Construction Of All-solid-state Cadmium Ion-selective Electrodes Based On COF@graphene And Their Application In The Detection Of Gonyautoxins

The on-site rapid detection of paralytic shellfish toxins is conducive to elucidate the temporal-spatial distribution characteristics and migration and transformation behavior of paralytic shellfish toxins,and provide the scientific basis for the early warning of paralytic shellfish toxins contamination.However,the commonly used method is only suitable for laboratory analysis,which cannot meet the needs of on-site rapid detection.In this thesis,the highly sensitive and rapid detection of paralytic shellfish toxins based on all-solid-state ion-selective electrodes will be investigated systematically.An all-solid-state ion-selective electrode with high stability and high reproducibility was constructed by selecting suitable solid contact materials.An all-solid-state ion-selective microelectrode was fabricated by using microelectrode technology.Through the synthesis of aptamer-functionalized magnetic microspheres and the introduction of DNase I,highly sensitive and rapid detection of paralytic shellfish toxins was realized by using an all-solid ion selective microelectrode.The studies are summarized as follows:1.All-solid-state cadmium ion-selective electrodes based on DAAQ-TFP@rGO as solid contactAll-solid-state ion-selective electrode based on a covalent organic framework@reduced graphene oxide（rGO）composite is proposed.The composite can be synthesized through the polycondensation of 1,3,5-triformylphloroglucinol（TFP）and 2,6-diaminoanthraquinone（DAAQ）on the rGO nanosheets,which shows high capacitance and good redox-active properties.By applying Cd²⁺-ISE as a model,the electrode exhibits a Nernstian slope of 29.7±0.4 m V/decade in the activity range of 1.0×10^-7～7.9×10^-4 mol?L^-1 and the limit of detection is 6.8×10^-8 mol?L^-1.Particularly,the electrode based on DAAQ-TFP@rGO exhibits a low potential drift of 1.2±0.2μV/h over 70 h due to the large capacitance of 2.0 m F.Moreover,the DAAQ-TFP@rGO-based Cd²⁺-ISE shows good reproducibility and the standard deviations of the standard potentials for single batch and batch-tobatch are 0.28（n=4）and 0.30 m V（n=4）,respectively.The developed Cd²⁺-ISE is not disturbed by light or gas and no aqueous layer occurs between the sensing membrane and DAAQ-TFP@rGO layer.2.All-solid-state cadmium ion-selective microelectrodes using the electrodeposited DAAQ-TFP@rGO as solid contactBased on the excellent properties of DAAQ-TFP@rGO,an all-solid-state cadmium ion-selective microelectrode was prepared through the electrodeposition of the DAAQ-TFP@rGO layer on the surface of a gold microelectrode with a diameter of about 50μm.The prepared all-solid-state cadmium ion-selective microelectrode has a good stability with a potential drift value of7.5±1.1μV/h over 80 h.In addition,the electrode shows a Nernstian slope of 27.4±0.4 m V/dec in the activity range of 8.7×10^-9～7.6×10^-4 mol?L^-1,and the detection limit is as low as 3.2×10^-9 mol?L^-1 under the background of p H=3.It can be seen that the prepared all-solid-state cadmium ion-selective microelectrode has the characteristics of small size,good stability and high sensitivity,which can be used as the transducer to provide technical support for the highly sensitive and rapid detection of paralytic shellfish toxins.3.Detection of gonyautoxins by an all-solid-state cadmium ion-selective microelectrode method based on aptamer-functionalized magnetic beads and nucleaseAll-solid-state ion-selective electrodes have been used for the detection of paralytic shellfish toxins,however,the detection method has poor selectivity and low sensitivity.Based on this,in this chapter,Cd S-labeled aptamer-functional magnetic beads were constructed with highly specific aptamer as the recognition molecule,and the nuclease assisted amplification strategy was introduced.Moreover,the highly sensitive all-solid-state cadmium ion-selective microelectrode constructed in the above-mentioned chapter was used as a transducer for the highly sensitive and rapid detection of paralytic shellfish toxins.Taking gonyautoxins 1/4 as an example,under the optimal conditions,the linear range of the method is 10～100 pmol?L^-1,and the detection limit is4.09 pmol?L^-1.This proposed method is universal and can be used to detect other paralytic shellfish toxins by using corresponding aptamers.