Deposition Raman Spectroscopy Research Articles

Exploring drying-induced separation of main constituents in melamine-blended milk infant formula using DCDR spectroscopy

Drop coating deposition Raman (DCDR) spectroscopy was employed to investigate the melamine compound susceptibility to milk infant formula main constituents as lactose and lipids (specifically 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), and 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE)). DCDR approach is based on the deposition and drying of a small droplet (a few µl) of liquid sample on a hydrophobic substrate. After complete evaporation, the analyte is preconcentrated into the dried pattern from which the classical Raman spectra are acquired. A simple melamine-blended model reactions were tested (melamine-blended lactose, DOPC, and DOPE). From these, lactose was shown to be the most potent reaction partner for melamine, where a significant difference in dried pattern between pure and blended lactose was noticed, and the relevant Raman spectral changes were observed. Pure and melamine-blended infant formula solutions from two kinds of powdered infant formula purchased in the local market were then studied. For pure milk solutions, the drying process, as an integral part of the DCDR approach, led to the spatial separation of lipids and carbohydrates in the resulting pattern. Acquired Raman spectra revealed that the ring edge of the dried pattern was composed mainly of lipids, while the thin film in the central part contained mainly carbohydrates, especially lactose. For the melamine-blended formula, the DCDR approach identified that melamine was present only in the central part of the dried pattern together with carbohydrates. As a result, it was assumed that melamine has a higher susceptibility for carbohydrates than for lipid molecules, even in milk infant formula.

Analytical applications of droplet deposition Raman spectroscopy.

The droplet deposition methods in Raman spectroscopy have received considerable attention in the field of analytical sensing focusing on effective pre-concentration of the studied analyte (coffee-ring effect or small spots). This review covers different analytical applications of drop-coating deposition Raman scattering (DCDRS) and droplet deposition surface-enhanced Raman scattering (SERS) spectroscopy. Two main advantages of droplet deposition Raman techniques are considered: the drying-induced segregation of the components from the mixtures (such as body fluids) and the sensitivity of detection of various analytically important molecules. Some recent advanced applications, including clinical cancer diagnosis, are discussed and summarized. Finally, the potential and further perspectives of the droplet deposition Raman methods for analytical studies are introduced.

Label-Free Detection and Classification of Glaucoma Based on Drop-Coating Deposition Raman Spectroscopy

Primary open-angle glaucoma (POAG) and primary angle-closure glaucoma (PACG) are prevailing eye diseases that can lead to blindness. In order to provide a non-invasive diagnostic method for glaucoma, we investigated the feasibility of using drop-coating deposition Raman spectroscopy (DCDRS) to discriminate glaucoma patients from healthy individuals based on tear samples. Tears from 27, 19 and 27 POAG patients, PACG patients and normal individuals, respectively, were collected for Raman measurement. For high-dimension data analysis, principal component analysis–linear discriminant analysis (PCA-LDA) was used to discriminate the features of the Raman spectra, followed by a support vector machine (SVM) used to classify samples into three categories, which is called a PCA-LDA-based SVM. The differences in the characteristic peaks of Raman spectra between glaucoma patients and normal people were related to the different contents of various proteins and lipids. For the PCA-LDA-based SVM, the total accuracy reached 93.2%. With the evaluation of 30% test dataset validation, the classification accuracy of the model was 90.9%. The results of this work reveal that tears can be used for Raman detection and discrimination by combining the process with the PCA-LDA-based SVM, supporting DCDRS being a potential method for the diagnosis of glaucoma in the future.

Drop coating deposition Raman (DCDR) spectroscopy of biologically important molecules

AbstractDrop coating deposition Raman (DCDR) spectroscopy introduces a simple and easily accessible approach to studying biologically important molecules and their mixtures. The method is based on drying a small drop of solution or suspension of studied molecules deposited on a special hydrophobic surface. The drying process efficiently accumulates the molecules in the ‘coffee‐ring’ or any small pattern from which the Raman spectrum can be measured. In this way, a significant (several orders of magnitude) improvement of the Raman detection sensitivity compared with Raman measurement from solution can be reached. Therefore, a small sample volume (several microliters), as well as a low initial concentration of studied molecules in deposited droplets, are important advantages of the DCDR method over the normal Raman one. Recently, many relevant DCDR applications on biomolecules and related molecules have been reported. The mini‐review covers a brief overview of the DCDR method (principle, short history, suitable hydrophobic surfaces and state‐of‐the‐art). It will be followed by a summary of the studies over the last 15–20 years on different biologically important molecules, including proteins, lipids (in the form of liposomes) and small molecules (e.g., porphyrins, anthrax marker dipicolinic acid and food and environmental contaminants). Finally, the application potential and further perspectives of the DCDR method for biomolecular studies will be discussed.

