Light-responsive cobalt-doped graphitic carbon nitride nanozyme for the colorimetric detection of acetylcholinesterase and its inhibitor.

The rational design of nanozymes with remarkable catalytic activity remains pivotal for advancing colorimetric biosensing platforms. Graphitic carbon nitride (g-CN) has emerged as a captivating photocatalytic material given its cost-effectiveness, ease of fabrication and outstanding stability. However, its practical implementation as a light-responsive nanozyme is fundamentally constrained by suboptimal catalytic activity.

Iron-doped carbon nitride with enhanced peroxidase-like activity for smartphone-based colorimetric assay of total antioxidant capacity.

The facile detection of total antioxidant capacity (TAC) is limited by in-situ analysis, because it usually requires complex laboratory equipments. Here, a colorimetric assay for TAC detection is developed based on the peroxidase-like activity of iron-doped carbon nitride (Fe/NC) and the smartphone platform. The peroxidase-like activity of carbon nitride is greatly improved by the introduction of Fe atoms, and the active sites turn to Fe-N coordination groups in the Fe/NC.

Regulating the N Coordination Environment of Co Single-Atom Nanozymes for Highly Efficient Oxidase Mimics.

Single-atom catalysts with well-defined atomic structures and precisely regulated coordination environments have been recognized as potential substitutes for natural metalloenzymes. Inspired by the metal coordination structure of natural enzymes, we show here that the oxidase-like activity of single-atom Co catalysts greatly depends on their local N coordination around the Co catalytic sites. We synthesized a series of Co single-atom catalysts with different nitrogen coordination numbers (Co-N(C), = 2, 3, and 4) and demonstrated that the oxidase-like activity of single-atom Co catalysts could be effectively tailored by fine-tuning the N coordination.

BSA-stabilized silver nanoclusters for efficient photoresponsive colorimetric detection of chromium(VI).

Hexavalent chromium is a highly toxic substance, which will pose a serious threat to human life and health and the entire ecosystem. Therefore, it is crucial to establish a simple and rapid detection method for hexavalent chromium. In this work, we fabricated bovine serum albumin-stabilized silver nanocluster (BSA-Ag NC) which exhibited photoresponsive oxidase-like activity, catalyzing the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to the blue oxidized state TMB (oxTMB) in a short time.

Rational design and fabrication of MoS nanoclusters decorated MnCdS nanorods with promoted interfacial charge transfer toward robust photocatalytic H generation.

In this work, we report a novel MoS/MnCdS composite catalyst that has been designed and fabricated by in situ coupling MoS nanoclusters with 1D MnCdS nanorods for photocatalytic H production. The catalyst features a 1D nanostructure with MoS nanoclusters uniformly dispersed along the MnCdS nanorod. It was found that an intimate interface is built between MoS nanoclusters and MnCdS nanorods thanks to the facile in situ photoreduction route, which contributes to a high-efficiency interfacial charge separation.

Emerging interstitial/substitutional modification of Pd-based nanomaterials with nonmetallic elements for electrocatalytic applications.

Palladium (Pd)-based nanomaterials have been identified as potential candidates for various types of electrocatalytic reaction, but most of them typically exhibit unsatisfactory performances. Recently, extensive theoretical and experimental studies have demonstrated that the interstitial/substitutional modification of Pd-based nanomaterials with nonmetallic atoms (H, B, C, N, P, S) has a significant impact on their electronic structure and thus leads to the rapid development of one kind of promising catalyst for various electrochemical reactions. Considering the remarkable progress in this area, we highlight the most recent progress regarding the innovative synthesis and advanced characterization methods of nonmetallic atom-doped Pd-based nanomaterials and provide insights into their electrochemical applications.

Manganese-doped iron coordination polymer nanoparticles with enhanced peroxidase-like activity for colorimetric detection of antioxidants.

A convenient and sensitive antioxidant assay with high performance is essential for assessing food quality and monitoring the oxidative stress level of biological matrices. Although coordination polymer nanoparticles (CPNs)-based nanozymes have emerged as candidates in the analytical field, strategies to improve the catalytic activity of CPNs have been scarcely revealed and studied. Herein, we demonstrate a manganese (Mn) doping strategy to enhance the peroxidase-mimetic activity of Fe-based CPNs.

Colorimetric detection of acetylcholinesterase and its inhibitor based on thiol-regulated oxidase-like activity of 2D palladium square nanoplates on reduced graphene oxide.

A convenient and sensitive colorimetric assay for acetylcholinesterase (AChE) and its inhibitor has been designed based on the oxidase-like activity of {100}-faceted Pd square nanoplates which are grown in situ on reduced graphene oxide (PdSP@rGO). PdSP@rGO can effectively catalyze the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) without the assistance of HO to generate blue oxidized TMB (oxTMB) with a characteristic absorption peak at 652 nm. In the presence of AChE, acetylthiocholine (ATCh), a typical AChE substrate, is hydrolyzed to thiocholine (TCh).

