Magnetic molecularly imprinting polymers and reduced graphene oxide modified electrochemical sensor for the selective and sensitive determination of luteolin in natural extract

Zongyi You; Yafen Fu; Aiping Xiao; Liangliang Liu; Siqi Huang

doi:10.1016/j.arabjc.2021.102990

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Original article

2021

:14;

202103

doi:

10.1016/j.arabjc.2021.102990

Magnetic molecularly imprinting polymers and reduced graphene oxide modified electrochemical sensor for the selective and sensitive determination of luteolin in natural extract

Zongyi You¹, Yafen Fu¹, Aiping Xiao, Liangliang Liu^⁎, Siqi Huang^⁎

Institute of Bast Fiber Crops, Chinese Academy of Agricultural Sciences, Changsha 410205, China

⁎Corresponding authors. liuliangliang@caas.cn (Liangliang Liu), huangsiqi@caas.cn (Siqi Huang)

Received: 2020-10-21, Accepted: 2020-12-20,

Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Abstract

Abstract

The rapid and sensitive determination of luteolin was important since it was an effective antioxidant and bioactive supplement in food. For this purpose, magnetic molecularly imprinted polymer (Fe₃O₄@MIP) using luteolin as template was prepared, and then modified on the surface of glassy carbon electrode together with reduced graphene oxide (Fe₃O₄@MIP/rGO/GCE) for the sensitive electrochemical detection of luteolin. Through characterizations and adsorption experiments, Fe₃O₄@MIP demonstrated sphere structure with rough surface, well magnetic response in solution and better selectivity for luteolin than molecularly imprinted polymer (SiO₂@MIP). After optimization of fabrication and electrochemical conditions, the Fe₃O₄@MIP/rGO/GCE exhibited satisfied anti-interference ability, linearity, detection limit, reproducibility and stability in detection. The linear detection range of luteolin using Fe₃O₄@MIP/rGO/GCE was from 2.5 pM to 0.1 μM, and the sensor could keep stable in six days. It was also successfully utilized in the determination of luteolin in lotus leaves extract with well recovery. Based on these results, the proposed electrochemical sensor Fe₃O₄@MIP/rGO/GCE had good prospects in evaluation of natural antioxidants.

Keywords

Electrochemical detection

Luteolin

Magnetic nanoparticles

Molecularly imprinted polymer

Reduced graphene oxide

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1 Introduction

Luteolin was a crucial biological flavonoid widely distributed in various plants, seeds and fruits (Haminiuk et al., 2012). Many studies shown it has a wide range of pharmacological effects and could be used in the treatments of anti-inflammatory, anti-allergic, anti-tumor and anti-cancer (Gao et al., 2017; Pang et al., 2014). Due to extensively applications in pharmacology, it was a pressing problem to establish rapid, effective and reliable methods for the detection and pharmaceutical analysis of luteolin. On this basis, many methods were reported such as high performance liquid chromatography, gas chromatography, spectrophotometry, capillary electrophoresis and so on (Juszczak et al., 2019; Wei et al., 2019). However, there were some inherent disadvantages such as time consuming, high cost and complicated experimental operation in these methods. Electrochemical technology had strengths of simple operation, high sensitivity and fast response (Singh, 2016), and luteolin was an electroactive compound due to the catechol group on its B ring (Zuo, 2016). Hence, intensive studies in applicable electrochemical determination of luteolin were conducted and still noteworthy (Gao et al., 2020; Li et al., 2020).

As a kind of two-dimension nanomaterial, reduced graphene oxide (rGO) became an optimal material with large specific surface area, high chemical stability and electrochemical conductivity (Hu et al., 2016; Sugimoto et al., 2020). It was often used to fabricate electrochemical sensors with enhanced performance in detection and catalysis with single component alone and combination of other materials (Ratinac et al., 2011; Rowley-Neale et al., 2018).

Molecular imprinting polymer (MIP) had the recognition property of template because of the multiple binding sites formed between template molecules and monomers (Wackerlig and Lieberzeit, 2015). Accordingly, it exhibited unique high selectivity and structural predictability during separation, purification and determination of template molecules in food and environmental fields (Bi et al., 2013). Especially in electrochemical analysis, MIP modified electrochemical sensor exhibited higher sensitivity and selectivity than traditional sensors (El Nashar et al., 2017; Fu et al., 2019). With the development of nanotechnology, combinations of MIP with other nanomaterials were designed and achieved good results (Gui et al., 2019; Jin et al., 2018). This kind of compositions exhibited a synergic effect that signal improvements and mechanical characteristics (Amatatongchai et al., 2020; Gui et al., 2018).

Many kinds of nanomaterials were used in the modification of glassy carbon electrode (GCE) and gold electrode for the detection of luteolin (Cheng et al., 2020; Liu et al., 2019a,b,c ). Several MIP modified electrode using luteolin as template through electropolymerization were proposed by Zeng and Du as well (Wei et al., 2019; Xu et al., 2017). However, the modifications of magnetic MIP (MIP using Fe₃O₄ magnetic nanoparticles as core, Fe₃O₄@MIP) and rGO on GCE for detection of luteolin was not reported. In this study, Fe₃O₄@MIP nanomaterials were prepared using luteolin as templates to improve the selectivity and electrical conductivity for application in electrochemical sensing of luteolin. The selectivity and signal enhancement were evaluated and compared with MIP prepared using silica nanoparticles as core materials (SiO₂@MIP). Fe₃O₄@MIP showed better signal improvement, adsorption capacity and selectivity for luteolin than those of SiO₂@MIP. Then, rGO and Fe₃O₄@MIP were successively modified on GCE (Fe₃O₄@MIP/rGO/GCE) to develop a simple, sensitive and specific sensor for detection of luteolin (Fig. 1). The prepared Fe₃O₄@MIP and rGO were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectra and vibration sample magnetometer (VSM). Under the optimized preparation and analytical conditions, Fe₃O₄@MIP/rGO/GCE demonstrated good enhancements in the selectivity and electrochemical signal, satisfied anti-interference, linearity and low detection limit for luteolin. The good performance of Fe₃O₄@MIP/rGO/GCE made this kind of electrochemical sensor having good application prospects in natural antioxidants evaluations in food and analytical fields.

