In Situ Localization and Structural Analysis of the Malaria Pigment Hemozoin

Spectrally Resolved and Highly Parallelized Raman Difference Spectroscopy for the Analysis of Drug-Target Interactions between the Antimalarial Drug Chloroquine and Hematin

Malaria is a severe disease caused by cytozoic parasites of the genus Plasmodium, which infiltrate and infect red blood cells. Several drugs have been developed to combat the devastating effects of malaria. Antimalarials based on quinolines inhibit the crystallization of hematin into hemozoin within the parasite, ultimately leading to its demise. Despite the frequent use of these agents, there are unanswered questions about their mechanisms of action. In the present study, the quinoline chloroquine and its interaction with the target structure hematin was investigated using an advanced, highly parallelized Raman difference spectroscopy (RDS) setup. Simultaneous recording of the spectra of hematin and chloroquine mixtures with varying compositions enabled the observation of changes in peak heights and positions based on the altered molecular structure resulting from their interaction. A shift of (-1.12 ± 0.05) cm-1 was observed in the core-size marker band ν(CαCm)asym peak position of the 1:1 chloroquine-hematin mixture compared to pure hematin. The oxidation-state marker band ν(pyrrole half-ring)sym exhibited a shift by (+0.93 ± 0.13) cm-1. These results were supported by density functional theory (DFT) calculations, indicating a hydrogen bond between the quinolinyl moiety of chloroquine and the oxygen atom of ferric protoporphyrin IX hydroxide (Fe(III)PPIX-OH). The consequence is a reduced electron density within the porphyrin moiety and an increase in its core size. This hypothesis provided further insights into the mechanism of hemozoin inhibition, suggesting chloroquine binding to the monomeric form of hematin, thereby preventing its further crystallization to hemozoin.

Molecular Interactions Identified by Two-Dimensional Analysis-Detailed Insight into the Molecular Interactions of the Antimalarial Artesunate with the Target Structure β-Hematin by Means of 2D Raman Correlation Spectroscopy

A thorough understanding of the interaction of endoperoxide antimalarial agents with their biological target structures is of utmost importance for the tailored design of future efficient antimalarials. Detailed insights into molecular interactions between artesunate and β-hematin were derived with a combination of resonance Raman spectroscopy, two-dimensional correlation analysis, and density functional theory calculations. Resonance Raman spectroscopy with three distinct laser wavelengths enabled the specific excitation of different chromophore parts of β-hematin. The resonance Raman spectra of the artesunate-β-hematin complexes were thoroughly analyzed with the help of high-resolution and highly sensitive two-dimensional correlation spectroscopy. Spectral changes in the peak properties were found with increasing artesunate concentration. Changes in the low-frequency, morphology-sensitive Raman bands indicated a loss in crystallinity of the drug-target complexes. Differences in the high-wavenumber region were assigned to increased distortions of the planarity of the structure of the target molecule due to the appearance of various coexisting alkylation species. Evidence for the appearance of high-valent ferryl-oxo species could be observed with the help of differences in the peak properties of oxidation-state sensitive Raman modes. To support those findings, the relaxed ground-state structures of ten possible covalent mono- and di-meso(Cm)-alkylated hematin-dihydroartemisinyl complexes were calculated using density functional theory. A very good agreement with the experimental peak properties was achieved, and the out-of-plane displacements along the lowest-frequency normal coordinates were investigated by normal coordinate structural decomposition analysis. The strongest changes in all data were observed in vibrations with a high participation of Cm-parts of β-hematin.

Investigations on the Novel Antimalarial Ferroquine in Biomimetic Solutions Using Deep UV Resonance Raman Spectroscopy and Density Functional Theory

