Highly cooperative fluorescence switching of self-assembled squaraine dye at tunable threshold temperatures using thermosensitive nanovesicles for optical sensing and imaging

Keitaro Sou,Li Yan Chan,Satoshi Arai,Chi-Lik Ken Lee

doi:10.1038/s41598-019-54418-1

Keitaro Sou, Li Yan Chan + Show 2 more

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https://doi.org/10.1038/s41598-019-54418-1

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Abstract

Thermosensitive fluorescent dyes can convert thermal signals into optical signals as a molecular nanoprobe. These nanoprobes are playing an increasingly important part in optical temperature sensing and imaging at the nano- and microscale. However, the ability of a fluorescent dye itself has sensitivity and accuracy limitations. Here we present a molecular strategy based on self-assembly to overcome such limitations. We found that thermosensitive nanovesicles composed of lipids and a unique fluorescent dye exhibit fluorescence switching characteristics at a threshold temperature. The switch is rapid and reversible and has a high signal to background ratio (>60), and is also highly sensitive to temperature (10–22%/°C) around the threshold value. Furthermore, the threshold temperature at which fluorescence switching is induced, can be tuned according to the phase transition temperature of the lipid bilayer membrane forming the nanovesicles. Spectroscopic analysis indicated that the fluorescence switching is induced by the aggregation-caused quenching and disaggregation-induced emission of the fluorescent dye in a cooperative response to the thermotropic phase transition of the membrane. This mechanism presents a useful approach for chemical and material design to develop fluorescent nanomaterials with superior fluorescence sensitivity to thermal signals for optical temperature sensing and imaging at the nano- and microscales.

Highlights

Thermosensitive fluorescent dyes can convert thermal signals into optical signals as a molecular nanoprobe
We investigated threshold temperature sensing based on the release-induced fluorescence emission of calseine from thermosensitive NV encapsulating concentration-quenching calseine solution (50 mM) at the phase transition temperature[27]
The results indicate the phase transition of the lipid bilayer membrane leads to aggregation and disaggregation of the fluorescent dye, which in turn induces the reversible fluorescence switching in a highly cooperative manner

Summary

Introduction

Thermosensitive fluorescent dyes can convert thermal signals into optical signals as a molecular nanoprobe. Spectroscopic analysis indicated that the fluorescence switching is induced by the aggregation-caused quenching and disaggregationinduced emission of the fluorescent dye in a cooperative response to the thermotropic phase transition of the membrane This mechanism presents a useful approach for chemical and material design to develop fluorescent nanomaterials with superior fluorescence sensitivity to thermal signals for optical temperature sensing and imaging at the nano- and microscales. The results indicate the phase transition of the lipid bilayer membrane leads to aggregation and disaggregation of the fluorescent dye, which in turn induces the reversible fluorescence switching in a highly cooperative manner This finding provides a useful and practical strategy based on molecular assembly control to create advanced fluorescent nanomaterials, which will further facilitate the development of temperature sensing and imaging at the nano- and microscales

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Results

Conclusion