Synthesis And Characterization Of Gold Nanoclusters Based On Mitochondrial Ferritin And β-lactoglobulin As Biotemplates

There are intensive relations between the characteristics and sizes of nanomaterial.Nanocluster means the nanoparticle with diameter within 2 nm.It was made by specific metal.The special configuration of extra-nuclear electron leads to the fluorescence emission of nanoclusters under excitation light.Among the nanoclusters,gold nanoclusters received wider attentions based on their good properties including low toxicity,simple synthesis,high fluorescence and chemical stability.Protein-gold nanoclusters complex can not only develop the stability of fluorescence,but also enlarge the application of the complex based on the proteins1 wide functions.However,there were few reports of the structures of protein-gold nanoclusters.The mechanism of gold binding and reduction by protein was still unclear.At the same time,the application of protein-gold nanoclusters in complex environment was also few.In this research,both of mitochondrial ferritin and P-lactoglobulin were used as model to prepare gold nonaclusters.We researched on the synthesis and application of the protein-gold nanoclusters.The major results were listed below:1.Mitochondrial ferritin is a kind of native existed nanocage protein in animals,tissues.It was composed by 24 totally same subunits,with Imolecule weight of 21 kD.The outer diameter is 12 nm,while inner diameter 8 nm.Its inner cage can be used as nanocarrier to load some medicine or active small molecules.In every subunit,there were two cysteine residues.Based on the X-ray crystal diffraction technology,the cysteine residue was proved to be the gold binding site in wild type MTF.The cysl30 was proved to be the gold accumulating site.To maintain the inner cage and out surface of ferritin for functional usage,we firstly mutated two cysteine residues to alanine residues;and then the ferric oxidation center was also reformed with the three glutamate residues mutated to cysteine residues.According to the X-ray crystal diffraction,gold was bound to the cysteine residues at the new ferric oxidation center.This result proved that the site for the formation of gold nanoclusters in MTF can be controlled.This further supplied the platform for applying MTF-AuNc in to a fluorescent nanocarrier.2.[P-lactoglobulin is a kind of protein with large sources.It also has good water solubility,however which was always discarded in the processing of cheese.According to the analysis of this protein’s amino acid sequence,the free cysteine was found,which supplied the possibility for binding and accumulating gold.In our experiment,we specialized the conditions to get highly fluorescent and stable p-Lg-AuNc.At the same time,the fluorescence of P-Lg-AuNc can be quenched by mercury ions with high selectivity and sensitivity.What’s more,this reaction can be continued without interference of complex environment.With this property,the[p-Lg-AuNc can be used in mercury detection in food and biological systems.Our study further proved that the P-Lg-AuNc can be used in cell imaging for the receptor of 3-Lg existed in the membrane of Caco-2 cells.What is more important,the(3-Lg-AuNc maintained high fluorescence even when it was injected into animal bodies.It can be metallized by kidney without harm for tissues.All the above results help us understand better the mechanism of protein-gold nanoclusters’synthesis.It help enlarge the application of p-Lg-AuNc,especially in food stuffs.