Deep ultraviolet (DUV) resonance Raman experiments are performed, investigating the novel, promising antimalarial ferroquine (FQ). Two buffered aqueous solutions with pH values of 5.13 and 7.00 are used, simulating the acidic and neutral conditions inside a parasite's digestive vacuole and cytosol, respectively. To imitate the different polarities of the membranes and interior, the buffer's 1,4-dioxane content was increased. These experimental conditions should mimic the transport of the drug inside malaria-infected erythrocytes through parasitophorous membranes. Supporting density functional theory (DFT) calculations on the drug's micro-speciation were performed, which could be nicely assigned to shifts in the peak positions of resonantly enhanced high-wavenumber Raman signals at λ_exc = 257 nm. FQ is fully protonated in polar mixtures like the host interior and the parasite's cytoplasm or digestive vacuole (DV) and is only present as a free base in nonpolar ones, such as the host's and parasitophorous membranes. Additionally, the limit of detection (LoD) of FQ at vacuolic pH values was determined using DUV excitation wavelengths at 244 and 257 nm. By applying the resonant laser line at λ_exc = 257 nm, a minimal FQ concentration of 3.1 μM was detected, whereas the pre-resonant excitation wavelength 244 nm provides an LoD of 6.9 μM. These values were all up to one order of magnitude lower than the concentration found for the food vacuole of a parasitized erythrocyte.

Cryogenically induced signal enhancement of Raman spectra of porphyrin molecules

Raman spectroscopy is a powerful analytical technique in contemporary medicine and biomedical research due to its exceptional ability to provide an unambiguous spectroscopic signature of the molecular chemical composition, structure and atom arrangements. Among other applications, investigations of the Raman spectra of porphyrins and their derivatives have been critical in the study of ligand binding mechanisms and drug interactions with healthy and diseased blood cells, as well as for the analysis of blood, hemoproteins and the oxygenation process of human erythrocyte. However, obtaining Raman spectra with satisfactory definition of porphyrin-based molecules can be challenging due to their inherent photo- and thermal sensitivity which leads to laser damage even at low laser power. This severely affects the Raman spectra of porphyrins and limits the Raman signal strength and spectra quality. In this study, we examine two important porphyrins, hemin and protoporphyrin IX, at cryogenic temperatures down to 77 K using a 532 nm excitation Raman instrument in order to study the Raman signal strength and spectral quality dependence on the sample temperature at these extreme low temperatures. We report a significant Raman signal enhancement of up to 310% in the spectra at cryogenic temperatures compared to room temperature measurements. This provides a remarkable improvement of the quality and definition within the spectra and demonstrates that cryogenic Raman measurements can be used as an exceptionally effective method of enhancing the Raman signal and spectra quality for investigations of porphyrins and their derivatives regardless of the excitation wavelength selection. This can greatly improve the effectiveness of Raman spectroscopy in biomedical research, especially in the field of drug design and development, medical diagnostics and disease monitoring and analysis.

Direct Quantification of Single Red Blood Cell Hemoglobin Concentration with Multiphoton Microscopy

Blood disorders, diseases, and infections often affect the shape, number, and content of red blood cells (RBCs) dramatically. To combat these pathologies, many therapies target RBCs and their contents directly. Mean corpuscular hemoglobin concentration (MCHC) is an important pathological metric in both identification and treatment. However, current methods for RBC analysis and MCHC quantification rely on bulk measurements. Single RBC measurements could provide necessary insight into the heterogeneity of RBC health and improve therapeutic efficacy. In this study, we present a novel multimodal multiphoton approach for quantifying hemoglobin concentration at single RBC resolution. We achieve this by collecting two images simultaneously that allows us to excite water with stimulated Raman scattering and hemoglobin with transient absorption. This multimodal imaging is enabled by a newly designed orthogonal modulation theme for dual-channel lock-in detection. By leveraging water as an internal standard, we quantify MCHC of healthy RBCs and RBCs infected with Plasmodium yoelii, a commonly studied rodent parasite model.

Raman spectroscopy-based biomarker screening by studying the fingerprint characteristics of chronic lymphocytic leukemia and diffuse large B-cell lymphoma

