Preparation And Optical Properties Of Highly Active Au/Cu Composite Nanomaterials

Gold nanorods?Au NRs?have important research value in biotherapy,catalysis and bioanalysis,owing to their unique optical properties.Au NRs have two characteristic absorption bands,which are transverse and longitudinal surface plasmon resonance band.The longitudinal surface plasmon resonance band?LSPR?is sensitive to the change of dielectric constant of the surrounding medium and the size of Au NRs.Therefore,changing the structure and external environment of Au NRs will lead to the shift of LSPR peak,and then affect the optical properties such as absorption and photothermal.In fact,Au NRs have high-index facets and low-index facets during the growth process.High-index facets exhibit obviously catalytic activity comparing with low-index facets due to the high density of atomic steps,ledges,and kinks.However,high-index facets of Au NRs are not easy to be formed due to their high surface energy.Therefore,it is very important to obtain high-index facets of Au NRs in order to improve their catalytic activity.The gold nanomaterials with high-index facets have strong catalytic activity and can be used as nanozymes for biological applications.Meanwhile,the LSPR peak of Au NRs is located in the near infrared region,which can absorb the near infrared light that matches the vibrational frequency of the phonon,thus producing the photothermal effect.Based on the same laser irradiation,changing the LSPR peak position of Au NRs will cause different temperature changes.Using this photothermal property,Au NRs can be applied to photothermal sensing.In summary,the research contents of this project are mainly about obtaining the high-index facets to improve catalytic activity of Au NRs and applying photothermal property of Au NRs to the photothermal sensing.For these purposes,the main research work is as follows:?1?First,it is studied that Cu²⁺ions doping the Au NRs could make high-index facets appear and increase their catalytic activity.The Au/Cu composite nanorods?Au/Cu NRs?were prepared by adding Cu²⁺into the growth solution of the Au NRs.It can show that Cu²⁺doping Au NRs can selectively inhibit the growth of low-index Au?111?crystal surface,and change the arrangement of atomic deposition to promote the appearance of high-index crystal surface Au?200?.Then,it is found that the catalytic activity of Au/Cu NRs could be enhanced due to the appearance of high-index facet Au?200?.These highly active Au/Cu NRs can be applied as nanozymes.Au/Cu NRs may possess high peroxidased-like properties,which can catalytically oxidize 3,3?,5,5?-tetramethylbenzidine?TMB?to oxidized TMB?oxTMB?under the condition of the existence of H₂O₂.In this study,during the oxidation process of TMB,the presence of ascorbic acid may reduce ox TMB to TMB,which leads to the color change from blue to colorless.Thus,the colorimetric detection method for antioxidant molecules could be developed.?2?Finally,the varied assembly state of Au NRs can change the peak position of LSPR,thus producing different photothermal effect.And using this photothermal property of Au NRs can detect metal ions by photothermal sensing.Utilize the strong interaction between Cu²⁺and cysteine?CYS?to induce the Au NRs assembly to adjust the location of LSPR peak.Based on the same laser irradiation,the LSPR peak shift will produce different temperature changes,which can be used to detect Cu²⁺.So,a new nanosensor for detecting Cu²⁺has been developed based on the varied photothermal effect.The photothermal sensor is sensitive to low concentration of copper ions,which is different from the colorimetric detection of Cu²⁺.Here,the detection limit for Cu²⁺is 5 nM.