Design And Sensing Of DNA-functionalized Silver Nanoparticles-based Probes

Silver nanoparticles?Ag NPs?,a common noble metal nanoparticles,receive increasing attentions due to the unique optical,electrical and catalytical properties.In recent years,with the development of the synthesis and functionalization of Ag NPs,DNA-functionalized Ag NPs are widely applied in biosensing.However,in these systems,complicated procedures of modification are always necessary,besides,the strategies for signal recognition and the targets are limited.Aimed at these problems,we exploited the super strong quenching effect of DNA-templated Ag NPs to construct novel sensing platforms for Hg²⁺and CH₃Hg⁺.In addition,Mo S₂-Ag NPs nanomaterials were synthesized as an active SERS substrate.By conjugation of the DNA probe,the DNA@Mo S₂-Ag NPs nano complex probe was successfully applied for intracellular Raman imaging of m RNA.1)Exploiting the Ag/Hg amalgamation with DNA-templated Ag NPs for high specific detection of Hg²⁺.Pollutions of the heavy metal ion lead to severe risks to the environment and human health.As it is necessary to detect the trace amounts of mercury,in this charpter,we firstly provide a method,which combining the natural phenomenon of silver/mercury amalgamation and DNA-templated Ag NPs,for rapid,easy and reliable assay of Hg²⁺ions with superior selectivity over competing ions and high sensitivity.In this approach,by the reduction of mercury species to elemental mercury,silver atoms act as the a cceptors of mercury atom and form Ag/Hg amalgam,thus achieving the detection of Hg²⁺.To transduce the signal of the silver amalgamation fluorescently,we employ a FAM-labeled ss DNA as the signal reporter.The formation of Ag NPs on the DNA strand leads to a great quenching of the FAM fluorescence,however,in the presence of Hg²⁺,Ag/Hg amalgam forms and suppresses the growth of Ag NPs on the DNA,which results in fluorescence signal increase compared with the fluorescence without Hg²⁺.The fluorescence enhancement of FAM is able to determin Hg²⁺at a few nanomolar levels.Moreover,because of the superior specificity of silver/mercury amalgamation,the probe is highy selective for Hg²⁺,while no obvious responses were showed for other metal ions even with concentrations up to millimolar levels.This sensor is successfully applied for determination of Hg²⁺in various water samples.This design puts important implications on the development of novel fluorescent sensors for fast,easy and selective detection of Hg²⁺in the environmental and biological samples.2)Combination of the DNA-templated Ag NPs and Ag/Hg amalgamation for ultrasensitive and highly selective determination of CH₃Hg⁺bioaccumulation in fish samples.Methylmercury?CH₃Hg⁺?is the most common form of organic mercury.It is well-known that CH₃Hg⁺is the most toxic mercury compound which is more dangerous than elemental or inorganic mercury.In seabeds,the bacteria convert the deposited Hg²⁺into CH₃Hg⁺.The CH₃Hg⁺ions are subsequently taken by fish and bioaccumulated in their tissue,and finally,entering the human diet,leading to severe health problems.Therefore,it is desirable to develop an approach for sensitive and selective detection of CH₃Hg⁺bioaccumulation in fish samples.However,as it is difficult to distinguish CH₃Hg⁺from Hg²⁺,selective assay of CH₃Hg⁺in the samples with Hg²⁺has been hampered seriously.In this charpter,we exploit Ag/Hg amalgamation,a natural phenomenon between Hg atoms and Ag atoms,in combination with DNA-templated Ag NPs,to detect CH₃Hg⁺with high sensitivity and moreover,superior selectivity over Hg²⁺as well as other metal ions.In this approach,by forming Ag/Hg amalgams on a CH ₃Hg⁺-specific DNA,We successfully distinguish CH₃Hg⁺from Hg²⁺.It is found that mercury atoms can form Ag/Hg amalgams with silver atoms on a CH₃Hg⁺-specific DNA,rather than CH₃Hg⁺.Thus,for a dye-labeled CH₃Hg⁺-specific DNA,both CH₃Hg⁺and Hg²⁺can suppress the formation of DNA-templated Ag NPs,but only CH₃Hg⁺can lead to the fluorescence enhancement.The sensor can detect CH ₃Hg⁺with the picomolar level,which is more than 125-fold sensitive over Hg²⁺.Moreover,it shows no response to50-fold Hg²⁺and 10⁶-fold other heavy metal ions.We study the bioaccumulation of CH₃Hg⁺in fish samples with this fast,easy and selective method.3)Sythesis of Mo S₂-Ag NPs nanocomposite for construction of novel SERS-active substrate.Transition-metal dichalcogenides?TMDCs?are a class of nano-layered analogue of graphene with excellent properties.Mo S₂ is a kind of typical TMDCs,which is commonly used in constructing field-effect transistors,electrocatalysis of hydrogen evolution and energy harvesting.In this chapter,by the assembly of Ag NPs on the single layer of Mo S ₂ nanosheet,we obtained Mo S₂-Ag NPs nanocomposite.Among the applications of nanocomposite formed with Mo S₂ nanosheet and metal nanoparticles,the Raman-active substrate is an attractive field.In the experiments,we have found that as the SERS substrate,Mo S₂-Ag NPs can lead to strong enhancement of the SERS signal in Raman reporters such as FAM,rhodamine 6G and 4-Amino-Benzenethiol.Compared to the carbon materials for constructions of similar substrates,the SERS spectra on Mo S ₂-Ag NPs show clear peak with strong signal witho ut the interference of D band and G band,which results in high sensitivity at lower concentration of analytes.The enhancement factor was calculated to be 1.28×10⁷.The substrate also exhibits good reproducibility of SERS signal.4)Construction of DNA@Mo S₂-Ag NPs complex probe for SERS imaing of intracellular m RNA.Message RNA?m RNA?plays a vital role in the celluar expressions of protein,which enables specific regulatory fuctions in the cell,abnormal behaviors of m RNA are usually related to some diseas es.So,it's of great value to image specific m RNA within the cell to understand the functions of m RNA on the molecule-scale,and develop the diagnostic tools as well as therapeutic interventions.In this chapter,we functionalized Mo S ₂-Ag NPs with DNA probe to construct the DNA@Mo S₂-Ag NPs complex probe.In the presence of target m RNA?DNA?,the comformation of the probe changed due to the hybridization,leading to the production of SERS signal.Thanks to the strong enhancement of signal by Mo S₂-Ag NPs,down to 50 p M target can be detected.Due to the nanocarrier of Mo S₂-Ag NPs,the complex probe successfully achieves intracellular Raman imaging of TK1 m RNA in Hep G2 cells.