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 Co²⁺, recovered the fluorescence of SiQDs and reduced the emission of oxOPD. Fluorescence ratio at F₄₅₇/F₅₇₂ serves as signal output for AChE detection within 5 × 10^-5-0.05 and 0.05-10 U mL^-1, with a limit of detection (LOD) of 3.2 × 10^-5 U mL^-1. The sensing strategy was applied for AChE assay in human blood and erythrocyte.