Abstract
Introduction
Amoxicillin (AMO) is the most consumed of the aminopenicillins. It is not regularly detected in water in-line for the lack of a standardized, sensitive and selective monitoring system that meets required limits. However, wastewater treatment plants cannot remove all antibiotics and thus release them into the environment, either without modification, or as metabolites [1]. This among others increases the risk of introducing antibiotic resistance, thus posing a serious threat to public health. Analytical method have been used as the detection techniques include mass spectrometry, chromatography or their combination. However, they suffer from some limitations mainly relating to sample preparation and stability [2]. Hence, it is necessary to design sensors for straightforward screening measurements. For this purpose, molecular imprinting is a technique to design robust receptor materials for any given analyte, thus mimicking natural recognition. The reusability of imprinted materials has a crucial role in developing applications that are reliable, economical and sustainable [3].
Experimental
To synthesize MIP thin films against AMO, we utilized methacrylic acid (MAA) as the functional monomer, and ethylene glycol dimethacrylate (EGDMA) as the cross-linker and thermally pre-polymerized them at 60 °C for 30 minutes. Then, we deposited them on quartz crystal microbalance (QCM) electrodes by spin coating and hardened overnight. The non-imprinted (NIP) sample was prepared in the same manner without template. QCM measurements served to characterize AMO MIP films according to their sensitivity and selectivity, respectively.
Results and Conclusion
Figure 1 shows the results of sensitivity assessment at three different AMO concentrations. It clearly reveals concentration-dependent sensor signals of the system. Evidently, the MIP yield substantially higher frequency shifts at all concentrations than the corresponding NIP. For instance, at 1000ppm AMO concentration the MIP exhibits a frequency shift of -540 Hz while NIP signal reaches only around -90 Hz. Thus, frequency shifts on MIP-coated electrodes against NIP-coated ones reveals more than five times higher sensitivity, which is strongly indicative of successful imprinting and thus the incorporation of AMO molecules into recognition sites. Additionally, sensor signals are fully reversible and reproducible.
Furthermore, selectivity is a key issue for any sensor: Figure 2 shows the outcome of selectivity studies toward PenicillinV (PenV) and PenicillinG (PenG), which demonstrate selectivity factors of around 1.3 each. This is even more remarkable given how similar the molecular structures of those three compounds are: they differ by an amino-group and hydroxyl-group; howover the core-structures are totally identical. Finally, sensor characteristics reveal limit of detection at 15ppm.
Acknowledgement
Authors gratefully acknowledge funding of this work by the Austrian Research Promotion Agency (FFG) through project AquaNOSE (Grant agreement no. 864893).
References
[1] A.G.Ayankojo, J.Reut, A.Öpik, A.Furchner, V.Syritski, Hybrid molecularly imprinted polymer for amoxicillin detection, Biosensors and Bioelectronics 118 (2018) 102–107. doi:10.1016/j.bios.2018.07.042.
[2] P.T.Phuong-Hoa, S.Managaki, N.Nakada, H.Takada, A.Shimizu, D.Hong-Anh, P. Hung-Viet, S.Suzuki, Antibiotic contamination and occurrence of antibiotic-resistant bacteria in aquatic environments of northern Vietnam, Science of The Total Environment 409 (2011) 2894-2901. doi:10.1016/j.scitotenv.2011.04.030.
[3] W.Cuypers, P.A.Lieberzeit, Combining Two Selection Principles: Sensor Arrays Based on Both Biomimetic Recognition and Chemometrics, Frontiers in Chemistry 6 (2018) 268-278. doi:10.3389/fchem.2018.00268.
Figure 1