Magnesium Ion Mediated One-step Method For Rapid Preparation Of High Density Spherical Nucleic Acids And Corresponding Investigation

The spherical nucleic acid with gold nanoparticles core and DNA shell bond which throught Au-S bonding,was been widely used in biological detection drug delivery and gene therapy for decade.Due to its combination of outstanding optical properties,chemical stability,biocompatibility of gold nanoparticles and specificity and customizability of DNA.However,the preparation of spherical nucleic acid facing the such problems as long preparation time,low loading density and low hybridization efficiency,which bringing negative effects on its application toword various fields.For this reason,we propose a new strategy for rapid preparation of three types of spherical nucleic acids with high loading density.The research contents as follws:Chapter 2:Using the excellent negative shielding effect of divalent Mg²⁺,a rapid one–step method for preparing high density single stranded DNA spherical nucleic acid which based on magnesium ions was developed.Using low concentration divalent Mg²⁺to replace the high concentration monovalent Na⁺ions needed for perpareing single stranded DNA with high density.With the help of microsurfactants the one-step loading of single stranded DNA onto gold nanoparticles can be achieve.By measuring the density of the single-stranded DNA,we knew that the magnesium ion method can reach 140%density compare to the salt-aging method.Which just took for 2 hours instead of 2?3 days.Chapter 3:In order to solve the problem which cause by the instable DNA secondary structure of hairpin DNA during the early stage of the modification process.We propose the one-step method that can directly funtionalizing gold nanoparticle with hairpin DNA by using the unqiue advantage of Mg²⁺.By using the low concentration divalent Mg²⁺ion as electrostatic shielding agent,successfully realized one-step rapid perparetion of hairpin DNA with well definite secondary structure.Avoding the negative effect cause by the non-specific adsorption of single strand DNA,achieving higt loading density.After investigation,we knew that the hairpin DNA loading density of this method was 80%higher than the traditional salt-aging protocol.Which just took for 2 hours to finish the modification process compareing 2?3days of salt-aging protocol.As it can can work stably under the Mg²⁺/Na⁺environment,and realizing the detection of target nucleic acid in 5 mins.Chapter 4:In order to solve the problems of low modification density which caused by the low hybridization efficiency during the preparation of double stranded spherical nucleic acid with salt-aging protocol.A strategy for directly modifying double-stranded DNA by using the Mg²⁺was been proposed for the first time.After corresponding testing,we knew that this method can reach 196%of the DNA loading density compare to the salt-aging protocol.Which just took for few hours.As prepared double strand spherical nucleic acid can remained stable under 1 M Na Cl harsh ionic condition.And 78%of the double stranded DNA on the surface could conduct the chain replacement reaction with the target nucleic acid,showing outstanding hybridization perfomence.