Construction Of DNA Shell At Micro-nano Interface And Application In Bioimaging And Food Safety Detection

DNA nanotechnology mainly refers to the self-assembly of DNA structures and devices using the double helix structure and base pairing interaction of DNA.The DNA shell structure is precisely and predictably regulated and constructed at the nanoscale using DNA nanotechnology.The density,mechanical properties and surface chemistry of the DNA shell layer can be designed on demand,and the functionality of the DNA shell layer can be extended by the modification of functionalized molecules such as functional recognition monomers,fluorescent signaling molecules and bioactive substrates.The use of DNA shell structures for surface design of micro-nano interfaces,such as protection,encoding,delivery and release of cells has been reported.Similarly,there are potential applications for the precise manipulation of nanoparticle surfaces.In this study,two DNA shell structures at the micro/nano interface were proposed,which were constructed by the framework nucleic acid（FNA）and poly adenine（poly A）structures,respectively,for application in the field of bioimaging and food safety detection.In this design,the target bacterium is efficiently captured by the aptamer sequences in the FNA and evenly distributed over its surface.The DNA shell structure was successfully assembled layer-by-layer at the micrometre interface by linking the biotin-modified FNA structure and the circularized padlock probes structure via streptavidin,triggering rolling circle amplification.In this study,using Salmonella typhimurium as the experimental object,the assembly ratio optimization and preparation of the DNA shell structure were characterized by agarose gel electrophoresis,and the use of this DNA shell structure for biological imaging studies was further observed in fluorescence microscopy.The experimental results show that the DNA shell structure based on FNA can be effectively applied to bioimaging at micron-scale interfaces.Through the formulation of aptamer sequences and the regulation of fluorescence performance,it provides a good operating platform for highly sensitive biological imaging of cells and tissues.The main mechanism of colorimetric biosensors based on gold nanoparticles（Au NPs）lies in the unique optical properties of Au NPs.In this paper,the DNA shell structure of poly A₂₀was used to protect the stability of Au NPs in the electrolyte environment for quick and simple visual detection of kanamycin.Firstly,Kanamycin-aptamer（Kana-Apt）functionalized with amino group functionalized Magnetic beads（MBs）by covalent binding to aldehyde groups.According to the sequence design,Kana-Apt linked to the MBs was complementary to the partial sequence of the hybridization block-poly A₂₀(HB-poly A₂₀)probe to form MBs@ds DNA complex.In this process,agarose gel electrophoresis and UV-visible absorption spectroscopy were used to characterize the complex.When kanamycin（Kana）was present in the tested substance,Kana-Apt on the MBs@ds DNA complex specifically bound to Kana,and HB-poly A₂₀was released from the surface of the MBs.After the free HB-poly A₂₀ in the supernatant was extracted by magnetic separation and added to the Au NPs solution,the collective interaction between poly A and Au NPs surface resulted in hydrophobic collapse,which triggered the high adsorption affinity of poly A and Au NPs.In the salt concentration environment,Au NPs are protected from aggregation triggered by the salt concentration environment by the poly A₂₀ structure,and the solution remains red.However,when Kana was not included in the assay system,the MBs@ds DNA structure did not change and HB-poly A₂₀ did not free into the supernatant.Nevertheless,the presence of electrolyte destroys the stable electric double layer structure on the surface of Au NPs,and the stability of Au NPs decreases and aggregation occurs,resulting in the color of the solution changing from red to blue gray.The colorimetric aptamer sensor has a wide detection range（0.01-500 n M）,high sensitivity（0.1 n M）and easy observation of the results,which is very suitable for the visualization and real-time detection of large numbers of samples in the field.This work has high generality and use value and provides a general platform for real-time sensing in the field of other antibiotics or food safety contaminants.This study provides a new idea for the development of novel colorimetric biosensors based on poly A structure and its application in the field of food safety detection.In conclusion,DNA shell structures with high stability and specific recognition capabilities are expected to provide flexible mechanisms to manipulate biophysical and physiological phenomena at micro-nano interfaces,thus enabling surface biomarker analysis and molecular event monitoring.