing a bionic antennae structure with dendritic Ag nanocrystals. Benefitting from the “cavity-vortex” effect, the dendritic Ag nanocrystals overcome a long-standing limitation by which gaseous molecules are difficult to absorb on solid substrates. The dendritic Ag nanocrystals can sensitively capture gaseous aldehyde molecules and detect them at the ppb (parts per billion) level. Zhai et al. [138] fabricated Ag@CD and Ag@CD@p-ATP@FA with excellent biocompatibility, water solubility and water stability, and the substrates can be used as effective SERS probes for the specific targeting and imaging of FR-positive cancer cells. Li et al. [119] demonstrated a facile finger-press-promoted SERS strategy using a self-energizing substrate (Fig. 13). The substrate combined an energy conversion film and a SERS-active Ag nanowire layer. The composite film was the key component prepared from a piezoelectric polymer matrix and surface-engineered rGO, which simultaneously had a high permittivity and low dielectric loss. The substrate converted a finger press that generated film deformations into stored electrical energy, which further injected electrons into the SERS-active layer to promote SERS intensities. This substrate can increase E-SERS signals up to 10-fold from a variety of molecules obtained in the open air. Various tests on real-life sample surfaces demonstrated the potentials of the substrate in fast on-site detection.

Fig. 13 a) Schematic illustration of the E-SERS-active device, b) Schematic illustration of the finger-press-promoted E-SERS, c) Schematic illustration of the charged and discharged states of the device and the measured Raman intensities during these states {Reprinted with permission

ACCEPTED MANUSCRIPT from [119], ©2017, John Wiley & Sons, Ltd}.

RI PT

Mettela et al. [118] fabricated large Ag microflowers (~50-100 mm) by thermal decomposition of a Ag–organic complex, which was followed by chemical reduction. Flower-like AgBr crystallites with a growth direction of {110} were first obtained by thermolyzing a complex obtained from the stabilization of [AgCl2]- anions with tetraoctylammonium bromide. Upon reduction with NaBH4, the crystallites developed into a nanostructured Ag surface, which had a high SERS enhancement factor (~106-108). The Ag microflowers are used for labeled and nonlabeled detection of both single- and double-stranded DNA, and SERS data can be collected from ultralow volumes of the analyte solution (~0.34 nL).

AC C

EP

TE D

M AN U

SC

4 Conclusions In this review, we summarized the recent progressive preparation and application of silver-based SERS enhancement substrate. The various supports and significant structures of the SERS substrates based on silver were discussed. Metal oxide, graphene, silica, and polymer are widely used as supports. The core-shell structure, 3D substrate, self-assembled substrate, recyclable substrate, magnetic substrate, and array-like substrate are the primarily used substrate structures. The main silver-based SERS substrates in this review and their enhancement effects were summarized in Table 1. The lowest reported detection limit is 10-13 mol L-1 for R6G with the sandwich structure between Ag nanohole arrays, AuNPs and graphene as well as the dendrite Ag arrays fabricated by a self-assembly method.[86, 87].

ACCEPTED MANUSCRIPT

Table 1 The main silver-based SERS substrates in this review and their enhancement effects

SERS substrates

structures

Limit of detection (mol L-1)

Ag-decorated CuO

10-10

Core-shell

/

2

Cu-AgNPs-embedded PVA thin film

Other

/

3

rGO/AgNPs

Other

1×10-7

6 7 8

3D

AgNPs/rGO

Other

Ag clusters/pSi

Other

Au, Ag NPs on glass

Array-like

ITO- rGO/AgNPs

9

AgNPs on basil seeds

10

AgNPs on S-g-C3N4

Other Other Other

Au@Ag core-shell nanoparticles coated by DMcT Hollow sea urchin-like TiO2@AgNPs

14 15 16 17 18

Ag2O@Ag/PMMA hybrids Porous silver coating fibers Ag/ZnO hybrids AgNPs on oxidized paper AgNPs/PAN nanohump Ag@ZnO nanorods

/ /

/

1.27×10

-9

-7

10 -10

8

R6G

[14]

10

/

-4

/

[30] [36]

R6G

[37]

4-aminothiophenol

[39]

R6G

[44]

o-chlorothiophenol

[48]

R6G

[50]

-11

5.9×10

10

-7

/

methyl parathion in juice

10

-6

/

melamine in milk

2.1×109

crystal violet

10

/

8

/ 4-aminothiophenol

Core-shell

1.0×10

/

Core-shell

1.45×10-9

/

Cr(VI)

-11

/

R6G

10-7

/

0.2 ppb

/

Core-shell

AC C

13

10 -10

-12

10

Ref.

-11

EP

11 12

10

7

M AN U

5

GO-AgNPs-pSi

TE D

4

Analytes

EF (a.u.)

SC

1

RI PT

Entry

Enhancement effects

Types and

Core-shell

10

1×10

3D

10

-11

10

-12

3D 3D

/

Hg

chlorpyrifos on cucumber and

[52] [70] [56] [75]

apple peels triphenyltin chloride

[79]

phenol red

[81]

/

R6G

[83]

/

trinitrotoluene

[84]

2×10 (in microfluidic

/

[85]

-9

3D

2+

[16]

3.18×10

6

9

ACCEPTED MANUSCRIPT

devices) Monolayer graphene sandwiched between silver nanohole arrays and AuNPs

3D

10-13

20

AgNP SAM SERS substrates

Self-assembled

10-5

21

Dendrite Ag arrays

Self-assembled

10-13

22

Graphene-Ag array SERS substrate

Recyclable

1.8×10-12

26 27

Recyclable

Cube-like Fe3O4@SiO2@Ag (FSA) Integrating silver dendrites SERS-active chip Gecko-inspired nanotentacle SERS platform (G-SERS) Hexagonally arranged urchin-like Ag-HS arrays

29

Ag-NCs@CA-MS membranes

Array-like Array-like Array-like Other

AC C

EP

28

Magnetic

[86]

/

Sudan III

[6]

R6G

[87]

/

methylated DNA

[89]

/

R6G

[92]

/

R6G

[95]

/

/

[97]

/

fluoranthene

[102]

/

4-mercaptobenzoic acid

[104]

/

dibutyl phthalate

/

PCB-77

10-9

/

p-aminothiophenol

-7

/

methyl parathion

10

-8

10

-7

SC

25

AgNP-decorated TiO2 nanorod

Recyclable

R6G

/

1×10

-6

M AN U

24

AgNP-modified TiO2 nanotubes

TE D

23

/

RI PT

19

4.5 × 10

−10

10−12 10−7

1.5 × 10 10

−5

[105] [137]

