GALD

During his tenure at Macquarie University, Russell Connally developed a novel technology to overcome a major problem in fluorescence microscopy. The technology was shown on ABC TV on the New Inventors program, winning on the night and making it through to the Grand Finals of the show in 2010. The device is known as the GALD which is an acronym derived from "Gated Auto-synchronous Luminescence Detector". The GALD has been patented throughout Europe, USA and Australia and development of the device continues today.

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Conventional microscopy makes wide use of fluorescent dyes coupled to bio-reactive molecules that can bind with specific cells or bacteria in a process known as labelling. This technique renders the target cells or bacteria brilliantly fluorescent when viewed through a fluorescence microscope; the problem with this method is the wide abundance of natural substances that exibit intrinsic fluorescence, that is they glow without having been 'labelled' with a fluorescent dye. This background fluorescence is known as autofluorescence and can be so intense as to render the conventional fluorescence microscopy useless.

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Russell developed a practical way to eliminate this problem by making use of fluorescent dyes that glow for a long time after brief exposure to a strong light. Most of us are familiar with the 'glow-in-the-dark' stickers often used for children's bedrooms - the compounds used in these stickers are usually derived from a special class of elements known as the lanthanides and it is possible to use these elements to label bacteria and make them glow 20,000 times longer than conventional fluorescent labels; a phenomenon known as delayed luminescence.

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So it is necessary initially to label the bacteria with a lanthanide derivative; europium is a particularly useful lanthanide for luminescent applications.

To visualize delayed luminescence in the absence of autofluorescence, we need to block our view of the sample whilst it is briefly exposed to a strong burst of light and then wait for a short time for the autofluorescing components to fade beyond detection. The obstruction blocking our view of the sample is then removed to reveal the remaining delayed luminescence to the eye. The GALD automatically performs all of these operations at around 800 times per second to give a full colour view of delayed luminescence in the complete absence of autofluorescence.

The end result is that even a single labelled cell can be easily resolved from complex fluorescent backgrounds and the process may be enhanced even further by coupling with an automated image recognition system that can fully scan a slide in tens of seconds.

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