Construction Phosphorescent Quantum Dots Sensors And Detection Of Water Environmental Contaminants And Biomolecules

Quantum dots（QDs）have become a research hotspot in the fields of chemistry,biology,materials and environment science owing to their uniform and adjustable sizes,high photostability,and broad emission spectral coverage.QDs are promising in substance detection since any tiny adjustment of surface physical structure or chemical composition will change their optical properties.In particular,phosphorescent QDs have attracted extensive attention owing to their long luminescent life,easy pretreatment and avoidance of interference from background environmental light.Thus,phosphorescent QDs are significant in analysis and detection.In this work,based on the excellent properties of Mn-doped ZnS（Mn-ZnS）phosphorescent QDs,we built phosphorescent sensors for some environmental pollutants（microcystin-LR,phosphates）and medical biomolecules（chloromycetin,butyrylcholinesterase）and applied them to analyze real samples.Also relevant detection mechanisms were preliminarily studied:1.An Mn-ZnS QDs/Ce³⁺nanoprobe was built on basis of electrostatic interaction. Owing to the high affinity between the lanthanide element Ce³⁺and phosphates,this nanoprobe can be used to selectively detect phosphates in water environments.Ce³⁺can coordinate with the carboxylate group on surfaces of the mercaptopropionic acid（MPA）-modified Mn-ZnS QDs,forming Mn-ZnS QDs/Ce³⁺nanohybrids via electrostatic interaction and thereby inducing the aggregation of QDs.After the addition of phosphates,the stronger affinity between phosphates and Ce³⁺led to the formation of more-stable hybrids,which desorbed Ce³⁺from the surfaces of Mn-ZnS QDs and recovered the RTP of Mn-ZnS QDs.This nanoprobe had a detection range of 8-320μM and a detection limit of 2.71μM.This probe showed high sensitivity and selectivity in detecting real water samples.2.Based on immunization and electron-transfer-induced phosphorescence,we prepared a novel type of phosphorescent immunosensors and used them to specifically identify and sensitively detect microcystin-LR（MC-LR）.The structurally specific binding between antibody and the antigen MC-LR led to the aggregation of antibody-crosslinked QDs,and the electron transfer between the carboxyl group of QDs and the primary amine group of MC-LR quenched the phosphorescence.Also the antigen-antibody specific binding site was preliminarily analyzed.This phosphorescent immunosensor can rapidly and sensitively detect MC-LR within linear ranges of 0.2-1.5 and 1.5-20μg/L and with a detection limit of 0.024μg/L.This sensor showed high selectivity and sensitivity in detecting MC-LR from real water samples.3.A novel MPA-modified Mn-ZnS QDs probe for detection of chloromycetin was built.This probe regularly quenched the phosphorescence intensity with the increasing dosage of chloromycetin and showed high linear relationship within 0.5-44.4μg/mL and a detection limit of 0.22μg/mL.The mechanism of phosphorescence quenching was ascribed to the electron transfer from the optical-excitation Mn-ZnS QDs to the electron receptor chloromycetin.The induced selection of Mn-ZnS QDs over chloromycetin significantly quenched the phosphorescence of Mn-ZnS QDs.This label-free RTP method can be used to conveniently,selectively and sensitively detect chloromycetin in biological fluids and avoided interference from autofluorescence.4.Based on the butyrylcholinesterase（BChE）reaction and the luminescent characteristics of RTP QDs,we designed a sensitive,precise and convenient BChE biosensor and used it to switch on and off BChE.This biosensor consisted of Mn-ZnS QDs and enzymes and avoided functional connection and other complicated preparation.The choline resulting from the BChE-catalyzed chlorination of butyrylcholine led to the aggregation of Mn-ZnS QDs,enhancing the RTP intensity of Mn-ZnS QDs,and thereby"switched on"the Mn-ZnS QDs.The oxidation of choline by the newly-added choline oxidase formed H₂O₂,which quenched the RTP of Mn-ZnS QDs and thereby"switched off"the Mn-ZnS QDs.Two types of BChE biosensors were developed.These biosensors can effectively avoid interference from the background fluorescence and scattering light of biological samples,do not need any complicated pretreatment,and thus can be used to efficiently detect BChE in biological samples.