SERS

The project for the scientific analysis of Kaitag textiles – the
results of which are reported here with special focus on the
identification of the dyes – was promoted by the MATAM
association (Museum of Ancient Textile Art Milan) and carried
out by the Universities of Bergamo and Milan as the logical
continuance and updating of the important analytical project
conducted by Harald Bohmer and Recep Karadag almost
two decades ago1.
On the one hand, our project was inspired by the need to
determine, for a given artefact, the execution technique and
the materials used, not only for the sake of knowledge but
also for practical conservation purposes. At the same time,
from a methodological point of view, the intent was to use not
only the most frequently-applied analytical procedures, but
also non-invasive techniques suitable for in-situ analysis, and
such as to safeguard the integrity of the objects examined.
The most representative tints were selected for analysis in
order to obtain a wider knowledge of the dyes, and their
combinations, used over the centuries in Daghestan. In addition,
special attention was paid to those tints for which the
identification of the dyes is notoriously more difficult (especially
yellow) and to cases of suspected alteration of the dye
or evident damage to the thread.
A total of 23 Kaitag textiles were examined, dating from the
17th to the 18th century. A preliminary imaging campaign
was performed on all of them using infra-red (IR) reflectography
and ultraviolet (UV) fluorescence, in order to better understand
the technique used and to highlight any later integrations
of the textiles (which, however, were detected in only
a few cases). In addition, the presence of a black-ink underdrawing
was observed using reflectography. Thereafter, the
dyes were analysed using non-invasive techniques such as
visible reflectance spectroscopy (vis-RS) on 250 measurement
points, and Fourier-transform infrared spectroscopy
(FTIR) on 30 measurement points. Colorimetric data were
acquired on each of the points studied during the vis-RS
measurements. Also, energy dispersive X-ray fluorescence
(ED-XRF) was performed on two of the fabrics using a portable
handheld spectrometer. Extracts from 65 tiny portions of
dyed thread were then examined by high-performance liquid
chromatography (HPLC) and surface-enhanced Raman
spectroscopy (SERS); other threads were analysed without
extraction by energy-dispersive X-ray analysis coupled with
scanning electron microscopy (SEM-EDS), attenuated total
reflection (ATR) FTIR spectroscopy and Fourier-transform
Raman (FT-Raman) spectroscopy.
The dyes identified, which were all of natural origin, include:
madder for red, indigo for dark and light blue, weld for yellow
(the substance or substances used to obtain the more intense
yellow hues, however, remains unidentified), weld (or sometimes
a different yellow dye) and indigo for green, tannins
mordanted with iron for dark brown, again tannins, sometimes
with the addition of indigo, for black. A high content of
iron is often accompanied by corrosion of the dyed thread.
Finally, the ink used for the underlying drawing was carefully
examined and identified as carbon ink.

This article reviews the most recent advances in the development of flexible substrates used as surface-enhanced Raman scattering (SERS) platforms for detecting several hazardous materials (e.g., explosives, pesticides, drugs, and dyes). Different flexible platforms such as papers/filter papers, fabrics, polymer nanofibers, and cellulose fibers have been investigated over the last few years and their SERS efficacies have been evaluated. We start with an introduction of the importance of hazardous materials trace detection followed by a summary of different SERS methodologies with particular attention on flexible substrates and their advantages over the nanostructures and nanoparticle-based solid/hybrid substrates. The potential of flexible SERS substrates, in conjunction with a simple portable Raman spectrometer, is the power to enable practical/on-field/point of interest applications primarily because of their low-cost and easy sampling.

