Fluorescence microscopy is a key diagnostic tool to identify pathogens such as Meningococcal, Tuberculosis, Staphylococcus, Cryptosporidium and Guardia, however their presence is often masked by the fluorescence of benign species. This natural or autofluorescence is typically short lived; τ < 20 ns. By selectively tagging the pathogen of interest with longer lived fluorescent molecules (for example lanthanide chelates which have lifetimes τ > 600 µs) and delaying the collection of the image, the background fluorescence has faded away and the presence of the tagged pathogen is easy to detect. The invention comprises a slotted wheel which, when fitted to a standard microscope, reflects ultraviolet light onto the sample momentarily while blocking the autofluorescence from the sample. A short time after the ultraviolet light pulse, the slotted wheel allows long-lived fluorescent light to pass through the microscope to be detected. The length of the ultraviolet light pulse and the delay between illumination and fluorescence detection can be adjusted by altering the rotation speed of the wheel, which is typically 6,000 rpm. In contrast, conventional delayed fluorescence microscopy requires electronic timing to drive pulsed UV sources and gate specialised, high-sensitivity, image intensified CCD cameras, usually built into microscopes dedicated to the task.

File Number: MQ2008009 

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