Chapter 7: Ratiometric Fluorescent Chemosensors: Photophysical/Chemical Mechanism Principles and Design Strategies

Fluorescent techniques have attracted significant attention in bioimaging, analyte sensing, and disease diagnosis in recent years. Conventional fluorescent chemosensors provide significant advantages in monitoring/detecting different analytes; however, physiological or experimental factors may influence the single-targeted fluorophore absolute intensity-dependent signal acquisition, which can be cause misleading and strong non-specific background signals in molecular sensing and imaging applications. The simple alternative to minimize these non-specific effects is a ratiometric measurement strategy. This is a self-calibration method for recording two or more analyte-induced signals, in which one signal is a reference factor to normalize other signals. Due to its self-calibrating internal standard system obtained from the ratio between two or more emission bands, ratiometric approaches have become the most effective fluorescence method for quantitative analysis measurements, compensating for a number of analyte-independent parameters and eliminating most ambiguities that may affect the fluorescence signal. In particular, by taking advantage of various photophysical/chemical sensing theories, ratiometric fluorophores successfully endow structural design for detection of biologically/environmentally important analytes. This chapter will highlight the basic principles and design strategies of ratiometric fluorescent chemosensors, including photophysical/chemical sensing mechanisms based on different molecular types (i.e., small molecules and nanoparticles) with appropriate examples.