One-step Hydrothermal Synthesis of Nitrogen-doped Carbon Dots for Fe3+ Detection and Their Application in Cellular Imaging

KeyWord:carbon dots  hydrothermal synthesis  fluorescence quenching  cellular imaging  Fe3+ detection

Abstract:

      Iron is one of the essential elements in the human body£¬while the confusion of iron content might cause a range of functions of the central nervous system disorder£¬including motional£¬physical and cognitive£¬and other aspects£®Therefore£¬it is very important to develop a convenient and low-cost detection method£®Amino acid is one of the ideal carbon sources for carbon dots£¬while heteroatom doping could be realized during the preparation process£¬and the fluorescence quantum yield will be raised£®The carbon dots prepared by utilizing amino acids also have good biocompatibility£¬which could be used as a probe to label cell and living organisms£®In this study£¬the water-soluble blue fluorescent nitrogen-doped carbon dots£¨N£­CDs£© were prepared by one-step hydrothermal method£¬with natural amino acid molecules tryptophan and threonine as the precursors£®Meanwhile£¬the N£­CDs were used for the detection of Fe3+ in actual water samples and cell imaging. The structure£¬composition and optical properties of N£­CDs were characterized by high-resolution transmission electron microscopy£¬X-ray diffraction spectrum£¬X-ray photoelectric energy spectrum£¬Fourier transform infrared absorption spectroscopy£¬ultraviolet spectroscopy and fluorescence spectroscopy£®The results showed that the N£­CDs have a uniform-size structure similar to graphite£¬with an average particle size of 4.1 nm£®Combined with Fourier transform infrared£¬ultraviolet and X-ray photoelectric energy spectral characterization£¬it was found that there were carboxyl£¬hydroxyl and amino groups on N£­CDs surface£¬which made the N£­CDs have good water solubility£®The composition of N£­CDs was determined by X-ray photoelectric energy spectroscopy£¬in which the contents of carbon£¬nitrogen and oxygen accounted for 70.8%£¬8.4% and 20.8%£¬respectively£®The N£­CDs showed a good fluorescence stability towards the irradiation by sunlight and the ionic strength£®The fluorescence intensity of the N£­CDs maintained stable in weak acid and neutral solution£¬with a fluorescence quantum yield high up to 87.09%£®The results showed that Fe3+ could significantly quench the fluorescence of the aqueous N£­CDs solution£®Base on the fluorescence quenching£¬a new analysis method was established for the detection of Fe3+ in drinking water samples£®There were good linear relationships for Fe3+ in the range of 1£­20 ¦Ìmol/L and 20£­50 ¦Ìmol/L£¬respectively£¬with two linear fitting equations of I0/I = 0.001 09£ÛFe3+£Ý + 1.011 7 and I0/I = 0.003 81£ÛFe3+£Ý + 0.954 9£¬and the correlation coefficients £¨r2£© of 0.999 4 and 0.997 3£®The limits of detection £¨LODs£¬S/N = 3£© were 0.36 ¦Ìmol/L£®In addition£¬the N£­CDs were applied to the determination of Fe3+ in drink bottled mineral water£¬with recoveries of 97.3%£­107%£¨RSD ¡Ü 2.0%£©£®With low detection limit£¬good selectivity£¬high sensitivity and good accuracy£¬this method could be used for the detection of Fe3+ content in water body£®Furthermore£¬a study on cytotoxicity was performed with HL£­7702 cells by this method£¬in which the N£­CDs exhibited low cytotoxicity and good biocompatibility£¬and was successfully used for in vitro imaging in HL£­7702 cell to achieve the visualization of Fe3+ in cells£®In conclusion£¬the N£­CDs with excellent optical properties have a great application potential in the field of analytical detection and cell imaging£®