Glasswing-Butterfly-Inspired Multifunctional Scleral Lens and Smartphone Raman Spectrometer for Point-of-Care Tear Biomarker Analysis.

Augmenting contact lenses with sensing capabilities requires incorporating multiple functionalities within a diminutive device. Inspired by multifunctional biophotonic nanostructures of glasswing butterflies, a nanostructured scleral lens with enhanced optical, bactericidal, and sensing capabilities is reported. When used in conjunction with a smartphone-integrated Raman spectrometer, the feasibility of point-of-care applications is demonstrated. The bioinspired nanostructures made on parylene films are mounted on the anterior and posterior side of a scleral lens to create a nanostructured lens. Compared to unstructured parylene, nanostructured parylene minimizes glare by 4.3-fold at large viewing angles up to 80o . When mounted on a scleral lens, the nanostructures block 2.8-fold more ultraviolet (UVA) light while offering 1.1-fold improved transmission in the visible regime. Furthermore, the nanostructures exhibit potent bactericidal activity against Escherichia coli, killing 89% of tested bacteria within 4 h. The same nanostructures, when gold-coated, are used to perform rapid label-free multiplex detection of lysozyme and lactoferrin, the protein biomarkers of the chronic dry eye disease, in whole human tears using drop-coating deposition Raman spectroscopy. The detection of both proteins in whole human tear samples from different subjects using the nanostructured lens produced excellent correlation with commercial enzyme-based assays while simultaneously displaying a 1.5-fold lower standard deviation.

Nanostructured Plasma Polymerized Fluorocarbon Films for Drop Coating Deposition Raman Spectroscopy (DCDRS) of Liposomes.

Raman spectroscopy is one of the most used biodetection techniques. However, its usability is hampered in the case of low concentrated substances because of the weak intensity of the Raman signal. To overcome this limitation, the use of drop coating deposition Raman spectroscopy (DCDRS), in which the liquid samples are allowed to dry into well-defined patterns where the non-volatile solutes are highly concentrated, is appropriate. This significantly improves the Raman sensitivity when compared to the conventional Raman signal from solution/suspension. As DCDRS performance strongly depends on the wetting properties of substrates, we demonstrate here that the smooth hydrophobic plasma polymerized fluorocarbon films prepared by magnetron sputtering (contact angle 108°) are well-suited for the DCDRS detection of liposomes. Furthermore, it was proved that even better improvement of the Raman signal might be achieved if the plasma polymer surfaces are roughened. In this case, 100% higher intensities of Raman signal are observed in comparison with smooth fluorocarbon films. As it is shown, this effect, which has no influence on the profile of Raman spectra, is connected with the increased hydrophobicity of nanostructured fluorocarbon films. This results in the formation of dried liposomal deposits with smaller diameters and higher preconcentration of liposomes.

Drop coating deposition Raman (DCDR) spectroscopy of contaminants

Raman spectroscopy is a useful technique to identify small organic molecules, including contaminants. The drop coating deposition Raman (DCDR) is more sensitive than conventional Raman spectroscopy from solution. It is based on Raman measurement from a small drop dried on a hydrophobic surface where studied molecules are preconcentrated. In this paper, DCDR spectra of dried drops of selected contaminants (food contaminant melamine, fungicide thiram, herbicides bentazon and picloram) on the hydrophobic substrate were acquired for the first time, whereas Raman spectra from stock solutions were impossible to obtain under the same experimental conditions. The lowest DCDR detected concentrations were determined as 6.4 µM, 0.31 µM, 20 µM and 2 µM in deposited concentrations for melamine, thiram, bentazon and picloram, respectively. Therefore, DCDR spectroscopy can serve to detect these molecules in concentrations relevant in food/groundwater contaminations.

