Novel extraction supports based on immobilised aptamers: evaluation for the selective extraction of cocaine

A new kind of selective sorbent based on the use of aptamers and dedicated to the selective solid phase extraction was developed. Cocaine aptamer was chosen as model aptamer to demonstrate the feasibility of this material and to provide a complete evaluation of the synthesized sorbent. The effect of different parameters such as the nature of the immobilisation support (silica, agarose), the type of immobilisation (covalent or non-covalent) and the length of the spacer arm (C₆ or C₁₂) were studied. Therefore, various oligosorbents based on different immobilisation strategies were synthesized and characterised by estimating the extraction recovery and the capacity of cocaine and the binding efficiency of aptamers. Control supports without immobilised aptamers were simultaneously studied in parallel to assess the selectivity brought by the oligosorbents. The oligosorbent based on CNBr-activated sepharose showed the best performances with an extraction recovery for cocaine of 90% while 6% was obtained on the control sorbent. The high selectivity brought by the oligosorbent was then illustrated by applying the oligoextraction followed by LC/MS analysis to a post-mortem blood (cocaine overdose). Results were compared to those resulting from a conventional protein precipitation procedure. The presence of co-extracted interfering compounds was strongly reduced with the treatment by oligoextraction. A limit of quantification of 0.5 ng/mL was obtained that is largely lower than the concentration found after a single intake of cocaine.