The surface-enhanced Raman spectra (SERS) of adenine and three deuterated analogues adsorbed on colloids, electrochemically roughened electrodes, and vacuum deposited island films of silver have been investigated. All normal Raman and SERS bands were assigned to normal modes on the basis of density functional theory (DFT) calculations (B3LYP/6-31 ++ G(d,p)) and isotope shifts. Surface selection rules derived from the electromagnetic enhancement model were employed to deduce adenine orientations on the different surfaces. On the colloids, adenine adopts an almost perpendicular orientation interacting with the metal surface via N7 and the exocyclic amino group. On the electrodes, adenine adsorbs in a more tilted orientation while on the island films the tilt is even more pronounced. Interaction with the electrodes takes place through N7 and the amino group, while interaction with the island film may be solely through N7.

Fourier Transform Infrared (FT-IR) spectroscopy was used to study carbon allocation patterns in response to changes in nitrogen availability in the diatom Chaetoceros muellerii Lemmerman. The results of the FT-IR measurements were compared with those obtained with traditional chemical methods. The data obtained with both FT-IR and chemical methods showed that nitrogen starvation led to the disappearance of the differences in cell constituents and growth rates existing between cells cultured at either high [NO 3 Ϫ ] or high [NH 4 ϩ ]. Irrespective of the nitrogen source supplied before nitrogen starvation, a diversion of carbon away from protein, chlorophyll, and carbohydrates into lipids was observed. Under these conditions, cells that had previously received nitrogen as nitrate appeared to allocate a larger amount of mobilized carbon into lipids than cells that had been cultured in the presence of ammonia. All these changes were reversed by resupplying the cultures with nitrogen. The rate of protein accumulation in the N-replete cells was slower than the rate of decrease under nitrogen starvation. This study demonstrates that the relative proportions of the major macromolecules contained in microalgal cells and their changes in response to external stimuli can be determined rapidly, simultaneously, and inexpensively using FT-IR. The technique proved to be equally reliable to and less labor intensive than more traditional chemical methods.

The ability to detect DNA conformation in eukaryotic cells is of paramount importance in understanding how some cells retain functionality in response to environmental stress. It is anticipated that the B to A transition might play a role in resistance to DNA damage such as heat, desiccation and toxic damage. To this end, conformational detail about the molecular structure of DNA has been derived primarily from in vitro experiments on extracted or synthetic DNA. Here, we report that a B- to A-like DNA conformational change can occur in the nuclei of intact cells in response to dehydration. This transition is reversible upon rehydration in air-dried cells. By systematically monitoring the dehydration and rehydration of single and double-stranded DNA, RNA, extracted nuclei and three types of eukaryotic cells including chicken erythrocytes, mammalian lymphocytes and cancerous rodent fibroblasts using Fourier transform infrared (FTIR) spectroscopy, we unequivocally assign the important DNA conformation marker bands within these cells. We also demonstrate that by applying FTIR spectroscopy to hydrated samples, the DNA bands become sharper and more intense. This is anticipated to provide a methodology enabling differentiation of cancerous from non-cancerous cells based on the increased DNA content inherent to dysplastic and neoplastic tissue.

Raman spectra are reported for oxygenated and deoxygenated haemoglobin contained within a single red blood cell in vivo using excitation wavelengths of 488, 514, 568 and 632.8 nm. The peak assigned in previous work to n 4 is observed at 1376 cm −1 in oxygenated cells and 1356 cm −1 in deoxygenated cells with the results from 488 nm excitation consistent with earlier Raman studies on isolated haem proteins. Exciting the cells with 514 nm radiation revealed two bands appearing in this region at 1372 and 1356 cm −1 in the oxygenated state, whereas in the deoxygenated state only one band at 1356 cm −1 is observed. At 632.8 nm excitation bands in the n 4 region appeared at 1367 and 1365 cm −1 in the oxygenated and deoxygenated states, respectively. Our results clearly show that the enhancement of bands in the vicinity of n 4 within single erythrocytes is influenced by the excitation wavelength. Furthermore, many other bands observed in oxygenated erythrocytes using 632.8 nm excitation were dramatically enhanced compared with the bands observed with other excitation wavelengths. Ruling out other explanations, it is hypothesized that the enhancement observed at 632.8 nm results from excitonic coupling between aligned porphyrins. The high concentration of haemoglobin in a single cell enables the porphyrins to be in close proximity to permit charge transfer between the haem moieties. The high signal-to-noise ratio and excellent reproducibility obtained using Raman water immersion microspectroscopy on single erythrocytes in vivo shows potential as a diagnostic tool for a variety of haemopathies. However, judicious choice of the excitation wavelength is a prerequisite especially if the technique is applied to diagnose oxidation status within erythrocytes.

