Surface-enhanced Raman Scattering Bands Research Articles

Detection of surface enhanced Raman scattering active hotspot using near field scanning optical microscopy

Hotspots are high-intensity electromagnetic zones that form, for example, at the interstitials of plasmonic nanoaggregates, resulting in a considerable rise in the enhancement factor. However, it is inevitable to achieve specific nanometric geometry as well as a suitable technique to capture the details of hotspots. We report near-field surface-enhanced Raman scattering (SERS) spectroscopy of a well-defined gold nanoaggregate of a few nanoparticles adsorbed with a small number of target analytes. A spectrally and spatially resolved SERS measurement setup using an aperture near-field scanning optical microscope (a-NSOM) facilitated the direct observation of localized electromagnetic (EM) fields at the interstitials through SERS. Correlated optical image and corresponding nanometric geometry were captured through the home-built a-NSOM setup. Near-field SERS spectra were recorded at different sites of interest. It was evident that the interstitial positioned at the center of the tetramer provided the most intense Raman scattering, implying the possibility of a SERS-active hotspot therein. SERS bands of the spectrum of the Raman-active dye Rhodamine 6G recorded at the same hotspot coincided well with those reported so far. It was noteworthy that most of the SERS bands in such scenery got enhanced. Such direct observation with high spatial resolution is indispensable to understanding the origin of localized EM fields at “hotspots” and the EM enhancement factor in the SERS process. A finite-difference time-domain (FDTD) analysis was carried out to validate the results.

SERS probing of fungal HET-s fibrils formed at neutral and acidic pH conditions

Advances in precision medical diagnostics require accurate and sensitive characterization of pathogens. In particular, health conditions associated with protein misfolding require an identification of proteinaceous amyloid fibrils or their precursors. These pathogenic entities express specific molecular structures, which require ultra-sensitive, molecular-level detection methods. A potentially transformative technique termed nanoplasmonics employs electro-optical phenomena in the vicinity of specially engineered metal nanostructures. A signature application of nanoplasmonics exploits enhancement of inelastic scattering of light in specific locations near metallic nanostructures, known as surface-enhanced Raman scattering (SERS). We applied SERS complemented with confocal microscopy imaging for ultra-sensitive, non-invasive, and label-free characterization of the fungal prion HET-s (218–289) as a model for β-sheet rich amyloid structures. This characterization employed Au-coated dielectric supports as plasmonic substrates. After confirming the formation of HET-s fibrils at both pH 7.5 and 2.8 using negative staining transmission electron microscopy, we subjected the fibril-containing solutions to multimodal analysis using confocal microscopy and SERS. The SERS spectral fingerprints from all HET-s samples expressed vibrational markers for β-structure, unstructured backbone, and aromatic side-chains. However, relative intensities of major SERS bands were pronouncedly different for the two pH levels. We have analyzed potential origins of the most pronounced SERS bands and proposed hypothetical mechanistic models that could explain the observed SERS fingerprints from HET-s fibrils grown at pH 7.5 and 2.8.

Voltage tuning of photoinduced charge transfer resonances between 2,2′-bipyridine and a nanostructured silver electrode

The effect of applied electric potentials and excitation wavelengths (785, 532, 473 nm) on the Surface-Enhanced Raman scattering (SERS) of 2,2′-bipyridine (2,2′-bpy) adsorbed on a silver electrode has been analyzed on the basis of a charge transfer (CT) resonance mechanism. DFT/TD-DFT calculations performed for a simple model of surface complex (Ag2-2,2′-bpy) point out that 2,2′-bpy preferably adsorbs through both nitrogen atoms in a cis-conformation with edge-on orientation. The calculated spectra in resonance with the two first bright metal-to-molecule charge transfer electronic states (CT0;B1 and CT1;B1) account for the main experimental features: the selective enhancement of the totally symmetric modes recorded at about 1585, 1560 and 1480 cm−1 under 532 nm line, staying the 1560 cm−1 band as the most intense under 473 nm line at more negative electrode potential. The split of SERS bands recorded in the 1600, 1000 and 600 cm−1 regions point to the existence of a monodentate coordination of the cis-conformer. The calculated resonance condition up to CT0 and CT1 states is fulfilled under 532 and 488 nm excitation lines, respectively, agreeing with the behaviour of the intensity-potential profile of the bands for each excitation wavelength.

