SERS spectroscopy for the therapeutic drug monitoring of the anticancer drug 6-Mercaptopurine: Molecular and kinetic studies.

Gold colloidal solutions were investigated as SERS platforms for the detection and the quantitative analysis of the anticancer drug 6-Mercaptopurine. The study was aimed at verifying the feasibility of a SERS-based assaying method for Therapeutic Drug Monitoring. The interaction mechanism and the adsorbate structure were investigated by a QM vibrational analysis of the title molecule. Furthermore, a kinetic analysis of the adsorption/aggregation processes made by time- resolved SERS experiments and DLS analysis provided relevant information on the complex behaviour of the system. It was found that the adsorption process is fast and produces significant SERS signalling in the 5 - 20 ?M range. At 15 and 20 ?M composition, the kinetic analysis evidenced the formation of long-lived metastable aggregates; at 50 ?M the colloidal solution collapsed immediately. A range of high linearity was identified between 5 and 20 ?M, wherein a reliable quantitative analysis could be performed, with an estimated limiting sensitivity (LOD) of 1.0 ?M.