Design And Preparation Of Nanomaterials Based On Gold And The Application In Biological Detection,Diagnosis And Treatment

Nanomaterials based on gold have a variety of excellent physical and chemical properties,including good stability and biocompatibility from gold,as well as unique imaging performance and easy-modification characteristic owing to the nano-level size,so they have been extensively studied,developed and applied in sensing,catalysis,medical and many other fields.Especially for biological application,they have attracted more and more attention.Based on sensing properties,they can detect bio-related ions and factors.Due to the ultrasmall size and high biocompatibility,they are easy to be endocytosed by cells,furthermore monitor and regulate cellular state as probes.They also improve the transfection efficiency of the target substance and optimize the effect as a carrier,giving credit to easy modification and large specific surface area.Moreover,they have wide applications in imaging as well as treatment owing to excellent optical properties,which offer new designs and approaches to conquer intractable diseases.Therefore,the development and exploration of nanomaterials based on gold have a wide range of application prospects and important practical effects,which have also attracted extensive attention from scientific researchers.This paper takes the synthesis of nanomaterials based on gold as the main line,the intersection of biology and chemistry as the entry point,and gradually realizes the goal of intelligent application by designing and synthesizing g nanomaterials based on gold with different functions.First,we synthesized a kind of bright fluorescent gold nanodots with a mild reaction method.Its structure and fluorescent properties are very stable with good performance retention under different p H values and UV irradiation conditions.Except for easy to prepare and store(room temperature),it can be observed with the naked eyes simply and intuitively owing to excellent fluorescence properties,so it is applied in detecting biological ions as a fluorescent probe.Cr?(Cr₂O₇^2-)is a heavy metal ion with strong oxidizing properties,which causes DNA damage,gene expression mutations,cell apoptosis,and further lead to teratogenesis,carcinogenesis and death.However,due to improper treatment and excessive discharge of industrial wastewater,some Cr?flows into our drinking water and causes serious problems.The World Health Organization(WHO)on the"Drinking Water Quality Standards"clearly stipulates that the content of Cr?in drinking water cannot exceed 0.05mg/L(1?M),so the detection of Cr?in drinking water is very important.Fluorescent gold nanodots are designed to quickly and accurately detect Cr?with ultra-low detection limit(0.35 n M),wide detection range(1 n M-10 m M).In order to explore the detection mechanism,we analyzed the results of XPS,TEM,fluorescence lifetime,and so on.It was found that the sulfhydryl(-SH)can be oxidized by Cr?,leading to the original stable Au-S bond breaking.And the charge transfer process between the ligand and the central metal was blocked,so the fluorescence was quenched and the unstable AuNDs aggregated.The change in fluorescence is visible to the naked eye,and the detection time is very short.The result can be obtained in 30seconds.More importantly,the process is easy to operate and don't require complicated pre-processing.This method possesses high selectivity to Cr?in the detection process.K⁺,Ca²⁺,Na⁺,Mg²⁺,Mn²⁺,Zn²⁺and other metal ions as well as NO₃^-,H₂PO₄^-,CH₃COO^-,Cl O^-,SO₄^2-,NO₂^-,HCO₃^-,C₆H₅O₇^3-,S₂O₃^2-,HPO₄^2-and other acid radical ion have no effect on the detection results.More importantly,the detection process is simple,no complicated pretreatment process is required,and the detection time is very short,the result can be obtained in 30 s with visible fluorescence change in naked eyes.The stability of fluorescent gold nanodots to the external environment is in contrast to the sensitivity of Cr?detection,so it has a good application prospect.Then,we explored the impact of gold nanodots on the smallest unit of the human body,cells.Stem cells are a kind of pluripotent cells,which are always favored by medical field because of their unique pluripotency.Bone marrow mesenchymal stem cells(h BMSCs)are an important member of the stem cell family.They are easy to cultivate with a wide range of sources and the potential for multi-directional differentiation,which can form bone,fat,muscle,nerve,endothelium,so they are considered to be the best stem cells for clinical application.Especially for bone injuries,the ability of bone cells to regenerate at the injured site is limited.Therefore,the introduction