Speaker
Description
Organophosphorus pesticides (OPs) are the most commonly used chemicals in today's agriculture to protect fruit and vegetable crops from pests because they have relatively low persistence in nature and show high activity against insects [1]. However, OPs are known to be toxic and pose serious threats to human health, the environment, and aquatic life, even when contamination is at very low residual concentrations in agricultural products and water. Therefore, many analytical methods have been used to determine pesticide residues in various samples with different matrices. Among the developed pesticide determination approaches, colorimetric methods have recently attracted increasing interest because of their superior properties such as low cost, simplicity, facileness, practicality, naked-eye visualization, miniaturization, and needlessness for complex instruments, and highly trained personnel [2]. One of the chromogenic agents commonly used in colorimetric sensors is the copper(II)-bis- neocuproine complex known as the CUPRAC reagent, first developed by Apak et al. in 2004 to be used in total antioxidant capacity determination [3]. Then, a great many optical sensor studies were carried out using the CUPRAC reagent. [4-6]. However, according to our literature review, a paraoxon ethyl (POE) biosensor using the CUPRAC reagent based on acetylcholine esterase (AcHE) inhibition has not yet been reported. Therefore, both the integration of the CUPRAC reagent with the AcHE enzyme and the implementation of the pesticide biosensor depending on this beneficial chromogenic oxidant for the first time provide an important novelty to this study. To initiate the biosensor, an enzymatic reaction takes place between AcHE and its substrate, acetylthiocholine (ATCh). Then, enzymatically produced thiocholine (TCh) reacts with the light blue [Cu(Nc)2]2+ complex, resulting in the oxidation of TCh to its disulfide form. On the other hand, [Cu(Nc)2]2+ reduces to a yellow-orange cuprous complex ([Cu(Nc)2]+ ) which gives maximum absorbance at 450 nm. However, the absorbance due to [Cu(Nc)2]+ proportionally decreased with the addition of POE because the inhibition of AChE by the organophosphate pesticide reduced the amount of TCh that would give a colorimetric reaction with the CUPRAC reagent. Based on this strategy, the linear response range of a colorimetric biosensor was found to be between 0.15 and 1.25 µM with a detection limit of 0.045 µM. The fabricated biosensor enabled the selective determination of POE in the presence of some other pesticides and metal ions. The acceptable recovery results were obtained from water samples spiked with POE, indicating that the determination of POE in real water samples can be performed with this simple, accurate, sensitive, and low-cost colorimetric biosensor.
Keywords: Acetylcholine esterase; Paraoxon ethyl; Enzyme inhibition; Colorimetric biosensor; CUPRAC reagent.
Acknowledgment
The authors thank the Scientific and Technological Research Council of TURKEY (TÜBİTAK) for financial support (Project number: 120Z963). This study has also been produced from a part of the Ph.D. thesis of Selen Ayaz, carried out under the supervision of Prof. Dr. Yusuf Dilgin and Prof. Dr. Reşat Apak.
References
[1] L. Guo, Z. Li, H. Chen, Y. Wu, L. Chen, Z. Song, T. Lin, Anal. Chim. Acta 967 (2017) 59-63.
[2] D. Liu, B. Xu, C. Dong, TrAC, Trends Anal. Chem. 142 (2021) 116320.
[3] R. Apak, K. Güçlü, M. Özyürek, S. E. Karademir, J. Agric. Food Chem. 2004, 52, 26, 7970–7981.
[4] A.N. Avan, S. Demirci-Çekiç, R. Apak, ACS Omega 7 (2022) 44372–44382.
[5] A. Avan, Ö. Karakaş, S. Demirci-Çekiç, R. Apak, Enzyme Microb. Technol. 162 (2023) 110137
