Design Of Highly Active Palladium-based Nanoenzymes And Their Applications In Biosensors

Nanozymes is one kind of new generation of artificial enzymes with the characteristics of natural enzymes.Due to the low cost,simple preparation process and high stability,nanozymes have been widely used in various fields such as biosensing,immunoassay,early diagnosis and treatment of cancer,environmental protection,agricultural production and so on.However,compared with natural enzymes,nanozymes have the disadvantage of low catalytic activity and poor selectivity,which greatly limit their practical applications in medicine,biological environment,chemical industry and so on.The enzymatic activities of nanozymes are closely related to its structural parameters such as size,crystal face,composition,and surface modification.In order to address the problem of low catalytic activity of nanozymes,we designed three kinds of palladium(Pd)-based noble metal nanomaterials with enhanced activity by controlling their surface facets,surface modification and composition,etc.In addition,the characterization test and performance analysis have also been carried out,and the as-prepared nanozymes have been successfully applied to biosensing.The following is a brief description:1.The two-dimensional (2D) square Pdnanoplates on reduced graphene oxide enclosed by{100}-facets[{100}PdSP@rGO]has been prepared.{100}PdSP@rGO exhibits the enhanced intrinsic oxidase-like activities relative to the{111}-facets ones and Pdnanocubes in catalyzing the chromogenic reaction of 3,3,5,5?-tetramethylbenzidine.By taking ascorbic acid2-phosphate(AAP)as substrate,which transforms to ascorbic acid(AA)in the presence of acid phosphatase(ACP),the{100}PdSP@rGO could be used as an efficient nanozyme for colorimetric ACP detection without restoring to destructive H₂O₂.A good linear relationship from 0.01 to 6.0 m U/m L with a detection limit of 8.3 U/m L is obtained by{100}PdSP@rGO.The proposed method is easy to operate and has been applied to detect ACP in serum samples with satisfactory results.However,2D Pdnanosheets are easy to stack closely,which lead to the coverage of active sites.Therefore,it is necessary to avoid the close stack of 2D Pdnanosheets.2.To address the problem of the close stack of 2D Pdnanosheets,the ultrathin PdCu alloy nanosheet–assembled three-dimensional(3D)nanoflowers(Pd₁Cu_x NAFs,x represents the ratio of Pd/Cu precursors)have been prepared.Pd₁Cu_x NAFs show obviously composition-dependent peroxidase-like catalytic activities because of the synergistic interaction of nanoalloy.Additionally,different from 2D Pdnanosheets,the distinctive 3D superstructures avoid stacking of nanosheets,which are in favor of exposure of active sites and electron transfers during the catalytic process.Among the studied Pd₁Cu_x NAFs,the Pd₁Cu_1.7NAFs shows the highest enzyme–like activities and can be successfully applied for the colorimetric detection of glucose with a low detection limit of 2.93±0.53?M.The method also realizes the detection of glucose in actual serum samples.3.The 3D network structure of polydopamine-coated PdCu cross-linked nanowires(PDA-PdCu)have been successfully prepared by one–pot aqueous reduction method.The addition of both dopamine and Cu elements promotes the enzyme–like activity of PDA–PdCu.Under acidic conditions,PDA–PdCu can catalyze oxygen in solution to generate singlet oxygen(¹O₂)and superoxide radical(O₂^·-),which can oxidize colourless TMB to generate the bule oxidized TMB(ox TMB).In the presence of alkaline phosphatase(ALP),AAP is hydrolyzed into AA,which can influence the color of PDA-PdCu-TMB system.Thus,a new strategy for the colorimetric detection of ALP based on the oxidase-like activity of PDA-PdCu can be proposed.There is an ALP linear scope of 0.03-3.0 U/L with a detection limit of 0.02 U/L.The proposed method is successfully applied to detect ALP in serum samples with satisfactory results.