Dual-Signal Readout By Hybrid Nanoflowers for Point-of-Care Ultrasensitive Detection of Organophosphorus Pesticide
Authors: Jin Rui , Yan Xu , Sun Peng , Lu Geyu 
Published: May 2020

Introduction

At present precise tracking of pesticide has become very important for safeguarding the environment and food resources owing to their very high toxicity [1]. The development of sensitive and convenient sensors for the sensitive detection of pesticides is imperative to overcome practical limitations encountered in conventional methodologies, which require skilled manpower at the expense of high cost and low portability [2–3]. However, there are increasing bottlenecks in terms of poor stability caused by recognition unit and false positive result induced by single-modal readout, especially the bad performance in on spot monitoring. Herein, taking advantage of all-in-one enzyme-inorganic hybrid nanoflowers (ACC-HNFs) to fabricate high-performance artificial enzyme cascade system, we newly designed a ultrasensitive and affordable lab-on-paper device that incorporated disposable screen-printed carbon electrode (SPCE) and colorimetric test strips (Scheme 1), which brought about the dual-modal readout (electrochemical and colorimetric signal) for on-site monitoring of pesticide, achieving an “on-demand” tuning of the detection performance.

Method

Typically, 200 mmol L–
1 PBS (pH 8.0) contained AChE (1.0 U mL−1) and ChO (2.0 U mL−1) was added to deionized water, then 200 mmol L–
1 CuSO4 was added to the mixture, followed by incubation at 4.0 °C for 18 h. Finally, ACC-HNFs were obtained. ACC-HNFs modified paper was directly added into the detection zone. Then, ACh, TMB, and stop solution was added into different regions in sequence. After paraoxon was introduced into detection zone, region Ⅰ, Ⅱ, and Ⅲ of the detection zone was folded and the fold of each region was maintained for 30 min, then a discernible colorimetric signal was observed with naked eyes in the hollow region. Meanwhile, the entire paper was folded above the electrodes, and the generated electrons can be better connected to the working electrode through the hollow region. All electrochemical measurement processes were performed at room temperature and each measurement was performed in a new disposable SPCE. Before the analysis of the paraoxon, parameters, such as ACh concentration, ACC-HNFs concentration, and incubation time, were further optimized. Amperometric i-t curves were recorded at +100 mV during 30 s. The detection mechanism of this dual-modal biosensor is based on inhibiting the activity of AChE, thus the inhibition rate (I%) can be expressed as a linear relationship with the concentration of paraoxon. I% was analyzed by the following relation:
I% = (I no inhibitor – I inhibitor) / (I no inhibitor ) ×100%
Where I no inhibitor and I inhibitor represented the response of ACC-HNFs-TMB and ACC-HNFs-TMB-OPs system, respectively.

Results and Conclusions

Using paraoxon as a model analyte, the ACC-HNFs-based lab-on-paper platform could reach a limit of detection down to the picogram/mL level (0.06 pg mL−1), which is over 10-fold lower than that of conventional electrochemical assay. This proposed platform possesses the following advantages: (1) In the artificial enzyme cascade system, ACC-HNFs exhibited high catalytic activity by integrating nanozyme and natural enzyme, which remarkably amplified detection signal. (2) This approach integrates electrochemistry and colorimetric patterns into one system for “on-demand” detecting pesticide. The two groups of results can mutually authenticate, which can effectively avoid false positive and negative detection. (3) This portable lab-on-paper device dispenses with complex sample pretreatment or sophisticated instruments, which makes it suitable for on-site monitoring. We anticipated that the meticulous design of ACC-HNFs provided a versatile approach for constructing artificial enzyme as a recognizer and amplifier to fill the gap in constructing robust artificial enzyme systems, making it practically functional for on-site applications in the contamination monitoring and biological diagnosis, just through changing the building blocks.

References

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[2] E. Cequier, A. K. Sakhi, L. S. Haug, C. Thomsen, Development of an ion-pair liquid chromatography–high resolution mass spectrometry method for determination of organophosphate pesticide metabolites in large-scale biomonitoring studies. J. Chromatogr. A. 1454 (2016) 32–41, doi: https://doi.org/10.1016/j.chroma.2016.05.067.
[3] F. Zhao, J. Wu, Y. Ying, Y. She, J. Wang, J. Ping, Carbon nanomaterial–enabled pesticide biosensors: Design strategy,biosensing mechanism, and practical application. TrAC-Trend. Anal. Chem. 106 (2018) 62–83, doi: https://doi.org/10.1016/j.trac.2018.06.017.

Figure 1