Graphene Quantum Dots as Intracellular Imaging-Based Temperature Sensors.

Bong Han Lee,Ryan Lee Mckinney,Md Tanvir Hasan,Anton V Naumov

doi:10.3390/ma14030616

Bong Han Lee, Ryan Lee Mckinney + Show 2 more

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https://doi.org/10.3390/ma14030616

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Abstract

Non-invasive temperature sensing is necessary to analyze biological processes occurring in the human body, including cellular enzyme activity, protein expression, and ion regulation. To probe temperature-sensitive processes at the nanoscale, novel luminescence nanothermometers are developed based on graphene quantum dots (GQDs) synthesized via top-down (RGQDs) and bottom-up (N-GQDs) approaches from reduced graphene oxide and glucosamine precursors, respectively. Because of their small 3–6 nm size, non-invasive optical sensitivity to temperature change, and high biocompatibility, GQDs enable biologically safe sub-cellular resolution sensing. Both GQD types exhibit temperature-sensitive yet photostable fluorescence in the visible and near-infrared for RGQDs, utilized as a sensing mechanism in this work. Distinctive linear and reversible fluorescence quenching by up to 19.3% is observed for the visible and near-infrared GQD emission in aqueous suspension from 25 °C to 49 °C. A more pronounced trend is observed with GQD nanothermometers internalized into the cytoplasm of HeLa cells as they are tested in vitro from 25 °C to 45 °C with over 40% quenching response. Our findings suggest that the temperature-dependent fluorescence quenching of bottom-up and top-down-synthesized GQDs studied in this work can serve as non-invasive reversible/photostable deterministic mechanisms for temperature sensing in microscopic sub-cellular biological environments.

Highlights

As the cell research advances towards closely studying intracellular mechanisms, so does the need for monitoring the dynamics of cells in real time
As the suspension temperature is increased inside the absorption spectrometer in 2 ◦ C increments, both reduced graphene oxide-derived quantum dots (RGQDs) and N-graphene quantum dots (GQDs) exhibit similar changes in their absorbance spectra
We demonstrate the use of highly biocompatible novel nitrogen-doped (N-GQDs) and reduced graphene-derived (RGQDs) graphene quantum dots as promising intracellular imaging-based temperature sensors

Summary

Introduction

As the cell research advances towards closely studying intracellular mechanisms, so does the need for monitoring the dynamics of cells in real time. Biological cell processes are governed by chemical reactions, which are fundamentally affected by temperature [1,2] These reactions within the cell can occur in different organelles, causing varying temperature gradients to be present at one time due to processes ranging from protein expression to expelled heat from tumors [3,4]. Nanothermometry aims to identify the temperature of the specimen with sub-micrometric spatial resolution [6] This technique of temperature assessment is used in varying systems such as photonic devices, micro-electronics, and biological cells [6,7]. In the latter, general functions of organelles such as hydrolysis of glucose for adenosine triphosphate (ATP)

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