ACCEPTED MANUSCRIPT

M AN U

SC

RI PT

Most of the SERS substrates with different structures are simple and efficient with high enhancement activity. The most useful hot spots for SERS substrates are Ag and Au, they both have the good SERS enhancement activity, and Ag has the better effect on enhancement.[140] However, compared with Au, Ag is not very stable, which might affect the substrate lifetime. Fortunately, there are many methods to overcome this disadvantage, including protecting the AgNPs with GO[36], synthesizing reproducible substrates with photocatalytically active TiO2[92-94], and combining the advantages of the high SERS effect of Ag and the stability of Au.[86] Another important SERS application is realized by combining the enhancement property and reaction process, which can sufficiently increase the enhancement to observe and monitor chemical reactions[53, 141]. This approach should be a significant focus of future study for SERS, and it could expand the SERS application from detection to studying reactions, especially for in situ applications. Nowadays, the in situ application has been applied by various SERS substrates in many fields, for example, the detection of chlorpyrifos on cucumber and apple peels by Ag2O@Ag/PMMA hybrids SERS substrate[75], monitoring the surface photodegradation processes of organic molecules by AgNP-modified TiO2 nanotubes SERS substrate [92], and the potential applications for simultaneous catalysis and in situ reaction monitoring based on the Fe3O4@TiO2@Ag-Au microspheres SERS substrate [100], and the utilization of time-dependent SERS in the adsorption and surface reactivity of 2,2′:6′,2″-terpyridine (tpy) [142]. Therefore, the in situ application will be more and more important not only in the analytical chemistry but also in other fields such as catalysis and research of the reaction mechanism.

TE D

Acknowledgments This work was supported by National High Technology Research and Development Program of China (863 program) (No. 2015AA03A401) and the National Natural Science Foundation of China (21427803, 21677069).

EP

References

[1] X. Wei, D. Jie, J. J. Cuello, D. J. Johnson, Z. Qiu, Y. He, Microalgal detection by Raman microspectroscopy, TrAC-Trend Anal. Chem., 53 (2014) 33-40.

AC C

[2] M. Fleischmann, P. J. Hendra, A.J. McQuillan, Raman-Spectra of pyridine adsorbed at a silver

electrode, Chem. Phys. Lett., 26 (1974) 163-166. [3] D. L. Jeanmaire, R.P. Vanduyne, Surface Raman spectroelectrochemistry. 1. Heterocyclic, aromatic, and aliphatic-amines adsorbed on anodized silver electrode, J. Electroanal. Chem., 84 (1977) 1-20.

[4] Z. Zeng, Y. Liu, J. Wei, Recent advances in surface-enhanced raman spectroscopy (SERS): Finite-difference time-domain (FDTD) method for SERS and sensing applications, TrAC-Trend Anal. Chem., 75 (2016) 162-173. [5] V. Iancu, L. Baia, N. Tarcea, J. Popp, M. Baia, Towards TiO2-Ag porous nanocomposites based SERS sensors for chemical pollutant detection, J. Mol. Struct., 1073 (2014) 51-57. [6] C. Leiterer, D. Zopf, B. Seise, F. Jahn, K. Weber, J. Popp, D. Cialla-May, W. Fritzsche, Fast self-assembly of silver nanoparticle monolayer in hydrophobic environment and its application as SERS substrate, J. Nanopart. Res., 16 (2014) 2467.

ACCEPTED MANUSCRIPT [7] K. Guo, R. Xiao, X. Zhang, C. Wang, Q. Liu, Z. Rong, L. Ye, S. Chen, Silver Nanopartical over AuFON Substrate for Enhanced Raman Readout and Their Application in Pesticide Monitoring, Mol., 20 (2015) 6299-6309. [8] S. Pang, T. Yang, L. He, Review of surface enhanced Raman spectroscopic (SERS) detection of synthetic chemical pesticides, TrAC-Trend Anal. Chem., 85 (2016) 73-82. [9] C. Wu, E. Chen, J. Wei, Surface enhanced Raman spectroscopy of Rhodamine 6G on agglomerates of different-sized silver truncated nanotriangles, Colloids Surf., A, 506 (2016) 450-456. identification of explosives, TrAC-Trend Anal. Chem., 54 (2014) 36-44.

RI PT

[10] M. Lopez-Lopez, C. Garcia-Ruiz, Infrared and Raman spectroscopy techniques applied to [11] L. He, M. Langlet, V. Stambouli, Role of the external NH2 linker on the conformation of surface immobilized single strand DNA probes and their SERS detection, Appl. Surf. Sci., 399 (2017) 702-710. [12] L. Wu, X. Xiao, K. Chen, W. Yin, Q. Li, P. Wang, Z. Lu, J. Ma, H. Han, Ultrasensitive SERS

SC

detection of Bacillus thuringiensis special gene based on Au@Ag NRs and magnetic beads, Biosens. Bioelectron., 92 (2017) 321-327.

[13] R. A. Wallace, N. V. Lavrik, M. J. Sepaniak, Ultra-thin layer chromatography with integrated silver colloid-based SERS detection, Electrophoresis, 38 (2017) 361-367.

M AN U

[14] R. Ban, Y. Yu, M. Zhang, J. Yin, B. Xu, D. Y. Wu, M. Wu, Z. Zhang, H. Tai, J. Li, J. Kang, Synergetic SERS Enhancement in a Metal-Like/Metal Double-Shell Structure for Sensitive and Stable Application, ACS Appl. Mat. Interfaces, 9 (2017) 13564-13570.

[15] N. D. Jayrarn, D. Aishwarya, S. Sonia, D. Mangalaraj, P. S. Kumar, G. M. Rao, Analysis on superhydrophobic silver decorated copper Oxide nanostructured thin films for SERS studies, J. Colloid Interface Sci., 477 (2016) 209-219.

[16] L. Hu, Y.J. Liu, S. Xu, Z. Li, J. Guo, S. Gao, Z. Lu, H. Si, S. Jiang, S. Wang, Facile and low-cost

TE D

fabrication of Ag-Cu substrates via replacement reaction for highly sensitive SERS applications, Chem. Phys. Lett., 667 (2017) 351-356.

[17] C. Chen, X. Zhou, T. Ding, J. Zhang, S. Wang, J. Xu, J. Chen, J. Dai, C. Chen, Preparation and characterization of ZnO/SiO2/Ag nanoparticles as highly sensitive substrates for surface-enhanced Raman scattering, Mater. Lett., 165 (2016) 55-58.

