Using Magnetic Pt/Os Nanozyme to Catalyze Methylene Blue Urea Derivative: A Novel Dual-Mode Strategy for the Detection of Acetylcholinesterase and Inhibitors

Abstract

The accurate detection of acetylcholinesterase (AChE) activity and its inhibitors is imperative for the timely diagnosis and precise therapy of neurodegenerative diseases. Though nanozyme-based biosensing offers high sensitivity, single-mode detection methods are not reliable enough, and some dual-mode detection strategies are complex and require expensive equipment. Here, we propose an innovative colorimetric/fluorescence dual-mode sensing platform for the detection of AChE and its inhibitors. Notably, this platform integrated methylene blue urea derivative (MBU-EP) and peroxidase-like nanozyme Fe₃O₄@polydopamine@Pt/Os, which catalyze MBU-EP turn from colorless and non-fluorescent emission to deep blue MB with significantly enhanced fluorescence emission, yielding both colorimetric and fluorescence signals. Concurrently, the production of thiocholine from AChE-catalyzed acetylthiocholine in vitro significantly inhibits the generation of MB, thereby enabling the sensitive detection of AChE activity and its inhibitors via a dual readout. The sensitive and convenient dual-mode sensor achieved low AChE detection limits of 0.13 mU mL⁻¹ (colorimetry) and 0.18 mU mL⁻¹ (fluorometry). The linear minimum value of 0.5 mU mL⁻¹ in colorimetric mode is superior to the corresponding value of 2 mU mL⁻¹ for the same concentration of 3,3′,5,5′-tetramethylbenzidine (TMB). Additionally, the sensor was employed for screening the AChE inhibitor, rivastigmine tartrate, with closely IC₅₀ values of 0.988 μM (colorimetry) and 0.924 μM (fluorometry). These results demonstrated the considerable potential of the innovative MBU-EP dual-mode sensing strategy for the detection of various molecules in biological applications.