A Highly Selective Mn(II)-Specific DNAzyme and Its Application in Intracellular Sensing

[Image: see text] Manganese is an essential trace element in the human body that acts as a cofactor in many enzymes and metabolisms. It is important to develop methods to detect Mn(2+) in living cells. While fluorescent sensors have been very effective in detecting other metal ions, Mn(2+)-specific fluorescent sensors are rarely reported due to nonspecific fluorescence quenching by the paramagnetism of Mn(2+) and poor selectivity against other metal ions such as Ca(2+) and Mg(2+). To address these issues, we herein report in vitro selection of an RNA-cleaving DNAzyme with exceptionally high selectivity for Mn(2+). Through converting it into a fluorescent sensor using a catalytic beacon approach, Mn(2+) sensing in immune cells and tumor cells has been achieved. The sensor is also used to monitor degradation of manganese-based nanomaterials such as MnOx in tumor cells. Therefore, this work provides an excellent tool to detect Mn(2+) in biological systems and monitor the Mn(2+)-involved immune response and antitumor therapy.