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A fluorescent and photothermal dual-mode assay method was established for the detection of acetylcholinesterase (AChE) activity based on in situ formation of o -phenylenediamine ( o PD) cascade polymers. First, copper metal–organic frameworks of benzenetricarboxylic acid (Cu-BTC) were screened out as nanozymes with excellent oxidase-like activity and confinement catalysis effect. Then, an ingenious o PD cascade polymerization strategy was proposed. That is, o PD was oxidized by Cu-BTC to o PD oligomers with strong yellow fluorescence, and o PD oligomers were further catalyzed to generate J-aggregation, which promotes the formation of o PD polymer nanoparticles with a high photothermal effect. By utilizing thiocholine (enzymolysis product of acetylthiocholine) to inhibit the Cu-BTC catalytic effect, AChE activity was detected through the fluorescence–photothermal dual-signal change of o PD oligomers and polymer nanoparticles. Both assay modes have low detection limitation (0.03 U L –1 for fluorescence and 0.05 U L –1 for photothermal) and can accurately detect the AChE activity of human serum (recovery 85.0–111.3%). The detection results of real serum samples by fluorescent and photothermal dual modes are consistent with each other (relative error ≤ 5.2%). It is worth emphasizing that this is the first time to report the high photothermal effect of o PD polymers and the fluorescence–photothermal dual-mode assay of enzyme activity.
Li et al. (Sun,) studied this question.