The fabrication of Fe3O4@MIP/rGO/GCE for the electrochemical detection of luteolin.

2 Materials and methods

2.1

2.1 Reagents

Luteolin (>98.0%), tetraethyl orthosilicate (TEOS, >97.0%), methacrylic acid (MAA), 4-vinylpyridine (4-VP), acrylamide (AM), acrylic acid (AA), ethyleneglycol dimethacrylate (EGDMA), 3-methacryloxypropyltrimethoxysilane (MPS, KH570) and azodiisobutyronitrile (AIBN) were bought from TCI (Shanghai) Development Co., Ltd. (Shanghai, China). Graphite flakes was purchased from Nanjing XFNANO Materials Tech Co., Ltd (Nanjing, China). Potassium permanganate, ferric chloride, sodium acetate, polyethylene glycol (PEG) 6000, and potassium ferricyanide were obtained from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Dry lotus leaves were bought from Qinyuan Chinese medicines company (Bozhou, China). All aqueous solutions were prepared with deionized water supplied by an ELGA water purification system (ELGA Berkefeld, Veolia, Germany). All other chemicals were bought from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China) with analytical grade.

2.2

2.2 Preparation of Fe₃O₄@MIP and SiO₂@MIP

Fe₃O₄ magnetic nanoparticles, SiO₂ nanoparticles and rGO were prepared according to previous reports and shown in Supplementary Information (SI) (Cen et al., 2017; Liu et al., 2019a,b,c; Orooji et al., 2020 ). The core nanoparticles (Fe₃O₄ and SiO₂) were firstly modified with MPS. 0.60 g of core nanoparticles were dispersed in 100 mL of ethanol and treated by ultrasonication for 30 min. Then, 5 mL of MPS were slowly added under mechanical stirring and the mixture was reacted at room temperature for 24 h. The products (Fe₃O₄@MPS and SiO₂@MPS) were collected by a magnet or centrifugation, washed with ethanol and stored for further use.

For polymerization, 0.3 mmol of luteolin and 1.8 mmol of MAA were preincubated in 30 mL of acetonitrile for 12 h under magnetic stirring in ice bath. 0.50 g of Fe₃O₄@MPS or SiO₂@MPS, 5.4 mmol of EGDMA and 50 mg of AIBN were dispersed in 100 mL of acetonitrile. The dispersion was submitted to ultrasonication for 30 min, mixed with template solution, bubbled by nitrogen gas for 5 min and reacted at 50 °C for 6 h and 60 °C for 24 h. After polymerization reaction, the products (Fe₃O₄@MIP and SiO₂@MIP) were collected and washed with acetonitrile. Finally, Fe₃O₄@MIP and SiO₂@MIP were refluxed in methanol using Soxhlet extraction for 24 h and collected for further use. For comparison, non-imprinted polymer using Fe₃O₄ magnetic nanoparticles as core materials (Fe₃O₄@NIP) was prepared according to the same procedures except the absence of template. The Fe₃O₄@MIP and SiO₂@MIP were characterized by TEM, SEM, FT-IR and VSM with detail equipment information shown in SI.

2.3

2.3 Adsorption of luteolin using Fe₃O₄@MIP and SiO₂@MIP

The adsorptions of luteolin were performed using Fe₃O₄@MIP and SiO₂@MIP for comparing the selectivity and adsorption capacity (Liu et al., 2019a,b,c ). 30 mg of Fe₃O₄@MIP or SiO₂@MIP was suspended into 5 mL of luteolin methanol solution (0.1 M) and shaken for 30 min at room temperature. After adsorption, Fe₃O₄@MIP was separated by a magnet and SiO₂@MIP was separated by centrifuge. Then, the change in adsorptions of luteolin solution was detected by a spectrophotometer at 350 nm (UV-2700 Shimadzu, Kyoto, Japan). The concentrations of luteolin were determined by a standard curve and the adsorption capacity of luteolin was calculated according to following formula:

(1)

Adsorption capacity = (C_{0} - C) / C_{0} \times 100 %

where C₀ and C are the concentration of luteolin before and after adsorption.

2.4

2.4 Fabrication of Fe₃O₄@MIP/rGO/GCE

Before the modification of GCE, the electrode was polished with alumina powders, washed with water and ultrasonic treated for 5 min. The water on surface of GCE was drying with nitrogen gas and stored for modifications. rGO and Fe₃O₄@MIP (5 mg mL⁻¹) suspensions were respectively treated by ultrasonication for 30 min. Firstly, 9 μL of rGO suspension was dripped on the fresh polished electrode surface, dried in the air and marked as rGO/GCE. Then, 7 μL of Fe₃O₄@MIP suspension was dripped on the surface of rGO/GCE and dried in the air, which was termed as Fe₃O₄@MIP/rGO/GCE. For comparison test, the same amount of Fe₃O₄@MIP was directly modified on fresh polished GCE under the same procedures and marked as Fe₃O₄@MIP/GCE.

2.5

2.5 Electrochemical measurements

The electrochemical measurements in this experiment were conducted by a CHI660E electrochemical workstation (Shanghai Chenhua Instrument Co., Ltd., Shanghai, China) with a standard three-electrode system: an Ag/AgCl electrode as the reference, a platinum wire as the auxiliary, and a bare or modified GCE as the working electrode. The three-electrode system was immersed in phosphate buffer saline (PBS) as supporting electrolyte containing luteolin or other solutes. The measurements were performed using cyclic voltammetry (CV) with the potential range from −0.2 V to 1.0 V and scan rate of 10 mV s⁻¹, and differential pulse voltammetry (DPV) with the potential range from −0.2 V to 0.6 V, scan rate of 10 mV s⁻¹, pulse amplitude of 50 mV and pulse width of 50 ms. All measurements were completed at room temperature (25 ± 2 °C) with three replications.