EP

[18] S. Y. Ding, D. Y. Wu, Z. L. Yang, B. Ren, X. Xu, Z. Q. Tian, Some Progresses in Mechanistic Studies on Surface-Enhanced Raman Scattering, Chem. J. Chin. Univ.-Chin., 29 (2008) 2569-2581. [19] Q. Fu, Z. Zhan, J. Dou, X. Zheng, R. Xu, M. Wu, Y. Lei, Highly Reproducible and Sensitive SERS

AC C

Substrates with Ag Inter-Nanoparticle Gaps of 5 nm Fabricated by Ultrathin Aluminum Mask Technique, ACS Appl. Mat. Interfaces, 7 (2015) 13322-13328. [20] Z. Chao, L. Song, Y. Zhou, W. Nie, P. Chen, Impact of PS/SiO2 morphologies on the SERS activity of PS/SiO2/Ag nanocomposite particles, Colloid. Polym. Sci., 292 (2014) 2841-2848. [21] G. Chin, J. Yeston, Editors' Choice, Science, 316 (2007) 19, 21. [22] J.M. Caridad, S. Winters, D. McCloskey, G.S. Duesberg, J.F. Donegan, V. Krstić, Hot-Volumes as Uniform and Reproducible SERS-Detection Enhancers in Weakly-Coupled Metallic Nanohelices, Sci. Rep. -UK, 7 (2017) 45548. [23] A. Araujo, C. Caro, M.J. Mendes, D. Nunes, E. Fortunato, R. Franco, H. Aguas, R. Martins, Highly efficient nanoplasmonic SERS on cardboard packaging substrates, Nanotechnol., 25 (2014) 415202. [24] L. Mikac, M. Ivanda, M. Gotic, T. Mihelj, L. Horvat, Synthesis and characterization of silver colloidal nanoparticles with different coatings for SERS application, J. Nanopart. Res., 16 (2014) 2748.

ACCEPTED MANUSCRIPT [25] S. Li, D. Li, Q.-Y. Zhang, X. Tang, Surface enhanced Raman scattering substrate with high-density hotspots fabricated by depositing Ag film on TiO2-catalyzed Ag nanoparticles, J. Alloys Compd., 689 (2016) 439-445. [26] Z. Li, K. Zhu, Q. Zhao, A. Meng, The enhanced SERS effect of Ag/ZnO nanoparticles through surface hydrophobic modification, Appl. Surf. Sci., 377 (2016) 23-29. [27] L. Ma, Y. Huang, M. Hou, J. Li, Z. Zhang, Pinhole Effect on the Melting Behavior of Ag@Al2O3 SERS Substrates, Nanoscale Res. Lett., 11 (2016) 170.

RI PT

[28] Z. Zeng, D. Tang, L. Liu, Y. Wang, Q. Zhou, S. Su, D. Hu, B. Han, M. Jin, X. Ao, R. Zhan, X. Gao, X. Lu, G. Zhou, S. Senz, Z. Zhang, J. Liu, Highly reproducible surface-enhanced Raman scattering substrate for detection of phenolic pollutants, Nanotechnol., 27 (2016) 455301.

[29] V. K. Rao, P. Ghildiyal, T.P. Radhakrishnan, In Situ Fabricated Cu-Ag Nanoparticle-Embedded Polymer Thin Film as an Efficient Broad Spectrum SERS Substrate, J. Phys. Chem. C, 121 (2017)

SC

1339-1348.

[30] Y. C. Ko, H. Y. Fang, D. H. Chen, Fabrication of Ag/ZnO/reduced graphene oxide nanocomposite for SERS detection and multiway killing of bacteria, J. Alloys Compd., 695 (2017) 1145-1153. [31] M. Macias-Montero, R. J. Pelaez, V. J. Rico, Z. Saghi, P. Midgley, C.N. Afonso, A. R.

M AN U

Gonzalez-Elipe, A. Borras, Laser Treatment of Ag@ZnO Nanorods as Long-Life-Span SERS Surfaces, ACS Appl. Mat. Interfaces, 7 (2015) 2331-2339.

[32] M. E. Koleva, N. N. Nedyalkov, P. A. Atanasov, J. W. Gerlach, D. Hirsch, A. Prager, B. Rauschenbach, N. Fukata, W. Jevasuwan, Porous plasmonic nanocomposites for SERS substrates fabricated by two-step laser method, J. Alloys Compd., 665 (2016) 282-287. [33] Y. Zhao, L. Sun, M. Xi, Q. Feng, C. Jiang, H. Fong, Electrospun TiO2 Nanofelt Surface-Decorated with Ag Nanoparticles as Sensitive and UV-Cleanable Substrate for Surface Enhanced Raman

TE D

Scattering, ACS Appl. Mat. Interfaces, 6 (2014) 5759-5767.

[34] S. S. Nanda, M. J. Kim, K. S. Yeom, S. S.A. An, H. Ju, D. K. Yi, Raman spectrum of graphene with its versatile future perspectives, TrAC-Trend Anal. Chem., 80 (2016) 125-131. [35] H. Mehl, M. M. Oliveira, A. J. Gorgatti Zarbin, Thin and transparent films of graphene/silver nanoparticles obtained at liquid-liquid interfaces: Preparation, characterization and application as SERS

EP

substrates, J. Colloid Interface Sci., 438 (2015) 29-38. [36] J. Guo, S. Xu, X. Liu, Z. Li, L. Hu, Z. Li, P. Chen, Y. Ma, S. Jiang, T. Ning, Graphene oxide-Ag nanoparticles-pyramidal silicon hybrid system for homogeneous, long-term stable and sensitive SERS

AC C

activity, Appl. Surf. Sci., 396 (2017) 1130-1137. [37] S. Jiang, J. Guo, C. Zhang, C. Li, M. Wang, Z. Li, S. Gao, P. Chen, H. Si, S. Xu, A sensitive, uniform, reproducible and stable SERS substrate has been presented based on MoS2@Ag nanoparticles@pyramidal silicon, RSC Adv., 7 (2017) 5764-5773. [38] K. C. Hsu, D. H. Chen, Microwave-assisted green synthesis of Ag/reduced graphene oxide nanocomposite as a surface-enhanced Raman scattering substrate with high uniformity, Nanoscale Res. Lett., 9 (2014) 193. [39] X. H. Pham, E. Hahm, H. M. Kim, S. Shim, T.H. Kim, D.H. Jeong, Y.-S. Lee, B. H. Jun, Silver Nanoparticle-Embedded Thin Silica-Coated Graphene Oxide as an SERS Substrate, Nanomater., 6 (2016) 176. [40] C. Wang, M. Li, Q. Li, K. Zhang, C. Wang, R. Xiao, S. Wang, Polyethyleneimine-mediated seed growth approach for synthesis of silver-shell silica-core nanocomposites and their application as a versatile SERS platform, RSC Adv., 7 (2017) 13138-13148.

