Fluorescence detected linear dichroism spectroscopy: a selective and sensitive probe for fluorophores in flow-oriented systems

Fluorescence detection typically enhances sensitivity and selectivity for fluorescent analytes. The potential for combining fluorescence detection with flow orientation of the sample in the normal configuration of linear dichroism experiments is explored in this work by measuring the fluorescence emitted from flow-orientated DNA-bound ligands and M13 bacteriophage. Data for ethidium bromide, Hoechst 33258, and 4,6-diamidino-2-phenyindole are presented. The theoretical basis of the technique is also presented for instruments running in both the fixed direct-current mode, which is the normal operation mode of circular dichroism spectropolarimeters, and also in fixed high-tension voltage mode. The role of the stray light reaching the detector that results in a spectral shape in fixed direct current mode that resembles the shape of a linear dichroism spectrum, rather than the expected reduced linear dichroism, is also explored.