Applications of Raman Spectroscopy in Agricultural Products and Food Analysis: A Review

Abstract

Raman spectroscopy has been gaining popularity as an analytical tool due to advances in development of Raman spectrometry and the power of personal computers. Due to to its narrow and highly resolved bands, Raman spectroscopy allows for nondestructive extraction of chemical and physical information about samples and aids in rapid on-line analysis without any special sample preparation. In this review, Raman spectroscopic techniques such as dispersive Raman spectroscopy, Fourier transform Raman spectroscopy, surface-enhanced Raman spectroscopy, and spatially offset Raman spectroscopy are briefly introduced. In addition, applications of Raman spectroscopy are explored, within various fields of agricultural products and food, including fruits and vegetables, crops, meat and dairy products, oil, as well as beverages. In addition, some discussion on the importance of Raman spectroscopy as fundamental and applied research of agricultural products and food is provided.     

Application of portable Raman spectroscopy and benchtop spatially offset Raman spectroscopy to interrogate concealed biomaterials

In this paper, we demonstrate the ability of portable Raman spectroscopy and benchtop spatially offset Raman spectroscopy (SORS) techniques to rapidly identify real and fake ivory samples. Both techniques were able to identify exposed genuine from fake ivory samples. In contrast to conventional Raman spectroscopy, SORS was, in addition, able to identify ivory concealed by plastics, paints, varnishes and cloth. Application of the SORS technique allows the interrogation of biomaterial samples through materials in which conventional Raman spectroscopic instrumentation cannot penetrate. Copyright © 2009 John Wiley & Sons, Ltd.     

Application of spectroscopic techniques for monitoring microbial diversity and bioremediation

Microbes are the most fascinating group, with huge diversity devising myriad functional applications in the field of medicine, pharmaceuticals, environmental remediation, and industries. Quantitative and qualitative determination of biomolecules and microbial assisted phenomena by spectroscopy is a pioneer approach. It facilitates the study of atomic and molecular geometries, energy levels, chemical bonds, and interactions between molecules and microbes. It produces fingerprints of the microbial species serving to characterize, differentiate, and identify microorganisms, in both the environment and at single-cell level. Spectroscopy-based bioremediation techniques like Fourier transform infrared spectroscopy, mass spectroscopy, force spectroscopy, Raman spectroscopy, photoemission spectroscopy, and laser-induced breakdown spectroscopy have been very well represented and linked with the microbial applications. This review summarizes the traditional spectroscopic techniques used for the study of microbes and microbial-assisted products as well as illustrates its application in the field of microbial diversity and remediation. This will provide an outlook for the intricate characterization and dimension of microbes to be used for effective application in bioremediation.     

Spectroscopic techniques for the forensic analysis of textile fibers

A review has been conducted on the application of the spectroscopic techniques to the comparative study and identification of different textile fibers. Microspectrophotometry in the ultraviolet-visible range and Raman spectroscopy are the main techniques investigated with this aim in the forensic field. UV-Vis MSP is the first recommended technique, which is principally used to study the color of the fibers. A more complete approximation focused on determining the specific color of the fibers providing adding Raman spectroscopy to the analytical scheme. Sometimes, it also provided information about the polymeric nature of the fibers. Regarding FTIR spectroscopy, it is the recommended tool to determine the fiber nature. Raman and FTIR spectroscopy are complementary techniques and a frequent recommendation is a combination of both techniques, in order to get a comprehensive analysis of textile fibers. On the other hand, new and more informative analytical techniques are emerging to the analysis of textile fibers as traces related with criminal contacts, such as infrared chemical imaging spectroscopy and X-ray fluorescence spectroscopy.     

FT‐Raman spectroscopy—a rapid and reliable quantification protocol for the determination of natural indigo dye in Polygonum tinctorium

