A combined theoretical and experimental analysis of dopamine (DA) is presented in this work with the objective of achieving more accurate detection and monitoring of this neurotransmitter at very low concentrations, specific to physiological levels. Surface-enhanced Raman spectroscopy on silver nanoparticles was employed for recording DA concentrations as low as 10−11 molar. Quantum chemical density functional calculations were carried out using Gaussian-09 analytical suite software. Relatively good agreement between the simulated and experimentally determined results indicates the presence of different DA molecular forms, such as uncharged DA±, anionic DA−, and dopaminequinone. Disappearance of the strongest bands of dopamine around 750 cm−1 and 790 cm−1, which suggests its adsorption onto the metallic surface, is not only consistent with all of these DA configurations, but also provides additional information about the analyte’s redox process and voltammetric detection. On the other hand, occurrence of the abovementioned Raman lines could indicate the formation of multilayers of DA or its presence in a cationic DA+ form. Thus, through coordinated experiment and theory, valuable insights into changes observed in the vibrational signatures of this important neurotransmitter can be achieved for a better understanding of its detection at physiological levels, which is crucial if further optovoltammetric medical device development is envisioned.

We present a detailed study of the morphology and composition of tungsten oxide (WO3) thin films, grown by radio frequency magnetron reactive sputtering at substrate temperatures varied from room temperature (RT) to 500 °C, using infrared (IR) absorption, Raman spectroscopy, and x-ray photoelectron spectroscopy (XPS). This work includes valuable new far-IR results about structural changes in microcrystalline WO3. Both IR absorption and Raman techniques reveal an amorphous sample grown at RT and initial crystallization into monoclinic structures for samples grown at temperatures between 100 and 300 °C. The Raman spectra of the samples grown at high temperatures indicate, apart from the monoclinic structure, a strain effect, with a distribution revealed by confocal Raman mapping. XPS indicates that the film surface maintains the stoichiometry WOx, with a value of x slightly greater than 3 at RT due to oxygen contamination, which decreases with increasing temperature.

Objectives We demonstrate that confocal Raman mapping spectroscopy provides rapid, detailed and accurate neurotransmitter analysis, enabling millisecond time resolution monitoring of biochemical dynamics. As a prototypical demonstration of the power of the method, we present real-time in vitro serotonin, adenosine, and dopamine detection, and dopamine diffusion in an inhomogeneous organic gel, which was used as a substitute for neurologic tissue. Materials and Methods Dopamine, adenosine and serotonin were used to prepare neurotransmitter solutions in DI water. The solutions were applied to the surfaces of glass slides, where they inter-diffused. Raman mapping was achieved by detecting non-overlapping spectral signatures characteristic of the neurotransmitters with an alpha 300 WITec confocal Raman system, using 532 nm Nd:YAG laser excitation. Every local Raman spectrum was recorded in milliseconds and complete Raman mapping in a few seconds. Results Without damage, dyeing, or preferential sample preparation, confocal Raman mapping provided positive detection of each neurotransmitter, allowing association of the high-resolution spectra with specific micro-scale image regions. Such information is particularly important for complex, heterogeneous samples, where changes in composition can influence neurotransmission processes. We also report an estimated dopamine diffusion coefficient two orders of magnitude smaller than that calculated by the flow-injection method. Conclusions Accurate nondestructive characterization for real-time detection of neurotransmitters in inhomogeneous environments without the requirement of sample labeling is a key issue in neuroscience. Our work demonstrates the capabilities of Raman spectroscopy in biological applications, possibly providing a new tool for elucidating the mechanism and kinetics of deep brain stimulation.

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We present a comparative microscopic and spectroscopic study of the morphology and composition of WO 3 and W 0.95 Ti 0.05 O 3 thin films, grown by radio-frequency magnetron reactive sputtering at substrate temperatures varied from room temperature to 500°C, using atomic force microscopy (AFM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). With increasing growth temperature, the AFM results show increase in the average crystallite size and in the surface roughness for both undoped and doped samples. The AFM data, along with the Raman results, clearly indicate that for the given set of experimental conditions, higher growth temperatures are required to obtain crystalline Ti-doped WO 3 films than for WO 3 films. Also, the Raman results suggest a potential phase transformation from a monoclinic WO 3 structure to an orthorhombic, but more probably a tetragonal, configuration in the W 0.95 Ti 0.05 O 3 thin films. This remark is based on the observed shifting, with Ti doping, to lower frequencies of the Raman peaks corresponding to W-O-W stretching modes of WO 3 at 806 and 711 cm -1 to 793 and 690 cm -1 , respectively. XPS data indicate that the doped material has a reduced WO 3-x stoichiometry at the surface, with the presence of W 6? and W 5? oxidation states; this observation could also be related to the existence of a different structural phase of this material, corroborating with the Raman measurements.

