Preparation Of Fluorescent Carbon Dots And Its Application For Metal Ions Detection

Carbon dots (C-dots) are a new class of fluorescent nanomaterials that have drawn great attention in biological assays due to their unique properties including good photostablity, impressive water-solubility, lack of blinking, upcoverted fluorescence emission and excellent biocompatibility. Meanwhile, most of the raw materials for synthesizing C-dots are organic molecules, so there are a lot of reactive functional groups on the surface of C-dots., which would be favorable for the detection of ions.Firstly, fluorescence C-dots having amino groups on the surface were prepared by using chitosan as raw materials. By conjugating with a strongly luminescent a europium complex, BHHCT-Eu3+, a novel type of dual-fluorophore nanoparticles, C-dot-BHHCT-Eu3+, has been successfully developed. Transmission electron microscopy (TEM) and fluorescence spectroscopy characterizations indicate that the nanoparticles are monodisperse, spherical and uniform in size (～8.6nm in diameter), and have well-resolved and stable dual fluorescence emission properties. Under excitation at337nm, the C-dot-BHHCT-Eu3+nanoparticles display two emission peaks at410nm and615nm. In the presence of Cu2+, the emission intensity of the C-dot-BHHCT-Eu3+nanoparticles at615nm is significantly decreased, while no fluorescence response can be observed at410nm. In addition, the emission intensity ratio of1615/1410shows a good linear with the concentration of Cu2+. The fluorescence response investigations of the nanoparticles to different metal ions indicate that the C-dot-BHHCT-Eu3+nanoparticles can be used as a ratiometric fluorescent sensing probe for the Cu2+detection with high selectivity and sensitivity.Another type of fluorescent C-dots has been prepared using citric acid as a carbon source by a one-step hydrothermal method. Under the excitation of310nm, the quantum yield of fluorescent C-dots is5.3%. The as-prepared fluorescence C-dots are well dispersed in water, and uniform in size (～2.9nm in diameter). FTIR and Zeta potential analysis show that the fluorescent C-dots have hydroxyl and carboxyl groups on the surfaces. The fluorescence of C-dots can be selectively quenched by Fe3+ions, suggesting that the fluorescent C-dots might be used for recognition of Fe3+ions. In a HEPES buffer (10mM, pH7.0), the fluorescence intensity of C-dots gradually decreases with the increase of Fe3+ion, and shows a good linear with Fe3+concentration in the range of100-500μM with the low detection limit (112.5nM). The result of cell imaging experiments indicates that the prepared C-dots can penetrate into the B16-F10cell, and emit multicolor fluorescence under405nm and 488nm laset irradiation.These results reveal that the C-dots derived from nitric acid might have a potential for the detection of Fe3+ions and cell imaging.