The Application Of Modified ZnO Quantum Dots In Analytical Chemistry

Quantum dots as a special fluorescent nanomaterials,has been widely used as fluorescent biosensor and cell imaging.ZnO as a new semiconductor quantum dots,has the same optical properties as other traditional quantum dots,and is environment-friendly and nontoxic.The ZnO quantum dots can be stable in water solution by modifying the surface of the ZnO quantum dots,then the modified quantum dots can be used in analysis of water sample and bio-sample.In this study,we obtain a water-soluble and fluorescence ZnO quantum dots by modifying the surface,and used it as the novel sensor.The results of the main study are listed as follows:Part 1: Indirect detection of alcoholic strength in spirits by fluorescence method using the polyethyleneimine capped ZnO QDs.We synthesized polyethyleneimine capped ZnO quantum dots?PEI-ZnO QDs?which dispersed well in ethanol by using a two-step method.UV-visible absorption spectroscopy,photoluminescence,Fourier transform infrared spectroscopy,high resolution transmission electron microscope,and field emission scanning electron microscope were used to characterize the as-prepared PEI-ZnO QDs.It emitted green-yellow fluorescence?527 nm?for excitation at 355 nm.We used the PEI-ZnO QDs to determine the alcoholic strength because of its different property in water and ethanol which caused decrease in the PEI-ZnO QDs fluorescence intensity with increasing water content.With this method,we determined the alcoholic strength of different artificial samples with a linear range from 20% to 60% vol and detected commercial spirits with satisfactory results.Part 2: A new fluorescent sensor for detecting p-nitrophenol based on ?-cyclodextrin-capped ZnO quantum dots.In this work,the fluorescent ?-cyclodextrin-capped ZnO quantum dots??-CD @ZnO QDs?with a good water-soluble have been synthesized via a facile method.And the synthesized ?-CD @ZnO QDs with a diameter ³.64 nm and a yellow fluorescence have been characterized by high resolution transmission electron microscope,UV-visible absorption,photoluminescence,and Fourier transform infrared spectroscopy.The ?-CD @ZnO QDs were used to be a fluorescent sensor for the detection of p-nitrophenol.A linear relationship to the concentration of the p-nitrophenol over the range of 1.0 – 40 ?M with the detection limit of 0.34 ?M was obtained.The sensing property of the ?-CD-capped ZnO QDs has been successfully examined in real water samples.And the quenching mechanism was proposed,which showed that the quenching effect may be caused by the inclusion complexation between ?-CD and p-nitrophenol and electron transfer.Part 3: A new fluorescence assay for Cobalt using?-cyclodextrin-capped ZnO quantum dots.A new method for detecting cobalt ions based on luminescent and water-soluble ?-cyclodextrin-capped ZnO quantum dots?QDs?has been developed in this work.The ?-cyclodextrin-capped ZnO quantum dots??-CD @ZnO QDs?showed strong yellow-green fluorescence.The Fourier transform infrared spectroscopy,high-resolution transmission electron microscopy,luminescence,and UV-visible absorption spectroscopy were used to elucidate the characters of the ?-CD @ZnO QDs.Furthermore,the fluorescence of the ?-CD @ZnO QDs can be quenched in the presence of Co²⁺ ions.Therefore,a novel fluorescent probe was designed to detect Co²⁺ in water solutions.The detection limit for Co²⁺ was 0.34 ?M based on 3?/slope with a linear range from 1.0 to 10 ?M.The sensing property of the ?-CD-capped ZnO QDs has been used in real samples.And we discussed the quenching mechanism,which showed that the aggregation induced quenching is the main effect.Part 4: Polyethylene glycol capped ZnO quantum dots as a fluorescent probe for determining copper?II?ion.As an important heavy metal ion,copper has the negative influence on otherwise healthy individuals,so establishing a valid way for the highly efficient,sensitive and quantitative determination of Cu²⁺ ions becomes emergency in the environment analysis.In the present work,water-soluble luminescent ZnO quantum dots?QDs?capped by polyethylene glycol?PEG?have been synthesized based on a simple solution route.The polyethylene glycol capped ZnO quantum dots?PEG@ZnO QDs?showed yellow fluorescence.High-resolution transmission electron microscope,UV-visible absorption,Fourier transform infrared spectroscopy,and luminescence can be applied to elucidate the properties of the PEG@ZnO QDs.In addition,the yellow fluorescence of the PEG@ZnO QDs was quenched when added Cu²⁺ ions into the PEG@ZnO QDs solutions.Therefore,a novel fluorescent probe was designed to detect Cu²⁺ in water solutions.The linear relationships were 10-200 n M and 2-10 ?M,respectively,with the detection limit for Cu²⁺ at 3.33 n M according to 3?/slope?where ? denotes the standard deviation of the blank measures?.The proposed sensor of the PEG@ZnO QDs has been also used in natural water samples to examine the valid of this method.In addition,the quenching mechanism was also discussed,which may be attributed to the aggregation induced quenching.