Preparation Of Doped Carbon Quantum Dots And Its Application In Smartphone Colorimetry

Carbon quantum dots（CDs）is a kind of green fluorescent nanomaterial,which has the advantages of low toxicity,good biocompatibility,strong water solubility,stable and adjustable fluorescence properties,simple preparation method and diverse carbon sources.CDs can be widely used in chemical sensing,biological imaging,and photocatalysis fields.Although the traditional fluorescence and colorimetric sensors based on fluorescence photometer and UV-Vis spectrophotometer have good sensitivity and accuracy,their operations suffer from heavy duty,complex procedure and expensive devices.With the continuous development and improvement,smartphones are emerging as powerful analytical devices for colorimetric,fluorescence,chemiluminescence and bioluminescence detection.In this paper,we first summarize the research status of carbon quantum dots,including synthesis methods,properties,characteristics and application.Then the following research work has been done:（1）The boron,nitrogen,and sulfur co-doped carbon quantum dots（BNS-CDs）and sulfur,nitrogen co-doped carbon quantum dots（SN-CDs）were synthesized by one-step hydrothermal method.The morphology,size,spectral properties,surface structure and elemental composition of BNS-CDs and SN-CDs were characterized by means of TEM、FT-IR、UV-vis、FL、XPS、XRD.（2）A method for the determination of hydrogen peroxide by using a smartphone with BNS-CDs as a promising peroxidase mimic was established.Under acid condition,the synthesized BNS-CDs showed excellent activity for catalyzing the colorimetric reaction of 3,3’,5,5’-tetramethylbenzidine（TMB）with H₂O₂ to generate a blue oxide product（ox-TMB）with maximum absorption at 652 nm.A smartphone colorimetric readout device was employed to record the RGB（red green blue）value of the ox-TMB solution via the Android application Color Grab for quantitative detection.The H₂O₂ concentration was linear with|R-R_blank|value in the range of 3-30μM（R²=0.9970）with a limit of detection（LOD）of 0.8μM.The method has been successfully used for the determination of H₂O₂ in mouthwash and milk with a recovery of 92.70%-108.30%.It is a potential portable detection platform for H₂O₂ with good sensitivity,selectivity,simple operation and low cost.（3）A method for the determination of glutathione in serum by using a smartphone with SN-CDs as a peroxidase mimic was established.In the presence of H₂O₂,SN-CDs catalyzed the oxidation of TMB to produce colored product ox-TMB.Glutathione can inhibit the formation of ox-TMB and result in the color fading.The RGB value of the solution was read using a smartphone.The effects of pH,temperature,TMB concentration,SN-CDs concentration and reaction time on the catalytic performance were studied.Under the optimum conditions,the linear relationship between glutathione concentration and R-R₀ was found in the range of0.03-0.1μM（R²=0.9982）,and the detection limit（LOD）was 0.0083μM.The method was applied to the determination of glutathione in mouse serum with a recovery of94.0%-106.2%.