Easy-to-Use Sensors for Field Monitoring of Copper Contamination in Water and Pesticide-Sprayed Plants.

Copper (Cu)-containing pesticides are commonly used in agriculture to control fungal and bacterial diseases, but the release of large quantities of Cu in water and soil can lead to harmful long-term consequences on the environment, organisms, and ecosystem health. Technology available to measure Cu accumulation in the field is too expensive and complicated for general population use. We describe a low-cost sensor with simplified user operation for measuring Cu content in environmental and agricultural samples at sensitivity levels comparable with a laboratory-based atomic absorption spectroscopy (AAS) method. The sensor is based on polyethyeleneimine (PEI), which has a strong chelating ability for Cu ions. The PEI is stabilized on paper by layer-by-layer assembly with the PEI deposited sequentially within electrostatically charged poly(styrenesulfonate) (PSS). The PEI-PSS layers develop a vivid blue complex when interacting with Cu, and the resulting color intensity varies with the Cu concentration. Our sensors give a yes or no response with the naked eye down to 10 μM when a preconcentration step was used. A more precise quantitative response can be obtained using a smartphone or scanner and free imaging software within a wide linear range from 10 to 2000 μM with a detection limit of 0.795 μM. The sensors were used for detecting commercial Cu-based pesticides in water and pesticide-sprayed plants within 15 min. Considering that these sensors are robust, simple to operate, and extremely stable, they could be ideal for remote monitoring of Cu ion exposure and for the analysis of Cu in environmental water and agricultural fields.