ACCEPTED MANUSCRIPT [41] J. Pilipavicius, R. Kaleinikaite, M. Pucetaite, M. Velicka, A. Kareiva, A. Beganskiene, Controllable formation of high density SERS-active silver nanoprism layers on hybrid silica-APTES coatings, Appl. Surf. Sci., 377 (2016) 134-140. [42] Y. Long, X. Wang, D. Chen, T. Jiang, Z. Zhao, J. Zhou, Intense and stable surface-enhanced Raman scattering from Ag@mesoporous SiO2 film, J. Lumin., 177 (2016) 387-393. [43] L. Mikac, M. Ivanda, V. Derek, M. Gotic, Influence of mesoporous silicon preparation condition on silver clustering and SERS enhancement, J. Raman Spectrosc., 47 (2016) 1036-1041.

RI PT

[44] T. Yang, H. Yang, S. J. Zhen, C. Z. Huang, Hydrogen-Bond-Mediated in Situ Fabrication of AgNPs/Agar/PAN Electrospun Nanofibers as Reproducible SERS Substrates, ACS Appl. Mat. Interfaces, 7 (2015) 1586-1594.

[45] Z. Zhang, Y. Wu, Z. Wang, X. Zou, Y. Zhao, L. Sun, Fabrication of silver nanoparticles embedded into polyvinyl alcohol (Ag/PVA) composite nanofibrous films through electrospinning for antibacterial

SC

and surface-enhanced Raman scattering (SERS) activities, Mater. Sci. Eng., C, 69 (2016) 462-469.

[46] A. Amarjargal, L. D. Tijing, C. S. Kim, Simple fabrication of Ag nanoparticle-impregnated electrospun nanofibres as SERS substrates, Bull. Mater. Sci., 38 (2015) 267-270.

[47] Y. Bu, S.J. Park, S. W. Lee, Diamine-linked array of metal (Au, Ag) nanoparticles on glass (2014) 784-789.

M AN U

substrates for reliable surface-enhanced Raman scattering (SERS) measurements, Curr. Appl. Phys., 14 [48] X. Cheng, J. Bian, Z. Huang, Z. Zhang, P. Dong, Q. Wang, Y. Chen, Y. Zhang, X. Zhang, Direct Electrodeposition of Hollowed Ag Nanostructures on ITO Glass for Reproducible SERS Application, Plasmonics, 11 (2016) 1279-1283.

[49] R. Wang, Y. Xu, C. Wang, H. Zhao, R. Wang, X. Liao, L. Chen, G. Chen, Fabrication of ITO-rGO/Ag NPs nanocomposite by two-step chronoamperometry electrodeposition and its

TE D

characterization as SERS substrate, Appl. Surf. Sci., 349 (2015) 805-810.

[50] Q. Zhou, G. Meng, N. Wu, N. Zhou, B. Chen, F. Li, Q. Huang, Dipping into a drink: Basil-seed supported silver nanoparticles as surface-enhanced Raman scattering substrates for toxic molecule detection, Sens. Actuators, B, 223 (2016) 447-452.

[51] L. Zhang, J. Fang, C. Wang, T. Xu, Y. Jin, Fabrication of Superior Au-Ag Composites

EP

Surface-Enhanced Raman Scattering Active Substrates Based on One-Step Method of Chemical Etching, Nano, 11 (2016) 1650080.

[52] J. Jiang, J. Zou, A.T.S. Wee, W. Zhang, Use of Single-Layer g-C3N4/Ag Hybrids for

AC C

Surface-Enhanced Raman Scattering (SERS), Sci. Rep. -UK, 6 (2016) 34599. [53] Q. Cao, K. Yuan, Q. Liu, C. Liang, X. Wang, Y.-F. Cheng, Q. Li, M. Wang, R. Che, Porous Au-Ag Alloy Particles Inlaid AgCl Membranes As Versatile Plasmonic Catalytic Interfaces with Simultaneous, in Situ SERS Monitoring, ACS Appl. Mat. Interfaces, 7 (2015) 18491-18500. [54] Y. Huang, H. Xu, H. Yang, Y. Lin, H. Liu, Y. Tong, Efficient Charges Separation Using Advanced BiOI-Based Hollow Spheres Decorated with Palladium and Manganese Dioxide Nanoparticles, ACS Sustainable Chem. Eng., 6 (2018) 2751-2757. [55] Y. Huang, K. Li, Y. Lin, Y. Tong, H. Liu, Enhanced Efficiency of Electron–Hole Separation in Bi2O2CO3 for Photocatalysis via Acid Treatment, ChemCatChem, 10 (2018) 1982-1987. [56] W. Zhou, B.-C. Yin, B.-C. Ye, Highly sensitive surface-enhanced Raman scattering detection of hexavalent chromium based on hollow sea urchin-like TiO2@Ag nanoparticle substrate, Biosens. Bioelectron., 87 (2017) 187-194. [57] L.-W. Liu, Q.-W. Zhou, Z.-Q. Zeng, M.-L. Jin, G.-F. Zhou, R.-Z. Zhan, H.-J. Chen, X.-S. Gao,

ACCEPTED MANUSCRIPT X.-B. Lu, S. Senz, Z. Zhang, J.-M. Liu, Induced SERS activity in Ag@SiO2/Ag core-shell nanosphere arrays with tunable interior insulator, J. Raman Spectrosc., 47 (2016) 1200-1206. [58] L. You, R. Li, X. Dong, F. Wang, J. Guo, C. Wang, Micron-sized surface enhanced Raman scattering reporter/fluorescence probe encoded colloidal microspheres for sensitive DNA detection, J. Colloid Interface Sci., 488 (2017) 109-117. [59] Q. Fu, H.L. Liu, Z. Wu, A. Liu, C. Yao, X. Li, W. Xiao, S. Yu, Z. Luo, Y. Tang, Rough surface Au@Ag core-shell nanoparticles to fabricating high sensitivity SERS immunochromatographic sensors,

RI PT

J. Nanobiotecg., 13 (2015) 81.

[60] L. Luo, Y. Chen, L. Zhang, Y. Li, H. Li, H. Zhang, Y. Tian, SERS assay for pyrophosphate based on its competitive binding to Cu(II) ion on silver nanoparticles modified with cysteine and rhodamine 6G, Microchim. Acta, 184 (2017) 595-601.

