Surface Enhanced Raman Spectroscopy Analysis Research Articles

Assessment of treatment efficacy using surface-enhanced Raman spectroscopy analysis of urine in rats with kidney transplantation or kidney disease.

Individuals who have kidney disease or kidney transplants need routine assessment of their kidney damage and function, which are largely measured based on histological examination of kidney biopsies, blood test, and urinalysis. These methods are practically difficult or inconvenient, and expensive. The objective of this study was to develop a model to estimate the kidney damage and function by surface-enhanced Raman spectroscopy (SERS). Urine samples were collected from two previous studies: renal allograft recipient Lewis rats receiving anti-TGF-β antibody or control antibody treatment and obese diabetic ZSF1 rats with kidney disease fed with whole grape powder-containing chow or control chow. Silver nanoparticle-based SERS spectra of urine were measured. SERS spectra were analyzed using principal component analysis (PCA) combined with linear discriminant analysis (LDA) and partial least squires (PLS) analysis. PCA/LDA separated anti-TGF-β antibody-treated group from control group with 90% sensitivity and 70% specificity in kidney transplants, and grape-fed group from controls with 72.7% sensitivity and 60% specificity in diabetic kidneys. The receiver operating characteristic curves showed that the integration area under the curve was 0.850 ± 0.095 (p = 0.008) in kidney transplant groups and 0.800 ± 0.097 (p = 0.02) in diabetic kidney groups. PLS predicted the biochemical parameters of kidney function using the SERS spectra, resulting in R2 = 0.8246 (p < 0.001,urine protein), R2 = 0.8438 (p < 0.001, urine creatinine), R2 = 0.9265 (p < 0.001, urea), R2 = 0.8719 (p < 0.001, serum creatinine), and R2 = 0.6014 (p < 0.001, urine protein to creatinine ratio). Urine SERS spectral analysis suggesting that it may become a convenient method for rapid assessment of renal impairment.

Synthesis of magnetic polyphosphazene-Ag composite particles as surface enhanced Raman spectroscopy substrates for the detection of melamine

Magnetic polyphosphazene (MPZS) particles coated by Ag nanoparticles (MPZS-Ag) have been developed as surface enhanced Raman spectroscopy (SERS) substrates for sensitive detection of melamine in aqueous solutions and milk samples. 5,5′-Dithiobis-(2-nitrobenzoic acid) (DTNB) was used as model analyte to test the SERS activity of the MPZS-Ag particles. The prepared MPZS-Ag particles possess both magnetic responsiveness and excellent SERS properties. SERS detection of different concentrations of melamine aqueous solutions and spiked milk samples were performed by the MPZS-Ag particles. The limit of detection (LOD) of the melamine in aqueous solutions was 10−7 mol/L (0.0126 mg/L) and 0.6 mg/L in real milk samples using the MPZS-Ag particles as SERS substrates. The LOD of the melamine are much lower than the safety values of Food and Drug Administration and Codex Alimentarius Commission. These results indicate that the MPZS-Ag particles have promising application prospect for SERS analysis in food safety fields.

An evaluation of monovalent, divalent, and trivalent cations as aggregating agents for surface enhanced Raman spectroscopy (SERS) analysis of synthetic cannabinoids.

In this study monovalent, divalent, and trivalent chloride, sulfate and nitrate salts were examined to determine the critical coagulation concentration (CCC) for each salt and its corresponding effect on detection limits for SERS analysis of cannabinoid extracts. The CCC of each salt was determined using UV-vis, particle size and zeta potential measurements. The results demonstrated that the divalent and trivalent cations produce a lower CCC when compared to monovalent cations. The data indicate the effect that cation valence has on nanoparticle destabilization. This information is essential because it permits the user to develop optimal conditions for aggregation of salts used in SERS. Tests were then performed to determine the best conditions for SERS detection of a small set of cannabinoids with naphthyl indole moieties. The results demonstrate the importance of salt concentration for colloid aggregation and illustrate the effect of aggregation on sensitivity for the SERS experiment.

Paper-based SERS analysis with smartphones as Raman spectral analyzers.

