Hydroxyl radical-mediated synthesis of carbonyl functionalized graphene quantum dots-like as enzyme mimics with tunable fluorescence emission.

The synthesis of graphene quantum dots-like enriched with specific oxygenated groups (o-GQDs) exhibiting great catalytic performance offers a promising tool for diagnosis and biomedicine, but introducing specific oxygen groups remains a challenge. Here, we propose a mild synthetic protocol for producing regulated fluorescence emission (from blue to yellow) carbonyl functionalized GQDs with double catalytic function through Fe3O4-catalyzed hydroxyl radical (·OH) oxidation the precursors like graphene oxide, polyaniline (PANI) and polydopamine (PDA). The method can be carried out at room temperature than the traditional high-temperature oxidation in concentrated acid. Interestingly, o-GQDs exhibit excellent peroxidase (POD)- and ascorbate oxidase-like activity. XPS characterization showed a significant increase in carbonyl content in o-GQDs compared to the precursor, even a 14-fold increase in blue-emitting iron-doped GQDs (b-Fe-GQDs). The introduction of Fe3O4 during the synthesis process results in a minor degree of Fe doping, which enhances the catalytic activity of b-Fe-GQDs through coordination with N. Based on this feature, highly sensitive single-signal and ultra-selective dual-signal methods for alkaline phosphatase detection were developed. This low cost and safe synthesis strategy paves the way for practical usage of o-GQDs.

Oxygen-functionalized Fe3O4@o-polypyrrole acting as high-efficiency oxidase mimics and their application in glutathione colorimetric sensing.

The enzyme-like properties of nanozymes may be considerably affected by the structure and surface groups, which thus need to be optimized. Here, through a simple NaOH chemical corrosion method, the chemical structure similar to N-Methylpyrrolidone (NMP), which possessed intrinsic oxidase-like activity, was introduced into polypyrrole (PPy), and then this nanomaterial became oxygen-functionalized PPy (o-PPy) with excellent oxidase-like activity from PPy without this property. Furthermore, after compounding magnetic Fe3O4, the obtained nanocomposites Fe3O4@o-PPy nanoparticles (Fe3O4@o-PPy NPs) showed superiorities in separation during synthesis and real-time control of enzyme catalysis. Studies have found that the enzymatic activity of Fe3O4@o-PPy NPs depended on the amount of functionalized oxygen and the conjugation extent of o-PPy. Fe3O4@o-PPy NPs had efficient oxidase-like activity under a wide range of pH and temperature. Based on the oxidase-like activity of Fe3O4@o-PPy NPs, a colorimetric sensor for glutathione (GSH), which presented rich color changes and satisfactory colorimetric resolution by adding the amaranth, was realized. We believe that the functional modification and structural regulation of PPy can not only realize its wider application but also promote the discovery of novel and efficient nanozymes.

Smartphone-assisted hydrogel platform based on BSA-CeO2 nanoclusters for dual-mode determination of acetylcholinesterase and organophosphorus pesticides.

A dual-mode sensor was developed for detecting acetylcholinesterase (AChE) and organophosphorus pesticides (OPs) via bifunctional BSA-CeO2 nanoclusters (NCs) with oxidase-mimetic activity and fluorescence property. The dual-mode sensor has the characteristics of self-calibration and self-verification, meeting the needs of different detection conditions and provide more accurate results. The colorimetric sensor and fluorescence sensor have been successfully used for detecting AChE with limit of detection (LOD) of 0.081 mU/mL and 0.056 mU/mL, respectively, while the LOD for OPs were 0.9 ng/mL and 0.78 ng/mL, respectively. The recovery of AChE was 93.9-107.2% and of OPs was 95.8-105.0% in actual samples. A novel strategy was developed to monitor pesticide residues and detect AChE level, which will motivate future work to explore the potential applications of multifunctional nanozymes.

