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Abstract

Food, water, and sleep form the foundation of human needs, all of which are indispensable. However, unlike sleep, food and water have historically been beyond direct human control. Since ancient times, hunter-gatherers have migrated in search of these essential resources. The advent of agriculture marked a turning point, allowing humans to settle in one place, solving the challenge of food acquisition but introducing new problems. Food preservation and protection from pests became critical issues, and despite over 12,000 years of progress, some challenges still remain. While refrigeration and pesticides have significantly mitigated these challenges, food spoilage persists, and pesticide residues continue to contaminate our food. In this context, sensors present a promising solution, enabling real-time monitoring of food spoilage and pesticide contamination.
In this work, we developed two fluorescent probes for the detection of the pesticides chlorpyrifos and dimethoate, as well as a sensor for ammonia, a common byproduct of food spoilage. The first probe leverages a naturally occurring phenomenon, the hydrolysis of organophosphates pesticides. By accelerating this reaction using concentrated NaOH, we detected the hydrolysis byproduct rather than the pesticide itself. While organophosphates are relatively unreactive, their breakdown products are much easier to identify. Specifically, we employed a coumarin-based dye to detect methylamine, achieving a detection limit of 3.2 μg/L, well below globally established regulatory limits in USA, China, Brazil, Russia and India. The probe was also tested in green tea, yielding a recovery rate of 95.4%.
The second probe was inspired by medical applications, where oximes are commonly used as antidotes for OP poisoning. We selected a fluorescent dye featuring an oxime functional group, which, when deprotonated, acts as a potent nucleophile. Since the oxime in water would compete with hydroxide ions (necessary for the oxime activation) for the pesticide, we employed a non-nucleophilic phosphazene base, P4, to facilitate the reaction. This approach enabled the detection of chlorpyrifos at concentrations as low as 15.5 μg/L, a value below regulatory limits in several countries (India, China, Brazil and Russia). The method was further validated using a tap-water extracted matrix.
Additionally, we developed a sensor based on reduced graphene oxide for ammonia detection. Reduction of graphene oxide was achieved using low-pressure H2 plasma, and we systematically investigated the effect of reduction time on sensor performance. Our findings revealed a transition from chemisorption-dominated to physisorption-driven sensing with prolonged reduction times. The optimal sensor, obtained after 20 seconds of plasma treatment, exhibited the highest sensitivity (relative resistance change), reaching 23.9% at 100 ppm and 47.1% at 1049 ppm, while maintaining good reversibility. Furthermore, tests conducted in ambient air confirmed the sensor’s reliability.
This work demonstrates the potential of fluorescence-based probes and graphene-based sensors in addressing food safety challenges, providing innovative approaches for pesticide detection and spoilage monitoring.