Surface-enhanced Raman Scattering Response Research Articles

Strongly coupled plasmonic metal nanoparticles with reversible pH-responsiveness and highly reproducible SERS in solution.

We report a facile method to prepare polymer-grafted plasmonic metal nanoparticles (NPs) that exhibit pH-responsive surface-enhanced Raman scattering (SERS). The concept is based on the use of pH-responsive polymers, such as poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH), as multidentate ligands to wrap around the surface of NPs instead of forming polymer brushes. Upon changing the solvent quality, the grafted pH-responsive polymers would drive reversible aggregation of NPs, leading to a decreased interparticle distance. This creates numerous hot spots, resulting in a secondary enhancement of SERS as compared to the SERS from discrete NPs. For negatively charged PAA-grafted NPs, the SERS response at pH 2.5 showed a secondary enhancement of up to 104-fold as compared to the response for discrete NPs at pH 12. Similarly, positively charged PAH-grafted AuNPs showed an opposite response to pH. We demonstrated that enhanced SERS with thiol-containing and charged molecular probes was indeed from the pH-driven solubility change of polymer ligands. Our method is different from the conventional SERS sensors in the solid state. With pH-responsive polymer-grafted NPs, SERS can be performed in solution with high reproducibility and sensitivity but without the need for sample pre-concentration. These findings could pave the way for innovative designs of polymer ligands for metal NPs where polymer ligands do not compromise interparticle plasmon coupling.

A highly selective SERS chip for rapid detection of copper ions in aquatic system

Abnormal amount of Cu2+ intake from foods and environment would interfere with cellular homeostasis and even trigger oxidative damage, cardiovascular disorders, severe neurodegenerative disorders, and cancer. In this work, a rapid surface enhanced Raman scattering (SERS) assay for picomolar copper ions (Cu2+) is developed based on the click reaction of Cu+-catalyzed alkyne azide cycloaddition (CuAAC). ITO supported 1,4-diethynylbenzene (DEB) modified silver-coated gold nanoparticles is prepared as a two-dimension SERS platform (designated as ITO-Ag-co-Au-DEB), and the other terminal alkyne (-CC-) of DEB exposes to provide the CuAAC reactive site. The generated click reaction product (1-benzyl-4-(4-ethynylphenyl)− 1 H-1,2,3-triazole) contributes to “turn on” SERS response, showing high detection sensitivity and selectivity. Furthermore, density functional theory (DFT) simulation is used to deepen understanding of sensing mechanism. Under optimal conditions, a linear range of concentrations from 6.35 ng/L to 6.35 mg/L and a detection limit of 33.45 pg/L for Cu2+ can be achieved. The SERS method based on the ITO-Ag-co-Au-DEB-click reaction is free from interference from co-existing metal ions in the aquatic system sample. Such a SERS strategy paves a novel route for continuous assessment of water quality safety in onshore and offshore water treatment systems.

Wet Chemical Synthesis and Characterization of Au Coatings on Meso- and Macroporous Si for Molecular Analysis by SERS Spectroscopy

Porous silicon (PS) is a promising material for nanostructure fabrication providing a precise control over its size, shape, and spatial distribution. This makes it an excellent candidate for constructing highly sensitive, reproducible, and low-cost platforms for surface enhanced Raman scattering (SERS) spectroscopy. In this work, we connect the PS structural parameters with the morphology of the gold nanostructures fabricated on its surface, placing the emphasis on the SERS response. Two different types of PS are considered here, namely meso- and macro-PS. The former is prepared by Si electrochemical etching, applying three different current densities: 100 mA cm−2, 60 mA cm−2, and 30 mA cm−2, while the technological parameters for the latter are selected to mimic metal nanovoids’ (Me NVs) configuration. The gold-coated PS surfaces are produced via an electroless chemical deposition method for different time periods. By performing comprehensive structural, morphological, and optical characterization, we show the importance of the size and density of the PS pore openings, which govern the Au growth kinetics. The results presented in this work assure a simple yet flexible approach for the fabrication of large-area plasmonic gold nanostructures, which are not only suitable for advanced SERS spectroscopy studies but can also serve for a wider range of plasmonic applications.

