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 Pb(2+) in blood samples. In this contribution, a novel colorimetric potassium sensing assay that functions in the presence of Pb(2+) 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(+), Pb(2+) 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 H(2)O(2). Importantly, studies presented here show that K(+) replaces Pb(2+) from the G-quadruplex to form K(+)-stabilized G-quadruplex, which differ in the catalytic behavior. With Pb(2+)-stabilized G-quadruplex as a probe, a highly sensitive and selective colorimetric detection of K(+) is achieved in the presence of Pb(2+) 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 Pb(2+). Finally, the sensor is successfully applied for K(+) detection in a real human serum sample containing Pb(2+).