2.6

2.6 Preparation of real sample

50.0 g of lotus leaves were ground, soaked in 200 mL of methanol solution (70%, v: v) and reflux extracted at 85 °C for 2 h. Then, the solution was cooled to room temperature, filtrated and stored at 4 °C. Before detection, 10 μL of sample solution was diluted to 100 mL with PBS for determination.

3 Results and discussion

3.1

3.1 Characterizations of Fe₃O₄@MIP and rGO

3.1.1

3.1.1 TEM and SEM

The structures and morphologies of rGO, Fe₃O₄ magnetic nanoparticles and Fe₃O₄@MIP were characterized by TEM and SEM. In Fig. 2a, rGO showed typical characters of two-dimension nanomaterials like translucent and wrinkled edges. The prepared Fe₃O₄ magnetic nanoparticles were black spheres with diameters at about 400 nm (Fig. 2b) (Chen et al., 2017). After polymerization, Fe₃O₄@MIP showed similar sphere structure and the surface became rougher and more porous (Fig. 2c), which might be caused by molecular imprinting and elution of templates. SEM image of Fe₃O₄@MIP was presented in Fig. 2d as well. It could be seen that the spherical polymers were distributed with uniform size. The morphology observed in SEM image was in an agreement with those in TEM image, and the size distribution of Fe₃O₄@MIP in a wider range was clearly displayed. Hence, spherical Fe₃O₄@MIP was successfully prepared with uniform size and well dispersion.

TEM images of (a) rGO, (b) Fe3O4 magnetic nanoparticles and (c) Fe3O4@MIP; (d) SEM image of Fe3O4@MIP.

3.1.2

3.1.2 FT-Ir

FT-IR spectra of Fe₃O₄ magnetic nanoparticles, SiO₂ nanoparticles, Fe₃O₄@MIP and SiO₂@MIP were conducted. As shown in Fig. 3a, both Fe₃O₄ magnetic nanoparticles and Fe₃O₄@MIP exhibited a typical absorption at 584 cm⁻¹ in their spectra, which was assigned to Fe-O stretching vibration and indicated the existence of Fe₃O₄ magnetic nanoparticles (Liu et al., 2013). While, SiO₂ nanoparticles and SiO₂@MIP showed some bands at 474 cm⁻¹, 1103 cm⁻¹ and 3432 cm⁻¹, which were attributed to vibration network of O-Si-O, irregular stretching vibration of Si-O and O-H stretching vibration from silanol groups (Imoisili et al., 2020). It could be found the band at 3432 cm⁻¹ increased after polymerization from Fe₃O₄ magnetic nanoparticles to Fe₃O₄@MIP (from SiO₂ nanoparticles to SiO₂@MIP), which might because more oxygen molecules were modified on the nanoparticles and related O-H vibrations enhanced (Hatamluyi et al., 2020).

(a) FT-IR spectra of Fe3O4 magnetic nanoparticles, SiO2 nanoparticles, Fe3O4@MIP and SiO2@MIP; (b) Magnetization curves of Fe3O4 magnetic nanoparticles and Fe3O4@MIP.

3.1.3

3.1.3 Vsm

In order to evaluate the magnetic response property, the magnetization curves of Fe₃O₄ magnetic nanoparticles and Fe₃O₄@MIP were characterized and plotted in Fig. 3b. It could be found the maximum saturation magnetization of Fe₃O₄ magnetic nanoparticles was 63.3 emu g⁻¹, and then this value of Fe₃O₄@MIP reduced to 49.1 emu g⁻¹. This kind of reduction was familiar in modification of magnetic materials and attributed to the existence of nonmagnetic coating after polymerization (Liu et al., 2019a,b,c ). However, Fe₃O₄@MIP was still sufficient for magnetic separation with ordinary magnets. It could be easily separated in solution within 2 min, which indicated that Fe₃O₄@MIP simplified the procedures and could be used in further experiments.

3.2

3.2 Optimization of preparation conditions of Fe₃O₄@MIP

3.2.1

3.2.1 Effect of monomer

Proper monomer could make a stable complex through binding to template molecules, which was conducive to the following polymerization. Accordingly, four typical monomers (MAA, 4-VP, AM and AA) were selected in the preparation of Fe₃O₄@MIP. The adsorption capacities of resulting polymers were compared and shown in Fig. 4a, four kinds of Fe₃O₄@MIP exhibited various adsorption capacities for luteolin. Among them, Fe₃O₄@MIP prepared using MAA had the maximum adsorption capacity, which might due to MAA could contribute to stronger molecular interactions with the template molecules than other monomers (Yang et al., 2020). Therefore, MAA was selected as the monomer for preparation of Fe₃O₄@MIP.

(a) Effect of monomer ratio on adsorption capacity, (b) Effect of mole ratio of template, monomer and crosslinker on adsorption capacity and (c) adsorption performances of Fe3O4@MIP, SiO2@MIP and Fe3O4@NIP.

3.2.2

3.2.2 Effect of mole ratios of template, monomer and crosslinker

In preparation of MIP, the amounts of template, monomer and crosslinker would affect the structures and adsorption abilities of resultant polymers. The effects of mole ratio of luteolin to MAA (1:2, 1:4, 1:6), and mole ratio of MAA to EGDMA (1:1, 1:3, 1:5) were conducted. The adsorption capacities of nine Fe₃O₄@MIP under the various ratios of template, monomer and crosslinker (1:2:2, 1:4:4, 1:6:6, 1:2:6, 1:4:12, 1:6:18, 1:2:10, 1:4:20 and 1:6:30) were shown in Fig. 4b. As a result, Fe₃O₄@MIP with ratio of 1:6:18 exhibited the maximum adsorption capacity for luteolin. The optimal mole ratio of luteolin to MAA (1:6) was in accordance with report, which indicated the mole ratio would change the number of active binding sites and film thickness, leading to the influence on electronic conductive property (Yang et al., 2017). Therefore, the mole ratios of luteolin, MAA and EGDMA were determined as 1:6:18.