Intracellular metabolic profiling of drug resistant cells by surface enhanced Raman scattering

BackgroundIntracellular metabolic profiling reveals real-time metabolic information useful for the study of underlying mechanisms of cells in particular conditions such as drug resistance. However, mass spectrometry (MS), one of the leading metabolomics technologies, usually requires a large number of cells and complex pretreatments. Surface enhanced Raman scattering (SERS) has an ultrahigh detection sensitivity and specificity, favorable for metabolomics analysis. However, some targeted SERS methods focus on very limited metabolite without global bioprofiling, and some label-free approaches try to fingerprint the metabolic response based on whole SERS spectral classification, but comprehensive interpretation of biological mechanisms was lacking. (95) ResultsWe proposed a label-free SERS technique for intracellular metabolic profiling in complex cellular lysates within 3 min. We first compared three kinds of cellular lysis methods and sonication lysis shows the highest extraction efficiency of metabolites. To obtain comprehensive metabolic information, we collected a spectral set for each sample and further qualified them by the Pearson correlation coefficient (PCC) to calculate how many spectra should be acquired at least to gain the adequate information from a statistical and global view. In addition, according to our measurements with 10 pure metabolites, we can understand the spectra acquired from complex cellular lysates of different cell lines more precisely. Finally, we further disclosed the variations of 22 SERS bands in enzalutamide-resistant prostate cancer cells and some are associated with the androgen receptor signaling activity and the methionine salvage pathway in the drug resistance process, which shows the same metabolic trends as MS. (149) SignificanceOur technique has the capability to capture the intracellular metabolic fingerprinting with the optimized lysis approach and spectral set collection, showing high potential in rapid, sensitive and global metabolic profiling in complex biosamples and clinical liquid biopsy. This gives a new perspective to the study of SERS in insightful understanding of relevant biological mechanisms. (54).

One-Pot Synthesis of Silica-Coated Gold Nanostructures Loaded with Cyanine 5.5 for Cell Imaging by SERS Spectroscopy

Anisotropic gold nanoparticles have been recognized as promising agents for medical diagnostics and cancer therapy due to their wide functionality, photothermal effect, and ability for optical signal amplification in the near-infrared range. In this work, a simple and rapid method for the preparation of bone-shaped gold nanoparticles coated with a dye-impregnated silica shell with an aminated surface is proposed. The possibility of further functionalization the nanostructures with a delivery vector using folic acid as an example is demonstrated. The average size of the resulting tags does not exceed 70 nm, meeting the criteria of cell endocytosis. The prepared tags exhibit surface-enhanced Raman scattering (SERS) spectra at excitation with lasers of 632.8 and 785 nm. Cell imaging is performed on HeLa cells based on the most pronounced SERS bands as a tracking signal. The obtained images, along with scanning electron microscopy of cell samples, revealed the tendency of tags to agglomerate during endocytosis followed by the "hot spots" effect. To evaluate the toxic and proliferative effect of the nanotags, an MTT assay was performed with two HeLa and HEP G2 cell lines. The results revealed higher viability for HEP G2 cells.

Challenges in surface-enhanced Raman scattering detection of pesticide carbendazim and ways to overcome

Considerable details in the sampling procedure for the detection of the pesticide carbendazim by surface-enhanced Raman scattering (SERS) were developed. Experimental parameters and recommendations were selected to minimize side processes of carbendazim photodestruction as well as to reduce the background signal from the silver substrate. It was found from the comparison of experimental and density functional theory calculations data that the position of the SERS bands in the carbendazim spectrum depends on the nature of the applied solvent due to different orientations of carbendazim with respect to the surface of silver nanoparticle film. Adsorption from a chloroform solution is preferable to form an aqueous solution for SERS because random adsorption of molecules on a silver surface provides robust carbendazim identification, displaying a larger number of bands in the SERS spectrum, a higher “signal-to-noise” ratio, and then the processes of carbendazim photodestruction slow down.

Study of Charge Transfer Contribution to Surface-Enhanced Raman Scattering Activity of Cu\(_2\)O Nano-octahedral Substrate

In this study, a surface-enhanced Raman scattering (SERS) substrate based on an octahedral cuprous oxide (Cu2O) nanostructure to probe methylene blue (MB) molecules as an analyte chemical has been implemented. Octahedral Cu2O nanocrystals were synthesized by a novel hydrothermal process using only ethylene glycol as both a reductant and organic solvent. The characteristics of Cu2O nanocrystals were well recognized by scanning electron microscope (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), FTIR, and Raman spectroscopy. The mechanism of the SERS surface has been thoroughly investigated and has been shown to involve the contributions of both surface plasmon resonance and charge transfer effects. Using a simple collection rule for SERS bands, the portion of charge transfer processes was estimated to be about 46%.