A molecularly imprinted ratiometric fluorescence sensor based on blue/red carbon quantum dots for the visual determination of thiamethoxam.

Neonicotinoids such as thiamethoxam (TMX) were widely used in agricultural production and tended to accumulate in the environment, potentially harming human and ecosystem health. To enable widespread monitoring of TMX residues, it was essential to design a reliable and sensitive detection method. Here, we developed a novel smartphone-enablled molecularly imprinted ratiometric fluorescence sensing system for selective on-site detection of TMX. It was based on blue-emission carbon dots (CDs) wrapped with a molecularly imprinted layer (B-CDs@MIPs), which provided the response signal, while red-emission CDs (R-CDs) served as an internal reference. The fluorescence signal ratio of the sensor increased with the TMX concentration, resulting in an obvious fluorescence color change from red to blue. The sensor exhibited a satisfactory limit of detection (LOD) of 13.5 nM in fluorescence analysis while LOD of 70.1 nM in visual determination. In addition, the sensing system was validated using food and environment samples, exhibiting recoveries from 91.40% to 105.7%, indicating excellent reliability for TMX detection in actual samples. Thus, the sensing system developed in this study offered promising prospects for visual detection of pesticide residues in complex environmental samples.

A biosensor based on Fe3O4@MXene-Au nanocomposites with high peroxidase-like activity for colorimetric and smartphone-based detection of glucose.

A novel magnetic nanozyme Fe3O4@MXene-Au nanocomposite, which possessed higher peroxidase-like activity than that of Fe3O4 nanoparticles and Fe3O4@MXene nanocomposites, was developed. The outstanding magnetic properties of the nanozyme endowed it with the ability of simple and rapid separation, achieving great recyclability. Based on Fe3O4@MXene-Au nanocomposites and glucose oxidase (Glu Ox), a highly selective colorimetric biosensor for glucose detection was developed. Fe3O4@MXene-Au nanocomposites can catalyze H2O2 produced from glucose catalyzed by glucose oxidase to ·OH and oxidize colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxidized TMB (oxTMB) with a significant absorbance at 652 nm. The linear range of glucose was 0-1.4 mM under optimal conditions, with a limit of detection (LOD) of 0.11 mM. Glucose in human whole blood was successfully detected with satisfactory recoveries. Furthermore, a facile agarose hydrogel detection platform was designed. With smartphone software, glucose detection can be realized by the agarose hydrogel platform, demonstrating the potential in on-site and visual detection of glucose.

Magnetic dummy template molecularly imprinted particles functionalized with dendritic nanoclusters for selective enrichment and determination of 4-methylnitrosamino-1-(3-pyridyl)-1-butanone (NNK) in tobacco products.

The compound 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), one of the tobacco specific nitrosamines (TSNAs), is widely recognized as a major carcinogen found in tobacco products, environmental tobacco smoke and wastewater. Thus, a selective enrichment and sensitive detection method for monitoring the risk of NNK exposure is highly desirable. In this study, a magnetic molecularly imprinted polymer (MMIP) functionalized with dendritic nanoclusters was synthesized to selectively recognize NNK via the dummy template imprinting strategy, aiming to avoid residual template leakage and increase the imprinting efficiency. The nanocomposites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, as well as vibrating sample magnetometry (VSM) and nitrogen adsorption/desorption analysis. The resulting MMIPs exhibited high adsorption capacity, fast binding kinetics and good selectivity for trace amounts of NNK. A rapid, low cost and efficient method for detecting NNK in tobacco products was established using magnetic dispersive solid-phase extraction coupled with HPLC-DAD with a good linear range of 0.1-250 µg mL-1. The limit of detection (LOD) and limit of quantification (LOQ) of NNK were 13.5 and 25.0 ng mL-1, respectively. The average recoveries were 87.8-97.3% with RSDs lower than 3%. The results confirmed that the MMIPs could be used as an excellent selective adsorbent for NNK, with potential applications in the pretreatment of tobacco products.