Design And Application Of The Dual Visual Assay Based On Gold Nanoparticles For Environmental Analysis

With the rapid development of social economy,environmental pollution has become one of the serious problems with worldwide concern.A large number of contaminants are now widely present in the environment,and some of which can pose a threat to human health,even at low concentrations.Therefore,it is essential to develop rapid and sensitive analysis techniques for environmental pollutants.Compared with traditional analysis techniques,colorimetric and fluorescent method with dual-response was established as a new technology for detecting environmental pollutants with high sensitivity,simple operation and portability,which has shown great superiority in the rapid detection of environmental pollutants with on-site feature.In recent years,with the rapid development of nanotechnology,gold nanoparticles?AuNPs?have been widely explored for the development of visualization methods due to their unique properties,such as surface plasmon resonance?SPR?,easy surface conjugation,and high extinction coefficient.The development of visualization methods based on gold nanoparticles with dual-response would provide a new analytical platform for the rapid on-site detection of environmental pollutants,which is of great significance for the quality assessment,environmental remediation and environmental management policy formulation of contaminated areas.In this work,gold nanoclusters with blue fluorescence were synthesized by surface functionalization of gold nanoparticles.By rationally regulating the competitive redox reaction and the enhanced oxidation ability of Au-NCs/MnO₂ nanocomposites,we established a colorimetric and fluorometric dual response assay for acid phosphatase?ACP?,a biomarker of soil cadmium?Cd?contamination.Besides,by exploring the size-dependent optical properties of gold nanoparticles,we combined the advantages of traditional low-toxicity gold nanoparticles with novel infinite coordination polymer?ICP?nanomaterials to obtain multi-guest functionlized composite infinite coordination polymer nanomaterials.By exploiting the stimulus response of the as synthesized nanomaterials and by taking adavantage of the optical properties ofthe core-shell structure as well as the guest molecules,we realized the colorimetric and fluorometric dual mode detection of total phosphorus in environmental samples with extremely high realialbitiy.Moreover,during the stimulus response towards target pollutants,not only the optical property,but also the size and amount of the composite infinite coordination polymer core-shell nanomatereials altered.These changes were combined with coffee ring effect on glass substrate to develop coffee ring chips with dual-channel response,which is of pratical application for on-site environmental analysis.These studies not only provide new strategies for the design of dual-response environment analytical methods with high reliability,but also open up a new anevenue for the synthesis,exploition and application of composite nanomaterials based on gold nanoparticles in environmental field.This article is divided into four chapters as follows:Chapter 1.OverviewThis part firstly introduced the synthesis method and characteristics of gold nanoparticles.We summarized the development and application of based colorimetric method,fluorometric method and the colorimetric and fluorometric dual-mode method based on gold nanoparticles.Then we emphasized the advantages of the colorimetric and fluorometric dual-mode method in environmental analysis.In addition,the development of chip technology based on the coffee ring effect and its application in quantitative analysis of environmental pollutants on-site were introduced.Finally,we expounded the research significance and content of this article.Chapter 2.Competitive Redox Reaction of Au-NCs/MnO₂ Nanocomposite:Toward Colorimetric and Fluorometric Detection of Acid Phosphatase as An Indicator of Soil Cadmium ContaminationThe smaller size Au-NCs?d<3 nm?are prepared with proteins,peptides,small organic molecules or end-capping agents as templates.it is very convenient to modify their surface.The fluorescence emission of Au-NCs can be tune from visible to near infrared region.Therefore,Au-NCs are widely used in the development of fluorescent analysis platforms.However,the one channel method is easily disturbed by environmental flunctuation to produce false positive signals.In this work,by rational regulating the competitive redox reaction of Au-NCs/MnO₂ nanocomposite between the dye indigo carmine?IC?and the enzymatic product L-ascorbic acid?AA?,we have established a colorimetric and fluorometric double-channel responsive assay for acid phosphatase?ACP?,which could serve as an indicator of soil cadmium?Cd?contamination.Initially,the gold nanoclusters?Au-NCs?were