Combining CeVO4 oxidase-mimetic catalysis with hexametaphosphate ion induced electrostatic aggregation for photometric sensing of alkaline phosphatase activity.

In the present work, a novel alkaline phosphatase (ALP) activity colorimetric assay is proposed by integrating the oxidase-mimicking catalytic characteristic of CeVO4 nanoparticles with the hexametaphosphate ion (HMPi) mediated electrostatic aggregation. The CeVO4 nanoparticles exhibit good oxidase-mimetic catalytic ability to promote the 3,3',5,5'-tetramethylbenzidine (TMB) oxidation to TMBox, offering a significant change from colorless to blue. After a small amount of HMPi is added, the strong electrostatic interaction between the negatively charged HMPi species and the positively charged TMBox product leads to the aggregation of the latter, generating an aubergine HMPi-TMBox agglomerate. After the agglomerate is filtered out, the reaction solution turns to be almost colorless. When ALP is used to hydrolyze the HMPi species in advance, the electrostatic aggregation process is remarkably restrained, thus retaining the blue color of the CeVO4 catalyzed TMB solution. According to the new sensing strategy, highly selective and sensitive analysis of ALP activity was realized, providing a wide detection range from 1 to 210 U/L and a detection limit of 0.68 U/L. Accurate measurement of ALP activity in clinical serum matrices was also validated, demonstrating the practicability of the proposed assay in practical applications.

A novel alkaline phosphatase activity sensing strategy combining enhanced peroxidase-mimetic feature of sulfuration-engineered CoOx with electrostatic aggregation.

Given alkaline phosphatase (ALP) takes part in the phosphorylation/dephosphorylation processes in the body, its activity is universally taken as an important indicator of many diseases, and thus developing reliable and efficient methods for ALP activity determination becomes quite important. Here, we propose a new sensing strategy for ALP activity by integrating the improved peroxidase-mimicking catalysis of sulfuration-engineered CoOx with the hexametaphosphate ion (HMPi)-mediated electrostatic aggregation. After sulfuration engineering, the CoOx composite coming from the pyrolysis of ZIF-67 exhibits enhanced peroxidase-mimetic catalytic ability to oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to its oxide TMBox, offering a remarkable color change from colorless to mazarine; with the presence of HMPi, the rapid electrostatic assembly of negatively charged HMPi and positively charged TMBox leads to the aggregation of the latter, resulting in a color fading phenomenon; when ALP is added in advance to hydrolyze the HMPi mediator, the aggregation procedure is significantly suppressed, and such that the solution color can be recovered. Based on this principle, efficient determination of ALP activity was gained, giving a wide detection scope from 0.8 to 320 U/L and a detection limit as low as 0.38 U/L. Reliable analysis of the target in serum samples was also achieved, verifying the feasibility and practicability of our strategy in measuring ALP activity for clinical applications. Graphical abstract.

Polyethylenimine-stabilized silver nanoclusters act as an oxidoreductase mimic for colorimetric determination of chromium(VI).

A new and efficient assay is proposed for the photometric determination of Cr6+ by employing polyethylenimine-stabilized Ag nanoclusters (PEI-AgNCs) as an oxidoreductase mimic. Cr6+ with certain oxidicability is able to specifically react with 3,3',5,5'-tetramethylbenzidine (TMB), giving a color change from colorless to blue indicating the presence of Cr6+. However, the redox kinetics is so slow that the sensitivity obtained for Cr6+ determination is very poor. It is interestingly found that PEI-AgNCs can act as an oxidoreductase-like nanozyme to significantly promote the sluggish reaction, making it possible to rapidly detect toxic Cr6+ with remarkably enhanced performance. With the use of PEI-AgNCs, fast and convenient determination of Cr6+ was realized, with a limit of detection as low as 1.1 µM. Additionally, the proposed assay exhibited excellent selectivity; other ions, including Cr3+, hardly affected the determination of Cr6+. Graphical abstract Polyethylenimine-stabilized silver nanoclusters (PEI-AgNCs) act as an oxidoreductase mimic to catalyze the redox reaction of Cr6+ and 3,3',5,5'-tetramethylbenzidine (TMB), enabling the high-performance colorimetric determination of toxic Cr6+.