3.2.3

3.2.3 Adsorption performances of Fe₃O₄@MIP and SiO₂@MIP

In order to compare the selectivity and adsorption capacities of Fe₃O₄@MIP, SiO₂@MIP and Fe₃O₄@NIP, three structural analogues along with luteolin were used as adsorption targets. During adsorption experiments, the concentrations of luteolin and structural analogues were the same, and the calculations were proceed using their own standard curves. As illustrated in Fig. 4c, both Fe₃O₄@MIP and SiO₂@MIP had the maximum adsorption capacity for luteolin. While, there was no specific adsorptions of Fe₃O₄@NIP among these four targets, which indicated the MIP was effective in specific adsorption of luteolin. For Fe₃O₄@MIP, the adsorption capacity of luteolin was 25.6 times that of catechin, 3.2 times that of p-hydroxybenzoic acid and 6.1 times that of puerarin. For SiO₂@MIP, the adsorption capacity of luteolin was 3.7 times that of catechin, 2.2 times that of p-hydroxybenzoic acid and 2.7 times that of puerarin. It demonstrated Fe₃O₄@MIP had a high selectivity for luteolin than that of SiO₂@MIP. Therefore, the adsorption performances of Fe₃O₄@MIP indicated that it had a good recognition and adsorption capacity for luteolin.

3.3

3.3 Electrochemical properties of modified electrodes

The electrochemical responses of luteolin on several modified electrodes were compared and shown in Fig. 5. The peak current was only 0.50 μA on bare GCE for 1.0 μM of luteolin. For the same concentration of luteolin, the modifications of rGO and Fe₃O₄@MIP respectively increased the peak current to 3.11 μA and 3.37 μA. These enhancements could be attribute to the large surface area, adsorption ability and electronic conductivity of rGO and the selectivity and enrichment of Fe₃O₄@MIP (Ross and Civilized Nqakala, 2020; Tang et al., 2020). While, the peak current of luteolin on Fe₃O₄@MIP/rGO/GCE reached 10.52 μA, which was 21 times higher than that on bare GCE. Compared with Fe₃O₄@MIP/rGO/GCE, the signal on SiO₂@MIP/rGO/GCE was moderate (3.05 μA). This comparison indicated the conductivity of core material was important to electrochemical signal of modified electrode, and Fe₃O₄@MIP made an improvement on signal for luteolin. The combination of rGO and Fe₃O₄@MIP in the modifications exhibited a synergic effect on signal improvement, which was mentioned in previous report (Amatatongchai et al., 2020). Accordingly, Fe₃O₄@MIP/rGO/GCE was selected as an electrochemical sensor for luteolin among these modified electrodes with the highest electrochemical signal.

DPV in luteolin solution with bare GCE, Fe3O4@MIP/GCE, rGO/GCE, SiO2@MIP/rGO/GCE and Fe3O4@MIP/rGO/GCE.

3.4

3.4 Optimization of electrochemical conditions

3.4.1

3.4.1 Effect of pH

In order to confirm the optimum pH value of electrolyte, different pH values of electrolyte from 4.0 to 9.0 were investigated by detection of luteolin with DPV using Fe₃O₄@MIP/rGO/GCE. As shown in Fig. 6a, the peak current reached the maximum value when pH was 7.0. In both acidic and alkaline electrolytes, the peak current showed decreases. Insufficient protons in solution at high pH could made the electrochemical reaction difficult. Moreover, luteolin would converted into anion status resulting electrostatic repulsion between luteolin anions and negative ions on electrode (Liu et al., 2019a,b,c; Xie et al., 2020 ). Hence, the pH value of electrolyte during test was set at 7.0.

(a) Effect of pH values on peak current of luteolin in DPV; (b) Effect of modification volumes of rGO on peak current of luteolin in DPV; (c) Effect of modification volumes of Fe3O4@MIP on peak current of luteolin in DPV; (d) CV of Fe3O4@MIP/rGO/GCE in luteolin solution at different scan rates; (e) DPV of Fe3O4@MIP/rGO/GCE in different concentrations of luteolin solution; (f) Plot of peak current versus concentration of luteolin in logarithmic form.

3.4.2

3.4.2 Effect of modification volumes of rGO and Fe₃O₄@MIP

Effects of modification volumes of rGO (from 5 μL to 10 μL) and Fe₃O₄@MIP (from 4 μL to 9 μL) were conducted to optimize the modification amounts of two materials. The concentrations of rGO and Fe₃O₄@MIP were 5.0 mg mL⁻¹. Firstly, the modification volume of rGO was investigated and shown in Fig. 6b. The peak current increased with increasing modification volume of rGO until the volume reached 9 μL. More volume of rGO like 10 μL reduced the current sharply. Then, after modification with 9 μL of rGO, the modification volume of Fe₃O₄@MIP was examined. With similar trends, the peak current reached the highest value when the modification volume of Fe₃O₄@MIP was 7 μL, and then decreased when the volume was more than 7 μL (Fig. 6c). Therefore, the modification volumes of rGO and Fe₃O₄@MIP were optimized at 9 μL and 7 μL, respectively.

3.4.3

3.4.3 Effect of scan rate

The effect of scan rate (from 0.01 V s⁻¹ to 0.3 V s⁻¹) on the electrochemical signals was investigated by detection of luteolin with CV using Fe₃O₄@MIP/rGO/GCE. As shown in Fig. 6d, the peak currents in CV were getting higher with increasing scan rate. A linear change could be found between peak current and scan rate, which could be fitted as: Ipa = 16.61 v + 0.3512 (r² = 0.994) (Fig. S1 in SI). The linear increasing of peak current indicated that the redox reaction occurred on the surface of Fe₃O₄@MIP/rGO/GCE was controlled by adsorption process (Yuan et al., 2020). Despite the higher signals during increasing scan rate, the fluctuation and signal-to-noise ratio were more apparent as well. Therefore, the scan rate was controlled at 0.05 V s⁻¹ during test considering these influences together.