In the recent years, Raman and IR spectroscopies have attracted increasing attention as fast, non‐invasive and widely applicable alternative analytical approaches for a variety of materials. Vibrational spectroscopy has been used in the analysis of herbal products, dyes and sensitive art objects, besides complex and aqueous biomaterials such as biopolymers or mammalian tissue. Compared to conventional analytical methods based on high‐performance liquid chromatography (HPLC) or gas chromatography, which often involves extensive and time‐consuming sample preparation, Raman or IR spectroscopy can avoid these procedures. The present work introduces a fast and reliable quantification method for the determination of naturally occurring indigo dye in dyer's knotweed (Polygonum tinctorium) based on Fourier transform (FT) Raman spectroscopy. The results were validated by HPLC‐UV, and the merits and drawbacks of the present method are elaborated. Besides the qualitative aspects of signal assignment and comparison to appropriate attenuated total reflectance Fourier transform infrared (ATR‐FT‐IR) measurements, the Raman spectrum of dihydro indigo, an important intermediate in the indigo dying process, is presented for the first time and discussed with regard to its spectroscopic behaviour. Copyright © 2010 John Wiley & Sons, Ltd.     

Spectroscopic and X-ray diffraction study of high Tc epitaxial YBCO thin films obtained by pulsed laser deposition

We report spectroscopic characterization of epitaxial YBCO thin films grown on LaAlO₃ by pulsed laser deposition. Raman spectroscopy and spectroscopic ellipsometry were used for film characterization and the results were correlated with X-ray diffraction measurements. The mentioned techniques allowed us to analyze crystallographic, micro-structural, and morphological properties of YBCO thin films. We also demonstrated that relatively low resolution Raman spectroscopy and spectroscopic ellipsometry are reliable techniques for a rapid and non-destructive characterization of epitaxial YBCO thin films.     

激光诱导击穿光谱与拉曼光谱技术在危险物检测中的研究进展

炸药、生物及化学危险物检测在反恐和公共安全领域具有重要应用价值,也是目前亟需解决的问题。激光诱导击穿光谱技术利用高能激光脉冲诱导材料产生等离子体,通过探测等离子体辐射光谱从而分析其组成成分。拉曼光谱技术是基于非弹性光散射的一种光谱检测方法,可以反映分子的振动信息。由于它们都具有快速和非接触遥测的优点,成为最有发展潜力和应用前景的危险物检测技术。介绍了激光诱导击穿光谱、拉曼光谱以及二者联合探测技术在危险物检测中的国内外发展现状,并对各自的优缺点进行了分析。激光诱导击穿光谱信号强、实时性好,但重复性差、基底效应影响显著,在判别组成元素相同而分子结构不同的危险物和干扰物时面临巨大挑战。拉曼光谱能够提供被测物的分子信息,适合于鉴别有机危险物,但信号弱、受荧光干扰大、检测低浓度样品及分析混合物的能力弱,外场使用时受周围杂散光以及环境变化的影响大。将这两种光谱探测技术相融合,发挥各自的优点,可以有效地提高探测危险物的准确度。但两种光谱联合探测系统结构和数据处理复杂,成本高,还有许多技术难点亟需解决。文章最后,对危险物激光诱导击穿光谱和拉曼光谱研究的前景进行了展望。     

Determination of Total Petroleum Hydrocarbon (TPH) and Polycyclic Aromatic Hydrocarbon (PAH) in Soils: A Review of Spectroscopic and Nonspectroscopic Techniques

Abstract: In the analysis of petroleum hydrocarbon–contaminated soils for total petroleum hydrocarbons (TPHs) and polycyclic aromatic hydrocarbons (PAHs), the roles of spectroscopic and nonspectroscopic techniques are inseparable. Therefore, spectroscopic techniques cannot be discussed in isolation. In this report, spectroscopic techniques including Raman, fluorescence, infrared, and visible and near-infrared (Vis-NIR) spectroscopies, as well as mass spectroscopy (coupled to a gas chromatograph) and nonspectroscopic techniques such as gravimetry, immunoassay, and gas chromatography with flame ionization detection are reviewed. To bridge the perceived gap in coverage of the quantitative applications of Vis-NIR spectroscopy in the rapid determination of TPHs and PAHs in soils, a detailed review of studies from the period 1999–2012 are presented. This report also highlights the strengths and limitations of these techniques and evaluates their performance from the perspective of their attributes of general applicability, namely economic portability, operational time, accuracy, and occupational health and safety considerations. Overall, the fluorescence spectroscopic technique had the best performance (85% total score) in comparison to the others, and the gravimetric technique performed the least (60% total score). Method-specific solutions geared toward performance improvement are also suggested.     

