Fluorometric determination of the activity of alkaline phosphatase based on the competitive binding of gold nanoparticles and pyrophosphate to CePO4:Tb nanorods

A sensitive fluorescence "turn on" nanosensor for glutathione detection based on Ce-MOF and gold nanoparticles

Glutathione (GSH) as an essential biothiol maintains redox homeostasis in human body, the aberrant level of it has been related to various diseases. In this work, we constructed a facile and environment-friendly strategy by using Ce based metal-organic frameworks and gold nanoparticles (AuNPs) for detection of GSH. The fluorescence intensity of the Ce-MOF was quenched by AuNPs, which is ascribed to the existence of fluorescence resonance energy transfer (FRET) and electrostatic interaction between Ce-MOFs and AuNPS. Because of the formation of Au-SH between AuNPs and GSH, the addition GSH induced the Ce-MOF/AuNPs and prevented the occurrence of FRET and electrostatic interaction between Ce-MOFs and AuNPS, which futher recovered the fluorescence of Ce-MOF. Under the optimized conditions, this "turn-on" sensing process revealed a high selectivity toward GSH and displayed good linearity in range of 0.2-32.5 μM with low detection limit of 58 nM. In addition, the practicability of the strategy was testified through analyzing GSH in real human serum samples.

Inhibition of the activated sludge-associated enzyme phosphatase by transition metal oxyanions

Organic esters of phosphoric acid and other organophosphorous compounds are enzymatically hydrolyzed during wastewater treatment by microbial phosphoesterases, especially by phosphomonoesterase (phosphatase). For physiological reasons, the enzyme is inhibited by its main inorganic reaction product, ortho-phosphate. It is known that oxyanions of transition metals, resembling the molecular topology of ortho-phosphate, e.g. vanadate and tungstate, are more potent inhibitors for microbial alkaline phosphatase than phosphate. To proof this effect for activated sludge, a multitude of samples from a communal wastewater treatment plant was exposed at pH values from 7.00 to 8.50 to tungstate, vanadate, and molybdate. Inhibition effects were determined by a sensitive fluorimetric microplate assay and characteristic parameters (IC₅₀ and IC₂₀ concentrations) were deduced from modelled dose-response functions. Mean inhibitor concentrations (in brackets: ranges) causing 50% inactivation (IC₅₀) at pH 7.50 were 2.5 (1.3-4.1) μM tungstate, 2.9 (1.6-5.5) μM vanadate, and 41.4 (33.6-56.7) μM molybdate. Vanadate and tungstate concentrations between 0.6 and 0.7 μM provoked a 20% (IC₂₀) inhibition. The inhibition efficiency of tungstate and molybdate decreased with increasing pH, whereas vanadate reacted pH independently. These results underline the necessity to consider enzyme inhibition assessing the limitations and potentials of biological wastewater treatment processes.

A colorimetric alkaline phosphatase biosensor based on p-aminophenol-mediated growth of silver nanoparticles

Alkaline phosphatase (ALP) is an enzyme that catalyzes the dephosphorylation of proteins, nucleic acids, and biomolecules. It is a potential biomarker for diverse diseases such as breast cancer, osteopenia, and hepatobiliary. Herein, we developed a colorimetric sensor for the ALP assay based on its enzymatic activity to dephosphorylate the p-aminophenol phosphate (pAPP) into pAP. In a solution containing silver nanoparticles (AgNPs) and Ag⁺ ions prepared using a low concentration of NaBH₄, pAP mediates the growth of AgNPs by reducing the concentration of Ag⁺ ions to enhance the intensity of localized surface plasmon resonance as the pAPP cannot induce a reduction of the remaining Ag⁺ due to the masking of the hydroxyl with phosphate. The quantitative assay of the ALP was demonstrated via the colorimetric detection of the pAP-mediated growth of AgNPs in the presence of an ALP. The highly sensitive enzymatic growth of AgNPs provided a wider dynamic linear range of 0.5-225 U/L with a lower limit of detection of 0.24 U/L than that previously reported. The use of pAP resulted in excellent selectivity of the sensor for the ALP assay in human serum, yielding a high recovery rate and a high precision of 99.2 ± 1.5 % for the standard addition method.

Praseodymium selective fluorescence recognition based on GdPO4: Tb3+ probe via energy transfer from Tb3+ to Pr3+ ions

A novel strategy is proposed based on the efficient energy transfer from Tb³⁺ to Pr³⁺ for the sensitive and selective discrimination of praseodymium ions due to the matched energy levels of ⁵D₄ (Tb³⁺) and ³P₀ (Pr³⁺). The electron of Tb³⁺ transfers from the ground state to the excited state under the excitation of ultraviolet light and relaxes to the ⁵D₄ level. In the presence of Pr³⁺ the electron has no time to return to the ground state, thus it transfers to the ³P₀ level of Pr³⁺ resulting in the quenching of Tb³⁺ luminescence. In the case of GdPO₄: Tb³⁺ nanowire, its fluorescence intensity at 545 nm linearly decreased when Pr³⁺ concentration ranged from 1 × 10^-7 to 1 × 10^-5 M, and the detection limit was 75 nM. To further investigate the sensing mechanism, CePO₄: Tb³⁺, YPO₄: Tb³⁺, and YBO₃: Tb³⁺ nanoparticles were also synthesized for Pr³⁺ ion detection. For all materials, similar fluorescence quenching by Pr³⁺ ions occurred, which confirmed the efficient energy transfer from Tb³⁺ to Pr³⁺ ions. Utilizing the matched energy levels of ⁵D₄ (Tb³⁺) and ³P₀ (Pr³⁺), for the first time, we proposed a novel strategy (taking GdPO₄: Tb³⁺ probe as the example) based on the efficient energy transfer from Tb³⁺ to Pr³⁺ for the sensitive and selective discrimination of praseodymium ions.