Drop-coating deposition Raman spectroscopy for quantitative detection of urinary creatinine: a feasibility study

We present the results of an exploratory study carried out to evaluate the applicability of drop coating deposition Raman spectroscopy (DCDRS) for quantitative determination of creatinine present in urine. A comparison of the conventional Raman and the DCDRS spectra measured from aqueous solutions of physiological concentration of creatinine showed significantly higher intensity for DCDRS. Although as compared to surface enhanced Raman spectroscopy (SERS) this intensity was considerably lower, the reproducibility of DCDRS was found to be significantly better (⩾92%) than that of SERS (∼75%). A multivariate chemometric algorithm based on partial least square regression was developed to predict the concentrations of creatinine on the basis of the measured set of DCDRS spectra of the aqueous creatinine solutions as well as artificial urine samples and the reference (known) concentrations of creatinine used for preparing the solutions. The algorithm, applied via leave-one-spectrum-out cross-validation, could detect creatinine present in the artificial urine samples with an accuracy of over 94% in the physiological concentration range. Further, the lower limit of detection was also found to be sufficient for determining the presence of the urinary creatinine levels lower than the physiological reference range. Overall, the findings of the study demonstrate a promising potential of DCDRS for quantitative analysis of creatinine present in urine.

Raman spectroscopy applications in rheumatology.

Raman spectroscopy is a type of vibrational spectroscopy based on the inelastic scattering of photons, which has attracted much attention due to its potential clinical application in rheumatology. In this review, we discuss the typical spectral features of cartilage, bone, synovial fluid, and pathologic crystal deposits, as well as methods of amplifying the Raman signal of biofluids such as drop-coating deposition Raman spectroscopy. Further, applications of Raman and drop-coating deposition Raman spectroscopy in osteoarthritis are described, highlighting the clinical potential of these methods. We also discuss the role of Raman and related techniques in analyzing pathologic crystals such as monosodium urate, calcium pyrophosphate dihydrate, and hydroxyapatite. The results presented in this review demonstrate that Raman spectroscopy has grown past the stage of proof-of-concept, especially in the case of pathologies involving crystal depositions such as gout and calcium pyrophosphate deposition disease, for which the method has been validated on large number of samples. As the medical community becomes more and more aware of Raman spectroscopy, it is envisioned that it will become a standard technique in the near future.

Ambient electrospray deposition Raman spectroscopy (AESD RS) using soft landed preformed silver nanoparticles for rapid and sensitive analysis.

We introduce a technique called ambient electrospray deposition Raman spectroscopy (AESD RS) for rapid and sensitive surface-enhanced Raman scattering (SERS) based detection of analytes using a miniature Raman spectrometer. Using electrospray, soft landing of preformed silver nanoparticles (AgNPs) was performed for 30-40 seconds for different concentrations of analytes deposited on conducting glass slides. Using AESD RS, SERS signals were collected within 4-6 minutes, including sample preparation. Transmission electron microscopy (TEM) and dark-field microscopy (DFM) were used to characterize the preformed AgNPs before and after electrospray. We achieved the nanomolar and micromolar detection of p-mercaptobenzoic acid (p-MBA) and 2,4-dinitrotoluene (2,4-DNT), respectively. In this work, 0.3 μL of preformed AgNPs were used, which is ∼33 times less in volume than the quantity needed for conventional SERS. Quantitation of unknown concentration of analytes was also possible. A similar amount of electrosprayed AgNPs was utilized to characterize Escherichia coli (E. coli) bacteria of different concentrations. Viability of bacteria was tested using fluorescence microscopic imaging. Besides reduced analysis time and improved reproducibility of the data in every analysis, which is generally difficult in SERS, the amount of AgNPs required is an order of magnitude lower in this method. This method could also be used to probe the real-time changes in molecular and biological species under ambient conditions.

Drop coating deposition Raman spectroscopy of dipicolinic acid

AbstractDipicolinic acid (DPA) is an important spore biomarker for Bacillus anthracis (anthrax). Drop coating deposition Raman (DCDR) spectroscopy on a commercial hydrophobic SpectRIM™ plate allowed DPA to be detected at 5 × 10−7‐M deposited concentration, equivalent to approximately 90 spores, significantly below the infective dose (104 spores). The DCDR spectra of DPA differ from Raman spectrum of DPA powder, crystalline state, and aqueous solution.