Hybrid silver−gold targets were achieved by effortless mixing
of pure silver (Ag) and gold (Au) metals at different ratios (Ag0.65Au0.35,
Ag0.5Au0.5, and Ag0.35Au0.65) and embracing a manual melting process. The
obtained targets were ablated by ultrafast (∼40 fs) laser pulses in acetone
ensuing the fabrication of Ag−Au bimetallic nanoparticles (NPs) and
nanostructures (NSs) in a single experiment. UV−visible extinction spectra
of Ag−Au colloids demonstrated the tuning of localized surface plasmon
resonance (LSPR) in the spectral range of 406−524 nm. The morphologies of
NSs were investigated by the field emission scanning electron microscopy
(FESEM) technique. Ag−Au NPs and NSs were utilized as surface enhanced
Raman scattering (SERS) platforms to detect secondary explosive molecules
such as 1,1-diamino-2,2-dinitroethene (FOX-7, 5 μM concentration) and 1-
nitro pyrazole (1NPZ, 20 nM concentration). Our experimental observations
clearly demonstrated that the increment in gold percentage reduced the surface activity of Ag−Au NPs/NSs. The estimated
enhancement factors (EFs) from the SERS data were typically >108. Our detailed investigations revealed that the NPs and NSs of
Ag0.65Au0.35 exhibited significant EFs compared to other ratios and pure metals of Ag and Au.

It is important to design and fabricate nanoporous metals (NPMs) with optimized microstructures for specific applications. In this contribution, nanoporous coppers (NPCs) with controllable thicknesses and pore sizes were fabricated via the combination of a co-sputtering of Cu/Ti with a subsequent dealloying process. The effect of dealloying time on porous morphology and the corresponding surface enhanced Raman scattering (SERS) behaviors were systematically investigated. Transmission electron microscopy (TEM) identified the presences of the gaps formed between ligaments and also the nanobumps on the nanoparticle-aggregated ligament surface, which were likely to contribute as the " hot spots " for electromagnetic enhancement. The optimal NPC film exhibited excellent SERS performance towards Rhodamine 6G (R6G) with a low limiting detection (10 −9 M), along with good uniformity and reproducibility. The calculated enhancement factor of ca. 4.71 × 10 7 was over Au substrates and comparable to Ag systems, promising the proposed NPC as a cheap candidate for high-performance SERS substrate.

In this paper we present a new protocol for the synthesis of Star-Like Gold Nanoparticles (SGNs) by a
simple one-step, room temperature procedure not involving the use of seeds or surfactants, that can be
performed in seconds in any laboratory without the need of special technologies. These particles
exhibited excellent properties for Surface Enhanced Raman Spectroscopy (SERS) and, when compared
with spherical nanoparticles with similar size and concentration, showed enhancing factors from 10 to
50 times higher depending on the dye and on the wavelength employed. SGNs could be used directly in
suspension as single, non-aggregating particles and were shown to be active in a remarkably broad range
of the light spectrum from green to near infrared. Moreover, SGNs were adsorbed on the surface of a
silicon slide to prepare SERS active solid substrate. Despite the fact that the surface of the solid substrate
was not perfectly homogeneous, the signals recorded from different positions acquired through DuoScan
averaging mode show excellent reproducibility, demonstrating how this simple and cheap protocol can be applied in order to generate reliable and homogeneous SERS substrates.

Raman and infrared (IR) spectroscopy are powerful analytical techniques, but have intrinsically low detection sensitivity. There have been three major steps (i) to advance the optical system of the light excitation, collection, and detection since 1920s, (ii) to utilize nanostructure-based surface-enhanced Raman scattering (SERS) and surfaceenhanced infrared absorption (SEIRA) since 1990s, and (iii) to rationally couple (i) and (ii) for maximizing the total detection sensitivity since 2010s. After surveying the history of SERS and SEIRA, we outline the principle of plasmonics and the different mechanisms of SERS and SEIRA. We describe various interactions of light with nano/microstructures, localized surface plasmon, surface plasmon polariton, and lightning-rod effect. Their coupling effects can significantly increase the surface sensitivity by designing nanoparticle-nanoparticle and nanoparticle-substrate configuration. As the nano/microstructures have specific optical near-field and far-field behaviors, we focus on how to systematically design the macro-optical systems to maximize the excitation efficiency and detection sensitivity. We enumerate the key optical designs in particular ATR-based operation modes of directional excitation and emission from visible to IR spectral region. We also present some latest advancements on scanning-probe microscopy-based nanoscale spectroscopy. Finally, prospects and further developments of this field are given with emphasis on emerging techniques and methodologies.