[61] P.-P. Fang, X. Lu, H. Liu, Y. Tong, Applications of shell-isolated nanoparticles in surface-enhanced

SC

Raman spectroscopy and fluorescence, TrAC Trends in Analytical Chemistry, 66 (2015) 103-117.

[62] H. Yang, L.Q. He, Y.W. Hu, X. Lu, G.R. Li, B. Liu, B. Ren, Y. Tong, P.P. Fang, Quantitative Detection of Photothermal and Photoelectrocatalytic Effects Induced by SPR from Au@Pt Nanoparticles, Angew. Chem. Int. Ed., 54 (2015) 11462-11466.

M AN U

[63] Z. Zheng, G. Shan, J. Li, Y. Chen, Y. Liu, Au/Ag nanoalloy shells as near-infrared SERS nanoprobe for the detection of protein, Mater. Res. Express, 1 (2014) 045408. [64] S.G. Jiji, K.G. Gopchandran, Au–Ag hollow nanostructures with tunable SERS properties, Spectrochim. Acta, Part A, 171 (2017) 499-506.

[65] X.-H. Pham, M. Lee, S. Shim, S. Jeong, H.-M. Kim, E. Hahm, S.H. Lee, Y.-S. Lee, D.H. Jeong, B.-H. Jun, Highly sensitive and reliable SERS probes based on nanogap control of a Au-Ag alloy on silica nanoparticles, RSC Adv., 7 (2017) 7015-7021.

TE D

[66] C. Wang, X. Wu, P. Dong, J. Chen, R. Xiao, Hotspots engineering by grafting Au@Ag core-shell nanoparticles on the Au film over slightly etched nanoparticles substrate for on-site paraquat sensing, Biosens. Bioelectron., 86 (2016) 944-950.

[67] Y. Zhao, J. Zhao, G. Shan, D. Yan, Y. Chen, Y. Liu, SERS-active liposome@Ag/Au nanocomposite for NIR light-driven drug release, Colloids Surf., B, 154 (2017) 150-159.

EP

[68] L. Jin, G. She, J. Li, J. Xia, X. Wang, L. Mu, W. Shi, A facile fabrication of Ag-Au-Ag nanostructures with nanogaps for intensified surface-enhanced Raman scattering, Appl. Surf. Sci., 389 (2016) 67-72.

AC C

[69] Z. Huang, G. Meng, Q. Huang, B. Chen, Y. Lu, Z. Wang, X. Zhu, K. Sun, Surface-enhanced Raman scattering from plasmonic Ag-nanocube@Au-nanospheres core@satellites, J. Raman Spectrosc., 48 (2017) 217-223.

[70] Y. Zeng, L. Wang, L. Zeng, A. Shen, J. Hu, A label-free SERS probe for highly sensitive detection of Hg2+ based on functionalized Au@Ag nanoparticles, Talanta, 162 (2017) 374-379. [71] P. Khurana, S. Thatai, S. Prasad, S. Soni, D. Kumar, Agcore-Aushell bimetallic nanocomposites: Gold shell thickness dependent study for SERS enhancement, Microchem. J., 124 (2016) 819-823. [72] M.-K. Nguyen, W.-N. Su, C.-H. Chen, J. Rick, B.-J. Hwang, Highly sensitive and stable Ag@SiO2 nanocubes for label-free SERS-photoluminescence detection of biomolecules, Spectrochim. Acta, Part A, 175 (2017) 239-245. [73] Y. Wang, M. Zhang, C. Yan, L. Chen, Y. Liu, J. Li, Y. Zhang, J. Yang, Pillar-cap shaped arrays of Ag/SiO2 multilayers after annealing treatment as a SERS-active substrate, Colloids Surf., A, 506 (2016) 96-103.

ACCEPTED MANUSCRIPT [74] R. Wang, Y. Yao, M. Shen, X. Wang, Green synthesis of Au@Ag nanostructures through a seed-mediated method and their application in SERS, Colloids Surf., A, 492 (2016) 263-272. [75] C. Li, C. Yang, S. Xu, C. Zhang, Z. Li, X. Liu, S. Jiang, Y. Huo, A. Liu, B. Man, Ag2O@Ag core-shell structure on PMMA as low-cost and ultra-sensitive flexible surface-enhanced Raman scattering substrate, J. Alloys Compd., 695 (2017) 1677-1684. [76] M. Kang, X. Zhang, L. Liu, Q. Zhou, M. Jin, G. Zhou, X. Gao, X. Lu, Z. Zhang, J. Liu, spectroscopy, Nanotechnol., 27 (2016) 165304.

RI PT

High-density ordered Ag@Al2O3 nanobowl arrays in applications of surface-enhanced Raman [77] A.K. Pal, D. Bharathi Mohan, SERS enhancement, sensitivity and homogeneity studies on bi-metallic Ag-Cu films through tuning of broad band SPR towards red region, J. Alloys Compd., 698 (2017) 460-468.

[78] M.T. Alula, S. Krishnan, N.R. Hendricks, L. Karamchand, J.M. Blackburn, Identification and detection via SERS, Microchim. Acta, 184 (2017) 219-227.

SC

quantitation of pathogenic bacteria via in-situ formation of silver nanoparticles on cell walls, and their [79] Z. Liu, L. Wang, W. Bian, M. Zhang, J. Zhan, Porous silver coating fiber for rapidly screening organotin compounds by solid phase microextraction coupled with surface enhanced Raman

M AN U

spectroscopy, RSC Adv., 7 (2017) 3117-3124.

[80] H. Liu, L. Yang, J. Liu, Three-dimensional SERS hot spots for chemical sensing: Towards developing a practical analyzer, TrAC-Trend Anal. Chem., 80 (2016) 364-372. [81] C. Huang, C. Xu, J. Lu, Z. Li, Z. Tian, 3D Ag/ZnO hybrids for sensitive surface-enhanced Raman scattering detection, Appl. Surf. Sci., 365 (2016) 291-295.

