Green synthesis of hawthorn polysaccharide-stabilized Pd@Ru nanozymes for sensitive colorimetric detection of organophosphorus pesticides.

Appropriate addition of phosphate salt in food can improve the food quality and taste. However, extensive intake of phosphate salt may lead to some human diseases such as hyperphosphatemia and renal insufficiency. Thus, it is essential to establish a cost-effective, convenient, sensitive, and selective method for monitoring phosphate ion (Pi) to ensure food quality control. In this work, a Co-based metal-organic frameworks (Co-MOF) nanomaterial with dual functions (peroxidase-like activity and specific recognition) was designed for acting as a catalytic chromogenic platform for sensitive detection of Pi. The Co2+ nodes not only provide high enzyme-like activity to catalyze the 3,3′,5,5′--tetramethylbenzidine (TMB) substrate to blue oxTMB (652 nm) but also act as selective sites for Pi recognition. The use of cationic organic ligands (2-methylimidazole) and cationic metal ions (Co2+) endows the Co-MOF with a strong positive surface charge, which is beneficial to the capture of negative-charged Pi and the dramatically suppressed TMB oxidation. When Pi exists, it specifically adsorbs onto the Co-MOF through the Co-O-P bond and the strong electrostatic interaction, leading to the change of surface charge on Co-MOF. The peroxidase-like catalytic activity of Co-MOF is thus restrained, causing a different catalytic effect on TMB oxidation from that without Pi. Based on this principle, a colorimetric assay was established for rapid and sensitive detection of Pi. A good linear relationship was obtained between Pi concentration and the absorbance at 652 nm, with a linear range of 0.009–0.144 mg/L and a detection limit of 5.4 μg/L. The proposed assay was applied to the determination of Pi in actual food samples with recoveries of 92.2–108% and relative standard deviations (RSDs) of 2.7–7.3%, illustrating the promising practicality for actual samples analysis.

The intrinsic peroxidase-like activity of hollow Prussian Blue nanoparticle-loaded with gold nanoparticles (Au@HMPB NPs) were applied to oxidize the substrate 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2 to give a blue-green coloration. The morphology of the Au@HMPB NPs and its peroxidase-mimicking activity was characterized in detail. The catalytic activity follows Michaelis-Menten kinetics and is higher than that of HMPB NPs not loaded with gold nanoparticles. The NPs were employed to detect L-lactic acid colorimetrically (at 450nm) via detection of H2O2 that is generated during enzymatic oxidation by L-lactate oxidase (LOx). The limit of detection is 4.2μM. The assay was successfully applied to the quantitation of L-lactic acid in spiker human serum samples. Graphical abstract Gold nanoparticle-loaded hollow Prussian Blue nanoparticles (Au@HMPB NPs) with peroxidase-like catalytic activity can oxidize the substrate 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2. The nanoparticles were applied for the detection of L-lactic acid through detection of H2O2 that is generated by L-lactate oxidase (LOx) catalyzed oxidation of L-lactic acid.

A peroxidase-like nanoenzyme based on strontium(II)-ion-exchanged Prussian blue analogue derivative SrCoO3/Co3O4 nanospheres and carbon quantum dots for the colorimetric detection of tigecycline in river water

An innovative multi-color colorimetric method integrated with smartphone detection was designed with great sensitivity and specificity for the determination of mercury ions (Hg2+) in aqueous samples based on platinum nanoparticles (PtNPs) and gold nanorods (AuNRs). The peroxidase-mimicking activity of PtNPs triggered the conversion of 3,3',5,5'-tetramethylbenzidine (TMB) into its oxidized form (TMB2+), and the resulting TMB2+ could quantitatively etch AuNRs, inducing a distinct color transition from blue-green to pale red. By forming metallophilic interactions with the PtNPs, Hg2+ effectively suppressed the etching process of the AuNRs by inhibiting PtNPs' peroxidase-like catalytic activity. Based on this principle, a correlation allowed for the quantification of Hg2+ by measuring the average color intensity (Ic) calculated from red, green, and blue (RGB) values of the reaction solution, exhibiting a linear response ranging from 10 to 400 nM with a detection limit (LOD) of 5.1 nM. The method also exhibited outstanding selectivity and anti-interference capability against competing metal ions. Robust practical applicability was confirmed in complex real water samples with satisfactory spike-and-recovery results. Moreover, the proposed sensor integrated AuNRs served as a multi-color indicator for Hg2+-modulated peroxide-mimicking enzyme activity of PtNPs, with smartphone-based RGB analysis, presenting a rapid and cost-effective solution for field-based environmental monitoring of mercury contamination.

