A Novel Aptasensor Based on the Formation of Intermolecular G Quadruplex DNA and Carbon Dots for Fluorescence Determination Potassium Ions in Human Urine and Blood Serum Samples

The development of a high-performance biosensor for potassium ion (K
⁺
) analysis is desirable for clinical diagnostics. In the present study, a sensitive and selective biosensor has been presented for the K
⁺
determination using G-rich ssDNA as a recognition tool. A fluorimetric assay based on intermolecular G-quadruplex was introduced using metal sulfide (CoS and CuS) nanosheets as quenchers and carbon dots (CDs) as fluorescence probes conjugated to a G-rich ssDNA (CDs-aptamer). This biosensor was based on the adsorption CDs-aptamer on the surface of nanosheets via van der Waals forces, which resulted in reducing the fluorescence signal. By addition K+ to the system, CDs-aptamer folded into G-quadruplex structure that causes to detach from nanosheets. As a result, the fluorescence signal was increased proportionally to K+ concentration. The present biosensor can detect K+ sensitively and selectively with 12.3 nmol L
^-1
as a low detection limit. A linear range was achieved from 50.0 nmol L
^-1
to 1000 nmol L
^-1
. Furthermore, this biosensor has been successfully applied for the detection of K+ in the real samples and was validated by comparing the data of analyzing real samples to results obtained by the ion-selective electrode (ISE).