The potential of chitosan-tripolyphosphate microparticles in the visualisation of latent fingermarks

Chitosan (CS) is a cationic polymer with excellent film, gel and particle-forming properties. This polymer has been investigated widely for its potential in the development of food and drug delivery systems and pharmaceutical applications, however it has not generally been considered in forensic applications for example fingerprints (fingermarks). Fingerprints are a very common form of physical evidence. The most commonly used procedure for revealing the ridge pattern is powder dusting, which relies on the mechanical adherence of fingerprint formulation to the fatty components of the skin deposit that are secreted by sweat pores that exist on friction ridges. Cross-linking between oppositely charged molecules can be used to prepare chitosan microparticles. Tripolyphosphate (TPP) is a nontoxic polyanion; it can form particles by ionic interaction between positively charged amino groups of CS and negatively charged counter ions of TPP. In the present study chitosan microparticles (CSMPs) were prepared under four different processing/formulation conditions. The development of latent fingermarks using CSMPs was analysed by using a 23 factorial design, which considered simultaneously three main factors: pH, ionic strength and CS: TPP (v/v) ratio. In this study CS: TPP ratio has the strongest effect on fingerprint quality. The best conditions for fingerprint visualisation were pH 4.8, CS: TPP of 2:1 and 0.2 M of ionic strength in buffer (AB-12).