[82] H. Dai, Y. Sun, P. Ni, W. Lu, S. Jiang, Y. Wang, Z. Li, Z. Li, Three-dimensional TiO2 supported silver nanoparticles as sensitive and UV-cleanable substrate for surface enhanced Raman scattering,

TE D

Sens. Actuators, B, 242 (2017) 260-268.

[83] Y. Li, K. Zhang, J. Zhao, J. Ji, C. Ji, B. Liu, A three-dimensional silver nanoparticles decorated plasmonic paper strip for SERS detection of low-abundance molecules, Talanta, 147 (2016) 493-500. [84] Z. Li, G. Meng, Q. Huang, X. Hu, X. He, H. Tang, Z. Wang, F. Li, Ag Nanoparticle-Grafted PAN-Nanohump Array Films with 3D High-Density Hot Spots as Flexible and Reliable SERS

EP

Substrates, Small, 11 (2015) 5452-5459.

[85] Y. Xie, S. Yang, Z. Mao, P. Li, C. Zhao, Z. Cohick, P.-H. Huang, T.J. Huang, In Situ Fabrication of 3D Ag@ZnO Nanostructures for Microfluidic Surface-Enhanced Raman Scattering Systems, Acs Nano,

AC C

8 (2014) 12175-12184.

[86] Y. Zhao, D. Yang, X. Li, Y. Liu, X. Hu, D. Zhou, Y. Lu, Toward highly sensitive surface-enhanced Raman scattering: the design of a 3D hybrid system with monolayer graphene sandwiched between silver nanohole arrays and gold nanoparticles, Nanoscale, 9 (2017) 1087-1096. [87] P. Huang, Z. Wang, L. Lin, Z. Feng, X. Wen, Z. Zheng, Self-assembled dendrite Ag arrays with tunable morphologies for surface-enhanced Raman scattering, Appl. Surf. Sci., 386 (2016) 345-351. [88] N. Slekiene, L. Ramanauskaite, V. Snitka, Surface enhanced Raman spectroscopy of self-assembled layers of lipid molecules on nanostructured Au and Ag substrates, Chem. Phys. Lipids, 203 (2017) 12-18. [89] L. Ouyang, Y. Hu, L. Zhu, G.J. Cheng, J. Irudayaraj, A reusable laser wrapped graphene-Ag array based SERS sensor for trace detection of genomic DNA methylation, Biosens. Bioelectron., 92 (2017) 755-762. [90] S. Mondal, U. Rana, S. Malik, Facile Decoration of Polyaniline Fiber with Ag Nanoparticles for

ACCEPTED MANUSCRIPT Recyclable SERS Substrate, ACS Appl. Mat. Interfaces, 7 (2015) 10457-10465. [91] L. Ma, H. Wu, Y. Huang, S. Zou, J. Li, Z. Zhang, High-Performance Real-Time SERS Detection with Recyclable Ag Nanorods@HfO2 Substrates, ACS Appl. Mat. Interfaces, 8 (2016) 27162-27168. [92] X. Chong, B. Zhao, R. Li, W. Ruan, X. Yang, Photocatalytic degradation of rhodamine 6G on Ag modified TiO2 nanotubes: Surface-enhanced Raman scattering study on catalytic kinetics and substrate recyclability, Colloids Surf., A, 481 (2015) 7-12. [93] Y. Ling, Y. Zhuo, L. Huang, D. Mao, Using Ag-embedded TiO2 nanotubes array as recyclable

RI PT

SERS substrate, Appl. Surf. Sci., 388 (2016) 169-173.

[94] Z. Zhang, J. Yu, J. Yang, X. Lv, T. Wang, Preparation of sensitive and recyclable porous Ag/TiO2 composite films for SERS detection, Appl. Surf. Sci., 359 (2015) 853-859.

[95] H. Fang, C.X. Zhang, L. Liu, Y.M. Zhao, H.J. Xu, Recyclable three-dimensional Ag nanoparticle-decorated TiO2 nanorod arrays for surface-enhanced Raman scattering, Biosens.

SC

Bioelectron., 64 (2015) 434-441.

[96] B. Liu, C. Bai, D. Zhao, W.-L. Liu, M.-M. Ren, Q.-Z. Liu, Z.-Z. Yang, X.-Q. Wang, X.-L. Duan, Novel ferroferric oxide/polystyrene/silver core-shell magnetic nanocomposite microspheres as regenerable substrates for surface-enhanced Raman scattering, Appl. Surf. Sci., 364 (2016) 628-635.

M AN U

[97] L. Li, A. Zhao, D. Wang, H. Guo, H. Sun, Q. He, Fabrication of cube-like Fe3O4@SiO2@Ag nanocomposites with high SERS activity and their application in pesticide detection, J. Nanopart. Res., 18 (2016) 178.

[98] Z. Liu, Y. Wang, R. Deng, L. Yang, S. Yu, S. Xu, W. Xu, Fe3O4@Graphene Oxide@Ag Particles for Surface Magnet Solid-Phase Extraction Surface-Enhanced Raman Scattering (SMSPE-SERS): From Sample Pretreatment to Detection All-in-One, ACS Appl. Mat. Interfaces, 8 (2016) 14160-14168. [99] J. Shen, Y. Zhou, J. Huang, Y. Zhu, J. Zhu, X. Yang, W. Chen, Y. Yao, S. Qian, H. Jiang, C. Li,

TE D

In-situ SERS monitoring of reaction catalyzed by multifunctional Fe3O4@TiO2@Ag-Au microspheres, Appl. Catal., B, 205 (2017) 11-18.

[100] M. Yan, Y. Shen, G. Zhang, H. Bi, Multifunctional nanotube-like Fe3O4/PANI/CDs/Ag hybrids: An efficient SERS substrate and nanocatalyst, Mater. Sci. Eng., C, 58 (2016) 568-575. [101] J. Tang, H. Guo, M. Zhao, W. Liu, X. Chou, B. Zhang, C. Xue, W. Zhang, J. Liu, Ag

EP

nanoparticles cladded with parylene for high-stability microfluidic surface-enhanced Raman scattering (SERS) biochemical sensing, Sens. Actuators, B, 242 (2017) 1171-1176. [102] H.-X. Gu, L. Xue, Y.-F. Zhang, D.-W. Li, Y.-T. Long, Facile Fabrication of a Silver

AC C

Dendrite-Integrated Chip for Surface-Enhanced Raman Scattering, ACS Appl. Mat. Interfaces, 7 (2015) 2931-2936.