Monodispersed silver-gold nanorods controllable etching for ultrasensitive SERS detection of hydrogen peroxide-involved metabolites

Hydrogen peroxide (H2O2)-involved metabolites are widely engaged in cellular metabolism, and play significant roles in cell proliferation, cell growth, and signaling transduction. It is highly desirable to establish a method for the detection of H2O2-involved metabolites for applications ranging from chemical sensing to biomedical diagnosis. Herein, monodispersed sandwich Au@4-MBN@Ag@PEG nanorods (referred to as AMPRs) with bright Raman emission were developed to serve as a universal platform for detecting H2O2-involved metabolites (4-mercaptobenzonitrile is abbreviated to 4-MBN as the Raman reporter and PEG is polyethylene glycol). The system detects metabolites through changes in the surface-enhanced Raman scattering (SERS) spectrum, resulting from the controllable etching of the silver layer by the H2O2 produced by the metabolites. The integrative nanoplatform was successfully used to quantify the levels of glucose, lactate, and choline in aqueous solutions by exploiting the close linear relationship between the intensity of a SERS band and the logarithmic concentration of H2O2. The presented SERS nanoplatform demonstrated considerable practicability for the detection of glucose in cerebrospinal fluid samples (with a limit of detection (LOD) of 1.76 μM), and was capable of distinguishing infected from uninfected individuals. Therefore, the SERS sensor provides a new platform for the detection of H2O2-involved metabolites in biological fluids, and has potential for use in metabolite analysis and biomedical diagnostics.

SERS Liquid Biopsy Profiling of Serum for the Diagnosis of Kidney Cancer.

Renal cancer (RC) represents 3% of all cancers, with a 2% annual increase in incidence worldwide, opening the discussion about the need for screening. However, no established screening tool currently exists for RC. To tackle this issue, we assessed surface-enhanced Raman scattering (SERS) profiling of serum as a liquid biopsy strategy to detect renal cell carcinoma (RCC), the most prevalent histologic subtype of RC. Thus, serum samples were collected from 23 patients with RCC and 27 controls (CTRL) presenting with a benign urological pathology such as lithiasis or benign prostatic hypertrophy. SERS profiling of deproteinized serum yielded SERS band spectra attributed mainly to purine metabolites, which exhibited higher intensities in the RCC group, and Raman bands of carotenoids, which exhibited lower intensities in the RCC group. Principal component analysis (PCA) of the SERS spectra showed a tendency for the unsupervised clustering of the two groups. Next, three machine learning algorithms (random forest, kNN, naïve Bayes) were implemented as supervised classification algorithms for achieving discrimination between the RCC and CTRL groups, yielding an AUC of 0.78 for random forest, 0.78 for kNN, and 0.76 for naïve Bayes (average AUC 0.77 ± 0.01). The present study highlights the potential of SERS liquid biopsy as a diagnostic and screening strategy for RCC. Further studies involving large cohorts and other urologic malignancies as controls are needed to validate the proposed SERS approach.

Ag-decorated polymer chip for the determination of the respective concentrations of TTD and Hg2+ by surface-enhanced raman scattering

A "hotspot"-rich Ag-nanoparticle-decorated three-dimensional polymer substrate was fabricated, exhibiting an excellent surface-enhanced Raman scattering (SERS) activity. 4-Mercaptobenzoic acid (MBA) was selected as a probe molecule for comparing the SERS activity on selected substrates. The proposed detection chip with the adsorption of tetramethylthiuram disulfide (TTD) shows an excellent sensitivity for the quantitative determination of TTD and mercury ions (Hg2+). This chip exhibited a high sensitivity for the trace detection of the targets. Interestingly, we found that the adsorbed TTD is selectively sensitive to Hg2+. The SERS band had a significant frequency shift of 11 cm-1 as the concentration of Hg2+ increased from 10-10 to 10-3 mol L-1. More importantly, the frequency shift of the SERS band exhibited an excellent linear relationship with the concentration of Hg2+, and the determination limit for Hg2+ was 10-10 mol L-1. Furthermore, the proposed detection chip shows great application potential for the determination of pesticides and Hg2+.

