Reaction pathway change on plasmonic Au nanoparticles studied by surface-enhanced Raman spectroscopy

Gold nanoparticles (Au NPs) are nanoscale sources of light and electrons, which are highly relevant for their extensive applications in the field of photocatalysis. Although a number of research works have been carried out on chemical reactions accelerated by the energetic hot electrons/holes, the possibility of reaction pathway change on the plasmonic Au surfaces has not been reported so far. In this proof-of-concept study, we find that Au NPs change the reaction pathway in photooxidation of alkyne under visible light irradiation. This reaction produces benzil (COCO) without the presence of Au NPs. In contrast, as indicated by surface-enhanced Raman spectroscopic (SERS) results, the CC triple bonds (CC) adsorbed on Au NPs are converted into carboxyl (COOH) and acyl chloride (COCl) groups. The plasmonic Au NPs not only provide energetic charge carriers but also activate the reactant molecules as conventional heterogeneous catalysts. This study discloses the second role of plasmonic NPs in photocatalysis and bridges the gap between plasmon-driven and conventional heterogeneous catalysis.     

Determination of primary aromatic amines using immobilized nanoparticles based surface-enhanced Raman spectroscopy

Primary aromatic amines(PAAs) are substances with toxicity and suspected human carcinogenicity. A facile method for highly sensitive detection of PAAs using surface-enhanced Raman spectroscopy(SERS)is reported. The immobilization of Au nanoparticles(AuNPs) on the glycidyl methacrylate–ethylene dimethacrylate(GMA-EDMA) materials makes the substrate a closely packed but not aggregated AuNP arrays which provides a prominent SERS enhancement. Four PAAs with different substituent groups,namely, p-toluidine, p-nitroaniline, benzidine and 4,4-methylene-bis-(2-chloroaniline) have been successfully identified and quantified. High sensitivity and good linear relationship between SERS signals and concentrations of PAAs are obtained for all four PAAs.     

Silver–platinum core–shell nanoparticles for surface-enhanced Raman spectroscopy

Core–shell Ag@Pt nanoparticles have been synthesised by the means of seed-growth reaction including reduction of PtCl₄²⁻ with silver and replacing Ag atoms with Pt. Surface-enhanced Raman scattering (SERS) spectra of pyridine (which gives slightly different spectra when interacting with various metals) adsorbed on synthesised Ag@Pt clusters were measured. SERS measurements have revealed that deposition of the platinum layer causes near elimination of the spectral interferences from pyridine directly interacting with the silver core. The average SERS enhancement factor for pyridine adsorbed on the Ag@Pt clusters was estimated as equal to about 10³–10⁴, significantly higher than the SERS enhancement factor achievable on the pure platinum nanostructures. Using the silver core (instead of the previously used gold cores) allows for measurement of strong SERS spectra on the Pt covered nanostructures for the wider range of the excitation radiation. This procedure of platinum deposition was tested with various silver nanoparticles – produced with borohydride, citrate and citrate/borohydride methods – which substantially differ in size distribution. The application of formed Ag@Pt structures for obtaining intense Raman spectra for molecules adsorbed on only slightly modified platinum surfaces is discussed.     

Advances in surface-enhanced Raman spectroscopy for analysis of pharmaceuticals: A review

Recently, Raman spectroscopy become a popular and potential analytical technique for the analysis of pharmaceuticals as a result of its advancement. The innovation of laser technology, Fourier Transform-Raman spectrometers with charge coupled device (CCD) detectors, ease of sample preparation and handling, mitigation of sub-sampling problems using different geometric laser irradiance patterns and invention of different optical components of Raman spectrometers are contributors of the advancement of Raman spectroscopy. Transmission Raman Spectroscopy is a useful tool in pharmaceutical analysis to address the problems related with sub-sampling in conventional Raman back scattering. More importantly, the development of surface-enhanced Raman scattering (SERS) has been a prominent advancement for Raman spectroscopy to be applied for pharmaceuticals analysis as it avoids the inherent insensitivity and fluorescence problems. As the active pharmaceutical ingredients (APIs) contain aromatic or conjugated domains with strong Raman scattering activity, Raman spectroscopy is an attractive alternative conventional analytical method for pharmaceuticals. Coupling of Raman spectroscopy with separation techniques is also another advancement applied to reduce or avoid possible spectral interferences. Therefore, in this review, transmission Raman spectroscopy, SERS, and SERS coupled with various separation techniques for pharmaceutical analysis are presented.     

