Construction Of Functionalized Fluorescent Gold Nanoclusters And Their Biosensing And Bioimaging Applications

Gold nanoclusters（AuNCs）,as new fluorescent nanomaterials,have gained tremendous advantages in biosensing,bioimaging,disease diagnosis and other biomedical applications due to their ultra-small size,excellent optical properties,and good biocompatibility.However,the synthesis of AuNCs is time-consuming and the synthesised AuNCs have poor fluorescence properties.In addition,the detection process is cumbersome and the detection mode is single when used as sensors.Moreover,when the functionalized AuNCs constructed are applied to biological imaging,the imaging function is relatively limited,mostly cell imaging,and functional modification in targeted imaging research is more complicated,which limits the wide application of AuNCs,so it is of great significance to use a simple and efficient one-step method to prepare functionalized AuNCs with strong fluorescence in biosensing and bioimaging.Based on the above research background,the following three parts of research were conducted in this thesis.1.Lysozyme-encapsulated gold nanoclusters（AuNCs@Lzm,AuL）were favorably obtained by a simple and economical synthesis.The resulting AuL exhibits low toxicity,exceptional stability and intense red fluorescence,which can enter living cells and is mainly located in lysosomes.The AuL selectively and sensitively drove to detect folic acid（FA）with a detection limit as low as 0.19 n M based on the combination of the static quenching and the internal filtering effect.Interestingly,the fascinating results discovered that the AuL with ignorable toxicity was adsorbed from the intestine into the liver,and essentially was cleared from the body in 6 days without significant bioaccumulation in zebrafish.Furthermore,the hyaluronic acid（HA）coating AuLH showed significant targeting to tumour cells and the order of targeting was MCF-7>He La>Hep G2>>NIH/3T3≈DC,which attributed to the differences in the number of receptors expressed by the cells.These advantages highlight that the AuL is a versatile nanoplatform for sensing,in vivo fluorescence imaging and tumor targeting.2.Gold nanoclusters（AuNCs@EW@Lzm,AuEL）with the bright red fluorescence were prepared by egg white and lysozyme as double protein ligands,which exhibited good fluorescence stability and high biocompatibility.The probe displayed highly selective detected pyrophosphate（PPi）based on Cu²⁺-mediated AuEL fluorescence quenching.Specifically,the fluorescence of AuEL was quenched when the Cu²⁺/Fe³⁺/Hg²⁺chelated with amino acids on the AuEL surface,respectively.Interestingly,the fluorescence of quenched AuEL-Cu²⁺was significantly recovered by PPi,but not the other two(AuEL-Fe³⁺,AuEL-Hg²⁺).This phenomenon was attributed to the stronger bond between PPi and Cu²⁺than that of Cu²⁺with AuEL.Futher results demonstrated a good linear relationship between PPi concentration and the relative fluorescence intensity of AuEL-Cu²⁺in the range of 131.00–685.40μM with a detection limit of 2.56μM.In addition,the quenched AuEL-Cu²⁺system can also be recovered in acidic environments（p H≤5）.And the as-synthesized AuEL showed excellent cell imaging and target the nucleus.Thus the fabrication of AuEL provides a facile strategy for efficient PPi assay and offers the potential for drug/gene delivery to the nucleus.3.The development of convenient and efficient fluorescent sensors for the identification of tumour cells is of great importance for the early diagnosis of cancer.Herein,the blue-emitting fluorescence gold-silver nanoclusters（Au Ag NCs@PEI,AuAgP）were obtained using PEI as stabilizer through a one-pot method.The AuAgP exhibits excellent fluorescence stability and cell imaging capability.It was found that Fe³⁺could significantly quench the fluorescence of AuAgP by interacting with the amino group on the surface of AuAgP.Excitingly,the fluorescence of AuAgP quenched by Fe³⁺could be recovered upon the addition of glutathione（GSH）based on the redox reaction between Fe³⁺and GSH,and an AuAgP-Fe³⁺based"off-on"fluorescent probe was constructed for the detection of GSH.More importantly,depending on the difference in GSH content between cancer cells and normal cells,AuAgP-Fe³⁺can enable cancer cell-targeted imaging.In addition,to further target imaging of cells with high CD44 receptor expression,HA-functionalised AuAgP（AuAgPH）was synthesised,which exhibited the ability to target imaging of target cells.This study provides some insights into the construction of new metal nanocluster probes for cancer diagnosis and therapy.