Triple-helix molecular switch-induced hybridization chain reaction amplification for developing a universal and sensitive electrochemical aptasensorElectronic supplementary information (ESI) available: Additional figures and tables as noted in the text. See DOI: 10.1039/c6ra19526a

In this work, a universal and sensitive "signal-on" electrochemical aptasensor platform has been developed based on a triple-helix molecular switch (THMS)-induced hybridization chain reaction (HCR) amplification. This aptasensor platform system consists of a THMS-based molecular recognition process in a homogeneous solution and a HCR amplification on a gold electrode. In the absence of a target, the aptamer sequence is flanked by two arm segments (APT) and the triplex-forming oligonucleotide (TFO), forming a rigid THMS. It is in the eT off state. However, upon the introduction of a target, the interaction between the target and the APT leads to the dissociation of the THMS and thereby liberates the TFO, allowing the TFO to hybridize with the capture probe (CP) DNA and trigger the formation of dsDNA polymers through in situ HCR amplification. The dsDNA polymers cause the electrostatic attraction of numerous electroactive indicators [Ru(NH 3 ) 6 ] 3+ , resulting in significantly amplified electrochemical signal output. It is in the eT on state. As proof-of-principle, we use this approach to detect adenosine and human α-thrombin (Tmb), achieving lowest limit of detection values of 0.6 nM and 70.9 pM, respectively. As an electrochemical aptasensor platform, its universality can be easily realized by altering only the sequence of the APT, which provides a promising alternative to the electrochemical detection of a variety of analytes and may have potential applications in biomedical research and clinical diagnosis. In this work, a universal and sensitive "signal-on" electrochemical aptasensor platform has been developed based on a triple-helix molecular switch (THMS)-induced hybridization chain reaction (HCR) amplification.