Surface Enhanced Raman Spectroscopy Intensity Research Articles

Ultrasensitive SERS aptasensor using Au@Ag bimetallic nanorod SERS tags for the selective detection of amantadine in foods

Herein, a novel surface enhanced Raman spectroscopy (SERS) aptasensor was developed for amantadine (AMD) detection, based on magnetite nanoparticles coated with polyethylenimine, silver nanoclusters and aptamers (Fe3O4@PEI@AgNC-apt) as the capture probe and complementary DNA-modified gold nanorods (AuNRs@4-MPBA@Ag-c-DNA containing 4-mercaptophenylboric acid molecules) as the reporter probe. In the presence of AMD, the AMD and the reporter probe competed for the aptamer on the surface of the capture probe, resulting in the reporter probe detaching from the capture probe leading to a decrease in intensity of the SERS signal at 1067 cm−1 for 4-MPBA. Under optimal conditions, a good linear relationship was established between the SERS intensity at 1067 cm−1 and the logarithm of the AMD concentration over the range 10−6-102 mg L−1, with a LOD of 0.50 × 10−6 mg L−1. The AMD levels in spiked samples were evaluated using the SERS aptasensor, with good recoveries ranging from 90.57% to 113.49% being obtained.

SERS detection of foodborne pathogens in beverage with Au nanostars.

The aim of this study is to develop a simple but rapid method for the determination of foodborne pathogens in complex matrices (beverages) by surface enhanced Raman spectroscopy (SERS) combined with Au nanostar solid-phase substrates. The star-shaped singlet Au nanostructure was formed on the surface of astainless steel sheetby chemical replacement reaction. Rhodamine 6G verified the sensitivity and reproducibility of this substrate, and the relative standard deviations of the SERS intensity at 1312 cm-1, 1364 cm-1, and 1510 cm-1 displacements were 3.40%, 5.64%, and 3.48%, respectively. By detecting four pathogens in beverage samples on Au nanostar substrates, the utility of the SERS assay was demonstrated, while the combination of principal component analysis (PCA) and hierarchical cluster analysis (HCA) further enabled the isolation and identification of pathogens. The results of spiked beverages were validated in conventional culture identification and Vitek 2 Compact biochemical identification system experiments. Thus, this research demonstrated that Au nanostar substrates can be effectively utilized for the recognition of pathogenic bacteria and have immense promise to advance the progress of quick detection of foodborne pathogens and food safety.

Preparation of 3D nano silver trees/sea urchin-like gold and SERS detection of uric acid

In this paper, 3D nano-silver trees/sea urchin-like gold Surface Enhanced Raman Spectroscopy (SERS) substrates were prepared by chemical reduction method, characterized by SEM, EDS, UV–Vis and XRD et.al, and the preparation process was optimized using Rhodamine B (RB) as the Raman signal molecule. The SERS characteristics of Uric Acid on this substrate were investigated and the results showed that the SERS substrate had a Raman enhancement factor of 1.9 × 107 for RB, and also had a significant Raman enhancement effect on Uric Acid. The SERS intensity (ISERS) at 1400 cm−1 showed a good linear relationship with the logarithm value of uric acid concentration (log C) between the range of 5 × 10−4 M to 1 × 10−7 M. The linear fitting equation was ISERS = 890 (log C) + 8066 (R2 = 0.983), and the LOD = 2.8 × 10−8 M. The spiked test was performed in human serum with recoveries ranging from 82.86% to 125.13% and RSD (n = 3) < 3.5%.

Real-time tracking of colloidal stability based on collision behaviors probed by surface-enhanced Raman spectroscopy

