Deep Eutectic Solvent-assisted Synthesis of Nitrogen-doped Carbon Quantum Dots for Cell Imaging
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doi: 10.1007/s40242-020-0015-4
Article
Deep Eutectic Solvent-assisted Synthesis of Nitrogen-doped Carbon Quantum Dots for Cell Imaging LI Long, HUANG Yan*, ZHAO Pei, MIAO Haochi and ZHAO Ting School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, P. R. China Abstract Carbon quantum dots(CQDs) are widely used in fluorescence imaging due to their negligible toxicity, low-cost and excellent fluorescence properties. The fluorescence properties of CQDs are greatly affected by the sy nthesis method, passivation agent and reaction media. In this study, the nitrogen-doped CQDs(N-CQDs) were synthesized by a facile microwave-assisted method with citric acid(CA) as a carbon source and deep eutectic solvents as a N-dopant as well as the reaction solvent. After detailed characterizations, the as-prepared N-CQDs exhibited near spherical morphology with an average size of (2.64±0.55) nm. Besides, the abundant hydrophilic functional groups including hydroxyl, carboxyl, amine and quaternary ammonium were present on the surface of the N-CQDs. The N-CQDs displayed the excitation-dependent fluorescence feature under the excitation wavelength of 350—480 nm. Moreover, the N-CQDs could be efficiently uptaken by RAW264.7 cells and emitted bright green light. Meanwhile, the resultant N-CQDs showed the low cytotoxicity in living cells, suggesting the great potential in bio-imaging applications. Keywords N-Dopant carbon quantum dot; Microwave; Deep eutectic solvent; Green light emission; Cell imaging
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Introduction
Nowadays, molecular imaging technology, such as magnetic resonance imaging(MRI), X-ray computed tomography(CT), positron emission tomography(PET), optical imaging, and ultrasound imaging, has become an essential tool for early diagnosis and follow-up treatment of malignant diseases[1]. Amid these efficacious imaging modalities, fluorescence imaging has been routinely applied in disease diagnosis since it reveals the merits of extraordinary sensitivity, subcellular resolution, real-time imaging and low cost[2]. Accordingly, much effort has been devoted to designing effective fluorescent probes for realizing fluorescence imaging. With the rapid development of nanotechnology in numerous fields, considerable attention has been paid to develop fluorescent nanoprobes as ideal alternatives to replace conventional organic dyes. Among many kinds of nanostructures, semiconductor quantum dots(QDs), such as CdS and CdTe, have garnered the extensive notice, owing to their unique electronic and luminescent properties[3,4]. However, these semiconductor QDs based on cadmium, tellurium or other heavy metals are unfortunately toxic even at low concentrations, which is limited for further applications in biomedical imaging[5,6]. Carbon quantum dots(CQDs), mainly comprised of nontoxic carbon, are emerging as newcomers of the family of fluorescent nanomaterials and have become powerful substitutes of semiconductor QDs[7]. By virtue of the attractive merits, such as negligible toxicity, excellent biocompatibility,
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