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Open AccessArticle

Carbon Dots for Intracellular pH Sensing with Fluorescence Lifetime Imaging Microscopy

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Department of Optical Science and Engineering, Shanghai Engineering Research Center of Ultra-precision Optical Manufacturing, Green Photoelectron Platform, Fudan University, Shanghai 200433, China
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State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
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Institute of Biomedical Engineering and Technology, Academy for Engineer and Technology, Fudan University, Shanghai 200433, China
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The Multiscale Research Institute of Complex Systems (MRICS), School of Life Sciences, Fudan University, Shanghai 200433, China
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Joint Key Laboratory of the Ministry of Education, Institute of Applied Physics and Materials Engineering, University of Macau, Avenida da Universidade, Taipa, Macau 999078, China
*
Authors to whom correspondence should be addressed.
Nanomaterials 2020, 10(4), 604; https://doi.org/10.3390/nano10040604 (registering DOI)
Received: 9 February 2020 / Revised: 11 March 2020 / Accepted: 24 March 2020 / Published: 25 March 2020
(This article belongs to the Special Issue Application of Carbon Nanomaterials in Biological Detection)
The monitoring of intracellular pH is of great importance for understanding intracellular trafficking and functions. It has various limitations for biosensing based on the fluorescence intensity or spectra study. In this research, pH-sensitive carbon dots (CDs) were employed for intracellular pH sensing with fluorescence lifetime imaging microscopy (FLIM) for the first time. FLIM is a highly sensitive method that is used to detect a microenvironment and it can overcome the limitations of biosensing methods based on fluorescence intensity. The different groups on the CDs surfaces changing with pH environments led to different fluorescence lifetime values. The CDs aqueous solution had a gradual change from 1.6 ns to 3.7 ns in the fluorescence lifetime with a pH range of 2.6–8.6. Similar fluorescence lifetime changes were found in pH buffer-treated living cells. The detection of lysosomes, cytoplasm, and nuclei in living cells was achieved by measuring the fluorescence lifetime of CDs. In particular, a phasor FLIM analysis was used to improve the pH imaging. Moreover, the effects of the coenzymes, amino acids, and proteins on the fluorescence lifetime of CDs were examined in order to mimic the complex microenvironment inside the cells. View Full-Text
Keywords: carbon dots; fluorescence lifetime imaging microscopy; pH sensor; intracellular sensing carbon dots; fluorescence lifetime imaging microscopy; pH sensor; intracellular sensing
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MDPI and ACS Style

Huang, M.; Liang, X.; Zhang, Z.; Wang, J.; Fei, Y.; Ma, J.; Qu, S.; Mi, L. Carbon Dots for Intracellular pH Sensing with Fluorescence Lifetime Imaging Microscopy. Nanomaterials 2020, 10, 604.

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