Extremely sensitive sandwich assay of kanamycin using surface-enhanced Raman scattering of 2-mercaptobenzothiazole labeled gold@silver nanoparticles

Herein, we report the development of extremely sensitive sandwich assay of kanamycin using a combination of anti-kanamycin functionalized hybrid magnetic (Fe₃O₄) nanoparticles (MNPs) and 2-mercaptobenzothiazole labeled Au-core@Ag-shell nanoparticles as the recognition and surface-enhanced Raman scattering (SERS) substrate, respectively. The hybrid MNPs were first prepared via surface-mediated RAFT polymerization of N-acryloyl-l-glutamic acid in the presence of 2-(butylsulfanylcarbonylthiolsulfanyl) propionic acid-modified MNPs as a RAFT agent and then biofunctionalized with anti-kanamycin, which are both specific for kanamycin and can be collected via a simple magnet. After separating kanamycin from the sample matrix, they were sandwiched with the SERS substrate. According to our experimental results, the limit of detection (LOD) was determined to be 2 pg mL⁻¹, this value being about 3–7 times more than sensitive than the LOD of previously reported results, which can be explained by the higher SERS activity of silver coated gold nanoparticles. The analysis time took less than 10 min, including washing and optical detection steps. Furthermore, the sandwich assay was evaluated for investigating the kanamycin specificity on neomycin, gentamycin and streptomycin and detecting kanamycin in artificially contaminated milk.     

Biocompatible core-shell nanoparticle-based surface-enhanced Raman scattering probes for detection of DNA related to HIV gene using silica-coated magnetic nanoparticles as separation tools

A novel, highly selective DNA hybridization assay has been developed based on surface-enhanced Raman scattering (SERS) for DNA sequences related to HIV. This strategy employs the Ag/SiO₂ core-shell nanoparticle-based Raman tags and the amino group modified silica-coated magnetic nanoparticles as immobilization matrix and separation tool. The hybridization reaction was performed between Raman tags functionalized with 3′-amino-labeled oligonucleotides as detection probes and the amino group modified silica-coated magnetic nanoparticles functionalized with 5′-amino-labeled oligonucleotides as capture probes. The Raman spectra of Raman tags can be used to monitor the presence of target oligonucleotides. The utilization of silica-coated magnetic nanoparticles not only avoided time-consuming washing, but also amplified the signal of hybridization assay. Additionally, the results of control experiments show that no or very low signal would be obtained if the hybridization assay is conducted in the presence of DNA sequences other than complementary oligonucleotides related to HIV gene such as non-complementary oligonucleotides, four bases mismatch oligonucleotides, two bases mismatch oligonucleotides and even single base mismatch oligonucleotides. It was demonstrated that the method developed in this work has high selectivity and sensitivity for DNA detection related to HIV gene.     

Focused-ion-beam-fabricated Au nanorods coupled with Ag nanoparticles used as surface-enhanced Raman scattering-active substrate for analyzing trace melamine constituents in solution

A well-ordered Au-nanorod array with a controlled tip ring diameter (Au_NRs_d) was fabricated using the focused ion beam method. Au_NRs_d was then coupled with Ag nanoparticles (Ag NPs) to bridge the gaps among Au nanorods. The effect of surface-enhanced Raman scattering (SERS) on Au_NRs_d and Ag NPs/Au_NRs_d was particularly verified using crystal violet (CV) as the molecular probe. Raman intensity obtained from a characteristic peak of CV on Au_NRs_d was estimated by an enhancement factor of ≈10⁷ in magnitude, which increased ≈10¹² in magnitude for that on Ag NPs/Au_NRs_d. A highly SERS-active Ag NPs/Au_NRs_d was furthermore applied for the detection of melamine (MEL) at very low concentrations. Raman-active peaks of MEL (10⁻³ to 10⁻¹² M) in water or milk solution upon Au_NRs_d or Ag NPs/Au_NRs_d were well distinguished. The peaks at 680 and 702 cm⁻¹ for MEL molecules were found suitable to be used as the index for sensing low-concentration MEL in a varied solution, while that at 1051 cm⁻¹ was practical to interpret MEL molecules in water or milk solution bonded with Au (i.e., Au_NRs_d) or Ag (i.e., Ag NPs/Au_NRs_d) surface. At the interface of Ag NPs/Au_NRs_d and MEL molecules in milk solution, a laser-induced electromagnetic field or hotspot effect was produced and competent to sense low-concentration MEL molecules interacting with Ag and Au surfaces. Accordingly, Ag NPs/Au_NRs_d is very promising to be used as a fast and sensitive tool for screening MEL in complex matrices such as adulteration in e.g., food and pharmaceutical products.     