A simple, readily available SERS substrate was investigated by utilizing the metallic layer of commercially available DVDs. The channel-like regions could trap metal NPs creating 'hotspots". Au nanoparticles fabricated using fs laser ablation technique were used.

Three-dimensional silver nanoparticles decorated vertically aligned Si nanowires (Si NWs) are effective surface-enhanced Raman spectroscopy (SERS) substrates for molecular detection at low concentration levels. The length of Si NWs prepared by silver assisted electroless etching is increased with an increase in etching time, which resulted in the reduced optical reflection in the visible region. These substrates were tested and optimized by measuring the Raman spectrum of standard dye Rhodamine 6G (R6G) of 10 nM concentration. Further, effective SERS enhancements of $10 5 and $10 4 were observed for the cytosine protein (concentration of 50 lM) and ammonium perchlorate (oxidizer used in explosives composition with a concentration of 10 lM), respectively. It is established that these three-dimensional SERS substrates yielded considerably higher enhancement factors for the detection of R6G when compared to previous reports. The sensitivity can further be increased and optimized since the Raman enhancement was found to increase with an increase in the density of silver nanoparticles decorated on the walls of Si NWs. Published by AIP Publishing. https://doi.org/10.1063/1.5000994

Background: Surface-enhanced Raman spectroscopy (SERS) is a reliable tool for the identification and differentiation of two different human pathological conditions sharing the same symptomology, typhoid and tuberculosis (TB). Objectives: To explore the potential of surface-enhanced Raman spectroscopy for differentiation of two different diseases showing the same symptoms and analysis by principal component analysis (PCA) and partial least square discriminate analysis (PLS-DA). Methods: Serum samples of clinically diagnosed typhoid and tuberculosis infected individuals were analyzed and differentiated by SERS using silver nanoparticles (Ag NPs) as a SERS substrate. For this purpose, the collected serum samples were analyzed under the SERS instrument and unique SERS spectra of typhoid and tuberculosis were compared showing notable spectral differences in protein, lipid and carbohydrates features. Different stages of the diseased class of typhoid (Early acute and late acute stage) and tuberculosis (Pulmonary and extrapulmonary stage) were compared with each other and with healthy human serum samples, which were significantly separated. Moreover, SERS data was analyzed using multivariate data analysis techniques including principal component analysis (PCA) and partial least square discriminate analysis (PLS-DA) and differences were so prominent to observe. Results: SERS Spectral data of typhoid and tuberculosis showed clear differences and were significantly separated using PCA. SERS spectral data of both stages of typhoid and tuberculosis were separated according to 1st principle component. Moreover, by analyzing data using partial least square discriminate analysis, differentiation of two disease classes were considered more valid with a 100% value of sensitivity, specificity and accuracy. Conclusion: SERS can be employed for identification and comparison of two different human pathological conditions sharing same symptomology.

We demonstrate the detection of picric acid (PA) and ammonium nitrate (AN) at mM concentrations by utilizing gold (Au) nanostructures (NSs) as surface enhanced Raman scattering (SERS) substrates fabricated using the technique of ultrafast laser ablation in liquids. Au NPs and NSs were also utilized for detecting Rhodamine 6G (Rh6G) and methylene blue (MB). Detection of all the molecules using the same substrates (NPs and NSs) demonstrated their versatility. Detection limits of 10 À5 , 10 À6 , 10 À7 , 10 À8 M were achieved for AN, PA, Rh6G and MB, respectively. Reproducibility of the SERS intensity using NSs and NPs as substrates demonstrate their efficacy.