added to the suspension of MnO₂ nanosheets to form Au-NCs/MnO₂ nanocomposite with enhanced oxidative degradation ability.When IC was subsequently added,the blue color of IC faded due to oxidative degradation,and the mixture showed the yellow color.Meanwhile,based on the inner filter effect?IFE?,the fluorescence of Au-NCs was suppressed by MnO₂nanosheets during this process.However,with the presence of AA,hydrolyzed from L-ascorbic-2-phosphate?AAP?by ACP,the MnO₂ nanosheets in Au-NCs/MnO₂nanocomposite were reduced to Mn²⁺immediately.As a consequence,IC remained its blue color,in the meantime,the fluorescence of Au-NCs recovered,which essentially constituted a new mechanism for ACP detection with colorimetric and fluorometric double-channel response.With the method we developed,soil ACP activity can either be directly visualized by bare eyes or detected reliably through double channels.Furthermore,the dynamic changes of ACP activity during soil Cd contamination could also be monitored;the sharp increase of ACP activity at an appropriate time point could serve as a unique alarm for cadmium?Cd?contamination in soil,which is of great importance for soil quality evaluation and ecological risk assessment.Chapter 3.Multi-guest Core-shell Nanoparticles AuNPs/AIE/ACQ@AgDMcT and Its Application for Colorimetric and Fluorometric Dual-mode Detection of Total Phosphorus in Landfill Leachate with Dual Ratiometric ResponseLarger size?d>3.5 nm?gold nanoparticles exhibit the characteristics of surface plasmon resonance effect.With the size of spherical gold nanoparticles?AuNPs?increasing from 10 nm to 100 nm,the corresponding absorption peaks range from 500to 550 nm,and the color changes from orange,red to purple.Unfortunately,the high salinity can cause non-specific aggregation of gold nanoparticles.Therefore,the stability of AuNPs has brought great challenges to the development of on-site detection methods.In this study,we combined the advantages of traditional low-toxicity gold nanoparticles with the new infinite coordination polymer?ICPs?nanomaterials to synthesize a functional ICP core-shell nanoparticle with multi guests in-situ wrapped?AuNPs/AIE/ACQ@AgDMcT?.Based on the regulation the stimulus response of AuNPs/AIE/ACQ@AgDMcT,a colorimetric and fluorometric double channel visualization assay with double ratiometric response was developed for the detection of total phosphorus in landfill leachate.The core-shell nanomaterials were rationally designed by using Au@Ag nanoparticles as the precursor of central metal ion,Au core,two kinds of dye molecules aggregation induced emission?AIE?and aggregation caused quedching?ACQ?as guests,and the oxidative DMcT as ligand to form the AuNPs/AIE/ACQ@AgDMcT infinite coordination polymer nanoparticles.Due to the confinement effect after encapsulation,the fluorescence of ACQ guest quenches,and fluorescence of AIE guest turns on.However,with the presence of orthophosphate ions,the core-shell structure of the nanomaterial was destroyed,the guests were then released.As a result,the fluorescence of the ACQ molecules turned on,while the fluorescence of the AIE molecule quenched.Meanwhile,the gold nanoparticles core released from the shell and turned to monodisperse state.Accordingly,the color of the solution changed from blue to pink-red?the mixed color of Au core and the ACQ guest?.The new mechanism of dual-mode colorimetric and fluorometric assay for the detection of orthophosphate with double ratiometic response was thereby established.With this method,visualization detection of total phosphorus in landfill leachate with high reliability was achieved,which has important practical significance for environmental applications.Chapter 4.Coffee Ring Chip for Quantitative Visualization Detection of Orthophosphate Based on AuNPs/AIE/ACQ@AgDMcT Core-shell NanoparticlesFrom the pratical view point,most of the developed methods can hardly meet the requirements for the rapid and on-site detection of large quantities of environmental samples.On the other hand,the strips and the chips with the advantages of low-cost,easy operation and portability are highly desirable.In this study,the size and amount changes of AuNPs/AIE/ACQ@AgDMcT core-shell nanoparticles,as well as the fluoresence color change from bule to orange during their stimulus response to orthophosphate ions was reflected by the deposition pattern of coffee ring on glass subtrate and explored as multi-channel coffee ring chips.The results demonstrated that,on a hydrophobic glass substrate,the coffee ring diameter and the fluorescence color changes show a good linear relationship with the concentration of orthophosphate,thereby quantitative detection of orthophosphate could be realized with high reliability.This method is propitious to realize rapid and high-flux detection of orthophosphate concentrations in resource-limited environments.