Novel Drug Carrier: 5-Fluorouracil Formulation in Nanoporous Biogenic Mg-calcite from Blue Crab Shells-Proof of Concept.

The ever-growing demand for novel, cheaper, and more effective drugs has put nanomedicine and targeted drug delivery to the forefront of scientific innovation. Owing to its porous three-dimensional (3D)-nanostructure and properties, the biogenic calcite from wasted blue crab shells is employed in the present work as a new drug carrier for 5-fluorouracil (5-FU), a drug widely used in cancer therapy. The drug solution has been loaded in the porous nanoarchitecture of the powdered biogenic material and further pelleted in tablets with a 5-FU concentration of 1.748 mg/g. Their structural and morphological properties were characterized using Raman, X-ray diffraction, and scanning electron microscopy. Confocal micro-Raman spectra of tablet surface showed a typical signal of biogenic carbonate with preserved carotenoids and carotenoproteins found in the native waste shell, while the drug Raman signal was absent, indicating its adsorption in the intricate nanoporous biogenic carrier. The slow release of the drug from the newly formulated tablet was investigated by tracking the surface-enhanced Raman scattering (SERS) signal of the tablet solution in a series of time-dependent experiments. The SERS signal quantification is achieved using the well-known SERS spectral fingerprint of 5-fluorouracil aqueous solution adsorbed on Ag nanoparticles. The proof of concept is demonstrated by quantifying the slow release of the drug through the characteristic SERS band intensity of 5-FU in a time course of 26 h. This proof of concept boosted further investigations concerning the released drug identity in simulated solutions that mimic the pH of the upper- and lower gastrointestinal tract, as well as the multiple possibilities to control porosity and composition during powdering and treatment of biogenic material, to achieve the most convenient formulation for relevant biomedical drug delivery. Nonetheless, the present results showed great promise for innovative reusing waste biogenic 3D-nanomaterials of aquatic origin as advantageous drug carriers for slow release purposes, in line with the concept of blue bioeconomy.

SERS-Based Evaluation of the DNA Methylation Pattern Associated With Progression in Clonal Leukemogenesis of Down Syndrome.

Here we show that surface-enhanced Raman scattering (SERS) analysis captures the relative hypomethylation of DNA from patients with acute leukemia associated with Down syndrome (AL-DS) compared with patients diagnosed with transient leukemia associated with Down syndrome (TL-DS), an information inferred from the area under the SERS band at 1005 cm–1 attributed to 5-methycytosine. The receiver operating characteristic (ROC) analysis of the area under the SERS band at 1005 cm–1 yielded an area under the curve (AUC) of 0.77 in differentiating between the AL-DS and TL-DS groups. In addition, we showed that DNA from patients with non-DS myeloproliferative neoplasm (non-DS-MPN) is hypomethylated compared to non-DS-AL, the area under the SERS band at 1005 cm–1 yielding an AUC of 0.78 in separating between non-DS-MPN and non-DS-AL. Overall, in this study, the area of the 1005 cm–1 DNA SERS marker band shows a stepwise decrease in DNA global methylation as cells progress from a pre-leukemia to a full-blown acute leukemia, highlighting thus the potential of SERS as an emerging method of analyzing the methylation landscape of DNA in the context of leukemia genesis and progression.

SERS-based DNA methylation profiling allows the differential diagnosis of malignant lymphadenopathy

This study highlights the potential of surface-enhanced Raman scattering (SERS) to differentiate between B-cell lymphoma (BCL), T-cell lymphoma (TCL), lymph node metastasis of melanoma (Met) and control (Ctr) samples based on the specific SERS signal of DNA extracted from lymph node tissue biopsy. Differences in the methylation profiles as well as the specific interaction of malignant and non-malignant DNA with the metal nanostructure are captured in specific variations of the band at 1005 cm−1, attributed to 5-methylcytosine and the band at 730 cm−1, attributed to adenine. Thus, using the area ratio of these two SERS marker bands as input for univariate classification, an area under the curve (AUC) of 0.70 was achieved in differentiating between malignant and non-malignant DNA. In addition, DNA from the BCL and TCL groups exhibited differences in the area of the SERS band at 730 cm−1, yielding an AUC of 0.84 in differentiating between these two lymphadenopathies. Lastly, using multivariate data analysis techniques, an overall accuracy of 94.7% was achieved in the differential diagnosis between the BCL, TCL, Met and Ctr groups. These results pave the way towards the implementation of SERS as a novel tool in the clinical setting for improving the diagnosis of malignant lymphadenopathy.

