Drop Coating Deposition Raman 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.

Insights into thiram fungicide: A comparative study of solution and solid phases through Raman, DCDR, and SERS measurements and DFT simulations

AbstractThiram, a widely known fungicide, has evinced a negative impact on the environment and human health that led to the banning of its use in plant protection products on all commodities in the European Union. Therefore, there is a need for monitoring possible illicit use, which requires sensitive and accurate detection methods. In this study, the behavior of thiram in different phases was investigated in order to better understand its properties. Raman spectra were obtained from thiram in the solid state as a crystalline powder, dissolved in different solvents, and from dried deposits using the drop coating deposition Raman (DCDR) method. The analyses of acquired Raman spectra revealed evidence of hydrogen bonding between thiram and chloroform in the solution phase. The reliability and sensitivity of DCDR measurements were also highlighted, with high‐quality spectra obtained from a dried pattern from droplet at a 40 μM concentration. Moreover, the study identified the most abundant conformer of intact (undegraded) thiram molecule and enabled reliable band assignment and vibrational analysis based on DFT simulations, providing a better understanding of the compound's properties. The results also suggested that thiram can be coordinated to silver in nanostructured SERS active substrates not only in the degraded form but also in the undegraded form. Overall, this study provides valuable insights into thiram's behavior and can be helpful in the further development of efficient and effective methods for its detection and analysis.

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.

Detection and Characterization of Nodularin by Using Label-Free Surface-Enhanced Spectroscopic Techniques.

Nodularin (NOD) is a potent toxin produced by Nodularia spumigena cyanobacteria. Usually, NOD co-exists with other microcystins in environmental waters, a class of cyanotoxins secreted by certain cyanobacteria species, which makes identification difficult in the case of mixed toxins. Herein we report a complete theoretical DFT-vibrational Raman characterization of NOD along with the experimental drop-coating deposition Raman (DCDR) technique. In addition, we used the vibrational characterization to probe SERS analysis of NOD using colloidal silver nanoparticles (AgNPs), commercial nanopatterned substrates with periodic inverted pyramids (KlariteTM substrate), hydrophobic Tienta® SpecTrimTM slides, and in-house fabricated periodic nanotrenches by nanoimprint lithography (NIL). The 532 nm excitation source provided more well-defined bands even at LOD levels, as well as the best performance in terms of SERS intensity. This was reflected by the results obtained with the KlariteTM substrate and the silver-based colloidal system, which were the most promising detection approaches, providing the lowest limits of detection. A detection limit of 8.4 × 10-8 M was achieved for NOD in solution by using AgNPs. Theoretical computation of the complex vibrational modes of NOD was used for the first time to unambiguously assign all the specific vibrational Raman bands.

Surface amplification of tetraphenylporphyrin overtone and combination Raman bands in drop coating deposition Raman (DCDR) on electrically conductive surfaces

We investigated the performance of Au, Ta, ITO glass, and Al substrates as drop coating deposition Raman (DCDR) substrates for tetraphenylporphyrin.

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.

Perspectives of DCDR-GERS in the analysis of amino acids.

Graphene-enhanced Raman scattering (GERS) has attracted increasing attention from many scientists in recent years as a novel and potentially strong analytical technique since its discovery in 2010. GERS combines the ultra-high sensitivity and spectral analysis of the structural properties of many molecules found in surface-enhanced Raman scattering (SERS) and graphene simple sample processing and excellent uniformity. This facilitates a fast and very sensitive analysis of a wide range of analytes. Here, we present a new method for amino acid analysis based on the combination of drop coating deposition Raman (DCDR) and GERS. The potential of the method was evaluated in the analyses of Trp, Leu, Phe, and DOPA. Achievable limits of detection for all the studied amino acids are in tens of ng mL-1.

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.

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 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.

Sensitive Raman spectroscopy of lipids based on drop deposition using DCDR and SERS

Raman spectroscopy is widely used for study of lipids and membrane models. A severe limitation of this technique lies in the low Raman cross section requiring high sample concentrations. We report sensitive detection of synthetic 1,2‐dimyristoyl‐3‐trimethylammonium‐propane (DMTAP) lipid employing two Raman techniques with improved sensitivity: drop coating deposition Raman (DCDR) and surface‐enhanced Raman scattering (SERS) spectroscopies. DCDR provided well‐reproducible DMTAP spectra without considerable loss of its solution properties if measured from the ‘coffee ring’ pattern of a drop dried on a SpectRIMTM plate. DMTAP was detected at ~10 μM initial solution concentration, which is about three orders of magnitude lower than that for conventional Raman spectroscopy. Moreover, SERS spectra from dried ring of Ag hydrosol/DMTAP system were obtained down to ~0.3 μM DMTAP concentration, which means that sensitivity of SERS is about five orders of magnitude higher than that of conventional Raman spectroscopy. In contrast to the DCDR technique, good SERS spectra of DMTAP were obtained only from some spots of the ring containing big nanoparticle aggregates, and the structural properties of DMTAP were significantly perturbed by adsorption on the Ag nanoparticles. Copyright © 2013 John Wiley & Sons, Ltd.

