800CW dye is a near-infrared high water-soluble fluorescent dye with excitation/emission maximum 780/800 nm. The dye has four water soluble SO3Na groups which make it more water soluble and less aggregation in bio application. The dye and its probes have enhanced sensitivity (higher signal-to-noise ratios) because media or tissues have very low background autofluorescence in the near-infrared region. 800CW dye-conjugated agents and probes are currently propelling more than a dozen Phase I or Phase II clinical trials, more than any other near-infrared fluorescent dye on the market. More than 4000 papers are cited in 800CW application worldwide.