Raman spectroscopy (RS) can provide fingerprint-type information on biochemical molecules. RS-based blood plasma analysis of solid tumors has been reported in recent years; however, there are no studies on the use of this analysis for detecting blood diseases. We studied the features of blood plasma in patients with diffuse large B-cell lymphoma (DLBCL) and chronic lymphocytic leukemia (CLL) by RS with the aim of developing a simple blood test for noninvasive DLBCL and CLL detection. We analyzed blood plasma from 33 DLBCL patients, 39 CLL patients and 30 healthy volunteers. Orthogonal partial least squares discriminant analysis (OPLS-DA) could build two clusters with almost no overlap between DLBCL/CLL and the controls. We used the prediction set to test the model built by OPLS-DA. For the CLL model, the sensitivity was 92.86%, and the specificity was 100%, whereas for the DLBCL model, the sensitivity was 80% and the specificity was 92.31%. We found Raman bands specific to both DLBCL and CLL patients in comparison with the healthy volunteers. Most importantly, we found that the combination of the 1445 cm^-1 and 1655 cm^-1 Raman shifts could discriminate DLBCL from CLL and even the other solid tumors reported to date. Further analysis of the assignments of 1655 cm^-1 also gave us a clue to find potential important variables hemoglobin and serum albumin related with the CLL prognosis. Our exploratory study primarily demonstrated the great potential of developing RS blood plasma analysis as a novel clinical tool for the noninvasive detection of DLBCL and CLL.

Antibody-free rapid diagnosis of malaria in whole blood with surface-enhanced Raman Spectroscopy using Nanostructured Gold Substrate

PURPOSE

The aim of this study is to establish a rapid antibody-free diagnostic method of malaria infection with Plasmodium falciparum and Plasmodium vivax in whole blood with Surface-enhanced Raman Spectroscopy using Nanostructured Gold Substrate.

MATERIALS AND METHODS

The blood samples collected from patients were first lysed and centrifuged before dropping on the gold nano-structure (AuNS) substrate. Malaria diagnosis was performed by detecting Raman peaks from Surface Enhanced Raman Spectroscopy (SERS) with a 532 nm laser excitation.

RESULTS

Raman peaks at 1370 cm-1, 1570 cm-1, and 1627 cm-1, known to have high specificity against interference from other mosquito-borne diseases such as Dengue and West Nile virus infection, were selected as the fingerprint markers associated with P. falciparum and P. vivax infection. The limit of detection was 10-5 dilution, corresponding to the concentration of parasitized blood cells of 100/mL. A total number of 25 clinical samples, including 5 from patients with P. falciparum infection, 10 with P. vivax infection and 10 from healthy volunteers, were evaluated to support its clinical practical use. The whole assay on malaria detection took 30 min to complete.

CONCLUSIONS

While the samples analyzed in this work have strong clinical relevance, we have clearly demonstrated that sensitive malaria detection using AuNS-SERS is a practical direction for rapid in-field diagnosis of malaria infection.

Whole-Organism Analysis by Vibrational Spectroscopy

Vibrational spectroscopy has contributed to the understanding of biological materials for many years. As the technology has advanced, the technique has been brought to bear on the analysis of whole organisms. Here, we discuss advanced and recently developed infrared and Raman spectroscopic instrumentation to whole-organism analysis. We highlight many of the recent contributions made in this relatively new area of spectroscopy, particularly addressing organisms associated with disease with emphasis on diagnosis and treatment. The application of vibrational spectroscopic techniques to entire organisms is still in its infancy, but new developments in imaging and chemometric processing will likely expand in the field in the near future.

Integration of diffraction phase microscopy and Raman imaging for label-free morpho-molecular assessment of live cells

Label-free quantitative imaging is highly desirable for studying live cells by extracting pathophysiological information without perturbing cell functions. Here, we demonstrate a novel label-free multimodal optical imaging system with the capability of providing comprehensive morphological and molecular attributes of live cells. Our morpho-molecular microscopy (3M) system draws on the combined strength of quantitative phase microscopy (QPM) and Raman microscopy to probe the morphological features and molecular fingerprinting characteristics of each cell under observation. While the commonr-path geometry of our QPM system allows for highly sensitive phase measurement, the Raman microscopy is equipped with dual excitation wavelengths and utilizes the same detection and dispersion system, making it a distinctive multi-wavelength system with a small footprint. We demonstrate the applicability of the 3M system by investigating nucleated and nonnucleated cells. This integrated label-free platform has a promising potential in preclinical research, as well as in clinical diagnosis in the near future.

