A novel colorimetric potassium sensor based on the substitution of lead from G-quadruplex

Potassium ions play diverse roles in biological processes, and abnormal K+ levels are the hallmarks of diseases. However, the potential clinical application of the developed DNA-based K+ sensors remains a challenge due to the presence of Pb2+ in blood samples. In this contribution, a novel colorimetric potassium sensing assay that functions in the presence of Pb2+ is reported. This approach is based on conformational switching of a hairpin DNA structure to a G-quadruplex. Specifically, the hairpin DNA containing G-rich aptamer T30695 is exposed to successive amounts of Na+, Pb2+ and K+. These cations induce formation of the corresponding metal-stabilized G-quadruplex, which acts as DNAzyme (with hemin as a cofactor) for the catalytic oxidation of ABTS by H2O2. Importantly, studies presented here show that K+ replaces Pb2+ from the G-quadruplex to form K+-stabilized G-quadruplex, which differ in the catalytic behavior. With Pb2+-stabilized G-quadruplex as a probe, a highly sensitive and selective colorimetric detection of K+ is achieved in the presence of Pb2+ and excessive Na+ (140 mM) with the detection limit of 1.9 nM. This system represents the first known DNAzyme-based colorimetric K+ sensor, which works in the presence of Pb2+. Finally, the sensor is successfully applied for K+ detection in a real human serum sample containing Pb2+.