Synthesis Of Carbon Quantum Dots And Graphene Quantum Dots With Their Applications In Analytical Sensing

In recent years,nanomaterials have been widely used in chemistry,biology,medical science and other relative fields due to their excellent optical properties,good size effect and easy preparation.Among these nanoparticles,carbon quantum dots（CQDs）and graphene quantum dots（GQDs）have received more and more attention owing to good water solubility,small size,stable optical properties and low toxicity.So far,many simple and convenient methods have been developed to detect metal ions and small molecule in aqueous solutions by CQDs or GQDs.In this work,we synthesized fluorescent CQDs and GQDs respectively.And the two fluorescent probes were applied to optical sensing detection.The main research works were as follows:（1）The blue fluorescent CQDs were prepared by hydrothermal method and the green fluorescent GQDs were prepared by high temperature calcination.The preparation conditions for the two quantum dots were optimized.The morphology and spectrum characterizations of the two kinds of nanoparticles were measured respectively.The results showed that the prepared CQDs and GQDs had good water solubility,stable optical properties,uniform size and good dispersibility.（2）Based on the fluorescence resonance energy transfer（FRET）process,we established an optical sensor to quantitative detection of·OH by CQDs and the 4-ASA-Fe²⁺complex.According the literature,the·OH could oxidize 4-ASA-Fe²⁺to 4-ASA-Fe³⁺complex,which have an obvious absorption band from 400 to 600 nm in UV-vis spectrum.Since the fluorescence band of CQDs overlapped the 4-ASA-Fe³⁺complex absorption band,the FRET process might happen and the fluorescence of CQDs was quenched.The degree of fluorescence quenching was linear with the concentration of·OH in the solution.The linear range is 0.5-4μM and the limit of detection（LOD）is 44 nM.Besides,the probe exhibited high selectivity.Herein,this sensing system is a simple and convenient way to detect·OH with high sensitivity and selectivity.（3）In this chapter,an optical sensor for quantitative detection ofβ-galactosidase activity was constructed based on the FRET process of the GQDs and 4-NP.β-galactosidase was able to catalyze the hydrolysis of 4-nitrophenol-β-D-galactoside to produce 4-NP molecules and glycosides,The fluorescence of GQDs could be quenched by 4-NP molecules.The degree of fluorescence quenching showed linear relationship of theβ-galactosidase activity.These experimental results showed that the system could quantitatively detectβ-galactosidase activity.The detection linear range is 20-200 U/L and LOD is 4.4 U/L.This method not only provides a simple and convenient way for the detection ofβ-galactosidase but also exhibit high sensitivity and selectivity.