Development of a label-free Raman imaging technique for differentiation of malaria parasite infected from non-infected tissue

During malarial infection, the host uses the spleen to clear the malaria parasites, however, the parasites have evolved the ability to bind to endothelial receptors in blood vessels of tissues to avoid removal, known as sequestration, and this is largely responsible for the symptoms and severity of infection. So a technique which could non-invasively diagnose tissue burden could be utilised as an aid for localised malaria diagnosis within tissue. Raman spectroscopy is a label-free imaging technique and can provide unique and chemically specific Raman 'fingerprint' spectrum of biological samples such as tissue. Within this study, Raman imaging was used to observe the changes to the molecular composition of mice spleen tissue under malarial infection, compared with non-infected samples. From analysis of the Raman imaging data, both tissue types showed very similar spectral profiles, which highlighted that their biochemical compositions were closely linked. Principal component analysis showed very clear separation of the two sample groups, with an associated increase in concentration of heme-based Raman vibrations within the infected dataset. This was indicative of the presence of hemozoin, the malaria pigment, being detected within the infected spleen. Separation also showed that as the hemozoin content within the tissue increased, there was a corresponding change to hemoglobin and some lipid/nucleic acid vibrations. These results demonstrate that Raman spectroscopy can be used to easily discriminate the subtle changes in tissue burden upon malarial infection.

Fiber enhanced Raman spectroscopic analysis as a novel method for diagnosis and monitoring of diseases related to hyperbilirubinemia and hyperbiliverdinemia

Fiber enhanced resonance Raman spectroscopy (FERS) is introduced for chemically selective and ultrasensitive analysis of the biomolecules hematin, hemoglobin, biliverdin, and bilirubin. The abilities for analyzing whole intact, oxygenated erythrocytes are proven, demonstrating the potential for the diagnosis of red blood cell related diseases, such as different types of anemia and hemolytic disorders. The optical fiber enables an efficient light-guiding within a miniaturized sample volume of only a few micro-liters and provides a tremendously improved analytical sensitivity (LODs of 0.5 μM for bilirubin and 0.13 μM for biliverdin with proposed improvements down to the pico-molar range). FERS is a less invasive method than the standard ones and could be a new analytical method for monitoring neonatal jaundice, allowing a precise control of the unconjugated serum bilirubin levels, and therefore, providing a better prognosis for newborns. The potential for sensing very low concentrations of the bile pigments may also open up new opportunities for cancer research. The abilities of FERS as a diagnostic tool are explored for the elucidation of jaundice with different etiologies including the rare, not yet well understood diseases manifested in green jaundice. This is demonstrated by quantifying clinically relevant concentrations of bilirubin and biliverdin simultaneously in the micro-molar range: for the case of hyperbilirubinemia due to malignancy, infectious hepatitis, cirrhosis or stenosis of the common bile duct (1 μM biliverdin together with 50 μM bilirubin) and for hyperbiliverdinemia (25 μM biliverdin and 75 μM bilirubin). FERS has high potential as an ultrasensitive analytical technique for a wide range of biomolecules and in various life-science applications.

Vibrational spectroscopic characterization of arylisoquinolines by means of Raman spectroscopy and density functional theory calculations

Seven new AIQ antimalarial agents were investigated using FT-NIR and deep-UV resonance Raman spectroscopy.

Malaria in cynomolgus monkeys used in toxicity studies in Japan

Plasmodium spp. protozoa cause malaria and are known to infect humans and a variety of animal species including macaque monkeys. Here we report both our experience with malaria recrudescence in cynomolgus monkeys (Macaca fascicularis) in a toxicity study and the results of a survey on Plasmodium infection in cynomolgus monkeys imported to Japan for laboratory use. A cynomolgus monkey from the toxicity study presented with severe anemia and Plasmodium protozoa in erythrocytes on a thin blood smear and was subsequently diagnosed with symptomatic malaria. In this animal, congestion and accumulation of hemozoin (malaria pigment) in macrophages were noted in the enlarged and darkly discolored spleen. As a follow-up for the experience, spleen sections from 800 cynomolgus monkeys in toxicity studies conducted between 2003 and 2013 were retrospectively examined for hemozoin deposition as a marker of Plasmodium infection. The origin of the animals included Cambodia, China, Indonesia, and Vietnam. Hemozoin deposition was confirmed in 44% of all examined monkeys. Monkeys from Indonesia showed the highest incidence of hemozoin deposition (approx. 80%). A high prevalence of Plasmodium infection in laboratory monkeys was also confirmed with polymerase chain reaction (PCR) by using Plasmodium genus-specific primers. Although Japan is not a country with endemic malaria, it is important to be aware of the prevalence and potential impact of background infection with Plasmodium spp. and recrudescence of symptomatic malaria in imported laboratory monkeys on pharmaceutical toxicity studies.