3.5

3.5 Quantitative analysis of luteolin

After the optimization of electrochemical conditions, the quantitative analysis of luteolin with DPV using Fe₃O₄@MIP/rGO/GCE was performed at concentrations ranged from 2.5 pM to 0.1 μM (Fig. 6e). As a result, the peak currents increased linearly with the logarithmic increase of luteolin. The linear equation concerned the peak currents and concentrations could be fitted as: y = 0.301 logC + 2.287 (r² = 0.995) (Fig. 6f). The limit of detection of luteolin reached 1 pM. Through the comparison of reported modified electrodes in detection of luteolin, the Fe₃O₄@MIP/rGO/GCE proposed in this study exhibited good linearity and low detection limit (Table S1 in SI).

3.6

3.6 Anti-interference, reproducibility and stability

For anti-interference ability of Fe₃O₄@MIP/rGO/GCE, some substances (NaCl, KCl, CaCl₂ and tectorigenin) were added into luteolin solution and detected with DPV. The concentrations of these interferents were 5000 times higher than that of luteolin. In order to evaluate the anti-interference ability of Fe₃O₄@MIP/rGO/GCE, the current ratio (%) was calculated as the ratio of peak current variation and original current value during the addition of interferent (Singh et al., 2020). As illustrated in Fig. 7a, the current ratio was from 1.4% to 2.7%, indicating the influence of interferents on the detection of luteolin was limited. When the same amount of luteolin was added, the current ratio was about 103.8%, which demonstrated the detection of luteolin was reliable.

(a) Peak current ratio of Fe3O4@MIP/rGO/GCE in luteolin containing interfering substances; (b) Reproducibility and (c) stability of Fe3O4@MIP/rGO/GCE in luteolin solution.

For reproducibility of Fe₃O₄@MIP/rGO/GCE, the peak currents of luteolin in DPV using the same electrode six times a day were monitored. It could be found in Fig. 7b that the results were stable with relative standard deviation at 4.23% (n = 6). The stability of Fe₃O₄@MIP/rGO/GCE was also investigated by consecutively detecting the peak currents of luteolin in DPV using the same electrode in six days (Fig. 7c). The relative standard deviation for stability test (n = 6) was just 4.67%. Therefore, the electrochemical detection of luteolin using Fe₃O₄@MIP/rGO/GCE showed anti-interference ability to some interferents, reproducibility and stability of results.

3.7

3.7 Determination of luteolin in real samples

In order to estimate the practicality of Fe₃O₄@MIP/rGO/GCE, the detection of luteolin in real samples were conducted, and the recovery test during detection was also carried out by standard addition method. As expressed in Table 1, there was 42.4 ± 0.5 nM of luteolin in lotus leaves extract and the recoveries in detection were ranged from 98.5% to 100.7%. Moreover, the relative standard deviation values were less than 1.24%. Therefore, the Fe₃O₄@MIP/rGO/GCE showed well detection of luteolin in real samples with satisfied recovery and accuracy.

Table 1 Determination of luteolin in lotus leaves sample (n = 3).

Samples	Added (nM)	Found (nM)	Recovery (%)	RSD (%)
Lotus leaves extract	–	42.4 ± 0.5	–	1.06
	5	47.3 ± 0.4	99.3	0.85
	10	52.4 ± 0.6	100.7	1.24
	20	62.1 ± 0.3	98.5	0.41

4 Conclusions

In this study, Fe₃O₄@MIP was prepared using luteolin as template under the optimal mole ratio of reactants. Compared with SiO₂@MIP, Fe₃O₄@MIP showed better adsorption performance and signal enhancement. With good selectivity and signal enhancement, Fe₃O₄@MIP and rGO were successively modified on GCE (Fe₃O₄@MIP/rGO/GCE) to develop a simple, high sensitivity and selectivity sensor for detection of luteolin. The modifications of Fe₃O₄@MIP and rGO exhibited the most enhancement than single modification and bare GCE. After optimization of fabrication and detection conditions, the Fe₃O₄@MIP/rGO/GCE demonstrated satisfied anti-interference, linearity, detection limit, reproducibility and stability for luteolin. The linear range reached from 2.5 pM to 0.1 μM with detection limit at 1 pM and the relative standard deviations in reproducibility and stability were lower than 4.7%. With well recovery in determination of luteolin in natural extract, Fe₃O₄@MIP/rGO/GCE could be further developed as a practical sensitive sensor for the applications in natural antioxidants evaluations in food and analytical fields.

Acknowledgments

This work was supported by the Central Public-interest Scientific Institution Basal Research Fund (No. 1610242020005), Open project of key laboratory of biology and processing for bast fiber crops, MARA, and National Agricultural Science and Technology Innovation Project and Genetic breeding and quality safety assessment of Southern characteristic fruit trees, CAAS-ASTIP-21-IBFC10 (Characteristic fruit and vegetable innovation team, ASTIP-IBFC05).

