Detection and FEM studies of dichromate (Cr2O72) by allyltriethoxysilane modified nanochannel

https://doi.org/10.1016/j.jelechem.2020.113818Get rights and content

Highlights

  • A strategy of preparing silanized quartz nanopore was developed for Cr2O72- detection.

  • Allyl modified nanopores are successfully and easily prepared with silylation reactions.

  • The established sensor was used for electrochemical sensing of Cr2O72- ions and reached ultra-trace concentration.

Abstract

Cr2O72 is one of the most toxic ions which leads to skin allergies, kidney disease and cancer. Thus, highly efficient and sensitive detection of Cr2O72 has drawn wide attentions. In this work, we developed a wide range and high accuracy sensor basing on Allyltriethoxysilane modified nanopipette for the ultra-trace dichromate (Cr2O72) ions' detection in an aqueous solution. The prepared Cr2O72 sensor showed a wide detection range from 10^(−16) M to 10^(−4) M and with an ultra-low detection limit down to 1.296 × 10^(−16) M.

Introduction

Chromium (Cr) is one of the most important metal elements and widely used in the field of chemical industry, metallurgy, and dyeing and printing industry [1]. In particular, its high oxidation state in Cr (VI) made it becomes one of the carcinogenic heavy metals recognized internationally. It has high toxicity to human, animals, plants and microorganisms. The accumulation of Cr (VI) in organs and tissues can lead to skin allergies, kidney disease and cancer [2]. Due to the wide application of Cr in the above manufacture fields, it thus can be released into the natural environment through like industrial wastewater. Accordingly, it's important for us to detect trace Cr(VI) accurately, especially in the form of Cr2O72. Until now, the major detection strategies for Cr(VI) are mainly basing on CV curves with nanoparticles modified electrode [with a detection limit of 2.0 × 10^(−12) M] [3], ICP-MS [2.0 × 10^(−8) M] [4], and AAS [6.0 × 10^(−9) M] [5]. These methods obtain high LOD but samples usually need complicated pre-treatment. It is necessary to develop a more convenient detection platform for highly efficient and accurate determination of Cr(VI).

Recently, nanopore platform attached more and more attention in the investigation of ions' transmission and detection [[6], [7], [8]]. Two main methods were developed for the detection of metal ions. One of which is based on Coulter's principle. In particular, kinds of suitable probe molecule (mainly proteins, or specific ions) were selected to react with specific analyte ions. The products are able to produce totally different resistive pulse signals when they translocating from one side to another side of a given nanopore [9,10]. The existence of these abnormal signals indicates the detection of analyte ions and the number of them reflects the ions' concentration. For example, Kang and co-workers successfully detected Cu2+ ions in the presence of the probe of 5,10,15,20-tetrakis(4-sulfonatophenyl)-porphyrin (TPPS). The interaction of Cu2+ ions and porphyrin increased both the positive charge and size of the probe molecule and resulted in a new type of resistive pulse signals with larger amplitude and longer dwell time. These new signals can be used to the quantitative analysis of Cu2+ ion measurement, giving a detection limit down to 16 nM [11]. The similar method was also used in the detection of Th4+ [12] and UO2+ [13] ions and obtained a satisfactory results. This method exhibits a low detection limit and high sensibility but requires expansive instruments (Patch Clamp) for signal recording.

By contrast to the resistive-pulse method, a modified nanopore surface was also available for the detection [[14], [15], [16], [17]]. Different from the previous method, this method is mainly basing on the nanopore properties. The interaction between free analytes and modified nanopore changes both the physical and chemical properties of a nanopore (Charge, hydrophilicity, steric hindrance and so on), and showing a totally different ion transfer behaviors within the Debye length. These changes can also be observed intuitively from the response ionic current [[18], [19], [20], [21]]. This method is also valued by researchers. For example, Jiang and co-workers successfully detected Fe3+ ions with a polydopamine (PDA) modified nanopore. The interaction of Fe3+ and PDA layer affects the wettability and charge distribution of the pore surface, resulting in a change of ionic current through the nanochannels. These modified nanochannels can enhance the sensing ability to the ultra-trace level [10^(−12) M] [22].