Towards ultrasensitive malaria diagnosis using surface enhanced Raman spectroscopy

We report two methods of surface enhanced Raman spectroscopy (SERS) for hemozoin detection in malaria infected human blood. In the first method, silver nanoparticles were synthesized separately and then mixed with lysed blood; while in the second method, silver nanoparticles were synthesized directly inside the parasites of Plasmodium falciparum. It was observed that the first method yields a smaller variation in SERS measurements and stronger correlation between the estimated contribution of hemozoin and the parasitemia level, which is preferred for the quantification of the parasitemia level. In contrast, the second method yields a higher sensitivity to a low parasitemia level thus could be more effective in the early malaria diagnosis to determine whether a given blood sample is positive.

The ring-stage of Plasmodium falciparum observed in RBCs of hospitalized malaria patients

Raman spectra of the blood samples obtained directly from hospitalized malaria patients with Plasmodium falciparum (P. falciparum) in the ring-stage were analyzed. Changes observed in the Raman band intensities of the infected patients compared to healthy volunteers are the result of parasite activity inside red blood cells. The obtained spectra were discussed by analyzing differences in particular spectral regions by evaluating changes in the band intensity ratios as well as using PCA analysis. The alterations of erythrocyte membranes caused by parasite penetration are visible by a reduced I1130/I1075 intensity ratio expressing the lowering of the amount of domains arranged in trans conformation. The I2930/I2850 ratio, which is a measure of modifications in structures of membrane proteins and lipids, in infected red blood cells increases, which is caused by malaria protein export to the erythrocyte membrane and expresses the membrane disarrangement. In the pyrrole ring vibration region, the ν4 band marker of the oxygenated-Hb shows at 1371 cm(-1) whereas the ν4 band at 1353 cm(-1) related to the deoxygenated-Hb is observed for malaria patients and is characterized by a higher intensity in infected erythrocytes. The amide I analysis shows the modifications in the secondary structure composition in the infected RBCs. We found that the P. falciparum infection leads to a decrease in the α-helical content and a concurrent increase in undefined (random-coil) structures. It was observed that the Raman spectra changes are also the result of the hemozoin formation process. In the pyrrole ring stretching vibration region, the increase of 1220 cm(-1) (deoxyHb) as against 1248 cm(-1) (oxyHb) may be considered as a signal of hemozoin formation in the RBCs. Relatively intense band patterns at 1560 cm(-1) and also at 1570 cm(-1) and 1552 cm(-1) may be due to the hemozoin that is formed according to parasite activity. The results of medical diagnostic tests had not presented changes in patient RBC parameters. A significant reduction in WBC count was noticed along with a decrease in neutrophil and platelet count when compared with the control group. Although no change is observed in the overall picture of the erythrocytes, pathological changes are evident in the Raman spectrum.

Fiber array based hyperspectral Raman imaging for chemical selective analysis of malaria-infected red blood cells

A new setup for Raman spectroscopic wide-field imaging is presented. It combines the advantages of a fiber array based spectral translator with a tailor-made laser illumination system for high-quality Raman chemical imaging of sensitive biological samples. The Gaussian-like intensity distribution of the illuminating laser beam is shaped by a square-core optical multimode fiber to a top-hat profile with very homogeneous intensity distribution to fulfill the conditions of Koehler. The 30 m long optical fiber and an additional vibrator efficiently destroy the polarization and coherence of the illuminating light. This homogeneous, incoherent illumination is an essential prerequisite for stable quantitative imaging of complex biological samples. The fiber array translates the two-dimensional lateral information of the Raman stray light into separated spectral channels with very high contrast. The Raman image can be correlated with a corresponding white light microscopic image of the sample. The new setup enables simultaneous quantification of all Raman spectra across the whole spatial area with very good spectral resolution and thus outperforms other Raman imaging approaches based on scanning and tunable filters. The unique capabilities of the setup for fast, gentle, sensitive, and selective chemical imaging of biological samples were applied for automated hemozoin analysis. A special algorithm was developed to generate Raman images based on the hemozoin distribution in red blood cells without any influence from other Raman scattering. The new imaging setup in combination with the robust algorithm provides a novel, elegant way for chemical selective analysis of the malaria pigment hemozoin in early ring stages of Plasmodium falciparum infected erythrocytes.

