Fluorescent DNA Probing Nanoscale MnO: Adsorption, Dissolution by Thiol, and Nanozyme Activity.

Manganese dioxide (MnO) is an interesting material due to its excellent biocompatibility and magnetic properties. Adsorption of DNA to MnO is potentially of interest for drug delivery and sensing applications. However, little fundamental understanding is known about their interactions. In this work, carboxyfluorescein (FAM)-labeled DNA oligonucleotides were used to explore the effect of salt concentration, pH, and DNA sequence and length for adsorption by MnO, and comparisons were made with graphene oxide (GO). The DNA desorbs from MnO by free inorganic phosphate, while it desorbs from GO by adenosine and urea. Therefore, DNA is mainly adsorbed on MnO through its phosphate backbone, and DNA has a stronger affinity on MnO than on GO based on a salt-shock assay. At the same time, DNA was used to study the effect of thiol containing compounds on the dissolution of MnO. Adsorbed DNA was released from MnO after its dissolution by thiol, but not from other metal oxides with lower solubility such as CeO, TiO, and FeO. DNA-functionalized MnO was then used for detecting glutathione (GSH) with a detection limit of 383 nM. Finally, DNA was found to inhibit the peroxidase-like activity of MnO. This study has offered many fundamental insights into the interaction between MnO and two important biomolecules: DNA and thiol-containing compounds.