On the basis of an infrared femtosecond Cr:forsterite laser, we developed a semiquantitative method to analyze the microscopic distribution of bilirubins. Using 1230 nm femtosecond pulses, we selectively excited the two-photon red fluorescence of bilirubin dimers around 660 nm. Autofluorescences from other endogenous fluorophores were greatly suppressed. Using this distinct fluorescence measure, we found that poorly differentiated hepatocellular carcinoma (HCC) tissues on average showed 3.7 times lower concentration of bilirubins than the corresponding nontumor parts. The corresponding fluorescence lifetime measurements indicated that HCC tissues exhibited a longer lifetime (500 ps) than that of nontumor parts (300 ps). Similarly, oral cancer cell lines had longer lifetimes (>330 ps) than those of nontumor ones (250 ps). We anticipate the developed methods of bilirubin molecular imaging to be useful in diagnosing cancers or studying the dynamics of bilirubin metabolisms in live cells.

中文翻译：

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内源性胆红素与胆红素二聚体的双光子荧光成像。

在红外飞秒铬：镁橄榄石激光器的基础上，我们开发了一种半定量方法来分析胆红素的微观分布。使用1230 nm飞秒脉冲，我们选择性地激发了660 nm附近的胆红素二聚体的两个光子红色荧光。来自其他内源性荧光团的自发荧光被大大抑制。使用这种独特的荧光测量方法，我们发现低分化肝细胞癌（HCC）组织的平均胆红素浓度比相应的非肿瘤部位低3.7倍。相应的荧光寿命测量结果表明，HCC组织比非肿瘤部位（300 ps）具有更长的寿命（500 ps）。同样，口腔癌细胞系的寿命（> 330 ps）比非肿瘤细胞系（250 ps）更长。