Gold has many diverse applications in the field of forensics, and was first utilized to identify remains by matching gold fillings in teeth to medical records. Recently, gold nanopowders have become a key component in obtaining complete, quality fingerprints from crime scenes. Forensic analysis with gold nanopowders methods use the interactions between positively charged finger ridge residue and negatively charged gold nanoparticles to create the fingerprint image. Fingerprints are composed of sodium chloride (NaCl) and a variety of organic chemicals, leaving a positively charged, acidic residue on the surface of the material, be it glass, metal, or paper. The residue, electrostatically attracted to the negatively charged gold nanoparticles, creates the characteristic fingerprint markings on alkaline paper. The gold nanoparticles act as a reducing agent to the components in sweat, meaning that the gold particle loses an electron to the positively charged NaCl from the fingerprints, creating an initial image of higher clarity. This method is superior to traditional fingerprinting techniques as it requires fewer stages of development to create an image.
To enhance visualization, the latent prints are further reacted with a reducing agent in glucose, a process known as single-metal nanoparticle deposition. In multi-metal deposition and single-metal deposition, required when not using nanoparticles, numerous stages of reduction and water treatments are necessary. Faster processing and increased quality of fingerprints results in a quicker, more accurate identification of the fingerprints left by people. Gold nanopowders and gold colloidal solutions have already been incorporated into American and Australian forensic labs, and will likely continue to be utilized in criminal proceedings and court cases.
Negatively charged gold nanoparticles in aqueous solution bond to the positively charged acidic residue of fingerprint ridge deposits to create reddish images of higher initial quality than alternative compounds. These images are then further developed through a process of single-metal nanoparticle deposition, which decreases processing time of the prints. Colloidal gold nanoparticles can be more readily applied to porous surfaces as compared to traditional black powder, as the nanoparticles are electrostatically attracted to the fingerprint residue rather than the raised surface area.
Due to their optical properties, gold nanoparticles are characterized by high sensitivity and luminesce, features that can be used to decrease background interference when developing images. Gold nanoparticles can be easily modified to increase their affinity for fingerprint residue, both electrostatically and chemically using the carboxyl groups of the nanoparticles and the amines in the organic matter of the deposits. They also allow for long-term storage of images with minimal degradation and application to a wider range of pH values, up to 5.0.
Potential inhalation of products can result in uncontrolled agglomeration of metal nanoparticles in the tracheobronchial and alveolar regions, which causes cytotoxicity and DNA damage. The agglomeration is caused by an increased effect of van der Waals forces (the sum of the attractive intermolecular forces) in nanoparticles due to their high surface area. In addition, social, ethical, and legal questions of nano-enabled identification techniques remain underexplored.