In Situ Synthesis And Application Of Noble Metal Nanoclusters Based On Reduced Coenzymes

Reduced coenzyme Ⅰ（NADH）and reduced coenzyme Ⅱ（NADPH）are not only strong reducing agents in vivo for electron transformation,but also enriched with multiple nitrogen/oxygen-containing electron donors,which provides binding sites for metal ions.In this study,NAD（P）H was employed as both the reducing and the stabilizing agent for one-step synthesis of Pd-based nanoclusters（NCs）with enzyme-like activities.Their applications in biological detection were also investigated.In Chapter 3,NADH was adopted as bifunctional biotemplate to synthesize Pd NCs.The particle size and valence distribution are closely related to the molar ratio of[NADH]/[Na₂PdCl₄].Pd NCs,synthesized at 10 mM NADH and the ratio of[NADH]/[Na₂PdCl₄]of 2,formed through the aggregation of Pd⁰ atoms,which were generated from the reduction of Pd（Ⅱ）precursors accompanied by the transformation of NADH to NAD⁺.Pd NCs were mainly stabilized by the adenosine group of NADH.Pd NCs with the mean diameter of 1.7 nm and the Pd⁰ content of 29.7%,possessed the optimal peroxidase-like and oxidase-like activities.A colorimetric assay was established by using the peroxidase mimicking activities of Pd NCs at pH 6 for quantitatively monitoring heparin in both aqueous solution and human serum.The linear response lied in the range of 0.5～25μg/m L,with the limit of detection（LOD）of1.1 ng/m L.In Chapter 4,bimetallic Au Pd NCs with enzyme-like activities were synthesized under the reduction and the stabilization of NADH.Their alloy structures are closely associated to the molar ratios of[Na₂PdCl₄]/[HAuCl₄].Au₁Pd₅ NCs,synthesized at 0.6mM NADH and the ratio of[NADH]/[metal precursor]and[Na₂PdCl₄]/[HAuCl₄]of 2and 5,possessed the highest peroxidase-like and oxidase-like activitie.Synergistic effects between Au and Pd played a particular role in both growth kinetics and catalytic performance of Au Pd NCs.The strong Au-Pd interactions remarkably adjusted the electronic properties of Au and Pd in bimetallic nanoclusters,thereby contributing to their superior enzymatic activities over two monometallic nanoclusters.Based on the peroxidase-like activity of Au Pd NCs at acidic condition,a colorimetric test was developed for monitoring acid phosphatase（ACP）quantitatively,giving the LOD of0.53 U/L,the linear response lies in the concentration range of 1～14 U/L.This method was also suitable for the detection of ACP in human serum.In Chapter 5,NADPH was employed as stabilizing and reducing agent to construct AgPd NCs with peroxidase mimicking activities.Bimetallic precursors formed alloy structures under the reduction of NADPH as the molar ratio of[K₂Pd（NO₂）₄]/[AgNO₃]was 0.5～1.0,showing a remarkable acceleration in growth kinetics with respect to monometallic Pd NCs or Ag nanoparticles（NPs）.Ag,as the secondary metallic element,was added to increase the content of Pd⁰ species and to promote the peroxidase activity of AgPd NCs.A rapid and sensitive response to I^-was achieved by Ag₁Pd₁ NCs（[K₂Pd（NO₂）₄]/[AgNO₃]=1）with the mean size of 2.0 nm.The linear response lied in the range of 0.5～180 n M with LOD of 1.5 n M.Moreover,it had high selectivity for interfering ions such as S^2-.