AIE-active non-conjugated poly(N-vinylcaprolactam) as a fluorescent thermometer for intracellular temperature imaging.

Biswajit Saha,Chitrangada Das Mukhopadhyay,Kamal Bauri,Bhuban Ruidas,Priyadarsi De,Sourav Mete

doi:10.1039/c9sc04338a

Abstract

Since temperature is one of the most significant physiological parameters that dictate the cellular status of living organisms, accurate intracellular temperature measurement is crucial and a valuable biomarker for the diagnosis and treatment of diseases. Herein, we introduce the foremost example of a non-conjugated polymer as a next generation fluorescent thermometer which is capable of addressing the key shortcomings including toxicity and thermal-induced fluorescence quenching associated with π-π conjugated system-based thermometers developed so far. We revealed, for the first time, the unique photophysical and aggregation-induced emission (AIE) characteristics of well-known thermoresponsive poly(N-vinylcaprolactam) (PNVCL) devoid of any classical fluorophore entity. PNVCL underwent a coil to globular conformational transition in an aqueous medium and appeared to be fluorescent above its lower critical solution temperature (LCST) near body temperature (38 °C). Eventually, this intriguing aspect enabled higher cellular uptake of PNVCL at the LCST boundary. By virtue of the AIE effect, the thermo-induced aggregation phenomenon has been ingeniously utilized to apply PNVCL as a novel fluorescent thermometer for intracellular temperature determination.

Highlights

Temperature is an important physiological parameter that governs a broad range of biological activities, especially all biological reactions within living cells.[1,2] In addition, various kinds of cellular disorders, such as in ammation and cancer cell growth, are o en accompanied by a temperature increase, an indication of microenvironment dysfunction.[3,4,5,6] the development of a thermo-sensitive device or a thermometer with the ability to detect and monitor the intracellular temperature with high sensitivity is highly desired
PNVCL was synthesized in one step by conventional free radical polymerization (FRP) of commercially available Nvinylcaprolactam (Scheme 1A). 1H NMR spectroscopy and size exclusion chromatography (SEC) were employed to characterize PNVCL
In order to explore the photophysical behaviour of PNVCL, UV-Vis absorption spectra of the polymer were recorded in different solvents (Fig. S3†)

Summary

Introduction

Temperature is an important physiological parameter that governs a broad range of biological activities, especially all biological reactions within living cells.[1,2] In addition, various kinds of cellular disorders, such as in ammation and cancer cell growth, are o en accompanied by a temperature increase, an indication of microenvironment dysfunction.[3,4,5,6] the development of a thermo-sensitive device or a thermometer with the ability to detect and monitor the intracellular temperature with high sensitivity is highly desired. By virtue of the AIE effect, the thermo-induced aggregation phenomenon has been ingeniously utilized to apply PNVCL as a novel fluorescent thermometer for intracellular temperature determination. Direct observation of the PNVCL lm under a uorescence microscope showed tunable photoluminescence from blue and green to red upon altering the emission channels (Fig. 2C).

Results

Conclusion