Construction And Application Of Branched Polyethylenimine-based Cu²⁺ Visual Detection Material System

Cu²⁺is an indispensable substance to keep the normal life activities of organisms.The lack or excess of Cu²⁺will seriously harm organisms and even the ecological environment.Therefore,the highly sensitive and selective detection of trace Cu²⁺is an important task in the fields of environmental monitoring,food safety,disease diagnosis and so on.Among them,the reasonable design and construction of material system are the key to improving the performance of Cu²⁺detection.Branched polyethyleneimine（BPEI）has high amino content and chemical reaction activity.Because the complexation ability of BPEI with Cu²⁺is much higher than that with other ions,BPEI has unique advantages in the field of Cu²⁺detection.However,there are few studies on the detection of Cu²⁺by using BPEI.In this thesis,a series of Cu²⁺detection material systems were constructed with BPEI as the research object,including liquid-phase Cu²⁺detection material system of BPEI,the evaporation-concentration-type Cu²⁺detection material system of BPEI droplet and the Cu²⁺detection material system of BPEI modified upconversion nanoparticles.The detection sensitivity of the systems was gradually improved,and the practical application of Cu²⁺detection material system was promoted.The details are as follows:（1）Based on the enhancement of UV-Visible absorption and the change of color caused by the ligand field and the metal-to-ligand charge transfer transition of the BPEI-Cu²⁺complexes,a liquid-phase Cu²⁺detection material system of BPEI was constructed.The results showed that with decreasing molecular weight and concentration of BPEI,the interface barrier of the material system was decreased,and the sensitivity of Cu²⁺detection was increased.The detection limit was as low as 1.21 μM,the linear range was from 2 μM to 50 μM,and the detection time of bare eye was only 5 s.This material system is suitable for the rapid screening and detection of Cu²⁺in the grass-roots domestic water and is expected to solve the detection problem of domestic water in remote and poverty-stricken areas.（2）Based on the evaporation-induced enrichment of droplets on the superwettable patterned surface,the evaporation-concentration-type Cu²⁺detection material system of BPEI droplet was constructed,which solved the problems of low sensitivity and large sample quantity of traditional material system.The superhydrophobic polystyrene film was prepared by electrospinning,and then the superhydrophilic-superhydrophobic polystyrene film was successfully prepared by partial oxygen plasma treatment.The superhydrophilic area on the membrane surface was used to anchor the droplets containing BPEI and Cu²⁺,while the superhydrophobic area was used to limit the diffusion of the droplets and thus reduce the contact area between the droplets and the surface.Then,through the droplet evaporation and concentration effect,the amount of sample was decreased from the milliliter level of the liquid-phase detection material system to the microliter level.The detection limit was reduced to 89.3 nM,and the linear range was widened to 5.0 μM-2.5 mM.A rapid detection of Cu²⁺in a drop of blood was also achieved.This kind of micro-droplet detection material system based on superwettable patterned surface provides a new idea for the highly sensitive detection of micro-samples.（3）Based on the color change induced by metal-to-ligand charge transfer transition and the upconversion fluorescence quenching caused by inner filter effect,colorimetric and fluorometric double signal Cu²⁺detection material system of BPEI modified upconversion nanoparticles was established.By adjusting the concentration of the upconversion nanoparticles and the pH value of the system,the most significant performance change of the material system was obtained.The introduction of the upconversion nanoparticles reduced the interference of background light,enhanced the detection sensitivity（the detection limits of colorimetry and fluorescence were reduced to 69 μM and 45 nM,respectively）and widened the detection range（50 nM-1 mM）.Moreover,the signals of upconversion fluorescence and UV-Vis absorption were mutually verified,and the detection accuracy was enhanced.With the stronger complexation of ethylenediaminetetraacetic acid disodium salt（EDTA-2Na）with Cu²⁺,the color and the upconversion fluorescence of the detection system were recovered,which verified the reusability of the material system.The accurate and highly sensitive Cu²⁺detection material system with mutual verification of dual readout signals can be further applied in the fields of environmental monitoring,food safety and so on.