Visual and Real-Time Monitoring of Cd2+ in Water, Rice, and Rice Soil with Test Paper Based on [2 + 2] Lanthanide Clusters

Cadmium ions (Cd2+) are highly toxic to animal and human health, especially through the drinking of Cd2+-contaminated water and eating Cd2+-contaminated rice. Therefore, accurate detection of Cd2+ in water, rice, and rice soil is urgent. In this work, two [2 + 2] lanthanide clusters of Tb2Tb2 and Eu2Eu2 were synthesized and characterized in detail. Interestingly, Tb2Tb2 is a rapid sensor for Cd2+ through luminescence "turn-off". Further studies show that Tb2Tb2 is a highly sensitive and selective sensor toward Cd2+ in water, rice supernatants, and rice soil supernatants, with a very short response time of 20 s. The limit of detection (LOD) in the above three real samples is as low as 0.0112, 1.1240, and 0.1124 ppb, respectively, which is lower than the national standards for food safety in China (GB 2762-2022). More interestingly, a portable sensing device of test paper based on Tb2Tb2 is developed with a facile method, which shows visible, highly sensitive, and selective sensing toward Cd2+ in real samples of water, rice supernatants, and rice soil supernatants. Tb2Tb2 and its sensing device of test paper are an on-site analysis sensor for potentially non-expert users, especially for people in remote rural areas.