We report results from our studies on the fabrication of bimetallic nanoparticles (NPs) and nanostructures (NSs) using femtosecond (∼50 fs) laser ablation technique. The NPs and NSs were achieved by immersing bulk targets with different Au–Ag compositions in acetone followed by ablation. We demonstrate their application towards detection of an explosive molecule of 2, 4-Dinitrotoluene, DNT (25 µM) using a portable Raman spectrometer (785 nm). A tuneable surface plasmon peak observed in the UV-Visible absorption spectra with varying Au proportions confirmed the formation of bimetallic NPs. The size, shape and crystallographic phases were investigated by transmission electron microscope (TEM) and selected area diffraction pattern (SAED). The surface morphology of fabricated NSs was characterized using field emission scanning electron microscope (FESEM). Both NPs and NSs were employed as Surface Enhanced Raman Scattering (SERS) substrates for sensing Methylene Blue (MB) and DNT. From the results obtained in this investigation we concluded that Au 70 Ag 30 NPs/NSs exhibited superior SERS performance compared to pure Ag, Au and other compositions. A detection limit of ∼10 −9 M for MB and ∼10 −6 M for DNT was achieved with corresponding enhancement factors of ∼10 7 and ∼10 4. Furthermore, we have also observed a 'factor of 3' increase in the SERS intensity by simply drop casting Ag NPs on the gaps of Au 70 Ag 30 NSs. This clearly demonstrates that individual NPs, NSs and NPs on NSs (hybrid SERS targets) can be achieved in a single experiment and in combination provide efficient means of detecting trace quantities of explosive molecules.

We present here the surface-enhanced Raman spectroscopic
(SERS)-based detection of the Wilm’s tumor gene
(WT1) sequence using dye-labeled reporter oligonucleotide
and magnetic core @ gold shell nanoparticles. Thiolated
single-stranded DNA (ssDNA) complementers of the WT1
sequence were used to functionalize the gold shell with capture
oligonucleotides in a facile and fast two-step method. The
signal amplification performance of the core@shell colloidal
SERS substrate was tested using malachite green as label dye.
The Raman signal enhancing efficacy of the magnetic core@
gold shell nanomaterial was compared with the efficacy of
spherical gold particles produced using the conventional citrate
reduction method. The core @ shell particles were found
to be superior both regarding robustness in SERS and facile
separation in a heterogeneous reaction system. The core @
shell particles functionalized with target specific oligonucleotide
were able to capture theWT1 target and worked as Raman
signal amplifiers in our assay system. The good physicochemical
characteristics of these particles and the sensitivity observed
in SERS experiments allow us to expect good performance
in the further development steps of a novel, fast and
reliable spectroscopic method for WT1 detection in minimal
residual disease patients.

We report, herein, novel processes of nanofabrication techniques for few molecules detection by generating surface plasmons, thus giving a giant electric field in a controllable and reproducible manner. Surface enhanced Raman scattering (SERS) measurements are performed for different proteins, namely, lysozyme, ribonuclease-B, bovin serum albumin, ferritin, and myoglobin in the temperature range between –65°C and 90°C, using “Device1”, which is fabricated by means of e-beam and electro-plating technique. The calculation shows the possible detection of myoglobin concentration down to attomole. The in-depth analysis even for small conformational changes is performed using 2D Raman correlation analysis and difference Raman analysis in order to gain straightforward understanding of proteins undergoing thermodynamical perturbation. “Device2” is fabricated by e-beam and metal electroless techniques to investigate the Rhodamine 6G (R6G) of different concentrations. Modifying this device by using bimetal (Ag and Au) electroless deposition permits us the further enhancement in Raman signal and better durability.

Raman and infrared (IR) spectroscopy are powerful analytical techniques, but have intrinsically low detection sensitivity. There have been three major steps (i) to advance the optical system of the light excitation, collection, and detection since 1920s, (ii) to utilize nanostructure-based surface-enhanced Raman scattering (SERS) and surface-enhanced infrared absorption (SEIRA) since 1990s, and (iii) to rationally couple (i) and (ii) for maximizing the total detection sensitivity since 2010s. After surveying the history of SERS and SEIRA, we outline the principle of plasmonics and the different mechanisms of SERS and SEIRA. We describe various interactions of light with nano/microstructures, localized surface plasmon, surface plasmon polariton, and lightning-rod effect. Their coupling effects can significantly increase the surface sensitivity by designing nanoparticle–nanoparticle and nanoparticle–substrate configuration. As the nano/microstructures have specific optical near-field ...

