Novel instrumentation in long wavelength fluorescence.

A fluorimeter was constructed which utilises solid state components. The novel arrangement of these components meant that an inexpensive, sensitive, robust and portable fluorimeter was feasible. If the optical components ofthe instrument were selected for a specific assay, a dedicated fluorimeter with comparable sensitivity to a research grade fluorimeter resulted. The construction and evaluation of such a fluorimeter is described. Nile Red is a hydrophobic phenoxazine fluorescent dye, which has an emission in the long wavelength region of the spectrum (600 - 1000 nm). Assays based on fluorescence measurements in this spectral region have the advantage oflower background, reduced scattering and decreased photodecompostion when compared with conventional fluorescence utilising UVNis wavelengths. Nile Red is also a solvatochromic dye, which means it emission wavelength is strongly dependant on its molecular environment. The property is utilised here in the development of a novel assay for the protein ~-lactoglobulin. As the fluorescence properties of the Nile Red:Protein complex differ form those ofthe unbound Nile Red molecule, the fluorescence intensity can be related to concentration of the protein present. The feasibility and development of such an assay is presented as one possible application for the fluorimeter described.