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

Abstract

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.