The thin film of a heptamethine cyanine chromophore HC was prepared by spin-coating technique. Its surface morphology and linear optical property were characterized by atomic force microscopy (AFM) and UV-visible absorption spectroscopy. The results show that HC molecules are arranged in a well-ordered H-aggregate type. The third-order nonlinear optical properties of the spin-coating film were also measured by degenerate four-wave mixing (DFWM) measurement. Enhanced third-order nonlinear susceptibility can be attributed to molecular aggregation effects, and the corresponding mechanism was dealt with by collective electronic oscillator (CEO) approach.
Dependence of surface-enhanced Raman scattering （SERS） from Calf thymus DNA on anions is investigated. With the silver colloid, the bands at 732, 960 and 1333 cm^-1 for adenine （A）, 1466 cm^-1 for deoxyribose, and 1652 cm^-1 for the C=O group of thymine （T） are observably enhanced. With the presence of the Cl^- or SO4^2- anions, the bands at 732 and 1326/1329 cm^-1 for the symmetric stretching and skeletal vibrational modes of adenine （A） are dramatically enhanced, and the enhancement effect with the SO4^2- ion is more than that with the Cl^- ion. The experimental results show that the DNA molecule can be adsorbed on the silver colloid particles through the C6N and N7 of adenine （A） the C=O of thymine （T） and deoxyribose. Moreover, the formed hydrogen bonding of the Cl^- or SO4^2- ions to the C6NH2 group of adenine （A） can induce larger C6N electronegativity, which is favor for the C6N/N7 cooperative adsorption on the （Ag）^＋ colloid particles.
Raman spectroscopy has strong potential for providing non-invasion diagnosis of cancers. In this paper, micro-Raman spectroscopy is used to diagnose one most common liver cancer, hepatocellular carcinoma （HCC）. The statistical analyzes, including t-test, principal component analysis （PCA）, and linear discriminant analysis （LDA）, are performed on the Raman spectra of malignant and normal hepatocytes. The t-test-LDA results show that the 786- and 1004-cm^-1 bands of the malignant and normal hepatocytes are significantly different, and PCA-LDA results show an overall accuracy of 100% for the Raman spectroscopic identification of normal and malignant hepatocytes in our experiment.
A femtosecond laser pulse can be tailored to control the two-photon transitions using the ultra-fast pulse-shaping technique. This paper theoretically and experimentally demonstrates that two-photon transitions in molecular system with broad absorption line can be effectively controlled by square phase-modulation in frequency domain, and the influence of all parameters characterizing the square phase-modulation on two-photon transitions is systemically investigated and discussed. The obtained results have potential application in nonlinear spectroscopy and molecular physics.
To study the efficacy and side effects of antitumor drug by the method of Raman spectroscopy, the cancerous （SGC-7901） and normal （GES-1） gastric cells were treated with 0, 25-, 100-, and 200-mg/L 5-fluorouracil （5-Fu） for 24 h, respectively, then Raman spectra of cells were recorded. The excitation wavelength was 514.5 nm and the Raman spectra in the region of 500 - 1800 cm^-1 were recorded. For the gastric cancer cells, as the concentration of 5-Pu increases, the band at 1094 cm^-1 attributed to the symmetric stretching vibration mode of PO2^- in the DNA backbone gradually decreases, and the intensity ratio of the band at 1315 cm^-1 to that at 1340 cm^-1 （I1315/I1340） shows the ascending trend, and the ratio of the band area at 1655 cm^-1 to that at 1450 cm^-1 （A1655/A1450） shows the slight ascending trend. For the normal gastric cells, these peaks also appear changes, however, the changes are weaker than those for the cancer cells. In SGC-7901 cells, 5-Pu can interfere with the DNA synthesis and result in the reduction of the DNA content. Besides, it can affect the unsaturation degree of the hydrocarbon chains and alter the external environment of guanine and adenine residues in cancer cells. The changes of Raman spectra for normal gastric cells reveal the side effect of 5-Fu.
