A novel colorimetric aptasensor for sensitive tetracycline detection based on the peroxidase-like activity of Fe3O4@Cu nanoparticles and "sandwich" oligonucleotide hybridization.

Colorimetric detection of tetracycline by enhancing peroxidase-like activity of polymerized MnO2@ZIF-67 nanocomposites.

AGolgi protein 73 (GP73) colorimetric biosensor based on the reduced graphene oxide-carboxymethyl chitosan-hemin/platinum@palladium nanoparticles (RGO-CMCS-Hemin/Pt@Pd NPs) with peroxidase-like activity was constructed. The RGO-CMCS-Hemin/Pt@Pd NPs with high peroxidase-like activity were successfully synthesized under mild conditions. Then, the aminylated GP73 aptamer (Apt) was bound to the RGO-CMCS-Hemin/Pt@Pd NPs to form the recognition probe. Another unmodified GP73 aptamer (AptI) was served as the capture probe. In the presence oftarget GP73, the capture probe and the recognition probe specifically bind to GP73 and form a RGO-CMCS-Hemin/Pt@Pd NP-Apt/GP73/AptI sandwich-type structure, which can oxidase thecolorless 3,3',5,5'-tetramethylbenzidine (TMB) into blue oxTMB inthe presence of H2O2. GP73 detection was achieved by measuring the peak UV absorption at 652nm. Under the optimum conditions, the GP73 concentration was linearly related to the absorbance intensity in the range 10.0-110.0ng/mL, and the limit of detection (LOD) was 4.7ng/mL. The proposed colorimetric biosensor was successfully applied to detect GP73 in spiked human serum samples with recoveries of 98.2-107.0% and RSDs of 1.90-5.44%, demonstrating the excellent potential for highly sensitive GP73 detection in clinical detection. A colorimetric biosensor for visual determination of GP73 based on RGO-CMCS-Hemin/Pt@Pd NPs nanozyme with peroxidase-like activity was designed. The GP73 biosensor responses linearly from 10.0-110.0ng/mL with LOD of 4.7ng/mL, and shows acceptable specificity and good recovery.

Adenosine triphosphate (ATP) is produced mainly in the mitochondrion, and its primary task is to function as a ubiquitous energy currency to meet the cellular metabolic demands in biological system...

A novel M-shape electrochemical aptasensor for ultrasensitive detection of tetracyclines

Facile synthesis of IrO2/rGO nanocomposites with high peroxidase-like activity for sensitive colorimetric detection of low weight biothiols

In recent years, great progress has been made on the study of nanozymes with enzyme-like properties. Here, bimetallic Fe and Ni nanoclusters were anchored on the nanosheets of nitrogen-rich layered graphitic carbon nitride by one-step pyrolysis at high temperature (Fe/Ni-CN). The loading content of Fe and Ni on Fe/Ni-CN is as high as 8.0%, and Fe/Ni-CN has a high specific surface area of 121.86 m2 g-1. The Fe/Ni-CN can effectively oxidize 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2, and exhibits efficient peroxidase-like activity, leading to a 17.2-fold increase compared to pure graphitic carbon nitride (CN). Similar to the natural horseradish peroxidase (HRP), the Fe/Ni-CN nanozyme follows catalytic kinetics. The Michaelis-Menten constant (Km) value of the Fe/Ni-CN nanozyme for TMB is about 8.3-fold lower than that for HRP, which means that the Fe/Ni-CN nanozyme has better affinity for TMB. In addition, the catalytic mechanism was investigated by combination of free radical quenching experiments and density-functional theory (DFT) calculations. The results show that the high peroxidase-like activity is due to the easy adsorption of H2O2 after bimetal loading, which is conducive to the production of hydroxyl radicals. Based on the extraordinary peroxidase-like activity, the colorimetric detection of p-phenylenediamine (PPD) was constructed with a wide linear range of 0.2-30 μM and a low detection limit of 0.02 μM. The sensor system has been successfully applied to the detection of residual PPD in real dyed hair samples. The results show that the colorimetric method is sensitive, highly selective and accurate. This study provides a new idea for the efficient enhancement of nanozyme activity and effective detection of PPD by a bimetallic synergistic strategy.

Ultra-fast colorimetric detection of glutathione by magnetic Fe NPs with peroxidase-like activity

Two-dimensional metal-organic framework nanosheets are attractive as peroxidase mimicking nanocatalysts due to their rich chemical functional groups, large surface area, high porosity, and accessible active sites. In this study, we synthesized FeCu bifunctional 2D MOF nanosheets using a solvothermal method. Fe and Cu ions were added as metal precursors, while organic amine and acid served as the organic ligands to construct the FeCu-MOF nanosheets. These nanosheets demonstrated robust peroxidase-like catalytic activities and were employed to develop a visual detection system for multiple targets, such as glucose and kanamycin. In the detection mechanism, glucose was oxidized into gluconic acid by glucose oxidase (GOx), leading to the generation of H2O2. When H2O2 is present, the FeCu-MOF NSs demonstrate high intrinsic peroxidase-like activity, which might catalytically oxidize 3,3',5,5'-tetramethylbenzidine (TMB) into a blue-coloured oxTMB product with a strong UV absorption at 654 nm. Subsequently, kanamycin was added to the above sensing system. The kanamycin strongly interacted with the FeCu-MOF NSs through H-bonding and blocked electron transfer, resulting in a colour change of the solution from blue to colourless with a weak UV absorption at 654 nm. Under the optimal conditions, the proposed colorimetric sensor exhibits an excellent linear response to glucose and kanamycin over the 0.25-5 μM and 0.02-0.1 μM ranges, respectively. The proposed colorimetric assay detection limits for glucose and kanamycin were found to be as low as 0.1 μM and 8 nM, respectively, and such a sensor shows excellent selectivity and sensitivity against different potential interferents. Thus, our proposed colorimetric assay was satisfactory when applied to glucose and kanamycin detection in agricultural and livestock husbandry samples.

