Etching Regulation Of Gold-Silver Nanobox And Its Application In The Treatment Of Drug-Resistant Bacterial Infection And Tumor Diagnosis And Treatments

Nanomaterials of noble metals such as gold and silver have been extensively studied because of their unique surface plasmon resonance（LSPR）characteristics.Among them,due to their excellent stability,biosafety,and flexible modifiability,pure gold nanomaterials have been widely used in biosensing,highly sensitive detection of marker molecules at tumor site,bioimaging and disease treatment.However,to achieve high absorption of LSPR in the visible light range（>600 nm）,gold nanomaterials need to have a large particle size.Once ingested by the human body,they are easily accumulated in the body,which greatly limits their wide clinical applications.Compared with gold nanomaterials,silver nanomaterials are less stable and easy to interact with biomolecules in the body.Because silver nanomaterials are oxidized to become silver ions and released into the cell matrix to bind amino acid molecules and proteins in the cells,which affects the normal metabolism of cells,also limiting their further biological applications.Galvanic reaction to encapsulate unstable nano-silver inside the gold shell to form gold-silver alloy nano-materials,can effectively solve above problems.On the one hand,the gold shell can effectively isolate the weak external oxidation from corroding the internal nano-silver and improve the stability of the silver nanomaterial;on the other hand,when the internal nano-silver is destroyed by the added oxidant in a controllable way,the entire cage structure is extremely easy to be destroyed and eventually becomes ultra-small alloy particles that can be excluded from the body,thereby reducing the accumulation of gold and silver in the body.Compared with simple nano silver and nano gold particles with the same size and morphology,the core-shell structured nanocage has more abundant and adjustable LSPR characteristics,and its LSPR absorption peak can be adjusted from visible light to near-infrared band,which has a wealth of applications scenes.This thesis mainly studies the etching phenomenon of alloy nanoboxes（GSNBs）with excellent stability and high silver/gold ratio in in vivo application scenarios.The focus is on the etching（silver release）behavior of GSNBs.It is ultimately expected that they will be used for accurate delivery of silver to living tumors.Two pathways for the rapid etching of GSNB were found in the sulfhydryl molecular system and the carboxylates system.Preliminarily,screening the optimal etching combination through treatment of bacterial infections;on this basis,try to combine the tumor microenvironment（such as high-level GSH and hydrogen peroxide）to achieve silver release at the tumor site.The specific results are as follows:（1）By controlling the amount of HAu Cl₄,GSNBs were synthesized with a high silver loading and a particle size distribution of 35 nm with an ultraviolet-visible light（UV/vis）absorption peak at about～532 nm.We compared its interactions with a group of small sulfhydryl molecules,paying particular attention to their differences in aggregation-induced photothermal enhancement and silver release efficiency.It was found that the amino-terminal modified sulfhydryl molecule（cysteamine）could significantly enhance the release of ultra-small nano silver from GSNBs.The results of mass spectrometry showed that these ultra-small nano-silver were essentially small nano-gold-silver alloy clusters.The combination of GSNBs-cysteamine was used for drug-resistant Staphylococcus aureus（MRSA）and drug-resistant Escherichia coli（MDR.E.coli）.With the assistance of near-infrared laser,the above-mentioned combination could significantly inhibit the development of drug-resistant bacteria.Furthermore,we separately analyzed the importance of photothermal effect and silver release for the inhibition of drug-resistant bacteria’s biofilm,and found that photothermal irradiation and ultra-small silver clusters showed a synergistic effect on the killing of drug-resistant bacteria.The GSNBs-cysteamine mixture irradiated with 1064 nm laser was applied to the wounds of MRSA-infected mice.The results showed that this strategy could effectively inhibit bacterial growth and promote wound healing in vivo.（2）On the basis of the above research,the interaction between GSNBs and high levels of glutathione at the tumor site was studied in detail.The results showed that GSNBs accumulated through passive targeting effects at tumor tissues after tail vein injection.Taking advantage of the high concentration of GSH,GSNBs aggregated and agglomerated rapidly at tumor site.During this process,their absorption spectrums were significantly enhanced in the near-infrared band,with a photothermal enhancement effect.At the same time,the coordination between the sulfhydryl group and the gold and silver atoms provided[H]for acceleration of reaction of oxygen and silver,which promoted the silver release.The stress difference of GSNBs in normal liver cells and liver cancer cells further confirmed the above conclusions.At a living scale,a photoacoustic microscope was used to detect the changes in the photoacoustic signal at the tumor site at different time points in the ear tumor-bearing mice injected with GSNBs.It was found that it first increased and then decreased at tumor site.Furthermore,using inductively coupled plasma mass spectrometry to analyze the metabolism of GSNBs in mice,it was found that GSNBs had a good passive targeting effect and could be eliminated from the body through feces and urine.The results of in vivo experiments effectively prove that high levels of GSH around the tumor tissue can trigger the enhancement of LSPR of GSNBs in the near-infrared region,supplemented by near-infrared phototherapy can effectively inhibit tumor growth.（3）In addition to glutathione regulating the etching of GSNBs,we also found that ultra-low concentration H₂O₂（0.25 m M,close to the corresponding concentration in the tumor environment）quickly etched GSNBs in the presence of sodium citrate.Further studies showed that this strategy regulated the electron compensation effect of GSNBs,so that Ag,which is originally difficult to oxidize,becomes easily oxidized by ultra-low concentration H₂O₂.This combination can achieve rapid silver release,which can be used to kill drug-resistant bacteria.This conclusion was also supported by the simulation calculation results based on first principles.It was further found that at an appropriate p H,a variety of carboxylates can adjust the electron compensation effect at the interface of GSNBs.The greater the number of ionizable carboxylates,the stronger the regulation and the easier the etching.This strategy can be used to treat wound infections caused by MRSA.In addition,because the intracellular energy metabolism contains a large amount of carboxylic acid molecules,and the concentration of H₂O₂（0.2 m M）in tumor cells is also higher than that in normal cells,this strategy provides a new way for GSNBs to be used delivery and silver release in tumor site.