The cationic dye basic orange 21 (BO21) as a potential fluorescent sensor

Area of Science:

• Biophysical Chemistry
• Fluorescence Spectroscopy
• Molecular Probes

Background:

• Understanding the fluorescence properties of novel molecular probes is crucial for developing advanced sensing technologies.
• BO21's structural similarity to fluorescein, yet distinct fluorescence characteristics, warrants detailed investigation.

Purpose of the Study:

• To investigate the fluorescence properties of BO21 and their dependence on intracellular conditions.
• To explore the potential of BO21 as a sensor for heparin and intracellular viscosity.

Main Methods:

• Spectroscopic analysis of BO21 in cell-free solutions under varying pH, temperature, viscosity, and in the presence of proteins and heparin.
• Measurement of quantum yield, fluorescence polarization (FP), and fluorescence lifetime (FLT).
• Analytical and experimental investigations, including theoretical calculations.

Main Results:

• Fluorescence spectra of BO21 are minimally affected by pH and temperature but significantly influenced by viscosity, proteins, and heparin.
• Heparin induces a red shift in the emission spectrum and increases fluorescence lifetime, suggesting aggregation.
• BO21 exhibits a surprisingly high FP (0.470) in water due to a very short lifetime, which decreases upon heparin addition.

Conclusions:

• BO21's high fluorescence polarization is linked to its short fluorescence lifetime.
• The molecule behaves as a molecular rotor, with its properties modulated by environmental factors like viscosity and heparin.
• BO21 shows promise as a sensor for detecting heparin levels and intracellular viscosity.