HypothesisThe dynamic behaviors of colloidal particles have already been considered as one of the key issues in their practical application, such as aggregation and dispersion. However, it is still remained significant challenge in developing the real time techniques to capture their dynamic tracks. The nano/subnanometer scale gap generated during the colloidal collisions served as the critical location for amplifying the Raman signal, so called as gap (“hot spots”) based surface enhanced Raman spectroscopy (SERS). The alternating reversible “spike” of SERS intensity and irreversible step in baseline intensity are contributed to the preferred stability and the aggregation of colloid respectively. ExperimentsA facile approach is developed to track colloidal stability in real-time based on collisions and SERS. The effects of particle concentration, the dispersion medium, and solution pH on colloidal stability are systematically investigated, and the SERS intensity of a simulated single-like “hot spot” was calculated by combining a SEM position with SERS mapping technology to estimate the intensity of single-particle collision. FindingsThe colloidal particles exhibited higher stability in the solution with lower particle concentration, higher viscosity and neutral medium. The SERS intensity of single-particle collision was estimated to be about 2.06 × 10-7 counts, and the average number of collisions for the 0.13 mmol/dm3 SiO2@Ag solution was about 1.11 × 108 times/spike in the “spikes” with SERS intensity of 23.0 cps. It is believed that the SERS based strategy would be developed as a promising tool for obtaining the deeper insight into the nature of collisions in the colloidal science.

A disposable ultrasensitive surface enhanced Raman spectroscopy biosensor platform fabricated from biodegradable zein nanofibers

AbstractIn this paper, a natural polymer, zein, is converted into a disposable and environmentally friendly surface enhanced Raman spectroscopy (SERS) biosensor platform to detect toxins. First, protein nanofiber mats were fabricated using electrospinning. Next, the surface of the fibers was decorated with metallic nanoparticles to create hotspots for the detection of the target molecule. Four types of metallic nanoparticles were tested for sensitivity optimization: gold, silver, silver‐shelled‐gold, and a mixture of gold and silver nanoparticles. Silver‐shelled‐gold nanoparticles gave the highest SERS intensity, and at the concentration of 1012 particles/ml, the highest enhancement factor (EF) of 2.49 × 106 was reached, which is the highest EF ever reported for a zein‐based biodegradable platform. Acrylamide was used as the model food carcinogenic toxin and its detection with this nanofiber‐based platform gave a limit of detection of 2.06 ng/ml. This LOD is 104 times lower than the limit of detection that was achieved previously with a zein‐based SERS platform. Other sensitive analytical methods (GC–MS and LC–MS/MS) gave LODs of 5–10 and 20–50 ng/ml for acrylamide, much higher than the method used in this study. This sensitivity is much lower than any other previous attempts to detect acrylamide with biodegradable sensors.

Influence of Ag Photodeposition Conditions over SERS Intensity of Ag/ZnO Microspheres for Nanomolar Detection of Methylene Blue.

Surface enhanced Raman spectroscopy (SERS) is considered a versatile and multifunctional technique with the ability to detect molecules of different species at very low molar concentration. In this work, hierarchical ZnO microspheres (ZnO MSs) and Ag/ZnO MSs were fabricated and decorated by hydrothermal and photodeposition methods, respectively. For Ag deposition, precursor molar concentration (1.9 and 9.8 mM) and UV irradiation time (5, 15, and 30 min) were evaluated by SEM, TEM, X-ray diffraction and Raman spectroscopy. X-ray diffraction showed a peak at 37.9° corresponding to the (111) plane of Ag, whose intensity increases as precursor concentration and UV irradiation time increases. SEM images confirmed the formation of ZnO MSs (from 2.5 to 4.5 µm) building by radially aligned two-dimensional ZnO nanosheets with thicknesses below 30 nm. The Raman spectra of Ag/ZnO MSs exhibited a vibration mode at 486 cm−1 which can be directly associated to Ag deposition on ZnO MSs surface. The performance of SERS substrate was evaluated using rhodamine 6G. The SERS substrate grown at 9.8 mM during 30 min showed the best SERS activity and the ability to detect methylene blue at 10−9 M.

Ammonia modified graphene oxide – Gold nanoparticles composite as a substrate for surface enhanced Raman spectroscopy

Simple treatment of graphene oxide (GO) with ammonia solution at room temperature changes its chemical composition as revealed by infrared, Raman and X-ray photoelectron spectroscopy results. Both - pristine GO and GO modified with ammonia solution (NH3-GO) were combined with spherical gold nanoparticles (AuNPs) or gold nanourchins (AuNURs) and studied as possible substrates for surface enhanced Raman spectroscopy (SERS) using Rhodamine 6G (R6G) as probe. AuNPs or (AuNURs) were adsorbed on thin layers of either as-prepared GO or NH3-GO. The AuNPs/NH3-GO support enables easy identification of the characteristic bands of R6G at the 10−7 M concentration, while for AuNPs/GO the R6G concentration must be at least ten times higher in order to obtain the same quality spectra. For AuNURs the difference between NH3-GO and GO is even more significant. The observed enhancement factors are higher for AuNURs too. The improved SERS intensity results mainly from more efficient adsorption of AuNPs on NH3-GO comparing to pristine GO, as suggested by SEM and EDS results. Another possible factor affecting the SERS activity may be partial reduction of GO by NH3 and introduction of nitrogen functionalities which in turn affects the chemical and dipole contribution to SERS enhancement.

