The Photothermal Effect Of Near-infrared Response Enzyme-conjugated Gold Nanorods And Its Application

Enzyme is a kind of biomacromolecule with high catalytic activity and high specificity,whose chemical essence is protein or RNA.However,the activity of enzymes is easily affected by many factors,such as temperature,pH value,inhibitors and so on,which limits its application in industry and medical science.According to the optimum temperature,enzymes can be divided into psychrophilic enzyme,mesophilic enzyme and thermophilic enzyme.Among them,mesophilic enzymes are unstable,difficult to preserve and limited in practical application,but easy to obtain.Although thermophilic enzymes possess high catalytic ability and excellent thermal stability,the temperature activating their catalytic activity often requires more energy consumption.Researchers enhance the catalytic capability of enzymes via mutation,modification and immobolization.As an emerging material,nanomaterials have attracted much attention.A significant number of studies have utilized the properties of nanomaterials,which are quite different from macromaterials,to ameliorate enzymes.One of the most striking characteristics of nanomaterials is their photothermal effect.Photothermal effect is a kind of electrical property,in which photon energy does not directly change the internal electronic state of photothermal materials,but intensifies the vibration of crystal lattice,ultimately leading to a rise of temperature after photothermal materials irradiated by a specific wavelength of light.Nowadays,nanomaterials with photothermal effects can be divided into four categories: noble metal nanomaterials,such as gold nanoparticles and silver nanoparticles;carbon nanomaterials,such as graphene;transition-metal dichalcogenide nanomaterials,such as CuS nanoparticle;organic dye nanomaterials,such as indocyanine green.Utilizing the photothermal effect of nanomaterials to regulate enzymatic activity and to expand the application fields of enzymes has become a new research focus.In addition,nanomaterial-based photothermal therapy has been widely used in cancer treatment as an invasive,non-toxic treatment without side-effect,in which intracorporal organs are exposed to temperatures higher than body temperature to promote the selective destruction of abnormal cells.Among the above materials,gold nanoparticles have been widely used intargeted drug delivery,photothermal therapy,bioimaging and bioprobe due to the unique surface plasmon resonance effect.In this paper,we modified different enzymes onto gold nanorods by self-assembly and utilized the photothermal effect to regulate and enhance the catalytic activity of enzymes for industrial catalysis and biomedicine.The main results are summarized as follows.1.We combined lipase PPL with gold nanorods(enzyme-conjugated gold nanorods complexes,EGCs)to explore the catalytic activity via illumination heating compared with that via traditional water bath heating.Although the overall temperature of the two seperate systems is the same,EGCs exhibited higher catalytic rate than free enzyme.Based on this,we proposed a hypothesis that the internal heating mode of GNRs was more efficient and increased enzyme activity compared to diffusion-limited water bath heating.In addition,EGCs also had long-term stability and reusability.We applied EGCs to catalyze Aldol reaction.The results showed that the reaction time was greatly shortened,indicating that EGCs had potential for industrial application.2.Generation of biofilm and exotoxin regulated by quorum sensing system is the main factor of bacterial resistance and pathogenicity,respectively.Since the main component of biofilm and the essence of exotoxin are proteins,we constructed bromelain-conjugated gold nanorods(protease-conjugated gold nanorods,PGs).Upon near-infrared irradiation,PGs effectively killed Escherichia coli and Staphylococcus aureus by destructing cell wall,and elimated the formed biofilm and exotoxins.In the absence of NIR,PGs also inhibited bacterial growth as well as the secretion of biofilm and exotoxin.Since Staphylococcus aureus was Gram-positive bacteria,in which the component of peptidoglycan in cell wall structure was higher,the killing effect of PGs on Staphylococcus aureus was more effective than Escherichia coli.In addition,in term of the signal of quorum sensing from Staphylococcus aureus was small peptide,we speculated that targeting the inhibition of quorum sensing had potential application significance in the treatment and prevention of inflammation caused by bacterial.Finally,PGs destroyed bacterial DNA and proteins to avoid the spread of drugresistant genes.3.In order to target the multiple causes of Alzheimer’s disease for treatment,we designed double-conjugated gold nanorods(GNRs-APH-scFv,GAS).Upon nearinfrared illumination,GAS effectively degraded Aβ monomers under the action of enzymes,inhibited Aβ fibrosis process to reduce the generation of more toxic Aβ oligomers and fibers.Moreover,due to the conjugated antibody and photothermal effect,oligomers and fibers were disaggregated into monomers,which degraded by thermophilic enzymes as followed.Based on this,the efficient elimination of various forms of Aβ was achieved.GAS reduced Aβ-mediated peroxidase-like activity and improved cell survival.GAS could also acted as bioprobes to detect the Aβ fibrosis process under the targeting effect of scFv.The in vivo studies showed that GAS delayed the onset of dementia and prolonged the life span of transgenic nematodes CL4176.