Study On The Photothermal Effect Of Polydopamine Coated Au-Pt Nanorods

Photothermal therapy（PTT）is a treatment method in which photothermal conversion materials gathered near a tumour are irradiated by an external light source to absorb light energy and convert it into heat energy to trigger the death of cancer cells.It has attracted widespread attention from researchers because of its effectiveness,low side effects and low cost.Noble metal nanomaterials have a unique local surface plasmon resonance（LSPR）effect,and are particularly suitable as photothermal conversion materials.However,the currently developed noble metal photothermal conversion materials still face serious problems such as complex preparation process,low photothermal conversion efficiency（PCE）,poor photothermal stability,and high biological toxicity.Therefore,it is very necessary to develop a photothermal conversion material with simple and controllable synthesis method,excellent photothermal performance and good biocompatibility.To solve the above problems,after briefly introducing the mechanism of PTT and comparing various types of photothermal conversion materials,gold nanorods（AuNRs）with LSPR effect but poor photothermal stability were combined with platinum（Pt）nanomaterials with good stability and catalytic activity to form AuPtNRs with ideal optical properties and structure in this study.They were also surface coated with polydopamine（PDA）,resulting in the final product AuPt@PDA with high PCE and photothermal stability as well as good biocompatibility,demonstrating good photothermal ablation of cancer cells in PTT.Also due to the modification and functionalisation of Ptand PDA,it enables AuPt@PDA to effectively scavenge intracellular reactive oxygen species（ROS）.The research content is divided into the following three parts:（1）Well-dispersed and uniformly sized AuNRs were synthesized by seedless method,on the basis of which the effects of Ag⁺and K₂PtCl₄concentrations on the growth pattern of Pton the surface of AuNRs were studied.A simple method for the precise and controllable synthesis of AuPtNRs was proposed,and dumbbell shaped nanorods（D-AuPtNRs）and core-shell nanorods（C-AuPtNRs）with ideal size and structure were optimally prepared.The LSPR peaks of D-AuPtNRs and C-AuPtNRs can be adjusted to a range close to the wavelength of the laser light source in the subsequent PTT.Kinetic analysis of the reduction of 4-NP by Na BH₄catalyzed by AuNRs,D-AuPtNRs and C-AuPtNRs revealed that the reaction rate constants of the D-AuPtNRs were 4.3 and 2.3 times higher than those of the AuNRs and C-AuPtNRs,respectively,attributed to the enhanced electronic effect due to the spatial separation and co-exposure of Auand Pton their surfaces,thus enhancing the catalytic activity.The D-AuPtNRs with LSPR closer to the wavelength of the laser source at 808 nm and better catalytic activity were eventually selected for subsequent experiments and abbreviated as AuPtNRs.（2）The surface coating of polyethylene glycol（PEG）-modified AuPtNRs was carried out using PDA to obtain the final product AuPt@PDA.The successful synthesis of AuPt@PDA was demonstrated by characterizing the products at each stage of the preparation process by TEM,absorption spectroscopy,FTIR and zeta potential.The photothermal conversion properties of AuNRs,AuPtNRs and AuPt@PDA were compared.The results showed that after10 min of laser irradiation,the temperature of AuPt@PDA increased by 41.5℃and the PCE reached 81.77%,which was significantly higher than that of AuPtNRs（78.76%）and AuNRs（52.32%）.In addition AuPt@PDA maintained essentially unchanged photothermal warming capacity after four laser on/off cycles of irradiation,and the optical properties and dispersion of AuPt@PDA solution in bio-buffer did not change significantly after being left for different times,demonstrating that AuPt@PDA has good photothermal and aqueous solution stability and can be used as an excellent photothermal conversion material.（3）The inhibitory effect of AuPt@PDA on cancer cells in PTT was contrastively discussed.The results of MTT toxicity assay showed that the viability of A375 cells treated with AuPt@PDA was still more than 85%,which was significantly higher than the cell viability of 65%in AuNRs and AuPtNRs groups,indicating that AuPt@PDA has good biocompatibility.Cell uptake experiments using FITC tracer nanomaterials and DAPI localized cells showed that AuPt@PDA could successfully enter the cytoplasm through the membrane.The killing ability of AuPt@PDA on A375 cells under laser irradiation was assessed by both MTT and live/dead cell double staining methods,and the results showed that the inhibition rate of AuPt@PDA on cancer cells reached 60.64%,which was significantly higher than that of AuNRs and AuPTNRs.The level of ROS in the cells of each experimental group were measured using the fluorescent probe DCFH-DA.The results showed that the level of intracellular ROS generated by heat stress was significantly reduced due to the ability of both Ptcoating and PDA coating in AuPt@PDA to scavenge ROS.All the results demonstrate that AuPt@PDA is an excellent photothermal conversion material with strong killing ability against cancer cells in PTT,showing good application prospects and values.