SERS (Surface Enhanced Raman Spectroscopy) can realize fingerprint recognition of molecular samples with high detection accuracy and sensitivity. However, rapid and convenient measurement of the Raman spectra of analytes for a point-of-care test (POCT) has put forward a high demand for portable Raman spectrometers, as well as reliable SERS substrates. Hereby, we first utilize a smartphone as a miniaturized Raman spectral analyzer, which has the revolutionary advantages of a friendly human-machine interface, fast measurement time, and good sensitivity. Meanwhile, a paper-based SERS chip was prepared based on commonly used filter paper and silver nanoparticles (AgNP), which was successfully used to detect low concentrations of typical SERS analyte model molecules including rhodamine 6G and crystal violet. The current method of smartphone-based SERS spectroscopy as a POCT device will greatly promote the application of Raman technology in a variety of scenarios, such as safety inspections, pesticide residue detection, water pollution monitoring, and so on. Coupled with paper-based SERS chips with advantages of facile preparation, low cost and good reliability, the current work proves to have a great potential for industrial production and for meeting the vast marketing demand of Raman based POCT technology.

Amplification-free SERS analysis of DNA mutation in cancer cells with single-base sensitivity.

Accurate and sensitive identification of DNA mutations in tumor cells is critical to the diagnosis, prognosis and personalized therapy of cancer. Conventional polymerase chain reaction (PCR)-based methods are limited by the complicated amplification process. Herein, an amplification-free surface enhanced Raman spectroscopy (SERS) approach which directly detects point mutations in cancer cells has been proposed. A highly sensitive and uniform SERS substrate was fabricated using gold@silver core-shell nanorods, achieving an enhancement factor of 1.85 × 106. By combining the SERS-active nanosubstrate with molecular beacon probes, the limit of detection reached as low as 50 fM. To enable parallel analysis and automated operation, the SERS sensor was integrated into a microfluidic chip. This novel chip-based assay was able to differentiate between mutated and wild-type KRAS genes among a variety of other nucleic acids from cancer cells in 40 min. Owing to the simple operation and fast analysis, the SERS-based DNA assay chip could potentially provide insights into clinical cancer theranostics in an easy and inexpensive manner at the point of care.

Photovoltaic cells as a highly efficient system for biomedical and electrochemical surface-enhanced Raman spectroscopy analysis.

Surface-enhanced Raman scattering (SERS) has been intensively used recently as a highly sensitive, non-destructive, chemical specific, and label-free technique for a variety of studies. Here, we present a novel SERS substrate for: (i) the standard ultra-trace analysis, (ii) detection of whole microorganisms, and (iii) spectroelectrochemical measurements. The integration of electrochemistry and SERS spectroscopy is a powerful approach for in situ investigation of the structural changes of adsorbed molecules, their redox properties, and for studying the intermediates of the reactions. We have developed a conductive SERS platform based on photovoltaic materials (PV) covered with a thin layer of silver, especially useful in electrochemical SERS analysis. These substrates named Ag/PV presented in this study combine crucial spectroscopic features such as high sensitivity, reproducibility, specificity, and chemical/physical stability. The designed substrates permit the label-free identification and differentiation of cancer cells (renal carcinoma) and pathogens (Escherichia coli and Bacillus subtilis). In addition, the developed SERS platform was adopted as the working electrode in an electrochemical SERS approach for p-aminothiophenol (p-ATP) studies. The capability to monitor in real-time the electrochemical changes spectro-electro-chemically has great potential for broadening the application of SERS.

Surface-Enhanced Raman Spectroscopy (SERS) of Mancozeb and Thiamethoxam Assisted by Gold and Silver Nanostructures Produced by Laser Techniques on Paper.

Advanced gold (Au) and silver (Ag) nanostructures were produced by laser techniques on printer paper substrate. Surface-enhanced Raman spectroscopy (SERS) analyses of the fungicide mancozeb (Dithane DG) and insecticide thiamethoxam (Aktara 25 BG) in quantities smaller than usually applied in agricultural medicine were performed for the first time assisted by the structures fabricated. The investigations and results show an easy alternative and cheap way to detect small amounts or residue of harmful environmental pollutants, which has a direct bearing on food quality and thus on human health.

Fast discrimination of bacteria using a filter paper-based SERS platform and PLS-DA with uncertainty estimation.