Magnetically controlled all-in-one sensing platform for triple-mode detection of organophosphorus pesticides using DNA tetrahedrons-polydopamine reporters.

Synergistic impact of cerium oxide decorated reduced graphene oxide (CeO2/r-GO) composite on peroxidase-mimic activity for sensitive colorimetric detection of H2O2 and glucose.

To enhance the peroxidase-like performance and its application in detection of toxic o-aminophenol (o-AP), a kind of bimetal Cu-Zn oxide-based mesoporous nanosphere (Cu2/3Zn1/3O PNPs) was constructed under microwave-radiation conditions. Its mesoporous microstructure and peroxidase-like catalytic activity were investigated in detail. The results showed that Cu2/3Zn1/3O PNPs possessed a high specific surface area of 34.89 m2g-1 and a well-distributed mesoporous size of approximate 6.07nm, which endowed the superior peroxidase-like performance. The materialcatalyzes the oxidization of 3,3',5,5'-tetramethylbenzidine (TMB) with Km/Vmax of 0.104mM/3.79 × 10-8M·s-1 in the presence of H2O2. Especially o-AP could exclusively deteriorate the characteristic UV-Vis absorbance intensity at 653nm (A653) of the Cu2/3Zn1/3O PNPs-TMB-H2O2 system with obvious color change from blue to colorless. Under the optimal conditions, the effect of some interfering substances was low and the limit of detection (LOD) for o-AP was 1.65 × 10-8mol/L (S/N = 3). When applied to thecolorimetric detection of o-AP in practice, the recovery was between 96.1 and 107.2% with R.S.D. less than 2.04%. The mechanism of synergic-enhancement peroxidase-mimic activity of Cu2/3Zn1/3O PNPs and its exclusive colorimetric response to o-AP were proposed as well.

An effective signal amplification strategy based on temperature-amplification synergistic pressure was designed for the sensitive detection of carcinoembryonic antigen (CEA) by using a noncontact point-of-care testing (POCT) aptasensor with a flexible pressure sensor based on a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)-modified sponge (PEDOT:PSS-sponge). In the biological recognition system, target analyte triggered the release of platinum nanoparticle-labeled complementary DNA (Pt-cDNA) from CEA aptamer-conjugated magnetic beads. On the basis of the unique characteristics of platinum nanoparticles (e.g., catalytic ability for H2O2 decomposition, peroxidase-like catalytic activity, and photothermal characteristics), the platinum nanoparticles (PtNPs) could not only catalyze hydrogen peroxide (H2O2) to produce a large amount of oxygen (O2) but could also assist the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to a photothermal agent ox-TMB with the increasing temperature. Under 808 nm near-infrared (NIR) laser irradiation, an increase in the pressure and temperature occurred simultaneously in the closed detection cell. Meanwhile, the increasing temperature could be helpful for further increasing the pressure. The flexible pressure sensor was compressed in a closed system to cause a decrease in contact resistance, thereby establishing a correlation between the concentration and the resistance-readable analysis. Under optimum conditions, the dynamic detection range of this detection strategy for target CEA was between 0.2 and 80 ng mL-1, and the limit of detection (LOD) was 0.15 ng mL-1. Overall, the signal amplification strategy of temperature coordination provides possibilities for the future development of sensitive and portable POCT protocols.

Construction of a bioinspired Fe3O4/N-HCS nanozyme for highly sensitive detection of GSH

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 (Pd1Cux NAFs) with tunable surface composition are obtained via a generalized strategy. In presence of H2O2, the as-synthesized Pd1Cux 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. Interestingly, Pd1Cux NAFs show obviously composition-dependent peroxidase-like catalytic activities because of the synergistic interaction of nanoalloy. Additionally, different from 2D Pd nanosheets, the distinctive 3D superstructures are featured with rich approachable sites and proper layer spacing, which are in favor of fast mass transport and electron transfers during the catalytic process. Among the studied Pd1Cux NAFs, the Pd1Cu1.7 NAFs show the highest enzyme-like activities and can be successfully applied for the colorimetric detection of glucose with a low detection limit of 2.93 ± 0.53μM. This work provides an efficient avenue to fabricate PdCu NAF nanozymes in biosensing toward glucose detection. Two-dimensional (2D) PdCu ultrathin nanosheet-assembled 3D nanoflowers (Pd1Cux NAFs) with tunable surface composition exhibit substantially enhanced intrinsic peroxidase-like catalytic activities. The Pd1Cu1.7 NAFs are successfully used as peroxidase mimic catalyst for the colorimetric detection of glucose with low detection limit of 2.93μM.

