Photochemically-made gold nanorods for adsorption and SERS detection of cocaine and benzoylecgonine in latent fingerprints.

Detection of illegal drugs in fingermarks is a routine activity of the scientific police and it can be better carried out with the help of more sensitive and faster analytical tools. In this regard, this contribution proposes and tests a SERS-based method for the rapid detection of cocaine hydrochloride (COC) in latent fingerprints (LFP) using photochemically-made CTAB-coated gold nanorods (AuNRs) as SERS-active substrates. As a key point, removal of excessive CTAB from the AuNR colloids is essential to achieve the largest Raman signal enhancement. The method is capable of detecting COC in dried solutions (∼1 nM) and in either male or female COC-doped LFPs (∼60 µM). The latter corresponds to ∼300 ng, which falls within the range reported for COC excreted through sweat. The method was also tested for its predominant metabolite, benzoylecgonine (BENZ), which exhibited a similar performance. Adsorption of analytes on AuNRs was investigated with the aid of different isotherm models. Freundlich and Frumkin models were the best and revealed that COC and BENZ are equally physiosorbed (Δ ∼ -30 kJ mol) onto a heterogenous surface (AuNRs) with a discrete attractive interaction between adsorbed species. Considering that the photochemical synthesis is completed in about 30 min, and that staining of LFPs is easily done, photochemically-made AuNRs offer a relatively simple yet very sensitive method for assisting in COC detection.