[103] C. Ma, Q. Gao, W. Hong, J. Fan, J. Fang, Real-Time Probing Nanopore-in-Nanogap Plasmonic Coupling Effect on Silver Supercrystals with Surface-Enhanced Raman Spectroscopy, Adv. Funct. Mater., 27 (2017) 1603233.

[104] P. Wang, L. Wu, Z. Lu, Q. Li, W. Yin, F. Ding, H. Han, Gecko-Inspired Nanotentacle Surface-Enhanced Raman Spectroscopy Substrate for Sampling and Reliable Detection of Pesticide Residues in Fruits and Vegetables, Anal. Chem., 89 (2017) 2424-2431. [105] H. Tang, G. Meng, Z. Li, C. Zhu, Z. Huang, Z. Wang, F. Li, Hexagonally arranged arrays of urchin-like Ag hemispheres decorated with Ag nanoparticles for surface-enhanced Raman scattering substrates, Nano Res., 8 (2015) 2261-2270. [106] A. Hakonen, F. Wang, P.O. Andersson, H. Wingfors, T. Rindzevicius, M.S. Schmidt, V.R. Soma, S. Xu, Y. Li, A. Boisen, H. Wu, Hand-Held Femtogram Detection of Hazardous Picric Acid with

ACCEPTED MANUSCRIPT Hydrophobic Ag Nanopillar SERS Substrates and Mechanism of Elasto-Capillarity, ACS Sens., 2 (2017) 198-202. [107] Y. Bai, L. Yan, J. Wang, L. Su, N. Chen, Z. Tan, Highly reproducible and uniform SERS substrates based on Ag nanoparticles with optimized size and gap, Photonics Nanostruc. Fundam. Appl., 23 (2017) 58-63. [108] Z. Zuo, K. Zhu, L. Ning, G. Cui, J. Qu, Y. Cheng, J. Wang, Y. Shi, D. Xu, Y. Xin, Highly sensitive surface enhanced Raman scattering substrates based on Ag decorated Si nanocone arrays and

RI PT

their application in trace dimethyl phthalate detection, Appl. Surf. Sci., 325 (2015) 45-51.

[109] L. Yang, W. Wang, H. Jiang, Q. Zhang, H. Shan, M. Zhang, K. Zhu, J. Lv, G. He, Z. Sun, Improved SERS performance of single-crystalline TiO2 nanosheet arrays with coexposed {001} and {101} facets decorated with Ag nanoparticles, Sens. Actuators, B, 242 (2017) 932-939.

[110] A. Wang, L. Jiang, X. Li, Q. Xie, B. Li, Z. Wang, K. Du, Y. Lu, Low-adhesive superhydrophobic molecular detection, J. Mater. Chem., B, 5 (2017) 777-784.

SC

surface-enhanced Raman spectroscopy substrate fabricated by femtosecond laser ablation for ultratrace [111] W. Xu, X. Zhu, Z. Chu, Z. Wang, Z. Xiao, Z. Huang, ScroBiculate sub-10 nm nanocavity arrays Sci., 399 (2017) 711-715.

M AN U

as effective sers substrate for the trace determination of 3,3',4,4'-Polychlorinated biphenyls, Appl. Surf. [112] Z. Zhu, M. Yu, Y. Jin, Surface-enhanced Raman Scattering Sensor Based on the Ag-Zn(OH)F Network, Chem. Lett., 45 (2016) 595-597.

[113] C. Song, B. Yang, Y. Zhu, Y. Yang, L. Wang, Ultrasensitive sliver nanorods array SERS sensor for mercury ions, Biosens. Bioelectron., 87 (2017) 59-65.

[114] A.S. Sarycheva, A.A. Semenova, E.Y. Parshina, N.A. Brazhe, A.Y. Polyakov, A.Y. Kozmenkova, A.V. Grigorieva, G.V. Maksimov, E.A. Goodilin, Ultrasonic-silver-rain preparation of SERS substrates,

TE D

Mater. Lett., 121 (2014) 66-69.

[115] C. Zhang, R. Hao, B. Zhao, Y. Fu, H. Zhang, S. Moeendarbari, C.S. Pickering, Y.-w. Hao, Y.-q. Liu, Graphene oxide-wrapped flower-like sliver particles for surface-enhanced Raman spectroscopy and their applications in polychlorinated biphenyls detection, Appl. Surf. Sci., 400 (2017) 49-56. [116] D.T. Cao, L.T.Q. Ngan, C.T. Anh, N.N. Hai, K.N. Minh, L.T. Thuy, L.V. Vu, Trace detection of

EP

herbicides by SERS technique, using SERS-active substrates fabricated from different silver nanostructures deposited on silicon, Adv. Nat. Sci.- Nanosci. Nanotech., 6 (2015) 1-6. [117] E.S. Babich, A.V. Redkov, I.V. Reduto, S.A. Scherbak, A.N. Kamenskii, A.A. Lipovskii, Raman

AC C

enhancement by individual silver hemispheroids, Appl. Surf. Sci., 397 (2017) 119-124. [118] G. Mettela, S. Siddhanta, C. Narayana, G.U. Kulkarni, Nanocrystalline Ag microflowers as a versatile SERS platform, Nanoscale, 6 (2014) 7480-7488. [119] H. Li, H. Dai, Y. Zhang, W. Tong, H. Gao, Q. An, Surface-Enhanced Raman Spectra Promoted by a Finger Press in an All-Solid-State Flexible Energy Conversion and Storage Film, Angew. Chem. Int. Ed., 56 (2017) 2649-2654.

[120] J. Bian, S. Shu, J. Li, C. Huang, Y.Y. Li, R.-Q. Zhang, Reproducible and recyclable SERS substrates: Flower-like Ag structures with concave surfaces formed by electrodeposition, Appl. Surf. Sci., 333 (2015) 126-133. [121] J. Du, H. Wang, H. Wang, Y. Chen, C. Guo, L. Gan, M. Du, Surface-enhanced Raman scattering of Ethyl carbamate adsorbed on Ag2O cluster: Enhancement mechanism, J. Mol. Struct., 1131 (2017) 212-217. [122]

L.

Alvarez-Fraga,

E.

Climent-Pascual,

M.

Aguilar-Pujol,

R.

Ramírez-Jiménez,

F.

