DOI: https://doi.org/10.55373/mjchem.v24i3.1

Keywords: Colorimetric; DNA aptamer; gold nanoparticles; methylphosphonic acid; RGB

Abstract

Methylphoshonic acid (MPA) is a metabolite of several organophosphorus (OP) nerve agents. The aim of this study was to optimise MPA detection by gold nanoparticles capped with DNA aptamer-citrate using a centred central composite design response surface methodology. The independent variables investigated included the concentration of citrate-capped gold nanoparticles (cit-AuNPs) (A), concentration of DNA aptamer (D), and the incubation period (P) for binding the cit-AuNPs to the DNA aptamer. Analysis of variance (ANOVA) was used to determine the significance of the variables and the interactions between them. A second-order polynomial model was developed to predict the detection response (∆RGB value). The results demonstrated that A, D, P, A2, D2, P2, AP, and DP were factors that significantly affected ∆RGB values at a 95% confidence level. Good correlations between the experimental and predicted values were supported by the high F-value (721.09), very low p-value (<0.0001), non-significant lack of fit, and a high coefficient of determination (R2 = 0.9944). The optimum concentration of cit-AuNPs, concentration of DNA aptamer, and incubation period for binding cit-AuNPs to the DNA aptamer were found to be 0.34 nM, 3.9 µM, and 18 min, respectively. A practical application of this sensor is as an environmental monitoring tool for on-site detection of MPA.