Near-infrared squaraine dyes for fluorescence enhanced surface assay

Commercially available, near-infrared fluorescent squaraine dyes (Seta-635 and Seta-670) were covalently bound to antibodies and employed in surface enhanced immunoassay. From fluorescence intensity and lifetime changes determined for a surface which had been coated with silver nanoparticles as well as a non-coated glass surface, both labeled compounds exhibited a 15- to 20-fold enhancement of fluorescence on the silver-coated surface compared to that achieved on the non-coated surface. In addition, the fluorescence lifetime changed drastically for both labels in the case of silver-coated surfaces. The fluorescence signal enhancement obtained for the two dyes was greater than that previously recorded for Rhodamine Red-X and AlexaFluor-647 labels.