Constructions Of Electrochemical Sensors For Some Small-molecular Compounds And Electrochemical Evaluations Of Antioxidant Activities For Some Antioxidants

As a kind of important materials,small molecular compounds are the key factors affecting food quality.On the one hand,endogenous or exogenous harmful molecules are a serious threat to food security.On the other hand,the small molecules with biological activity determine the nutritional value of agricultural products.Because of their various structures,low contents,and complicated biological activities,the content evaluation and activity detection of small molecules are quietly difficult.Therefore,it is urgent to develop some accurate,rapid and efficient detection methods,which help to ensure food safety and quality of agricultural products.The electrochemical technology owns unique advantages of high sensitivity,high selectivity,low cost and simple operation in content determination and activity evaluation of small molecular substances.Salbutamol residue and fumonisins pollution have become the issue in food safety.At the same time,the antioxidant activity of phenolic compounds and their content have also been widely used as important indexes for the evaluation of agricultural products.By using nanomaterials,we established electrochemical immunosensors for the detection of salbutamol and fumonisins based on the molecular recognition between antigen and antibody.Besides,the content and antioxidant activity of natural antioxidant substances including phenolic acid and chalcone were analyzed by using electrochemical method.1.An multilayer structured immunosensor for determination of salbutamolIn this part,an immunosensor was developed by using glass carbon electrode?GCE?modified with a conductive multilayer film comprised of multi-wall carbon nanotubes?MWCNT?,polythionine,and gold nanoparticles.Salbutamol antibody was immobilized on the surface of the modified GCE which was blocked with bovine serum albumin?BSA?.The detection was based on competitive binding of salbutamol to the sensor surface.Differential pulse voltammetric?DPV?signal decreases after competitive binding occurring between the salbutamol-BSA conjugate and free salbutamol to the salbutamol antibody.The sensor responded to salbutamol in 1.5?35 ng mL^-1concentration range,with a detection limit of 0.26 ng mL^-1.This method was applied to the precise and sensitive determination of salbutamol in spiked feed samples.2.An immunosensor based on screen-printed electrode modified by MWCNT for detection of Fumonisins B1In this part,an FB1 electrochemical immunosensor was developed by the immobilization of FB1-BSA conjugate on an MWCNT-TH modified SPE.FB1-BSA showed high activity and stability due to the biocompatibility of functioned-MWCNT.The experimental procedure involved the competition between free FB1 and the immobilized FB1-BSA conjugate for the binding sites of FB1-Ab.Under optimal conditions,FB1 could be detected in range of5.0?1000 ng mL^-1 with detection limit of 1.5 ng mL^-1.The average actual sample recovery ratio was 93.05%.With a wide detection range,high sensitivity and precision,the sensor is expected to be used for the detection of fumonisins contamination in food and feed.3.Electrochemical behavior of phenolic acid substances and their antioxidant activity in honeyIn this part,a simple and expeditious analytical technique including cyclic voltammetry?CV?and DPV was used to analyze the content and antioxidant activity of phenolic acid in honey.A positive correlation exists between antioxidant activity and phenolic content.The highest content of phenolic compounds(57.22?g g^-1)was found in Astragalus sinicus honey,while the content(9.06?g g^-1)in Coptis chinensis honey was the lowest.Astragalus sinicus honey and Black Locust honey showed higher antioxidant activity and phenolic content,in comparison with those of Zizyphus honey,Coptis chinensis honey,and Eriobotrya japonica honey.Moreover,the content and antioxidant capacity of phenolic acid in these honey samples were further performed by chemical methods?F-C?DPPH and FRAP?.A positive correlation can be found between electrochemical method and traditional chemical method.It was well demonstrated that the electrochemical technology can be used to determine the contents of phenolic compounds and their antioxidant activities so as to assess the qualities of agricultural products mainly containing phenolic acid compounds.4.Evaluation of antioxidant properties of chalcone extracted from Angelica keiskei using electrochemical method.In this part,we firstly used ultra-high performance liquid chromatography mass spectrometry to determine 10 kinds of main components in the leaves of Angelica keiskei.On basis of these,we used the electrochemical method to detect the chalcone content of the different parts in the plant and found that the chalcone content(839.55?M g^-1)of leaf was the highest.At the same time,the heavy metal chelating effect of chalcone was evaluated by electrochemical method.The data showed that cation interactions(Cu²⁺,Pb²⁺and Cd²⁺)with chalcone were pH dependent and the strongest interactions between chalcone with Cu²⁺or Pb²⁺happened at pH 7.0 or 8.0.In addition,we also applied spectral method,in vitro experiments,and in vivo experiments of rat model with intracerebral hemorrhage to confirm that chalcone extracted from Angelica keiskei had good antioxidant activity.Chalcone could effectively resist oxidative damage to neurons,improve perihematomal glucose metabolism,reduce brain edema,and influence neurological behavior of ICH rats.These data were in agreement with electrochemical detection results and indicated electrochemical techniques could well determine the chalcone content and antioxidant activity in order to evaluate the qualities of functional products with chalcone as main constituent.