A simple label-free electrochemical aptamer sensor was developed based on dialdehyde cellulose/carbon nanotube/ionic liquid nanocomposite. Aptamers labeled with -NH2 groups can be immobilized onto DAC template by a chemical modification approach. The addition of carbon nanotube and ionic liquid improved the conductivity of the sensing interface and therefore enhanced the electrochemical signal. The interaction of aptamer and thrombin on the electrode interface results in a barrier for electrons and the electro-transfer, which decrease the DPV signals with increasing the thrombin concentration. Using this strategy, we detected thrombin within the range from 0.15 to 15 nM with a detection limit of 0.05 nM based on S/N = 3. The aptamer sensor had a good specificity, stability and reproducibility, and it may be used to develop biosensors for the detection of other proteins. (c) 2014 The Electrochemical Society. All rights reserved.