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Gui R., Guo H., Jin H., . Preparation and applications of electrochemical chemosensors based on carbon-nanomaterial-modified molecularly imprinted polymers. Nanoscale Adv.. 2019;1:3325-3363.
[Google Scholar]
Gui R., Jin H., Guo H., Wang Z., . Recent advances and future prospects in molecularly imprinted polymers-based electrochemical biosensors. Biosens. Bioelectron.. 2018;100:56-70.
[Google Scholar]
Haminiuk C.W.I., Maciel G.M., Plata-Oviedo M.S.V., Peralta R.M., . Phenolic compounds in fruits – an overview. Int. J. Food Sci. Tech.. 2012;47:2023-2044.
[Google Scholar]
Hatamluyi B., Rezayi M., Beheshti H.R., Boroushaki M.T., . Ultra-sensitive molecularly imprinted electrochemical sensor for patulin detection based on a novel assembling strategy using Au@Cu-MOF/N-GQDs. Sensor. Actuat. B-Chem.. 2020;318:128219
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Hu Y., Wei J., Liang Y., Zhang H., Zhang X., Shen W., Wang H., . Zeolitic imidazolate framework/graphene oxide hybrid nanosheets as seeds for the growth of ultrathin molecular sieving membranes. Angew. Chem. Int. Edit.. 2016;55:2048-2052.
[Google Scholar]
Imoisili P.E., Ukoba K.O., Jen T.-C., . Green technology extraction and characterisation of silica nanoparticles from palm kernel shell ash via sol–gel. J. Mater. Res. Technol.. 2020;9:307-313.
[Google Scholar]
Jin H., Guo H., Gao X., Gui R., . Selective and sensitive electrochemical sensing of gastrodin based on nickel foam modified with reduced graphene oxide/silver nanoparticles complex-encapsulated molecularly imprinted polymers. Sens. Actuat. B-Chem.. 2018;277:14-21.
[Google Scholar]
Juszczak A.M., Zovko-Končić M., Tomczyk M., . Recent trends in the application of chromatographic techniques in the analysis of luteolin and its derivatives. Biomolecules. 2019;9:731.
[Google Scholar]
Li Y., Ji Y., Li Y., Li Y., Ma G., Liu X., . Construction of poly(methylene blue)/copper nanowires modified electrode for high-performance luteolin sensing. J. Electrochem. Soc.. 2020;167:147513
[Google Scholar]
Liu H., Hassan M., Bo X., Guo L., . Fumarate-based metal-organic framework/mesoporous carbon as a novel electrochemical sensor for the detection of gallic acid and luteolin. J. Electroanal. Chem.. 2019;849:113378
[Google Scholar]
Liu J., Cheng H., Xie H., Luo G., Niu Y., Zhang S., Li G., Sun W., . Platinum nanoparticles decorating a biomass porous carbon nanocomposite-modified electrode for the electrocatalytic sensing of luteolin and application. RSC Adv.. 2019;9:33607-33616.
[Google Scholar]
Liu L.L., Shi S.Y., Chen X.Q., Peng M.J., . Analysis of tyrosinase binders from Glycyrrhiza uralensis root: Evaluation and comparison of tyrosinase immobilized magnetic fishing-HPLC and reverse ultrafiltration-HPLC. J. Chromatogr. B. 2013;932:19-25.
[Google Scholar]
Liu Y., Huang Y.M., Xiao A.P., Qiu H.J., Liu L.L., . Preparation of magnetic Fe3O4/MIL-88A nanocomposite and its adsorption properties for bromophenol blue dye in aqueous solution. Nanomaterials. 2019;9:14.
[Google Scholar]
Orooji Y., Mortazavi-Derazkola S., Ghoreishi S.M., Amiri M., Salavati-Niasari M., . Mesopourous Fe3O4@SiO2-hydroxyapatite nanocomposite: Green sonochemical synthesis using strawberry fruit extract as a capping agent, characterization and their application in sulfasalazine delivery and cytotoxicity. J. Hazard. Mater.. 2020;400:123140
[Google Scholar]
Pang P., Liu Y., Zhang Y., Gao Y., Hu Q., . Electrochemical determination of luteolin in peanut hulls using graphene and hydroxyapatite nanocomposite modified electrode. Sensor. Actuat. B-Chem.. 2014;194:397-403.
[Google Scholar]
Ratinac K.R., Yang W., Gooding J.J., Thordarson P., Braet F., . Graphene and related materials in electrochemical sensing. Electroanalysis. 2011;23:803-826.
[Google Scholar]
Ross N., Civilized Nqakala N., . Electrochemical determination of hydrogen peroxide by a nonenzymatic catalytically enhanced silver-iron (III) oxide/polyoxometalate/reduced graphene oxide modified glassy carbon electrode. Anal. Lett.. 2020;53:2445-2464.
[Google Scholar]
Rowley-Neale S.J., Randviir E.P., Abo Dena A.S., Banks C.E., . An overview of recent applications of reduced graphene oxide as a basis of electroanalytical sensing platforms. Appl. Mater. Today. 2018;10:218-226.
[Google Scholar]
Singh S., Numan A., Zhan Y., Singh V., Van Hung T., Nam N.D., . A novel highly efficient and ultrasensitive electrochemical detection of toxic mercury (II) ions in canned tuna fish and tap water based on a copper metal-organic framework. J. Hazard. Mater.. 2020;399:123042
[Google Scholar]
Singh V.V., . Recent advances in electrochemical sensors for detecting weapons of mass destruction. A Review. Electroanalysis. 2016;28:920-935.
[Google Scholar]
Sugimoto Y., Irisawa T., Hatori H., Inagaki M., . Yarns of carbon nanotubes and reduced graphene oxides. Carbon. 2020;165:358-377.
[Google Scholar]
Tang J., Zheng S.B., Jiang S.X., Li J., Guo T., Guo J.H., . Metal organic framework (ZIF-67)-derived Co nanoparticles/N-doped carbon nanotubes composites for electrochemical detecting of tert-butyl hydroquinone. Rare Metals 2020
[Google Scholar]
Wackerlig J., Lieberzeit P.A., . Molecularly imprinted polymer nanoparticles in chemical sensing - Synthesis, characterisation and application. Sensor. Actuat. B-Chem.. 2015;207:144-157.
[Google Scholar]
Wei M., Geng X., Liu Y., Long H., Du J., . A novel electrochemical sensor based on electropolymerized molecularly imprinted polymer for determination of luteolin. J. Electroanal. Chem.. 2019;842:184-192.
[Google Scholar]
Xie Y., Zhang T., Chen Y., Wang Y., Wang L., . Fabrication of core-shell magnetic covalent organic frameworks composites and their application for highly sensitive detection of luteolin. Talanta. 2020;213:120843
[Google Scholar]
Xu B., Zhang B., Yang L., Zhao F., Zeng B., . Electrochemical determination of luteolin using molecularly imprinted poly-carbazole on MoS2/graphene-carbon nanotubes nanocomposite modified electrode. Electrochim. Acta. 2017;258:1413-1420.
[Google Scholar]
Yang J.C., Lee J., Hong S.W., Park J., . Molecularly imprinted quartz crystal microbalance sensors with lithographically patterned frisbee-like pillar arrays for sensitive and selective detection of iprodione. Sens. Actuat. B-Chem.. 2020;320:128366
[Google Scholar]
Yang L., Xu B., Ye H., Zhao F., Zeng B., . A novel quercetin electrochemical sensor based on molecularly imprinted poly(para-aminobenzoic acid) on 3D Pd nanoparticles-porous graphene-carbon nanotubes composite. Sensor. Actuat. B-Chem.. 2017;251:601-608.
[Google Scholar]
Yuan M.M., Zou J., Huang Z.N., Peng D.M., Yu J.G., . PtNPs-GNPs-MWCNTs-β-CD nanocomposite modified glassy carbon electrode for sensitive electrochemical detection of folic acid. Anal. Bioanal. Chem.. 2020;412:2551-2564.
[Google Scholar]
Zuo Y., . Application of poly(3,4-ethylenedioxythiophene)/manganese Dioxide Composite-Modified Electrode for Sensitive Electrochemical Detection of Luteolin. Int. J. Electrochem. Sc.. 2016;11:3776-3785.
[Google Scholar]