One-step method to prepare coccinellaseptempunctate-like silver nanoparticles for high sensitivity SERS detection

The surface morphology of metal particles can be adjusted by the annealing process to enhance the activity of Raman substrate and achieve an ultra-low concentration detection limitation. In this study, a surface-enhanced Raman scattering (SERS) substrate of coccinellaseptempunctate-like silver nanospheres coated with a silver nanoisland structure (Ag NI@Ag NSs) was prepared using a simple annealing process. Numerous silver nanospheres were dispersed on the surface of the silver nanoislands, which exhibited a single crystal plane (111) orientation. The SERS substrate had an enhancement factor of 108 for Rhodamine B (Rh B) and was highly sensitive to phosphoethanolamine (PETA). The SERS response toward PETA showed excellent correlation during the range of 5 × 10−7 - 1 × 10−5 mol/L with the detection limitation as low as 5 × 10−7 mol/L, and the correlation coefficient is 0.9918. The simulated high-pressure test showed that the SERS response could be still observed at 1100 m sub ocean pressure even with a PETA concentration of 1 mM. The test results of selectivity, reproducibility, and accuracy indicated that the Ag NI@Ag NS sensor possessed potential applications in the deep-sea analytical and other related fields.

MnO2 coated Au nanoparticles advance SERS detection of cellular glutathione

Glutathione, referred to as GSH, abnormal physiologic level of GSH is an indication to some neurodegenerative diseases and cancers. A measurement of cellular GSH calls for rapid, sensitive, and selective methods. In this work, we rationally design and prepare Au@MnO2 core-shell composite nanoparticles combining with tetramethylbenzidine (TMB) molecules to determine intracellular GSH by Surface enhanced Raman scattering (SERS) technique. MnO2 plays multifunctional roles in the method, including the participation in catalyzing TMB to molecules form dimer charge-transfer complex (CTC) which own a great SERS signal reporter. With the addition of GSH, the MnO2 will be dissolving detaching CTC molecules from the surface of Au@MnO2 and resulting in a signal-off off SERS response and indirect and sensitive detection of GSH could be realized. The limit of detection of GSH by SERS method is as low as 0.1 μmol/L and a good linear relationship of GSH is found in the range from 0.5 to 30 μmol/L. Au@MnO2-SERS assay is successfully applied to detect cellular GSH, which is validated by using Enzyme-linked-immunoassay-based Kit. The Au@MnO2-SERS protocol has promising potential for clinical application.

Effect of glycine on aggregation of citrate-functionalised gold nanoparticles and SERS measurements

Surface enhanced Raman Scattering (SERS) can be used as a novel way of probing local liquid composition and structure at solid-liquid interfaces. This is particularly important for understanding the mechanism of heterogeneous nucleation from solution, where solutes are present at relatively high concentrations. To obtain information about the solution composition and structure near a gold nanoparticle (AuNP) surface, which facilitates SERS, it is thus necessary to understand the role of the analyte in AuNP aggregation, and its effect on the SERS signal and the Raman signal from the bulk. We have used dynamic light scattering and UV-Vis spectroscopy to investigate how glycine influences the aggregation of citrate-functionalised gold nanoparticles (AuNPs), and thus the SERS response, in glycine aqueous solutions. At pH 4 the AuNP suspensions in aqueous solutions (without glycine) did not aggregate due to the electrostatic stabilisation by negatively charged citrate functional groups. However, the addition of glycine promoted aggregation of the AuNPs, concomitantly increasing the strength of the SERS signal. Under these conditions glycine is zwitterionic, and its effect on the colloidal stability of AuNPs is most likely due to its association with citrate, affecting its charge state, resulting in reduction of the electrostatic stabilisation of the AuNPs. Using SERS as a solid-liquid interface probe provides a window into an interplay of interfacial and colloidal phenomena in the AuNP suspensions.

DNA detection by SERS: hybridisation parameters and the potential for asymmetric PCR.

The use of surface enhanced Raman scattering (SERS) for the detection of DNA has significant potential in terms of sensitivity, multiplex target detection and robust signal detection from nanoparticles. Current methods are usually performed with short chain DNA fragments or require additional separation steps for detection of longer chain fragments. We present an integrated method for the rapid and sensitive detection of extended (≥100-base) nucleic acids with reduced preparation and sample separation steps. Key to this is the DNA sequence-specific assembly of silver nanoparticles labelled with a Raman tag to provide an enhanced signal from the tag and hence molecular recognition of the target DNA. DNA probe orientation and hybridisation procedures are critical for the success of this assay. Effective detection of extended nucleic acids was achieved with head-to-head probes and by adding polyethylene glycol 10 000 (PEG 10 000) to the hybridisation buffer. This gave a 34-fold discriminatory enhancement factor when applied to a synthetic target. A structured approach toward maximising hybridisation procedures and SERS response is described, followed by an initial demonstration of SERS detection of single-stranded DNA target amplified by asymmetric PCR which was used without further separation. This has implications for future developments in using SERS for DNA detection due to the new-found ability to integrate SERS with asymmetric PCR.

