Ultrasmall Magneto-chiral Cobalt Hydroxide Nanoparticles Enable Dynamic Detection of Reactive Oxygen Species in Vivo

Biological application of chiral nanoparticles (NPs) has aroused enormous levels of attention over recent years. Here, we synthesized magneto-chiral cobalt hydroxide (Co(OH)₂) NPs that exhibited strong chiroptical and unique magnetic properties and applied these NPs to detect and monitor reactive oxygen species (ROS) in living cells and in vivo. Circular dichroism (CD) and magnetic resonance imaging (MRI) signals of the magneto-chiral Co(OH)₂ NPs exhibited a wide intracellular ROS detection range from 0.673 to 612.971 pmol/10⁶ cells with corresponding limits of detection (LOD) at 0.087 and 0.179 pmol/10⁶ cells, far below that of currently available probes; the LOD for d-aspartic acid coated Co(OH)₂ NPs (d-Co(OH)₂ NPs) was 5.7 times lower than that for l-aspartic acid coated Co(OH)₂ NPs (l-Co(OH)₂ NPs) based on the CD signals. In addition, d-Co(OH)₂ NPs also exhibited dynamic ROS monitoring ability. The high levels of selectivity and sensitivity to ROS in complex biological environments can be attributed to the Co²⁺ oxidation reaction on the surface of the NPs. Furthermore, magneto-chiral Co(OH)₂ NPs were able to quantify the levels of ROS in living mice by fluorescence and MRI signals. Collectively, these results reveal that magneto-chiral Co(OH)₂ NPs exhibit a remarkable ability to quantify ROS levels in living organisms, and could therefore provide new tools for exploring chiral nanomaterials as a potential biosensor to investigate biological events.