Comparing to resistive-pulse signals, ionic current signals are much more convenient to be obtained and analyzed. The rectification effect of ionic currents is usually seen in asymmetric nanopores (e.g. Conical shape) as asymmetric current-voltage (I-V) curves [6,17,19,23]. This special property has been deeply studied and confirmed by both experiments and Finite Element Analysis (FEA) [[24], [25], [26]]. For example, the piranha solution cleaned quartz nanopipettes are negatively charged and show strong rectify effect in most cases due to the silanol groups on the inner wall. To quantitatively evaluate the changes of surface charge, we defined the absolute ratio of negative ionic current value to positive ionic current value at the potentials of ±1 V (I-1V/I1V) as the Ionic Current Rectification value (ICR value) to evaluate the charge changes of the nanopores. Besides that, the resistance of the nanopore and the ionic current value are also available for describing the properties of a given nanopore from different angles.

As reported previously, alkenes (-C=C-) are with strong reducibility [27] and easily oxidized by Cr2O72 to vicinal diol under an alkaline condition [28] or even carboxyl groups under an acidic condition [29]. Basing on above conclusions, we prepared an allyltriethoxysilane (ATS) modified quartz nanopipette platform for highly sensitive and selective determination of Cr2O72 herein. The oxidization of modified allyl groups strongly decreased the resistance of the nanopore and leads to the increase of response ionic current. On the other hand, the transformation from allyl groups into carboxyl also increased the negatively charged density and leads to the linearly increase of ICR value. Based on the above phenomena, we built up the correlation between ionic current responses and concentrations of Cr2O72 solutions by optimizing the experimental conditions such as balance time, pH values, diameters of nanopipettes and measuring voltages. We achieved a significantly low detection limit down to 1.296 × 10^(−16) M by optimizing the experimental parameters. This result meets the detection requirement of ultra-trace Cr2O72 ions. This method would have a tremendous impact on ultra-trace ionic detection in pharmaceutical and biological analysis.

Section snippets

Materials and reagents

Quartz pipettes with 1 mm outer diameter and 0.5 mm inner diameter were purchased from Sutter Co., Ltd. Allyltriethoxysilane was purchased from J&K Scientific Ltd. Potassium chloride (KCl), potassium hydroxide (KOH) and potassium dichromate (K2Cr2O7), Potassium sulfate (K2SO4), potassium nitrate (KNO3), potassium bromide (KBr), dipotassium hydrogen phosphate (K2HPO4), potassium dihydrogen phosphate (KH2PO4), potassium perchlorate (KClO4), potassium chlorate (KClO3) were all purchased from

Characterization of modified nanopipette

To characterize the allyl modified nanopipette sensors and their interaction with Cr2O72, we obtained I-V curves for the nanopipettes before and after allyl modification and results are shown in Fig. 1. The I-V curves in Fig. 1a directly demonstrated that the nanopipette was successfully modificated by allyl groups. For a piranha solution cleaned quartz nanopipette, the I-V curves showed strong ionic current rectification response by giving a maximum ICR value much greater than 1 due to the

Conclusion

In summary, we developed a selective and sensitive nanopipette sensor for the determination of Cr2O72 by using an allyl modified nanopipette. Due to the oxidization of allyl groups and the negative charge increases followed, Cr2O72 ions as low as 1.296 × 10^(−16) M can be detected by negative ionic current changes under the optimized conditions with good selectively. Besides that, this nanopipette sensor has been applied to the Cr2O72 detection in tap water and giving satisfied recoveries.

CRediT authorship contribution statement

Xuye Liu: Conceptualization, Methodology and Writing - original draft. Cheng Liu: Writing - original draft. Jie Yang: Writing - review & editing. Rui Zhang: Investigation. QiangZeng: Writing - review & editing. LishiWang: Conceptualization, Project administration and Resources.

Declaration of competing interest

There are no conflicts of interest.

Acknowledgment

This work was financially supported by the National Natural Science Foundation of China (Grant Nos. 21874047, 21475046, 21427809 and 21645004) and the Fundamental Research Funds for the Central Universities (Grant Nos. 2015ZP028 and 2017MS094).

