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  • Nitrite is commonly used as an

    2018-10-30

    Nitrite is commonly used as an industrial salt and food additive. Thus, nitrite is widespread within environment and physiological systems. According to World Health Organization, the maximum permissible amount of nitrite KU60019 in drinking water is 50mg/L [1,2]. Nitrite, in high levels, can form nitrosamines by interacting with amines, which are toxic and carcinogenic substances [3]. So an accurate determination of nitrite is important to protect environmental and reduce the health risks. Many techniques have been developed for determining nitrite, such as flow injection analysis, colorimetric method, chemiluminescence, electrochemical analysis and so on [4–7]. Among them, electrochemical methods are often favored over others due to the easy operation, fast response and relatively low cost [8]. Recently, different kinds of electrochemical nitrite sensors have been fabricated based on the chemical modification of electrode [9–12]. Fe3O4 magnetic nanoparticles (NPs), a half-metallic metal oxide with the inverse spinel structure [13], possess appealing magnetic properties, nontoxicity, easy synthesis and electrocatalytic capability. From the references, nitrite sensors based on Fe3O4 NPs have been reported with excellent electrocatalytic performance toward nitrite oxidation [14–16]. However, pure magnetic nanoparticles are very likely to aggregate and sensitive to oxidation for their large ratio of surface area to volume and high chemical reactivities, resulting in poor dispersibility and limiting their application to some extent [17]. Among extensive applications in magnetic resonance imaging, drug delivery, catalyst and biosensor [18–21], surface modification of Fe3O4 NPs is an important step because it prevents the Fe3O4 NPs from aggregating, improves NPs stability in suspension and enhances biocompatibility of NPs [22]. Thus, numerous coating materials, such as Pt [14], Au [16], polypyrrole [17], polydopamine [23] and citrate [24] were used to modify the surface of Fe3O4 NPs. Satisfactorily, polymer coating has good biocompatibility, stability, and provides a useful platform for further functionalization. As reported by Cheng et al. [25], Fe3O4 NPs were functionalized with cationic poly(diallyldimethylammonium chloride) (PDDA) and applied to colorimetric sensing of glucose and selective extraction of thiol, developing a new way for the synthesis of bifunctional NPs. In this paper, positively charged PDDA coated Fe3O4 NPs (PDDA–Fe3O4) were prepared successfully by coprecipitation method. Based on this, a novel sensor was constructed through immobilization PDDA–Fe3O4 on miltiwalled carbon nanotubes (MWCNTs) film modified with l-cysteine at glassy carbon (GC) matrix. The proposed composite film combined the high surface-to-volume ratio of MWCNTs, the electrocatalytic activity of l-cys and PDDA–Fe3O4 NPs, their synergistic effect was contributed to excellent electrocatalytic performance for the oxidation of nitrite. Compared with other related reports, the proposed nitrite sensor showed high sensitivity, wide linear range, low detection limit, good stability and repeatability.
    Experimental
    Results and discussions
    Conclusions In this paper, PDDA coated Fe3O4 NPs were prepared by the coprecipitation method. PDDA–Fe3O4/l-cys/MWCNTs/GC modified electrode was constructed via electropolymerization and electrostatic interaction. Cyclic voltammetry was applied to investigate the performance of nitrite on the sensor. Combined the advantages of PDDA–Fe3O4, l-cys and MWCNTs, the prepared sensor showed good electrocatalytic activity for nitrite oxidation and displayed wide linear range, low detection limit, good stability and selectivity, which showed a wide prospect for potential applications.
    Conflict of interest
    Acknowledgments This work was supported by the Education Department of Henan Province (No. 13A150077).
    Introduction Biofouling, i.e., the colonisation of an interface by a diverse array of organisms, affects surfaces and by that may have detrimental effects on the operation of processes in the field of water technology such as, raw water pre-treatment, drinking water production and distribution, wastewater treatment, industrial water cooling and water quality analysis [1–6].