Study On Detection Of Heavy Metal Ions Based On Fluorescent Carbon Quantum Dots

Heavy metal ions are widely present in our lives and have an important impact on the environment and human health.The current heavy metal ion detection method can basically achieve high selectivity and low detection limit detection,but there are still shortcomings such as cumbersome sample preparation process,high detection cost,probe raw material harmful to human health,and difficulty in specific detection.Therefore,achieving efficient and sensitive detection of heavy metal ions is very important for environmental protection and human health.In response to the above problems,this paper is based on low-toxic,easy-to-prepared fluorescent carbon quantum dots（CDs）,through the regulation and modification of their surface groups,respectively designed to detect heavy metal ions(Fe³⁺,Hg²⁺,Cd²⁺)in different media,the fluorescent probe realizes highly sensitive detection and meets the detection standards of the World Health Organization（WHO）.The main research contents are as follows:（1）Fluorescent carbon quantum dots（N,S-CDs）co-doped with nitrogen and sulfur were synthesized by microwave-assisted method,which can be used to detect Fe³⁺quickly,with high selectivity and sensitivity.The characterization results show that the surface of N,S-CDs contains amino groups and sulfonic acid groups.Fe³⁺can react with these groups,so that the blue fluorescence at the excitation/emission peak at 350 nm/420 nm is quenched statically.In the concentration range of 0-500μmol/L,the fluorescence intensity of N,S-CDs and Fe³⁺concentration showed a good linear relationship,and the detection limit in tap water was 200 nmol/L.In addition,N,S-CDs have the potential to detect Fe³⁺in cells,expanding its application in the field of biosensors.（2）A mercury ion(Hg²⁺)fluorescent nanoprobe based on phosphate ion modified carbon quantum dot（PP-CDs）was first proposed and synthesized.Hg²⁺can react with PP-CDs surface-modified pyrophosphate groups to form non-fluorescent complexes,which leads to the quenching of green fluorescence at excitation/emission peaks at 400 nm/513 nm.Static quenching is its main quenching mechanism.When the concentration of Hg²⁺is in the range of 0.1-1.4μmol/L,the fluorescence intensity of PP-CDs has a good linear relationship with the concentration of Hg²⁺,and the detection limit in tap water is 2 nmol/L.The quenched system PP-CDs-Hg²⁺can achieve fluorescence recovery by adding GSH,so that the probe can be reused.In addition,PP-CDs have the potential to detect Hg²⁺in cells,expanding its application in the field of biosensors.（3）Gold nanoclusters（AuNCs）with red fluorescence were used as internal reference fluorescence molecules,and nitrogen and sulfur co-doped carbon quantum dots（N,S-CDs）with blue fluorescence were used as analysis signal molecules.The fluorescence enhanced ratio probe N,S-CDs/AuNCs was formed by electrostatic action to detect Cd²⁺concentration.Cd²⁺was added to the N,S-CDs/AuNCs nanometer fluorescence probe,and the fluorescence of N,S-CDs（435 nm）and AuNCs（630 nm）increased to different degrees.When the concentration of Cd²⁺is 0-2.1μmol/L,the fluorescence intensity ratio F₄₃₅/F₆₃₀has a good linear relationship with the concentration of Cd²⁺,and the detection limit in tap water is 62 nmol/L.The prepared fluorescence ratio probe can be used for the determination of Cd²⁺in actual water samples.