| With the rapid development of Molecule Biology, bioscience, medicine and pharmacology, the study of detecting, identifying and controlling ultra-trace and single biological molecule in water is one of the profound and significant projects.Measuring the molecule's vibration spectrum is one of the most important means that study on molecule structures, interaction and reaction. For many years laser Raman spectroscopy has been an important tool for the investigation of microscopic molecular structure. There is close relation between molecule's inner structure and other else information. Compared with infrared spectroscopy, Raman spectroscopy has natural advantages. Raman spectroscopy is able to be applied in measuring samples in water, but infrared spectroscopy can not because of the strong absorption. This advantage makes it easy to research biological molecules because water is the basic condition of their life and actions. In particular, without necessary of specially processing sample Raman spectroscopy can realize measuring on the spot. So Raman spectroscopy is one important means of measuring biological molecules in water.In this paper we used liquid-core optical fiber (LCOF). When the excited laser light launched into the LCOF, the Raman scattering (forwards and backwards, only the forwards is useful for us) is produced and gradually cumulated with the light transmitting in the fiber. On the other hand, the intensity of excited laser light and Raman scattering light were attenuated by the all sorts of loss factors in LCOF. So the intensity of Raman spectroscopy is the strongest only when the length of LCOF meets a need. The value of this length, called the optimum length. It depends on the concentration of sample and the molar absorptivity for the exciting light and for the Raman band. It is noted that when the sample concentration is low enough the absorption loss due to sample is very small. Furthermore, the absorption loss of sample for the exciting light is equal to that of sample for a Raman light. Thus, the total loss coefficient of the optical fiber for exciting light is equal to that for Raman light. It can be computed by a formula, which can give off a conclusion , it is evident that the optimum length of a liquid core optical fiber is the reciprocal of the total loss coefficient. When the concentration of sample is very low, the total loss coefficient of the optical fiber is mainly due to the structural defects of the optical fiber. It is reported that the Raman spectrum intensity can be enhanced 102~104 tines by means of a liquid core optical fiber. Moreover, the Raman spectrum intensity can be enhanced 106 times using a resonance Raman technique. Hence , if the resonance Raman effect is produced in a liquid core optical fiber, the Raman spectrum intensity can be enhanced 108~1010 times. It is very significance for us to study on the molecules' inner structures.We designed the technique of the resonance Raman spectrum in liquid-core optical fiber, used it to detect the trace biological molecules in water, and obtained the high intensity, high sensitivity Raman spectrum. In our experiment, we used the hollow-core optical fiber was made of high quality quartz which was produced in Germany and whose inner diameter is 200μm, β-carotene that was bought from Biosciences Inc, DILORï¼OMARS89 Raman spectrometer that was produced in France and whose sensitivity is 1~2, CCD(LN/CCD-1100-PB/UVAR)that was produced by PI company and used to incept the signal, the wavelengths of exciting light were Ar+ laser ,514.5 nm. Because of the high refractive index, lower fluorescence background and other excellence, we used the pyridine to enhance the refractive index of the solution which we would pour into hollow-core optical fiber. The solution in LCOF is airtight in order to keep it stabilization. So we get the Raman spectrum of β-carotene in water phase with the concentration of 10-7~10-8mol/L, and observed the C=C bond π—π* transition (1520cm-1) and C-C bond transition (1155 cm-1) v... |
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