Dual responsive magnetic Fe3O4-TiO2/graphene nanocomposite as an artificial nanozyme for the colorimetric detection and photodegradation of pesticide in an aqueous medium

Facile preparation of Fe3O4 nanospheres/reduced graphene oxide nanocomposites with high peroxidase-like activity for sensitive and selective colorimetric detection of acetylcholine

In the present study, we present nanostructured bimetallic Cu/CuCl/Cu2S/Au(Ag) supports that exhibit plasmonic electromagnetic field enhancement and peroxidase-like catalytic activity. The Cu2S component acts as the peroxidase-like catalyst, while the Au or Ag component provides the necessary light enhancement for surface enhanced Raman spectroscopic (SERS) studies of surface bound molecular reactants. As a test reaction the catalytic oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in presence of H2O2 was investigated. The comparison of product evolution in solution measured by UV-Vis spectroscopy and on the surface measured via SERS is able to give more insight into the different steps involved in the overall catalysis.

A simple and sensitive colorimetric assay for detecting organophosphorus pesticides (OPs) was developed based on 3,3',5,5'-tetramethylbenzidine (TMB)/hydrogen peroxide (H2O2)/dodecyl trimethylammonium bromide (DTAB)-tetramethyl zinc (4-pyridinyl) porphyrin (ZnTPyP). In this system, based on the peroxidase-like activity of DTAB-ZnTPyP, H2O2 decomposes to produce hydroxyl radicals, which oxidize TMB, resulting in blue oxidation products. The OPs (trichlorfon, dichlorvos, and thimet) were first combined with DTAB-ZnTPyP through electrostatic interactions. The OPs caused a decrease in the peroxidase-like activity of DTAB-ZnTPyP due to spatial site blocking. At the same time, π-interactions occurred between them, and these interactions also inhibited the oxidation of TMB (652 nm), thus making the detection of OPs possible. The limits of detection for trichlorfon, dichlorvos, and thimet were 0.25, 1.02, and 0.66 μg/L, respectively, and the corresponding linear ranges were 1-35, 5-45, and 1-40 μg/L, respectively. Moreover, the assay was successfully used to determine OPs in cabbage, apple, soil, and traditional Chinese medicine samples (the recovery ratios were 91.8-109.8%), showing a great promising potential for detecting OPs also in other complex samples.

To achieve selectivity in direct chemiluminescence (CL) detection is very significant and a great challenge as well. Here, we report a novel concept of developing intrinsically selective CL switching at the surface of Fe(3)O(4) nanoparticles for the sensitive detection and simultaneous determination of various pesticides. Fe(3)O(4) nanoparticles have peroxidase-like catalytic activity and catalyze the decomposition of dissolved oxygen to generate superoxide anions, so that the CL intensity of luminol was amplified by at least 20 times. The CL signals can be quenched by the addition of ethanol because ethanol readily reacts with superoxide anions as a radical scavenger. However, the quenching effect can be inhibited through the specific binding of target molecules on Fe(3)O(4) nanoparticles, leading to CL "turn-on" in the presence of ethanol. The novel CL "switching-on" concept demonstrated unique advantages in the detection of pesticide residues. Using the surface coordinative reactions, nonredox pesticide ethoprophos were sensitively detected with a detection limit of 0.1 nM and had a very wide detection range of 0.1 nM to 100 μM. More importantly, the selectivity of CL switching is tunable through the special surface modification of Fe(3)O(4) nanoparticles, and these Fe(3)O(4) nanoparticles with different surface groups can generate unique CL response pattern for the simultaneous determination of various pesticides. Meanwhile, the superparamagnetic properties of Fe(3)O(4) nanoparticles provide a simple magnetic separation approach to attain interference-free measurement for real detection. The very facile and versatile strategy reported here should open a new window to exploration of selective CL molecular switching and application of magnetic nanoparticles for chemo/biodetection.