FINGERPRINT DEVELOPMENT BY 1,2-INDANEDIONE AND OTHER CHEMICAL METHODS ON SO-CALLED DIFFICULT ABSORBENT SURFACES
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Given their potential for direct and individual identification of people, fingerprints are recognised as powerful evidence with unquestionable identification value. Fingerprints are developed using physical, chemical, physicochemical and biological methods. Application of a method and its effectiveness depend, e.g. on the kind of substance forming the print, surface type and features, development conditions and time span. Under laboratory conditions, the fingerprint examiner attempts to detect prints on various surfaces, using chemical methods. Very often, fingerprints are recovered from absorbent surfaces, called (with good reason) 'difficult surfaces', such as anonymous letters, invoices, bills, bank cheques. These surfaces have a loose, porous, capillary internal structure, which allows liquid components of eccrine and sebaceous gland secretions to be gradually absorbed. To detect fingerprints on absorbent surfaces, used are chemical methods based on solutions of DFO, 1,2-IND, ninhydrin, RTX or zinc chloride. Especially noteworthy is 1,2-IND, which has this advantage over comparable methods that its application does not leave the surface permanently stained or contaminated and prevents the writing substance from being washed away. Currently investigated for fingerprint visualisation is a plant reagent called genipin. This method involves genipin solution reacting with amino acids contained in eccrine and sebaceous gland secretions depositing finger marks. The developed blue and purple images are not only visible in daylight, but are also highly fluorescent. Although the genipin-based method is not totally new, it still has not been introduced into the Polish laboratory practice.
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