Application Of Colorimetric Aptasensor For The Detection Of Microcystin-LR In Water

With the acceleration of social industrialization,human production and life discharged a large number of nitrogen and phosphorus pollutants into the water body,which intensified the eutrophication of the water body,resulting in frequent outbreaks of blue-green algae blooms.Microcystin-LR（MC-LR）,which is highly toxic and produced by the bursting of cyanobacteria cells,can pose a threat to the ecosystem and human health in small amounts.Therefore,it is very important to establish a fast and highly sensitive method for the detection of MC-LR in water.Based on the optical changes of gold nanoparticles（AuNPs）in different states,a biosensing detector can be constructed with the aptamer to detect a specific substance through the color change of the reaction system.In this study,magnesium chloride（MgCl₂）and polyethylene imine（PEI）were used as AuNPs aggregation inducers,and hydroxylamine hydrochloride（NH2OH·HCl）and tetrachlorauric acid（HAuCl4）were used as sensitizers to induce AuNPs aggregation and growth.After AuNPs aggregation growth,the solution color change principle was applied to the detection of MC-LR,and the research results obtained are summarized as follows:（1）A colorimetric aptasensor based on MgCl₂ and Gold nanoparticles（AuNPs）was used for the detection of MC-LR.With MC-LR aptamer as recognition element,AuNPs as sensing material,and MgCl₂ solution as color inducer,a highly sensitive and rapid detection of microcystin-LR（MC-LR）in water samples was constructed by using gold nanoparticles biosensor colorimetry.By optimizing the experimental conditions,the best detection effect of MC-LR was achieved when500.0 nmol/L aptamer and 70.0 mmol/L MgCl₂ were added into the wash solution with p H 6 25.0mmol/L MES.Further experiments showed that the absorbance ratio A615/A525 showed a good linear relationship with the concentration of MC-LR in the range of 0.001-0.5μmol/L to 0.0-10.0μmol/L.The linear relationship was y=0.1103x+0.4721（R²=0.9902）,the lowest detection limit was 0.8nmol/L（0.8μg/L）.It was found that the system had high sensitivity and specificity for MC-LR.The recoveries of 96.19%-102.35%were obtained by adding standard in five actual water samples.（2）A colorimetric aptasensor based on polyethylene imine（PEI）and AuNPs is used for the detection of MC-LR.A colorimetric aptamer sensor was developed for the rapid and simple detection of microcystin-LR（MC-LR）using PEI as aggregation inducer,AuNPs as color indicator and aptamer as sensing element.Through experimental optimization,the sensitivity of detection can be improved by adding 1.0 mmol/L magnesium chloride and 0.02%Tween 20,and the reaction between aptamer and the target is basically stable after 30 min,and the color change of AuNPs can be observed by naked eye.At this time,the system has the best detection effect on MC-LR.Further experiments showed that the difference between absorbance A525（ΔA525）and concentration of MC-LR showed a good linear relationship when the concentration of MC-LR was 0.001-0.02μmol/L.The linear relationship was y=0.0007x+0.0174（R²=0.9915）,the lowest detection limit was 0.26nmol/L（0.26μg/L）.It can be seen that the analytical method has good sensitivity.The recoveries were 94.65%-101.12%in five actual water samples.（3）A colorimetric aptasensor based on sensitizer HAuCl4、hydroxylamine hydrochloride（NH2OH·HCl）and AuNPs was used for detection of MC-LR.According to the color change of AuNPs in the reaction system,it can be used for visual detection of MC-LR,and the highly sensitive detection of MC-LR can be realized through instrumental analysis.Through experimental optimization,the single-chain aptamer,AuNPs and the sample to be tested were successively added into MES buffer to form the reaction system solution,which was reacted at 37℃for 45 min.When the concentration of aptameris 50.0 nmol/L,the absorbance value of AuNPs at 525 nm is 0.25,and the volume of AuNPs accounts for half of the solution volume,the colorimetric detection effect is the best.Under the optimal detection conditions,MC-LR of 0.0-5.0μmol/L was detected.In the range of MC-LR concentration 0.001-0.02 nmol/L,the difference of UV-vis absorbance ratio（ΔA650/A525）showed a good linear relationship with the concentration of MC-LR.The linear equation is y=0.0058x+0.0013（R²=0.9976）,the lowest detection limit is 0.1 nmol/L（0.1μg/L）,and the LOQ is 0.8μg/L.Therefore,this analysis method has high sensitivity.The recoveries were 95.3%-107.73%in five water samples.In summary,gold nanoparticles were successfully prepared in this experiment,and MC-LR was detected by using its optical properties,and successfully applied to the detection of target objects in actual water bodies,showing good detection effects.The results of this experiment can lay a theoretical foundation for the rapid detection of MC-LR in water.