Fingermark detection using metal nanoparticles and metal oxide nanostructured particles
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NO FULL TEXT AVAILABLE. This thesis contains 3rd party copyright material. ----- Fingermarks are considered a useful type of evidence for identifying individuals in the investigation of a crime scene due to the characteristic ridge patterns of each person; these are immutable and universal. The most common form of fingermarks found at a crime scene is invisible (or latent). In order to visualise latent fingermarks, an optical, chemical or physical application is required before they can be used for criminal investigation purposes. Nanoscience opens new possibilities in the forensic science, including fingermark detection. Nanoscience includes the study of objects and systems on the nanometre-length scale (1-100 nanometres). At that length scale, nanomaterials exhibit interesting and useful physical, chemical, biological, mechanical and electrical properties. This thesis begins with a review of the application of metal-containing nanoparticles and nanostructured particles to fingermark detection. The most common metal nanoparticles that have been used for fingermark detection are gold nanoparticles. Metal oxide nanoparticles such as titanium oxide, zinc oxide, iron oxide and europium oxide have been used through the small particle reagent (SPR) technique or powder technique. The possibilities of fluorescent nanoparticles (semiconductor nanoparticles) for improving current techniques are also discussed. Some other nanoparticles used in the detection of latent fingermarks are also included in this review. Chapter 2 describes the investigation of the binding of gold nanoparticles to fingermarks placed on nonporous surfaces using scanning electron microscopy. The results show that gold nanoparticles bind preferentially to latent fingermark ridges on nonporous surfaces. Variations in surfactant concentration influence background development but do not affect the binding of gold nanoparticles to the ridges, while pH variations influence the binding to ridges but leave the valley regions unaffected. In Chapter 3, water-dispersible gold nanoparticles stabilised with functionalised alkanethiols are used to elucidate the influence of nanoparticle charge on the mechanism of gold binding to latent fingermarks. Chapter 4 discusses the synthesis of new gold and silver nanopowders and investigates their applications in the development of latent fingermarks. Gold and silver nanoparticles using oleylamine as a stabiliser have been formulated for developing latent fingermarks on nonporous surfaces. These nanopowders are compared with some conventional powders. Gold nanopowder produces sharp and clear development of latent fingermarks without background staining. Scanning electron microscope images reveal that particles were concentrated in the fingermark ridge area, with only minor amounts located in the valley regions. New fluorescent metal oxide particles for visualising latent fingermarks are presented in Chapter 5. A new, highly fluorescent dye was synthesised using oleylamine combined with a perylene dianhydride compound. The dye was adsorbed onto titanium dioxide nano-structured particles for use as a fingermark powder. The new fluorescent powder was applied to latent fingermarks deposited onto nonporous surfaces and compared with commercial fluorescent powders. On glass surfaces, the new powder gave images showing tertiary-level detail of the fingermark ridges -with almost no background development. Compared with current magnetic fluorescent powders, the new powder was slightly weaker in fluorescence intensity but produced significantly less background development, resulting in a good contrast between the fingermark and the substrate. Chapter 6 presents an evaluation of zinc oxide as a fluorescent powder for the detection of fingermarks on non-porous surfaces. Pure and lithium-doped nanostructured zinc oxide powders were characterised using scanning electron microscopy, x-ray diffraction and fluorescence spectroscopy. The zinc oxide powders were applied to fresh and aged fingermarks deposited on non-porous surfaces such as glass, polyethylene and aluminium foil. Zinc oxide was found to produce clear fluorescent impressions of the latent fingermarks when illuminated with long-wave UV light. A general discussion and conclusions to this project are presented in Chapter 7. Some possible future directions of fingermark detection using metal nanoparticles is also discussed.
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