Determination of alkaline phosphatase activity based on enzyme-triggered generation of a thiol and the fluorescence quenching of silver nanoclusters

Photothermal visual sensing of alkaline phosphatase based on the etching of Au@MnO2 core-shell nanoparticles

Alkaline phosphatase (ALP), as a crucial enzyme involved in many physiological activities, is always used as one of the significant biomarkers in clinical diagnosis. Herein, a novel, simple, and effective photothermal quantitative method based on the etching of MnO₂-coated gold nanoparticles (Au@MnO₂ NPs) was established for ALP activity assay with a household thermometer-based visual readout. The photothermal effect of Au@MnO₂ NPs is much higher than that of MnO₂ NPs or Au NPs. The MnO₂ shell of Au@MnO₂ NPs can be etched by ascorbic acid, a product of ALP-catalyzed hydrolysis of 2-phospho-l-ascorbic acid. With the etching of Au@MnO₂ NPs, the photothermal conversion efficiency decreased gradually, causing the decrease of the temperature increment of the solutions by degrees. A household thermometer, instead of large-scale and professional instruments, was used as a signal reader to realize the visual quantitative detection. The photothermal platform was used successfully for the determination of ALP with a wide linear range from 2.0 to 50 U/L and a detection limit as low as 0.75 U/L. Moreover, the inhibition efficiency of sodium vanadate for ALP activity was investigated, proving the photothermal quantitative method will be a potential platform for screening enzyme inhibitors. Such a sensitive, facile, and low-cost sensing assay provides a new prospect to develop platforms for point-of-care testing.

Polyethyleneimine-protected silver cluster for label-free and highly selective detection of 2,4,6-trinitrotoluene

Sensitive and selective detection of 2,4,6-trinitrotoluene (TNT) is critical for environmental protection and public health. In this work, a convenient synthesis strategy for preparation of fluorescent PEI-AgNCs was described and further a facile and label-free sensing strategy for detection of TNT was developed. The hyperbranched polyethyleneimine (PEI) were used as template to one-step synthesize functional PEI-AgNCs with bright fluorescence signal and rich amino groups on their surface. PEI can specifically bind to electron-deficient TNT through donor-receptor interaction to form Meissenheimer complex. Interestingly, the absorption spectra of the Meissenheimer complex overlap with the fluorescence emission peak of PEI-AgNCs, thus quenching fluorescence of PEI-Ag NCs through fluorescence resonance energy transfer (FRET). Furthermore, this bonding process also initiate aggregation of PEI-AgNCs and quench the fluorescence of PEI-AgNCs by the aggregation-induced quenching (AIQ) effect. The novel method demonstrates sensitivity with a detection limit for TNT have been obtained as 17 nM. In addition, the proposed sensing method also has good selectivity over other potential interference and displayed a good potential application value in real water samples with satisfactory recoveries, offering a promising platform for sensing TNT in public safety and security environment protection.

Sensitive detection of glutathione through inhibiting quenching of copper nanoclusters fluorescence

A method for a sensitive fluorescence detection of glutathione was established. Glutathione-stabilized copper nanoclusters (CuNCs) were synthesized via a facile process. These CuNCs showed blue fluorescence with a peak around 450 nm. In the presence of p-benzoquinone (PBQ), the electron transfer from the copper nanoclusters to PBQ quenched the fluorescence of the CuNCs. Glutathione (GSH), as a reducing agent, formed a complex with PBQ. This formation inhibited the quenching from PBQ, and a restored fluorescence was obtained. This interaction provided a fluorescence enhancement for the measurement of GSH. Under the optimal condition, linear responses were obtained toward GSH in the ranges of 0.06-6.0 μM, with a limit of detection at 20 nM. This developed assay was easy in operation with high sensitivity and selectivity. The applicability was approved with successful glutathione measurements in real samples.