Oxidation of Sodium Deoxycholate Catalyzed by Gold Nanoparticles and Chiral Recognition Performances of Bile Salt Micelles.

Au nanoparticles (NPs) were prepared by UV light irradiation of a mixed solution of HAuCl4 and sodium deoxycholate (NaDC) under alkaline condition, in which NaDC served as both reducing agent and capping agent. The reaction was monitored by circular dichroism (CD) spectra, and it was found that the formed gold NPs could catalyze the oxidation of NaDC. A CD signal at ~283 nm in the UV region was observed for the oxidation product of NaDC. The intensity of the CD signal of the oxidation product was enhanced gradually with the reaction time. Electrospray ionization (ESI) mass spectra and nuclear magnetic resonance (NMR) spectra were carried out to determine the chemical composition of the oxidation product, revealing that NaDC was selectively oxidized to sodium 3-keto-12-hydroxy-cholanate (3-KHC). The chiral discrimination abilities of the micelles of NaDC and its oxidation product, 3-KHC, were investigated by using chiral model molecules R,S-1,1'-Binaphthyl-2,2'-diyl hydrogenphosphate (R,S-BNDHP). Compared with NaDC, the micelles of 3-KHC displayed higher binding ability to the chiral model molecules. In addition, the difference in binding affinity of 3-KHC micelles towards R,S-isomer was observed, and S-isomer was shown to preferentially bind to the micelles.

Yolk-shell structured Au@Ag@mSiO2 as a probe for sensing cysteine enantiomers and Cu2+ based on circular dichroism.

A yolk-shell structured Au@Ag@mSiO2 probe was fabricated by coating a layer of mesoporous silica on the surface of a Au@Ag core-shell nanosphere, followed by partially removing the Ag shell. Mirror symmetrical chiral signals at ∼258 nm in the UV region were observed for the probe upon coupling with cysteine enantiomers on the surface of Au@Ag. The intensity of the CD signal of the probe is enhanced by increasing l/d-Cys concentration, allowing the quantitative determination of the cysteine enantiomers. The developed method shows an excellent linear relationship between the CD signal and l-Cys concentration ranging from 10 µM to 90 µM with a limit of detection of 8.5 µM. In the presence of Cu2+, the CD signal of the probe weakened due to the oxidation of l-cysteine to l-cystine catalyzed by Cu2+. Based on this phenomenon, a new strategy for the detection of Cu2+ can be developed. Under the optimized conditions, the CD signal decreases linearly with the log of the concentration of Cu2+ in the range from 1 to 250 nM with a detection limit of 0.1 nM.

Facile colorimetric detection of alkaline phosphatase activity based on the target-induced valence state regulation of oxidase-mimicking Ce-based nanorods.

Alkaline phosphatase (ALP) is widely recognized as a significant biomarker for lots of diseases. For this reason, developing effective and simple methods to monitor ALP activity is strongly necessary. Herein, we propose a novel strategy based on the target-induced valence state regulation of oxidase-mimicking Ce-based nanorods for ALP activity sensing. The mixed-valent Ce-based material (MVCM) with a relatively high Ce(iv)/Ce(iii) ratio can exhibit good oxidase-like activity to trigger the catalytic oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue TMBox in the presence of O2, resulting in a notable chromogenic reaction. When ALP hydrolyzes ascorbic acid phosphate into ascorbic acid (AA), the formed AA induces the partial reduction of the MVCM to one with a low Ce(iv)/Ce(iii) ratio, which shows much less activity to trigger the chromogenic reaction. According to the above principle, a facile colorimetric assay was developed for ALP activity detection, providing a linear range of 0.5-25 U L-1 and a limit of detection of 0.1 U L-1. Besides, the proposed strategy could offer favorable selectivity for ALP activity determination. Accurate sensing of the target in serum was demonstrated by our assay as well, revealing its promise as a reliable tool for clinical diagnosis.

Dye adsorption by self-recoverable, adjustable amphiphilic graphene aerogel.

