Study On The Construction Of Electrochemical Sensors Sensitized With Metal-organic Frameworks For Monitoring Heavy Metals In Tea

In recent years,heavy metals seriously restricted the sustainable development of tea industry,and thus it is of great significance to develop a rapid and sensitive method for detecting heavy metals in tea.Owing to its simplicity,rapid response and sensitivity,electrochemical sensor has shown broad application prospects in heavy metal assay.In order to overcome the limitation of biological enzyme and mercury-film modified platform commonly used in electrochemical sensing toward heavy metals,metal-organic framework materials(MOFs)with high stability,good catalysis and large surface area were utilized as biomimetic enzyme and sensor interface for electrochemical detection.The proposed sensor exhibited high sensitivity,good anti-interference,acceptable accuracy for evaluating Pb²⁺,Hg²⁺and Cd²⁺in tea.The specific content includes the following three parts:Part 1:Electrochemical sensor sensitized with MIL-88 for monitoring Pb²⁺in teaThe electrochemical sensor was developed by using AuNPs-modified MIL-88 as the sensing platform.Benefiting from the specific recognition of DNA and Pb²⁺,the anti-interference ability could be attained.Firstly,a specific DNA sequence was designed with-SH and methylene blue(MB).Secondly,DNA was immobilized on AuNPs-modified MIL-88 surface by Au-S bond.In the presence of Pb²⁺,DNA was cut off,and triggered MB left from the sensing surface.Based on the synergistic catalysis of AuNPs and MIL-88 toward MB.There was a good linear relationship between electrochemical signal and logarithm of Pb²⁺concentration from 5 p M to 100n M,and the detection limit was 4.73 p M.The sensor was applied to the determination of Pb²⁺in tea samples,and the recovery rate was from 98.7%to 101.4%,providing a useful tool for monitoring tea polluted with Pb²⁺.Part 2:Electrochemical sensing toward Hg²⁺in tea by using EXO?for cyclic amplification and MOFs as biomimetic catalystUiO-66 was designed as biomimetic catalyst,which was used as effective carrier for loading thionine(THi)and gold-platinum nanoparticles(AuPts)to design probe.With the presence of Hg²⁺,T-Hg²⁺-T mismatch was formed,which could activate EXO?.As a result,Hg²⁺was released from T-Hg²⁺-T by enzyme digestion,and then participated in circulation again.With the use of UiO-66 and AuPts for THi catalysis,dual signal amplification could be achieved.A good linear relationship was achieved between response current and the logarithm of mercury concentration in range of 10p M?15 n M,the detection limit was 4.45 p M.Moreover,this sensor exhibited good performances for assessing Hg²⁺in tea with recovery rate from 93.7%to 103.4%.Part 3:Electrochemical sensor based on Bi-BTC for sensitive detection of Cd²⁺in teaMOFs with lots of bismuth ions(Bi-BTC)was first synthesized by solvothermal method.In the process of electrochemical analysis of Cd²⁺,bismuth ions in Bi-BTC and Cd²⁺were co-deposited on the electrode surface,which improved the sensitivity of Cd²⁺determination.At the same time,the above co-deposition could be realized in one step,greatly simplifying the electroplating process of bismuth film.In addition,combining the strong complexing ability of cysteine to Cd²⁺,and the good film-forming ability of Nafion,high sensitivity was realized for Cd²⁺analysis in tea.Under the optimized experimental conditions,the response current was linear with Cd²⁺concentration in the range of 5?50?g/L,and the detection limit was 2.9?g/L.The recovery rate of Cd²⁺in tea was 91.6%?101.1%.In conclusion,three kinds of MOFs were studied in this paper,which were used as biomimetic enzyme and sensor interface.The constructed electrochemical sensors showed high sensitivity,good selectivity,fast response for Pb²⁺?Hg²⁺?Cd²⁺detection.Thus,it provided a new idea for the accurate and rapid analysis of heavy metals in tea.