Synergistic Enhancement Of Noble Metal/Semiconductor Oxide Heterostructures By Surface Plasmon For Highly Sensitive Optical Detection Of Bacterial Genes

Surface plasmon effect(SPR)has been widely used in photocatalysis,metal enhanced fluorescence,surface enhanced Raman scattering,surface enhanced infrared absorption,and other applications.The commonly used substrates include noble metal nanomaterials such as Au,Ag,and Cu.Through simple design of the morphology and structure of noble metal materials,metal nanomaterials with high enhancement factors can be obtained,such as spheres,stars,rods,flowers,bows,and dendritic structures.There are abundant gaps and tips in these structures,and the strong electromagnetic hot spots generated will amplify the optical signals of the molecules to be tested for highly sensitive detection purposes.However,the disadvantages of precious metals such as high cost,scarcity of species,and poor biocompatibility limit their application.Semiconductor materials,due to their adjustable band gaps,exhibit novel surface characteristics,diverse active substrates,and controllable photoelectric properties,which have received widespread attention.Oxygen defect and doping strategies are effective methods for obtaining active semiconductor substrates by adjusting energy bands or increasing free electron concentrations.Precious metal semiconductor composite nanomaterials combine the advantages of both.After some morphological design and defect engineering,an active substrate with large specific surface area,high sensitivity,and stable signal can be obtained.Surface enhanced Raman scattering(SERS)and metal enhanced fluorescence(MEF)have been widely used in the fields of biosensors,environmental monitoring,and biological imaging.Therefore,starting from the above two research directions,this thesis has synthesized Au-N-Ta Ox and Ag-Ti Ox,respectively,using precious metal/semiconductor composite nanomaterials as the research object,and studied their applications in bacterial target genes.The main work is as follows:(1)The surface plasmon synergistic effect of gold/nitrogen doped tantalum oxide heterojunctions for highly sensitive SERS detection of bacterial nucleic acidsUsing surface enhanced Raman scattering as a powerful tool for molecular recognition,has been strictly restricted to precious metals.Semiconductor based surface enhanced Raman scattering substrates will overcome the shortcomings of metal substrates and promote the development of surface enhanced Raman spectroscopy technology in surface science,spectroscopy,and biomedical research.However,the detection sensitivity and enhancement effect of semiconductor substrates are affected by their weak activity.In this work,nitrogen doped defect tantalum oxide based on Au NPs loading was applied to highly sensitive surface enhanced Raman scattering detection.For crystal violet detection,the substrate has an enhancement factor(EF)of10~6 under laser excitation at 532 nm.This is due to the existence of physical and chemical synergistic enhancement mechanisms in noble metal/semiconductor systems.Then,the amino modified probe was assembled onto Au-N-Ta Ox via an Au-N bond,and SERS detection was performed on the fem A gene of Staphylococcus aureus and the opr L gene of Pseudomonas aeruginosa based on the principle of nucleic acid probe hybridization.The Au-N-Ta Ox substrate exhibits high detection sensitivity and a certain linear relationship,with detection limits of 6.5 nmol/L and 5.6 nmol/L,respectively.Finally,we designed a chromatographic microfluidic array chip and successfully detected the target genes of pathogenic bacteria extracted from the human body.The chip has the potential to detect multiple pathogens and has shown great application potential in biological related fields.(2)Surface plasmon synergistic effect of silver/titanium oxide heterojunction for highly sensitive MEF detection of bacterial nucleic acidsMetal enhanced fluorescence(MEF)is an optical phenomenon caused by localized surface plasmon resonance(LSPR)of metal nanostructures.The excitation enhancement of the fluorophore and the increase of the radiation attenuation rate can be achieved through the generation of a highly restricted local electric field induced by LSPR,thereby significantly improving the fluorescence intensity.Therefore,the MEF phenomenon has great potential for highly sensitive biological analytical applications,such as biosensors,immunoassays,and fluorescence based imaging.In this work,we successfully synthesized Ag-Ti O_x nanocomposites through laser etching and in situ photoreduction methods and applied them to highly sensitive metal enhanced fluorescence detection.Using calcein as a reactive dye,the amount of the spacer layer(APTES)between the substrate and the dye was optimized,and the active substrate with the best performance was obtained.The enhanced fluorescence results can be attributed to the combined effects of fluorescence resonance energy transfer and surface plasmon resonance effects caused by the presence of Ag nanoparticles in the nanocomposite sample.For the fluorescence visual detection method used in the detection of polycyclic mediated isothermal amplification results,the substrate has a high detection sensitivity and a linear relationship within a certain concentration range,with a detection limit of 40 fg/μL.This strategy has developed a noble metal/semiconductor composite nanomaterial that can be applied to actual sample detection using MEF,which has certain application value.