Cuttlebone-derived organic matrix as a scaffold for assembly of silver nanoparticles and application of the composite films in surface-enhanced Raman scattering

Biologically derived materials provide a rich variety of approaches toward new functional materials because of their fascinating structures and environment-friendly features, which is currently a topic of research interest. In this paper, we show that the cuttlebone-derived organic matrix (CDOM) is an excellent scaffold for the one-step synthesis and assembly of silver nanoparticles (AgNPs), which can be further used as substrate for surface-enhanced Raman scattering (SERS). Formation of AgNPs–CDOM composite was accomplished by the reaction of CDOM with AgNO₃ and NH₃·H₂O solution at 80 °C without using any other stabilizer and reducing agents. UV–vis spectra and TEM were utilized to characterize the AgNPs and investigate their formation process. Results demonstrate that the size and distribution of AgNPs can be partly regulated by changing incubation time; the concentration of NH₃·H₂O is critical to the formation rate of AgNPs. As a proof of principle, we show that the AgNPs–CDOM composite can be employed in trace analysis using SERS.     

Planar monolithic porous polymer layers functionalized with gold nanoparticles as large-area substrates for sensitive surface-enhanced Raman scattering sensing of bacteria

For the first time, large-area surface-enhanced Raman scattering sensing active substrates using porous polymer monolithic layers have been successfully prepared. Our approach includes a simple photoinitiated polymerization process using glycidyl methacrylate and ethylene dimethacrylate in a glass mold, followed by a chemical reaction of the epoxy functionalities leading to thiols, and the attachment of preformed gold nanoparticles. We demonstrated that this very simple process produced uniform and reproducible large area surfaces that significantly enhance sensitivity of Raman spectroscopy. Experiments were also carried out that confirmed preferential adsorption of living bacteria Escherichia coli from a very dilute solution on the surface of the monolithic layer, and immediate detection of the captured microorganisms using the SERS spectrum.     

One-pot synthesis of silver colloid with body-heat for surface-enhanced Raman spectroscopy detections

In this study, a convenient method of preparing the substrate is proposed with one-pot synthesis of silver colloid under body heat, and the SERS detection uses the fresh substrate to avoid the drawback of substrates' short life of use. The synthesis of silver colloid is carried out in a 10 mL vial by using ascorbic acid as a reductant and trisodium citrate as a stabilizer. The vial is grasped with the palm of the experimenter for several minutes without shaking. The proposed method is simple, rapid, green energy and cost-effective. By adjusting the concentration of trisodium citrate, not only the particle size can be controlled from about 110 nm to 50 nm but also the homogeneity of nanoparticles can be improved. As a SERS substrate, the silver colloid has high batch reproducibility and showed good SERS activity. The relative standard deviation between different manufacturers is 5.51% when the substrate of silver colloid is used for the detection of rhodamine 6 G. Using the substrate, the lowest detection concentrations of rhodamine 6 G, crystal violet, enrofloxacin, melamine and leucomalachite green are 1.0×10~(-8), 6.1×10~(-8),1.4 × 10~(-6), 7.1 ×10~(-5) and 5.1 ×10~(-8) mol/L, respectively. Results demonstrate that the developed method has the advantage of convenience and high efficiency in the field preparation of reliable SERS substrate.     

