Detection Of Copper Ions,EDTA,Vitamin B6 And P-glycoprotein Using Amino-functionalized Graphene Quantum Dots As Fluorescent Probes

Graphene quantum dots are a typical carbon-based nanomaterial,which have attracted more and more attention due to their excellent optical property,catalytic ability,low toxicity and high stability.They are widely used as a fluorescent probe for chemical/biological sensing.In the present thesis,amino-functionalized graphene quantum dots?af-GQDs?were prepared and several simple methods for detecting copper ions(Cu²⁺),EDTA,vitamin B6(V_B6)and P-glycoprotein?P-gp?were designed and developed.The main works are listed as follows.1.A fluorescence method with high sensitivity for quantitative detection of Cu²⁺and EDTA was proposed.Af-GQDs were characterized by transmission electron microscopy?TEM?and infrared spectroscopy?IR?.Fluorescence resonance energy transfer?FRET?between af-GQDs and 1-?2-pyridylazo?-2-naphthol?PAN?could quench the fluorescence of af-GQDs.After Cu²⁺were added,they formed complex with PAN,which enhanced the FRET effect and further quenched the fluorescence of af-GQDs.The fluorescence intensity change of af-GQDs was linear with the logarithm of the Cu²⁺concentration in the range of 1 nM to 10?M.A detection limit of 0.87 nM was obtained at a signal-to-noise ratio of 3.EDTA could decompose the Cu²⁺-PAN complex and liberate PAN.Due to the declined FRET efficiency,the fluorescence of af-GQDs was turned on to some extent.As a result,the detection of EDTA was realized.There was a good linear relationship between the fluorescence intensity change and the logarithm of EDTA content in the range of 10 nM-10?M.The detection limit was measured to be 2.8 nM at a signal-to-noise ratio of 3.The good recovery rates were obtained for the detection of Cu²⁺in the water samples and the detection of EDTA in the trypsin-EDTA solution,the recovery rates varied from 93%to 106%and 97%to 105%,respectively.2.Trimanganese tetraoxide nanoparticles?Mn₃O₄ NPs?were synthesized and they were characterized by TEM,UV-visible absorption spectroscopy and X-ray photoelectron spectroscopy?XPS?.The inner filter effect and FRET between Mn₃O₄ NPs and af-GQDs resulted in the fluorescence quenching of af-GQDs.After the addition of vitamin B6,Mn³⁺in Mn₃O₄ NPs was reduced to Mn²⁺.The absorbance of Mn₃O₄ NPs was greatly reduced,the inner filter effect and FRET effeciency were inhibited,and the fluorescence of af-GQDs was partly recovered.When the concentration of V_B6 was in the range of 10 nM to 50?M,the fluorescence intensity change of af-GQDs was in proportion to the logarithm of V_B6 concentration.The detection limit was calculated to be0.49 nM at a signal-to-noise ratio of 3.The analysis of V_B6 content in vitamin B6 injection was realized by using the developed method,the recovery was found to vary from 97%to 108%,and the experimental results was satisfactory.3.Twoquantumdots-biomaromoleculescomplexes,af-GQDs-P-glycoproteinantibodies?af-GQDs-Ab?and af-GQDs-P-glycoprotein?af-GQDs-Ag?were prepared,respectively.Both the two nanocomposites displayed a certain fluorescence intensity.When they were mixed together,the fluorescence intensity of the mixture solution was less than the sum of the fluorescence intensities of the two components due to the optical collision of af-GQDs.After the addition of P-gp,the immunoreaction between af-GQDs-Ab and P-gp weakened the binding of the two nanocomposites and the above mentioned optical collision,which led to the fluorescence recovery.The fluorescence intensity change of the mixture solutions was linearly related to the logarithm of the P-gp concentration in the range of 10 pg mL^-1 to 10?g mL^-1,with a detection limit of 4.8 pg mL^-1 at a signal-to-noise ratio of 3.The sensitive detection of P-gp was achieved and the proposed method exhibited good selectivity.