Aptamers are synthetic RNA or DNA single-stranded oligonucleotide sequences folding into different three-dimensional shapes that exhibit high specificity and affinity for a target molecule . Aptamers are obtained by an in vitro process called SELEX. In recent years, aptamers, single-stranded oligonucleotides, have been promoted as ideal diagnostic reagents and potential antibody replacements for the development of biorecognition nanosensors due to their high affinity, specificity and stability[1-2]. Adenosine, an endogenous nucleoside, has potent biological activities including extension of the blood vessels, increment of the blood flow of the arteries, anti-arrhythmia and improvement of the oxygen supply of cardiac muscle. Some evidences indicate that in has some important function in the immune system. Adenosine concentration in normal human blood ranged between 0.05 and 0.1µM. therefore the detection of adenosine is a challenge in bioscience field [3-4]. The aim of present study is design and presentation of a simple and label-free electrochemical biosensor for adenosine detection based on immobilization of aptamer onto glassy carbon electrode modified with multi walled carbone nanotubes, ionic liquid and chitosan. At first an amino terminated capture probe 3′-NH2-TCT CTT GGA CCC-5 was covalently attached onto GC electrode modified with nanocomposite containing ionic liquids, multi-walled carbon nanotubes and chitosan, using glutaraldehyde as linking agent. Then adenosine aptamer labeled with platinum nanoparticles 5′-AGA GAA CCT GGG GGA GTA TTG CGG AGG AAG GT3-Thiol -3′ was hybridized with capture probe with the complementary part. Platinum nanoparticles were used as catalytic labels for the decrease reduction of H2O2. Sensitive quantitative detection of adenosine is realized by monitoring differences of voltammetric responses of H2O2 peak. The peak current of H2O2, decreased with the concentration of adenosine over a range of 1-750 nM. The detection limit was 1
