Construction Of Pesticides Biosensors Based On Upconversion Fluorescent Nanoprobe And Their Application

The unique optical properties of the trivalent lanthanide ions have attracted the attention over a century.Due to the special electronic layer structure of the trivalent lanthanide ion in the 4f,5s~25p~6 electron orbital,the trivalent lanthanide element can emit a sharp and narrow transition peak at 4f-4f.Since the emission wavelength of these ions is not substantially affected by the external environment,different research purposes can be achieved by combining into different substrates.Upconversion is an anti-Stokes luminescence phenomenon whereby two or more low energy photons,commonly near-infrared,are absorbed sequentially to excited electronic states,upon which a single photon of higher energy is emitted.The use of resonance energy transfer mechanisms of upconversion nanoparticles(UCNPs)fluorescence to detect biomolecules,metal ions and other analytes has also become a current research hotspot.Nano-sensors for specific analytes can be designed by combining different materials.In this paper,the optical properties of upconverting fluorescent nanoparticles based on rare earth ions are explored and studied in the following aspects:1.Although rare earth ion doped UCNPs have abundant luminescence levels and can obtain different color emission,there are few reports on UCNPs for white light emission.Most of the white-light emissive materials reported so far rely on combination of specific amounts of fluorophores with red-green-blue(RGB)emission together.The mixture of multicomponent emitting materials makes it difficult to realize uniform and controllable fluorescent response for each emitter after targets binding.Therefore,we designed and synthesized a UCNPs fluorescent nanoprobe based on polymer-modified white light emission.Specifically,we have prepared and synthesized UCNPs that can achieve white light emission by adjusting the doping ratio of different rare earth ions.By exploring different doping ratios,the controllable synthesis of white light is realized.The oil-soluble UCNPs were modified by polymaleic anhydride octadecene co-polymer to form water-soluble polymer-UCNPs,and then combined with the complex of dithizone and lead ions to prepare upconversion fluorescent nanoprobes.2.We used the prepared fluorescent nano-probe to realize the quantitative detection of the pesticide thiram,and combined with the smartphone imaging platform to realize the naked eye visualization of thiram.Firstly,we prepared the fluorescent nanoprobes in different concentrations of thiram solution to test the actual detection ability of the nanoprobe.Then,we used the prepared fluorescent nano-probe to detect the concentration of thiram in the actual samples of soil and apple.Finally,we used the smartphone imaging platform to transfer the designed fluorescent nanoprobe to the test strip,real-time monitoring of the color change in the thiram detection,and the naked-eye detection of the thiram concentration.The pesticide detection probes we prepared can achieve linear detection of thiram concentration ranging from 2nM to20nM with a detection limit of 0.26nM.The concentration-dependent color change that varies from red to cyan and bluish violet and then to white can be visually distinguished.