Long-Wavelength and Near-Infrared Fluorescence: State of the Art, Future Applications, and Standards

Abstract

Near-infrared fluorescence (i.e. at wavelengths above 600 nm) provides many advantages over conventional measurements at shorter wavelengths. This chapter highlights the availability of simple and robust solid-state instrumentation and the great reduction in unwanted background fluorescence and scattered light signals. A wide range of long-wavelength fluorophores suitable as labels and probes are available. Some are naturally occurring proteins, while others are newly synthesised organic molecules, many of them commercially available: tandem fluorophores, providing larger Stokes shifts, may also be valuable. Examples of instrument systems using laser or light-emitting diode light sources and photodiode and other detectors are provided. Some example applications are summarised, and the need for further high-quality fluorescence standards in the long-wavelength region is highlighted. Particularly important are new standards for the correction of emission spectra at >700  nm, and lifetime standards.