CoOOH nanosheets ensure ratiometric fluorescence assay of acetylcholinesterase.

Cobalt oxyhydroxide nanosheets (CoOOH) with peroxidase-like activity provide a promising probe for acetylcholinesterase (AChE) sensing through a ratiometric fluorescence strategy. Fluorescence of silicon quantum dots (SiQDs) at 457 nm was quenched by CoOOH on account of inner-filter effect (IFE). Meanwhile, the nonfluorescent o-phenylenediamine (OPD) was catalytically oxidized to 2,3-diaminophenazine (oxOPD) by CoOOH nanosheets with emission at 572 nm. The acetylcholine (ATCh) was catalytically hydrolyzed by AChE to enzymatic thiocholine (TCh), which decomposed CoOOH to Co, recovered the fluorescence of SiQDs and reduced the emission of oxOPD. Fluorescence ratio at F/F serves as signal output for AChE detection within 5 × 10-0.05 and 0.05-10 U mL, with a limit of detection (LOD) of 3.2 × 10 U mL. The sensing strategy was applied for AChE assay in human blood and erythrocyte.