One-step microwave synthesis of N,S co-doped carbon dots from 1,6-hexanediamine dihydrochloride for cell imaging and ion detection
Graphical abstract
Introduction
Trace anions play an essential role in various fields such as biology, chemistry and environment. The detection of these anions has become one of the important research fields [[1], [2], [3]]. However, the application of various detection methods has encountered challenges due to the diversity and complexity of ions. Among various detection technologies, fluorescence detection method is easy operation with good selectivity, sensitivity and response time, and thus this method is widely used in the field of biological detection [[3], [4], [5], [6], [7]]. Although traditional fluorescent chemical sensors can also detect biomolecules, most of these probes are based on small organic molecules. Some small molecular probes are complex in design with poor water solubility, and cannot detect molecules in pure aqueous phase [8]. As a new form of fluorescent luminescent material, fluorescent nano-materials have obvious advantages compared with traditional organic dyes, such as good water solubility and light stability, so they are widely used in ion detection fluorescent sensors [[9], [10], [11], [12]]. The fluorescent sensor of the traditional quantum dot has a potential impact to the environment and human health because of the presence of heavy metal atoms with strong toxic and side effects, so it is difficult to be clinically applied [[13], [14], [15]].
As a novel fluorescent carbon nanomaterial, carbon dots (CDs) possess outstanding photoluminescence properties and small size characteristics with favourable low cytotoxicity and biocompatibility, which are the best choice for replacing quantum dots [[16], [17], [18], [19]]. For instance, Feng et al. synthesized carbon dots through hydrothermal method employing ethylenediamine and citric acid [20]. The fluorescence response of CDs for NO2− was studied at different pH, manifesting the CDs synthesized by this method can be used in the quantitative analysis of NO2−. The blue fluorescence N, B co-doped carbon quantum dots were acquired in our previous study using polyethylenimine and 4-formylphenylboronic acid [21]. Then it was used for the detection of Fe3+ in solution, and the limit of detection (LOD) was 1.62 μM. Furthermore, we successfully synthesized N, S co-doped CDs by hydrothermal method employing cystamine dihydrochloride and citric acid as precursor, and the quantum yield (QY) of CDs reached up to 39.7 % [22]. The N, S/C-dots was applied to the detection of Cr2O72−, and the LOD was 0.86 μM.
Here, we successfully synthesized the N, S co-doped carbon quantum dots (N/S-CDs) using 1,6-hexanediamine dihydrochloride and dimethyl sulfoxide. The optimal wavelength of emission for the N/S-CDs was 512 nm with a quantum yield of 24 %. Furthermore, we used it for the detection of MnO4− with a LOD of 0.34 μM. Finally, cell imaging of the N/S-CDs was also successfully photographed, demonstrating its excellent biocompatibility.
Section snippets
Material
1,6-hexanediamine dihydrochloride was bought from Sigma-Aldrich, and dimethyl sulfoxide (DMSO) was bought from Richjoint Chemical Reagents. 3-(4,5-dimethyl-2-thiazolyl) -2,5-diphenyl-2-H-tetrazolium bromide (MTT), dulbecco's modified eagle medium (DMEM) and phosphate buffer saline (PBS) were obtained from Gibco, and human breast cancer cell (MCF-7) was purchased from the cell repository of Chinese Academy of Sciences. Total reagents were obtained from Shanghai, China. The purity of all reagents
Characterization of the N/S-CDs
The N/S-CDs were synthesized using 1,6-hexanediamine dihydrochloride as carbon sources in DMSO by simple microwave method (Fig. 1). The synthesized N/S-CDs displayed outstanding dispersibility and photoluminescence stability.
The morphology and size of the sample was measured by TEM. Fig. 2a showed the particle size lay within the limits of 1–6.6 nm, and the average diameter of particles was about 4.35 nm. The XRD pattern (Fig. 2b) implied that the N/S-CDs has a wider graphitic carbon
Conclusions
In conclusion, one-step microwave method was utilized for the simple synthesis of N/S-CDs with respectable QY of 24 %, and these synthesized carbon dots have excellent optical properties and emit blue, green, yellow and orange fluorescence as the excitation wavelength increases. The N/S-CDs has excellent thermal stability and can further enhance fluorescence emission under medium and acidic conditions. Then, the N/S-CDs exhibited certain selectivity for MnO4− and Cr2O72−, and the limits of
Credit author statement
Jiucun Chen, Yanzi Jin and Zhiqin Deng conceived and designed the study and wrote the manuscript. Caihe Ding and Zhiqin Deng performed all the synthesis and characterization experiments. Yanzi Jin revised the manuscript.
Declaration of Competing Interest
There are no conflicts of interest to declare.
Acknowledgements
We gratefully acknowledge the financial support of the Fundamental Research Funds for Central Universities (SWU118035 and XDJK2019B001), the Transformative Project for Excellent Scientific and Technological Achievements in University (KJZH17108) and the Special Program for Chongqing Social Business and People’s Livelihood Guarantee of Science and Technology (cstc2017shmsA30001).
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These authors contributed equally to this work.