Fluorescent probes and labels for biomedical applications.

Fluorescence probes and labels have become indispensable tools for clinical diagnostics, high-throughput screening, and other biomedical applications. We have developed several classes of new squaraine-based red and near-infrared (NIR) probes and labels (SETA and Square series), naphthalimide-based fluorescence lifetime dyes (SeTau series), and cyanine- and squaraine-based quenchers (SQ series). This report discusses the spectral and photophysical properties of these new markers.

Synthesis of water-soluble, ring-substituted squaraine dyes and their evaluation as fluorescent probes and labels.

A series of ring-substituted squaraines absorbing and emitting in the red and NIR spectral region was synthesized and their spectral and photophysical properties (quantum yields, fluorescence lifetimes) and photostabilities were measured and compared to Cy5, a commonly used fluorescent label. The absorption maxima in aqueous media were found to be between 628 and 667 nm and the emission maxima are between 642 and 685 nm. Squaraine dyes exhibit high extinction coefficients (163,000-265,000 M(-1) cm(-1)) and lower quantum yields (2-7%) in aqueous buffer but high quantum yields (up to 45%) and long fluorescence lifetimes (up to 3.