PBXL Fluorescent Dyes for Ultrasensitive Direct Detection

PBXL dyes are a group of phycobilisome-based fluors that provide high sensitivity in direct fluorescent detection formats. Phycobilisomes are proteinaceous, supramolecular complexes that are photosynthetic antennae complexes in red algae and cyanobacteria. For the PBXL dyes, the phycobilisome has been chemically cross-linked in such a way that it remains water soluble and stable. Stabilized phycobilisomes (PBXL dyes) have high complex weights (between 10 and 15 million daltons) and Stokes shifts (up to 121 nm). They contain many hundreds of chromophores coordinated to transfer green and yellow light efficiently down an energy gradient to emit red light at wavelengths around 666 nm. Each PBXL dye can deliver up to 1400 chromophores per binding event without additional signal generation steps, signal amplification, or enzyme substrates. PBXL dyes provide a physical amplification of signal, enabling ultrasensitive, direct fluorescent detection of specific binding events. A number of studies done in our laboratory and in collaborating laboratories are summarized in this article. These studies demonstrated the utility of PBXL dyes in select high-sensitivity applications, such as a thyroid stimulating hormone (TSH) microplate immunoassay, detection of the low-density cell surface marker CD56 using flow cytometry, BSA–biotin, and actin detection in a western blot format and paternity testing using a DNA array on glass slides. PBXL dyes have the potential for providing a highly sensitive, simple, and direct fluorescent detection method to a wide range of targets and assay formats that could reduce costs associated with reagents and labor as well as decreasing the time to the first result.