Nanoarchitectonics of Metal-Coordinated Schiff Base Materials for Environmental and Biological Sensing

Metal-coordinated Schiff base materials, including complexes, polymers and nanoparticles, have been studied for their use as highly sensitive and selective sensors. These sensors generally utilize two main signal transduction methodologies: optical or electrochemical. Optical sensors can either produce fluorescence or alter absorbance properties, causing colour changes, via a number of intra- or intermolecular processes, including photoinduced electron transfer (PET), chelation-enhanced fluorescence (CHEF), intramolecular charge transfer (ICT), aggregation-induced emission (AIE), ligand–metal charge transfer (LMCT), excited-state intramolecular electron transfer (ESIPT), transmetalation and inner filter effects. Electrochemical sensors rely on detection of changes in potential, voltage, or current caused by binding to the Schiff base complexes. This review will discuss recent progress, primarily over the past five years, in the design of Schiff base complex sensors and some examples of their potential applications in environmental sensing for food, water, and soil, as well as their use in biological sensing and bioimaging.