A type of self-recoverable, adjustable amphiphilic graphene aerogel (GA) was prepared and applied to the dye adsorption. The GA with polyvinyl alcohol (PVA) as its cross-linking agent has the characteristics of adjustable amphiphilicity. By adjusting the PVA content in GA, the later can be used to adsorb dyes with different hydrophobic and hydrophilic properties. Four kinds of dyes (Malachite green, Rhodamine B, Methylene blue and Methyl orange) were applied as targets and the saturated adsorption amounts were calculated. The Langmuir adsorption model and the Lagrange pseudo-second-order equation mathematical model were used to study the behavior of dye adsorption by GA, and the experimental data was in full compliance with the mathematical models. The excellent mechanical properties (compressibility and recoverability) make the GA suitable for dye adsorption. A computational simulation was also performed to verify the adsorption energy of GA to dyes. The GA was able to retain 89.5% of its initial removal efficiency (for malachite green) after 10 cycles of application.

Colorimetric evaluation of the hydroxyl radical scavenging ability of antioxidants using carbon-confined CoOx as a highly active peroxidase mimic.

The authors present a colorimetric method for the evaluation of the hydroxyl radical scavenging capability of antioxidants by exploiting carbon-confined mixed cobalt oxide nanoparticles (denoted as C-confined CoOx NPs) as a novel peroxidase mimic. The nanozyme can be prepared from the metal-organic framework ZIF-67 by calcination at a moderate temperature. It exhibits peroxidase-mimicking activity and catalyzes the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to form a blue product in the presence of H2O2 via generation of hydroxyl radicals. However, in the presence of an antioxidant, the color reaction is suppressed due to scavenging of hydroxyl radicals by the antioxidant. Based on this principle, the hydroxy radical scavenging ability of glutathione (GSH), cysteine (Cys), tannic acid (TA) and tea polyphenols (TP) was assessed. It was found that these antioxidants can scavenge hydroxyl radicals in the following decreasing order: TA>Cys>GSH>TP. The assay was also used to quantify the antioxidative power of common fruit extracts. Graphical abstract Schematic presentation for evaluating the hydroxyl radical scavenging ability of different antioxidants using carbon-confined mixed cobalt oxide nanoparticles (denoted as C-confined CoOx NPs) as a highly active peroxidase mimic. With excellent activity, the C-confined CoOx NPs together with the visible peroxidase reaction can be employed as a powerful tool to rapidly screen appropriate antioxidants from natural samples and measure their activity for guiding their usage in related products.

Enzyme-triggered in situ formation of Ag nanoparticles with oxidase-mimicking activity for amplified detection of alkaline phosphatase activity.

Given that alkaline phosphatase (ALP) is an important biomarker for many diseases, monitoring of its activity turns to be of great significance for related disease diagnosis and treatment. Herein, we report a new colorimetric assay based on the enzyme-triggered in situ formation of Ag nanoparticles (NPs) with high oxidase-mimicking activity for ALP activity detection. ALP first hydrolyzes the ascorbic acid phosphate (AAP) substrate to produce ascorbic acid (AA); the produced AA with strong reducing capacity then transforms Ag+ into Ag NPs; compared with the Ag+ precursor, the in situ formed Ag NPs have much higher oxidase-like activity to catalyze the 3,3',5,5'-tetramethylbenzidine (TMB) color reaction mediated by dissolved O2 at neutral pH. On the basis of this principle, amplified colorimetric detection of ALP activity with a linear scope of 0.15-5 U L-1 and a limit of detection down to 0.037 U L-1 was realized. In addition, our assay exhibited specific response toward ALP against other biological enzymes and species. Accurate and reliable determination of ALP activity in human plasma was also demonstrated by our assay, suggesting its great potential as a facile and efficient tool for monitoring of ALP activity in clinical practice.

Silver-modified porous polystyrene sulfonate derived from Pickering high internal phase emulsions for capturing lithium-ion.

