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

Copper (Cu2+)-containing pesticides are commonly used in agriculture to control fungal and bacterial diseases, but the release of large quantities of Cu2+ in water and soil can lead to harmful long-term consequences on the environment, organisms, and ecosystem health. Technology available to measure Cu2+ 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 Cu2+ 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 Cu2+ 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 Cu2+, and the resulting color intensity varies with the Cu2+ 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 Cu2+-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 Cu2+ ion exposure and for the analysis of Cu2+ in environmental water and agricultural fields.