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.

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.

The persistence of tetracycline (TC) antibiotic residues in foodstuffs and aquatic systems poses critical threats to human health and the ecological environment, driving an imperative demand for developing multifunctional platforms capable of simultaneous visual monitoring and high-efficiency elimination of these contaminants. Herein, a simple yet novel colorimetric sensor that integrates detection and degradation of TCs has been constructed based on the excellent peroxidase-like activity of the metal-organic frameworks (MOFs) MIL-101(Fe). Colorless 3,3',5,5'-tetramethylbenzidine (TMB) can be effectively oxidized to generate blue oxidized TMB (ox-TMB) by MIL-101(Fe), which exhibits a characteristic peak at 652 nm. The presence of TCs at varying concentrations can specifically inhibit this oxidation reaction, leading to different degrees of decrease in the intensity of the characteristic peak. Based on this concentration-dependent chromogenic behavior, TCs are quantitative identified by the dual-mode detection of UV-Vis absorbance and with the naked eye. The as-fabricated colorimetric sensor displays superior selectivity toward TCs, with its detection capability in complex matrices being successfully validated in environmental water and commercial milk samples. To avoid accessional antibiotic contamination, MIL-101(Fe) can also be served as a scavenger to degrade TCs efficiently under visible light irradiation, achieving up to 92.01% removal efficiency within 3 h. The developed strategy has the advantages of visual recognition, rapid field detection and no requirement of large-scale instruments. Most critically, it cleverly realizes the integration of antibiotic detection and degradation, which provides a low-cost and high-efficiency solution to fundamentally solve the problem of antibiotic contamination.

A new Prussian blue analog (PBA) that contains three metal elements and has peroxidase-like activity was synthesized by a simple method. Then, AgNO3 solution was added slowly to the PBA solution under continuous stirring. We found that this synthesis method could be used to prepare other PBAs, and that the anchoring of Ag+ on the surface of PBA could enhance the peroxidase-like activity of the material, suggesting potential applications for the Ag+-decorated Prussian blue analog (Ag-PBA) in traditional Chinese medicine. Ag-PBA is a new type of multi-metal cubic nano-enzyme that exhibits good stability and excellent peroxidase-like activity; as such, it could catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2 and Ag-PBA. We then developed a new method to measure the content of antioxidant substances in Chinese herbs by using the excellent peroxidase-like activity of Ag-PBA. Using the Chinese herb Lycium ruthenicum Murr. as a model compound, we measured the content of the antioxidant substances in Lycium ruthenicum Murr. by this new method. After optimization of reaction temperature, concentrations of TMB and H2O2, and reaction time, the content of the antioxidant substances was measured and calculated in comparison with anthocyanidin standards. The results of the Ag-PBA method and the classical DPPH method were compared by a paired t-test, with no statistically significant difference found between the methods. Hence, these two methods can be used interchangeably, although the Ag-PBA method had the advantages of simplicity, rapidness, and good stability. Moreover, the Ag-PBA method has a low limit of quantification and a shorter reaction time, which are improvements on the DPPH method, and it is not necessary to avoid light. Therefore, we anticipate that the Ag-PBA method may be used widely for the measurement of the content of antioxidant substances in Chinese herbs.

A novel colorimetric triple-helix molecular switch aptasensor for ultrasensitive detection of tetracycline

Developing artificial nanoparticles with peroxidase-like activity have attracted great interests because their catalytic activity is not easy to lose under harsh conditions compared with natural enzymes. In this work, the N-doped carbon dots (CDs) were prepared; it was found that the N-doped CDs showed high peroxidase-like catalytic activity towards the reaction system of hydrogen peroxide:3,3',5,5'-tetramethylbenzidine (TMB). The catalytic mechanism of the N-doped CDs was explored using electron spin resonance spectra, cyclic voltammetry methods and simulation of density functional theory calculations. This work can offer a new feasible method for synthesizing N-doped carbon quantum dots used as artificial peroxidases in biological and environment applications.

Anew colorimetric aptasensor equipped with a novel composite of graphitic carbon nitride (g-C3N4) nanosheets and copper oxide(I) (Cu2O) nanocrystals is presented for Salmonella typhimurium (S .typhimurium). The dual-purpose structure of this composite simultaneously contributes to superb peroxidase-like activity and interaction with a label-free aptamer. Although g-C3N4@Cu2O effectively creates a visible blue color following the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in presence of hydrogen peroxide (H2O2), this catalytic activity of the composite severely decreases after the interaction with aptamers. In the presence of S. typhimurium in sample, aptamers bound to their specific target. Subsequently, g-C3N4@Cu2O catalytic activity was enhanced in proportion to S. typhimurium concentration. Under optimized conditions, this aptasensor exhibited an excellent detection performance in a range from 1.5 × 101 to 1.5 × 105CFU/ml, with a detection limit of 15CFU/ml. Besides, portable detection of S. typhimurium by paper-based model of this method operated successfully in just 6min. Analysis of spiked milk samples revealed high potential of this method as a sensitive, rapid, and label-free promising tool for S. typhimurium detection. A novel composite of g-C3N4 nanosheets and Cu2O nanocrystals was constructed through this study, which represented a collection of significant properties for designing an aptasensor. The simultaneous capability of this composite for peroxidase-like activity and interaction with aptamer led to design a fast accurate biosensor for detecting as low as 15CFU/ml Salmonella typhimurium as one of the most important foodborne pathogens which is a persistent burden for societies.