Substrates for the at-line coupling of capillary electrophoresis and surface-enhanced Raman spectroscopy

In this preliminary study, we evaluated four different types of substrate for the at-line coupling of capillary electrophoresis and surface-enhanced (resonance) Raman spectroscopy, CE-SER(R)S, with emphasis on spectral repeatability. We tested Sub1: etched silver foil, Sub2: a vapour-deposited silver film, Sub3: a silver oxalate-precoated silica TLC plate and Sub4: a silica TLC plate on which colloid and poly(l-lysine) were manually added to the analyte spots, used earlier in at-line CE-SE(R)RS. All substrates were first tested by manual spotting using trans-1,2-bis(4-pyridyl)ethylene (BPE) as a model compound for SERS and crystal violet (CV) as a model compound for SE(R)RS. The spectral features of the SE(R)RS spectra of BPE and CV showed a most satisfactory repeatability on all substrates. As expected, the signal intensities varied considerably between runs; this implies that quantification in at-line CE-SE(R)RS should rather be done by means of an on-line absorbance detector. In addition, the suitability of Sub1, Sub2 and Sub4 as deposition substrates after CE was explored using two cationic dyes: CV and basic fuchsin (BF). Good-quality SERRS spectra could be recorded on all three substrates. Although Sub1 and Sub2 have a poor water-sorptivity, they were found to be good substrates for at-line CE-SERRS. They do not require any post-deposition addition of silver colloid and could therefore become attractive alternatives for Sub4.     

Imaging the cell wall of living single yeast cells using surface-enhanced Raman spectroscopy

The surface of a living yeast cell (Saccharomyces cerevisiae strain W303-1A) has been labeled with silver (Ag) nanoparticles that can form nanoaggregates which have been shown to have surface-enhanced Raman scattering (SERS) activity. The cell wall of a single living yeast cell has been imaged by use of a Raman microspectroscope. The SERS spectra measured from different Ag nanoaggregates were found to be different. This can be explained on the basis of detailed spectral interpretation. The SERS spectral response originates from mannoproteins which cover the outermost regions of the yeast cell wall. Analysis of SERS spectra from the cell wall and the extracted mannoproteins from the yeast has been performed for the clarification of variation in SERS spectra.     

表面增强拉曼光谱在毒品检测中的应用进展

表面增强拉曼光谱(surfaced-enhanced Raman spectroscopy, SERS)作为一种借助贵金属纳米材料可以增强目标分子信号的拉曼光谱技术,由于其具有指纹识别、高灵敏、高准确度、快速无损、不受水分子干扰等特点,在法庭科学领域中的痕量毒品检测方面逐渐受到人们的关注.SERS不仅用于毒品纯品的检测...     

Vertical-flow paper SERS system for therapeutic drug monitoring of flucytosine in serum

A number of life-saving drugs require therapeutic drug monitoring (TDM) for safe and effective use. Currently, however, TDM is performed using sophisticated analytical techniques relegated to central labs, increasing the cost per test and time to answer. Here, using a novel vertical flow membrane system with inkjet-printed surface enhanced Raman sensors, along with a portable spectrometer, we demonstrate a low cost and easy to use device to quantify levels of flucytosine, an antifungal that requires TDM for effective patient care, from undiluted human serum. To our knowledge, this work represents the first report of a passive vertical flow sample cleanup method with surface enhanced Raman detection. We first investigated and optimized the parameters of the vertical flow system for the detection of flucytosine in spiked serum samples. Then, using an optimized vertical-flow system utilizing nitrocellulose membranes and a paper SERS sensor, we achieved detection of down to 10 μg mL⁻¹ flucytosine in undiluted serum, with quantitative detection across the entire therapeutic range. This system reduces the assay time to about 15 min, far quicker than the current gold standards. We anticipate that this novel system will enable near-patient therapeutic drug monitoring, leading to the safe and effective administration of a number of life-saving drugs. Furthermore, it will spawn the development of SERS detection systems capable of separating target analytes from real-world biological matrices.     

Surface-enhanced Raman scattering for perchlorate detection using cystamine-modified gold nanoparticles

Perchlorate (ClO₄⁻) has recently emerged as a widespread environmental contaminant found in groundwater and surface water, and there is a great need for rapid detection and monitoring of this contaminant. This study presents a new technique using cystamine-modified gold nanoparticles as a substrate for surface-enhanced Raman scattering (SERS) detection of perchlorate at low concentrations. A detection limit of 5 × 10⁻⁶ M (0.5 mg/L) has been achieved using this method without sample preconcentration. This result was attributed to a strong plasmon enhancement by gold metal surfaces and the electrostatic attraction of ClO₄⁻ onto positively charged, cystamine-modified gold nanoparticles at a low pH. The methodology also was found to be reproducible, quantitative, and not susceptible to significant interference from the presence of anions such as sulfate, phosphate, nitrate and chloride at concentrations <1 mM, making it potentially suitable for rapid screening and routine analysis of perchlorate in environmental samples.     

