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  • Küçük Resim
    Öğe
    A novel acetylcholinesterase inhibition based colorimetric biosensor for the detection of paraoxon ethyl using CUPRAC reagent as chromogenic oxidant
    (Elsevier B.V., 2024) Ayaz, Selen; Ulucay, Sude; Uzer, Ayşem; Dilgin, Yusuf; Apak, Reşat
    A novel colorimetric biosensor for the sensitive and selective detection of an organophosphate pesticide, paraoxon ethyl (POE), was developed based on its inhibitory effect on the acetylcholine esterase (AChE) enzyme. The bis-neocuproine copper (II) complex ([Cu(Nc)2]2+) known as the CUPRAC reagent, was used as a chromogenic oxidant in the AChE inhibition-based biosensors for the first time. 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 of [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 recovery results between 92% and 104% were obtained from water and soil samples spiked with POE, indicating that the determination of POE in real water and soil samples can be performed with this simple, accurate, sensitive, and low-cost colorimetric biosensor.
  • Küçük Resim
    Öğe
    Flow injection amperometric sensing of hydroxylamine at a Cu(ii)-neocuproine-functionalized multiwalled carbon nanotube/screen printed carbon electrode
    (Royal Society of Chemistry, 2021) Ayaz, Selen; Dilgin, Yusuf; Apak, Reşat
    This work describes a flow injection analysis (FIA) method for a sensitive, selective and fast detection of hydroxylamine (NH2OH) at a multiwalled carbon nanotube/screen-printed carbon electrode (MWCNT/SPCE) modified with an effective redox mediator of bis-neocuproine Cu(ii) complex ([(Cu(Ncp)(2)](2+)). To fabricate the modified electrode ([(Cu(Ncp)(2)](2+)/Nf-MWCNT/SPCE), negatively charged Nafion (Nf) molecules and [(Cu(Ncp)(2)](2+) complex were consecutively adsorbed onto MWCNT/SPCE through pi-pi stacking and electrostatic interactions, respectively. Cyclic voltammograms of the modified electrodes displayed an efficient redox pair, attributed to the reversible oxidation of Cu(i)-Ncp to Cu(ii) chelate complexes. Moreover, this redox couple showed superior electrocatalytic activity towards NH2OH oxidation compared to bare SCPE and Nf-MWCNT/SPCE due to the synergistic combination of MWCNT with the redox mediator. The FI amperometric current response towards electrocatalytic oxidation of NH2OH at +0.35 V vs. Ag/AgCl (0.10 M KCl) exhibited two linear dynamic concentration ranges between 0.25 and 100.0 mu M with a detection limit of 0.08 mu M (3 sigma) and between 100.0 and 3000.0 mu M. The FI amperometric sensor had high precision and stability, with RSD values of 2.7 and 4.8% (n = 3) for intra-day and inter-day repeatability, respectively. The developed method owes its high sensitivity and selectivity to the 2-e(-) oxidation of NH2OH to N2O catalyzed by [(Cu(Ncp)(2)](2+) as the redox mediator, with no side reactions, excellent electrode stability and low pH dependence, unlike other similar literature studies. The proposed electrode was also successfully used for the selective determination of NH2OH in two different real sample types (water and pharmaceutical samples) with satisfactory results.