Engineering an Enzymatic Cascade Catalytic Smartphone-Based Sensor for Onsite Visual Ratiometric Fluorescence-Colorimetric Dual-Mode Detection of Methyl Mercaptan.

Precise and reliable onsite detection of methyl mercaptan (CH 3 SH) is of great significance for environmental surveillance. Here, we synthesized a novel blue fluorescence nanozyme CeO 2 @TPE with high peroxidase-like activity by employing aggregation-induced emission (AIE) tetraphenylethene (TPE) to embed into hollow CeO 2 nanospheres. In the presence of ethanol oxidase (AOX) and o -phenylenediamine (OPD), we engineered an enzymatic cascade activation ratiometric fluorescence-colorimetric dual-mode system AOX/CeO 2 @TPE + OPD toward CH 3 SH. In this design, CH 3 SH initiated AOX catalytic activity to convert it into H 2 O 2 for activating the peroxidase-like activity of CeO 2 @TPE, producing • OH for oxidizing the naked-eye colorless OPD into deep yellow 2,3-diaminophenazine (DAP) with an absorption enhancement at ∼425 nm, companied by a new emission peak at ∼550 nm to match with the intrinsic emission at ∼441 nm for observing ratiometric fluorescence response, enabling a ratiometric fluorescence-colorimetric dual-mode analysis. Interestingly, both the ratiometric fluorescence and colorimetric signals could be gathered for being converted into the hue parameter on a smartphone-based sensor, achieving the onsite visual fluorescence-colorimetric dual-mode detection of CH 3 SH in real environmental media with acceptable results. This study gave a novel insight into designing target-responsive enzymatic cascade activation system-based efficient and reliable dual-mode point-of-care sensors for safeguarding environmental health.