Molecularly imprinted polypyrrole nanotubes based electrochemical sensor for glyphosate detection
Introduction
Glyphosate (Gly), a commonly used herbicide, is widely used to reduce the impacts of weeds and pests on the agricultural production process. However, Gly exposure can cause persistent damage to human health. The U.S. Environmental Protection Agency has reported that Gly could enhance the incidence of renal cancer in mice. The International Agency for Research on Cancer also stated that Gly was a causing agent for human cancer (Ansari et al., 2019). Therefore, developing a high-efficiency strategy to detect Gly is of significance to monitor the environment and reduce public health risks. Pesticides are usually detected using various chromatography techniques (liquid, gas, or ion) coupled with mass spectrometry, which is highly sensitive but requires meticulous sample preparation, expensive equipment, and highly qualified technicians (van Pinxteren et al., 2009; Zhang et al., 2014). Most common pesticides possess chemical groups (thiocarbamates, organophosphates, phenyl ureas, dinitroanilines, organochlorines, carbamates, phenoxys, pyrethroids, chloroacetanilides, triazines, triazinones, etc.) (Leon et al., 2019) that can be easily detected using photometric or fluorometric methods (Li et al., 2018). For example, Liu et al. detected the organophosphates using fluorescence and colorimetric methods simultaneously via an AuNPs-Rhodamine B system (Liu et al., 2012). However, Gly lacks chemical groups that can be quickly and directly analyzed by traditional fluorescent and colorimetric techniques, which complicates the development of selective and sensitive sensors for Gly detection.
Recently, the use of precise molecular recognition technology to specifically capture the interested target (“key”), especially through the design of “lock”, has attracted increasing interest for selective detection of specific chemical targets (Ariga et al., 2012). The main principle of such technique is to form some specific molecular structures or intermolecular interactions, such as natural receptors (Edwardson et al., 2016; MacCallum et al., 1996), assembled supermolecules (Harada et al., 2011; Xiao et al., 2015), and molecularly imprinted polymers (MIPs), which have specific recognition sites complementary to the targets (Chen et al., 2016; Zhang et al., 2019). As a potential “plastic antibody”, MIPs have attracted much attention due to their economic and straightforward preparation as well as efficient and specific target recognition in complex environment matrices (Polyakov, 1931; Hoshino et al., 2008). MIPs are usually prepared by assembling the template and functional monomers and subsequently cross-linking to each other to form an imprinted matrix (Lofgreen and Ozin, 2014). With subsequent removal of the templates, the obtained imprinted cavities provide binding sites and complementary spatial structures to target molecules (Ding et al., 2020; Ding et al., 2018). The unique properties of structure predictability, recognition specificity and stability have made MIP widely used in various high-sensitivity sensors (Bai et al., 2020; Cai et al., 2010; Yáñez-Sedeño et al., 2017). For herbicide analysis, electrochemical sensors usually offer low-cost and rapid detection capability in soil, water, and food samples (Zhu et al., 2015). MIPs have played a unique role in developing high-performance electrochemical sensors because of their excellent affinity and sensitivity to recognize target analytes (Jin et al., 2019; Wackerlig and Lieberzeit, 2015).
For MIPs-based electrochemical sensors, the matrix and structure of the sensing material are the critical factors to sensors’ performance. Extensive studies on developing various MIP materials have been reported to improve sensitivity and fast response for detecting herbicides. Polypyrrole (PPy), a conductive polymer, possesses outstanding mobility of charge carriers, fast electron transfer rate, and exceptional environmental stability (Deng et al., 2012; Gu and Ruan, 2021). Thus, PPy-based MIPs are good candidates for developing high-performance electrochemical sensors. However, most studies of synthesizing PPy-based MIPs used approaches of bulk imprinting or directly synthesizing the MIPs on the electrode surface, which usually generates low imprinted cavity utilization and slow adsorption rate (Yang et al. 2015, 2016). Surface imprinting, which results in high-affinity recognition sites in the nanoscale surface layer of the polymer matrix, allows easy access to binding sites and enhances recognition efficiency (Hayden et al., 2006; Kazuhiko et al., 1993; Menaker et al., 2009; Pérez et al., 2001; Xing et al. 2017, 2019; Yu et al., 1992). Especially, imprinting on nanostructured matrices, such as nanotubes, will further improve the performance of MIPs due to the extremely high surface areas of nanomaterials. Moreover, MIPs based on nanotube structure can enable numerous imprinted sites both in and on the surface of the walls. The concentration difference of Gly between the inside and outside of porous nanotubes can also provide a driving force to promote the adsorption rate (Tofighy and Mohammadi, 2011; Zhou et al., 2019). However, using PPy nanotubes as a MIP matrix to fabricate an electrochemical sensor for glyphosate detection has not been exploited.
