We report the structural chemistry and optical properties of tin (Sn)mixed gallium oxide (Ga 2 O 3 ) compounds, where the interfacial phase modulationinduced structural distortion in turn induces variations in the band gap and nonlinear optical activity. The Sn incorporation into Ga 2 O 3 causes significant reduction in the band gap and induces nonlinear optical activity upon chemical composition tuning. Detailed investigation performed on the structural chemistry, phase stabilization, surface morphology, and optical and electrochemical properties of Sn-mixed Ga 2 O 3 compounds (Ga 2−2x Sn x O 3 , 0.00 ≤ x ≤ 0.3, Ga-Sn-O) indicates that the Sn-incorporation-induced effects are significant. To produce Ga-Sn-O materials of high structural and chemical quality, we adopted a simple solid-state chemical reaction route involving first calcining and then sintering the material at higher temperatures. Structural chemistry analyses of sintered Ga-Sn-O compounds by X-ray diffraction (XRD) showed solid solution formation at lower Sn concentrations (x ≤ 0.10). The XRD analyses indicate the SnO 2 secondary phase formation at higher (x > 0.10) Sn concentrations. Surface morphology analysis using scanning electron microscopy (SEM) also showed a positive relationship between phase separation and Sn concentration. Optical absorption spectra showed a substantial redshift in the band gap (E g ), which would allow Ga-Sn-O compounds to have wide spectral selectivity. At higher Sn concentrations (x = 0.25−0.30), corroborating with structural/chemical analyses, an additional lower-energy sub-band transition that explicitly corresponds to SnO 2 appears in the optical absorption data. Importantly, the evidence of nonlinear optical activity in Ga-Sn-O, which is otherwise not traditionally known for such an activity, as well as dipolar-and quadrupolar-shaped dependence of activity with the polarization angle of the excitation source was detected. At higher concentrations (x ≥ 0.15), Sn was found to be insoluble, which can be attributed to Ga 2 O 3 and SnO 2 possessing different formation enthalpies and cation (Ga 3+ and Sn 4+ ) chemistries. The fundamental scientific understanding of the interdependence of synthetic conditions, structure, chemistry, and optical and electrochemical properties could be useful to optimize Ga-Sn-O inorganic compounds for optical, optoelectronic, and photocatalytic device applications.

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.

Combined theoretical and experimental analysis of serotonin by quantum chemical density functional calculations and surface-enhanced Raman spectroscopy, respectively, is presented in this work to better understand phenomena related to this neurotransmitter’s detection and monitoring at very low concentrations specific to physiological levels. In addition to the successful ultrasensitive analyte detection on silver nanoparticles for concentrations as low as 10−11 molar, the relatively good agreement between the simulated and experimentally determined results indicates the presence of all serotonin molecular forms, such as neutral, ionic, and those oxidized through redox reactions. Obvious structural molecular deformations such as bending of lateral amino chains are observed for both ionic and oxidized forms. Not only does this combined approach reveal more probable adsorption of serotonin into the silver surface through hydroxyl/oxygen sites than through NH/nitrogen sites, but also that it does so predominantly in its neutral (reduced) form, somewhat less so in its ionic forms, and much less in its oxidized forms. If the development of opto-voltammetric biosensors and their effective implementation is envisioned for the future, this study provides some needed scientific background for comprehending changes in the vibrational signatures of this important neurotransmitter.

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.

Defining the pathogenesis of renal osteodystrophy (ROD) and its treatment efficacy are difficult, since many factors potentially affect bone quality. In this study, confocal Raman microscopy and parallel statistical analysis were used to identify differences in bone composition between healthy and ROD bone tissues through direct visualization of three main compositional parametric ratios, namely, calcium content, mineral-to-matrix, and carbonate-to-matrix. Besides the substantially lower values found in ROD specimens for these representative ratios, an obvious accumulation of phenylalanine is Raman spectroscopically observed for the first time in ROD samples and reported here. Thus, elevated phenylalanine could also be considered as an indicator of the disease. Since the image results are based on tens of thousands of spectra per sample, not only are the average ratios statistically significantly different for normal and ROD bone, but the method is clearly powerful in distinguishing between the two types of samples. Furthermore, the statistical outcomes demonstrate that only a relatively small number of spectra need to be recorded in order to classify the samples. This work thus opens the possibility of future development of in vivo Raman sensors for assessment of bone structure, remodeling, and mineralization, where different biomarkers are simultaneously detected with unprecedented accuracy.