Fluorescent DNA Probing Nanoscale MnO₂: Adsorption, Dissolution by Thiol, and Nanozyme Activity

Abstract

Manganese dioxide (MnO₂) is an interesting material due to its excellent biocompatibility and magnetic properties. Adsorption of DNA to MnO₂ 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 MnO₂, and comparisons were made with graphene oxide (GO). The DNA desorbs from MnO₂ by free inorganic phosphate, while it desorbs from GO by adenosine and urea. Therefore, DNA is mainly adsorbed on MnO₂ through its phosphate backbone, and DNA has a stronger affinity on MnO₂ 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 MnO₂. Adsorbed DNA was released from MnO₂ after its dissolution by thiol, but not from other metal oxides with lower solubility such as CeO₂, TiO₂, and Fe₃O₄. DNA-functionalized MnO₂ 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 MnO₂. This study has offered many fundamental insights into the interaction between MnO₂ and two important biomolecules: DNA and thiol-containing compounds.