Rapid and reliable identification of bacteria is an important issue in food, medical, forensic, and environmental sciences; however, conventional procedures are time-consuming and often require extensive financial and human resources. Herein, we present a label-free method for bacterial discrimination using surface-enhanced Raman spectroscopy (SERS) and partial least squares discriminant analysis (PLS-DA). Filter paper decorated with gold nanoparticles was fabricated by the dip-coating method and it was utilized as a flexible and highly efficient SERS substrate. Suspensions of bacterial samples from three genera and six species were directly deposited on the filter paper-based SERS substrates before measurements. PLS-DA was successfully employed as a multivariate supervised model to classify and identify bacteria with efficiency, sensitivity, and specificity rates of 100% for all test samples. Variable importance in projection was associated with the presence/absence of some purine metabolites, whereas confidence intervals for each sample in the PLS-DA model were calculated using a resampling bootstrap procedure. Additionally, a potential new species of bacteria was analyzed by the proposed method and the result was in agreement with that obtained via 16S rRNA gene sequence analysis, thereby indicating that the SERS/PLS-DA approach has the potential to be a valuable tool for the discovery of novel bacteria. Graphical abstract This paper describes the discrimination of bacteria at the genus and species levels, after minimal sample preparation, using paper-based SERS substrates and PLS-DA with uncertainty estimation.

Correlation between Cancerous Exosomes and Protein Markers Based on Surface-Enhanced Raman Spectroscopy (SERS) and Principal Component Analysis (PCA).

Exosomes, which are nanovesicles secreted by cells, are promising biomarkers for cancer diagnosis and prognosis, based on their specific surface protein compositions. Here, we demonstrate the correlation of nonsmall cell lung cancer (NSCLC) cell-derived exosomes and potential protein markers by unique Raman scattering profiles and principal component analysis (PCA) for cancer diagnosis. On the basis of surface enhanced Raman scattering (SERS) signals of exosomes from normal and NSCLC cells, we extracted Raman patterns of cancerous exosomes by PCA and clarified specific patterns as unique peaks through quantitative analysis with ratiometric mixtures of cancerous and normal exosomes. The unique peaks correlated well with cancerous exosome ratio ( R2 > 90%) as the unique Raman band of NSCLC exosome. To examine the origin of the unique peaks, we compared these unique peaks with characteristic Raman bands of several exosomal protein markers (CD9, CD81, EpCAM, and EGFR). EGFR had 1.97-fold similarity in Raman profiles than other markers, and it showed dominant expression against the cancerous exosomes in an immunoblotting result. We expect that these results will contribute to studies on exosomal surface protein markers for diagnosis of cancers.

Rapid determination of atrazine in apple juice using molecularly imprinted polymers coupled with gold nanoparticles-colorimetric/SERS dual chemosensor.

Rapid and reliable determination of atrazine, a common chemical contaminant, in agri-foods is highly necessary. We reported a novel dual-chemosensor coupling, a separation [molecularly imprinted polymers (MIPs)], an instrumental-free detection [gold nanoparticles (AuNPs)-based colorimetric assay] and an instrument-based quantification [surface enhanced Raman spectroscopy (SERS)] method for high-throughput and sensitive determination of atrazine in apple juice. Used as the selective sorbent for the solid phase extraction, MIPs effectively extracted atrazine from apple juice with high recoveries (∼93%). AuNPs of different sizes (large; medium; and small) performed differently in the two analytical methods. Large-AuNPs provided the highest sensitivity in colorimetric analysis (<0.01 mg L-1), while medium-AuNPs achieved the lowest limit of detection (0.0012 mg L-1) and quantification (0.0040 mg L-1) in SERS analysis. With minor modifications, protocols for both analytical methods can rapidly detect and/or quantify atrazine in different food products complying with the Health Canada regulation (0.005 mg L-1).