Appendix A

Supplementary material

Supplementary data to this article can be found online at https://doi.org/10.1016/j.arabjc.2021.102990.

Appendix A

Supplementary material

The following are the Supplementary data to this article:

Supplementary data 1

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[Google Scholar]

[9] Gao F., Tu X., Ma X., Xie Y., Zou J., Huang X., Qu F., Yu Y., Lu L., . NiO@Ni-MOF nanoarrays modified Ti mesh as ultrasensitive electrochemical sensing platform for luteolin detection. Talanta. 2020;215:120891
[Google Scholar]

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[Google Scholar]

[11] Gui R., Jin H., Guo H., Wang Z., . Recent advances and future prospects in molecularly imprinted polymers-based electrochemical biosensors. Biosens. Bioelectron.. 2018;100:56-70.
[Google Scholar]

[12] Haminiuk C.W.I., Maciel G.M., Plata-Oviedo M.S.V., Peralta R.M., . Phenolic compounds in fruits – an overview. Int. J. Food Sci. Tech.. 2012;47:2023-2044.
[Google Scholar]

[13] Hatamluyi B., Rezayi M., Beheshti H.R., Boroushaki M.T., . Ultra-sensitive molecularly imprinted electrochemical sensor for patulin detection based on a novel assembling strategy using Au@Cu-MOF/N-GQDs. Sensor. Actuat. B-Chem.. 2020;318:128219
[Google Scholar]

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[Google Scholar]

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[Google Scholar]

[16] Jin H., Guo H., Gao X., Gui R., . Selective and sensitive electrochemical sensing of gastrodin based on nickel foam modified with reduced graphene oxide/silver nanoparticles complex-encapsulated molecularly imprinted polymers. Sens. Actuat. B-Chem.. 2018;277:14-21.
[Google Scholar]

[17] Juszczak A.M., Zovko-Končić M., Tomczyk M., . Recent trends in the application of chromatographic techniques in the analysis of luteolin and its derivatives. Biomolecules. 2019;9:731.
[Google Scholar]

[18] Li Y., Ji Y., Li Y., Li Y., Ma G., Liu X., . Construction of poly(methylene blue)/copper nanowires modified electrode for high-performance luteolin sensing. J. Electrochem. Soc.. 2020;167:147513
[Google Scholar]

[19] Liu H., Hassan M., Bo X., Guo L., . Fumarate-based metal-organic framework/mesoporous carbon as a novel electrochemical sensor for the detection of gallic acid and luteolin. J. Electroanal. Chem.. 2019;849:113378
[Google Scholar]

[20] Liu J., Cheng H., Xie H., Luo G., Niu Y., Zhang S., Li G., Sun W., . Platinum nanoparticles decorating a biomass porous carbon nanocomposite-modified electrode for the electrocatalytic sensing of luteolin and application. RSC Adv.. 2019;9:33607-33616.
[Google Scholar]

[21] Liu L.L., Shi S.Y., Chen X.Q., Peng M.J., . Analysis of tyrosinase binders from Glycyrrhiza uralensis root: Evaluation and comparison of tyrosinase immobilized magnetic fishing-HPLC and reverse ultrafiltration-HPLC. J. Chromatogr. B. 2013;932:19-25.
[Google Scholar]

[22] Liu Y., Huang Y.M., Xiao A.P., Qiu H.J., Liu L.L., . Preparation of magnetic Fe3O4/MIL-88A nanocomposite and its adsorption properties for bromophenol blue dye in aqueous solution. Nanomaterials. 2019;9:14.
[Google Scholar]

[23] Orooji Y., Mortazavi-Derazkola S., Ghoreishi S.M., Amiri M., Salavati-Niasari M., . Mesopourous Fe3O4@SiO2-hydroxyapatite nanocomposite: Green sonochemical synthesis using strawberry fruit extract as a capping agent, characterization and their application in sulfasalazine delivery and cytotoxicity. J. Hazard. Mater.. 2020;400:123140
[Google Scholar]

[24] Pang P., Liu Y., Zhang Y., Gao Y., Hu Q., . Electrochemical determination of luteolin in peanut hulls using graphene and hydroxyapatite nanocomposite modified electrode. Sensor. Actuat. B-Chem.. 2014;194:397-403.
[Google Scholar]

[25] Ratinac K.R., Yang W., Gooding J.J., Thordarson P., Braet F., . Graphene and related materials in electrochemical sensing. Electroanalysis. 2011;23:803-826.
[Google Scholar]

[26] Ross N., Civilized Nqakala N., . Electrochemical determination of hydrogen peroxide by a nonenzymatic catalytically enhanced silver-iron (III) oxide/polyoxometalate/reduced graphene oxide modified glassy carbon electrode. Anal. Lett.. 2020;53:2445-2464.
[Google Scholar]