Periodic ZnO-Elevated Gold Dimer Nanostructures for Surface-Enhanced Raman Scattering Applications

Electron beam lithography-defined periodic ZnO-elevated gold dimer nanostructures for surface-enhanced Raman spectroscopy with strong electromagnetic field enhancements were fabricated in the present work. The ZnO nanorods (NRs) were grown on the patterned substrate using a hydrothermal process, and Au dimers were deposited on the top surface of ZnO NRs, forming suspended gold dimers and providing plasmonic hot-spots with nanocavity effect. Effects of the dimer radius, gap size, and ZnO NR height on the dark-field scattering spectra and surface-enhanced Raman scattering (SERS) were investigated experimentally and theoretically. The SERS response was enhanced with increasing dimer radius and decreasing gap size. The SERS enhancement factor (EF) due to the localized surface plasmon resonance was calculated from simulation results. The calculated EF as a function of ZnO NR height showed the periodic trend of electric field intensity with the periodicity of about half of the exciting laser wavelength, and was...

Gold nanoparticles/glycine derivatives/graphene quantum dots composite with tunable fluorescence and surface enhanced Raman scattering signals for cellular imaging

Controllable assembly of the hybrids composed of various types of nanoscale objects provides new opportunities for material fabrication. Herein, the tunable bi-functionalities of fluorescence and surface enhanced Raman scattering (SERS) signals were collected by the assembled composites of gold nanoparticles (AuNPs)/glycine derivatives (Gn, n=0, 3, 4, 5, 6 and 9)/graphene quantum dots (GQDs). The composition and structure of the AuNPs/Gn/GQDs composites were characterized by Fourier-transform infrared (FT-IR) spectroscopy and high resolution transmission electron microscope (HRTEM). Results indicated that the fluorescence and SERS response could be tuned effectively by changing the chain length of Gn. Also, the AuNPs/Gn/GQDs composites could be used in a wide pH range and exhibited good stability at room and physiological temperatures. Moreover, the AuNPs/Gn/GQDs composites displayed low cytotoxicity in A549 cells, and the cell viability was found to be above 90% at concentrations ranging from 6.42 to 200μg/mL, which made AuNPs/Gn/GQDs composites very attractive for biological imaging applications in vivo.

Identification of Al13 on the Colloid Surface Using Surface-Enhanced Raman Spectroscopy.

Al13 is the most active polymeric Al species responsible for coagulation at the solid-liquid interface, whereas the detection techniques for Al13 at the interface are currently limited. In this study, for the first time, the identification of Al13 on the silicon dioxide-based colloid surface was realized by using surface-enhanced Raman scattering (SERS), which is an ideal surface method sensitive for single-molecule detection. The high purity Al13 salts were prepared by an electrolysis procedure followed by precipitation or metathesis. Al13-Cln was determined to be feasible for the Raman detection as it exhibited more noticeable signals in comparison to Al13-(SO4)p and Al13-(NO3)m. The peak of Al13-Cln at 635 cm-1 could be the major characteristic peak of Al13, and the other two peaks at 300 and 987 cm-1 could be accessorial evidence for the identification. Further, the identification of Al13 adsorbed on the surface of Ag and gold-core/silica-shell colloids was confirmed by the SERS response at the above three wavenumbers with a higher signal-to-noise ratio than the normal Raman scattering. According to the least-squares fitting computed Raman spectra, each of the characteristic peaks was associated with specific vibrational modes.

A close-packed 3D plasmonic superlattice of truncated octahedral gold nanoframes.

We report the surface-enhanced Raman scattering (SERS) enhancement of three-dimensional (3D) close-packed plasmonic superlattices of truncated octahedral gold nanostructures. Experimentally, we resolved two different types of hot spots, one originates from the face-to-face contacts and the other is from the edge-to-edge contacts among the 3D close-packed plasmonic superlattice of gold nanostructures. The high degree of homogeneity of truncated octahedral Au@Pt nanoparticles (TOh Au@Pt NPs) and truncated octahedral Pt@Au nanoframes (TOh Pt@Au NFs) allowed them to self-assemble into remarkable 3D close-packed plasmonic superlattices. The morphological evolution and the corresponding optical behavior of TOh Pt@Au NFs were systematically monitored during each synthetic process. The measured SERS enhancement on the hot spots from the edge-to-edge contacts of TOh Pt@Au NFs was five times greater than the SERS response from the analogous face-to-face contacts of TOh Au@Pt NPs under the same given experimental conditions. The hollow interior and well-defined structural morphology of TOh Pt@Au NFs will allow researchers to design highly programmable 3D plasmonic superlattices for efficient SERS enhancement.