We herein report a one-pot synthesis method of molecularly imprinted polypyrrole nanotubes (MIPNs), in which specific Gly recognition sites are formed on the surface of nanotubes. The Gly sensor was fabricated by coating a thin layer of the MIPNs on the surface of a screen-printed electrode (SPE) (Scheme 1). The obtained MIPNs were fully characterized. Furthermore, a SPE holder was designed and fabricated in our lab using 3D-printing to integrate with the Gly sensor. The electrochemical properties of the MIPNs-based sensor were analyzed by differential pulse voltammetry (DPV). The results demonstrated that the sensor exhibited superior sensitivity and specificity for sensing Gly compared with non-molecularly imprinted polypyrrole nanotubes (NIPNs).
Section snippets
Preparation of molecularly imprinted polypyrrole nanotubes (MIPNs)
Typically, a solution of methyl orange (MO, 500 mg) in 300 mL DI H2O was first prepared at room temperature. Iron (III) chloride was added and stirred for 10 min. Subsequently, the template, Gly (145 mg) and the functional monomer/crosslinker, pyrrole (1.5 mL) were added dropwise and reacted for 2 h. The formed black precipitate was washed repeatedly by water. The Gly template was eluted by methanol and acetic acid (1:9) complex solution. The comparable material (NIPNs) was synthesized in a
Sensor principles
This proposed sensor used the MIPNs based SPE to construct a convenient electrochemical detection platform, and the preparation process is illustrated in Scheme 1. Herein, MIPNs are used as the sensing material. We developed a new MIPNs that possesses imprinted cavities complementary to the 3D spatial structure of the target Gly molecule. Such MIPNs provide binding sites with high affinity and specificity for target recognition. The thin walls of MIPNs can enable numerous imprinted sites
Conclusion
In summary, we have synthesized a novel MIPNs-based electrochemical sensor for the detection of Gly with high sensitivity and specificity. By imprinting high affinity and specific Gly binding sites on the surface of PPy nanotubes, the MIPNs possess high specificity, excellent electrical conductivity, and large accessible surfaces. The MIPNs inherit all advantages of surface imprinting technology and provide a concentration driving force for fast recognition. The proposed electrochemical sensor
CRediT authorship contribution statement
Shichao Ding: Writing – original draft, Writing – review & editing. Zhaoyuan Lyu: Writing – original draft, Writing – review & editing. Suiqiong Li: Writing – review & editing. Xiaofan Ruan: Writing – review & editing. Mingen Fei: Writing – review & editing. Yang Zhou: Writing – review & editing. Xiangheng Niu: Writing – review & editing. Wenlei Zhu: Writing – review & editing. Dan Du: Writing – original draft, Writing – review & editing. Yuehe Lin: Writing – original draft, Writing – review &
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.
Acknowledgment
This work was supported by WSU startup fund and National Institute of Environmental Health Sciences of the National Institutes of Health (1R43ES031885-01). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. We would like to thank the WSU Franceschi Microscopy & Imaging Center for TEM and SEM measurements. FT-IR characterization supported by Dr. Jinwen Zhang are also acknowledged.
References (56)
- et al.
Anal. Chim. Acta
(2019) - et al.
Biosens. Bioelectron.
(2020) - et al.
Sensor. Actuator. B
(2019) - et al.
Colloid. Surface.
(2012) - et al.
Biosens. Bioelectron.
(2020) - et al.
Biosens. Bioelectron.
(2013) - et al.
Biosens. Bioelectron.
(2019) - et al.
Biosens. Bioelectron.
(2019) - et al.
Sensor. Actuator. B
(2018) - et al.
J. Mol. Biol.
(1996)
Biosens. Bioelectron.
Polym. Degrad. Stabil.
J. Hazard Mater.
Sens. Actuators, B
Chem. Sci.
Anal. Chim. Acta
Biosens. Bioelectron.
Talanta
Sens. Actuators, B
Synth. Met.
Trac. Trends Anal. Chem.
Chem. Eng. J.
Chem. Soc. Rev.
Phys. Chem. Chem. Phys.
Nat. Nanotechnol.
Chem. Soc. Rev.
RSC Adv.
Cited by (92)
Chemometric-assisted eMIP-modified screen-printed sensor for robust herbicide MCPA determination
2024, Sensors and Actuators Reports