Coronavirus Disease-2019, known as COVID-19, has been declared a public health emergency of worldwide concern [1-4]. This paper reports a new design of Surface Enhance Raman Spectroscopy (SERS) substrate that can deliver higher sensitivity and the closest interaction to the target structure of the hot spots for the immunomagnetic capturing based concentration method. This substrate contains Polydimethylsiloxane (PDMS) inverted nanocavity arrays, which can funnel the light to the top where plasmonic gold nanorods occur. A high reflective and low loss layer is deposited at the outer surface, which reflects the photons multiple times and hence the number of photons is increased. After monitoring the consistent pattern and geometric shape of inverted cavities, the hot spots of the suggested Surface Enhance Raman Spectroscopy (SERS) substrate might have improved influence of 10 10 or even higher, which could be sufficient to discover the immunomagnetically densified virus. Raman spectroscopy is a promising candidate in virus diagnosis given its fast and label-free nature, so long as the concentration of the pathogen is high enough to provide reasonable sensitivity [5-9].

Silver nanoparticles (Ag NPs) have found widespread applications as antibacterial agents, catalysts and in chemical detection via surface-enhanced Raman spectroscopy (SERS). To avoid agglomeration and unwanted release to the environment, Ag NPs are usually loaded onto various substrates. However, simple procedures for large-scale synthesis of this important material are still lacking. Here, we demonstrate a facile, green and scalable synthesis of Ag NPs loaded to ceramic substrates. Environment-friendly biopolymer (gum arabic) and ceramic (silica) nanoparticles were spray-dried to obtain surface-functionalized mesoporous silica substrate. Thereafter, the silver precursor was reduced in situ to obtain Ag NPs attached to the silica substrate. Gum arabic played a crucial role in reducing and attaching Ag NPs to the substrate. The resulting composite material was characterized using X-ray diffraction, high-resolution transmission electron microscopy, field emission scanning electron microscopy and Fourier transform infrared spectroscopy. The antimicrobial efficacy of the synthesized composite was evaluated against a gram-negative bacterium, Escherichia coli and a gram-positive bacterium, Staphylococcus aureus. Complete bactericidal effect was observed for composite harboring silver concentration as low as 19 µg ml −1 and 76 µg ml −1 for Escherichia coli and Staphylococcus aureus, respectively. Furthermore, the composite was used as a catalyst in the reduction reaction of 4-nitrophenol and rhodamine B by sodium borohydride. The rate constant for 4-nitrophenol reduction was found to be 1750 s −1 g −1. The composite demonstrated its applicability as a substrate for surface-enhanced Raman spectroscopy (SERS) wherein very dilute concentration (10 −9 M) of crystal violet and rhodamine 6G could be easily detected.

In this work active SERS (surface enhanced Raman scattering) substrates are obtained by electron beam lithography and site selective electroless deposition technique. The combination of these two techniques allows to obtain well-defined metal structures, with a considerable advantage in Raman signal enhancement and in device reproducibility. The active-substrates are composed of silver, gold or a combination of the two metals, with different nanoparticles characteristics, obtained by varying metal deposition time. Rhodamine 6G was used as probe molecules for SERS experiments, showing that this new active substrate has high sensitivity to SERS response and allows to give Raman scattering also for diluted solutions (10−20 M).

We report results from our studies on the fabrication of bimetallic nanoparticles (NPs) and nanostructures (NSs) using femtosecond (∼50 fs) laser ablation technique. The NPs and NSs were achieved by immersing bulk targets with different Au–Ag compositions in acetone followed by ablation. We demonstrate their application towards detection of an explosive molecule of 2, 4-Dinitrotoluene, DNT (25 µM) using a portable Raman spectrometer (785 nm). A tuneable surface plasmon peak observed in the UV-Visible absorption spectra with varying Au proportions confirmed the formation of bimetallic NPs. The size, shape and crystallographic phases were investigated by transmission electron microscope (TEM) and selected area diffraction pattern (SAED). The surface morphology of fabricated NSs was characterized using field emission scanning electron microscope (FESEM). Both NPs and NSs were employed as Surface Enhanced Raman Scattering (SERS) substrates for sensing Methylene Blue (MB) and DNT. From t...