Reassessing SERS enhancement factors: using thermodynamics to drive substrate design.

Over the past 40 years fundamental and application research into Surface-Enhanced Raman Scattering (SERS) has been explored by academia, industry, and government laboratories. To date however, SERS has achieved little commercial success as an analytical technique. Researchers are tackling a variety of paths to help break through the commercial barrier by addressing the reproducibility in both the SERS substrates and SERS signals as well as continuing to explore the underlying mechanisms. To this end, investigators use a variety of methodologies, typically studying strongly binding analytes such as aromatic thiols and azarenes, and report SERS enhancement factor calculations. However a drawback of the traditional SERS enhancement factor calculation is that it does not yield enough information to understand substrate reproducibility, application potential with another analyte, or the driving factors behind the molecule-metal interaction. Our work at the US Army Edgewood Chemical Biological Center has focused on these questions and we have shown that thermodynamic principles play a key role in the SERS response and are an essential factor in future designs of substrates and applications. This work will discuss the advantages and disadvantages of various experimental techniques used to report SERS enhancement with planar SERS substrates and present our alternative SERS enhancement value. We will report on three types of analysis scenarios that all yield different information concerning the effectiveness of the SERS substrate, practical application of the substrate, and finally the thermodynamic properties of the substrate. We believe that through this work a greater understanding for designing substrates will be achieved, one that is based on both thermodynamic and plasmonic properties as opposed to just plasmonic properties. This new understanding and potential change in substrate design will enable more applications for SERS based methodologies including targeting molecules that are traditionally not easily detected with SERS due to the perceived weak molecule-metal interaction of substrates.

Carbon-Dot/Silver-Nanoparticle Flexible SERS-Active Films.

Development of effective platforms for surface enhanced Raman scattering (SERS) sensing has mostly focused on fabrication of colloidal metal surfaces and tuning of their surface morphologies, designed to create "hot spots" in which plasmonic fields yield enhanced SERS signals. We fabricated distinctive SERS-active flexible films comprising polydimethylsiloxane (PDMS) embedding carbon dots (C-dots) and coated with silver nano-particles (Ag NPs). We show that the polymer-associated Ag NPs and C-dots intimately affected the physical properties of each other. In particular, the C-dot-Ag-NP-polymer films exhibited SERS properties upon deposition of versatile targets, both conventional SERS-active dyes as well as bacterial samples. We show that the SERS response was correlated to the formation C-dots within the polymer film and the physical proximity between the C-dots and Ag NPs, indicating that coupling between the plasmonic fields of the Ag NPs and C-dots' excitons constituted a prominent factor in the SERS properties.

On-Fly Femtosecond-Laser Fabrication of Self-Organized Plasmonic Nanotextures for Chemo- and Biosensing Applications.

Surface-enhanced Raman scattering (SERS) and surface-enhanced photoluminescence (SEPL) are emerging as versatile widespread methods for biological, chemical, and physical characterization in close proximity of nanostructured surfaces of plasmonic materials. Meanwhile, single-step, facile, cheap, and green technologies for large-scale fabrication of efficient SERS or SEPL substrates, routinely demonstrating both broad plasmonic response and high enhancement characteristics, are still missing. In this research, single-pulse spallative micron-size craters in a thick Ag film with their internal nanotexture in the form of nanosized tips are for the first time shown to demonstrate strong polarization-dependent enhancement of SEPL and SERS responses from a nanometer-thick covering Rhodamine 6G layer with average enhancement factors of 40 and 2 × 10(6), respectively. Additionally, the first detailed experimental study is reported for physical processes, underlying the formation mechanisms of ablative nanotextures on such "thick" metal films. Such mechanisms demonstrate a complex "hybrid" fluence-dependent ablation character-appearance of spallative craters, typical for bulk material, at low fluences and formation of upright standing nanotips (frozen nanojets), usually associated with thin-film ablation, in the crater centers at higher fluences. Moreover, special emphasis was made on the possibility to reshape the nanotopography of such spallative craters through multipulse laser-induced merging of their small nanotips into larger ones. The presented approach holds promise to be one of the cheapest and easiest-to-implement ways to mass-fabricate various efficient spallation-nanotextured single-element plasmonic substrates for routine chemo- and biosensing, using MHz-repetition-rate femtosecond fiber laser sources with multiplexed laser-beams.