Diagnosis of chronic kidney diseases based on surface-enhanced Raman spectroscopy and multivariate analysis

A simple and fast non-invasive diagnostic method based on surface-enhanced Raman spectroscopy (SERS) and multivariate analysis for diagnosis of chronic kidney diseases (CKD) is presented in this paper. Silver nanoparticles were utilized as the SERS substrate and mixed with the serum samples to enhance the Raman signals of various biomolecular in serum samples. SERS spectra were obtained from serum samples of normal subjects (n = 50) and CKD patients (n = 60). Principal component analysis and linear discriminate analysis were performed to classify the normal and CKD patients. Then, the training set database and the classification model were constructed. The classification model was further validated with the spectra of independent 10 normal subjects and 11 CKD patients serum samples with a sensitivity and specificity of 100%. These results establish that this non-invasive diagnostic method is able to directly diagnose CKD and has a significant potential in clinical diagnosis applications.

Rapid and Quantitative Determination of Soil Water-Soluble Nitrogen Based on Surface-Enhanced Raman Spectroscopy Analysis

An accurate and rapid determination of soil water-soluble nitrogen is conducive to scientific fertilization in precision agriculture. Surface-enhanced Raman spectroscopy (SERS) is a highly sensitive fingerprint with the advantages of simple operation and high detection efficiency. In this paper, partial least squares (PLS), principal components analysis (PCA), and least squares supports vector machine (LS-SVM) were applied to analyze the relationship between soil water-soluble nitrogen concentration and SERS. The results showed that the SERS-enhancing effect based on Opto Trace Raman 202 (OTR 202) was better than that of silver nanosubstrate and gold nanosubstrate. In addition, the prediction accuracy of soil water-soluble nitrogen in PLS was the highest ( R p 2 = 0.91 , RMSE p = 8.76 mg / L , R P D = 3.00 ) when the original spectra were preprocessed with first-derivative. Moreover, 1028, 1370, 1436, and 1636 cm−1 could be determined as characteristic peaks of soil water-soluble nitrogen, the association between soil water-soluble nitrogen concentration and a SERS intensity of 1370 cm−1 was the highest ( R p 2 = 0.94 ) , and the regression equation was y = 93.491x + 1771.5. Beyond that, the prediction accuracy of distinguishing between a low soil water-soluble nitrogen concentration (22.7–63.7 mg/L) and a high soil water-soluble nitrogen concentration (70.5–118.3 mg/L) based on PCA and LS-LVM was 86.67%. In conclusion, soil water-soluble nitrogen could be detected rapidly and quantitatively using SERS, which was beneficial to provide a rapid, accurate, and reliable scheme for scientific and precise fertilization.

Combining Multiplex SERS Nanovectors and Multivariate Analysis for In Situ Profiling of Circulating Tumor Cell Phenotype Using a Microfluidic Chip.

Isolating and in situ profiling the heterogeneous molecular phenotype of circulating tumor cells are of great significance for clinical cancer diagnosis and personalized therapy. Herein, an on-chip strategy is proposed that combines size-based microfluidic cell isolation with multiple spectrally orthogonal surface-enhanced Raman spectroscopy (SERS) analysis for in situ profiling of cell membrane proteins and identification of cancer subpopulations. With the developed microfluidic chip, tumor cells are sieved from blood on the basis of size discrepancy. To enable multiplex phenotypic analysis, three kinds of spectrally orthogonal SERS aptamer nanovectors are designed, providing individual cells with composite spectral signatures in accordance with surface protein expression. Next, to statistically demultiplex the complex SERS signature and profile the cellular proteomic phenotype, a revised classic least square algorithm is employed to obtain the 3D phenotypic information at single-cell resolution. Combined with categorization algorithm partial least square discriminate analysis, cells from different human breast cancer subtypes can be reliably classified with high sensitivity and selectivity. The results demonstrate that this platform can identify cancer subtypes with the spectral information correlated to the clinically relevant surface receptors, which holds great potential for clinical cancer diagnosis and precision medicine.

