Study On Detection Of Ag⁺、Hg²⁺、Cu²⁺ In Water Environment Based On Fluorescence Method

With development of human social activities, the environmental pollution hasbecome more and more serious. The heavy metal pollution is one of the mostimportant aspects that enviroment pollution problems must be face. In recent years,numerous techniques, such as atomic absorption method, atomic emissionspectrometry （mainly refer to the inductively coupled plasma atomic emissionspectrum）, spectrophotometry, fluorescence spectrometry, X-ray fluorescencespectrometry, and electrochemical analysis have been employed for heavy metal ionsdetection. Among these analytical methods, fluorescence analysis attracts moreattention by researchers both at home and abroad because of its advantages, such ashigh sensitivy, good selectivy, and so on. In this dissertation, we combined theadvantages of quantum dot and gold nanoparticle in luminous performance, andapplied the fluorescence analysis method in detection of heavy metal ions and othersamples. The developed detection systems have these virtues, such as satisfactorysensitivity, good selectivity, low background noises and were easy to operation.The details are summarized as follows:（1） We design a sensor for detection of Ag⁺, the sensing system are consist ofquantum dot, gold nanoparticle and two DNA strands. The quantum dot is the Mn：CdS/ZnS, one of long life quantum dots, and it could be measured by time-resolvedfluorescence method. Two complementary ssDNA strands with few deliberately C-Cmismatches were designed and labeled with QDs and Au NPs, respectively. WhenAg⁺are present in the aqueous solution, DNA duplex formed due to the strong bindbetween Ag⁺ions and cytosines forms stable C-Ag⁺-C structures. As a result, theQDs and the Au NPs are brought into close proximity, which caused the fluorescenceresonance energy transfer. The methodology presented short hybridization time,satisfactory stability, sensitivity, and selectivity.（chapter2）.（2） We established a fast testing method for Hg²⁺ monitor by using electrontransfer quench principle. The long life quantum dot described above was still usedin this sening system, and two T-rich ssDNA strands were design, one strand waslabeled with quantum dot, the other one was free in sample solution. After Hg²⁺ wereadded to the aqueous solution, DNA duplex formed due to the strong bind betweenHg²⁺ and thymine forms stable T-Hg²⁺-T structures. As a result, the fluorescenceemission of quantum dot was quenched due to the electron transfer between quantum dot and Hg²⁺. The methodology showed easy to operate, satisfactory stability, andhigh selectivity （chapter3）.（3） The long lifetime quantum dot, Mn-CdS/ZnS, used for the determination ofCu²⁺ in aqueous solutions was described. In the presence of several metal ions suchas Ag⁺, Cd²⁺, Co²⁺, Cr³⁺, Fe²⁺, Fe³⁺, Ni²⁺, Pb²⁺, Zn²⁺, Hg²⁺ and Cu²⁺, only Cu²⁺ resulted in the quantum dot’s fluorescence remarkable decreases. In the presentsystem, the fluorescence intensity of the quantum dot decreased with increasingconcentration of Cu²⁺, and there is a good linear relationship between the fluorescentintensity and the concentration of Cu²⁺ within a certain range. Under the optimizedconditions, the prepared sensing system presented satisfactory sensitivity andselectivity. The developed approach is simple, easy to operate and was successfullyemployed for preliminary application in real samples （chapter4）.