Specific Adsorption and Determination of Aspartame in Soft Drinks with A
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RSC Advances View Article Online PAPER View Journal | View Issue Specific adsorption and determination of aspartame in soft drinks with a zein magnetic Cite this: RSC Adv.,2021,11, 13486 molecularly imprinted modified MGCE sensor† Ling Tan,ac Qing-Yao Li,‡a Yan-Jun Li,a Rong-Rong Ma,a Jia-Yuan He,a Zhuang-Fei Jiang,a Li-Li Yang,a Chong-Zhi Wang,d Ling Luo,*b Qi-Hui Zhang *ad and Chun-Su Yuand In this work, an efficient and sensitive magnetic molecularly imprinted polymer with zein and deep eutectic solvents (ZDM-MIPs) was designed and synthesized to exclusively adsorb and detect aspartame (ASP). We used zein, together with deep eutectic solvents (DESs) and Fe3O4 as the cross-linker, functional monomer and support material, respectively. A magnetic glassy carbon electrode (MGCE) modified with ZDM-MIPs was used for selective recognition of ASP. The electrochemical response of the ZDM-MIPs-MGCE for quantification of ASP was evaluated with a portable electrochemical detection station with differential Creative Commons Attribution-NonCommercial 3.0 Unported Licence. pulse voltammetry and cyclic voltammetry. The responses of ZDM-MIPs-MGCE signified a good linear Received 25th December 2020 À relationship with ASP concentrations in the range of 0.1–50 mgmL 1. The sensor systems showed good Accepted 31st March 2021 accuracy and precision, with recovery percentages between 84% and 107%. These results suggested that DOI: 10.1039/d0ra10824c the obtained ZDM-MIPs exhibited good adsorption performance for ASP in soft drinks, and this method rsc.li/rsc-advances could be used to determine ASP content in actual food samples. 1. Introduction promising methods for the determination of ASP. Electro- chemical methods offer many advantages for tracking analytes, 10,11 This article is licensed under a Aspartame (L-aspartyl-L-phenylalanine methyl ester; ASP) has because of their relatively low cost and short analysis time. A been widely used in the food industry as an alternative to sugar.1 magnetic glassy carbon electrode (MGCE) is among the widely To decrease sugar and caloric content, the food industry uses used electrodes,12 such as for the analysis and detection of – Open Access Article. Published on 23 1400. Downloaded 07/07/1400 11:36:53 .. articial sweeteners to produce a variety of foodstuffs, including pigments, drugs, proteins and organic pollutants.13 15 MGCE powdered drinks, chewing gum, and jellies.2 However, some has several advantages, including good electrical conductivity, animal studies have indicated that ASP is a carcinogenic agent high chemical stability, a low thermal expansion coefficient, in mice.3,4 Because the effects of ASP on human health continue hard texture, good air tightness, and a broad application to be controversial,5 the acceptable daily intake of ASP is rec- potential (approximately À1 to 1 V relative to a saturated À ommended not to exceed 40 mg kg 1 of body weight.6 There- calomel electrode).14 MGCE is increasingly being used in elec- fore, the developing an assay for the accurate and sensitive trochemical and electroanalytical chemistry experiments.15 The determination of this articial sweetener in food is essential. newly developed portable electrochemical workstations also Various technologies have been developed to determine ASP, have many favorable characteristics, such as small size and such as high-performance liquid chromatography (HPLC),7 portability. Similarly, the portable electrochemical workstations mass spectrometry (MS)8 and electrochemical analysis.9 Among can perform various electrochemical techniques such as cyclic them, electrochemical analysis is regarded as one of the most voltammetry (CV) and differential pulse voltammetry (DPV), thus meaning the different requirements of electricity chemical measurements. The combined use of MGCE and portable aSchool of Chemistry and Chemical Engineering, Chongqing University, Chongqing 400044, China. E-mail: [email protected]; Fax: +86-023-65102531 electrochemical workstations can greatly increase the range of bChongqing Cancer Institute, Chongqing Cancer Hospital, Chongqing University application and portability. However, the interfering substances Cancer Hospital, Chongqing, 400030, China. E-mail: [email protected]; in the actual samples can affect the accuracy of the method. Fax: +86-023-65311341 Therefore, it is necessary to selectively detect ASP. cSchool of Pharmaceutical Sciences, Chongqing University, Chongqing, 400044, China Molecularly imprinted polymers (MIPs) with specic binding d Tang Center for Herbal Medicine Research, Department of Anesthesia & Critical Care, sites exhibit ultrahigh selectivity for template molecules or ions, University of Chicago, Chicago, IL 60637, USA and are recognized as synthetic antibody mimics.16 Compared † Electronic supplementary information (ESI) available. See DOI: 10.1039/d0ra10824c to other absorbents, MIPs have the advantage of easy prepara- 17,18 ‡ Co-rst author: these authors contributed