Synthesis and characterization of carbon quantum dots by microwave-assisted pyrolysis method from citrus juices and application in fluorescent bioimaging
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Paola Sánchez-Navarro
Abstract
Carbon quantum dots (CQDs) are carbon-based nanoparticles which are less than 10 nm in size and are characterized by having modulable properties of luminescence and conductivity while presenting low toxicity, high water solubility, and biocompatibility, among others. These characteristics make them a good option for possible applications in the industrial, chemical, and biomedical fields. In this study, carbon quantum dots were synthesized using juices of seven different fruits as precursors. The syntheses are carried out by microwave-assisted hydrothermal reaction at 200 °C, and reaction mixtures are purified by column chromatography, followed by characterization via absorbance, fluorescence, infrared spectroscopy and transmission electron microscopy. Comparison of relative concentration of CQDs after 2, 4, and 6 h of reaction show that the best quantum yield obtained (6.3 %) corresponds to the mandarin lime after 6 h pyrolysis (with excitation at 410 nm and maximum emission at 505 nm) with a 4.1 ± 0.8 nm particle size determined via transmission electron microscopy. The synthesized CQDs are shown to be usable in fluorescence bioimaging of Escherichia coli when excited at 450–490 nm, while few or no significant emission is observed at other excitation wavelengths (365 nm and 546 nm), which establishes complementarity and non-interference with other dyes that are used in bioimaging.
Funding source: Office of Naval Research Global
Award Identifier / Grant number: N62909-20-1-2031
Funding source: Consejo Nacional de Rectores
Award Identifier / Grant number: Beca CeNAT 2022
Funding source: Vicerrectoría de Investigación, Universidad de Costa Rica
Award Identifier / Grant number: 540-C1-116
Acknowledgments
Access to lab equipment and instruments in Cenibiot/CENAT, Biodess/UCR, Labquimar/UNA, School of Chemistry/UCR and CICIMA/UCR is acknowledged. The support of LANOTEC Director Dr. José Vega-Baudrit was greatly appreciated. We thank Jessica Nock-Paniagua for fluorescence measurements and proof-reading, and Gerardo Rodriguez-Díaz for XRD measurements.
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Research ethics: Not applicable.
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Informed consent: Not applicable.
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Author contributions: All authors have accepted responsibility for the entire content of this manuscript and approved its submission.
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Use of Large Language Models, AI and Machine Learning Tools: None declared.
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Conflict of interests: The authors state no conflict of interest.
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Research funding: This work was supported by Office of Naval Research Grant N62909-20-1-2031, University of Costa Rica Project 540-C1-116, and Centro Nacional de Alta Tecnología (CeNAT-CONARE) 2022–2023 scholarship.
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Data availability: Data available within the article or its supplementary materials.
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Supplementary Material
This article contains supplementary material (https://doi.org/10.1515/pac-2025-0431).
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