Image digitization colorimetric detection of acephate based on acephatethiolated acephate binding aptamer-gold nanoparticle complex

For years, organophosphates (OPs) compounds are used for pest control in agriculture. However, uncontrolled usage of OPs causes genotoxic, teratogenic as well as other environmental and ecological adverse impacts. The detection of OPs using conventional methods gives good results but existed with several limitations such as bulky, time-consuming analysis and expensive. A colorimetric detection method receives an attention as it can be modified to overcome these limitations due to its simplicity. In this study, colorimetric detection of Ac was conducted by surface functionalisation of gold nanoparticles with thiolated acephate binding aptamer (TABA). Preparation of gold nanoparticles (AuNPs) was conducted using two heating techniques. Preparation of AuNPs using microwave radiation technique resulted in smaller particles size (of 10 + 3nm) compared to that of the conventional heating technique (of 16 + 4nm). Ultra-violet visible (UV-Vis) analysis showed the existent of surface plasmon resonance phenomenon for both prepared AuNPs whereas Fourier transformed infra-red spectrometer (FTIR) analysis suggested there was a physical interaction at the surface of AuNPs. Study on the effect of AuNPs to Ac mole concentration ratio revealed that the best ratio for the detection was 1:35. In addition, better detection of Ac was also achieved using smaller particles size AuNPs. Assessments of the distinct colour change (from red to dark purple) of the complex were carried out by comparing the value of red fragment of the digitized images. Analyses of high-resolution transmission electron microscope (HRTEM), UV-Vis and FTIR spectroscopy confirmed that aggregation of particles complex occurred. A study on the effect of ions on TABA towards the detection of Ac revealed that detection capability towards Ac was enhanced with the introduction of Mg2+. Optimised sensor parameters obtained from central composite design response surface methodology (CCD-RSM) were validated and good lowest limit of detection which was 11 ppb, was achieved. In addition, selectivity and reproducibility of the optimized method for the real sample analysis was good. Based on the results of this study, it can be concluded that the proposed image digitization colorimetric detection method produced a rapid, sensitive, and selective detection towards Ac.