3D silver nanoparticles with multilayer graphene oxide as a spacer for surface enhanced Raman spectroscopy analysis

We report a three-dimensional (3D) SERS substrate with different numbers of silver nanoparticle (Ag NP) layers using multilayer graphene oxide (GO) as a spacer. The SERS performance of the 3D nanostructure was investigated and it was found that the SERS effect increased as the number of Ag NP layers increased, and showed almost no change for more than four layers. We found that the SERS performance of the 3D nanostructures can be mainly attributed to the topmost hot spots which are closely related to the Ag NP layers in the 3D nanostructure. Furthermore, we explored 3D nanostructures with different Ag NP layers using the finite difference time domain method (FDTD). The 3D SERS substrates also exhibit excellent detection capability. The limit of detection (LOD) was calculated down to 10-15 M for R6G and 10-12 M for CV. In addition, the reproducibility of the 3D SERS substrate was attributed obviously to the increasing number of Ag NP layers. Based on these promising results, the highly sensitive detection of molecules such as malachite green was demonstrated for food safety inspection.

SERS analyses of thiamethoxam assisted by Ag films and nanostructures produced by laser techniques

AbstractThis study deals with the use of laser techniques for preparation of advanced Ag nanostructure on quartz substrates that can be applied in high‐resolution analyses, namely, surface enhanced Raman spectroscopy (SERS). The active system was a two dimensional array of nanoparticles produced by laser annealing of thin silver film. The optical and morphological properties of the nanostructure were compared with those of an as deposited thin film in order to estimate their role in the detection efficiency. The activity of the structures fabricated as substrates for SERS of usually applied in agricultural medicine small quantities of Aktara 25 BG (thiamethoxam) insecticide was tested. To the best of our knowledge, SERS spectra of Aktara 25 BG are presented for the first time. The minimum detected concentration of thiamethoxam was evaluated to be in the order of μg/ml. The simple fabrication method and demonstrated efficiency focus the presented study to direct bearing on the human health and food quality area as a way of assisting the detection of small amounts or residue of harmful pollutants.

Measurement of engineered nanoparticles in consumer products by surface-enhanced Raman spectroscopy and neutron activation analysis

There has been an increasing number of consumer and food products sold on the market that contain various engineered nanomaterials (ENMs) such as silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs). These nanomaterials possess novel physical and chemical properties that can be used for wide applications in agriculture and food safety. However, current analytical methods to detect and measure ENMs are time-consuming, labor-intensive, and expensive. The objective of this study was to develop a novel, simple, rapid, and accurate method to detect AgNPs and AuNPs in consumer products using surface-enhanced Raman spectroscopy (SERS). SERS measurement was conducted to detect AgNPs and AuNPs using an effective Raman indicator, 4-aminothiophenol (pATP). The pATP can strongly bind onto nanoparticles, generating greatly enhanced Raman signals that can be used for measurement. The pATP was combined with Ag or Au stock solution, AgNO3, citrate-coated AgNPs, citrate-coated AuNPs, AuCl, AgNPs, AuNPs, and five commercial products to study the differences in their SERS spectral data. The observed spectra of AgNPs and AuNPs have similar peaks at ~ 390, ~ 1087, and ~ 1590 cm−1 that can be attributed to the C–S stretching vibration, C–C stretching vibration, and C–H stretching vibration, respectively. Neutron activation analysis (NAA) and electron microscopy was used to characterize and quantify AgNPs and AuNPs in the consumer products. The results demonstrate that SERS method in combination with NAA can be an effective method for detection of ENMs, and it can easily distinguish AgNPs and AuNPs from other non-nanoparticle species in the complex matrices.

Fast and non-invasive serum detection technology based on surface-enhanced Raman spectroscopy and multivariate statistical analysis for liver disease

This study explored a rapid and nondestructive liver disease detection technique based on surface-enhanced Raman spectroscopy (SERS) to realize the early diagnosis, prevention, and treatment of liver disease. SERS signals of serum were obtained from 304 normal individuals, 333 patients with hepatopathy, and 99 patients with esophageal cancer. The Raman spectra of different diseases were compared and diagnostic models of liver disease were established using orthogonal partial least squares discriminant analysis (OPLS-DA). The classification efficiencies of the different models were comprehensively evaluated through the receiver operating characteristic (ROC) curve and ten-fold cross validation. Area under the ROC curve is of greater than 0.97, indicating excellent classification of the groups. The accuracy rate of the test set reached 95.33%, and the lowest was 81.76% using the ten-fold cross validation. Thus, OPLS-DA combined with serum SERS is a rapid and non-invasive technique for the diagnosis of liver disease.