Although not yet ready for clinical application, methods based on Raman spectroscopy have shown significant potential in identifying, characterizing, and discriminating between noncancerous and cancerous specimens. Real-time and accurate medical diagnosis achievable through this vibrational optical method largely benefits from improvements in current technological and software capabilities. Not only is the acquisition of spectral information now possible in milliseconds and analysis of hundreds of thousands of data points achieved in minutes, but Raman spectroscopy also allows simultaneous detection and monitoring of several biological components. Besides demonstrating a significant Raman signature distinction between nontumorigenic (MCF-10A) and tumorigenic (MCF-7) breast epithelial cells, our study demonstrates that Raman can be used as a label-free method to evaluate epidermal growth factor activity in tumor cells. Comparative Raman profiles and images of specimens in the presence or absence of epidermal growth factor show important differences in regions attributed to lipid, protein, and nucleic acid vibrations. The occurrence, which is dependent on the presence of epidermal growth factor, of new Raman features associated with the appearance of phosphothreonine and phosphoserine residues reflects a signal transduction from the membrane to the nucleus, with concomitant modification of DNA/RNA structural characteristics. Parallel Western blotting analysis reveals an epidermal growth factor induction of phosphorylated Akt protein, corroborating the Raman results. The analysis presented in this work is an important step toward Raman-based evaluation of biological activity of epidermal growth factor receptors on the surfaces of breast cancer cells. With the ultimate future goal of clinically implementing Raman-guided techniques for the diagnosis of breast tumors (e.g., with regard to specific receptor activity), the current results just lay the foundation for further label-free optical tools to diagnose the disease.

In this investigation, we address the question of how organic thioindigo binds to inorganic palygorskite to form a pigment similar to Maya Blue. We also address how such binding, if it occurs, might be affected by varying the proportion of dye relative to that of the mineral, and by varying the length of heating time used in preparation of the pigment. In addition to samples of palygorskite and thioindigo both alone, four synthetic pigment samples were prepared; two samples of 8 wt.% dye, one heated at 170°C for 3 h and one at 170°C for 9 h, and two samples of 16 wt.% dye, one heated at 170°C for 3 h and one at 170°C for 9 h. All samples were examined using Fourier transform-infrared (FT-IR) and FT-Raman spectroscopy. For the pigment samples, FT-IR peaks at 1627 cm −1 are attributed to a downshifted C O stretching mode of thioindigo due to dye-clay interaction. This interpretation is corroborated by FT-Raman C O peaks with 14 cm −1 shifts to lower wavenumber for the pigment relative to thioindigo alone. Additional Raman scattering between 550 cm −1 and 650 cm −1 also suggests dye-clay interaction through metal-oxygen bonding. We are thus led to the possibility of mostly hydrogen bonding between silanol and carbonyl at lower dye concentration, with a predominance of metal-oxygen bonding at higher dye concentration.

With the goal of accurately detecting and quantifying the amounts of dopamine (DA) and serotonin (5-HT) in mixtures of these neurotransmitters without using any labelling, we present a detailed, comparative computational and Raman experimental study. Although discrimination between these two analytes is achievable in such mixtures for concentrations in the millimolar range, their accurate quantification remains unattainable. As shown for the first time in this work, the formation of a new composite resulting from their interactions with each other is the main reason for this lack of quantification. While this new hydrogen-bonded complex further complicates potential analyte discrimination and quantification at concentrations characteristic of physiological levels (i.e., nanomolar concentrations), it can also open new avenues for its use in drug delivery and pharmaceutical research. This remark is based not only on chemical interactions analyzed here from both theoretical and experimental approaches, but also on biological relationship, with consideration of both functional and neural proximity perspectives. Thus, this research constitutes an important contribution toward better understanding of neural processes, as well as toward possible future development of label-free biosensors.