DFT, SERS-concentration and solvent dependent and docking studies of a bioactive benzenesulfonamide derivative

Spectroscopic analysis, DFT studies and surface enhanced Raman scattering (SERS) of antimicrobial bioactive 4-[(5-tert-butyl)2-hydroxybenzylidene]amino-N-(4,6-dimethylpyrimidin-2-yl)benzenesulfonamide (THPB) have been studied on different silver sols. Intensity and hence enhancement variations are observed for Raman and SERS bands. Observed changes in the ring modes may be due to surface π-electron interactions and presence of this indicated that molecule is inclined with respect to the metal surface. Changes in orientation are seen in SERS spectra depending on concentration. The molecular docking results show that binding affinity and interactions with the receptors may be supporting evidence for further studies in design further THPB pharmaceutical applications. Reactivity properties are obtained from DFT analysis.

Label-Free Detecting of the Compaction and Decompaction of ctDNA Molecules Induced by Surfactants with SERS Based on a nanoPAA-ZnCl2-AuLs Solid Substrate.

DNA molecular compaction/decompaction is of great significance for the exploration of basic life processes, the research of biomedical and genetic engineering, and so forth. However, the detailed mechanism of DNA compaction/decompaction caused by surfactants remains an open and challenging problem that has not been fully solved so far. In this paper, a sort of novel solid substrate, nanoPAA-ZnCl2-AuLs, with good stability and high sensitivity, was prepared by a self-assembly method. Based on this substrate, the surface-enhanced Raman scattering (SERS) technology was employed to investigate characteristics of interactions between DNA molecules and surfactants at a single molecular level. SERS spectra of calf thymus DNA (ctDNA), cetyl trimethyl ammonium bromide (CTAB), and sodium dodecyl sulfate (SDS) with a concentration as low as 10–9 M, and SERS spectra of ctDNA–CTAB and ctDNA–CTAB–SDS composites were collected, respectively. The interactions between ctDNA and surfactants were analyzed by changes in SERS spectra, for example, disappearances and appearances of SERS bands and relative changes of peak intensity, in which CTAB resulted in the compaction of the DNA molecule while SDS induced the decompaction of the ctDNA–CTAB complex. Moreover, UV–visible spectrophotometry was employed to demonstrate the compaction/decompaction of ctDNA molecules caused by surfactants. The local binding modes of ctDNA molecules and surfactant molecules were expounded. This work will be helpful for understanding biological processes such as DNA compaction and recombination within nucleus or/and cells and for the development of gene therapy technologies.

Intramolecular and Metal-to-Molecule Charge Transfer Electronic Resonances in the Surface-Enhanced Raman Scattering of 1,4-Bis((E)-2-(pyridin-4-yl)vinyl)naphthalene.

Electrochemical surface-enhanced Raman scattering (SERS) of the cruciform system 1,4-bis((E)-2-(pyridin-4-yl)vinyl)naphthalene (bpyvn) was recorded on nanostructured silver surfaces at different electrode potentials by using excitation laser lines of 785 and 514.5 nm. SERS relative intensities were analyzed on the basis of the resonance Raman vibronic theory with the help of DFT calculations. The comparison between the experimental and the computed resonance Raman spectra calculated for the first five electronic states of the Ag2-bpyvn surface complex model points out that the selective enhancement of the SERS band recorded at about 1600 cm−1, under 785 nm excitation, is due to a resonant Raman process involving a photoexcited metal-to-molecule charge transfer state of the complex, while the enhancement of the 1570 cm−1 band using 514.5 nm excitation is due to an intramolecular π→π* electronic transition localized in the naphthalenyl framework, resulting in a case of surface-enhanced resonance Raman spectrum (SERRS). Thus, the enhancement of the SERS bands of bpyvn is controlled by a general chemical enhancement mechanism in which different resonance processes of the overall electronic structure of the metal-molecule system are involved.

SERS determination of the antihypertensive drugs prazosin and losartan by using silver nanoparticles coated with β-cyclodextrin.