Vibrational spectroscopy of selective dental restorative materials

Recently, significant advancement has occurred in vibrational (Fourier transform infrared [FTIR] and Raman) spectroscopy associated with dental materials. FTIR and Raman spectroscopies have emerged as significant breakthrough techniques and offer exciting new possibilities in the area of dental materials. These techniques have been used to obtain chemical images of formulations and allow researchers to find out the in situ structure of materials. This review summarizes the information obtained from these two techniques and their application in dental material sciences. The presented database of vibrational spectroscopy facilitated the appropriate identification of frequently used dental materials ranging from filling, obturating, adhesive, lining/luting materials, and prosthodontics materials. Spectral peaks that are related to these materials are discussed in detail, which provided crucial data in understanding the chemical structural properties. The application of vibrational spectroscopy allowed for a quick differential identification of typical dental materials composed of organic and inorganic compounds. From our study as well as the literature reviewed, it appeared that investigators uniformly confirmed the benefits of vibrational spectroscopy concerning identification of chemical functional groups of different chemical compositions. The diagnostic and prognostic tools based on these technologies have the potential to revolutionize our concepts leading to improve materials sciences and clinical application.     

The quality control of two Pueraria species using Raman spectroscopy coupled with partial least squares analysis

The dried roots of Pueraria lobata (Puerariae Lobatae Radix; PLR) and Pueraria thomsonii (Puerariae Thomsonii Radix; PTR) are medicinal herbs that are used interchangeably in clinical practice, even though their chemical profiles are different. Therefore, the aim of this study was to develop a rapid and non‐destructive method for the quality control of Pueraria species using Raman spectroscopy in combination with partial least squares analysis. Partial least squares‐discriminant analysis (PLS‐DA) was used to differentiate PLR from PTR, whereas partial least squares regression (PLSR) was used to predict the total phenolic content (TPC) and antioxidant capacities of the Pueraria species. Raman spectroscopy revealed that spectral characteristics of starch and polyphenols differentiated the two species, with the PLS‐DA model giving 100% classification accuracy for the tested samples. A significantly higher TPC (p < 0.001), 2,2′‐azino‐bis(3‐ethylbenzothiazoline‐6‐sulfonic acid) (ABTS) radical scavenging activity (p < 0.001) and cupric reducing antioxidant capacity (CUPRAC; p < 0.001) were observed for PLR as compared to PTR. The high ratio of performance to deviation values (TPC: 9.84; ABTS: 7.11; CUPRAC: 7.13) indicated the PLSR models were robust for predicting TPC and antioxidant capacities. The loading plot revealed that the content of starch and polyphenols were important factors in differentiating PLR from PTR and predicting TPC and antioxidant capacities. The results demonstrate that Raman spectroscopy coupled with chemometrics is a rapid method for the quality control of PLR and PTR. These methods can be applied as a template for the quality control of other herbal medicines and products to promote the correct identification of herbs for clinical practice. Copyright © 2015 John Wiley & Sons, Ltd.     

Raman spectroscopy and microscopy of individual cells and cellular components

Raman spectroscopy provides the unique opportunity to nondestructively analyze chemical concentrations in individual cells on the submicrometer length scale without the need for optical labels. This enables the rapid assessment of cellular biochemistry inside living cells, and it allows for their continued analysis. Here, we review recent developments in the analysis of single cells, subcellular compartments, and chemical imaging based on Raman spectroscopy. Spontaneous Raman spectroscopy provides for the full spectral assessment of cellular biochemistry, while coherent Raman techniques, such as coherent anti‐Stokes Raman scattering is primarily used as an imaging tool comparable to confocal fluorescence microscopy. These techniques are complemented by surface‐enhanced Raman spectroscopy, which provides higher sensitivity and local specificity, and also extends the techniques to chemical indicators, i.e. pH sensing. We review the strengths and weaknesses of each technique, demonstrate some of their applications and discuss their potential for future research in cell biology and biomedicine.     

Validation of Raman and FTIR Spectroscopy Methods in Forensic Analysis of Questioned Documents

Abstract

Paper is of great interest to the examiner of questioned documents and forensic chemists because its examination can often answer questions concerning the identity of paper, its source or origin, and its date of manufacture. This information is often used to determine whether a document is authentic or fraudulent. Raman and infrared spectroscopy are two complementary spectroscopic techniques that can produce fast and efficient analysis of the paper of questioned documents. Considering the applicability of quantitative methods of analysis and the importance of the fields in which they are used, method validation is fundamental to the quality of the final results. In this study, a validation of infrared and Raman spectroscopy methods used to differentiate paper samples is described.     

