Fluorescent carbon dots (FCDs) have attracted tremendous attention in biological applications. The short-wave infrared (SWIR, 900–1700 nm) spectral range is considered as a novel optical tissue window due to low photon scattering. In this work, we investigated the fluorescence characteristics of FCDs based on the SWIR spectral range. SWIR emissions were observed from FCDs for the first time, when long-wavelength excitation (e.g. longer than 731 nm) was adopted. Wavelength-tunable two-photon fluorescence could also be obtained from the FCDs, under 1000–1560 nm SWIR femtosecond (fs) excitation. Interestingly, when an fs excitation wavelength as long as 1560 nm was adopted, two typical nonlinear optical signals, namely two-photon fluorescence and third harmonic generation (THG), could be observed. Based on the one-photon SWIR fluorescence, FCDs were successfully utilized for in vivo sentinel node mapping and tumour imaging. Under SWIR fs excitation, FCD-assisted two-photon fluorescence microscopy realized deep-tissue imaging of zebrafish embryos and the brain neuron networks of mice. SWIR excited and emitting FCDs have potential as fluorescent probes for deep-tissue and high-contrast functional bioimaging and related applications in the future.

中文翻译：

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碳点的短波红外发射/激发荧光及其在生物成像中的初步应用†

荧光碳点（FCD）在生物学应用中引起了极大的关注。由于低的光子散射，短波红外（SWIR，900-1700 nm）光谱范围被认为是一种新颖的光学组织窗口。在这项工作中，我们根据SWIR光谱范围研究了FCD的荧光特性。当长波长激发时（例如，大于731 nm）。在1000-1560 nm SWIR飞秒（fs）激发下，也可以从FCD获得波长可调的双光子荧光。有趣的是，当采用长达1560 nm的fs激发波长时，可以观察到两个典型的非线性光学信号，即双光子荧光和三次谐波（THG）。基于单光子SWIR荧光，FCD已成功用于体内前哨淋巴结定位和肿瘤成像。在SWIR fs激发下，FCD辅助的双光子荧光显微镜实现了斑马鱼胚胎和小鼠脑神经网络的深层组织成像。SWIR激发和发射的FCD在未来的深层组织和高对比度功能性生物成像及相关应用中具有作为荧光探针的潜力。