Two - Photon Enhanced Fluorescence Enhancement Of Coumarin Molecules By Gold Nanorods

Two photon excited fluorescence spectrum is an important part of nonlinear spectroscopy. Due to the fact that the excited light is in long wavelength, the emission light is in short wavelength, excitation is only occurred around the focus point and so on, TPEF has presented high spatial discrimination and low damage in biological detection. It is widely used in physics, chemistry, biology, material and medical science. However, because the nonlinear property of the TPEF, the fluorescence intensity is much lower than one photon excited fluorescence, which limits the application of its technology. Thus it is very important to improve the efficiency of TPEF. In recent years, metal nanoparticles have been widely used in the enhancement of fluorescence spectroscopy, which is supposed to be a very good method for the enhancement of TPEF. The research results show that the metal nanostructures can effectively control the resonance characteristics of surface plasmon. Investigation on the relationship between metal nano structure and TPEF has important scientific value and practical applications.Considering the big gap between the TPEF excited light and the emission light and two SPR peaks of Au nanorods, we use Au nanorods to obtain the enhancement of TPEF. By using two different molecules, Coumarin480and Coumarin540A, the effect of Au nanorods in the enhancement of TPEF is studied. This paper is divided into two parts:In the first part, the effect of the longitudinal SPR is discussed by the TPEF enhancement of Coumarin480. In the second part, after the comparison between the TPEF enhancement of Coumarin480and Coumarin540A, we analyzed the effect of transverse surface plasmon resonance on the TPEF enhancement. Specific work is followed:Part one:the influence of longitudinal SPR and the excitation light on the TPEF enhancement.Au nanorods with different aspect ratios are prepared by seed-growth method. The Au nanorods has good dispersibility. And then, in the spectroscopy experiment, the wavelength of the excitation light is adjusted, the change of TPEF emission intensity is observed. It is found that the TPEF emission of Coumarin480is the best when the wavelength of the excitation light is at730nm. The intensity of the TPEF is lower when the excited light changed. The TPEF enhancement of Coumarin480is achieved by Au nanorods with different aspect ratios(a.r=2.4, a.r=3, a.r=3.5, a.r=4) under different excitation light. By analyzing the enhancement of TPEF, the effect of longitudinal SPR of Au nanorods on the enhancement is researched. It is found that the best enhancement occurred when longitudinal SPR peak is matched with excitation light. The effect of excitation light on the enhancement is researched, too.Part two:the influence of the transverse SPR on the TPEF enhancement.Au nanorods with different aspect ratios and fluorescent molecule membrane were prepared with the same method as that in the part one. The TPEF enhancement of Coumarin540A under different excitation light is observed. We used the same Au nanorods and excitation light in this experiment with part one. The influence of longitudinal SPR is verified by analyzing the TPEF enhancement of Coumarin540A under certain excitation light. The influence of transverse SPR in the TPEF enhancement is researched by comparising Coumarin540A and Coumarin480. It is found that when the transverse SPR peak is matched with the emission light, we can realize an obvious TPEF enhancement.