Time-Resolved Luminescence Detection and Imaging Promises a Bright Future

Fluorescence/phosphorescence (referred in this article simply as luminescence) based-detections arguably are the most widely used detection technique for biological assays, imaging, and sensing. This is primarily due to its high detection sensitivity and the commercial availability of a large number of fluorescence probes [1-3]. Key to the usefulness of luminescence methods is the ability to separate the luminescence signal of interest from the background. Such background includes scattered excitation photons and autofluorescence of sample matrices and substrates and it is often several orders of magnitude higher than the signal luminescence of interest. This low luminescence signal intensity relative to background sometimes presents a huge challenge when high detection sensitivity is required for the application at hand. Conventional luminescence detection technique uses wavelength differences to separate the luminescence of interest from background photons through optical filters or monochromators. Wavelength-based separation techniques sometimes face significant hurdles because most of the widely used luminescence probes have a very small Stokes shift and a broad luminescence spectrum. Hence, the complete elimination of the much stronger scattered excitation background is almost impossible. Complicating the issue further is the fact that the auto fluorescence from complex biological sample matrices and substrates sometimes overlaps with the luminescence of the probe. This makes it impossible to completely reject the background and results in a lower signal/noise ratio and therefore lower detection sensitivity.