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

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 mu M and 0.5 mu M 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.