Enhanced Raman spectroscopy coupled to chemometrics for identification and quantification of acetylcholinesterase inhibitors

In this work, we present a new complete method using Surface Enhanced Raman Spectroscopy (SERS) and chemometrics for the qualitative and quantitative detection of pesticides by measuring the acetylcholinesterase (ACHE) activity. The Raman SERS is not only used for measuring the ACHE activity, but also for the direct detection of pesticides individually and for their identification. Gold nanoparticles (AuNPs) were used as dynamic SERS substrates for sensitive monitoring of ACHE activity in the presence of very low levels of organophosphate and carbamate pesticides, chemical warfare agents that are known to be ACHE inhibitors. The lowest detectable level for paraoxon was determined at 4.0 × 10⁻¹⁴ M and 1.9 × 10⁻⁹ M for carbaryl. The use of the enzyme allowed limits of detection for both pesticides that were much lower than the limits obtained by direct SERS analysis of the pesticides. The system shows a linear relationship between the intensity band at 639 cm⁻¹ and pesticide concentration. These results suggest that this biosensor could be used in the future for the non-selective detection of all ACHE inhibitors at very low concentrations with possible identification of the inhibitor.     

Photochemical decoration of silver nanoparticles on magnetic microspheres as substrates for the detection of adenine by surface-enhanced Raman scattering

In this work, silver nanoparticles (AgNPs) decorated magnetic microspheres (MMs) are prepared as surface-enhanced Raman scattering (SERS) substrate for the analysis of adenine in aqueous solutions. To prepare these substrates, magnetic particles were first synthesized by coprecipitation of Fe(II) and Fe(III) with ammonium hydroxide. A thin layer of cross-linked polymer was formed on these magnetic particles by polymerization through suspension of magnetic particles into a solution of divinyl benzene/methyl methacrylate. The resulted polymer protected magnetic particles are round in shape with a size of 80 μm in diameter. To form AgNPs on these MMs, photochemical reduction method was employed and the factors in photochemical reduction method were studied and optimized for the preparation of highly sensitive and stable AgNPs on MMs substrates (abbreviated as AgMMs substrates). By dispersing the AgMMs in aqueous samples, cylindrical magnet was used to attract the AgMMs for SERS detections. The observed enhancement factor of AgMMs reached 7 orders in magnitude for detection of adenine with a detection limit approaching to few hundreds of nanomolar.     

Coating of silver nanoparticles (AgNPs) on glass fibers by a chemical method as plasmonic surface-enhanced Raman spectroscopy (SERS) sensors to detect molecular vibrations of Doxorubicin (DOX) drug in blood plasma

In the present study, Doxorubicin (DOX) drug in healthy blood plasma was the focus of the investigation by surface-enhanced Raman scattering (SERS). In recent years, chemotherapy has been the most popular treatment for various types of cancer; however, its adverse side effects on the patient's health have made a negative aspect regarding the use of this technique. DOX is the most common chemotherapy drug and is used for the treatment of an extensive range of human malignancies. The surface-enhanced Raman scattering (SERS) is a precise technique for the detection of chemicals and biomaterials with significantly low concentrations. The glass fiber substrates coated with silver nanoparticles (AgNPs) have been used to detect DOX. First, the Tollens' method was applied to prepare the AgNPs, and the characteristics of fabricated AgNPs were evaluated using ultraviolet–visible spectroscopy (UV–Vis) and X-ray diffraction (XRD). Then, AgNPs were coated on the glass fiber substrate by a chemical method. Finally, the enhancement of the Raman signal resulted from the molecular vibrations of DOX was evaluated using these SERS-active substrates as plasmonic and Raman spectroscopy sensors. Afterward, for making the sensors practical, the DOX in blood plasma were deposited on the fabricated sensors, and the Raman vibrations were evaluated. The SERS-active substrates, AgNPs deposited on glass fiber substrates, were fabricated for the detection of DOX in and out of the blood plasma; the limit of detection (LOD) for both was 10^?10 M, and the mean relative standard deviation at concentrations of 10^?10 M of DOX out of blood plasma, and 10^?10 M of DOX in blood plasma were obtained to be 3.76% and 3.61%, respectively for ten repeated measurements in which the AgNPs were SERS-active substrates of the biosensors for detecting the DOX. In addition, the enhancement factor was calculated both experimentally and via finite-difference time-domain (FDTD) simulation, which was 29.76 × 10³ and 24.95 × 10³, respectively. Therefore, these SERS-active substrates can be used to develop microsensors and show positive results for SERS-based investigations.     

