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Home > Articles > Fluorescence Photography > Applications of the ultraviolet technique
FLUORESCENCE PHOTOGRAPHYAuthors: Prof. Robin Williams and Gigi Williams Applications of the ultraviolet techniqueMany fungi and some bacteria exhibit autofluorescence when stimulated by ultraviolet - the colour often being characteristic, eg., tinea fluoresces blue/white (Figure 11), pityriasis fluoresces gold, erythrasma fluoresces coral pink. H. Pertussis characteristically fluoresces in culture (Figure 12). Bacterial invasion of epidermoid carcinoma often glows deep red; first described by Ronchese in 1954 as 'live coal' fluorescence (Figure 13). In disease, some body fluids take on an abnormal fluorescence, such as plasma in Porphyria which fluoresces a deep red colour (Figure 14). In dentistry ultraviolet fluorescence detects many abnormalities, can distinguish between natural enamel and restorative work, and can reveal such things as tetracycline uptake (Figure 15). Callosities on the surface of the skin often fluoresce (Figure 16). In forensic work there are many compounds and body fluids which autofluoresce, for example, wood and bone fragments can be clearly distinguished (as seen in Figure 17 and Figure 18), and plasma, semen and gunshot residue identified. The most stunning and public example of plasma fluorescence is probably the Shroud of Turin: where supposedly an image of Christ has been formed on a cloth alleged to be his funereal shroud. The image was enhanced considerably by being recorded with ultraviolet fluorescence (Figure 19). Authur Wall - a postgraduate student at the Royal Melbourne Institute of Technology (Figure 20) has demonstrated that whole blood - either fresh or coagulated does not fluoresce, but plasma clearly does (Figure 21). Wall also demonstrated that the fluorescent image is concentrated at the edges of the absorption of the plasma by any porous substrate (Figure 22). An outstanding application is in the field of law enforcement, particularly in the examination of questioned documents (Tholl, 1967). Figure 23 shows an example. Paintings are often examined by ultraviolet fluorescence (along with other invisible radiation techniques). Ultraviolet fluorescence is often used in mineralogy for identification purposes (Gleason, 1960); some forms of calcite, for example, which look white to the naked eye fluoresce red (Figure 24), Willemite fluoresces bright green (Figure 25) and Wernerite bright yellow. The technique is also used routinely for chromatography (Figure 26). It is worth mentioning that many soaps and dermatological cleansing creams fluoresce strongly under ultraviolet (Figure 27) and as noted by Williams (1988) this can complicate the recording of dermatological conditions in ultraviolet. Ultraviolet fluorescence photography has occasionally been used to delineate anatomical details - Figure 28 is such an application. The addition of fluorescent marker dyes extends the applications of the ultraviolet fluorescence technique considerably. In industry, for example, minute cracks in machine parts can be identified by the use of penetrating fluorescent mineral oil (Figure 29) - sold commercially as 'Zyglo'. In medical research, fluorescent markers are added to growing tissue for tumour and bone growth studies (Figure 30). Auramine is used to locate Koch's bacillus, Thioflavine to locate albumin and Sulphoflavine to identify bacterial spores. Acridine orange is able to distinguish between RNA and DNA, as when bonded to the former exhibits an orange fluorescence, and to the latter a green fluorescence (Figure 31). In forensic science, 'Luminol' may be added to minute traces of blood to cause an intense chemiluminescence (Zweidinger et al., 1973). Similarly, there are fluorescent chemicals, which will bind minute traces of metals. These have been used on several occasions to link suspects to crimes and obtain convictions (West et al., 1989; Frair et al., 1989). In the examination of fingerprint evidence, fluorochromes are commonly used. Cyanoacrylates treated with cadmium, Ninhydrin, Rodamine 6G and Diazofluoren all fluoresce strongly to give excellent representation of prints that ordinarily would be invisible (Figure 32 and Figure 33). For convenience the more common biomedical applications of the ultraviolet induced fluorescence method are listed in tabular form, by subject, on the following pages: References
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