[27] Rowley-Neale S.J., Randviir E.P., Abo Dena A.S., Banks C.E., . An overview of recent applications of reduced graphene oxide as a basis of electroanalytical sensing platforms. Appl. Mater. Today. 2018;10:218-226.
[Google Scholar]

[28] Singh S., Numan A., Zhan Y., Singh V., Van Hung T., Nam N.D., . A novel highly efficient and ultrasensitive electrochemical detection of toxic mercury (II) ions in canned tuna fish and tap water based on a copper metal-organic framework. J. Hazard. Mater.. 2020;399:123042
[Google Scholar]

[29] Singh V.V., . Recent advances in electrochemical sensors for detecting weapons of mass destruction. A Review. Electroanalysis. 2016;28:920-935.
[Google Scholar]

[30] Sugimoto Y., Irisawa T., Hatori H., Inagaki M., . Yarns of carbon nanotubes and reduced graphene oxides. Carbon. 2020;165:358-377.
[Google Scholar]

[31] Tang J., Zheng S.B., Jiang S.X., Li J., Guo T., Guo J.H., . Metal organic framework (ZIF-67)-derived Co nanoparticles/N-doped carbon nanotubes composites for electrochemical detecting of tert-butyl hydroquinone. Rare Metals 2020
[Google Scholar]

[32] Wackerlig J., Lieberzeit P.A., . Molecularly imprinted polymer nanoparticles in chemical sensing - Synthesis, characterisation and application. Sensor. Actuat. B-Chem.. 2015;207:144-157.
[Google Scholar]

[33] Wei M., Geng X., Liu Y., Long H., Du J., . A novel electrochemical sensor based on electropolymerized molecularly imprinted polymer for determination of luteolin. J. Electroanal. Chem.. 2019;842:184-192.
[Google Scholar]

[34] Xie Y., Zhang T., Chen Y., Wang Y., Wang L., . Fabrication of core-shell magnetic covalent organic frameworks composites and their application for highly sensitive detection of luteolin. Talanta. 2020;213:120843
[Google Scholar]

[35] Xu B., Zhang B., Yang L., Zhao F., Zeng B., . Electrochemical determination of luteolin using molecularly imprinted poly-carbazole on MoS2/graphene-carbon nanotubes nanocomposite modified electrode. Electrochim. Acta. 2017;258:1413-1420.
[Google Scholar]

[36] Yang J.C., Lee J., Hong S.W., Park J., . Molecularly imprinted quartz crystal microbalance sensors with lithographically patterned frisbee-like pillar arrays for sensitive and selective detection of iprodione. Sens. Actuat. B-Chem.. 2020;320:128366
[Google Scholar]

[37] Yang L., Xu B., Ye H., Zhao F., Zeng B., . A novel quercetin electrochemical sensor based on molecularly imprinted poly(para-aminobenzoic acid) on 3D Pd nanoparticles-porous graphene-carbon nanotubes composite. Sensor. Actuat. B-Chem.. 2017;251:601-608.
[Google Scholar]

[38] Yuan M.M., Zou J., Huang Z.N., Peng D.M., Yu J.G., . PtNPs-GNPs-MWCNTs-β-CD nanocomposite modified glassy carbon electrode for sensitive electrochemical detection of folic acid. Anal. Bioanal. Chem.. 2020;412:2551-2564.
[Google Scholar]

[39] Zuo Y., . Application of poly(3,4-ethylenedioxythiophene)/manganese Dioxide Composite-Modified Electrode for Sensitive Electrochemical Detection of Luteolin. Int. J. Electrochem. Sc.. 2016;11:3776-3785.
[Google Scholar]

Magnetic molecularly imprinting polymers and reduced graphene oxide modified electrochemical sensor for the selective and sensitive determination of luteolin in natural extract

Abstract

Abstract

Keywords

Electrochemical detection

Luteolin

Magnetic nanoparticles

Molecularly imprinted polymer

Reduced graphene oxide

1 Introduction

2 Materials and methods

2.1 Reagents

2.2 Preparation of Fe3O4@MIP and SiO2@MIP

2.3 Adsorption of luteolin using Fe3O4@MIP and SiO2@MIP

2.4 Fabrication of Fe3O4@MIP/rGO/GCE

2.5 Electrochemical measurements

2.6 Preparation of real sample

3 Results and discussion

3.1 Characterizations of Fe3O4@MIP and rGO

3.1.1 TEM and SEM

3.1.2 FT-Ir

3.1.3 Vsm

3.2 Optimization of preparation conditions of Fe3O4@MIP

3.2.1 Effect of monomer

3.2.2 Effect of mole ratios of template, monomer and crosslinker

3.2.3 Adsorption performances of Fe3O4@MIP and SiO2@MIP

3.3 Electrochemical properties of modified electrodes

3.4 Optimization of electrochemical conditions

3.4.1 Effect of pH

3.4.2 Effect of modification volumes of rGO and Fe3O4@MIP

3.4.3 Effect of scan rate

3.5 Quantitative analysis of luteolin

3.6 Anti-interference, reproducibility and stability

3.7 Determination of luteolin in real samples

4 Conclusions

Acknowledgments

Declaration of Competing Interest

References

Appendix A

Supplementary material

Appendix A

Supplementary material

Suggested read for related articles:

2.2 Preparation of Fe₃O₄@MIP and SiO₂@MIP

2.3 Adsorption of luteolin using Fe₃O₄@MIP and SiO₂@MIP

2.4 Fabrication of Fe₃O₄@MIP/rGO/GCE

3.1 Characterizations of Fe₃O₄@MIP and rGO

3.2 Optimization of preparation conditions of Fe₃O₄@MIP

3.2.3 Adsorption performances of Fe₃O₄@MIP and SiO₂@MIP

3.4.2 Effect of modification volumes of rGO and Fe₃O₄@MIP