Abstract
Acephate (Ac), an organophosphate (OP) insecticide, is very harmful to human and the environment. Conventional techniques of detection are sensitive and selective but relatively time-consuming, expensive, and require trained personnel. This paper describes the use of an image processing technique to digitize the red values (RVs) of the colour image of Ac-capped gold nanoparticles (Ac-Cit-AuNPs) complex captured using a digital microscope to improve the detection accuracy and precision. The formation of the suspension was characterised using laser test, ultraviolet-visible spectrophotometer (UV-Vis), high-resolution transmission electron microscope (HRTEM), and Fourier Transform infrared spectroscope (FTIR). The linear regression analysis revealed that the detection sensitivity improved as the smaller gold nanoparticles were used. For quantitative measurement using image processing, a good linear relationship (R2 = 0.9905 and 0.9924) for Cit-HAuNPs and Cit-MAuNPs, respectively, between the concentration of Ac and average red values was obtained in the range of 0–8 mM. The limit of detection (LOD) for Ac was found to be 0.3 mM and 0.4 mM for Cit-MAuNPs and Cit-HAuNPs, respectively.
Highlights
Conventional techniques that are commonly used for the detection of organophosphates (OPs) include high-performance liquid chromatography (HPLC) [1], mass spectrometry [2,3,4], enzyme-linked immunosorbent assay (ELISA) [5], nanoparticle colour complex formation [6], and biosensors based on inhibition of cholinesterase activity [7, 8]. ese methods provided a high selectivity of the detection, but they are relatively time-consuming, expensive, and require trained personnel [2, 9, 10]. erefore, discovery of a simple, rapid, and less expensive but reliable, sensitive and selective method for the analysis of OPs, especially for onsite detections, is desirable, especially for quick data gathering in OPs poisoning management
Interaction of OPs and citrate ion-gold nanoparticle(Cit-AuNP-) based colorimetric assays are very attractive for rapid detection due to the ease of procedures and visualization of results [11, 12]. e colour change of red CitAuNPs suspension to steel-purple complex upon aggregation of the particles has been used as the basis of the colorimetric OPs sensing [13]
Previous study has reported that there are several steps involved in the formation of Cit-AuNPs [30]. e formation of Cit-AuNPs was indicated by the formation of a diamond red suspension [31,32,33] and confirmed by a laser test whereby surface plasmon resonance (SPR) phenomenon was observed as shown by the appearance of a laser beam through the suspension (Figures 2(a) and 2(b)) [34]. e SPR phenomenon arose from collective oscillation of the conduction band of electron in Cit-AuNPs [35]
Summary
Conventional techniques that are commonly used for the detection of organophosphates (OPs) include high-performance liquid chromatography (HPLC) [1], mass spectrometry [2,3,4], enzyme-linked immunosorbent assay (ELISA) [5], nanoparticle colour complex formation [6], and biosensors based on inhibition of cholinesterase activity [7, 8]. ese methods provided a high selectivity of the detection, but they are relatively time-consuming, expensive, and require trained personnel [2, 9, 10]. erefore, discovery of a simple, rapid, and less expensive but reliable, sensitive and selective method for the analysis of OPs, especially for onsite detections, is desirable, especially for quick data gathering in OPs poisoning management. Conventional techniques that are commonly used for the detection of organophosphates (OPs) include high-performance liquid chromatography (HPLC) [1], mass spectrometry [2,3,4], enzyme-linked immunosorbent assay (ELISA) [5], nanoparticle colour complex formation [6], and biosensors based on inhibition of cholinesterase activity [7, 8]. Citrate-capped gold nanoparticles (Cit-AuNPs) are widely used materials in colorimetric detection methods because of the colour stability, excellent biocompatibility, and convenience for surface functionalization. E detection was based on the colour change produced from the reaction of Ac and Cit-AuNPs that results distinct colour change from diamond red to dark purple for Ac-Cit-AuNPs complex. To improve its accuracy and precision, the colours of the solutions were photographed and digitised using ImageJ software to obtain their red values (RVs)
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