Gold/Platinum Nanoenzymes With Dual Enzymatic Activity For Photothermal Sensing Applications

The development of rapid and simple real-time detection（Point of care testing,POCT）methods is crucial for environmental monitoring,food safety,disease diagnosis and other fields.In recent years,nanozymes brought new opportunities for the development of new POCT methods because of their high stability and durability,as well as the ability to simulate the activities of various natural enzymes simultaneously.At present,most nanozymes-based POCT methods are mainly constructed by colorimetric sensing principle generated by the oxidation of some chromogenic substrates such as 3,3’,5,5’-tetramethylbenzidine（TMB）.Such colorimetric sensors can usually only sensing target with semi-quantitative results and its sensitivity and color resolution are often limited.Therefore,the development of alternative simple analytical signals and improving the sensitivity and signal resolution of nanozymes-based POCT sensing methods are of great significance for both nanozymes sensing applications and the development of POCT methods.Recently,we have found that photothermal sensing based on temperature signal readout has higher signal resolution and detection sensitivity compared with color signal readout,which has certain advantages in the field of fast,convenient and accurate quantitative analysis.Based on this,gold@platinum nanoparticles（Au@Pt NPs）with dual enzyme activity were synthesized,the change of enzyme activity of Au@Pt NPs under different conditions was studied,and the POCT photothermal sensing based on temperature analytical signal was successfully constructed in this work.This thesis mainly includes the following two parts:1.Au@Pt NPs nanozyme was synthesized and characterized by seed growth method.It was found that the prepared Au@Pt NPs nanozyme has good peroxidase-like activity at p H=5.5 and can catalyzes hydrogen peroxide（H₂O₂）to oxidize the chromogenic substrate TMB to produce blue oxidized products（TMBox）.When the target Hg²⁺was added,due to the interaction between Hg²⁺and and Pt⁰ on the surface of Au@Pt NPs nanozymes,the deposition of Hg⁰on the surface of Au@Pt NPs nanozymes then inhibited the peroxidase-like activity of Au@Pt NPs nanozymes.Based on this,we constructed a simple,fast,and sensitive Hg²⁺photothermal sensing platform.The experimental results exhibit an excellent performance for the photothermal detection of Hg²⁺in the dynamic working range from 10 to 500 n M with a detection limit of 4.88 n M（S/N=3）.2.Through intensive research,it is found that the good oxidase-like activity of Au@Pt NPs nanozymes can also easily catalyze dissolved oxygen to produce singlet oxygen（¹O₂）under acidic conditions,the produced ¹O₂then oxidize TMB to form the oxidized product TMB（TMBox）.When the target I^-was added,the interaction between I^-and the Pt shell on Au@Pt NPs led to Pt²⁺on Au@Pt NPs nanozymes elevated,and the Pt⁰decreased,thus inhibiting the oxidase-like activity of Au@Pt NPs nanozymes.With the increase of target I^-in the system,the blue TMBox generated by nanozymes catalytic oxidation process decreases accordingly,resulting in significant photothermal signal changes in the system.Based on this,we constructed a simple,fast,and sensitive I^-photothermal sensing platform.The experimental results exhibits an excellent performance for the photothermal detection of I^-in the dynamic working range from 0.05 to 4μM with a detection limit of 21.67n M（S/N=3）.