Surface Morphology of a Gold Core Controls the Formation of Hollow or Bridged Nanogaps in Plasmonic Nanomatryoshkas and Their SERS Responses

Surface-enhanced Raman scattering (SERS) probes with a nanometer-sized interior gap between the Au core and shell, also called nanomatryoshkas (NMs), have attracted great interest in SERS-based bioimaging and biosensing. Recently, seed-mediated growth has been shown to be effective for NM synthesis. We found that the structure of nanogaps inside Au NMs depends strongly on the core surface morphology. Specifically, when the initially citrate-stabilized 15 and 35 nm smooth Au cores were further functionalized with 1,4-benzenedithiol (BDT) in the presence of cetyltrimethylammonium chloride (CTAC), the Au shell growth led to the formation of a subnanometer hollow interior gap containing BDT molecules. In contrast, the use of 23 and 35 nm faceted polygonal CTAC-stabilized Au cores for Au shell growth resulted in NMs with small bridged gaps. The formation of incomplete outer shells with one or two nanometer-sized hollow gaps was also observed for 23 nm polygonal cores but not for 35 nm ones. The experimental SERS response from BDT molecules in bridged-gap NMs was an order of magnitude higher than that for hollow-gap NMs. This finding is in agreement with the finite-difference time-domain (FDTD) simulations predicting stronger electromagnetic fields inside nanobridged gaps, as compared to hollow-gap NMs. The major SERS peaks from BDT inside NMs of both types (two sizes, four samples) was an order of magnitude higher than the near-field SERS peaks recorded for the corresponding 15CIT, 23CTAC, 35CIT, and 35CTAC cores alone after surface functionalization with BDT molecules. This observation is explained by a simple dipole approximation (DA) theory, which was developed to estimate the structure- and wavelength-dependent electromagnetic SERS enhancement in the hollow-gap NMs with good accuracy, as confirmed by comparison with exact multilayered Mie (ML Mie) calculations. With a double increase in the core size, the NM SERS response also increased, and the ratio between the major peak intensities of the larger and smaller NMs was about 2. Finally, the calculated SERS spectra of the hollow-gap NMs agree with the data reported for 532, 633, and 785 nm laser excitations. The physical insights acquired from this study open the way for rational design and efficient optimization of new SERS platforms based on electromagnetic field enhancement in subnanometer gaps within plasmonic nanostructures.

SERS detection and DFT calculation of 2-naphthalene thiol adsorbed on Ag and Au probes

Two different surface enhanced Raman scattering (SERS) sensors are described, tested and compared against the detection of 2-naphthalenethiol (2NPT, a volatile compound) in both solution state as well as vapor phase. The first sensor is based on an optical fiber properly modeled to induce the adhesion of colloidal Ag nanoparticles on its surface. Excitation and detection of the Raman signal is performed through the optical fiber that can be used as in situ probe for the detection of molecules adsorbed on the SERS sensitized surface. The second SERS sensor is based on nanostructured substrates consisting of Au nanoparticles produced by pulsed laser deposition in presence of a controlled Ar atmosphere. Details at the nanometer scale were observed by SEM and TEM imaging to understand the size and structure of the islands formed as a function of deposition parameters that were selected in order to maximize their SERS response. The sensitivity of the substrates to volatile species was tested by letting evaporate controlled drops of a methanol solution of 2NPT in a chamber of known volume, where the substrate was placed. After complete evaporation of the drops, this provided an in-situ environment suitable for vapor phase measurements at known concentration. SERS spectra were collected after exposing the substrates to the environment within the chamber (vapor phase measurements) or dipping them in a solution for condensed state measurements. The complete absence of the SH stretching peak in the SERS spectra proves the covalent bonding of 2NPT to the metal substrates via the sulfur atom. DFT calculations, including metal-sulfur interaction, provide a good description of the observed SERS spectra. The reported data allow concluding that our SERS substrates are suitable for detection of volatile compounds.

