A novel label-free fluorescent sensor for the detection of potassium ion based on DNAzyme

A novel label-free and sensitive fluorescent aptasensor for the detection of potassium ion (K+) was developed based on the horseradish peroxidase–mimicking DNAzyme (HRP–DNAzyme). In this work, we selected a K+-stabilized single stranded DNA (ssDNA) with G-rich sequence as the recognition element. In the presence of K+, the G-rich DNA folded into the G-quadruplex structure, and then hemin can bind to the G-quadruplex structure as a co-factor and form HRP–DNAzyme. 3-(p-Hydroxyphenyl)-propanoic acid (HPPA) can be oxidized by H2O2 into a fluorescent product in the presence of DNAzyme. The fluorescence intensity of the HPPA oxidative product increased with the K+ concentration. Under the optimal conditions, the fluorescence intensity was linearly related to the logarithm of K+ concentration in the range of 2.5 μM to 5 mM. Other metal ions, such as Na+, Li+, NH4+, Mg2+ and Ca2+ caused no notable interference on the detection of K+.