ACCEPTED MANUSCRIPT Jiménez-Villacorta, C. Prieto, A.d. Andrés, Efficient Heterostructures for Combined Interference and Plasmon Resonance Raman Amplification, ACS Appl. Mat. Interfaces, 9 (ACS Applied Materials & Interfaces) 4119-4125. [123] L. B. He, Y. L. Wang, X. Xie, M. Han, F. Q. Song, B.J. Wang, W. L. Chen, H. X. Xud, L. T. Sun, Systematic investigation of the SERS efficiency and SERS hotspots in gas-phase deposited Ag nanoparticle assemblies, Phys. Chem. Chem. Phys., 19 (2017) 5091-5101. AgVO3 nanobelts, J. Alloys Compd., 677 (2016) 12-17.

RI PT

[124] L. Dong, G. Guan, X. Wei, X. Zhao, M. Xv, Creating SERS hot spots on length adjustable [125] M. Fan, Z. Zhang, J. Hu, F. Cheng, C. Wang, C. Tang, J. Lin, A.G. Brolo, H. Zhan, Ag decorated sandpaper as flexible SERS substrate for direct swabbing sampling, Mater. Lett., 133 (2014) 57-59.

[126] M. Xu, Y. Zhang, Hierarchical Ag mesostructures for single particle SERS substrate, Appl. Surf. Sci., 393 (2017) 197-203.

SC

[127] N. Duan, B. Chang, H. Zhang, Z. Wang, S. Wu, Salmonella typhimurium detection using a surface-enhanced Raman scattering-based aptasensor, Int. J. Food Microbiol., 218 (2016) 38-43. [128] Q. Chen, Y. Fu, W. Zhang, S. Ye, H. Zhang, F. Xie, L. Gong, Z. Wei, H. Jin, J. Chen, Highly substrate, Talanta, 165 (2017) 516-521.

M AN U

sensitive detection of glucose: A quantitative approach employing nanorods assembled plasmonic [129] R. Li, J. Yang, J. Han, J. Liu, M. Huang, Quantitative determination of melamine in milk using Ag nanoparticle monolayer film as SERS substrate, Physica E, 88 (2017) 164-168. [130] S. Kumar, P. Goel, J.P. Singh, Flexible and robust SERS active substrates for conformal rapid detection of pesticide residues from fruits, Sens. Actuators, B, 241 (2017) 577-583. [131] S. Ren, L. Dong, X. Zhang, T. Lei, F. Ehrenhauser, K. Song, M. Li, X. Sun, Q. Wu, Electrospun Nanofibers Made of Silver Nanoparticles, Cellulose Nanocrystals, and Polyacrylonitrile as Substrates

TE D

for Surface-Enhanced Raman Scattering, Mater., 10 (2017) 68.

[132] S. Shin, J. Lee, S. Lee, H. Kim, J. Seo, D. Kim, J. Hong, S. Lee, T. Lee, A Droplet-Based High-Throughput SERS Platform on a Droplet-Guiding-Track-Engraved Superhydrophobic Substrate, Small, 13 (2017) 1602865.

[133] S. Wijesuriya, K. Burugapalli, R. Mackay, G. C. Ajaezi, W. Balachandran, Chemically

EP

Roughened Solid Silver: A Simple, Robust and Broadband SERS Substrate, Sens., 16 (2016) 1742. [134] S. G. Harroun, Y. Zhang, T.-H. Chen, C.-R. Ku, H.-T. Chang, Biomarkers of cigarette smoking and DNA methylating agents: Raman, SERS and DFT study of 3-methyladenine and 7-methyladenine,

AC C

Spectrochim. Acta, Part A, 176 (2017) 1-7. [135] X. Meshik, X. Wu, Y. Zhao, J. Schwartz, M. Dutta, M. Stroscio, SERS spectrum of the peptide thymosin-beta 4 obtained with Ag nanorod substrate, J. Raman Spectrosc., 46 (2015) 194-196. [136] Y. Kang, H. Zhang, L. Zhang, T. Wu, L. Sun, D. Jiang, Y. Du, In situ preparation of Ag nanoparticles by laser photoreduction as SERS substrate for determination of Hg2+, J. Raman Spectrosc., 48 (2017) 399-404. [137] Y. Ke, G. Meng, Z. Huang, N. Zhou, Electrosprayed large-area membranes of Ag-nanocubes embedded in cellulose acetate microspheres as homogeneous SERS substrates, J. Mater. Chem., C, 5 (2017) 1402-1408. [138] Z. Zhai, F. Zhang, X. Chen, J. Zhong, G. Liu, Y. Tian, Q. Huang, Uptake of silver nanoparticles by DHA-treated cancer cells examined by surface-enhanced Raman spectroscopy in a microfluidic chip, Lab Chip, 17 (2017) 1306-1313. [139] Z. Zhang, W. Yu, J. Wang, D. Luo, X. Qiao, X. Qin, T. Wang, Ultrasensitive Surface-Enhanced

ACCEPTED MANUSCRIPT Raman Scattering Sensor of Gaseous Aldehydes as Biomarkers of Lung Cancer on Dendritic Ag Nanocrystals, Anal. Chem., 89 (2017) 1416-1420. [140] L. Mikac, M. Ivanda, M. Gotic, A. Maksimovic, S. Trusso, C. D'Andrea, A. Foti, A. Irrera, B. Fazio, P.G. Gucciardi, Metal Nanoparticles Deposited on Porous Silicon Templates as Novel Substrates for SERS, Croat. Chem. Acta, 88 (2015) 437-444. [141] Y. Li, Y. Ye, Y. Fan, J. Zhou, L. Jia, B. Tang, X. Wang, Silver Nanoprism-Loaded Eggshell Membrane: A Facile Platform for In Situ SERS Monitoring of Catalytic Reactions, Cryst., 7 (2017) 45.

RI PT

[142] I. Šloufová , B. Vlčková, P. Mojzeš, I. Matulková, I. Císařová, M. Procházka, J. Vohlídal, Probing the Formation, Structure, and Reactivity of Zn(II), Ag(I), and Fe(II) Complexes with 2,2':6',2"-Terpyridine on Ag Nanoparticles Surfaces by Time Evolution of SERS Spectra, Factor

AC C

EP

TE D

M AN U

SC

Analysis, and DFT Calculations, J. Phys. Chem. C, 122(2018) 6066-6077.

ACCEPTED MANUSCRIPT

Highlights

AC C

EP

TE D

M AN U

SC

RI PT

•Recent progress on the silver-based SERS enhancement substrates was summarized. •The preparations and applications of the SERS substrates were discussed. •Significant supports and structures of the SERS substrates were discussed variously. •The future development trends of silver-based SERS substrates were discussed.