Studies on the development of latent fingerprints by the method of solid–medium ninhydrin

• Fingerprint developing membrane were prepared using ninhydrin as the developing agent.
• The membrane can be successfully applied to both latent fingerprints.
• The sensitivity toward the latent sweat fingerprint is 0.1 mg/L amino acid.
• The membrane can be applied to both porous and non-porous surfaces.

A new series of fingerprint developing membrane were prepared using ninhydrin as the developing agent, and pressure-sensitive emulsifiers as the encapsulated chemicals. The type of emulsifier, plastic film, concentration of the developing agent, modifying ions and thickness of the membrane were studied in order to get the optimized fingerprint developing effect. The membrane can be successfully applied to both latent sweat fingerprints and blood fingerprint on many different surfaces. The sensitivity of the method toward the latent sweat fingerprint is 0.1 mg/L amino acid. The membrane can be applied to both porous and non-porous surfaces. Fingerprints that are difficult to develop on surfaces such as leather, glass and heat-sensitive paper using traditional chemical methods can be successfully developed with this membrane.