Spectroscopic and in silico investigation of the interaction between GH1 β-glucosidase and ginsenoside Rb1

The function and application of β-glucosidase attract attention nowadays. β-glucosidase was confirmed of transforming ginsenoside Rb1 to rare ginsenoside, but the interaction mechanism remains not clear. In this work, β-glucosidase from GH1 family of Paenibacillus polymyxa was selected, and its gene sequence bglB was synthesized by codon. Then, recombinant plasmid was transferred into Escherichia coli BL21 (DE3) and expressed. The UV-visible spectrum showed that ginsenoside Rb1 decreased the polarity of the corresponding structure of hydrophobic aromatic amino acids (Trp) in β-glucosidase and increased new π-π* transition. The fluorescence quenching spectrum showed that ginsenoside Rb1 inhibited intrinsic fluorescence, formed static quenching, reduced the surface hydrophobicity of β-glucosidase, and KSV was 8.37 × 103 L/M (298K). Circular dichroism (CD) showed that secondary structure of β-glucosidase was changed by the binding action. Localized surface plasmon resonance (LSPR) showed that β-glucosidase and Rb1 had strong binding power which KD value was 5.24 × 10-4 (±2.35 × 10-5) M. Molecular docking simulation evaluated the binding site, hydrophobic force, hydrogen bond, and key amino acids of β-glucosidase with ginsenoside Rb1 in the process. Thus, this work could provide basic mechanisms of the binding and interaction between β-glucosidase and ginsenoside Rb1.

Fluorescence detections of hydrogen peroxide and glucose with polyethyleneimine-capped silver nanoclusters

Detection of hydrogen peroxide is of significant importance for biological assays, and fluorescence methods are intensively reported for this purpose. Due to the highly oxidative property of this species, usually fluorescence quenching is obtained during the interactions and decreased signals are rendered. In this report, this oxidative property was adopted for an increased fluorescence signaling. Photoluminescent silver nanoclusters (AgNCs) were synthesized with polyethyleneimine as the stabilizer. This fluorescence from these nanoclusters could be quenched by reduced glutathione (GSH) through an interaction from its thiol group. As an oxidant, hydrogen peroxide converted GSH into an oxidized form (GSSG) with an elimination of the free thiols, and inhibited the quenching. This interaction presented an increased response toward hydrogen peroxide in the range of 0.1-20 μM with a detection limit of 35 nM. The scheme was further coupled with glucose oxidase for a glucose analysis down to 0.11 μM. This method was selective and was successfully applied for glucose measurement in human serum samples.

Applications of fluorescent materials in the detection of alkaline phosphatase activity

Alkaline phosphatase (ALP) is important in the diagnosis of many diseases. Because ALP is used to detect biomarkers for many diseases, many researchers conduct investigations to develop ALP detection strategies. The use of fluorescent material has attracted attention because of the technique's high sensitivity and the low sample volume required. Herein, we review and discuss the working mechanisms and advantages of four main categories:DNA fluorescent probes, molecular fluorescent probes, chemical coordination-based probes, and nanoparticle probes. Development prospects and trends are also discussed.

A review on emerging principles and strategies for colorimetric and fluorescent detection of alkaline phosphatase activity

Alkaline phosphatase (ALP) is a natural enzyme that is able to catalyze the dephosphorylation of phosphate esters. It participates in a great number of biological processes ranging from various metabolisms to signal transduction and cellular regulation. Since the abnormality of ALP activity in body is closely associated with many diseases, it has become an important biomarker for clinical diagnosis and treatment. Besides, it is often utilized in enzyme-linked immunosorbent assays. Given these demands, in the last few years considerable interest has been focused on exploring new materials and methods for ALP activity detection. In this review, we first made a clear classification on the principles that could be used for ALP activity determination. After that, emerging colorimetric and fluorescent strategies designed on the basis of these principles were systematically summarized. Finally, some perspectives on ALP activity analysis were discussed, hoping to inspire future efforts in the field.