Importance of control experiments in toxicity test of metal-organic frameworks: Recent advances and challenges

The commercial application of metal-organic frameworks (MOFs) in gas separation, catalysis, sensing, energy conversion, and storage inevitably leads to the release of MOFs into the environment, posing a great threat to the eco-environment. The toxic risk assessment of MOFs is necessary to achieve their sustainable applications. Reproducible and accurate measurement in toxicity assays is the first step in the risk evaluation of MOFs. However, a broad range of artifacts may occur in previous toxicity tests of MOFs due to diverse interferences. Therefore, control experiments are needed to discriminate such interferences and to revise the experimental protocol for the reduction and elimination of the artifacts. Herein, we present a review of the artifacts and control experiments in toxicity assays of MOFs in terms of MOF preparation, toxicity test, labeling and tracking, and co-exposure test. We also discuss the differences in the results of the toxicity test with and without a control experiment to illustrate the impact of the control experiment on the conclusion. We highlight the importance of a control experiment to reduce false negative or false positive results and to guarantee accurate toxicity data in the toxicity study of MOFs, which could advance the ecological risk assessment of MOFs as well as the safe-to-sustainable design of MOFs in tackling various challenges of future applications.