Adsorption separation based on porous polystyrene sulfonate is an important method of extracting lithium ion (Li+). In this work, silver-modified porous polystyrene sulfonate (PHIPEs-SS-Ag) derived from Pickering high internal phase emulsions was fabricated for the selective binding of Li+. PHIPEs-SS-Ag possessed porous polymer matrix, sufficient sulfonic acid functional groups, and uniformly immobilized silver particles, which were beneficial for improving mass transfer, binding amount and antifouling performance. In batch mode experiments, the adsorption capacity reached a maximum value (i.e. 14.09 mg g-1) under alkaline conditions, and the adsorption mechanism between PHIPEs-SS-Ag and Li+ was electrostatic attraction. PHIPEs-SS-Ag exhibited fast binding kinetics at 25 °C (i.e. 300 min), and the maximum monolayer adsorption amount from the Langmuir model for Li+ are 59.85 mg g-1, 35.06 mg g-1, and 27.09 mg g-1 at 15 °C, 25 °C, and 35 °C, respectively. Moreover, PHIPEs-SS-Ag displayed excellent selectivity for Li+ in the presence of K+, Mg2+, and Na+, and maintained 80.71% of the initial adsorption capacity after seven sequential cycles of adsorption-regeneration. Therefore, this work opened up a universal route for the development of composite adsorbents for the specific separation of Li+.

A Surface Mediated Supramolecular Chiral Phenomenon for Recognition of l- and d-Cysteine.

Chiral recognition is of fundamental importance in chemistry and life sciences and the principle of chiral recognition is instructive in chiral separation and enantioselective catalysis. Non-chiral Ag nanoparticles (NPs) conjugated with chiral cysteine (Cys) molecules demonstrate strong circular dichroism (CD) responses in the UV range. The optical activities of the l-/d-Cys capped Ag NPs are associated with the formation of order arrangements of chiral molecules on the surface of Ag NPs, which are promoted by the electrostatic attraction and hydrogen bonding interaction. The intensity of the chiroptical response is related to the total surface area of Ag NPs in the colloidal solution. The anisotropy factor on the order of 10-2 is acquired for Ag NPs with the size varying from ~2.4 to ~4.5 nm. We demonstrate a simple and effective method for the fabrication of a quantitative chiral sensing platform, in which mesoporous silica coated Ag nanoparticles (Ag@mSiO2) were used as chiral probes for recognition and quantification of Cys enantiomers.

Sensitive and selective colorimetric detection of alkaline phosphatase activity based on phosphate anion-quenched oxidase-mimicking activity of Ce(â £) ions.

As alkaline phosphatase (ALP) plays crucial roles in disease warning and dephosphorylation-related cellular regulation, it is widely recognized as an important biomarker for clinical diagnosis. In this work, we proposed a facile colorimetric assay based on phosphate anion-quenched oxidase-mimicking activity of Ce(Ⅳ) ions for sensitive and selective detection of ALP activity. Free Ce(Ⅳ) ions exhibited a strong oxidase-like capability (providing a 40-fold catalytic turnover number compared with CeO2) to catalyze the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) into its blue product TMBox mediated by dissolved O2 at neutral pH, thus triggering a remarkable color reaction visually. When PO43- was added, its strong affinity to Ce(Ⅳ) ions rapidly precipitated the free Ce(Ⅳ) ions, resulting in the quenching of their enzymatic ability. Given that ALP catalyzed the hydrolysis of adenosine triphosphate to produce PO43-, determination of ALP activity could be achieved using the colorimetric assay with no need of complicated instrumentation and protocol. As demonstrated, our assay offered a highly sensitive readout for ALP activity in two linear scopes of 0-50 U L-1 and 50-250 U L-1, providing a detection limit down to 2.3 U L-1. Besides, it could provide specific response toward ALP against other enzymes and biological species. Furthermore, the developed assay was successfully applied to evaluate ALP activity in human plasma accurately and reliably, indicating its great promise as a powerful and convenient tool for monitoring of ALP activity in clinical practice.

Synthesis and Plasmonic Chiroptical Studies of Sodium Deoxycholate Modified Silver Nanoparticles.

Sodium deoxycholate modified silver nanoparticles prepared in the presence of sodium deoxycholate as a chiral inducer exhibit plasmonic circular dichroism (CD) signals. The plasmon-induced chirality arises from the presence of chiral molecules (sodium deoxycholate) on the surface of Ag nanoparticles, which transfer their chiral properties to the visible wavelength range due to the Coulomb interactions between the chiral molecules and plasmonic nanoparticles. The prepared Ag nanoparticles (NPs) exhibit distinct line shapes of plasmonic CD, which can be tailored by varying the pH values of the solutions. A mechanism was proposed to explain the generation of the distinct plasmonic CD shapes, which indicated that the arrangements of chiral molecules in the plasmonic hot spots between Ag NPs are crucial for the induced plasmonic CD.