Sun Chi-Kuang, Liu Wei-Min, Liao Yi-Hua
Department of Electrical Engineering and Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei 10617, Taiwan.
Graduate Institute of Biomedical Electronics and Bioinformatics, National Taiwan University, Taipei 10617, Taiwan.
Biomed Opt Express. 2019 Oct 14;10(11):5716-5723. doi: 10.1364/BOE.10.005716. eCollection 2019 Nov 1.
Melanin dominates the endogenous contrasts of in vivo third harmonic generation (THG) imaging of human skin. A recent study investigated the THG in melanin solution and a linear relationship between melanin concentration and THG intensity was reported, in contrast to the expected nonlinear relationship. Since melanin hydrocolloid solution is very different from the skin tissue, here we report our study on the origin of the melanin-enhanced THG by using a live cell model. Different from the previous conclusion, our live cell study has indicated an initial nonlinear process where the THG intensity was enhanced according to the 3.5th power of melanin mass density (MMD). When the MMD is higher than 11 mg/ml, a transition from the resonance-enhanced THG to the high-order hyper-Rayleigh scattering process occurs. This saturation phenomenon of the virtual-transition-based THG nonlinear process is attributed to the multi-melanosome-induced scattering within the sub-femtoliter focal volume.
黑色素主导了人体皮肤体内三次谐波产生（THG）成像的内源性对比度。最近的一项研究调查了黑色素溶液中的THG，并报告了黑色素浓度与THG强度之间的线性关系，这与预期的非线性关系形成对比。由于黑色素水胶体溶液与皮肤组织有很大不同，在此我们报告我们利用活细胞模型对黑色素增强THG起源的研究。与之前的结论不同，我们的活细胞研究表明存在一个初始非线性过程，其中THG强度根据黑色素质量密度（MMD）的3.5次方增强。当MMD高于11毫克/毫升时，会发生从共振增强THG到高阶超瑞利散射过程的转变。这种基于虚拟跃迁的THG非线性过程的饱和现象归因于亚飞升焦体积内多黑素体诱导的散射。
