Design And Preparation Of Fluorescent Carbon Dots And Their Detection Of Heavy Metal Ions

The development of carbon dots（CDs）has dragged increasing attention owing to their good biocompatibility,excellent photostability,photoluminescence（PL）properties,favorable water solubility and inexpensive and abundance of precursors.These peculiarities make CDs an ideal fluorescent nano-probe material.In this paper,a variety of CDs with different fluorescent colors（including blue,orange,pink,yellow and green）were successfully synthesized through different synthesis strategy.Many applications in the fields of metal ions,biomolecules and latent fingerprints have been explored based on their respective luminescence and response properties.Silicon doped carbon dots（Si-CDs）with bright blue emission were fabricated by a facile one-step synthesis method and employed as fluorescent probe for quantitative detection of Hg²⁺.Possessing high photostability and excellent solubility in water,the Si-CDs exhibit efficient response to Hg²⁺by a“on-off”switch strategy.As sensing probe,Si-CDs exhibited a good linear relationship with Hg²⁺in the concentration range of 0.008～0.4μM with limit of detection of 33 n M.Moreover,the proposed method was successfully applied to monitor Hg²⁺in different real water samples with satisfactory recoveries of 96.2%～99.5%,manifesting their excellent accuracy and environment tolerance.Notably,the Si-CDs powder obtained by lyophilization achieved the visualization of latent fingerprints with second-level details.A ratiometric fluorescence probe（P-R-CDs）were fabricated by two different emissive CDs for quantitative detection of Hg²⁺.Blue N doped CDs（B-CDs）were chosen as sensing probe,while orange CDs（O-CDs）were employed as reference unit,respectively.The P-R-CDs demonstrated a consecutive fluorescence color transformation from pink to orange with Hg²⁺as elimination of blue emission,which exhibited visible distinguishable determination for Hg²⁺with detection limit of 2.9 n M.Furthermore,smartphone supported detection platform were exploited for visual determination of Hg²⁺by capturing the variation of fluorescent color precisely.The terrific recoveries in real water and food samples confirmed the environmental tolerance of P-R-CDs,which implied a promising application for quantitative assay of Hg²⁺in food safety and environmental inspection.Two kinds of magnetic carbon dots（Fe₃O₄-CDs）with different fluorescence were facilely fabricated through a hydrothermal method by using RhB and AFC as precursor.The synthesized two kinds of Fe₃O₄-CDs emitted stable blue and bright yellow fluorescence,respectively.The optimal excitation wavelengths are 360 nm and 550 nm,and quantum yield up to 54.7%and 60.9%,respectively.The two Fe₃O₄-CDs probes showed extremely selectivity and excellent sensitivity in the analysis of Hg²⁺with the detection limit of 4.7 n M and 7.1 n M,respectively.Further,the magnetic removal of Hg²⁺process could be realized with high recovery.The two sensors has been successfully applied to the Hg²⁺determination in practical water samples with satisfactory recoveries.The above results demonstrated that the multifunctional application of the two designed magnetic probes will provide new ideas and insights in the field of environmental monitoring and reconnaissance.The Si-CDs with green luminescence was facilely fabricated through one-step strategy with a combination of p-phenylenediamine（PPD）and triaminopropyl trimethoxysilane（APTMS）as precursors.The synthesized Si-CDs with colorimetric and fluorescent dual-signal was utilized to highly sensitive and selective determination of three heavy metal ions(Cu²⁺,Mn²⁺and Co²⁺)and dopamine（DA）.When exposed to different amounts of Cu²⁺,Mn²⁺and DA,the fluorescence emission at 500 nm is remarkably quenched,accompanied by a change in the solutions fluorescence color under UV irradiation.Besides,the Si-CDs solutions display an excellent colorimetric response for Cu²⁺,Mn²⁺,Co²⁺and DA and produce an obvious color change that is visible to the naked eye.More importantly,Cu²⁺,Mn²⁺,Co²⁺and DA could be distinguished according to the color changes of fluorescence and colorimetric.More importantly,the practical applicability of the dual-mode sensing platform has been authenticated by the monitoring of Cu²⁺,Mn²⁺,Co²⁺and DA in real samples with satisfying accuracy and recoveries.