Optimization and performance analysis of SERS-active suspended core photonic crystal fibers

Recently, surface enhanced Raman spectroscopy (SERS)-active photonic crystal fiber (PCFs) probes have gained great interest for biosensing applications due to the tremendous advantages it has over the conventional planar substrate based SERS measurements, with improvements on the detection sensitivity and reliability in measurements. So far, two main approaches were employed to get the analyte molecule in the vicinity of nanoparticles (NPs) inside PCFs in order to achieve the SERS effect. In the first case, analyte and NPs are pre-mixed and injected inside the holes of the PCF prior to the measurement. In the second approach, controlled anchoring of the NPs inside the inner walls of the PCF was achieved prior to the incorporation of the analyte. Although many studies have been conducted using one configuration or the other, no clear trend is emerging on which one would be the best suited for optimizing the biosensing properties offered by SERS active-PCF. In this paper, we investigate the performances of both configurations along with their interplays with the core size of the PCF probe. We have fabricated several samples of a standard PCF design with different core sizes, and SERS measurements of a standard Raman-active molecule are realized in the same conditions for enabling direct comparisons of the SERS intensity and measurement reliabilities between each configuration, yielding clear directions on the optimization of the SERS-active PCF probe. We envision that this study will pave the way for next-generation clinical biosensors for body fluid analysis, as it exhibits high sensitivity and excellent reliability.

Direct quantification of sulfur dioxide in wine by Surface Enhanced Raman Spectroscopy

A rapid Surface Enhanced Raman Spectroscopy (SERS) method to detect SO2 in wine is presented, exploiting the preferential binding of silver nanoparticles (AgNPs) with sulfur-containing species. This interaction promotes the agglomeration of the AgNPs and inducing the formation of SERS “hot spots” responsible for SO2 signals enhancement. For increasing SO2 concentrations from 0 to100 mg/l in wine simulant, SERS intensity showed an increasing trend, following a Langmuir absorption function (R2 = 0.94). Due to the wine matrix variability, a standard additions method was then employed for quantitative analysis in red and white wines. This method does not require the SO2 separation but only a matrix pre-cleaning by solid phase extraction. The limit of detection (LOD) was defined for each wine tested, ranging from 0.6 mg/l to 9.6 mg/l. The results obtained were validated by comparison with the International Organization of Vine and Wine method (OIV-MA-AS323-04A).

Surface-enhanced Raman spectroscopic–based aptasensor for Shigella sonnei using a dual-functional metal complex-ligated gold nanoparticles dimer

Herein, we constructed an aptamer-based sensor for the sensitive and highly specific detection of Shigella sonnei via surface enhanced Raman spectroscopy (SERS) analysis. A composite material integrated of the Raman active 4-MBA ligand of the Eu-complex and citrate-stabilized Au nanoparticles (cit-Au NPs) was synthesized and served as both active substrate and Raman reporter. Aptamers targeted to S. Sonnei was then modified onto the surface of this dual-functional material. With the introduction of S. Sonnei, aptamer bound with target with high affinity and specificity, leaving the dual-functional material onto the bacteria. The SERS intensity response showed a strong positive linear correlation (R = 0.9956) with increasing concentrations of S. sonnei (ranging from 10 to 106 cfu/mL). High specificity was achieved at Shigella species (S. dysenteriae, S. flexneri, S. boydii) and other common bacteria (Salmonella typhimurium, Staphylococcus aureus and Escherichia coli). When applied in real samples, the approach showed recoveries from 92.6 to 103.8 %. The designed approach holds great potential for the construction of various aptasensors for the effective and convenient detection of different food hazards.

