Stimulated Raman scattering investigation of isotopic substitution H2O/D2O system

Stimulated Raman generation of aqueous singlet oxygen without photosensitizers

Singlet oxygen is traditionally produced via photosensitizer molecules such as methylene blue, which function as catalysts. Here we investigate stimulated Raman generation of singlet oxygen from dissolved oxygen in both water (H₂O) and heavy water (D₂O) using nanosecond-pulsed visible blue laser light in the 400-440 nm spectral region without singlet oxygen photosensitizers. We report an oxygen-dependent Stokes peak in the red spectrum (600-670 nm) that is identical when produced in H₂O and D₂O. These red Stokes photons are not detected when an oxygen quencher is present. Temporal photodepletion of the uric acid absorbance peak at 294 nm is consistent with singlet oxygen generation. We postulate that a two-photon stimulated Raman process produces singlet oxygen from O₂ dissolved within the solvents. We note that the energy difference between input and output photons of 0.97 eV is precisely the energy needed to excite O₂ to its singlet state.

Interaction between Heavy Water and Single-Strand DNA: A SERS Study

The structure and function of biological macromolecules change due to intermolecular deuterium bond formation or deuterium substitution with environmental D₂O. In this study, surface-enhanced Raman spectroscopy (SERS) was used to detect interaction sites between D₂O and ssDNA and their action mechanisms. SERS peaks of ssDNA changed with increasing D₂O proportions, and the site of action mainly involved A and G bases, whose number strengthened the interaction between sequences and D₂O and hence the SERS peak intensities. Fixing the number of A and G bases prevented changes in their positions from significantly altering the map. We also identified the interaction between ssDNA sequences that easily formed a G-quadruplex structure and D₂O. The amplitude of the SERS peak intensity change reflected the ssDNA structural stability and number of active sites. These findings are highly significant for exploring genetic exchanges and mutations and could be used to determine the stability and structural changes of biological macromolecules.

Determination of IC50 values of anticancer drugs on cells by D2O - single cell Raman spectroscopy

A simple, sensitive and repeatable D₂O-single cell Raman spectroscopy method is developed to quantify the inhibitory activity of anticancer drugs on cancer cell metabolism. The IC₅₀ values obtained from A549 cells incubated with cisplatin and taxol are comparable with results of CCK-8 and ATP luminescent cell viability assays.

Investigated coherent anti-Stokes Raman scattering in the process of cascaded stimulated Raman scattering in liquid and ice-Ih D2O

Stimulated Raman scattering (SRS) of liquid and ice-Ih D₂O was investigated using a pulsed Nd:YAG laser with a wavelength of 532 nm. The high-order Stokes peaks and corresponding anti-Stokes SRS [Coherent Anti-Stokes Raman Spectroscopy (CARS)] peaks were obtained. Two symmetric and antisymmetric Raman modes of stretching vibrations were observed in liquid D₂O, while only a symmetric stretching vibration mode was observed in ice-Ih D₂O. Pure Stokes SRS is always collinear with the pump beam along the axial direction. Some ring-like Stokes SRS and CARS shifts, which originate from four-wave mixing processes, can also be observed only in the forward direction along with different angles meeting the phase-matching criteria, respectively. Simultaneously, the temporal behavior of SRS in liquid and ice-Ih D₂O was examined, and the temporal waveforms of the pump laser pulse, transmitted pump pulse, and the forward SRS pulse were measured. In both cases, SRS was the dominant contributor to stimulated scattering. However, the efficiency values drastically decreased due to the self-termination behavior of SRS in liquid D₂O, which arose from the thermal self-defocusing of both the pump beam and the SRS beam, owing to the Stokes shift-related opto-heating effect. In contrast, for the SRS process in ice-Ih D₂O, the thermal self-defocusing influence was negligible, benefitting from a much greater thermal conductivity and a higher conversion efficiency of SRS generation retained under both of the conditions.