Center for Biomedical Optics and Photonics & College of Physics and Optoelectronic Engineering, Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, Shenzhen University, Shenzhen 518060, China.
Department of Physics School of Science, Beijing Jiaotong University, Beijing 100044, China.
Spectrochim Acta A Mol Biomol Spectrosc. 2023 Jan 5;284:121793. doi: 10.1016/j.saa.2022.121793. Epub 2022 Aug 29.
Stimulated emission depletion nanoscopy (STED) is increasingly applied for the insights into the ultra-structures of organelles in live cells because of the bypassing of the Abbe's optical diffraction limit. Theoretically, with the increase of excitation and depletion laser power, the imaging resolution can be accordingly enhanced and even close to the infinity. Unfortunately, powerful laser illuminations usually produce severe phototoxicity and photobleaching, which will lead to more extra-interference with biological events in live cells and accelerate the decomposition of the fluorescent probes. In view of the trade-off of cell viability and imaging resolution, excellent probes with superior photophysical properties are great in demand. For a qualified STED probes, the saturated stimulated emission intensity (I) is considered as a key evaluating factor. According to the formula, I is inversely proportional to the stimulated emission cross section (σ) of the fluorescent probe. However, the relationship between the σ and chemical structure of the STED probe remain to be unclear. In this work, we explore the influence factors by theoretical calculations on a squaraine dye (MitoEsq-635) and a commercial dye (Atto647N). The results indicate that the increase of transition dipole moment (μ) are beneficial for the increase of σ, thereafter reducing I. Furthermore, we firstly proposed that stimulated emission depletion was qualitatively interpreted by the investigation on the potential energy surfaces of ground states (S) and the first excited states (S) of the dyes.
受激发射耗散纳米显微镜（STED）由于能够突破阿贝光学衍射极限，在活细胞中对细胞器的超微结构进行研究方面得到了越来越广泛的应用。理论上，随着激发和耗尽激光功率的增加，成像分辨率可以相应提高，甚至可以接近无限。不幸的是，强大的激光照射通常会产生严重的光毒性和光漂白，这将导致更多的额外干扰活细胞中的生物事件，并加速荧光探针的分解。鉴于细胞活力和成像分辨率之间的权衡，具有优异光物理性质的优秀探针的需求很大。对于合格的 STED 探针，饱和受激发射强度（I）被认为是一个关键的评价因素。根据公式，I 与荧光探针的受激发射截面（σ）成反比。然而，STED 探针的 σ 与化学结构之间的关系尚不清楚。在这项工作中，我们通过对吖啶染料（MitoEsq-635）和商业染料（Atto647N）的理论计算来探讨影响因素。结果表明，增加跃迁偶极矩（μ）有利于σ的增加，从而降低 I。此外，我们首次通过对染料的基态（S）和第一激发态（S）的势能面的研究，定性地解释了受激发射耗散。