Highly Sensitive and Rapid Surface Enhanced Raman Spectroscopic (SERS) Determination of Thiram on the Epidermis of Fruits and Vegetables Using A Silver Nanoparticle-Modified Fibrous Swab

A surface enhanced Raman spectroscopy (SERS) substrate with high sensitivity for the rapid determination of pesticide residues was developed by combining silver nanoparticles (AgNPs) and a fibrous swab. The SERS substrate was prepared simply by forming a SERS-active area on the section of fibrous swab and centrifuge tube with a soak-absorb approach. Rhodamine 6 G (R6G), a common SERS probe molecule, was used for performance characterization of the prepared SERS substrate that was shown to have high sensitivity, good stability and good reproducibility. Due to its good flexibility, the prepared SERS substrate was used to wipe contaminated surfaces for residue extraction. High sensitivity for detecting trace-level pesticides was verified for thiram. The limits of detection (LODs) for thiram on apple, grape and eggplant epidermis were calculated to be as low as 0.5313, 0.5768, and 0.5495 ng·cm−2, respectively, nearly 2 orders of magnitude below the maximum residue limit (MRL) for pesticide in food issued by the National Food Safety Standard of China. In addition, there was a linear relationship between the SERS intensity and the concentration of thiram in these three samples, indicating the good potential of this substrate for quantitative SERS analysis.

Aptamer-based SERS biosensor for whole cell analytical detection of E. coli O157:H7

Infectious outbreaks caused by foodborne pathogens such as E. coli O157:H7 are still imposing a heavy burden for global food safety, causing acute illnesses and significant industrial impact worldwide. Despite the growth of biosensors as a research field, continuous innovation on detection strategies, novel materials and enhanced limits of detection, most of the platforms developed at the laboratory scale never will get to meet the market.The use of aptamers as capture biomolecules has been proposed as a promising alternative to overcome the harsh environmental conditions of industrial manufacturing processes, and to enhance the performance under real, complex, conditions. In this work, we present the feasibility of using aptameric DNA sequences, covalently conjugated to 4-aminothiophenol-gold nanoparticle complexes for the sensitive and highly specific detection of E. coli O157:H7 via surface enhanced Raman spectroscopy (SERS) analysis. Low concentrations of E. coli O157:H7 were detected and quantified within 20 min in both pure culture (∼101 CFU mL−1) and ground beef samples (∼102 CFU mL−1). The SERS intensity response showed a strong negative linear correlation (r2 = 0.995) with increasing concentrations of E. coli O157:H7 (ranging from 102 to 106 CFU mL−1). High specificity was achieved at genus (L. monocytogenes, S. aureus S. typhimurium) species (E. coli B1201) and serotype (E. coli O55:H7) level, demonstrating with 95% of confidence that the interferent microorganisms tested generated a Raman signal response not significantly different from the background (p = 0.786).This work evaluates the incorporation of aptameric DNA sequences as bio capture molecules exclusively. The successful performance presented using non-modified citrate reduced GNPs, is promising for potential low-cost, high-throughput applications. The findings might be applied simultaneously to the detection of a wide variety of foodborne pathogens in a multiplexed fashion employing unique Raman probes and strain-specific aptamer sequences.

Optimally distributed Ag over SiO2 nanoparticles as colloidal SERS substrate

Surface enhanced Raman spectroscopy (SERS) is a versatile and unique technique for the detection and identification of molecules. Over the past few decades this unique technique has grown as a tool for the qualitative and quantitative analysis. We report a novel and simple method for the synthesis of silica‑silver nanospheres (Ag-SiO2) which can be used as colloidal SERS substrate. Geometrically confined hotspots with stable silver nanoparticles are obtained allowing a preferrential arrangement of hotspots. The prepared Ag-SiO2 nanospheres with varying size are used for the SERS detection of Rhodamine 6G. The SERS intensity is found to vary with the change in size of silica and distribution of silver nanoparticles. Both these quantities are optimized to get maximum enhancement of Raman signal and the detection limit is found to be 10−18 M for Rhodamine 6G. Further, the work is extrapolated to an application which involves the SERS detection of Sudan I, a carcinogenic food adulterant, with a detection limit of 10−8 M.