电化学原位表面增强拉曼光谱研究Au@Pd纳米粒子薄膜电极上吸附 CO的斯塔克效应

电化学 Stark效应是指电极溶液界面的吸附物或金属-吸附物之间的化学键的振动频率随电极电势而发生变化的现象.研究该效应,可以更好地理解吸附物与基底的相互作用(如吸附构型、吸附取向和覆盖度等随电位的变化),也可反过来推断电极基底的电子构型及其随电势的变化规律,对理解电化学双电层的结构以及电催化反应的构效关系都很有帮助.多年以来,电极表面吸附 CO的电化学 Stark效应广受关注,是由于 CO为很多小分子氧化的中间产物,研究 CO的谱学行为,可加深对 CO以及其它能产生 CO中间物有机小分子的电催化氧化机理和动力学的理解;另一方面, CO与过渡金属之间普遍存在s给电子以及p反馈电子作用,因此 CO也可作为探针分子,通过考察 COad以及 M–COad的振动频率的变化,可推断相应条件下基底的电子与几何结构等信息.
　　本文使用电化学原位表面增强拉曼技术,在一个大的电势范围内考察了 Au@Pd纳米粒子薄膜电极上饱和吸附 CO的振动光谱行为,以期更好地理解 COad与基底的成键作用与电极电势之间的关系.由于纯 Pd电极表面的拉曼信号太弱,实验使用具有核壳结构的 Au@Pd纳米粒子薄膜作为模型电极,并利用 Au核的拉曼增强特性.宽广的电势范围约–1.5到0.55V vs. NHE,通过使用酸性、中性以及碱性电解质得以实现.实验考察的电势上限由 COad氧化起始电位决定,而下限由强烈氢析干扰测量所限制.结果表明,在检测的电势范围内, C–OM(M指在电极表面的桥式吸附CO和穴位吸附 CO所形成的谱带重叠)和 Pd–COM键的振动频率可以分为三段： dνC–OM/dE在–1.5~–1.2 V范围内是185~207 cm–1/V,在–1.2~–0.15 V是83~84 cm–1/V,在–0.2~0.55 V是43 cm–1/V;而 dνPd–COM/dE在–1.5~–1.2 V范围内是–10~–8 cm–1/V,在–1.2~–0.15 V是–31~–30 cm–1/V,在–0.2~0.55 V是–15 cm–1/V.与同时记录的极化曲线对比,认为在中性和碱性介质中所观察到 dνC–OM/dE在–1.2 V附近的急剧变化与电极表面发生了强烈的析氢反应有关.另外,结合密度泛函理论模型计算,认为共吸附的 H减少了 COad从桥式构型到穴位构型的转变,在酸性介质中这种变化不明显,可能是由于对应的电势较高,桥式吸附的 CO比例越大,桥式向穴位的转变本身相对较少.     

A surface-enhanced Raman scattering method for detection of trace glutathione on the basis of immobilized silver nanoparticles and crystal violet probe

Unsatisfactory sensitivity and stability for molecules with low polarizability is still a problem limiting the practical applications of surface-enhanced Raman scattering (SERS) technique. By preparing immobilized silver nanoparticles (Fe₃O₄/Ag) through depositing silver on the surface of magnetite particles, a highly sensitive and selective SERS method for the detection of trace glutathione (GSH) was proposed on the basis of a system of Fe₃O₄/Ag nanoparticles and crystal violet (CV), in which the target GSH competed with the CV probe for the adsorption on the Fe₃O₄/Ag nanoparticles. Raman insensitive GSH replaced the highly Raman sensitive CV adsorbed on the surface of Fe₃O₄/Ag particles. This replacement led to a strong decrease of the CV SERS signal, which was used to determine the concentration of GSH. Under optimal conditions, a linear response was established between the intensity decrease of the CV SERS signal and the GSH concentration in the range of 50–700 nmol L⁻¹ with a detection limit of 40 nmol L⁻¹. The use of a Fe₃O₄/Ag substrate provided not only a great SERS enhancement but also a good stability, which guarantees the reproducibility of the proposed method. Its use for the determination of GSH in practical blood samples and cell extract yielded satisfactory results.