Electrochemical aptasensor based polypyrrole-iron oxyhydroxide nanocomposite for detection of dimethyl methylphosphonate (DMMP)

Chemical warfare agents (CWAs) such as nerve agents, blister agents, blood agents and incapacitating agents were used by various military and terrorist groups in several conflicts in previous decades, prompting the need to construct and improve existing sensor systems for detecting these compounds. Many methods have been used to detect these substances, including traditional methods involving large instruments (gas chromatography, liquid chromatography and ion mobility spectrometry). Since more human resources are required to handle the equipment and it is heavy to move around the place, these procedures come at a high cost. Furthermore, there is a biosensor that can give on-site detection that is rapid, portable, low-cost and selective. However, due to the obvious extreme toxicity of CWAs, dimethyl methylphosphonate (DMMP) has been used to simulate their effects due to their almost identical molecular structures. The present biosensors, on the other hand, only use sensing materials that are either sensitive or selective to DMMP. In an electrochemical sensor, there are no sensing materials that combine the traits of being very sensitive and selective towards DMMP. This work was carried out in order to build and improve the existing biosensor for detecting DMMP. The polypyrrole nanoparticles (PPy NPs) and polypyrroleiron oxyhydroxide (PFFs) nanocomposite were successfully synthesised using a chemical oxidative polymerization method with two different sonication periods (one and three hours). One-hour sonication produced finer nanoparticles than three hours of sonication. The enlargement of the sharp peak of NH stretching at 3217 cm-1 confirmed the polymerisation of the pyrrole monomer, whereas the disappearance of the N-H band and the appearance of a new OH sharp band at roughly 3500 cm-1 indicated the interaction between iron oxyhydroxide (FeOOH) and PPy NPs. FESEM pictures demonstrated that the 5 wt% FeOOH nanocomposites had iron metals that were well distributed in the PPy NPs, as opposed to the 10 wt % FeOOH nanocomposites, which displayed particle aggregation. The obtained PPy NPs and PFFs nanocomposite sizes were between 50 and 70 nm and 110 and 160 nm, according to TEM examination. Using cyclic voltammetry, the best sensing materials for the electrochemical inquiry were found to be one hour sonication of PPy NPs (36%) and 5 wt% PFFs (22%) nanocomposites (CV). The successful synthesised PPy NPs and PFFs nanocomposite as sensing materials were determined as the initial objective. The aptasensor made from PPy NPs and PFFs are optimised under two conditions: aptamer concentration and incubation times. 1 µM of aptamer incubated for 1 hour is optimal for the PPy NPs aptasensor, while 5 µM of aptamer incubated for the same 1-hour time is optimal for the PFFs aptasensor. Newly developed electrochemical sensors based on aptamer functionalized PPy NPs and PFFs were also evaluated for sensitivity and selectivity. The PPy NPs sensor has a higher sensitivity of LOD 3.576 ppm than the PFFs nanocomposites sensor LOD of 5.802 ppm. The finer the particles, the greater the sensor's electron transfers, resulting in a rise in peak current. Furthermore, when other analytes (methanol, DCM, acetonitrile, and hexane) were present, the presence of aptamer integration of PPy NPs and PFFs nanocomposites sensors improved the sensor's selectivity towards the target analyte DMMP.