Ultrathin PdCu alloy nanosheet-assembled 3D nanoflowers with high peroxidase-like activity toward colorimetric glucose detection.

Enzyme-mimetic properties of nanomaterials can be efficiently tuned by controlling their size, composition, and structure. Here, ultrathin PdCu alloy nanosheet-assembled three-dimensional (3D) nanoflowers (PdCu NAFs) with tunable surface composition are obtained via a generalized strategy. In presence of HO, the as-synthesized PdCu NAFs can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to the oxidized form of TMB (oxTMB) with a characteristic absorption peak at 652 nm.

Light-responsive Au nanoclusters with oxidase-like activity for fluorescent detection of total antioxidant capacity.

A fluorescent assay for total antioxidant capacity (TAC) detection based on the light-responsive oxidase-like activity of bovine serum albumin-stabilized gold nanoclusters (BSA-AuNCs) has been developed. Thiamine (TH) as the peroxidase substrate usually works at alkaline conditions and thus limits its practical applications. Here, by utilization the light-responsive oxidase-like activity of BSA-AuNCs, TH is oxidized to fluorescent thiochrome under neutral condition in two minutes due to the single oxygen generated by BSA-AuNCs upon light irradiation.

Formation of 2,3-Diaminophenazine for Evaluation of Alkaline Phosphatase Activity via the Inner Filter Effect.

We report a fluorescence assay for alkaline phosphatase (ALP) detection using generation of 2,3-diaminophenazine (OPDox) through an inner filter effect (IFE). AgNO can oxidize -phenylenediamine in a short time to obtain fluorescent OPDox. -nitrophenol is obtained from ALP-catalyzed hydrolysis of -nitrophenylphosphate, which can result in the fluorescence quenching of OPDox via the IFE.

Alkaline Phosphatase-Triggered in Situ Formation of Silicon-Containing Nanoparticles for a Fluorometric and Colorimetric Dual-Channel Immunoassay.

Enzyme-triggered in situ chromogenic and/or fluorogenic reactions under accessible conditions are significant for developing enzyme activity and related spectroscopic assays. Here, we describe a facile one-pot synthetic strategy to prepare silicon-containing nanoparticles with yellow-green fluorescence and orange-red color by mixing -[3-(trimethoxysilyl)propyl]ethylenediamine and -aminophenol (AP) in aqueous solution at a mild temperature. Encouraged by the AP-regulated simple synthetic procedure and the generation of AP from alkaline phosphatase (ALP)-catalyzed hydrolysis of 4-aminophenol phosphate (APP), a fluorometric and colorimetric dual-readout ALP activity assay can be rationally envisioned and developed by employing APP as the substrate.

Colorimetric determination of the activity of alkaline phosphatase by exploiting the oxidase-like activity of palladium cube@CeO core-shell nanoparticles.

Core-shell palladium cube@CeO (Pd cube@CeO) nanoparticles are shown to display oxidase-like activity. This is exploited in a method for determination of the activity of alkaline phosphatase (ALP). The Pd cube@CeO nanoparticles were thermally synthesized from Ce(NO), L-arginine and preformed Pd cube seeds in water.

Engineering Two-Dimensional Pd Nanoplates with Exposed Highly Active {100} Facets Toward Colorimetric Acid Phosphatase Detection.

Enzyme-like activity and efficiency of nanomaterials are strongly controlled by their size, composition, and structure, and hence the structural parameters need to be optimized. Here, we report that two-dimensional Pd nanoplates enclosed by {100}-facets [{100}PdSP@rGO] exhibit substantially enhanced intrinsic oxidase-like activities relative to the {111}-facets ones and Pd nanocubes in catalyzing the chromogenic reaction of 3,3',5,5'-tetramethylbenzidine. By taking ascorbic acid 2-phosphate as the substrate, which transforms to ascorbic acid in the presence of acid phosphatase (ACP), the {100}PdSP@rGO could be used as an efficient nanozyme for colorimetric ACP detection without resorting to destructive HO.

Logically Regulating Peroxidase-Like Activity of Gold Nanoclusters for Sensing Phosphate-Containing Metabolites and Alkaline Phosphatase Activity.

Phosphate-containing metabolites and alkaline phosphatase (ALP) activity are useful biomarkers for many types of diseases. However, there are few straightforward, sensitive, and efficient colorimetric methods for the quantification of them only when resorting to unstable transition metal ions or specially designed organic substrates. Herein, we have demonstrated that histidine-protected gold nanoclusters (His-AuNCs) possess intrinsic peroxidase-like activity with Au atom facilitated formation of superoxide anions (O) and their electron transfer ability.

Fluorometric and colorimetric dual-readout alkaline phosphatase activity assay based on enzymatically induced formation of colored Au@Ag nanoparticles and an inner filter effect.

