In Situ Formation of o-Phenylenediamine Cascade Polymers Mediated by Metal–Organic Framework Nanozymes for Fluorescent and Photothermal Dual-Mode Assay of Acetylcholinesterase Activity

Abstract

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 (oPD) 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 oPD cascade polymerization strategy was proposed. That is, oPD was oxidized by Cu-BTC to oPD oligomers with strong yellow fluorescence, and oPD oligomers were further catalyzed to generate J-aggregation, which promotes the formation of oPD 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 oPD 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 oPD polymers and the fluorescence−photothermal dual-mode assay of enzyme activity.

Revisiting o-Phenylenediamine as a Nanomaterial-Catalyzed Signaling Agent: Dimerization versus Polymerization

“…Importantly, this result is the first observation of a nonmonotonic kinetic transition in extinction during the nanoparticle-catalyzed oxidation of OPD, which is similarly obtained with NaF and NaBr (Figure S1, Supporting Information). Previously, the decrease in fluorescent signal intensity of DAP owing to its polymerization was reported . This finding raises questions about the quantitative use of OPD as a signaling agent in bioanalysis.…”

“…OPD is often used as a precursor of heterocyclic compounds whose aromatic rings exhibit distinctive physical properties such as absorption in the visible range and electrical conductivity. Based on such properties, OPD has been intensively studied for its wide applications such as colorimetric and photothermal signaling agents in biosensing systems, − organic electrode material, , and corrosion inhibitor . In particular, colorimetric quantification of specific targets has taken advantage of the color changes of OPD from colorless to yellow, where the wavelength at which the maximum absorption occurs (λ max ) is 425 nm.…”

Dual-functional Nanomaterials Polyo-phenylenediamine and Ru–Au Complement Each Other to Construct an Electrochemical and Electrochemiluminescent Dual-Mode Aptamer Sensor for Sensitive Detection of Alternariol

“…However, these single-signal technologies may produce false positive output, representing an inherent vulnerability in individual detection methods. To address this limitation, researchers increasingly focus on dual-signal output through dual-mode detection technologies . This approach offers the advantage of mutually supporting monitoring results between the two modes, thereby significantly enhancing accuracy and reliability. − For instance, Mi et al designed an electrochemical luminescence/impedance spectroscopy dual-mode sensor to detect cardiac troponin I. Deng et al used photoelectrochemical and electrochemical dual-signal output to sensitively monitor miRNA.…”

“…To address this limitation, researchers increasingly focus on dual-signal output through dual-mode detection technologies. 14 This approach offers the advantage of mutually supporting monitoring results between the two modes, thereby significantly enhancing accuracy and reliability. 15−17 For instance, Mi et al 18 designed an electrochemical luminescence/impedance spectroscopy dual-mode sensor to detect cardiac troponin I. Deng et al 19 demonstrate satisfactory detection performance using the aforementioned strategies.…”

Ultrasensitivity Detecting AChE through “Covalent Assembly” and Signal Amplification Strategic Approaches and Applied to Screen Its Inhibitor

“…There are a number of methods for detecting AChE, such as colorimetric methods, − electrochemical assay, high-efficiency chromatography, and fluorescence methods. − Among them, fluorescence detection has attracted attention and great prospects due to its simplicity, convenience, and high sensitivity. The most common fluorescence detection strategy for AChE now was coupling of AChE with thiocholine (TCh), where AChE was used to catalyze acetylthiocholine (ATCh) to generate TCh and then induce the reproductive behavior from organic small-molecule fluorescent probes , or advanced nanomaterials (such as metal nanomaterials, − carbon dots, , polymers, − aggregation-induced luminescent materials, − etc.). In spite of this, the coupling strategy still has problems such as low sensitivity and poor portability and thus directly affects the sensitive, quantitative detection of early diagnosis of related diseases.…”