Polytetrafluoroethylene tape as a low‐cost hydrophobic substrate for drop‐coating deposition Raman spectroscopy of proteins

AbstractHighly hydrophobic substrates are desirable for drop coating deposition Raman spectroscopy of proteins, because they concentrate the analyte during drying. Most of the commercial substrates used to date are comparatively expensive, whereas thiol or silane functionalisation of surfaces requires a degree of experience not available in a typical biology laboratory. Here, we show that polytetrafluoroethylene tape, commercially available as thread sealing tape, can be stretched across a washer to yield a highly hydrophobic surface, which is thin enough to produce only a very small Raman signal itself. We demonstrate that this simple substrate can be used to yield high‐quality spectra of biomolecules such as human insulin and lysozyme in both native and fibrillated forms.

Drop coating deposition Raman spectroscopy of proteinogenic amino acids compared with their solution and crystalline state

The Raman spectra of 20 proteinogenic amino acids were recorded in the solution, glass phase (as drop coating deposition Raman (DCDR) samples) and crystalline forms in the wide spectral range of 200–3200cm−1. The most apparent spectral differences between the Raman spectra of the crystalline forms, glass phases and aqueous solutions of amino acids were briefly discussed and described in the frame of published works. The possible density dependencies of spectral bands were noted. In some cases, a strong influence of the sample density, as well as of the organization of the water envelope, was observed. The most apparent changes were observed for Ser and Thr. Nevertheless, for the majority of amino acids, the DCDR sample form is an intermediate between the solution and crystalline forms. In contrast, aromatic amino acids have only a small sensitivity to the form of the sample. Our reference set of Raman spectra is useful for revealing discrepancies between the SERS and solid/solution spectra of amino acids. We also found that some previously published Raman spectra of polycrystalline samples resemble glassy state rather than crystalline spectra. Therefore, this reference set of spectra will find application in every branch of Raman spectroscopy where the spectra of biomolecules are collected from coatings.

Thiol‐modified gold‐coated glass as an efficient hydrophobic substrate for drop coating deposition Raman (DCDR) technique

In this paper we report an easy and low‐cost way to prepare a hydrophobic substrate for drop coating deposition Raman (DCDR) spectroscopy. This substrate is formed by a thiol‐modified Au‐coated glass and provides the Raman spectra with the same quality as the commercial Teflon‐coated stainless steel substrate (SpectRIM™, Tienta Sciences, Inc.) for model molecular systems – albumin solution and liposome suspension. Gold layer, similarly to polished steel in the commercial substrate, served as a highly refractive layer strongly increasing the Raman signal. The main advantage of introduced substrate is that it is simple and a low‐cost preparation easily manageable in every standard laboratory. Thus, it represents a promising alternative to commercial Teflon‐coated stainless steel substrate. Copyright © 2016 John Wiley & Sons, Ltd.

Raman spectroscopy for detection of imatinib in plasma: A proof of concept

Imatinib is the standard first line treatment for chronic myeloid leukemia (CML). Owing to dose-related toxicities of Imatinib such as neutropenia, there is scope for treatment optimization through therapeutic drug monitoring (TDM). Trough concentration of 1 μg/mL is considered the therapeutic threshhold. Existing methods for the detection of Imatinib in plasma are limited by long read out time and expensive instrumentation. Hence, Raman spectroscopy was explored as a rapid and objective tool for monitoring Imatinib concentration. Three approaches: conventional Raman spectroscopy (CRS), Drop coating deposition Raman (DCDR) spectroscopy and surface-enhanced Raman spectroscopy (SERS) were employed to detect the required trough concentration of 1 μg/mL and above. Detection of therapeutically relevant concentrations (1 μg/mL) using SERS and suitable nanoparticle substrates has been demonstrated. Prospectively, rigorous validation using clinical samples is necessary to confirm the utility of this approach in routine clinical usage.

Drop-Coating Deposition Raman (DCDR) Spectroscopy as a Tool for Membrane Interaction Studies: Liposome-Porphyrin Complex.

