A novel label-free homogeneous electrochemical immunosensor based on proximity hybridization-triggered isothermal exponential amplification induced G-quadruplex formation

A label-free homogeneous electrochemical immunosensor was developed for sensitive and selective detection of carcino-embryonic antigen (CEA) based on proximity hybridization triggered isothermal exponential amplification induced G-quadruplex formation. The presence of CEA promoted the formation of a proximate complex via the proximity hybridization of the DNA strands labelled to affinity ligands, which unfolded the molecular beacon, the stem part of molecular beacon as a primer hybridize with the template to initiate the isothermal exponential amplification process. Thus, with the electrochemical indicator hemin selectively intercalated into the multiple G-quadruplexes, a significant electrochemical signal drop is observed, which is dependent on the concentration of the target CEA. Thus, using this "signal-off" mode, a simple, label-free homogeneous electrochemical strategy for sensitive CEA assay with a detection limit of 3.4 fg/mL is readily realized. Furthermore, this method also exhibits additional advantages of simplicity and low cost, since both expensive labeling and sophisticated probe immobilization processes are avoided. Its high sensitivity, acceptable accuracy, and satisfactory versatility of analytes led to various applications in bioanalysis. (C) 2017 Elsevier B.V. All rights reserved.