Facile Synthesis Of Long-wavelength Emissive Carbon Quantum Dots For Analysis And Detection

Carbon dots（CDs）are novel zero-dimensional nanomaterials whose diameters are generally lower than 10 nm.CDs have attracted massive attention and are extensively researched and reported in analysis,bioimaging and environmental monitoring because of outstanding characteristics such as ideal fluorescence property,stability,and low toxicity.The main structure of CDs is composed of carbon core and surface function groups.The functional groups on surface of CDs could interact with some certain analytes,resulting in optical performance change of CDs.Colorimetric and fluorescence probes could be developed based on CDs for detection of different substances,such as ions,amino acid and antibiotic.Long-wavelength emissive carbon dots（L-CDs）refers to CDs whose emission peak is located in the range of 550-700 nm.Compared to short-wavelength emission,long-wavelength emission has better penetration capacity and is much safer in biological samples.Besides,excited living cells could emit blue fluorescence（auto-fluorescence effect）,which means that L-CDs could help to avert background inference.Herein,it is necessary to fabricate facile synthesis strategy of L-CDs with low toxicity for biomedicine and environmental monitoring.In this study,three kinds of L-CDs were synthesized for fluorescence detection and cellular imaging analysis.Chapter Ⅰ:Structure,classifications,optical characteristics and synthesis strategy were elucidated,and some research and applications were cited and summarized.Chapter Ⅱ:The major research methods were summarized.Chapter Ⅲ:Yellow-emissive L-CDs were synthesized through hydrothermal method using safranine T and polyethyleneimine as precursors.The maximum excitation and emission wavelength were 438 nm and 554 nm respectively.There were an overlapping area between UV/Vis absorbance spectra of Mn（Ⅶ）and fluorescence spectra of as-prepared L-CDs,and as a result sensing strategy of Mn（Ⅶ）based on as-prepared L-CDs was fabricated.The linear range was 2.5-125μmol/L,and LOD was calculated as0.63μmol/L.The L-CDs could be used for semiquantitative detection of Mn（Ⅶ）in living cells for promising biocompatibility and low toxicity of L-CDs.Chapter Ⅳ:Yellow-emissive L-CDs were synthesized from hydrothermal process of neutral red and L-cysteine.Fluorescence intensity of as-prepared L-CDs kept good linear relationship with pH in the range of 4.2 to 7.4 as result of protonation and deprotonation of nitrogen-containing function groups on surface of L-CDs.Sensitive detection method of hypochlorite was fabricated based on conjugate structure of precursors.The linear range was 10 to 162.5μmol/L,and the limit of detection（LOD）was 1.021μmol/L.Intracellular pH detection and hypochlorite sensing were achieved owing to good biocompatibility and low toxicity of as-prepared L-CDs.Chapter Ⅴ:Green,yellow dual-emissive L-CDs were synthesized from hydrothermal process of neutral red and sodium 2,4-dinitrobenzene sulfonate.Sensing platform of pH and H₂S was established based on specific structure of as-prepared L-CDs.The linear relationship between fluorescence intensity and pH was excellent when pH was in the range of 2.0 to 3.0 and 5.4 to 9.6,which resulted from protonation and deprotonation of nitrogen-containing function groups on surface of L-CDs.H₂S could interact with surface function groups of as-prepared L-CDs and lead to fluorescence enhancement of L-CDs.The linear range was 25-500μmol/L while LOD was 9.7μmol/L.Besides,as-prepared L-CDs could be applied for H₂S detection and pH sensing in living cells and zebrafish owing to high biocompatibility and low toxicity of L-CDs.In summary,three kinds of L-CDs were prepared through one-pot hydrothermal process,using safranine T,polyethyleneimine,neutral red,L-cysteine and sodium2,4-dinitrobenzene sulfonate as precursors.Fluorescence monitoring platforms of Mn（Ⅶ）,pH,hypochlorite and H₂S were fabricated based on L-CDs,and intracellular imaging and sensing were successfully achieved.