Applications of ratio fluorescence microscopy in the study of cell physiology

Quantitative fluorescence microscopy is becoming an increasingly important tool in the study of cell biology. Fluorescence microscopy has long been used for qualitative characterizations of subcellular distributions of proteins, lipids, nucleic acids, and ions, but quantifying these distributions is complicated by a variety of optical, biological, and physical factors. Many factors that complicate quantification of fluorescence in cells can be circumvented by analyzing fluorescence ratios derived from pairs of fluorescence images. In this review we will discuss the factors that affect fluorescence quantification, the advantages of quantifying fluorescence as a ratio, and give examples of how fluorescence ratio microscopy is being applied in studies of cell biology.