Preparation And Application Of Fulorescent Probe In Environmental Detection

In this work,a"off-on"fluorescent method was developed for the detection of hydroquinone using the silver nanoclusters（AgNCs@CAZ）as a probe because manganese dioxide nanosheets（Mn O₂-NS）can effectively quench the fluorescence of AgNCs@CAZ that were synthesized by a template method.In addition,in-situ synthesis of azabuteramine was achieved by mixing resorcinol and dopamine hydrochloride.Use this as a fluorescent probe to realize the detection of heavy metal Cr⁶⁺based on the fluorescence characteristics of azabuteramine at the same time.2,3-Diaminophenazine（OPDox）is synthesized in situ by the reaction of o-phenylenediamine and AgNO₃,which was used as a fluorescent probe to detect catechol.The specific content is as follows:A one-step method was developed for the preparation of yellow silver nanocluster with strong fluorescence by using CAZ and AgNO₃ as precursors at 85℃for 4 h.High-resolution transmission electron microscopy（HRTEM）showed that the shape of the synthesized silver nanoclusters is spherical with obvious lattice fringes and diffraction spots.X-ray powder diffraction（XRD）showed that the crystalline form of AgNCs@CAZ was amorphous silver,which was attributed to highly disordered silver particles.The infrared transform spectrum（FTIR）indicated that the surface of the AgNCs@CAZ was rich in hydrophilic groups,so it had good water solubility.Then the ultraviolet-visible spectra（UV-Vis）of the AgNCs@CAZ was measured.There was an obvious absorption peak at 262 nm,which was the characteristic ultraviolet-visible absorption peak of AgNCs@CAZ.The fluorescence spectra results showed that AgNCs@CAZ could emit blue fluorescence with highest fluorescence intensity.When the optimal excitation wavelength and the maximum emission wavelength were 368 nm and 432 nm,respectively,the fluorescence quantum yield of AgNCs@CAZ measured by the reference method was 4.99%.Corresponding AFM imagefully showed the ultrathin structure of Mn O₂-NS.UV-vis absorption spectrum showed that Mn O₂-NS had a wide absorption spectrum from 200 to 800 nm.The results indicated that in the Britton-Robinson buffer solution at the p H of 6.09,when Mn O₂-NS was added in AgNCs@CAZ solution,the fluorescence of AgNCs@CAZ was quenched,and the fluorescence signal of the system was in the"off"state.To investigate the fluorescence quenching mechanism of the system,the fluorescence lifetimes of AgNCs@CAZ and AgNCs@CAZ-Mn O₂-NS systems were fitted and they were estimated to be 8.87 ns and 8.93 ns,respectively.The fluorescence quenching type of Mn O₂-NS on AgNCs@CAZ was static quenching.In the presence of HQ,the fluorescence of AgNCs@CAZ was recovered,which resulted in the departure of Mn O₂-NS from the surface of the AgNCs@CAZ and the fluorescence signal of the system was"open".The measuring method for HQ was established based on the"off-on"fluorescence system.The recovered fluorescence value△F of AgNCs@CAZ were linearly related with the HQ concentration in the range 5～500μM,the detection limit was 4.87μM and the coefficient of determination R~2 was 0.9979.The method was sensitive,selective,simple and rapid.It has been applied to the determination of HQ in practical samples with satisfactory results.The recovery efficiency was between99.26%and 100.46%.A simple and sensitive fluorescent assay for determination of Cr⁶⁺has been developed by using azabuteramine as a fluorescent probe,where azabuteramine was synthesized by the in-situ reaction of resorcinol and dopamine hydrochloride in the alkaline condition.It was measured by fluorescence emission spectrum that the maximum emission wavelength of azabuteramine was at 468.03 nm when the excitation wavelength was 420 nm.The addition of Cr⁶⁺could lead to the the fluorescence quenching of azamonardine due to the intramolecular charge transfer（ICT）between Cr⁶⁺and the fluorescent probe.With the changing of the Cr⁶⁺concentration,the adsorption intensity at 420 nm gradually decreased,new adsorption peaks appeared and the absorption spectrum of azabuteramine shifted.In order to verify the mechanism of the fluorescence quenching of azamonardine,the fluorescence lifetime of fluorophore with various concentrations of Cr⁶⁺were measured.The results showed that the fluorescent life time remained almost unchanged after the addition of Cr⁶⁺.Therefore,the type of fluorescence quenching by Cr⁶⁺might be static quenching based on ICT.There was a good linear relationship betweenΔF and Cr⁶⁺concentration in the range from 15 to 50μM.The linear regression equation isΔF=19.068C_Cr6+-126.68（R~2=0.9948）.The detection limit is calculated to be 1.2μM based on a signal-to-noise of 3.This fluorometric method has been successfully applied to actual water samples.Ag⁺can oxidate o-phenylenediamine（OPD）to 2,3-diaminophenazine（OPDox）,and the addition of catechol inhibited the generation of OPDox and quenched the fluorescence of OPDox.When Ag⁺and OPD were added in the solution,a fluorescence excitation peak was at 430 nm,a fluorescence emission peak was at 567.94 nm,and an absorption peak the system was at 430 nm.The fluorescence lifetime of the system changed after catechol was added into the solution containing Ag⁺and OPD,which was attributed to the dynamic quenching caused by Internal filtration effect（IFE）.There was a a good linear relationship between the fluorescence intensity differenceΔF and the concentration of catechol in the 0.08～1μM range.The linear equation isΔF=460.87C_CC+22.653（R~2=0.9973）.LOD is as low as 24 n M.The experimental results exhibited that recoveries of CC reached to 99.7%～103.7%with the relative standard deviation（RSD）of 1.2～3.0%,suggesting the applicability of the developed method to the detection of catechol in organic water samples.