Luminescent nanomaterials for developing high contrast latent fingerprints

Fingerprint pattern (or epidermal ridges) is by far one of the most reliable techniques for individual identification. Fingerprint patterns get deposited on any kind of solid surfaces due to human transudation or exudation process. Bodily fluids through sweat glands contain moisture, natural oils and proteins. Since latent fingerprint patterns are not readily recognisable thus they are collected from a crime scene and are further processed physically or chemically. Fingerprints obtained using conventional black and white powders; face severe drawbacks including low sensitivity, high background interference from the substrates, involvement of toxic materials, and poor stability. To overcome the above listed issues, especially for coloured and transparent substrates, luminescent materials have emerged as potential agents for rapid visualization of high contrast latent fingerprints. This review article covers the recent advancements in luminescent nanomaterials of both kinds (up and down conversion) and persistent nanophosphors for developing latent fingerprints. Special emphasis has been given to unusual class of luminescent materials known as persistent nanophosphors, which does not need a constant excitation thereby completely eradicating background noise. Review also covers different approaches of gathering fingerprints such as powder dusting, cyanoacrylate fuming, ninhydrin fuming and vacuum metal deposition.