An exploration of surface enhanced Raman spectroscopy (SERS) for in situ detection of sulfite under high pressure

In this work, silver nanoparticles film was directly fabricated on the surface of the diamond anvil as SERS active substrate for the first time by using a simple and convenient method. With this approach, the SERS spectrum of sulfite was obtained with a detection limit of 5 μmol/L in diamond anvil cell (DAC) at ∼50 MPa. The SERS signal intensity of the two main vibration modes, νsymSO and δsymOSO, showed good linearity with the Na2SO3 concentrations in the range from 5 to 40 μmol/L under high pressure. The linear correlation coefficients were 97.67% and 96.08%, respectively. The effects of pressure on the SERS intensity and Raman shift of the two modes were also studied. The SERS intensity dropped with the increase of pressure and the two main vibration modes shifted to high wave-number when the pressure increased in the pressures ranging from 54 MPa to 330 MPa. The experiments indicate that this method is rapid, convenient and sensitive in detecting sulfite at high pressures. It can be developed as an effect in situ method to detect sulfite in the process of high pressure reaction.

Combinatorial Thin Film Sputtering Au xAl1- x Alloys: Correlating Composition and Structure with Optical Properties.

The Au-Al alloy system was investigated via a combinatorial thin film sputtering method for its potential as a plasmonic material. Au xAl1- x combinatorial libraries were cosputtered from Au and Al elemental targets and the composition, phase, and dielectric function of a ∼350 nm film was determined using energy dispersive spectroscopy (EDS), grazing incidence X-ray diffraction (GIXRD), and spectroscopic ellipsometry, respectively. The phase evolution and optical properties were analyzed after annealing various compositions under a vacuum. The phases present matched the expected phases based on the published Al-Au binary phase diagram at all compositions. Interestingly, the mixed phase Al-AuAl2 region showed the most optical tunability, where a maximum in the real part of the dielectric function progressively shifted to higher energy for increasing gold concentration. For almost pure AuAl2, the imaginary component is largely reduced in the visible range and is comparable to that of pure Al in the UV region. A 20-nm-thick film with composition Au0.74Al0.26 was studied using a (scanning) transmission electron microscope with an in situ laser heating system. The structures of the as-deposited and laser annealed films were determined using selected area diffraction and the bulk plasmon of AuAl2 and Al realized with electron energy loss spectroscopy. Last, the Au-rich solid solution region was investigated as a surface enhanced Raman spectroscopy (SERS) substrate using the benezenethiol (BT) molecule. Good SERS intensity was maintained up to 30% Al addition where enhancements of 105 to 107 were still observed.

Sensitive detection of bisphenol A by coupling solid phase microextraction based on monolayer graphene-coated Ag nanoparticles on Si fibers to surface enhanced Raman spectroscopy

In this work, a facile method coupling solid phase microextraction (SPME) with surface enhanced Raman spectroscopy (SERS) was developed for the detection of trace bisphenol A (BPA). Monolayer graphene-coated Ag nanoparticles (Ag NPs) were fabricated on the Si fiber, which made the Si fiber retain functions of both as a SERS-active substrate and SPME fiber to realize in situ rapid determination of BPA. The SERS-active SPME fiber was immersed in water to extract BPA prior to its detection by SERS. The relative standard deviation (RSD) values of the uniformity and the reproducibility of the SERS-active SPME fiber are 14% and 13%, respectively. The characteristic SERS intensity versus BPA concentration showed a linear relationship (R2 = 0.958). Due to the combination of the SERS method with SPME, this method exhibits extremely high sensitivity and excellent stability for the detection of BPA, with a limit of detection as low as 1 μg L−1. The method was successfully used for the determination of BPA in water samples with spiked recoveries ranging from 97% to 110%. Compared to the conventional SERS methods used for the detection of BPA, the present method not only retains the advantages of SERS but also provides several unique advantages including preconcentration of analytes, separation of analyte from sample matrices and improvement of sensitivity, thus making its promising application in environmental analysis of BPA.