Sensitive Fluorescence Assay for the Detection of Alkaline Phosphatase Based on a Cu2+-Thiamine System

The authors describe a novel, facile, and sensitive fluorometric strategy based on a Cu²⁺-thiamine (Cu²⁺-TH) system for the detection of alkaline phosphatase (ALP) activity and inhibition. The principle of the method is as follows. Under a basic conditions, TH, which does not exhibit a fluorescence signal, is oxidized into fluorescent thiochrome (TC) by Cu²⁺. Ascorbic acid 2-phosphate (AAP), which is the enzyme substrate, is hydrolyzed to produce ascorbic acid (AA) by ALP. The newly formed AA then reduces Cu²⁺ to Cu⁺, which prevents the oxidation of TH by Cu²⁺; as a result, the fluorescent signal becomes weaker. On the contrary, in the absence of ALP, AAP cannot reduce Cu²⁺; additions of Cu²⁺ and TH result in a dramatic increase of the fluorescent signal. The sensing strategy displays brilliant sensitivity with a detection limit of 0.08 U/L, and the detection is linear in the concentration range of 0.1 to 100 U/L. This approach was successfully applied to ALP activity in human serum samples, indicating that it is reliable and may be applied to the clinical diagnosis of ALP-related diseases.

Bifunctional MIL-53(Fe) with pyrophosphate-mediated peroxidase-like activity and oxidation-stimulated fluorescence switching for alkaline phosphatase detection

Alkaline phosphatase (ALP) is extensively used as a clinical biomarker because of its close relevance with a variety of diseases. Thus, exploring reliable and practical methods for ALP analysis is of great significance. In the present work, we explored MIL-53(Fe) as a bifunctional platform with pyrophosphate (PPi)-mediated peroxidase-like activity and oxidation-stimulated fluorescence switching for ALP sensing. The proposed MIL-53(Fe) could exhibit favorable peroxidase-mimicking activity to catalytically decompose H2O2 to hydroxyl radicals, which had strong oxidizing ability to oxidize the terephthalic acid bridging ligand, resulting in the oxidation-stimulated turn-on fluorescence of MIL-53(Fe) itself. Due to the strong coordination interaction between PPi and Fe3+, the former with a relatively large molecular structure was able to inhibit the catalytic activity of MIL-53(Fe) via capping active Fe3+ sites, leading to the suppression of its self-fluorescence response. When ALP was present, it could hydrolyze the PPi inhibitor and restore the dual functions of MIL-53(Fe) to provide fluorescence again. With the above principle, highly sensitive and selective determination of ALP with a linear scope of 2-80 U L-1 and a detection limit down to 0.7 U L-1 was achieved. The MIL-53(Fe) was also demonstrated to be very reliable in measuring the target in human serum, indicating its great promise as an integrated tool for ALP detection in clinical practice.

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 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 CoO_x with the hexametaphosphate ion (HMPi)-mediated electrostatic aggregation. After sulfuration engineering, the CoO_x 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.

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.

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. Specifically, nanoceria catalyzes the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to give a blue product (oxTMB) with an absorption peak at 645 nm in the presence of PPi. If, however, alkaline phosphatase (ALP) is present, it will hydrolyze PPi, and this results in a decreased oxidase-like activity of nanoceria. Hence, less blue oxTMB willl be formed. On the other hand, if the ALP inhibitor Na₃VO₄ is added to the system, the oxidase-like activity of nanoceria is gradually restored. On the basis of the above results, a spectrophotometric method was developed for determination of the activity of ALP. It works in the 0.5 to 10 mU.mL^-1 activity range and has a 0.32 mU.mL^-1 detection limit. Na₃VO₄ causes a 50% ALP inhibition if present in 71 μM concentration. The assay was successfully applied to the determination of ALP in spiked human serum and gave good recoveries. Graphical abstract Schematic presentation of pyrophosphate (PPi)-induced acceleration of the oxidase-like activity of nanoceria (CeO₂) for determination of alkaline phosphatase enzyme (ALP) activity and its inhibitor NaVO₃.

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

A fluorimetric method is described for the determination of alkaline phosphatase (ALP) activity. It is based on the use of polyethyleneimine-coated silver nanoclusters (AgNCs), which display an intense blue fluorescence peaking at 450 nm (under 375 nm excitation). ALP catalyzes the dephosphorylation of the thiophosphate amifostine to generate a thiol that binds to the AgNCs and causes its fluorescence to be quenched. Under the optimal experimental conditions, fluorescence linearly drops in the 0.08-2.0 U L^-1 ALP activity range, and the limit of detection is 0.02 U L^-1. The method was successfully applied to the determination of ALP activity in spiked human serum samples. Graphical abstract Alkaline phosphatase (ALP) catalyzes the degradation of amifostine with a generation a thiol product. The thiol quenches the fluorescence of silver nanoclusters, and a method for the detection of ALP down to 0.02 U L^-1 was developed.