Enhanced Raman multigas sensing - a novel tool for control and analysis of (13)CO(2) labeling experiments in environmental research

Cavity-enhanced Raman multigas spectrometry is introduced as a versatile technique for monitoring of (13)CO2 isotope labeling experiments, while simultaneously quantifying the fluxes of O2 and other relevant gases across a wide range of concentrations. The multigas analysis was performed in a closed cycle; no gas was consumed, and the gas composition was not altered by the measurement. Isotope labeling of plant metabolites via photosynthetic uptake of (13)CO2 enables the investigation of resource flows in plants and is now an important tool in ecophysiological studies. In this experiment the (13)C labeling of monoclonal cuttings of Populus trichocarpa was undertaken. The high time resolution of the online multigas analysis allowed precise control of the pulse labeling and was exploited to calculate the kinetics of photosynthetic (13)CO2 uptake and to extrapolate the exact value of the (13)CO2 peak concentration in the labeling chamber. Further, the leaf dark respiration of immature and mature leaves was analyzed. The quantification of the photosynthetic O2 production rate as a byproduct of the (13)CO2 uptake correlated with the amount of available light and the leaf area of the plants in the labeling chamber. The ability to acquire CO2 and O2 respiration rates simultaneously also simplifies the determination of respiratory quotients (rate of O2 uptake compared to CO2 release) and thus indicates the type of combusted substrate. By combining quantification of respiration quotients with the tracing of (13)C in plants, cavity enhanced Raman spectroscopy adds a valuable new tool for studies of metabolism at the organismal to ecosystem scale.

Microbial respiration and natural attenuation of benzene contaminated soils investigated by cavity enhanced Raman multi-gas spectroscopy

Soil and groundwater contamination with benzene can cause serious environmental damage. However, many soil microorganisms are capable to adapt and are known to strongly control the fate of organic contamination. Innovative cavity enhanced Raman multi-gas spectroscopy (CERS) was applied to investigate the short-term response of the soil micro-flora to sudden surface contamination with benzene regarding the temporal variations of gas products and their exchange rates with the adjacent atmosphere. (13)C-labeled benzene was spiked on a silty-loamy soil column in order to track and separate the changes in heterotrophic soil respiration - involving (12)CO2 and O2- from the natural attenuation process of benzene degradation to ultimately form (13)CO2. The respiratory quotient (RQ) decreased from a value 0.98 to 0.46 directly after the spiking and increased again within 33 hours to a value of 0.72. This coincided with the maximum (13)CO2 concentration rate (0.63 μmol m(-2) s(-1)), indicating the highest benzene degradation at 33 hours after the spiking event. The diffusion of benzene in the headspace and the biodegradation into (13)CO2 were simultaneously monitored and 12 days after the benzene spiking no measurable degradation was detected anymore. The RQ finally returned to a value of 0.96 demonstrating the reestablished aerobic respiration.

Rapid monitoring of intermediate states and mass balance of nitrogen during denitrification by means of cavity enhanced Raman multi-gas sensing