Micro‐Raman spectroscopy and VP‐SEM/EDS applied to the identification of mineral particles and fibres in histological sections

Histological sections of a patient affected by an important respiratory disease were analysed firstly by optical microscope(OM)—crossed polarisers—to identify the presence of incorporated inorganic particles, with particular attention to the fibrous ones. Then, the particles/fibres that were found were studied both with micro‐Raman spectroscopy and variable‐pressure scanning electron microscopy with energy‐dispersive spectroscopy (VP‐SEM/EDS). The two techniques allowed the in situ characterisation of the inorganic phases without disintegration of the organic matter. Micro‐Raman spectroscopy was able to identify the vibrating chemical groups of the mineral phase associated with the inorganic grain while the crystalline structure was preserved by the biological system. The VP‐SEM/EDS characterisation, defining the elemental chemical composition of the analysed particle/fibre, allowed confirmation of the mineral phase deducible from spectroscopic data or its identification with certainty when the spectroscopic data were not exhaustive. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectroscopic characterization of cinnabarin produced by the fungus Pycnoporus sanguineus (Fr.) Murr.

Raman spectroscopy with 1064 nm laser excitation is used here to identify the chemical composition of the extracts obtained from Pycnoporus sanguineus fungus, in comparison with the data produced from the red fungus itself. Polar and non‐polar solvents were used to separate cinnabarin and ergosterol, respectively, the main components of each extract. The Raman spectra of the extracts are dominated by specific vibrational modes that can be related to these components; in the case of ergosterol the main bands are those assignable to CH stretching and deformation along with bands related to the aryl skeletal rings. The cinnabarin fraction, on the other hand, gives a Raman spectrum where the most important bands are those related to NH₂ bending (1510 cm⁻¹) and C quinonoid stretching (1647 cm⁻¹) modes. The Raman spectrum obtained directly from the fungus shows similarity with the cinnabarin fraction, in agreement with the literature information from extracts that cinnabarin is the most significant component present in the red fungus. This result highlights the potential of Raman spectroscopic techniques for the monitoring of the fungus extraction process undertaken in small industries. Copyright © 2007 John Wiley & Sons, Ltd.     

Non‐invasive depth profiling by space and time‐resolved Raman spectroscopy

Time‐resolved Raman spectroscopy, spatially offset Raman spectroscopy and time‐resolved spatially offset Raman spectroscopy (TR‐SORS) have proven their capability for the non‐invasive profiling of deep layers of a sample. Recent studies have indicated that TR‐SORS exhibits an enhanced selectivity toward the deep layers of a sample. However, the enhanced depth profiling efficiency of TR‐SORS, in comparison with time‐resolved Raman spectroscopy and spatially offset Raman spectroscopy, is yet to be assessed and explained in accordance to the synergistic effects of spatial and temporal resolutions. This study provides a critical investigation of the depth profiling efficiency of the three deep Raman techniques. The study compares the efficiency of the various deep Raman spectroscopy techniques for the stand‐off detection of explosive precursors hidden in highly fluorescing packaging. The study explains for the first time the synergistic effects of spatial and temporal resolutions in the deep Raman techniques and their impact on the acquired spectral data. Copyright © 2013 John Wiley & Sons, Ltd.     

Application of Vibrational Spectroscopy in Combination with Chemometrics Techniques for Authentication of Herbal Medicine

Abstract: One of the emerging issues in herbal medicine is its authenticity. The substitution of highly valuable materials in herbal medicine with lower ones is common practice in the herbal medicine industry. This practice can cause serious effects or be harmful to human health; therefore, the authentication of herbal medicine using analytical techniques is necessary. Due to its capability as fingerprint technique, vibrational spectroscopy (infrared and Raman), especially in combination with several chemometrics techniques, is the method of choice for authentication purposes. This review highlights the use of mid-infrared, near-infrared, and Raman spectroscopy for authentication of herbal medicine, either in raw materials or in final products.     

