Department of Electrical and Computer Engineering, Duke University, Durham, North Carolina 27708, USA.
Department of Chemistry, Duke University, Durham, North Carolina 27708, USA.
Sci Rep. 2016 Nov 11;6:36871. doi: 10.1038/srep36871.
Pump-probe microscopy is an emerging technique that provides detailed chemical information of absorbers with sub-micrometer spatial resolution. Recent work has shown that the pump-probe signals from melanin in human skin cancers correlate well with clinical concern, but it has been difficult to infer the molecular origins of these differences. Here we develop a mathematical framework to describe the pump-probe dynamics of melanin in human pigmented tissue samples, which treats the ensemble of individual chromophores that make up melanin as Gaussian absorbers with bandwidth related via Frenkel excitons. Thus, observed signals result from an interplay between the spectral bandwidths of the individual underlying chromophores and spectral proximity of the pump and probe wavelengths. The model is tested using a dual-wavelength pump-probe approach and a novel signal processing method based on gnomonic projections. Results show signals can be described by a single linear transition path with different rates of progress for different individual pump-probe wavelength pairs. Moreover, the combined dual-wavelength data shows a nonlinear transition that supports our mathematical framework and the excitonic model to describe the optical properties of melanin. The novel gnomonic projection analysis can also be an attractive generic tool for analyzing mixing paths in biomolecular and analytical chemistry.
泵浦探针显微镜是一种新兴的技术，它可以提供亚微米空间分辨率的吸收体的详细化学信息。最近的研究表明，来自人类皮肤癌中黑色素的泵浦探针信号与临床关注密切相关，但很难推断出这些差异的分子起源。在这里，我们开发了一个数学框架来描述人类色素组织样本中黑色素的泵浦探针动力学，该框架将构成黑色素的单个发色团的集合视为具有带宽的高斯吸收体，带宽通过 Frénkel 激子相关。因此，观察到的信号是由单个基础发色团的光谱带宽和泵浦和探针波长的光谱接近度之间的相互作用产生的。该模型通过双波长泵浦探针方法和基于正形投影的新型信号处理方法进行了测试。结果表明，信号可以用单个线性跃迁路径来描述，对于不同的泵浦-探针波长对，其进展速度不同。此外，组合的双波长数据显示出非线性跃迁，这支持了我们的数学框架和激子模型来描述黑色素的光学性质。新颖的正形投影分析也可以成为分析生物分子和分析化学中混合路径的有吸引力的通用工具。