of h BMSCs and the study of inducing them to differentiate into osteoblasts have become important topics.Meanwhile,it is still a medical challenge to use nanomaterials to promote h BMSCs differentiate into osteocyte.Therefore,we prepared ultra-small size gold nanodots and explored the effect of its surface charge on the differentiation of h BMSCs.The prepared fluorescent gold nanodots are protected and coated by the biotic amino acid cysteine(Au-Cys).On one hand,Cys improves the biocompatibility of the nanodots,which increases cell uptake efficiency with easier endocytosis.On the other hand,the sulfhydryl group(-SH)in Cys combined with Au stably,improving the stability of the nanodots.At the same time,based on the large specific surface area and the negative charge provided by the-COO^-functional group in Cys also play an important role in the process of directional induction of osteogenic differentiation from stem cells.Owing to the fluorescence stability of Au-Cys,the entire osteogenic differentiation process of stem cells can be monitored in real time via fluorescence properties.The results show that the prepared negatively charged fluorescent gold nanodots(Au-Cys)have obvious effects on the gene expression level,the activity of osteogenic enzymes and the formation of the cytoskeleton to promote bone differentiation.The quantitative results show that it is even better than commercial osteogenic induction medium on some indicators.Further,it was found that gold nanodots with more negative charges on the surface(Au-Cys)have obvious advantages in promoting osteoinduction compared with less negative charges nanodots(Au-GSH).At the same time,the effect of negative surface charges in promoting bone differentiation is also proved by other nanomaterials,such as Ag nanodots(Ag-Cys and Ag-GSH)and Carbon nanodots(Cys-CDs and GSH-CDs).Finally,through the detection of related cell pathways,we found that the bone-promoting effect of the negatively charged fluorescent gold nanodots on h BMSCs is mainly due to its promotion of autophagy.In the next two chapters,we focused on the application of nanomaterials based on gold in diagnosis and treatment of cancer.Cancer is still a difficult problem in the world with the high mortality rate.Many drugs have been used in clinical to fight cancer effectively.Paclitaxel(PTX)is one of them.It has good effects on non-small cell lung cancer,ovarian cancer,and breast cancer.However,there are still many limitations in clinical,such as poor water solubility,strong drug resistance during therapeutics and large side effects on healthy tissues.We use gold nanodots as a carrier to load PTX,and then,a p H-responsive biocompatible polymer(polylysine,PLL)is assembled on the outer layer to build water-soluble nano-system AuNDs-PTX-PLL with integration diagnosis and treatment.On the one hand,it solves the problem of poor water solubility of PTX.On the other hand,it increases the cell uptake rate and reduces the drug resistance caused by drug efflux.And the nano-system is designed with intelligent response:the drug can only be released in the slightly acid environment of the tumor,thus it can reduce damage to normal tissues and weaken side effects.Further,the nano-system can be tracked in real time through dual imaging modes of fluorescence(FL)and photoacoustics(PA),achieving the purpose of visualization,integrating diagnosis and treatment with broad application prospects.Finally,considering the complexity of the nano-system construction in the previous chapter,we further explored the one-step synthesis of Au/Mn NDs that integrate diagnosis and treatment.We added Mn element into the system,adjusting the fluorescence emission wavelength of nanodots to the near-infrared long wavelength region of 814 nm.At meantime,T₁ and T₂ magnetic resonance imaging(MRI)methods from Mn are supplement to the Au system owing CT imaging property.It can improve the accuracy of diagnosis by complementing advantages and disadvantages from a variety of imaging modes currently applied in clinical practice.Moreover,the doping of Mn improves the photothermal performance of Au nanodots(AuNDs),and the temperature is about three times higher than pure AuNDs under the same conditions.Photothermal therapy(PTT)is one of the emerging treatment methods with obvious advantages in tumor therapy.It has many advantages such as non-invasive,short treatment time(only a few minutes each time),precise killing tumors,repeatable treatment with no drug resistance and small side effects.What's more,Au/Mn NDs are ultra-small in size(?3 nm)with better penetration ability for tumors.After PTT treatment in mice,the tumors ablated or even disappeared,which has important application value.