Label-free fluorescent aptasensor for potassium ion using structure-switching aptamers and berberine

• A label-free fluorescent aptasensor for K+ ion in aqueous solution is fabricated.
• Berberine is applied in aptasensor based on its senstivity for DNA for the first time.
• The limit of the detection is 31 nM, lower than those of previously reported aptamer-based K+ ion assays.
• The presented approach is rapid, simple, cost-effective and suitable for real sample.

A simple, rapid and label-free fluorescent aptasensor was fabricated for the detection of potassium ion (K+ ion) in aqueous solution using K+ ion-stabilized single stranded DNA (ssDNA) with G-rich sequence as the recognition element and a fluorescent dye, berberine, as the fluorescence probe. In the presence of K+ ion, the G-rich ssDNA is promoted to form the aptamer–target complex with a G-quadruplex conformation, and berberine binding to the G-quadruplex structure results in the enhancement of its fluorescence. The fluorescence intensity of the sensing system displayed a calibration response for K+ ion in the range of 0–1600 μM with a detection limit of 31 nM (S/N = 3) and a relative standard deviation (RSD) of 0.45%. This label-free fluorescence aptasensor is conveniently and effectively applicable for analysis of K+ ion in blood serum samples with the recovery range of 81.7–105.3%. The assay for detection of potassium ion is easy, economical, robust, and stable in rough conditions.

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