The comprehensive investigation of changes in N cycling has been challenging so far due to difficulties with measuring gases such as N2 and N2O simultaneously. In this study we introduce cavity enhanced Raman gas spectroscopy as a new analytical methodology for tracing the stepwise reduction of (15)N-labelled nitrate by the denitrifying bacteria Pseudomonas stutzeri. The unique capabilities of Raman multi-gas analysis enabled real-time, continuous, and non-consumptive quantification of the relevant gases ((14)N2, (14)N2O, O2, and CO2) and to trace the fate of (15)N-labeled nitrate substrate ((15)N2, (15)N2O) added to a P. stutzeri culture with one single measurement. Using this new methodology, we could quantify the kinetics of the formation and degradation for all gaseous compounds (educts and products) and thus study the reaction orders. The gas quantification was complemented with the analysis of nitrate and nitrite concentrations for the online monitoring of the total nitrogen element budget. The simultaneous quantification of all gases also enabled the contactless and sterile online acquisition of the pH changes in the P. stutzeri culture by the stoichiometry of the redox reactions during denitrification and the CO2-bicarbonate equilibrium. Continuous pH monitoring - without the need to insert an electrode into solution - elucidated e.g. an increase in the slope of the pH value coinciding with an accumulation of nitrite, which in turn led to a temporary accumulation of N2O, due to an inhibition of nitrous oxide reductase. Cavity enhanced Raman gas spectroscopy has a high potential for the assessment of denitrification processes and can contribute substantially to our understanding of nitrogen cycling in both natural and agricultural systems.

Fiber-enhanced Raman multigas spectroscopy: a versatile tool for environmental gas sensing and breath analysis

Versatile multigas analysis bears high potential for environmental sensing of climate relevant gases and noninvasive early stage diagnosis of disease states in human breath. In this contribution, a fiber-enhanced Raman spectroscopic (FERS) analysis of a suite of climate relevant atmospheric gases is presented, which allowed for reliable quantification of CH4, CO2, and N2O alongside N2 and O2 with just one single measurement. A highly improved analytical sensitivity was achieved, down to a sub-parts per million limit of detection with a high dynamic range of 6 orders of magnitude and within a second measurement time. The high potential of FERS for the detection of disease markers was demonstrated with the analysis of 27 nL of exhaled human breath. The natural isotopes (13)CO2 and (14)N(15)N were quantified at low levels, simultaneously with the major breath components N2, O2, and (12)CO2. The natural abundances of (13)CO2 and (14)N(15)N were experimentally quantified in very good agreement to theoretical values. A fiber adapter assembly and gas filling setup was designed for rapid and automated analysis of multigas compositions and their fluctuations within seconds and without the need for optical readjustment of the sensor arrangement. On the basis of the abilities of such miniaturized FERS system, we expect high potential for the diagnosis of clinically administered (13)C-labeled CO2 in human breath and also foresee high impact for disease detection via biologically vital nitrogen compounds.

Raman spectroscopic analysis of malaria disease progression via blood and plasma samples

In this study Raman spectroscopy has been used to monitor the changes in erythrocytes and plasma during Plasmodium infection in mice, following malaria disease progression over the course of 7 days. The Raman spectra of both samples are dominated by the spectra of hemoglobin and hemozoin, due to their resonant enhancement. In plasma samples, due to the inherently low heme background, heme-based changes in the Raman spectra could be detected in the very early stages of infection, as little as one day after Plasmodium infection, where parasitemia levels were low, on the order of 0.2%, and typically difficult to detect by existing methods. Further principal component analysis also indicates concurrent erythrocyte membrane changes at around day 4, where parasitemia levels reached 3%. These results show that plasma analysis has significant potential for early, quantitative and automated detection of malaria, and to quantify heme levels in serum which modulate malarial effects on the immune system.

Malaria pigment crystals as magnetic micro-rotors: key for high-sensitivity diagnosis

The need to develop new methods for the high-sensitivity diagnosis of malaria has initiated a global activity in medical and interdisciplinary sciences. Most of the diverse variety of emerging techniques are based on research-grade instruments, sophisticated reagent-based assays or rely on expertise. Here, we suggest an alternative optical methodology with an easy-to-use and cost-effective instrumentation based on unique properties of malaria pigment reported previously and determined quantitatively in the present study. Malaria pigment, also called hemozoin, is an insoluble microcrystalline form of heme. These crystallites show remarkable magnetic and optical anisotropy distinctly from any other components of blood. As a consequence, they can simultaneously act as magnetically driven micro-rotors and spinning polarizers in suspensions. These properties can gain importance not only in malaria diagnosis and therapies, where hemozoin is considered as drug target or immune modulator, but also in the magnetic manipulation of cells and tissues on the microscopic scale.

