| "People depend on food",food is one of the most important factors for people’s survival and development.But nowadays,serious food pollution has being threatened the healthy,life and safety of human beings.Although a series of analytic method shave been developed and reported for food analyses with satisfitary results,most of them need complicated operation prosess,expensive experimental instruments,which could not meet the requirement for portable,on-site,real-time monitoring of these organic contaminations.With this in mind,we will by liquid reduction method at room temperature,bioactive folic acid molecule functionalized Ag-based quantum dots,i.e.,FA@AgNPs,FA@Ag-PtQDs and FA@Ag-Ir QDs were first constructed by on-pot homogeneous reduction-assembly methods at room temperature in the mixed solvent of glycol and water.Taking virtue of the superior peroxidase-like activity and excellent fluorescent peroperty,the proposed Ag-based quantum dots were successfully applied for colorimetric,fluorescent and other multi-mode detection of dopamine,I-,cysteine and Hg2+in food or drinkings in practice.In this dissertation,the main contents are illustrated as follows:1.Agnanozyme strengthened by folic acid:Superior peroxidasemimicking activity and application for visual monitoring of dopamine:To monitor DA efficiently and conveniently,an Agnanozyme strengthened by bioactive folic acid（FA@AgNPs）was developed by homogeneous redox assembly.After the microstructure and performance were characterized in detail,it was noted that the proposed FA@AgNPs possessed superior peroxidase-like activity due to the ultra-small Agnanoparticles and multiple amino,hydroxyl,and aromatic rings in FA.FA@AgNPs accelerated the oxidation of 3,3′,5,5′-tetramethylbenzidine（TMB）with a low Michaelis constant（Km）and high maximal reaction rate(Vmax).Importantly,the characteristic absorbance intensity of FA@AgNPs-TMB-H2O2 at652 nm(A652)was exclusively deteriorated in the presence of trace DA,accompanied by a visual color change from blue to colorless.Under the optimized conditions,there expressed an excellent linear relationship between lg A0/A652 and c DA from 1.0×10-8 to 6.67×10-6 mol·L-1with a low limit detection of 7.1×10-10 mol·L-1（S/N=3）.When applied for monitoring of DA in real fruit juice and pharmaceutical samples,the recovery was between 96.6%and 104.9%,with R.S.D.less than 2.2%.The enhanced peroxidase-like activity of the FA@AgNPs system and its selective recognition mechanism for DA are also proposed.2.Convenient colorimetric-fluorescent dual-mode recognition of I-in agricultural products and visual determination of Hg2+in drinking beverages using Ag-Pt bimetal quantum dot nanozyme:In this part,an Ag-Pt bimetal quantum dot nanozyme boosted by bioactive folic acid（FA@Ag-PtQDs）was first developed for multichannel monitoring of I-and Hg2+,using a two-step liquid-phase reduction method.Not only did the present FA@Ag-PtQDs possess superior peroxidase-like activity with Michaelis constant（Km）and maximal reaction rate(Vmax)of 0.01 m M/2.95×10-8 M·s-1 and 1.15 m M/3.88×10-8 M·s-1,respectively,trace Hg2+or I-could exclusively alter their enzyme-mimic performance with obvious color changes from blue to colorless or dark blue.I-could also strengthen the inherent fluorescence property of FA@Ag-PtQDs.When applied for visual monitoring of I-and Hg2+in real beverages or iodine-containing agricultural products,the detection recoveries were93.9%-105.3%and 96.8%-104.3%with low detection limits of 6.56×10-8 mol·L-1 and4.00×10-10 mol·L-1（S/N=3）,respectively.The recovery and detection limit for fluorescent detection of I-were 95.8%-104.1%and 1.75×10-8 mol·L-1（S/N=3）,respectively.The mechanisms for improved peroxidase-like activity of FA@Ag-PtQDs and their selective monitoring of Hg2+and I-were illustrated in detail.The proposed FA@Ag-PtQDs will act as an efficient sensor for the practical multichannel monitoring of Hg2+and I-,with superior catalytic signal amplification.3.FA strengthening Ag-Ir bimetal quantum dot nanozyme for enzyme-like catalytic detection of dopamine and fluorescent recognition of cysteine and Hg2+:In order to detect several analytes using a single sensor,folic acid functionalized Ag-Ir bimetallic quantum dots（FA@Ag-Ir QDs）were developed by two-step liquid phase reduction-assembly method.The present FA@Ag-Ir QDs possess excellent peroxide-like performance,which can accelerate the redox of H2O2 and TMB with improved Km and Vmax,i.e.,23.64 m M/4.74×10-8 M·s-1 for H2O2and 0.049 m M/5.05×10-8 M·s-1 for TMB.Especially,FA@Ag-Ir QDs could be applied for simultaneous detection of DA,Cys and Hg2+by virtue of the inherent fluorescent or enzyme-like catalytic performances.For catalytic colorimetric detectionof DA in juice and dopamine injection samples,the detection limit is 8.34×10-9 mol·L-1（S/N=3）with detection recovery rate between 97.3%and 107.8%,and R.S.D.less than 3.3%.For turn-on fluorescent determination of Cys in serum,drinking water and beverage samples,its detection limit is 7.07×10-9 mol·L-1 etection recovery rate between 96.7%and 101.7%and R.S.D.less than 2.1%;For turn-off detection of Hg2+in drinking water and beverage samples,its detection limit is 3.71×10-10 mol·L-1（S/N=3）etection recovery rate between 98.6%and104.9%and R.S.D.less than 3.2%,well meeting the basic definition by WHO.The mechanism for improved peroxidase-like activity of FA@Ag-Ir QDs and the ones for the recognition of DA,Cys and Hg2+were investigated in detail. |
PDF Full Text Request