Efficient SERS and electrocatalytic activities of micro/nano-structured shower-nozzle-like volcanic ash

Volcanic ashes (VA) are often referenced as examples for natural particles, yet the application in sensors is only rarely documented. Here, a unique kind of micro/nano-structured shower-nozzle-like VA was explored. The natural VA showed an ordered porous structure with an average diameter of ca. 20μm, and it was constituted by regular ca. 200nm macroporous and ca. 4nm mesoporous. The surface enhanced Raman scattering (SERS) activity of the VA was investigated by using crystal violet (CV) as a probe. It was found that shower-nozzle-like VA itself possessed a certain SERS response. Moreover, the VA/Ag nanoparticles hybrid exhibited a strong SERS enhancement effect with an enhancement factor of 8×108. Meanwhile, cyclic voltammetry was applied to investigate the electrochemistry performance of the VA-dopamine-glassy carbon (VA-DA-GCE) modified electrode. It was found that the VA possessed high electrocatalytic activity to octylphenol. This good analytical performance makes micro/nano-structured shower-nozzle-like VA as promising SERS or electrochemical sensor for the detection of trace organic pollutants.

Preparation of surface-enhanced Raman scattering(SERS)-active optical fiber sensor by laser-induced Ag deposition and its application in bioidentification of biotin/avidin

A surface-enhanced Raman scattering(SERS) optical fiber sensor was prepared by the laser-induced deposition of Ag nanoparticle membrane on a silica optical fiber tip, which was applied to the real time SERS spectral monitoring on the biorecognition of biotin/avidin. The bioidentification of biotin/avidin was carried out through a indirect method, in which the bioidentification is based on the SERS response signal of a labeled dye(Atto610) after its fluorescence has been quenched totally by the deposited Ag nanoparticle membrane. By SERS monitoring the bioidentification process of biotin/avidin, it has been found that this recognition process is finished in 40 min. The lowest detection concentration of biotin is 1.0×10−7 mg/mL. This research is promising in the application of immunoassays on line and in vivo.

Localized surface plasmon resonance and surface enhanced Raman scattering responses of Au@Ag core-shell nanorods with different thickness of Ag shell.

The properties of the localized surface plasmon resonance (LSPR) and the surface enhanced Raman scattering (SERS) of the core-shell bimetallic nanostructures, that is the monodisperse Au@Ag core-shell nanorods with different thickness of Ag shell, are theoretically and experimental researched. The UV-vis-NIR absorption spectra of the Au@Ag core-shell nanorods are measured and displayed their blue-shifts of the longitudinal plasmon resonance peaks with increasing of Ag concentrations in the colloidal solution. And the absorption spectra of the Au@Ag core-shell nanorods are simulated by the Finite Element Method (FEM), which are in agreement with the experimental measurements and reveal their LSPR mechanism as the varying structures. In addition, Rhodamine 6G, as a Raman reporter molecule, is used to investigate SERS of gold nanorods and Au@Ag core-shell nanorods. It is found that Au@Ag core-shell nanorods have better SERS responses, comparing with those of Au nanorods, and their SERS intensities are increased with the increases of the Ag shell thickness, which demonstrate that the chemisorptive bond effect and the morphology of the nanoparticle play key roles to the SERS signals. It is significant to design the biosensor based on the properties of Au@Ag core-shell nanorods.

Multiscale electromagnetic SERS enhancement on self‐assembled micropatterned gold nanoparticle films

In this work, we demonstrate a cascaded, multiplicative electromagnetic enhancement effect in surface‐enhanced Raman scattering (SERS) on periodically micropatterned films made of colloidal gold nanoparticles, prepared by a self‐assembly approach, without implying lithography procedures. The multiplicative enhancement effect is obtained by combining surface plasmon near‐field enhancement due to nanoscale features with far‐field photonic coupling by periodic microscale features. The effect is observed for both internal Raman reporters (molecules attached to the Au colloids before their assembly) and external Raman probes (molecules adsorbed on the samples after film assembly). The ability of the patterned films for far‐field light coupling is supported by reflectivity spectra, which present minima/maxima in the visible spectral range. Finite‐difference time‐domain computer simulations of the electric field distribution also support this interpretation. The fabricated dual‐scale SERS substrates exhibit a good spot‐to‐spot reproducibility and time stability, as proved by the SERS response over a time scale longer than 1 month. The experimental demonstration of this cascaded electromagnetic enhancement effect contributes to a better understanding of SERS and can affect future design of SERS substrates. Moreover, such dual‐scale colloidal films prepared by convective self‐assembly can be of general interest for the broader field of nanoparticle‐based devices. Copyright © 2014 John Wiley & Sons, Ltd.