Pesticides, in particular organophosphorus (OP) pesticides, are widely used across the agricultural sector to protect crops and increase the yield of food production. However, many pesticides have raised concerns regarding safety and public health, with some chemicals even becoming banned.
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Now, an international team of scientists have a developed a nanocomposite composed of silver and graphene nanoribbons (GNRs) to detect methyl parathion residues (the most common type of OP pesticide) in various fruits and vegetables.
More than 70% of all pesticides used around the world are of the organophosphorus (OP) variety. Out of these, methyl parathion (MP) is the most widely used on agricultural crops to increase the food productivity.
However, it has arisen that lethal amounts of MP residues have been found in various foodstuffs and has raised a serious concern regarding food safety standards.
Due to the concerns of methyl parathion, new methods have been required for the quick and easy detection in food samples. Gas chromatography (GC), high performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS) have all been used in the past but are limited in their run times and availability.
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Other attempts have included biological detection methods using immunoassays and acetylcholine esterase, enzymatic sensing approaches, various composites using both organic and inorganic materials and electroanalytical sensors, all of which have not quite reached sensitivities and detection limits that would enable them to be used commercially.
The research team have now developed a nanocomposite composed of graphene nanoribbons (GNRs) and silver nanoparticles through simple wet-chemical techniques and modified it with a screen-printed electrode. GNRs are strips of graphene nanosheets with a confined width of less than 50 nm. The result was a sensor that can detect in MP in fruit and vegetable samples, namely in cabbage, green beans, strawberries and nectarines.
The researchers produced the nanocomposites by acidifying and reducing the GNRs, whilst simultaneously decorating the sheets with the silver nanoparticles. The researchers used scanning electron microscopy (SEM, Hitachi S-3000 H), transmission electron microscopy (TEM, Hitachi H-7600), energy dispersive X-ray spectroscopy (EDX, Horiba Emax x-act), X-ray diffraction (XRD, PANalytical B.V. XPERT-PRO), Raman spectroscopy, UV-visible spectroscopy and electrochemical impedance spectroscopy (EIS, Zahner EIM6ex) to characterise the nanocomposite and a CH Instruments (CHI 1205A) electrochemical work station was used to produce all of the electrochemical results.
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The combination of the silver nanoparticles and the GNRs produced a synergistic effect that allowed for a reduction in the overpotential that reduced the energy consumption, eliminated interferences and ultimately produced a high sensitivity.
From various tests, the sensor also shows characteristic behaviour of a surface-confined diffusion controlled electrocatalytic process.
The sensor showed excellent limits of detection (LOD) and sensitivities across all of the fruit and vegetable samples.
In cabbage samples the LOD and sensitivities were found to be 1.0 nM and 0.559 μAμM cm-2, respectively; for green beans, they were 2.0nM, and 0.569 μAμM cm-2, respectively; for strawberries they were 2.0 nM, and 0.611 μAμM cm-2, respectively; and for nectarine samples the values were 3.0 nM, and 0.683 μAμM cm-2, respectively. These were all produced with a very high response rate of 92-95%.
The sensor also possesses other excellent benefits including a high reproducibility, selectivity, stability, repeatability, fast response time and a low fabrication cost.
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The researchers have found that by combining the nanocomposite with the screen-printed electrode, they have produced a device with a high applicability for electroanalytical applications. The combination of the excellent properties and ease of fabrication has produced a device that will be useful in years to come in the agricultural and food industries as real-time food analysis tool.
Sources and Further Reading
- “Methyl parathion detection in vegetables and fruits using silver@graphene nanoribbons nanocomposite modified screen printed electrode”- Govindasamy M., et al, Scientific Reports, 2017, DOI: 10.1038/srep46471