Red laser-induced fluorescence energy transfer in an immunosystem

Area of Science:

• Biochemistry
• Analytical Chemistry
• Spectroscopy

Background:

• Fluorescence resonance energy transfer (FRET) is a powerful technique for studying molecular interactions.
• Development of novel fluorescent dyes is crucial for advancing FRET-based assays.
• Near-infrared (NIR) dyes offer advantages due to reduced background autofluorescence.

Purpose of the Study:

• To synthesize and characterize two new near-infrared fluorescent squaraine dyes, Sq635 and Sq660.
• To evaluate their spectral properties and quantum yields in free and protein-bound forms.
• To demonstrate their utility as a donor-acceptor pair in a FRET immunoassay.

Main Methods:

• Synthesis of squaraine dyes with N-hydroxysuccinimide esters for protein conjugation.
• Introduction of sulfo groups to enhance water solubility.
• Spectroscopic analysis of absorption and emission spectra.
• Demonstration of FRET in an immunoassay for human serum albumin (HSA) using red lasers.

Main Results:

• Sq635 and Sq660 were successfully synthesized and functionalized for protein linkage.
• Free dye quantum yields were ~10%, increasing to up to 68% upon protein binding.
• The emission spectrum of Sq635 overlaps the absorption spectrum of Sq660, suitable for FRET.
• Successful application in a FRET immunoassay for human serum albumin.

Conclusions:

• The developed squaraine dyes are effective for protein labeling and FRET applications.
• Enhanced quantum yields upon protein conjugation improve assay sensitivity.
• These NIR dyes are promising tools for developing advanced FRET immunoassays using red laser excitation.