The oxygenation process of a human erythrocyte is monitored using a Raman microimaging technique. Raman images of the 1638 cm(-1) band are recorded in the oxygenated and deoxygenated state using only 120 s of laser exposure and approximately 1 mW of defocused laser power. The images show hemoglobin oxygenating and deoxygenating within the cell. Prolonged laser imaging exposure (<180 s) at low temperatures results in photoinduced and/or thermal degradation. The effect of thermal degradation is investigated by recording spectra of erythrocytes as a function of temperature between 4 and 52 degrees C. Five bands at 1396, 1365, 1248, 972, and 662 cm(-1) are identified as markers for heme aggregation. Raman images recorded of cells after prolonged laser exposure appear to show heme aggregation commencing in the middle and moving toward the periphery of the cell. UV-visible spectra of erythrocytes show the Soret band to be broader and red shifted (approximately 3 nm) at temperatures between 45 and 55 degrees indicative of excitonic interactions. It is postulated that the enhancement of the aggregation marker bands observed at 632.8-nm excitation results primarily from excitonic interactions between the aggregated hemes in response to protein denaturation. The results have important medical implications in detecting and monitoring heme aggregation associated with hemopathies such as sickle cell disease.

The Raman and surface-enhanced Raman spectra of uracil have been recorded under a range of experimental conditions and the vibrational spectra of uracil and deprotonated uracil in the condensed phase are predicted by density functional theory (DFT) calculations at the B3LYP/6-31++G(d,p) level. Solvation effects are taken into consideration in two different ways:  in the context of a self-consistent reaction field of a dielectric continuum and by the explicit addition of two water molecules that can form H-bonds with the CO and N−H moieties of uracil. On the basis of these calculations combined with normal Raman spectroscopy (NRS), two different tautomers corresponding to N1- and N3-deprotonated uracil are identified in alkaline aqueous solution, the N1-deprotonated species being slightly more common. In the SERS spectra of alkaline uracil solution in a silver sol, contributions from both tautomers are detected. The ratio of the two tautomers depends on the analyte concentration. At submonolayer concentrations (ca. 10-6 M) both tautomers interact with the silver surface via the respective deprotonated nitrogens adopting tilted orientations. At higher concentrations the competition for adsorption sites leads to a more upright orientation of the adsorbed species and the N3-deprotonated tautomer being favored. DFT calculations at the B3LYP/LanL2DZ level prove that N3-deprotonated uracil is stabilized more by the presence of Ag+ ions at the metal surface than N1-deprotonated uracil. At neutral pH uracil adsorbs to the silver colloid exclusively in its N-3 deprotonated form. The interaction between uracil and an electrochemically roughened silver electrode is similar to the interaction between uracil and the silver colloid. Spectral changes caused by varying the applied electrode potential are most likely due to the inductive effect of the metal rather than a molecular reorientation at the metal surface.

Tip-enhanced Raman scattering (TERS) is a powerful technique to obtain molecular information on a nanometer scale, however, the technique has been limited to cell surfaces, viruses, and isolated molecules. Here we show that TERS can be used to probe hemozoin crystals at less than 20 nm spatial resolution in the digestive vacuole of a sectioned malaria parasite-infected cell. The TERS spectra clearly show characteristic bands of hemozoin that can be correlated to a precise position on the crystal by comparison with the corresponding atomic force microscopy (AFM) image. These are the first recorded AFM images of hemozoin crystals inside malaria-infected cells and clearly show the hemozoin crystals protruding from the embedding medium. TERS spectra recorded of these crystals show spectral features consistent with a five-coordinate high-spin ferric heme complex, which include the electron density marker band ν(4) at 1373 cm(-1) and other porphyrin skeletal and ring breathing modes at approximately 1636, 1557, 1412, 1314, 1123, and 1066 cm(-1). These results demonstrate the potential of the AFM/TERS technique to obtain nanoscale molecular information within a sectioned single cell. We foresee this approach paving the way to a new independent drug screening modality for detection of drugs binding to the hemozoin surface within the digestive vacuole of the malaria trophozoite.

New diagnostic tools that can detect malaria parasites in conjunction with other diagnostic parameters are urgently required. In this study, Attenuated Total Reflection Fourier transform infrared (ATR-FTIR) spectroscopy in combination with Partial Least Square Discriminant Analysis (PLS-DA) and Partial Least Square Regression (PLS-R) have been applied as a point-of-care test for identifying malaria parasites, blood glucose, and urea levels in whole blood samples from thick blood films on glass slides. The specificity for the PLS-DA was found to be 98% for parasitemia levels >0.5%, but a rather low sensitivity of 70% was achieved because of the small number of negative samples in the model. In PLS-R the Root Mean Square Error of Cross Validation (RMSECV) for parasite concentration (0-5%) was 0.58%. Similarly, for glucose (0-400 mg/dL) and urea (0-250 mg/dL) spiked samples, relative RMSECVs were 16% and 17%, respectively. The method reported here is the first example of multianalyte/disease diagnosis using ATR-FTIR spectroscopy, which in this case, enabled the simultaneous quantification of glucose and urea analytes along with malaria parasitemia quantification using one spectrum obtained from a single drop of blood on a glass microscope slide.