Preparation Of Carbon Quantum Dots And Application For Non-enzymatic Detection Of Glucose

Diabetes is a metabolic disease characterized by hyperglycemia.Long-term existence of hyperglycemia leads to chronic damage and dysfunction of various tissues,especially eyes,kidneys,heart,blood vessels and nerves.Glucose is one of the most important metabolites and plays an important role in human physiological process.Carbon quantum dots(CQDs),a new type of carbon nanomaterials,have been widely used in many fields such as photocatalysis,biosensors and biological imaging due to their unique properties.Although some research has been done on the detection of glucose by CQDs,the convenience and speed of the detection conditions need to be improved.There is also room for improvement in accuracy and detection limits.The fluorescence quenching mechanism of CQDs and the detection mechanism of glucose need to be further explored.Therefore,different kinds of carbon quantum dots were prepared,and then CQDs were modified by Ag⁺,KMnO₄and V₂O₅nanometer material.Finally,the obtained three different fluorescent probes were used for the detection of glucose.The research contents are as follows:(1)The silver mirror reaction,a classical chemical reaction of glucose,is used to analyze and detect glucose.The silver mirror reaction is a reaction in which the silver ammonia complex is reduced to metallic silver by the aldehyde group in glucose,while the aldehyde group is oxidized to carboxylate.The Silver mirror reaction is a qualitative experiment for the determination of the aldehyde group and glucose.Therefore,the glucose can be recognized based on the reaction between the aldehyde group and the silver ammonia complex.In present paper,nitrogen-doped carbon quantum dots(NCQDs)with silver ions are introduced to detect glucose.With the addition of Ag⁺ions and glucose in sequence,NCQDs presents an interesting“on-off-on”pattern,realizing the detection of trace amount glucose in the human body.A hydrothermal method was used for the preparation four kinds of nitrogen-doped carbon quantum dots(NCQDs)by using citric acid as the carbon source and ethylenediamine(EDA),urea(U),melamine(MA)and ammonia solution(AS)as the nitrogen source,respectively.The NCQDs were characterized by TEM,FT-IR and XPS,and the optical properties were studied by UV-vis and fluorescence spectra.It is found that the NCQDs(AS)from ammonia solution(AS)as nitrogen source are uniform size spherical nanoparticles and have prominent optical properties.In addition,influencing factors including solution acidity,interfering substances,Ag⁺ions concentration and glucose concentration on the detection of glucose are taken into account.In the presence of Ag⁺ions,the fluorescence of NCQDs(AS)in aqueous solution was severely quenched due to the surface energy transfer from NCQDs(AS)to Ag⁺ions.In weakly alkaline condition,the detected glucose is oxidized to gluconic acid and Ag⁺ions are reduced to Ag in aqueous solution at 60?.Thereby,the abscission of Ag⁺ions from the surface of NCQDs(AS)results in the fluorescence recovery of NCQDs(AS).The glucose can be analyzed quantitatively by NCQDs(AS)in the presence of Ag⁺ions with a wide linear region(0.1?M-1000?M)and low limit of detection(LOD)(0.375?M).Also,the selectivity and anti-interference ability experiment of the NCQDs(AS)in the presence of Ag⁺ions for glucose detection were discussed.In addition,cytotoxicity and cell imaging experiments of NCQDs(AS)were researched.Overall,the prepared NCQDs(AS)are expected to be widely used in the detection of glucose in the field of biological research.(2)MnO₂ nano materials have strong oxidation properties and can oxidize many reductive organic compounds,such as glucose.MnO₂nano materials were introduced into nitrogen-doped carbon quantum dots(NCQDs),and the non-enzymatic detection of glucose was realized through the specific redox reaction between MnO₂nano materials and glucose.A hydrothermal method was used for the preparation of nitrogen-doped carbon quantum dots(NCQDs)by using citric acid as the carbon source and histidine as the nitrogen source.MES buffer and KMnO₄solution were added into NCQDs aqueous solution,and ultrasonic treatment was carried out for 30 min to form NCQDs-MnO₂nanocomposites.The NCQDs-MnO₂nanocomposites were characterized by TEM,FT-IR and XPS,and the optical properties were studied by UV-vis and fluorescence spectra.Influencing factors including solution acidity,interfering substances,KMnO₄concentration and glucose concentration on the detection of glucose are taken into account.After the addition of KMnO₄into NCQDs aqueous solution,the fluorescence of NCQDs aqueous solution was quenched obviously,which was due to the fluorescence resonance energy transfer(FRET)between NCQDs and MnO₂nano materials.When glucose is added to the NCQDs-MnO₂nanocomposites,the MnO₂nano materials are decomposed into Mn²⁺,and the fluorescence of NCQDs was restored.Under optimal conditions,the fluorescence intensity of NCQDs and glucose concentration showed a wide linear range(0.1?M-1000?M)and a low detection limit(0.268?M).Importantly,NCQDs-MnO₂nanocomposites can be used to detect glucose in human urine without the influence of other interfering substances in human body.In addition,the cytotoxicity and cell imaging experiments of NCQDs were also studied.(3)Vanadium pentoxide(V₂O₅) has glucose-like oxidase properties,which is used to analyze and detect glucose.Vanadium pentoxide(V₂O₅)is one of the most important transition metal oxides in VO_xsystem.It has an"oxygen saturated state"(the highest oxidation state of vanadium),which has aroused great interest in the sensor field.V₂O₅nano materials were introduced into carbon quantum dots(CQDs),and the non-enzymatic detection of glucose was realized through the specific redox reaction between V₂O₅nano materials and glucose.In this paper,carbon quantum dots(CQDs)were prepared by one-step hydrothermal method from glucose and citric acid.The CQDs+V₂O₅nanocomposites were characterized by TEM,FT-IR and XPS,and the optical properties were studied by UV-vis and fluorescence spectra.Influencing factors including solution acidity,interfering substances,V₂O₅nano materials concentration and glucose concentration on the detection of glucose are taken into account.In the presence of V₂O₅nano materials,the fluorescence of CQDs in aqueous solution was severely quenched,which is due to the internal filtration effect between CQDs and V₂O₅nano materials.In weakly alkaline condition(pH=8.2),after adding glucose to the solution of CQDs+V₂O₅nanocomposites,V⁵⁺is partially reduced to V⁴⁺in V₂O₅.Then the V₂O₅nano materials are decomposed and the fluorescence of CQDs in aqueous solution is restored.Under optimal conditions,the fluorescence intensity of CQDs and glucose concentration showed a wide linear range(0.1?M-1000?M)and a low detection limit(0.539?M).Importantly,CQDs+V₂O₅nanocomposites can be used to detect glucose in human urine without the influence of other interfering substances in human body.In addition,the cytotoxicity and cell imaging experiments of CQDs were also studied.