The change in charge-transfer resistance (Rct) was found to be linear with DCL concentration in the 30 pM-1 µM range. The detection limit was calculated to be 0.02 nM. The improvement of the limit of detection can be mainly attributed to the threedimensional environment of the hydrogel matrix which improves the grafting density of aptamer and the affinity of the aptamer to DCL.

Diclofenac (DCL) is a nonsteroidal anti-inflammatory commonly prescribed to treat inflammatory joint diseases and mild to moderate pain. DCL residues have often been detected in freshwater environments and it belongs to the list of emerging pollutants (EPs) because of the risk it presents for health and environment. Many studies have described the potential effects of DCL on organisms when exposed to environmental levels ranging from a few ng L À 1 to tens of μg L À 1 in surface water. Until now, its detection essentially depends on conventional techniques, such HPLC and GC/MS. Although these analytic techniques are very robust, they are expensive, require experts, and are not portable. Electrochemical sensors are an attractive alternative. They provide many benefits over thermal, optical, and piezoelectric detection including ease of use, rapidity, costeffectiveness, high sensitivity and selectivity, ease of miniaturization and robustness. The aim of this review is to report electrochemical methods used for the detection of DCL and to describe strategies for improving performances of each sensors.