Fluorescent nanomaterial could transform how we view fingerprints

Researchers have created a fluorescent nanoparticle from a combination of materials (MCM-41, chitosan and dansylglycine) to examine latent fingerprints. These nanoparticles have special properties that allow them to adhere perfectly to fingerprint residue, even old ones.

The nanoparticles work on a variety of surfaces including metal, plastic, glass and complex objects such as polymer banknotes. They can be used directly at crime scenes without a laboratory, a significant advantage over some previous reagents. They produce high-quality fingerprint images, with the vast majority of prints tested meeting the UK Home Office’s standards for successful identification.

This new method allows the capture of the finest details of a fingerprint, making it easier to identify individuals and should greatly aid forensic investigations. The research was published in a RSC Progress A paper was published highlighting that the new nanomaterial proved to be a versatile and effective tool for visualizing fingerprint evidence. Diamond’s small-angle X-ray scattering (SAXS) techniques provided useful data to validate these results.

Fingerprints remain unchanged throughout and after a person’s life. They are the primary method of personal identification in criminal investigations. When the surface of an object is touched by a finger, sweat and oily substances are transferred and deposited on the surface, resulting in the formation of a mark. Most fingerprints are invisible to the naked eye and are called latent fingerprints.

An international collaboration of researchers has developed a new nanostructured hybrid material, MCM-41@chitosan@dansylglycine, to visualize latent fingerprints. This material combines mesoporous silica nanoparticles with a fluorescent dye (dansylglycine) and chitosan, a polysaccharide derived from the exoskeletons of shrimp, crabs and lobsters.

Latent fingerprints require physicochemical development techniques to improve their visibility and make them interpretable for forensic purposes. Traditional fingerprint development methods include optical, physical, and chemical processes that involve interaction between the developing agent (often a colored or fluorescent reagent) and the fingerprint residue. These methods have limitations in obtaining high-quality results under certain conditions.

Recently, new methods using mass spectrometry, spectroscopy, electrochemistry, and nanoparticles have improved the development of latent fingerprints. These techniques provide better contrast, sensitivity, and selectivity, with low toxicity. The ability to tune the properties of nanomaterials further improves the detection of fresh and old fingerprints.

Mesoporous silica nanoparticles (MSNs) have attracted considerable interest since the discovery of the M41S family of molecular sieves, which includes MCM-41, MCM-48, and SBA-15. These nanoparticles are characterized by their controlled particle size, porosity, high specific surface area, chemical stability, and ease of surface functionalization.

Professor Adriana Ribeiro, Federal University of Alagoas, comments: “There are few studies using chitosan for the detection and enhancement of latent fingerprints and, to our knowledge, there have been no reports of using hierarchical structured MSNs modified with chitosan (MSN@Ch) for such applications, which was our strategy in this research. We exploited the desirable characteristics of MCM, including its large surface area and surface modification, for the case of MCM-41 to improve the interaction between the developing reagent and the fingerprint residue.”

The team added dansyl fluorophores that exhibit intense absorption bands in the near-UV region and emit strong fluorescence in the visible spectrum with high emission quantum yields.

Robert Hillman, Professor of Physical Chemistry at the University of Leicester, concludes: “The main objective of this study was to create a versatile and effective latent fingerprint visualization material based on MSN, chitosan and dansyl derivatives. These nanoparticles were used as latent fingerprint developers for marks on surfaces of varying chemical composition, topography, optical characteristics and spatial nature, typical of challenging forensic evidence.

“To assess the quality of the enhanced fingerprints, we analysed the developed images using the UK Home Office scale, forensic protocols and, in terms of constituent features (minutiae), specialist forensic software. Across a substantial collection of marks deposited on chemically diverse surfaces with complex environmental and temporal histories, the vast majority of enhanced images had sufficient minutiae to be compared with the model fingerprint images.”

Professor Gianluigi Botton, CEO of Diamond Light Source, added: “It is pleasing to see that Diamond’s unique analytical tools have once again delivered exceptional scientific results. Our international user network is essential to ensuring our science delivers results. This advancement in nanomaterials could be a step change in how forensics can be applied in the future.”

The research team includes scientists from the Technical and Scientific Section of the Federal Police of Alagoas, Brazil; the National Institute of Forensics of the Federal Police of Brazil; the School of Chemistry of the University of Leicester; the Federal University of Alagoas, Brazil; and the United Kingdom’s national synchrotron, Diamond Light Source.