Cadmium sulfide quantum dot/chitosan nanocomposites for latent fingermark detection.

The detection of latent fingermarks is a challenging task in forensic science. Here we present work using highly photoluminescent cadmium sulfide (CdS) quantum dots (QDs) encapsulated in an inexpensive biopolymeric chitosan matrix for latent fingermark detection. Cadmium ions were chelated within the chitosan matrix followed by the rapid addition of sodium sulfide to produce a CdS/chitosan nanocomposite. The average QD size was investigated as a function of precursor concentrations using ultra-violet-vis (UV-vis) spectrophotometry and the QDs were imaged with transmission electron microscopy (TEM). Fluorescence spectrophotometry of the QDs at an excitation of 450 nm showed a narrow emission at 531 nm and broad emission between 600 and 850 nm with a maximum at 716 nm. Freshly deposited latent fingermarks deposited on aluminium foil were clearly detected under a Rofin Polilight at 450 nm by dusting with a freeze-dried suspension of the CdS/chitosan nanocomposite and a surfactant, tergitol, giving a so-called quantum dot surfactant (QDS) powder.