equally to the article. tion, high speci city, and broad adaptability. Therefore, 13486 | RSC Adv.,2021,11,13486–13496 © 2021 The Author(s). Published by the Royal Society of Chemistry View Article Online Paper RSC Advances 6 MIPs are widely used in a variety of areas, including separation (Chengdu, China). Potassium ferricyanide (K3[Fe(CN) ]) was science, solid phase extraction, and sensors.19–21 However, with obtained from Tianjin Zhiyuan Chemical Reagent Co. Ltd the traditional molecular imprinting method, the most recog- (Tianjin, China). All reagents were analytical reagent grade and nition sites of the obtained polymers are embedded in the water used in the experiments was double distilled. interior of the MIPs, thus decreasing the recognition sites in the material and the binding ability. Surface imprinting technology 2.2 Apparatus has been demonstrated to overcome these problems. Further- A scanning electron microscope (SEM, Japan Electronics JEM- more, common support materials oen include SiO , TiO , 2 2 2100F, Japan) and transmission electron microscopy (TEM, carbon materials, and magnetic materials.22–24 Among them, Zeiss ultra-high resolution thermal eld electron microscope, Fe3O4 nanoparticles have been widely used in the synthesis of 25 Germany) were used to characterize the morphology of mate- MIPs, owing to their advantages of simple preparation, À rials. The infrared spectrum (4000–400 cm 1) was recorded on sensitivity, rapid separation, and low cost. Magnetic MIPs a Fourier-transform infrared spectrometer (FT-IR, Nicolet 6700, (MMIPs) with Fe O nanoparticles as the core material provide 3 4 Thermo Nicolet Co. Waltham, MA, USA). A thermogravimetric good magnetic response and strong electrochemical signal for 26 analysis (TGA) was carried out from 25 to 800 C with a heating the polymer. And under the action of a magnetic eld, the À rate of 10 C min 1 under air environment (TGA/DSC1/1600LF, magnetic molecularly imprinted polymer is easily separated Mettler-Toledo, Switzerland). Magnetization was measured at from the sample solution, without ltering or centrifugation. room temperature using a vibrating sample magnetometer Unfortunately, the large amounts of organic solvents used in (VSM, MicroSense-EZ9, USA). the synthesis are not consistent with the idea of green chem- The concentration of ASP was detected by HPLC (Agilent istry. In addition, the materials used to detect analytes in food Technologies, Santa Clara, CA, USA) with C (Agilent, 250 Â 4.6 samples should be non-toxic and environmentally friendly. 18 mm, Agilent Technologies) at a mobile phase ow rate of 0.6 Deep eutectic solvents (DESs) can be attained by heating À mL min 1. The mobile phase for ASP determination was 0.05% Creative Commons Attribution-NonCommercial 3.0 Unported Licence. a mixture of hydrogen bond acceptor (HBA) and a metal salt or phosphoric acid/methanol (40 : 60, v/v) at 25 C. The UV hydrogen bond donor (HBD) in a proper ratio.27 DESs are new detector spectra was set at 210 nm. types of organic or pseudo-organic ionic liquids with merits such as non-toxicity, biocompatibility and so on. Consequently, DESs were applied to the synthesis of MIPs to improve the 2.3 Synthesis of ZDM-MIPs and ZDM-NIPs materials selectivity of MIPs. Zein is a mixture of proteins with an average 2.3.1 Synthesis of DESs. Deep eutectic solvents (DESs) were molecular weight of 25 000 to 45 000, which can be classied prepared according to the method previously used by our group. into a-, b-, g-, and d-zein according to solubility and amino acid Briey, choline chloride, caffeic acid, and formic acid (molar sequence homology.28,29 It is hydrogen-bonded to the imino ratio 1 : 6 : 3) were added to the ask and stirred at 90 C for one This article is licensed under a group in the main chain of the peptide and has unique lm- hour, until homogeneous liquid formed. 30,31 forming property, biodegradability, and biocompatibility. 2.3.2 Prepare Fe3O4 nanoparticles. The spherical Fe3O4 Therefore, zein has many potential applications in the food and nanoparticles were synthesized by solvothermal method Open Access Article. Published on 23 1400. Downloaded 07/07/1400 11:36:53 .. pharmaceutical industries. according to the literature.32 In a general synthesis, 5.4 g In this study, we described novel zein magnetic MIPs (ZDM- FeCl3$6H2O was dissolved in 160 mL ethylene glycol under MIPs), which were successfully prepared with ASP as an alternate magnetic stirring and ultrasonic dispersion at room imprinted template. DESs were used as functional monomers, temperature. Then, 12.4 g sodium acetate anhydrous and 1.6 g and zein was used as the cross-linker. Biocompatible zein is sodium citrate were added to the orange solution. The mixture non-toxic, and DESs can provide hydrogen bond acceptors and was heated under magnetic stirring at 150 C, until a uniform donors to improve the selectivity of polymers. Aer removal of dark brown solution was formed. The solution was transferred the template molecule ASP, ZDM-MIPs were obtained and into a Teon lined stainless steel autoclave to be heated at combined.