An aptamer-based electrochemical sensing platform for the direct protein detection has been developed using IgE and a specifically designed aptamer with hairpin structure as the model analyte and probe sequence, respectively. In the absence of IgE, the aptamer immobilized on an electrode surface forms a large hairpin due to the hybridization of the two complementary arm sequences, and peak currents of redox species dissolved in solution can be achieved. However, the target protein binding can not only cause the increase of the dielectric layer but also trigger the significant conformational switching of the aptamer due to the opening of the designed hairpin structure that pushes the biomolecule layer/electrolyte interface away from the electrode surface, suppressing substantially the electron transfer (eT) and resulting in a strong detection signal. The detection limit of 3.6x10(-11)M and linear response range of 5.4x10(-11) to 3.6x10(-8)M are achieved without any amplifier. The selectivity is confirmed by interference test. More importantly, an innovative concept of adapting intelligently a surface-confined aptamer sequence is introduced, and the limitations of the conventional electrochemical aptasensors have been overcome. The proposed sensing scheme is expected to become a promising strategy for the detection of proteins and other biomacromolecules.