Evanescent-wave Biosensor For Detection Of Mercury And Lead Ions In Environment Based On Functional Nucleic Acids

In consideration of its unique advantages of high affinity for heavy metal ions,the Functional Nucleic Acids?such as DNAzyme,Aptamer?show great promise in the development of novel biosensors for heavy metal ion assay.Here,new biosensors for the determination of Pb²⁺ and Hg²⁺ in water by coupling nucleic acid probes and selfdeveloped evanescent wave all-fiber biosensor platform were developed.Our biosensors are sensitive,rapidly and simple;the detailed contents are described as follows:?1?Established immobilization method of FNAs onto fiber optical sensor surfaceThe fiber was prepared first in dehydrated toluene mixed with 2%?v/v?APTES for60 min for amination and then dried in an oven at 200 °C for 60 min.Therefore,the density of APTES on fiber was decreased and the nonspecific adsorption was suppressed.The hybridizations and regenerations between FNAs probes with its complementary DNA were realized after FNAs probes were fixed on fiber surface.XPS analysed the surface elemental compositions and the Si2 p,C1s,and O1 s of the silanized,dried,immobilized and used fiber was characterized by high-resolution spectra XPS.The reason for the decline in performance was the removal of some of the immobilized FNAs on fiber.In addition,the storage and use conditions of the optical fibers were optimized,and the performance of the FNAs probes improved significantly.?2?Developed a highly sensitive and rapid evanescent-wave biosensor for detection of Hg²⁺and Pb²⁺in waterA “turn-on” evanescent-wave fiber biosensor based on functional nucleic acids was developed for detection of Hg²⁺and Pb²⁺in environmental water samples.Two-step strategy was conducted to take advantage of the rapid binding of T-T mismatches with Hg²⁺and the cleavage of a substrate by 8-17 DNAzyme with Pb²⁺in solution,as well as sensitive DNA detection on a liquid–solid interface based on evanescent wave.The biosensor demonstrated high sensitivity(with detection limit of 22 pM?4.2mg/L?for Hg²⁺ and 20 nM?4.2mg/L?for Pb²⁺)and selectivity without any signal amplification,rapid detection?within 13 min per test?,low cost and multiple-cycle regeneration?at least 18 times?.The methods were applied to Hg²⁺and Pb²⁺detection in real environmental water samples.?3?Developed optical fiber-based evanescent wave biosensor for Hg²⁺detection with wide detection range and sensitive via twice target-induced conformational changesAn optical-fiber-based evanescent-wave biosensor for Hg²⁺detection based on an“off–on–off” approach was demonstrated based on twice target-induced conformational changes.The addition of Hg²⁺induced conformational changes of polythymine?T?strands in the liquid phase and on the fiber surface along with the fluorescence intensity changes.the biosensor not only could detect Hg²⁺over a broad concentration range from 0.4 nM to 50 mM,but also achieves fast and highly accurate analysis with a detect limit of 0.4 nM?80ng/L?without any signal amplification.The method was applied to Hg²⁺ detection in real environmental water samples.In addition,based on the conversions of detection modes,a simple calculation method of the hybrid efficiency was proposed.?4?Developed sensitive optical fiber-based evanescent wave biosensor for simultaneous detection of Hg²⁺ and Pb²⁺ based on GR-5 DNAzymeThe core sequence of GR-5 DNAzyme is preserved,and the Hg²⁺ specific nucleic acid sequences were fued with the substract chain of DNAzyme.Hence,the activate DNAzyme GR-5 by Pb²⁺ was maintained,and the hybridizations between GR-5DNAzyme and its substract chain were separated by adding Hg²⁺.Coulped with abovementioned the two-step strategy,the new biosensor based on GR-5 DNAzyme could detect Pb²⁺ and Hg²⁺ simultaneously.The biosensor demonstrated high sensitivity with a detection limit of 7 nM?1.4 m g/L?for Hg²⁺ and 10 nM?2.1m g/L?for Pb²⁺,and the detection could completed within 5 min.finally,the Hg²⁺detection in Danjiangkou reservoir were analysed successfully using the biosensor.