Sensing Heavy Metal In Tea Using Upconversion Fluorescence Method

Tea,as one of important agricultural crop in China,ranked second in the world with its export volume.Due to frequent tea safety accidents,China's tea export competitiveness is decreasing gradually.The existing detection methods can finish the concentration detection,but have some limitations of infective,expensive instruments universally.Therefore,developing a novel,rapid and sensitive method is significant.Nowdays,fluorescence method becomes major scope for rapid detection of pollutants.Due to the advantages of high sensitivity,high stability and no fluorescence background,Upconversion fluorescence method has been paid more and more attention.In this study,cadmium ions,mercury ions and lead ions in tea were selected to as research objects.Based on aptamer specific recognition,magnetic separation,fluorescence resonance energy transfer and inner filter,a series of upconversion fluorescence sensors were developed for trace metals ions(Cd²⁺,Hg²⁺,Pb²⁺).It is significant to do our research which improves tea safety quality and promote healthy and sustainable development of the tea industry.The details are as follows:1.A method for rapid detection of Cd²⁺in tea.The UCNPs-dithizone mixed system was developed based on inner filter for detection of Cd²⁺in tea rapidly.With addition of Cd²⁺,the Uv-vis absorption peak of UCNPs-dithizone solution showed a bathochromic shift,resulting in a spectral overlap between upconversion fluorescence emission and the ultraviolet absorption band,leading to decreasing of fluorescence intensity.Therefore,the concentration of Cd²⁺can be monitored based on inner filter between UCNPs and dithizone.Under the optimal condition,a wide linear detection range from 0.01-1.0?M was achieved,with a detection limit of 3.7 nM for detecting Cd²⁺.The proposed method and atomic absorption spectrometry method were applied to detect Cd²⁺,and the results are similar,confirming that our method can detect Cd²⁺rapidly.2.A method for rapid detection of Hg²⁺in tea.The UCNPs-RhDCP mixed system was developed based on inner filter for detection of Hg²⁺in tea rapidly.With addition of Hg²⁺,Hg²⁺can be captured by RhDCP to form a RhDCP-Hg²⁺complex,causing Uv-vis absorption peak of UCNPs-RhDCP solutions between 500-600 nm enhancing,leading to decreasing of fluorescence intensity.Therefore,the concentration of Hg²⁺can be monitored based on inner filter between UCNPs and RhDCP.Under the optimal condition,a wide linear detection range from 0.05-10?M was achieved,with a detection limit of 13.5 nM for detecting Hg²⁺.The proposed method and atomic absorption spectrometry method were applied to detect Hg²⁺,and the results are similar,confirming that our method can detect Hg²⁺rapidly.3.A method for rapid detection of Pb²⁺in tea.The UCNPs-MNPs-GNPs mixed system was developed based on fluorescence resonance energy transfer for detection of Pb²⁺in tea rapidly.Fisrt,the aptamer-modified UCNPs and MNPs-GNPs were synthesized and combined with complementary base pairing aptamer.The fluorescence was quenching through FRET between UCNPs and MNPs-GNPs.With addition of Pb²⁺,the catalytic strand was cut off by Pb²⁺,leading to separation of UCNPs and MNPs-GNPs,causing in the quenched fluorescence restoration through removing the effect of FRET.Therefore,the concentration of Pb²⁺can be monitored based on FRET between UCNPs and GNPs-MNPs.Under the optimal condition,a wide linear detection range from 25-1400 nM was achieved,with a detection limit of 5.7 nM for detecting Pb²⁺.The proposed method and atomic absorption spectrometry method were applied to detect Pb²⁺,and the results are similar,confirming that our method can detect Pb²⁺rapidly.