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 (Rct) 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 Rct. The Rct increased with K+ concentration, and the plot of Rct 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.