Visualized sensing through fluorescence signal is a powerful method for chemical and physical detection. In addition to sense those certain species and substances, it becomes much prosperous currently to apply fluorescent sensors into the local microenvironment, for monitoring different behaviours of the surroundings in various chemical or biological process. Most of these fluorescent sensors work through the responsive variation of a single emission signal, thus fluctuations in probe concentration or fluid property can easily cause erroneous signal reading during a practical sensing process (Science, 2003, 300, 87; Chem. Rev. 2016, 116, 7768). Recently, a remarkable progress has been achieved to address these disturbance factors by utilizing fluorescence calibration methods. For example, complex fluorescence strategy with a dual-band inverse is a popular and practical self-calibration method (Nat. Chem. 2009, 1, 69; J. Am. Chem. Soc. 2011, 133, 6626). These approaches can also be, however, easily limited by the overlap of background autofluorescence upon using the fluorescence type only (Nat. Chem. Biol. 2018, 14, 15; J. Am. Chem. Soc. 2010, 132, 1276). There remains a considerable challenge to explore new photoluminescent technique or strategy to simultaneously overcome all these dilemmas.
Recently, Zhu’s group at Fudan University presented a new paradigm for the creation of Fluorescence (FL)–Thermally Activated Delayed Fluorescence (TADF) Dual Emission on a single molecular emitter. TADF emitters have been recognized as the third class OLED materials, as their metal-free long lifetime emission facilitates smart molecular engineering as well as the improvement of internal quantum efficiency. We expect that simultaneous change in emission wavelength and lifetime of the TADF signal from the emitter in sensing will ultimately generate a breakthrough to address the above-mentioned obstacles from a multi-mode perspective. Furthermore, from the self-calibration perspective, the general strategy also relies on the dual-emission characteristic, in which the TADF signal served as a sensing signal with its wavelength and lifetime both altered correlated to environmental polarity, whereas the FL one always kept unchanged and played the role as an internal reference. We demonstrated that a 3-D ratiometric luminescent sensing system upon the ratiometric wavelength (Y-axis) and lifetime (Z-axis) versus polarity (X-axis) can be built, which can be applied to reduce the measurement error by half in average, relative to that with generally using a 2-D curve only.
After the establishment of 3-D ratiometric luminescent sensing strategy, our sensor was further applied into a precise detection of the microenvironmental polarity variation in complex phospholipid system both in vitro and in vivo, towards providing new insights for convenient and accurate diagnosis of membrane lesions. This work demonstrated a multiple self-calibration for avoiding the disturbance factors during a practical sensing process to the most extent, as compared with the traditional fluorescence and ratiometric fluorescence methods (Angew. Chem. Int. Ed. 2015, 54, 2510; Biomaterials 2018, 164, 98).
The related paper has been published in Nature Communications, with Ms. Xuping Li in the group as the first author.
See details: Xuping Li, Gleb Baryshnikov, Chao Deng, Xiaoyan Bao, Bin Wu, Yunyun Zhou, Hans Ågren, Liangliang Zhu*, A Three-Dimensional Ratiometric Sensing Strategy on Unimolecular Fluorescence–Thermally Activated Delayed Fluorescence Dual Emission, Nat. Commun. 2019, 10, 731.