| Dairy products are rich in nutrition,and thus can be acted as "the closest food".Recently,the dairy safety can not be ignored stemming from the excess addition of trace metal elements and the pollution of heavy metals.Electrochemical sensors have attracted great interests because of their high sensitivity,and provide a useful tool to ensure the safety of dairy industry.In this study,three different electrochemical DNA sensors have been developed based on metal-organic frameworks for detecting Hg2+,Cu2+,Zn2+in dairy products.The main research content is divided into the following three parts:Part 1:Simple electrochemical sensing for Hg2+in dairy product using optimal Cu-MOFs as signal reporting.A convenient sensor was developed for electrochemical assay of Hg2+in dairy product using the optimal Cu2+-based metal-organic frameworks(Cu-MOFs)as signal reporting.Benefiting from specific recognition between Hg2+and thymine(T)-rich DNA strands,the interferences of milk matrices were effectively eliminated,thereby greatly improving the accuracy of test results.Moreover,the suitable Cu-MOFs offered an efficient carrier for probe design,and the contained Cu2+ions could be directly detected to output electrochemical signal of Hg2+presence without labor-or time-intensive operations.Compared with previous methods,this sensor substantially simplified the process of electrochemical measurement and faciliatates highly sensitive,selective and rapid analysis of Hg2+with the detection limit of 4.8 fM,offering a valuable means for monitoring dairy product contamination with Hg2+.Part 2:Electrochemical DNA sensor for Cu2+determination in dairy product using Ce-MOFs as mimic enzyme.Ce-MOFs were prepared as mimic enzyme with high catalytic activity.On basis of specific recognition of DNA1 toward Cu2+,an electrochemical DNA sensor was developed for detecting Cu2+in dairy products.During the preparation process,the signal probe was first fabricated by fixing DNA2 on Ce-MOFs/AuNPs,which was then attached to the DNA1-modified electrode.Using the catalytic activity of Ce-MOFs toward ascorbic acid,high current response could be obtained because of large amounts of Ce-MOFs immobilized on the electrode.With the presence of Cu2+,DNA1 was cleaved at G site,resulting in the loss of Ce-MOFs from the electrode surface.Based on the change of current response,the concentration of Cu2+could be detected with the linear range from 0.10 pM to 100 nM,and detection limit of 0.034 pM.Overall,the electrochemical DNA sensor had the advantages of high sensitivity,good selectivity and rapid response,offering a promising method for rapid detection of Cu2+in dairy products.Part 3:Electrocehical DNA sensor for Zn2+determination in dairy product using ZIF-67 as mimetic enzyme.ZIF-67 metal-organic frameworks(MOFs)were prepared with excellent catalytic performance toward glucose oxidization.With the use of ZIF-67 as mimetic enzyme and Zn2+-induced specific digestion of DNA1,a highly sensitive electrocehmical DNA sensor was designed for detecting Zn2+in dairy products.When Zn2+was present,the site rA on the hairpin-like DNA1 was specifically recognized and cleaved,and the resulting residue could hybridize with DNA2 to make ZIF-67 attach to the electrode surface.The catalytic ability of ZIF-67 toward glucose was used to generate electrochemical signal.The proportional relationship was achieved between current response and the logarithm of Zn2+concentration from 1 × 10-12 M to 1 × 10-6 M.The detection limit of the electrocehmical DNA sensor was 0.17 fM(S/N=3),offering a useful tool for Zn2+assay in dairy products with high sensitivity and selectivity.In summary,three electrochemical DNA sensors were developed by using MOFs for detecting Hg2+,Cu2+ and Zn2+in dairy products,providing a useful solution for the assay of metal ions in food matrix. |
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