Drop-coating deposition Raman (DCDR) spectroscopy is based on the measurement of a sample that has been preconcentrated by being dried on a special hydrophobic plate. In addition to its higher sensitivity, the advantage of DCDR over the conventional Raman spectroscopy is the small sample volume needed, the lack of interference from solvents, and the capability of segregating any impurities present and separating components in more complex samples. In this study, DCDR spectroscopy was employed to investigate the complex of the cationic copper(II) 5,10,15,20-tetrakis(1-methyl-4-pyridyl) porphyrin (CuTMPyP) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) liposomes. Drop-coating deposition Raman spectra were treated using factor analysis (FA), which led to the following conclusions: (i) the distribution of CuTMPyP in the complex is not homogenous, (ii) the DCDR technique segregates complexed and noncomplexed parts of the sample, (iii) the spectral changes caused by the drying process and by the interaction of CuTMPyP with the DPPC liposomes can be distinguished, and (iv) the porphyrin molecules interacting with DPPC affect both the order-disorder properties of the lipid chains and the lipid head.

Drop coating deposition Raman spectroscopy of blood plasma for the detection of colorectal cancer.

We have recently applied the technique of drop coating deposition Raman (DCDR) spectroscopy for colorectal cancer (CRC) detection using blood plasma. The aim of this study was to develop a more convenient and stable method based on blood plasma for noninvasive CRC detection. Significant differences are observed in DCDR spectra between healthy (n = 105) and cancer (n = 75) plasma from 15 CRC patients and 21 volunteers, particularly in the spectra that are related to proteins, nucleic acids, and β-carotene. The multivariate analysis principal components analysis and the linear discriminate analysis, together with leave-one-out, cross validation were used on DCDR spectra and yielded a sensitivity of 100% (75/75) and specificity of 98.1% (103/105) for detection of CRC. This study demonstrates that DCDR spectroscopy of blood plasma associated with multivariate statistical algorithms has the potential for the noninvasive detection of CRC.

Drop‐coating deposition Raman spectroscopy of porphyrins

We report an improvement of the Raman detection sensitivity of porphyrins by factor of 105 using drop‐coating deposition Raman spectroscopy (DCDR). We were able to obtain Raman spectra from ~20 nM initial (deposited) concentrations of cationic and anionic porphyrin. This detection limit is comparable with or even better than that of surface‐enhanced Raman scattering spectroscopy using Ag nanoparticles. Moreover, DCDR spectrum of protoporphyrin IX, which is known as a marker in clinical diagnostics of cancer, was also obtained from 10 nM deposited concentration. To our knowledge, it is the first demonstration of the resonance DCDR spectroscopy. Copyright © 2015 John Wiley & Sons, Ltd.

Drop coating deposition Raman spectroscopy as a potential tool for identification and determination of fructose in seminal plasma

The detection of fructose in the seminal plasma has significant value to evaluate the function of seminal vesicles and evaluate male fertility. In this study, drop coating deposition Raman (DCDR) method was utilized to quantitative determination of fructose in seminal plasma. Optimization of experimental parameters to achieve reagent‐free and rapid detection of fructose was also investigated. Different fructose concentrations within physiological level demonstrated a linear relationship with the band intensity of 627 cm−1 (assigned to fructose), and the relative error of predicted fructose concentration was 10.23%. Our results show that DCDR method has the potential for the determination of fructose concentration. Copyright © 2014 John Wiley & Sons, Ltd.

Drop‐coating deposition and surface‐enhanced Raman spectroscopies (DCDRS and SERS) provide complementary information of whole human tears

Raman spectroscopy has received increasing interest in biomedical applications because of its label‐free and in vivo detection capabilities. The main challenge for a wider application lies in its low detection sensitivity, especially for biomolecules. Various strategies have been employed to improve the detection sensitivity of Raman spectroscopy. In this work, we systematically compared two Raman techniques with improved sensitivity for the detection of microliter quantities of whole human tears: drop‐coating deposition Raman spectroscopy (DCDRS) and surface‐enhanced Raman spectroscopy (SERS). High‐quality and highly reproducible DCDR spectra of tears can be obtained in the ring zone of the dried coffee‐ring deposit. The major contribution is from the high‐abundant proteins, including lysozyme, lactoferrin, and albumin. Good SER spectra with excellent reproducibility can also be acquired in the deposit area and are contributed by uric acid and hypoxanthine in tears with a low abundance but strong interactions with the silver nanoparticles. The result demonstrates that DCDRS is advantageous for detection of some high‐abundant components and SERS for some low‐abundant components in the whole tears. A combination of both techniques is able to extract multiparameter information for a systematic analysis of clinical tears and can be further extended to the analysis of other body fluids. Copyright © 2014 John Wiley & Sons, Ltd.