Aptamer biosensor for label-free impedance spectroscopy detection of potassium ion based on DNA G-quadruplex conformation.

Herein, a label-free and highly sensitive electrochemical impedance spectroscopy (EIS) aptasensor for the detection of potassium ion (K⁺) was developed based on a conformational change in which a K⁺-stabilized single stranded DNA (ssDNA) with G-rich sequence was used as the recognition element. In the measurement of K⁺ ions, the change in interfacial electron transfer resistance (R(ct)) of the sensor using a redox couple of [Fe(CN)₆]³⁻/⁴⁻ as the probe was monitored. In the presence of K⁺, the G-rich DNA folded into the G-quadruplex structure, and then K⁺ can bind to the G-quadruplex structure, leading to an increase in the R(ct). The Rct increased with K⁺ concentration, and the plot of R(ct) against the logarithm of K⁺ concentration is linear over the range from 0.1 nM to 1 mM with a detection limit of 0.1 nM. Other metal ions, such as Ca²⁺, Mg²⁺, Na⁺, Li⁺, Al³⁺, Zn²⁺, Cu²⁺, and Ni²⁺ caused no notable interference on the detection of K⁺. The scheme reported herein is applicable to the detection of other kinds of G-rich aptamer-binding chemicals and biomolecules.