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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