An extended model for open-ended fluorosensor probes

Measurements on pure solutions of NADH (8-800 microM) were made at different path lengths (0-140 mm) with an open-ended fluorosensor. It was shown that a geometric factor must be included in a model to quantitatively explain the results. A mathematical expression for this factor was found, and parameter estimations were made. It was shown that the often-used implicit assumption of a completely directed emitted light is not correct. A better fit was obtained by assuming the emitted light to be uniformly distributed in all directions. However, it was necessary to consider the slight divergence of the excitation light beams in the model.