Different number of silver nanoparticles layers for surface enhanced raman spectroscopy analysis

For application in practice, reducing the cost and simplifying the steps in fabrication of SERS substrates with excellent property are still the important factors. Here, a three-dimensional (3D) Ag nanoparticles (NPs) obtained by facile thermal evaporation is obtained for SERS. The Raman enhancement effect gradually become strong as the number of Ag NPs layers increase and attain the best until four layers Ag NPs deposited for the finite penetration depth of incident laser. The intensity of Raman signal collected from the four-layer Ag NPs substrate is around 11.3 times stronger than that from one-layer Ag NPs. Besides, the reproducibility of the SERS substrate was also significantly promoted as the layers of Ag NPs increases. The SERS substrate exhibits temporal stability and its enhancement factor attains 6.8×108. Furthermore, the SERS substrate can easily combine with some other blocks with superior SERS property and show better SERS ability. Additionally, the in-situ trace analyses in aquatic products were realized by flexible Ag NPs/PET substrate.

Silver nanoparticles from leafy green extract of Belgian endive (Cichorium intybus L. var. sativus): Biosynthesis, characterization, and antibacterial activity

We report for the first time a green, simple, and low-cost synthesis of silver nanoparticles (AgNPs) by mixing AgNO3 solution with the aqueous leaf extract of Belgian endive, a variety of Cichorium intybus L., without any harmful reducing and capping agents. The biosynthesis of AgNPs was observed by the color charge from colorless (metal salt solution) to a yellowish brown (nanoparticle colloidal dispersion), which was confirmed by UV–vis spectroscopy, transmission electron microscopy (TEM), and X-ray diffraction (XRD). UV–vis spectra showed the surface plasmon resonance signature of AgNPs around 420nm, TEM revealed that nanoparticles were quasi-spherical with an average diameter ranging from 19 to 64nm depending on the metal salt concentration, and XRD pattern indicated that the biosynthetic process produced face-centered cubic AgNPs. Surface-enhanced Raman spectroscopy analysis showed that the AgNPs were capped with bioactive molecules from the leaf extract, which are also believed to be responsible for the bio-reduction of silver ions. The antibacterial activity of the biosynthesized AgNPs was studied using both the disk diffusion and minimum inhibitory concentration methods against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa, and they were found to be effective at picomolar concentration levels.

Potential targetability of multi-walled carbon nanotube loaded with silver nanoparticles photosynthesized from Ocimum tenuiflorum (tulsi extract) in fertility diagnosis

Nanocarrier mediated targeted delivery and biosensing in reproductive health care is a major exploratory domain. This work demonstrates the loading of silver nanoparticle (AgNP) inside the multiwalled carbon nanotube (MWCNT) and their targetability to the intracellular part of the sperm cell for its further application in biosensing based infertility diagnosis. Ocimum tenuiflorum (tulsi extract) mediated photosynthesized AgNP exhibited spherical shape, 5–40 nm size and surface plasmonic resonance at 430 nm. After loading of freshly prepared AgNP into emulsified MWCNT, the loading was confirmed with spectroscopic and microscopic methods. FTIR analysis displayed significant shifting at 3450 cm−1 (–OH stretching) and 1615 cm−1 (CNT back bone) which validated the binding of AgNP with MWCNT and interestingly heat flow analysis revealed that Ag loaded MWCNT has greater stability than AgNP. Moreover, AFM based surface profile height analysis clearly showed the loading of AgNP inside MWCNT as surface height of MWCNT increased from 22 to 32 nm, which in turn confirmed the encapsulation of 10 nm size of AgNP inside the tube. Furthermore, surface enhanced Raman spectroscopy (SERS) confirmed the homogeneous loading as there were no changes in D/G ratio. SERS analysis for the interaction of AgNP loaded MWCNT with freshly collected healthy, motile human spermatozoa showed a significant Raman shift at 800–780 cm−1 (NH2+ twist) and 1050–1060 cm−1 (vas PO3−) for change in DNA packaging process and its stabilizing protein polyamine respectively. Finally, DNA fragmentation and morphological examination confirmed the binding and targetability of AgNP to the sperm nucleus. Improved targeting efficiency and biosenssing ability make AgNP-MWCNT composite suitable in fertility diagnosis.