Colorimetric Detection Of Heavy Metal Ions Based On The Analyte-Regulated Growth Of Gold Nanoparticles

After heavy metal ions pollute environment water,they gradually accumulate in the ecosystem along with the food chain,posing a serious threat to the environment and human health due to their toxicity.The portable quantitative detection of trace heavy metal ions remains one of the major challenges in the field of analytical chemistry.In this thesis,taking Cu²⁺and Hg²⁺as model analytes,three new methods are developed by sensitively regulating the growth process of gold nanoparticles（AuNPs）and their Tyndall effect to achieve instrument-free quantitative detection of heavy metal ions only with a hand-held laser pen and smart phone.The specific research content is as follows:（1）In Chapter 2,a new colorimetric Cu²⁺assay based on analyte-catalyzed growth of AuNPs enhancing their Tyndall effect was proposed for the first time.4-Morphine ethylene sulfonic acid（MES）,which contains a morpholine molecular skeleton and a-SO₃H group,can slowly reduce chloroauric acid（HAuCl₄）to generate AuNPs.In this process,MES not only acts as a weak reducing agent,but also as a reaction buffer reagent and particle surface modification ligand.When Au³⁺ions are reduced to Au⁰ by MES,the latter is simultaneously oxidized to 2-（（2-hydroxyethyl）amino）ethane-1-sulfonic acid and oxalic acid.Subsequently,Auatoms nucleate and gradually grow from small gold seeds to large colloidal gold particles.The reaction solution shows certain Tyndall effect.In the presence of Cu²⁺,the analyte ion can significantly accelerate the nucleation rate of Auatoms in the MES-HAuCl₄ redox system,generating a larger number of AuNPs per unit time,leading to a significantly enhanced Tyndall signal in the reaction solution.The enhancement of Tyndall signal is proportional to the concentration of Cu²⁺in the sample.In the study,the main experimental conditions such as HAuCl₄ concentration,reaction p H,reaction time,and reaction temperature were optimized.The microstructure of the products before and after Cu²⁺introduction in the MES-HAuCl₄ redox system was characterized using transmission electron microscopy.The results indicate that under the optimal experimental conditions,the two linear concentration ranges of the new method for detecting Cu²⁺are 6.10-390.6 n M and 390.6 n M-6.25,respectivelyμM.According to 3δrule,its detection limit is estimated to be 1.27 n M.In addition,when it was applied to actual water sample analysis,the recovery range obtained is 96.05%-110.83%.（2）During the process of studying the Cu²⁺-catalyzed MES-HAuCl₄ redox system in Chapter 2,it was unexpectedly found that under specific experimental conditions,red reaction solutions containing uniformly-sized AuNPs could be obtained when detecting other ion（or blank sample）samples.When analyzing Hg²⁺,only purple or blue-gray reaction solutions can be obtained.Therefore,in Chapter 3,inspired by this special phenomenon,another new method for visual detection of Hg²⁺based on analyte-catalyzed AuNPs’growth amplifying their Tyndall effect was further developed.The possible reaction mechanism is that Hg²⁺can also be reduced to Hg⁰and form a gold amalgam in the MES-HAuCl₄ system.This product can not only catalyze the in situ nucleation rate of AuNPs in the system,but also catalyze the continuous growth of the generated AuNPs into larger particles;the latter aggregates in order to reduce the surface potential energy,making the reaction solution produce a significantly-amplified Tyndall effect.The amplification degree of the Tyndall signal is proportional to the Hg²⁺concentration in the sample.In the study,the main experimental conditions such as HAuCl₄ concentration,reaction p H,reaction time,and reaction temperature were optimized.The microstructure of the products before and after the introduction of Hg²⁺in the MES-HAuCl₄ redox system was characterized using transmission electron microscopy.The results indicate that under the optimal experimental conditions,the two linear concentration ranges of the new method for detecting Hg²⁺are 6.10-97.66 n M and 97.66 n M-1.56μM,respectively.According to 3δrule,its detection limit as low as 0.1 n M is estimated.In addition,when it was applied to actual water sample analysis,the recovery range obtained is90.43-102.60%.（3）Although the method shown in Chapter 3 can achieve high sensitivity for Hg²⁺detection,it takes up to 1 hour to finish a assay run.To address this problem,in the Chapter 4,by adjusting hydroxylamine（NH₂OH）as a new reducing agent and a surfactant as the particle surface modification ligand,another method for rapid（completed within several minutes）and sensitive instrument-free quantitative detection of Hg²⁺based on analyte-regulated AuNPs’growth and their Tyndall effect was established.The Hg²⁺in the sample can also be reduced to Hg⁰ and form a gold amalgam in the NH₂OH-HAuCl₄ system.This product can not only catalyze the in situ nucleation rate of blocky AuNPs in the system,but also catalyze the continuous growth of the generated AuNPs to larger size;the latter aggregates in order to reduce the surface potential energy,which makes the reaction solution produce a significantly-amplified Tyndall effect.The amplification degree of the Tyndall signal is proportional to the Hg²⁺concentration in the sample.In the study,the main experimental conditions such as NH₂OH concentration,surfactant type,reaction p H,reaction time,and reaction temperature were optimized.The microstructure of the products before and after the introduction of Hg²⁺in the NH₂OH-HAuCl₄ redox system was compared and characterized using transmission electron microscopy.The results indicate that under the optimal experimental conditions,the linear concentration range of the new method for detecting Hg²⁺is 3.05 n M-6.67μM.According to 3δrule,its detection limit is estimated to be approximately 0.55 n M.In addition,when it was applied to actual water sample analysis,the recovery range obtained is 98.57-109.59%.