Substrate-Immersed Solvothermal Synthesis of Ordered SiO2/Ag Arrays as Catalytic SERS Substrates

In this work, we designed a simple substrate-immersed solvothermal route for the one-step synthesis of novel ordered SiO2/Ag arrays, employing SiO2 colloidal crystals as templates and alcohol as reducing agent. The Ag nanoparticles were uniformly deposited in situ onto SiO2 colloidal crystals, which exhibited high surface enhanced Raman spectroscopy (SERS) activity and uniform SERS intensity. It was found that ordered SiO2/Ag arrays could rapidly scavenge the absorbed-Nile blue A (NBA) molecules from the surfaces with the assistance of H2O2, while the SERS signals of NBA decreased sharply and almost completely disappeared within four minutes. This can be attributed to the superior catalytic activity of Ag nanoparticles. After five times of re-immersion and re-absorbing process of NBA, the substrates could still keep [Formula: see text] 74.8% SERS intensity versus the original. The high activity and durability of the as-prepared SiO2/Ag SERS substrate endow them as a promising candidate for trace detection.

Alkaline phosphatase labeled SERS active sandwich immunoassay for detection of Escherichia coli

In this study, a sandwich immunoassay method utilizing enzymatic activity of alkaline phosphatase (ALP) on 5-bromo-4-chloro-3-indolyl phosphate (BCIP) for Escherichia coli (E. coli) detection was developed using surface enhanced Raman spectroscopy (SERS). For this purpose, spherical magnetic gold coated core-shell nanoparticles (MNPs-Au) and rod shape gold nanoparticles (Au-NRs) were synthesized and modified for immunomagnetic separation (IMS) of E. coli from the solution. In order to specify the developed method to ALP activity, Au-NRs were labeled with this enzyme. After successful construction of the immunoassay, BCIP substrate was added to produce the SERS-active product; 5-bromo-4-chloro-3-indole (BCI). A good linearity (R2=0.992) was established between the specific SERS intensity of BCI at 600cm−1 and logarithmic E. coli concentration in the range of 1.7×101–1.7×106cfumL−1. LOD and LOQ values were also calculated and found to be 10cfumL−1 and 30cfumL−1, respectively.

Rapid identification of gutter oil by detecting the capsaicin using surface enhanced Raman spectroscopy

AbstractAccurate determination of the gutter oil represents a major food safety challenge. Here, we propose to use the surface enhanced Raman spectroscopy (SERS) with silver nanorod array substrates to detect the capsaicin, a marker of the gutter oil that is difficult to remove. The capsaicin has several characteristic SERS peaks at Δv = 807 cm−1, Δv = 1, 264 cm−1, and so forth, which correspond to the C39‐C37‐C43 stretching vibrational mode at the alkyl chain, the ring stretching vibrational mode, and so forth, confirmed by our density functional theory calculation. This SERS‐based method enabled the rapid and highly sensitive detection of the gutter oil with minimum pretreatment. The concentration dependent SERS investigation shows that the SERS intensity of these characteristic peaks has a linear relationship with the capsaicin concentration when 1 mg/L &lt; C &lt; 60 mg/L. By combining a liquid phase extraction method and the SERS detection strategy, the capsaicin concentration as low as 30 mg/L can be detected from inoculated corn oil samples.

Structure elucidation and degradation kinetic study of Ofloxacin using surface enhanced Raman spectroscopy

A simple, fast and sensitive surface enhanced Raman spectroscopy (SERS) method for quantitative determination of fluoroquinolone antibiotic Ofloxacin (OFX) is presented. Also the stability behavior of OFX was investigated by monitoring the SERS spectra of OFX after various degradation processes. Acidic, basic and oxidative force degradation processes were applied at different time intervals. The forced degradation conditions were conducted and followed using SERS method utilizing silver nanoparticles (Ag NPs) as a SERS substrate. The Ag NPs colloids were prepared by reduction of silver nitrate using polyethyelene glycol (PEG) as a reducing and stabilizing agent. Validation tests were done in accordance with International Conference on Harmonization (ICH) guidelines. The calibration curve with a correlation coefficient (R=0.9992) was constructed as a relationship between the concentration range of OFX (100–500ng/ml) and SERS intensity at 1394cm−1 band. LOD and LOQ values were calculated and found to be 23.5ng/ml and 72.6ng/ml, respectively. The developed method was applied successfully for quantitation of OFX in different pharmaceutical dosage forms. Kinetic parameters were calculated including rate constant of the degradation of the studied antibiotic.