Nitrogen and fluoride co-doped graphdiyne with metal-organic framework (MOF)-derived NiCo₂O₄–Co₃O₄ nanocages as sensing layers for ultra-sensitive pesticide detection

Highlights

• Nitrogen and fluoride co-doped GDY (N–F-GDY) has been synthesized.

• The as-prepared biosensor possesses a wide linear range of 0.448 pM–44.8 nM.

• The as-prepared biosensor possesses a low detection limit of 0.0166 fM (S/N = 3).

Abstract

Heteroatom doped graphdiyne (GDY) has been demonstrated to be an effective strategy for achieving outstanding electrochemical properties, including improved electrocatalytic activity, tunable electronic properties and high electronic conductivity, by producing numerous heteroatomic defects as well as active sites. Extensive efforts have been devoted to the issue of single element doping of GDY. Introducing two or more kinds of heteroatoms into GDY materials may create a synergic effect between the co-dopants, thus generating superior electrochemical performance. Nevertheless, little research on multiple elements co-doped GDY, especially in the application of constructing electrochemical biosensor. Herein, nitrogen and fluoride co-doped GDY (N–F-GDY) has been synthesized and employed to combine with NiCo₂O₄–Co₃O₄ hollow multishelled nanocages to establish an ultrasensitive electrochemical biosensor for the assay of pesticide residue. The as-prepared electrochemical biosensor possesses a wide linear range of 0.448 pM–44.8 nM for monocrotophos detection and a low detection limit of 0.0166 fM (S/N = 3).

Introduction

The discovery and widespread use of organophosphorus pesticides (OPs) have played a vital role for the control of insects, pests and weeds, thus guaranteeing the yield of agricultural products [[1], [2], [3], [4]]. However, the inappropriate use of pesticides is accompanied by issues including pest resistance, nontarget toxicity, persistent residue, and environmental issues. Therefore, great attention is paid to the development of a rapid, accurate and sensitive analytical technology for pesticide residues. Electrochemical biosensor, which possesses favorable specificity and sensitivity toward the target analytes, is broadly recognized as a popular biosensor type for biomolecular/hazardous analysis [[5], [6], [7], [8]]. An attractive approach for achieving high selectivity and specificity of the electrochemical biosensors is to introduce bioreceptors (enzyme, antibody, DNA/RNA, organelle etc.) into the transducer surface of sensing device [[9], [10], [11]]. Nevertheless, owing to vulnerability to microenvironment, different degrees damage of enzyme activity and instability have become major hindrance for constructing highly sensitive biosensors, which largely restricts its application. It should be noted that the introduction of advanced nanomaterials could not only bring unique properties, including superior electrical conductivity, high electron transfer rate and surface hydrophilicity, but also make for exposing electroactive centers of biomolecules, thereby improving the sensing performances [12,13]. Therefore, the modification of advanced nanomaterials on the electrode interface is of crucial importance for establishing high-efficiency and sensitive electrochemical biosensing systems.

Graphdiyne (GDY), a unique allotrope of two-dimensional (2D) carbon nanomaterials, is constituted by 18-C hexagon units and benzene rings linked by butadiyne linkages [14,15]. In particularly, GDY possesses sp and sp2 hybridized carbon atoms [16], endowing it with a unique electronic structure as well as superior electrical conductivity, which are extremely beneficial to promote electron transfer and strengthen the catalytic effects [17,18]. Meanwhile, GDY and its derivatives present good stability and favorable biocompatibility in some in vivo researches [[19], [20], [21]], thus exhibiting advantageous biological properties in cancer therapy and biosensing. Additionally, several nonmetal atoms including nitrogen [[22], [23], [24]], chlorine [25], boron [26], phosphorus and sulphur [27], have been doped into GDY to improve their chemical/physical properties for certain applications. In comparation of GDY, the introduction of heterogeneous elements into GDY could generate numerous heteroatomic defects and active sites, displaying outstanding conductivity and enhanced electrochemical properties [[28], [29], [30], [31], [31][a], [31][b], [32]]. Moreover, introducing two or more kinds of heteroatoms into carbon materials will create a synergic effect, occurred within a certain distance among the co-dopants [33]. In consideration of the aforementioned advantages, multiple non-metallic elements co-doping GDY is anticipated to be an ideal electrode material to construct enzyme-based biosensors. However, it is rarely reported compared to the single element doping. Thus, it is very necessary to further probe into sensing functions of multiple non-metallic elements co-doping GDY.

Great attentions have been given to the hollow micro/nanostructured materials for their intriguing structural features, abundant beneficial physicochemical properties and great potentials in applications such as drug delivery [34], catalysis [35], sensing device [36], energy storage and conversion systems [37,38]. In particularly, the hollow structured materials as sensing materials could provide numerous electroactive sites and large specific surface area, thus improving the sensitivity of biosensors [39,40]. However, most of reported hollow structured materials for constructing sensing platform possess a single shell of one composition as well as relatively simple configurations, thereby limiting the application on sensors. To synthesize a hollow multishelled structure with complex composition is highly desirable for assembling an ultrasensitive biosensor. Metal-organic frameworks (MOFs) are considered as ideal templates for the preparation of novel hollow multishelled structures of transition metal oxides [41,42]. In view of the aforementioned advantages and considerations, the MOF-derived transition metal oxides with hollow multishelled structure are used to coordinate with GDY as promising sensing materials.

Herein, in this contribution, a highly-efficient synergistic signal amplification strategy based on the nitrogen-fluoride co-doped GDY (N–F-GDY) and NiCo₂O₄–Co₃O₄ hollow double-shelled nanocages were designed and applied for organophosphorus pesticides analysis by using acetylcholinesterase (AChE) as the bio-recognition element. N–F-GDY was first synthesized via a simple and controllable strategy. Due to the nitrogen and fluoride co-doping, the resulting N–F-GDY possessed a highly π-conjugated framework, large surface area with porous structure and excellent electronic conductivity. Meanwhile, NiCo₂O₄–Co₃O₄ hollow double-shelled nanocages were used for modification of the sensing platform, which dramatically enhances the interfacial stability and realizes the effective immobilization of enzyme. The possible mechanism of improving the electrochemical sensing performance was investigated and discussed in depth. The result manifests that the proposed biosensor delivers outstanding analytical performances including a low limit of detection, a wide linearity range, superior selectivity and sensitivity. This novel amplification strategy presented a highly effective approach for electrochemical pesticide assay, which could be extended to monitor other hazardous materials or biomarkers, and pave the way in the application of environmental monitoring and bioanalysis.