| Nitrite is a type of inorganic compound,which has been widely distributed in drinking water,food and environment,and is used as food preservative and coloring agent in food processing.However,the abuse and potential toxicity of nitrite pose a major threat to human health.Therefore,it is necessary to design a fast,effective,sensitive and stable analytical method for the determination and analysis of nitrite in food.Based on the characteristics of electrochemical sensors,Methanobactin(Mb)was used to mediate the synthesis of gold nanoclusters(Mb/AuNPs)by a one-step in situ biological reduction method.HS-βCD@Mb/AuNPs was obtained by adding HS-β-CD at the same time during the mediation of Mb/AuNPs.Mb/AuNPs and HS-β-CD@Mb/AuNPs were modified on the surface of the gold electrode by electrodeposition method,respectively.In order to evaluate the electrochemical performance of Mb/AuNPs and HS-β-CD@Mb/AuNPs modified electrode,nitrite and ascorbic acid were detected simultaneously by electrochemical method.The main research contents are as follows.Mb was extracted from the fermentation broth of Methanoxidizing Bacteria(M.trichosporium OB3b),and bio-mediated the synthesis of gold nanoclusters(Mb/AuNPs),and simultaneously mediated HS-β-CD and Mb to produce HS-β-CD@Mb/AuNPs.Mb/AuNPs and HS-β-CD@Mb/AuNPs were characterized by TEM,ultraviolet spectroscopy,fluorescence spectroscopy and infrared spectroscopy.The Mb/AuNPs and HS-β-CD@Mb/AuNPs were respectively modified on the surface of the gold electrode by electrodeposition.It was found that in the range of-0.6～2.4 V,Mb/AuNPs and HS-β-CD@Mb/AuNPs modified electrode showed better electrochemical performance,which prepared with 15.84 nm Mb/AuNPs,100 mV/s,19.77 nm HS-β-CD@Mb/AuNPs,200 mV/s with 30 cycles of cyclic voltammetry,respectively.And the Mb/AuNPs and HS-β-CD@Mb/AuNPs electrode in the electrolyte electrochemical performance parameters were analyzed as follows:the reactions on both modified electrodes are reversible controlled by diffusion in the electrolyte;there are the same number of electron transfer;the electron transfer coefficients all meet the theoretical value requirements;compared with Mb/AuNPs modified electrode,the effective surface area and electron transfer rate of HS-β-CD@Mb/AuNPs modified electrode are increased by 2.09 and 1.42 times,respectively.Therefore,the HS-β-CD@Mb/AuNPs modified electrode provides more abundant and efficient electron transport channels than the Mb/AuNPs modified electrode,and reduces the charge conduction resistance,thus increasing the reaction rate,the electrode surface coverage and the peak current.The results show that the two electrodes could be further used for the electrochemical analysis of nitrite.The electrochemical behaviors of nitrite on Mb/AuNPs and HS-β-CD@Mb/AuNPs modified electrodes were investigated.It was determined that Mb/AuNPs modified electrode and HS-β-CD@Mb/AuNPs modified electrode had the opimal electrocatalytic effect on nitrite in sodium citrate buffer solution with 0.05 mol/L pH of 5 and 0.1 mol/L pH of 4,respectively.Through the relationship between pH and peak potential,it was found that all protons participate in the electrocatalytic reaction of nitrite,but the number of protons is different.The electrochemical behavior of nitrite obtained by cyclic voltammetry is still a reversible reaction controlled by diffusion.By calculating the kinetic parameters of the electrocatalytic reaction,the electrochemical catalytic reaction process of the two modified electrodes in the nitrite system were clarified as follows:the final oxidation product is NO3-;the electron transfer number is 2;and the electron transfer coefficient meet the theoretical requirements;the electron transfer rate of HS-β-CD@Mb/AuNPs modified electrode was 1.39 times higher than that of Mb/AuNPs modified electrode.It was found that the peak current of Mb/AuNPs and HS-β-CD@Mb/AuNPs modified electrodes had a good linear relationship with the concentration of nitrite in the range of 0.0065～100 μmol/L and 0.00036～100 μmol/L,and the detection limits were 4.43 nmol/L and 1.09 nmol/L.Compared with Mb/AuNPs modified electrode,HS-β-CD@Mb/AuNPs modified electrode has lower detection limit and quantification limit.Both electrodes have good anti-interference performance against other ions that are 100 times the concentration of nitrite.The results showed that the spike recovery rates of Mb/AuNPs modified electrode and HS-β-CD@Mb/AuNPs modified electrode were between 94.62%～106.22%and 96.53%～102.54%,and the relative standard deviation within the group was both 5%Below,indicating that the two modified electrodes have good accuracy and high reliability in detecting nitrite.In order to further expand the application of the two gold nanoclusters in multi-component detection,The electrochemical catalytic performances of the two gold nanoclusters modified electrodes for the simultaneous detection of nitrite and ascorbic acid were investigated.The results showed that the optimal current response and selectivity of nitrite and ascorbic acid were obtained when sodium citrate buffer solution with pH of 4 at 0.1 mol/L and pH of 5 at 0.15 mol/L were selected by the Mb/AuNPs modified electrode and the HS-β-CD@Mb/AuNPs modified electrode,respectively.The quantitative relationships between the two modified electrodes for simultaneous detection of nitrite and ascorbic acid were determined,and it was found that the peak currents at the same time with nitrite(0.00557～10 μmol/L and 0.00218～10μmol/L)and ascorbic acid(0.23～10 μmol/L and 0.097～10 μmol/L)concentration have a good linear relationship.Compared to the single detection NO2-detection,the detection limit and quantification limit of simultaneous detection were increased by 4-6 times,but it still had a wider linear range and lower detection limit and quantification limit.The spiked recovery rate of the actual sample detection was in the range of 93.77%～108.20%and the relative standard deviations within the group were all less than 5%.It was concluded that the gold nanoclusters modified electrodes can be used for simultaneous determination of nitrite and ascorbic acid within the allowable accuracy range,which indicates that they have a promising application for multicomponent electrochemical analysis. |
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