Notes

The authors declare no competing financial interest.

References (35)

  • H. Cai et al.

    Resistive-pulse measurements with nanopipettes: detection of vascular endothelial growth factor C (VEGF-C) using antibody-decorated nanoparticles

    Anal. Chem.

    (2015)
  • S. Rauf et al.

    Label-free nanopore biosensor for rapid and highly sensitive cocaine detection in complex biological fluids

    ACS Sens.

    (2017)
  • G.M. Roozbahani et al.

    Computation-assisted nanopore detection of thorium ions

    Anal. Chem.

    (2018)
  • G.M. Roozbahani et al.

    Computation-assisted nanopore detection of uranyl ions, TechConnect Briefs 2018

    Adv. Mater.

    (2018)
  • X.P. Zhao et al.

    Asymmetric nanochannel-ionchannel hybrid for ultrasensitive and label-free detection of copper ions in blood

    Anal. Chem.

    (2018)
  • E.J. Kang et al.

    Improved ion-selective detection method using nanopipette with poly(vinyl chloride)-based membrane

    J. Phys. Chem. B

    (2014)
  • C.R. Crick et al.

    Selectively sized graphene-based nanopores for in situ single molecule sensing

    ACS Appl. Mater. Interfaces

    (2015)
  • Cited by (8)

    • Sensing with ion current rectifying solid-state nanopores

      2022, Current Opinion in Electrochemistry
      Citation Excerpt :

      Immobilization of the analyte is not a prerequisite for ICR sensors as analyte-induced reactions can also be utilized. At its simplest, these systems involve a direct reaction such as the allytriethoxysilane modified nanopore whose surface is oxidized in the presence of the analyte, dichromate, allowing its quantification with a 0.1296 fM detection limit [19]. In another work Ochratoxin A was detected using a nanopore modified with a target specific aptamer which, in the presence of the analyte, dissociates from the pore surface resulting in the surface charge change [20].

    • Designed multifunctional ratiometric fluorescent probe for directly detecting fluoride ion/ dichromate and indirectly monitoring urea

      2021, Journal of Hazardous Materials
      Citation Excerpt :

      Finally, on the basis of the aforesaid results, we quantitatively analyzed the relationship between the altered fluorescent ratio (I435/I543) and concentration of F- /Cr2O72-, respectively. After linear fitting, the limit of detection (LOD) of F- /Cr2O72- were found to be 34.7 nM /22.3 nM, which were superior to most of the reported F- -sensitive /Cr2O72--sensitive MOFs till date (Zhu et al., 2011; Kong et al., 2019; Yao et al., 2019; Jeong et al., 2017; Yang et al., 2019; Salomon-Flores et al., 2017; Kaur et al., 2020; Che et al., 2020; Xu et al., 2019; Wu et al., 2018; Xu et al., 2018a, 2018b, 2018c; Liu et al., 2016; Guo et al., 2017; Lin et al., 2017a, 2017b; He et al., 2018a, 2018b; Chang et al., 2018; Zou et al., 2018; Zhang et al., 2020a, 2020b; Xu et al., 2020; Liu et al., 2020a, 2020b, 2020c; Liu et al., 2019)(Fig. 3D and E, Table S1). Additionally, the fluorescence sensing effect of urease-incorporated UiO-66-NH2@EY with incremental concentrations of urea was explored.

    • High selectivity sensing of bovine serum albumin: The combination of glass nanopore and molecularly imprinted technology

      2021, Biosensors and Bioelectronics
      Citation Excerpt :

      Based on the specific affinity between Fe3O4–Au linked with aptamer and CEA, Li et al. not only amplified the resistive-pulse signals but also distinguished the aptamer modified Fe3O4–Au nanoparticles (Apt-MNPs) and CEA-Apt-MNPs successfully (Tang et al., 2020). To overcome similar problems, our group introduced a novel data process method (FTSM) for nanopore analysis to distinguish Au, Ag and SiO2 with similar size, achieving good results (Liu et al., 2020a,b). However, the above methods need either complicated modification and expensive reagents or complex data processing equipment and software, which is difficult for extensive application.

    View all citing articles on Scopus
    View full text