Drop coating deposition Raman spectroscopy of liposomes: role of cholesterol

Drop coating deposition Raman (DCDR) spectroscopy was used to study liposomes (DPPC and asolectin) with growing proportion of cholesterol. Deposited samples of both liposomes on special hydrophobic surface formed a dried drop with a circular shape with a ring of concentrated liposomes at the outer edge. The presence of cholesterol in liposome causes a diminishing of the drop size and an increasing in diameter of the ring, but DPPC with 20% of cholesterol forms the compact drop without the ring. Raman spectra contain characteristics of both lipids and cholesterol, liposomes do not change their initial phase state after drying. Spectral mapping shows that maximum Raman intensity originated from the inner part of the ring. Our results suggest that DCDR spectroscopy can be used for studying lipids containing cholesterol in situ.

Off-line reaction monitoring of the oxidation of alkenes in water using drop coating deposition Raman (DCDR) spectroscopy

The application of drop coating deposition Raman (DCDR) spectroscopy to the field of reaction progress monitoring is addressed in this contribution. Although, DCDR spectroscopy has seen recent application in the study of biological fluids, its application in other areas has not yet been explored. Here we apply the technique to the catalysed oxidation of alkenes to epoxides in aqueous solutions at concentrations <10 mM. The effect of surface characteristics, background interferences, homogeneity of distribution of analytes, drying time, as well as instrumental limits of detection and calibration are discussed. We demonstrate that reproducible spectra can be obtained routinely, with relatively little variance, with short acquisition times and samples volumes of 2-10 μl and as little as 1 μg of analyte. The utility of the technique compared with online reaction monitoring by (1)H NMR and Raman spectroscopy is demonstrated in the excellent correlation between data obtained off and on-line.

Structural changes of human RNase L upon homodimerization investigated by Raman spectroscopy

RNase L, a key enzyme in the host defense system, is activated by the binding of 2′–5′-linked oligoadenylates (2–5A) to the N-terminal ankyrin repeat domain, which causes the inactive monomer to form a catalytically active homodimer. We focused on the structural changes of human RNase L as a result of interactions with four different activators: natural 2–5 pA4 and three tetramers with 3′-end AMP units replaced with ribo-, arabino- and xylo-configured phosphonate analogs of AMP (pA3X). The extent of the RNase L dimerization and its cleavage activity upon binding of all these activators were similar. A drop-coating deposition Raman (DCDR) spectroscopy possessed uniform spectral changes upon binding of all of the tetramers, which verified the same binding mechanism. The estimated secondary structural composition of monomeric RNase L is 44% α-helix, 28% β-sheet, 17% β-turns and 11% of unordered structures, whereas dimerization causes a slight decrease in α-helix and increase in β-sheet (ca. 2%) content. The dimerization affects at least three Tyr, five Phe and two Trp residues. The α–β structural switch may fix domain positions in the hinge region (residues ca. 336–363) during homodimer formation.

Raman spectroscopy-based sensitive and specific detection of glycated hemoglobin.

In recent years, glycated hemoglobin (HbA1c) has been increasingly accepted as a functional metric of mean blood glucose in the treatment of diabetic patients. Importantly, HbA1c provides an alternate measure of total glycemic exposure due to the representation of blood glucose throughout the day, including post-prandially. In this article, we propose and demonstrate the potential of Raman spectroscopy as a novel analytical method for quantitative detection of HbA1c, without using external dyes or reagents. Using the drop coating deposition Raman (DCDR) technique, we observe that the nonenzymatic glycosylation (glycation) of the hemoglobin molecule results in subtle but discernible and highly reproducible changes in the acquired spectra, which enable the accurate determination of glycated and nonglycated hemoglobin using standard chemometric methods. The acquired Raman spectra display excellent reproducibility of spectral characteristics at different locations in the drop and show a linear dependence of the spectral intensity on the analyte concentration. Furthermore, in hemolysate models, the developed multivariate calibration models for HbA1c show a high degree of prediction accuracy and precision--with a limit of detection that is a factor of ~15 smaller than the lowest physiological concentrations encountered in clinical practice. The excellent accuracy and reproducibility achieved in this proof-of-concept study opens substantive avenues for characterization and quantification of the glycosylation status of (therapeutic) proteins, which are widely used for biopharmaceutical development. We also envision that the proposed approach can provide a powerful tool for high-throughput HbA1c sensing in multicomponent mixtures and potentially in hemolysate and whole blood lysate samples.

DCDR Spectroscopy as Efficient Tool for Liposome Studies: Aspect of Preparation Procedure Parameters

Drop-coating deposition Raman (DCDR) spectroscopy was employed to study liposome suspensions. The method is based on a specific drying process on the hydrophobic surface that efficiently accumulates the macromolecular sample in a ring of the edge of the dried drop. We studied liposome suspensions purchased from two sources (Avanti Polar Lipids, Inc. and Sigma-Aldrich, Co.) and prepared under different conditions. Structure of the dried drop substantially depends on the lipid concentration, lipid composition of the sample, and used solvent. Optimal lipid concentration is about 0.3 mg/ml in all cases, asolectin and DSPC suspensions form compact dried drops when dissolved in water and phosphate buffer, respectively. Drying process of the sample drop does not influence the initial phase state (gel or liquid-crystalline) of the studied liposomes excepting DSPC from Sigma-Aldrich, Co.