Aptasensor for label-free square-wave voltammetry detection of potassium ions based on gold nanoparticle amplification

Abstract

Herein, we present a very simple and label-free square-wave voltammetry (SWV) aptasensor to detect potassium ions (K⁺), in which a K⁺-specific aptamer was used as an ion recognition element, and a redox couple [Fe(CN)₆]^3−/4− as a redox probe. At the bare gold electrode, the redox couple [Fe(CN)₆]^3−/4− can very easily access the electrode surface to produce a very strong SWV signal. At the K⁺-specific aptamer/gold electrode surface, in the presence of K⁺, the single-stranded DNA with guanine (G)-rich sequences could fold into a secondary structure, G-quadruplex, which resulted in less availability for a redox reaction, and led to a smaller SWV current. To improve signal intensity, gold nanoparticles (AuNPs) were anchored to a gold electrode surface which had been previously modified with self-assembled monolayers of p-aminothiophenol. The SWV peak current decreased with K⁺ concentration, and the plot of the SWV peak current against the logarithm of K⁺ concentration is linear over the range from 10 pM to 0.1 μM and 0.5 μM to 1 mM, with a detection limit of 0.13 pM. The aptasensor also showed a very good selectivity for K⁺ without being affected by the coexistence of other ions.