Preparation Of Bromelain-stabilized Nanomaterials And Their Application In Biosensing

Nanomaterials such as gold nanoclusters and MnO₂nanosheets are two newly emerged nanomaterials of the field of nanomaterials.They are attracting extensive attention due to unique physical and chemical properties.Nevertheless,high cost of gold nanoclusters and lower catalytic activity than natural enzymes of MnO₂nanosheets still limit their further investigations and applications.Therefore,the development of new nanomaterials with low cost and high catalytic activity is of great research significance.This paper has the innovative of select bromelain as a biological template,and nanomaterials with good dispersibility,high stability,and cost effective was prepared.It was successfully used for the analysis of small biomolecules in the serum and heavy metal ions in the environment.In Chapter 1,the significance and research status of glucose and dopamine detection are briefly described.The synthesis methods of gold nanoclusters and manganese dioxide tablets and their applications in analytical detection are described.The main contents and innovations of this research are introduced.In Chapter 2,gold nanoclusters（AuNCs）and MnO₂ nanocomposites were designed as a new fluorescence sensing platform for fluorescent probes.A new method for fluorescence sensing and the mechanism of MnO₂ inhibition of AuNCs fluorescence are discussed.Firstly,bromelain-AuNCs were synthesized using bromelain as a template.MnO₂was added into the system to form a stable AuNCs-MnO₂ complex in 5min due to the inner filter effect（IFE）and static quenching effect（SQE）in the system.However,in the presence of H₂O₂ produced by the enzymatic reaction of glucose oxidase,the MnO₂ nanosheets were reduced to Mn²⁺ions,releasing gold nanoclusters.At this point,the fluorescence of the system was restored.The method is label-free,simple,economical,and biocompatible and has been successfully applied to serum samples of normal people and diabetic patients.In Chapter 3,bromelain-gold nanoclusters（bromelain-AuNCs）were successfully prepared.Possessing a simulated peroxidase activity,they catalyze color development in a 3,3’,5,5’-tetramethylbenzidine（TMB）–H₂O₂ system.A new method for detecting Hg²⁺in environmental water samples based on colorimetric sensing with gold nanoclusters showing the peroxidase activity and the mechanism of the catalytic color reaction were discussed.By the addition of Hg²⁺,the particle size of AuNCs increased due to high metal affinity between Hg²⁺and Au⁺on the surface of AuNCs,greatly reducing the catalytic ability of AuNCs and resulting in weaker coloration in the system.The linear range of detection of Hg²⁺extended from 6.25 nmol/L–3.5μmol/L,and the lower detection limit was 4.3 nmol/L.The method is less expensive,simple,and feasible with high selectivity and thus serves as a new strategy for Hg²⁺detection in environmental water samples.In Chapter 4,bromelain-based MnO₂ nanosheets that possess a high oxidase activity.Bromelain-MnO₂ nanosheets have the ability to directly catalyze oxidation of 3,3’,5,5’-tetramethylbenzidine（TMB）to the blue oxTMB product.By the addition of dopamine,the MnO₂ nanosheets were reduced to Mn²⁺ions,the nanosheets structure decomposed,and their oxidase activity was markedly inhibited with the absorbance at 652 nm gradually decreasing.The linear range of the dopamine detection was 100nmol/L to 10μmol/L,and the detection limit（LOD）was 39.8 nmol/L.The method was successfully applied in blank spike experiments with human serum samples and fetal bovine serum samples,and the dopamine content in the human serum samples could be determined quantitatively and accurately.