An ultrasensitive fluorometric and colorimetric dual-mode assay is described for the determination of the activity of alkaline phosphatase (ALP). ALP catalyzes the decomposition of 2-phospho-L-ascorbic acid, and the ascorbic acid thus generated reduces silver ions. In the presence of gold nanoparticles, gold-silver nanoparticles (Au@Ag NPs) are formed.

Spectrophotometric determination of the activity of alkaline phosphatase and detection of its inhibitors by exploiting the pyrophosphate-accelerated oxidase-like activity of nanoceria.

The oxidase-like activity of nanoceria is low. This limits its practical applications. It is demonstrated here that pyrophosphate ion (PPi) can improve the oxidase-like activity of nanoceria.

Fluorometric determination of the activity of alkaline phosphatase and its inhibitors based on ascorbic acid-induced aggregation of carbon dots.

The authors describe a fluorometric method for determination of the activity of alkaline phosphatase (ALP) and its inhibitors. Nitrogen and boron co-doped carbon dots (C-dots) with excitation/emission peaks at 490/540 nm act as the fluorescent probe. The C-dots were prepared by hydrothermal carbonization starting from 3-aminophenylboronic acid as the sole precursor.

Highly sensitive fluorescent detection of glutathione and histidine based on the Cu(ii)-thiamine system.

In this work, we propose a fluorescence method for the simultaneous detection of glutathione (GSH) and histidine (His) based on the Cu(ii)-thiamine (Cu(ii)-TH) system. It is well established that non-fluorescent thiamine (TH) can be oxidized by Cu(ii) to generate fluorescent thiochrome (TC) under alkaline conditions. The introduction of GSH and His can inhibit the oxidation of TH by Cu(ii) due to the strong affinity between Cu(ii) and GSH or His.

Fluorescence assay for alkaline phosphatase based on ATP hydrolysis-triggered dissociation of cerium coordination polymer nanoparticles.

Alkaline phosphatase (ALP) is a significant biomarker for diagnostics. Simple, selective and sensitive detection of ALP activity is thus of critical importance. In this study, an artful fluorescence assay for ALP is proposed based on adenosine triphosphate (ATP) hydrolysis-triggered disassociation and fluorescence quenching of cerium coordination polymer nanoparticles (CPNs).

Fluorometric determination of sulfide ions via its inhibitory effect on the oxidation of thiamine by Cu(II) ions.

A fluorometric assay is described for sulfide ions determination. It is based on the finding that the oxidation of the non-fluorescent substrate thiamine (TH) by Cu(II) in basic solution to form fluorescent thiochrome is inhibited by sulfide ions. This results in a decrease in fluorescence intensity which is proportional to the concentration of sulfide ions.

Carbon dots based fluorescent sensor for sensitive determination of hydroquinone.

In this paper, a novel biosensor based on Carbon dots (C-dots) for sensitive detection of hydroquinone (H2Q) is reported. It is interesting to find that the fluorescence of the C-dots could be quenched by H2Q directly. The possible quenching mechanism is proposed, which shows that the quenching effect may be caused by the electron transfer from C-dots to oxidized H2Q-quinone.

Nitrogen and fluorine dual-doped mesoporous graphene: a high-performance metal-free ORR electrocatalyst with a super-low HO2(-) yield.

In this study, we successfully, for the first time, prepared nitrogen and fluorine dual-doped mesoporous graphene (NF-MG) via the thermal treatment of graphene oxide/polyaniline composites (GO/PANI) and NH4F. Benefiting from the synergistic effect of N and F co-doping into the G framework, the oxygen reduction reaction performance of the optimal catalyst (NF-MG3) is comparable with the-state-of-the-art Pt/C catalyst in an alkaline medium, which makes it an ideal candidate as an efficient metal-free ORR electrocatalyst in fuel cells.

Label-free fluorescence detection of mercury ions based on the regulation of the Ag autocatalytic reaction.

In this work, a novel facile nanoparticle autocatalytic sensor based on the inhibition of the Ag autocatalytic reaction for the determination of Hg(2+) was developed. o-Phenylenediamine (OPD) tended to be oxidized into 2,3-diaminophenazine (OPDox) by silver ions (Ag(+)) followed by the formation of silver nanoparticles (AgNPs). Employed as a catalyst, the thus-formed AgNPs would further promote the reaction between OPD and Ag(+).

Aptamer-based colorimetric biosensing of abrin using catalytic gold nanoparticles.

In this study we propose a simple and sensitive colorimetric aptasensor for the quantitative analysis of abrin by using catalytic AuNPs for the first time. AuNPs possess the peroxidase-like activity that can catalyse 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2, leading to color change of the solution. It is interesting to find that the peroxidase-like activity of AuNPs can be improved by surface activation with a target-specific aptamer.