Fluorescent Environment-Sensitive Dyes as Reporters of Biomolecular Interactions - Progress in Molecular Biology and Translational Science - page 36

3-hydroxychromone family that undergo excited-state intramolecular proton transfer
and show solvent-sensitive dual emission. Examples of existing solvatochromic dyes
and their biosensing applications are given, with particular focus on the
3-hydroxychromones. It is shown that solvatochromic dyes are powerful tools for mon-
itoring conformation changes of proteins and their interactions with nucleic acids, pro-
teins, and lipid membranes.
1. INTRODUCTION
Monitoring biomolecular interactions is a fundamental issue in
biosensing, with numerous applications ranging from basic biological
research to clinical diagnostics. Fluorescence techniques are particularly well
suited for this purpose. 1,2 The most established one is the F ¨ rster resonance
energy transfer (FRET)-based approach, where interacting partners are
labeled with donor and acceptor molecules. 3,4 The interaction event results
in an energy transfer between the proximal donor and acceptor, providing
the analytical signal. Though the approach is robust, it requires double
labeling, which is complicated and cannot be realized in many screening
assays. Therefore, single fluorescence labeling techniques, where only one
of the partners is labeled, are of high interest. The most well-established
single-labeling approach is based on fluorescence anisotropy, which follows
changes in the mobility of the fluorescent label that is grafted to one of the
interacting partners. 5 The other approach, which has emerged only
recently, is utilization of environment-sensitive dyes. 6,7
Unlike “classical” dyes, environment-sensitive dyes can change their
fluorescence properties, fluorescence intensity or emission color, in response
to changes in the physicochemical properties of their molecular environ-
ment. 8 While classical dyes are perfect markers of biological molecules,
the environment-sensitive dyes are “smart molecules” that can be used as
sensors for probing the local biological environment and monitoring biomo-
lecular interactions. Within this approach, the interaction between the
molecules changes the properties of the local site of interaction, which in
turn affects the fluorescence properties (emission maximum or intensity)
of the environment-sensitive labels ( Fig. 2.1 ). 6,7
The response of environment-sensitive dyes to the environment is driven
by excited-state reactions (conformational change, charge, electron and pro-
ton transfer, etc.) and noncovalent interactions with the surrounding, such as
universal interactions (van der Waals, dipole-dipole, dipole-external electric