In this work, a novel electrochemical microRNA (miRNA) detection method based on enzyme amplified biosensing of mir21 from cell lysate of total RNA was demonstrated. The proposed enzymatic detection method was detailed and compared with the conventional guanine oxidation based assay in terms of detection limit and specificity. For the detection of mir21, capture probes and/or cell lysates were covalently attached onto the pencil graphite electrode (PGE) by coupling agents of N-(dimethylamino)propyl-N'-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysulfosuccinimide (NHS). Having immobilized the capture probe onto the surface of PGE, hybridization was achieved with a biotinylated (from its 3' end) complementary target. Extravidin labeled alkaline phosphatase (Ex-Ap) binds to the biotinylated target due to the interaction between biotin-avidin and the enzyme converts electro-inactive alpha naphtyl phosphate (the substrate) to electro-active alpha naphtol (alpha-NAP, the product). alpha-NAP was oxidized at +0.23 V vs Ag/AgCl and this signal was measured by Differential Pulse Voltammetry (DPV). The signals obtained from alpha-NAP oxidation were compared for the probe and hybrid DNA. The specificity of the designed biosensor was proved by using non-complementary sequences instead of complementary sequences and the detection limit of the assay was calculated to be 6pmol for cell lysates. (C) 2012 Elsevier B.V. All rights reserved.