Smartphones, paper enable low-cost optical detection to analyze pesticide concentrations

An international team of researchers has developed optically driven paper sensors that can be analyzed using an Android program on a smartphone, and could be used to detect pesticides rapidly and cheaply.

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As the role of pesticides in the decline of pollinator populations and their potential effect on health becomes clearer, it is increasingly important to be able to detect them in the environment and on foods. Usually, the equipment used to detect pesticides and other chemicals is large, expensive, and slow, making on-the-spot detection challenging.

Smaller detectors have been developed using paper as a sensor material, but they have not produced strong enough signals for detection. So the researchers at Hefei University of Technology (China) and the National University of Singapore developed a portable smartphone-based detection system using a paper sensor that produces strong signals that can detect the pesticide thiram. Prof. Yong Zhang, a lead author of the study from the National University of Singapore, thinks that the research team can develop their system further to detect many different molecules in a sample.

To make the detector, the researchers had to develop three components: nanoparticles to detect the pesticide and emit a fluorescent signal on the paper, a 3D-printed piece of equipment made of a smartphone attached to a mini-laser, an optical filter and a mini-cavity, and a piece of software that runs on Android. The nanoparticles—called upconversion nanocrystals—are decorated with copper ions and fixed onto the paper. A sample is then put on the paper, and pesticide molecules attach to the copper ions on the nanoparticles. The device shines a light onto the paper and, using the specially developed software, the smartphone reads the fluorescent light emitted from the nanoparticles. The fluorescent light differs according to the amount of pesticide present in the sample, so the software can translate that signal into a concentration of pesticide. The system gives a reliable and accurate detection reading at low concentrations of 0.1 µM.

Although tested on pesticide molecules, the research team’s system could be used to detect any molecule, including drugs, proteins, and antibodies. For medicine, where care is moving from hospitals to homes, small, cheap detection systems are vital.

The researchers are now developing kits that can detect different molecules. “We’re now making the system useful for real-world application,” Prof. Zhang says. “We’re planning to use the technology to detect multiple molecules at the same time—something called multiplex detection. In this way we could, for example, test the quality of the food we eat every day.”

Full details of the work appear in the journal Biosensors and Bioelectronics; for more information, please visit http://dx.doi.org/10.1016/j.bios.2015.08.054.

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