Fluorescein Fluorophores

Introduction

Fluorescein is also a kind of widely used xanthene fluorescent dyes, which is hydroxyl substituted derivative of rhodamine. Due to the large extinction coefficient and high fluorescence quantum efficiency of fluorescein in aqueous solution, fluorescein is still one of the most widely used fluorescent dyes in modern biology, biochemistry and medical research, although the excitation and emission wavelengths of fluorescein are only in the visible region. Researchers can modify the structure of fluorescein to change its pKa, light stability, absorption and emission wavelength, so as to achieve better utilization value.

Fig.1 Chemical structure of fluorescein and derivatives

Application

Fluorescein fluorophores are widely used in ion recognition probes, biomarker and other research fields due to its special photochemical properties.

• Fluorescence ion probe: Fluorescein has been widely used in the research and application of ion probes. At present, fluorescent probes developed with fluorescein fluorophore can be roughly divided into three categories: 1) a recognition site was introduced into fluorescein median benzene ring which is based on Photoinduced Electron Transfer (PET) mechanism; 2) probe developed based on the "off - on" mechanism of fluorescein derivatives; 3) reactive fluorescent probe developed by protection and de-protection strategies of hydroxyl groups on fluorescein. For example, as early as 1989, Tsien ^[1] introduced Ca²⁺ receptor into the median benzene ring of fluorescein, and designed and synthesized a series of Ca²⁺ fluorescent-enhanced probes based on PET mechanism.

Fig.2 Ca²⁺ fluorescent-enhanced probes based on PET mechanism

• Biomarker: Fluorescein, as a widely used labeling reagent, has the advantages of high extinction coefficient, excitation and emission wavelength in the visible region, high fluorescence quantum yield, non-toxicity and low cost. By introducing different functional groups to modify the structure of fluorescein, scientists have developed many fluorescein derivatives containing active groups for application in biomarkers. For example, Feng, G ^[2]. et al. synthesized a variety of fluorescein esters for fluorescence analysis and detection of lipase.

Fig.3 Chemical structure of fluorescein esters

References

1. Minta A.; et al. Fluorescent indicators for cytosolic calcium based on rhodamine and fluorescein chromophores. The Journal of Biological Chemistry, 1989, 264(14): 8171-8178.
2. Ge F Y.; et al. Synthesis and study on hydrolytic properties of fluorescein ester. Dyes Pigments, 2007,72(3): 1261-1268.