In this work a new strategy for growth of nanostructured indium tin oxide (ITO) by RF sputtering is presented. ITO is deposited in the presence of a carbon plasma which reacts with the free oxygen atoms during the deposition, forming species like CO x. These species are removed from the chamber by the pumping system, and one-dimensional ITO nanostructures are formed without the need for a seed layer. Different values of substrate temperature and power applied to the gun containing the carbon target were investigated, resulting in different nanostructure morphologies. The samples containing a higher density of nanowires were covered with gold and evaluated as surface-enhanced Raman scattering substrates for detection of dye solutions. The concept might be applied to other oxides, providing a simple method for unidimensional nanostructural synthesis.

Chlorpyrifos (CPF), an organophosphate insecticide, is widely identified in fruit juices. In this study, a novel molecularly imprinted polymers-surface-enhanced Raman spectroscopy (MIPs-SERS)/colorimetric dual sensor was developed to determinate CPF in apple juice. MIPs were synthesized using bulk poly-merization to rapidly and selectively adsorb and separate CPF from apple juice. A colorimetric method was developed based upon color changes of synthesized silver nanoparticles (AgNPs) by interacting with CPF, while SERS spectra were directly collected by illuminating the aggregated AgNPs with Raman laser. Colorimetric method rapidly screened and semi-quantified CPF in apple juice ≥5 mg L −1 by naked eye, or accurately quantified CPF in apple juice ranging 0.1–10 mg L −1 by UV–vis spectroscopy. Principle component analysis and partial least-squares regression models (RMSEC = 0.0453, R 2-C = 0.9885) validated using SERS to further quantify CPF in apple juice at extremely low concentration (0.01 mg L −1). This MIPs-SERS/colorimetric dual sensor can rapidly (<25 min), accurately, and cost-efficiently determine CPF in apple juice and meet the worldwide regulation of maximum residue limit.

— This study deals with the use of laser techniques for preparation of advanced Au and Ag nanostructures on SiO 2 (001) substrates to be applied to high-resolution analyses, namely, surface enhanced Raman spectroscopy (SERS) analyses. The optical and morphological properties of the nanostructures are compared with those of the PLD thin films. The activity is tested of the structures fabricated as substrates for SERS covered by small quantities (usually applied in agricultural medicine) of the Aktara 25 BG (thiamethoxam) insecticide and the Dithane DG (mancozeb) fungicide. To the best of our knowledge, Raman spectra of Aktara 25 BG are presented for the first time. The study has a direct bearing on the human health and food quality by way of assisting the detection of small amounts or residue of harmful pollutants. Keywords— laser deposition and annealing, Ag and Au nanostructures, SERS, insecticide Aktara 25 BG, fungicide Dithane DG.

We report glucose sensing 10 mM to 0.1 mM in water using stamping surface-enhanced Raman spectroscopy (S-SERS) technique with nanoporous gold disk (NPGD) plasmonic substrates, a reagent-and separation-free technique. OCIS codes: (240.6695) Surface-enhanced Raman scattering; (280.1415) Biological sensing and sensors.

The geometry of individual plasmonic nanostructures and their collective arrangement plays a critical role in electromagnetic enhancement of surface-enhanced Raman scattering (SERS). Concomitantly, the same attributes also have a direct implication on plasmon resonance line-shapes that further affect the far-field radiation pattern of SERS in Rayleigh, Stokes and anti-Stokes spectral regimes. Here we numerically show how Fano-type plasmon resonance lineshapes in certain geometrical configurations of gold nanorod dimers can selectively influence the far-field radiation pattern in the anti-Stokes spectral region of SERS. We explored a variety of dimer angles (0° to 180°) between the gold nanorods, and compared their far-field radiation patterns in the anti-Stokes, Rayleigh and Stokes regions of their plasmon resonance. We found that angles 30° to 60° exhibited greater in-plane forward-to-backward intensity ratios in the anti-Stokes region, compared to other configurations. The results discussed herein highlight a three-way connection between the geometrical arrangement of plasmonic nanostructures, Fano-type lineshapes and far-field radiation patterns in SERS, especially in the anti-Stokes region. Our work will have implications not only in designing optical antennas for linear and nonlinear Raman scattering, but also in creating directional light sources based on nonlinear optical processes such as two-photon fluorescence and photon frequency upconversion.