12 February 2009 Enhancement of multiphoton excitation-induced photoacoustic signals by using gold nanoparticles surrounded by fluorescent dyes
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Abstract
Recently, we have developed multiphoton excitation-induced photoacoustic imaging for thick tissues employing a 1064-nm nanosecond pulsed laser. The combination of multiphoton excitation and photoacoustic imaging improves the depth resolution. To apply the multiphoton-photoacoustic imaging for precise investigation in living tissues, it is important to enhance only the photoacoustic signals induced by multiphoton excitation, because the generation of multiphotonphotoacoustic signals is less efficient than that of one-photon photoacoustic signals. In this study, we investigated the relation between the signal intensity and the thermophysical properties of various solutions of fluorescent dyes in multiphoton-photoacoustic imaging. We found that the signal intensity is proportional to the coefficient of thermal expansion divided by the specific heat of the solvent. Thus thermophysical properties are also important, together with absorption properties, in enhancing the multiphoton-photoacoustic signal. Based on our findings, we propose the use of gold nanoparticles surrounded by fluorescent dyes as contrast agents. Rhodamine B, which is employed in fluorescent dyes, selectively evokes the two-photon absorption. In addition, because gold nanoparticles have a small specific heat, the multiphoton-photoacoustic signal generated is strong due to effective photon-to-heat conversion. We conclude that this combination allows deeper observation in living tissues by multiphoton-photoacoustic imaging.
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Yoshihisa Yamaoka, Yoshihisa Yamaoka, Tetsuro Takamatsu, Tetsuro Takamatsu, } "Enhancement of multiphoton excitation-induced photoacoustic signals by using gold nanoparticles surrounded by fluorescent dyes", Proc. SPIE 7177, Photons Plus Ultrasound: Imaging and Sensing 2009, 71772A (12 February 2009); doi: 10.1117/12.808367; https://doi.org/10.1117/12.808367
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