利用拉曼光谱技术研究低剂量X射线辐射对人神经母细胞瘤细胞的影响

低剂量电离辐射引发的生物效应复杂而多样,其研究往往又受到辐射标志物和检测技术手段的限制。将拉曼光谱技术应用于低剂量辐射生物效应研究,利用10 mW,532 nm共聚焦拉曼光谱对经过100,200和500 mGy三种辐射剂量的X射线辐照之后的人神经母细胞瘤细胞进行检测,发现细胞嘌呤核苷酸（722～728和1 572～1 581 cm-1等等）、嘧啶核苷酸（770～785 cm-1等等）等DNA相关的拉曼特征峰受到电离辐射影响而发生变化,说明低剂量X射线辐照造成细胞DNA水平改变。采用流式细胞术对同样条件辐照后培养6 h的人神经母细胞瘤细胞进行细胞周期分析发现,三种剂量的X射线电离辐射均造成细胞在G2期阻滞,同样提示电离辐射引起DNA水平升高。通过划痕实验分析辐照后20 h的细胞迁移能力,结果显示,相较于未接受X射线照射的对照细胞,受到三种剂量电离辐射的人神经母细胞瘤细胞均出现迁移水平下降。研究结果表明,通过拉曼光谱分析发现低剂量X射线电离辐射引起人神经母细胞瘤细胞DNA水平变化,其结果与细胞周期分析和迁移分析的结果相一致,但检测时间大大提前,利用拉曼光谱技术可以实现低剂量辐射损伤等细胞生物学效应的早期发现与监测。     

激光拉曼光谱法验证中草药有效成分的结构特征

用激光拉曼乐谱和红外光谱测定了中草药的有效成分齐墩果酸，基本确定了齐墩果酸结构中特征官能团的归属，特别是激光拉曼光谱补充了红外光谱的信息，可用于鉴定中草药成分结构的有效测试手段。     

Characterization of the products of aniline peroxydisulfate oligo/polymerization in media with different pH by resonance Raman spectroscopy at 413.1 and 1064 nm excitation wavelengths

The pH–structure correlation of the products of aniline peroxydisulfate reaction was mainly investigated by resonance Raman spectroscopy. The reactions of aniline and ammonium peroxydisulfate were carried out in aqueous solutions of initial pH ranging from 4.9 to 13.2 and monomer/oxidant molar ratio of 4/1. For an initial pH of 4.9, the spectroscopic techniques showed that the emeraldine salt form of polyaniline (PANI–ES) is the main product, corroborating that the usual head‐to‐tail coupling mechanism is taking place. The resonance Raman spectra at 1064 nm exciting wavelength were useful to detect the emeraldine salt as a minor product for reactions at an initial pH of 5.3–11.5. The Raman spectra of the main product of the reaction at initial pH of 13.2 excited at 1064 and 413.1 nm showed new spectral features consistent with 1,4‐Michael‐type adducts of aniline monomers and 1,4‐benzoquinone‐monoimine unit. These compounds and their products of hydrolysis/oxidation are the predominant species for the reaction media of initial pH from 5.3 to 13.2. In order to get PANI with different nanoscale morphologies, a pH value of more than 0 or 1 was used in the aniline polymerization. The spectroscopic data obtained in this work reveal that head‐to‐tail coupling does not occur when aniline reacts at media pH higher than about 5. It is suggested that chemical structures of the products of aniline oxidation by an unusual mechanism are the driving force for the development of assorted morphologies. Copyright © 2011 John Wiley & Sons, Ltd.     

基于拉曼光谱技术的甲状腺疾病检测的研究

基于光学成像与光谱技术的无损检测是生物医学光学交叉领域研究的重要发展方向。其中拉曼光谱技术可获得检测对象的生化成分的“指纹信息”,被广泛应用于面向生物分子,细胞以及生物组织的检测诊断研究。甲状腺疾病尤其肿瘤的临床检测往往涉及多方法和技术手段的结合,且存在一定的诊断难度,因此发展新的检测技术方法具有重要的意义。首先综述了拉曼光谱技术在甲状腺细胞系的单细胞拉曼光谱检测与分析,然后介绍甲状腺病理组织和甲状腺正常组织的拉曼光谱鉴别诊断(特别介绍了本研究小组开展以银纳米粒子为增强基底的甲状腺离体组织SERS光谱研究情况),以及拉曼光谱技术在甲状腺激素等方面的研究概况。最后简要探讨了拉曼光谱技术在该领域的研究应用前景和发展方向。