Fiber-optics based fluorescence detection. Part I: Basic concepts.

Continuous in-line detection and process monitoring are essential for industrial, analytical, and biomedical applications. Lightweight, highly flexible, and low-cost fiber optics enable the construction of compact and robust hand-held devices for in situ chemical and biological species analysis in both industrial and biomedical in vitro/in vivo detection. Despite the broad range of fiber-optic based applications, we lack a good understanding of the parameters that govern the efficiency of light collection or the sensitivity of detection. Consequently, comparing samples of different optical density and/or geometry becomes challenging and can lead to misinterpretation of results; especially when we lack the approaches necessary to correct the detected signal (spectra) for artifacts such as inner-filter effect or scattering. Hence, in this work, we discuss factors affecting the signal detected by the fiber optic in the bare and lens-coupled flat-tipped configurations that lead to signal/spectral distortions. We also present a simple generic model describing the excitation profile and emission collection efficiency that we verify with experimental data. Understanding the principles governing the signal collected by the fiber will provide rationales for correcting the measured emission spectra and recovering the true emission profile of optically dense samples.