A surface-enhanced Raman scattering (SERS) method is described for the determination of prazosin (PRH) and losartan (LOS). Silver nanoparticles modified with β-cyclodextrin (CD-S-Ag NPs) were prepared and serve as a sensitive SERS substrate. β-CD is both a reductant for silver ions and a host molecule that binds the analytes which leads to strong SERS enhancement. The method has distinct features: (a) The linear response extends from 0.1 to 60μM for PRH, and from 1.0 to 100μM for LOS; (b) the respective limits of detection are as low as 15nM and 0.92μM; and (c) the specific SERS bands of PRH and LOS are located at 703 and 1298cm-1 respectively. The method was successfully applied to the determination of PRH and LOS illegally added to healthcare products. The recovery of PRH and LOS from spiked samples ranges between 91.3 and 109.3%, and from 87.4 to 105.2%, respectively, both with relative standard deviation of <5%. Graphical abstractSchematic representation of a SERS method involving β-CD-S-Ag nanoparticles for determination of prazosin and losartan via formation of an inclusion complex.

Simultaneous Detection of Intracellular Nitric Oxide and Peroxynitrite by a Surface-Enhanced Raman Scattering Nanosensor with Dual Reactivity

A functional surface-enhanced Raman scattering (SERS) nanosensor which can simultaneously detect nitric oxide (NO) and peroxynitrite (ONOO-) in living cells is explored. The SERS nanosensor is fabricated through modifying gold nanoparticles (AuNPs) with newly synthesized 3,4-diaminophenylboronic acid pinacol ester (DAPBAP), which has two reactive groups. The simultaneous detection achieved in this work is not only because of the SERS spectral changes of the nanosensor resulting from the dual reactivity of DAPBAP on AuNPs with NO and ONOO- but also by the narrow SERS bands suitable for multiplex detection. Owing to the combination of SERS fingerprinting information and chemical reaction specificity, the nanosensor has great selectivity for NO and ONOO-, respectively. In addition, the nanosensor has a wide linearity range from 0 to 1.0 × 10-4 M with a submicromolar sensitivity. More importantly, simultaneous monitoring of NO and ONOO- in the Raw264.7 cells has been fulfilled by this functional nanosensor, which shows that the SERS strategy will be promising in comprehension of the physiological issues related with NO and ONOO-.

Spectroscopic, DFT and trace detection study of procaine using surface-enhanced Raman scattering technique

Spectroscopic trace-level detections (as low as 1 × 10−11 M) of procaine using surface-enhanced Raman scattering (SERS) technique and utilizing silver nanoparticle (Ag-Np) substrates were successfully accomplished. Significant intensity enhancements of the Raman bands associated with CO stretching, CN stretching and NH2 bending vibrations were observed. Possible modes of SERS interaction between the procaine molecule and Ag-Np were investigated theoretically, and the results were found consistent with experimental data. The intensities of SERS band at 1607 cm−1 were successfully correlated with the concentrations of procaine solutions. The present approach exhibits a high sensitivity and low limit of detection.

A calcium alginate sponge with embedded gold nanoparticles as a flexible SERS substrate for direct analysis of pollutant dyes.

A surface-enhanced Raman scattering (SERS) substrate with good flexibility and high water absorbing capacity is reported. It consists of a calcium alginate sponge incorporating gold nanoparticles. These are in close contactwith thesponge without the need for amino or sulfhydryl modification. The substrate is capable of detecting the dyes crystal violet (CV) and malachite green (MG) in water directly and rapidly by immersing it into the liquid sample. Preconcentration and separation are not required. The dyes absorbed on the sponge can be detected without drying and thus the whole analytical process can be completed within 3min. The results show that the lowest detectable concentrations are 0.1 and 0.25μg⋅L-1 for CV and MG, respectively. This is lower than the minimum required performance limits set by the European Commission and the US EPA. Moreover, MG and CV can be simultaneously detected in liquid samples due to their different SERS bands (at 1216 and 1534cm-1, respectively). It should be noted that the molecular structures of MG and CV are very similar. Therefore, the method has a large potential for determination of several analytes simultaneously even in complex sample metrics. Graphical abstract Schematic presentation of the fabrication ofa sodium alginate sponge loaded with gold nanoparticles. Gold nanoparticles together with gel-like alginate were freeze-dried to form the sponge. The sponge was cross-linked by CaCl2 solution and then it was freeze-dried again.