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. 2022 Apr 2;22(7):2754.
doi: 10.3390/s22072754.

An Aptasensor Based on a Flexible Screen-Printed Silver Electrode for the Rapid Detection of Chlorpyrifos

A K M Sarwar Inam  1   2 , Martina Aurora Costa Angeli  1 , Ali Douaki  1 , Bajramshahe Shkodra  1 , Paolo Lugli  1 , Luisa Petti  1
Affiliations

An Aptasensor Based on a Flexible Screen-Printed Silver Electrode for the Rapid Detection of Chlorpyrifos

A K M Sarwar Inam et al. Sensors (Basel). .

Abstract

In this work, we propose a novel disposable flexible and screen-printed electrochemical aptamer-based sensor (aptasensor) for the rapid detection of chlorpyrifos (CPF). To optimize the process, various characterization procedures were employed, including Fourier transform infrared spectroscopy (FT-IR), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). Initially, the aptasensor was optimized in terms of electrolyte pH, aptamer concentration, and incubation time for chlorpyrifos. Under optimal conditions, the aptasensor showed a wide linear range from 1 to 105 ng/mL with a calculated limit of detection as low as 0.097 ng/mL and sensitivity of 600.9 µA/ng. Additionally, the selectivity of the aptasensor was assessed by identifying any interference from other pesticides, which were found to be negligible (with a maximum standard deviation of 0.31 mA). Further, the stability of the sample was assessed over time, where the reported device showed high stability over a period of two weeks at 4 °C. As the last step, the ability of the aptasensor to detect chlorpyrifos in actual samples was evaluated by testing it on banana and grape extracts. As a result, the device demonstrated sufficient recovery rates, which indicate that it can find application in the food industry.

Keywords: aptasensor; chlorpyrifos; electrochemical sensor; flexible substrate; organophosphorus pesticide; screen-printed sensor.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
The step-by-step fabrication process and working mechanism of the printed aptasensor for chlorpyrifos detection. The sensor is made of a three-electrode system: working electrode (WE), counter electrode (CE), and reference electrode (RE). (A) Bare working Ag electrode (WE), (B) 11-MUA attached to the WE with thiol bond, (C) EDC/NHS immobilization with 11-MUA, (D) covalent bonding between the amine group of aptamers with the carboxylic group of 11-MUA, (E) BSA immobilized on top of the electrode to eliminate non-specific binding, and (F) CPF attached with aptamer.
Figure 2
Figure 2
FT-IR spectra during step-by-step fabrication process of the aptasensor. Spectra of (a) Ag electrode, (b) 11MUA-Ag electrode, (c) EDC/NHS-11MUA-Ag electrode, (d) Aptamer-EDC/NHS-11MUA-Ag electrode, (e) BSA- Aptamer-EDC/NHS-11MUA-Ag electrode, and (f) Sensor after electrochemical measurements.
Figure 3
Figure 3
CV (A) and EIS (B) during the step-by-step fabrication process of the aptasensor. (a) Ag electrode, (b) 11MUA-Ag electrode, (c) EDC/NHS-11MUA-Ag electrode, (d) Aptamer-EDC/NHS-11MUA-Ag electrode, and (e) BSA-Aptamer-EDC/NHS-11MUA-Ag electrode. Here, 0.01 M PBS containing 5.0 mM [Fe(CN)6]3−/4− and 0.1 M KCl was used as an electrolyte, and screen-printed Ag/AgCl was used as the RE.
Figure 4
Figure 4
CV analysis without the presence of CPF (blank solution containing 0.01 M PBS) (blue) and with the presence of 100 ng/mL CPF in 0.01 M PBS solution (red). Screen-printed Ag/AgCl was used as the RE.
Figure 5
Figure 5
(A) Optimization of pH of PBS for the aptasensor characterization. The reduction peak current (absolute value) obtained from the aptasensor through CV at different pH of PBS (6, 6.5, 7, 7.5, and 8). (B) Optimization of aptamer concentration for the aptasensor characterization. The reduction peak current (absolute value) obtained from the aptasensor through the CV with different aptamer concentrations (0.25, 0.5, 1, 1.5, and 2 µM). (C) Optimization of CPF incubation time for the aptasensor characterization. The reduction peak current (absolute value) obtained from the aptasensor through CV achieved by different incubation times (5, 10, 20, 30, 40, 50, and 60 min) of CPF.
Figure 6
Figure 6
(A) CV at different concentrations of CPF (0, 100, 101, 102, 103, 104, 105 ng/mL) in 0.01 M PBS. (B) Calibration plot of aptasensor for CPF detection, where the highest reduction peak current is shown in absolute value versus CPF concentration. Here, 1 µM of aptamer was used as previously optimized, and the optimized incubation time of CPF was set as 40 min. The average reduction peak current was obtained from three sensors where SD with error bar is shown.
Figure 7
Figure 7
Selectivity test of aptasensor where the average reduction peak current (absolute value) of different pesticides (carbofuran, dichlorvos, malathion, deltamethrin, metamitron, chlorpyrifos, and mixture of all) were obtained through the CV.
Figure 8
Figure 8
Stability over time for the aptasensor until 1 month. Here, the average reduction peak current shown in the absolute value of the aptasensor through CV was obtained every week.
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