Recent advances in the design of colorimetric sensors for environmental monitoring

Colorimetric sensors and biosensors exhibit promising potential toward the detection of metallic cations, anions, organic dyes, drugs, pesticides and other toxic pollutants due to their easy fabrication, quick detection, and high sensitivity and selectivity, as well as easy naked-eye sensing. In this work, we present the recent advances (since 2014) made in the fabrication of colorimetric sensors for the environmental monitoring of toxic pollutants. To understand the relationships between the type, structure, and functions of nanomaterials as building units and the sensing performance of the designed colorimetric sensors, the fabrication of several sensor platforms based on functional nanomaterials (such as metal nanoparticles, metal oxides, quantum dots, two-dimensional nanozymes, organic probes, and Schiff bases) are demonstrated and discussed. The sensing mechanisms of the considered colorimetric sensors based on the aggregation of nanoparticles, decomposition of nanoparticles, nanozymes, fluorescence on-off, ligand-receptor interactions, and photonic structures are introduced and discussed in detail. In addition, instrument-based colorimetric sensors and advanced colorimetric sensor products for high-performance environmental monitoring are presented. Finally, the advantages and disadvantages of various colorimetric sensors in environmental monitoring are analyzed and compared. It is expected that this work will be valuable for readers to understand the fabrication and sensing mechanisms of various colorimetric biosensors and promote their development in environmental science, materials science, nanotechnology, food science, and bioanalysis.