A New Method For Fluorescence Detection Of Rifampin,Chlorogenic Acid,Cu²⁺ And Glutathione Based On Carbon Dots

Carbon dots(CDs)was a new type zero-dimensional carbon-based fluorescent nanomaterials with diameter less than 10 nm.Compared with traditional organic dyes and semiconductor quantum dots(QDs),CDs were found to display many unique properties,for instance,low toxicity,high water solubility,good biocompatibility,tunable stable fluorescence emission,unique optical and physical and chemical properties,facile preparation.Therefore,CDs was regarded as an environmentally friendly nanomaterial,have been considered to be promising nanomaterial in many feld,including biosensing,biochemical analysis,photocatalyst,fluorescence imaging and drug delivery.In this work,ammonium citrate and citric acid were used as carbon sources respectively,and CDs with different characteristics were synthesized by a simple one-step hydrothermal method.The morphological characteristics,chemical structure,and optical properties of CDs were analyzed using various characterization methods.In addition,new methods for detecting rifampicin,chlorogenic acid,Cu2+ and glutathione were established using the fluorescence characteristics of CDs,and the reaction mechanism was also carefully discussed.The specific research content was as follows:1.Efficient one-pot synthesis of carbon dots as a fluorescent probe for the selective and sensitive detection of rifampicin based on the inner filter effectIn this paper,carbon dots(CDs)emitting blue fluorescence were prepared using ammonium citrate and ammonium thiocyanate through a low-cost hydrothermal approach.The synthesized carbon dots with maximum excitation and emission wavelengths at 350 nm and 443 nm,respectively,displayed excitation-independent photoluminescence behavior.The relative quantum yield of the as-prepared carbon dots was measured to be 14%.Importantly,a novel method was designed for rifampicin detection as the fluorescence intensity of carbon dots could be quenched significantly by rifampicin on the basis of the inner filter quenching effect.Under optimal experimental conditions,a satisfactory linear response relation was observed between the fluorescence quenching intensity of the carbon dots and the concentration of rifampicin in the range from 0.43 to 49.0 mg L-1;moreover,the detection limit for rifampicin was as low as 0.13 mg L-1.Therefore,a new method has been successfully established,and it is capable of quantification of rifampicin in real samples.2.Hydrothermal synthesis of carbon dots and their application for detection of chlorogenic acid A novel and sensitive fluorescence analysis platform was constructed for the detection of chlorogenic acid(CGA)by carbon dots(C-dots)with prominent sensitivity and selectivity.Excitation-dependent emission fluorescence C-dots were fabricated using citric acid and L-histidine as precursors by an efficient one-step hydrothermal treatment.The maximum excitation and emission wavelength of as-synthesized C-dots were 340 nm and 414 nm,respectively.Moreover,the as-prepared C-dots displayed excellent water solubility and good photostability.The fluorescence quantum yield of as-prepared C-dots was measured to be about 22%using quinine sulfate as reference.Furthermore,the obtained C-dots were applied to the detection of CGA accompanied with a wide linear range from 1.53 ?mol L-1 to 80.0 ?mol L-1 as well as a limit detection of 0.46 ?mol L-1.More importantly,the proposed fluorescent method was successfully used to the analysis of CGA in coffee and honeysuckle.3.Carbon quantum dots based ratiometric fluorescence probe for sensitive and selective detection of Cu2+and glutathioneA novel method was established for the ratiometric fluorescence detection of Cu2+and glutathione(GSH)by carbon quantum dots(CQDs),and it was fabricated through one-pot facile hydrothermal treatment using ophenylenediamine(OPD)and citric acid as precursors.Based on the selective oxidation reaction of OPD with Cu2+,the detection strategy of Cu2+was proposed using ratiometric fluorescence probe.The oxidation production(2,3-diaminophenazine)of OPD,obtained through the oxidation reaction of OPD and Cu2+,not only emerged a new emission peak at 562 nm,but also quenched the fluorescence of CQDs with maximum emission at 446 nm.The mechanism was Forster resonance energy transfer(FRET)between CQDs and 2,3-diaminophenazine(oxOPD).Furthermore,when glutathione was added to the mixed solution of CQDs and Cu2+,Cu2+and glutathione were chelated first,followed by the addition of OPD,the free Cu2+oxidizes OPD to oxOPD.As the concentration of glutathione increased,the free Cu2+decreased,resulting in an increase in the fluorescence of the carbon dots and a decrease in the fluorescence at 562 nm.The sensing system showed high sensitivity toward Cu2+and GSH in a range of 0.25-10.0 ?mol L-1 and 1.0-80.0 ?mol L-1 with a detection limit 0.076 ?mol L-1 and 0.30 ?mol L-1,respectively.Besides,the proposed method could apply to efficient quantification of Cu2+and GSH in practical samples with satisfactory results.