Magnetic field enriched surface enhanced resonance Raman spectroscopy for early malaria diagnosis

Hemozoin is a by-product of malaria infection in erythrocytes, which has been explored as a biomarker for early malaria diagnosis. We report magnetic field-enriched surface-enhanced resonance Raman spectroscopy (SERRS) of β-hematin crystals, which are the equivalent of hemozoin biocrystals in spectroscopic features, by using magnetic nanoparticles with iron oxide core and silver shell (Fe(3)O(4)@Ag). The external magnetic field enriches β-hematin crystals and enhances the binding between β-hematin crystals and magnetic nanoparticles, which provides further improvement in SERRS signals. The magnetic field-enriched SERRS signal of β-hematin crystals shows approximately five orders of magnitude enhancement in the resonance Raman signal, in comparison to about three orders of magnitude improvement in the SERRS signal without the influence of magnetic field. The improvement has led to a β-hematin detection limit at a concentration of 5 nM (roughly equivalent to 30 parasites/μl at the early stages of malaria infection), which demonstrates the potential of magnetic field-enriched SERRS technique in early malaria diagnosis.

Combined confocal Raman and quantitative phase microscopy system for biomedical diagnosis

We have developed a novel multimodal microscopy system that incorporates confocal Raman, confocal reflectance, and quantitative phase microscopy (QPM) into a single imaging entity. Confocal Raman microscopy provides detailed chemical information from the sample, while confocal reflectance and quantitative phase microscopy show detailed morphology. Combining these intrinsic contrast imaging modalities makes it possible to obtain quantitative morphological and chemical information without exogenous staining. For validation and characterization, we have used this multi-modal system to investigate healthy and diseased blood samples. We first show that the thickness of a healthy red blood cell (RBC) shows good correlation with its hemoglobin distribution. Further, in malaria infected RBCs, we successfully image the distribution of hemozoin (malaria pigment) inside the cell. Our observations lead us to propose morphological screening by QPM and subsequent chemical imaging by Raman for investigating blood disorders. This new approach allows monitoring cell development and cell-drug interactions with minimal perturbation of the biological system of interest.

Combination of patch clamp and Raman spectroscopy for single-cell analysis

In this contribution we present the combination of patch clamp with Raman spectroscopy for a label-free quantitative detection of intracellular components. Patch clamp is used to gain controlled access to the cytosol and internalize water-soluble compounds into the cell. The presence and concentration of these substances inside the living mammalian cell are probed by means of Raman spectroscopy in a label-free manner. A proof of principle was given using the carotinoid crocin as a sample compound that does not show specific interaction with the cell. When the intracellular crocin concentration as determined from the Raman spectra was monitored, the kinetics of internalization/diffusion into the cell could be characterized by a single-exponential function. Furthermore, the technique was successfully applied to observe differences in the internalization of free and protein-bound heme into the living cell. Although the peptide-capped microperoxidase MP-11 did not show specific interactions, free heme accumulated in the cell by binding to cellular components.

Structural analysis of the antimalarial drug halofantrine by means of Raman spectroscopy and density functional theory calculations

The structure of the antimalarial drug halofantrine is analyzed by means of density functional theory (DFT) calculations, IR, and Raman spectroscopy. Strong, selective enhancements of the Raman bands of halofantrine at 1621 and 1590 cm(-1) are discovered by means of UV resonance Raman spectroscopy with excitation wavelength lambda(exc)=244 nm. These signal enhancements can be exploited for a localization of small concentrations of halofantrine in a biological environment. The Raman spectrum of halofantrine is calculated by means of DFT calculations [B3LYP/6-311+G(d,p)]. The calculation is very useful for a thorough mode assignment of the Raman bands of halofantrine. The strong bands at 1621 and 1590 cm(-1) in the UV Raman spectrum are assigned to combined C[Double Bond]C stretching vibrations in the phenanthrene ring of halofantrine. These bands are considered as putative marker bands for pipi interactions with the biological target molecules. The calculation of the electron density demonstrates a strong distribution across the phenanthrene ring of halofantrine, besides the electron withdrawing effect of the Cl and CF(3) substituents. This strong and even electron density distribution supports the hypothesis of pipi stacking as a possible mode of action of halofantrine. Complementary IR spectroscopy is performed for an investigation of vibrations of polar functional groups of the halofantrine molecule.