Study on Enhancement Principle and Stabilization for the Luminol-H2O2-HRP Chemiluminescence System

A novel ultrasensitive chemiluminescence enzyme immunoassay by employment of a signal enhancement of horseradish peroxidase-luminol-hydrogen peroxide reaction for the quantitation of atezolizumab, a monoclonal antibody used for cancer immunotherapy

This study describes, for the first time, the development and validation of a novel ultrasensitive chemiluminescence enzyme immunoassay (CLEIA) for the quantification of atezolizumab (ATZ), a monoclonal antibody approved by the FDA for treatment of different types of cancer. The assay involved the non-competitive binding of ATZ to its specific antigen (PD-L1 protein). The immune complex of PD-L1/ATZ formed on the internal surface of the plate wells was quantified by a novel chemiluminescence (CL)-producing horseradish peroxidase (HRP) reaction. The reaction employed a highly efficient CL enhancer for the HRP-luminol-hydrogen peroxide reaction which was 4-(imidazol-1-yl)phenol. The conditions of the CLEIA and its detection system were refined, and the optimum procedures were established. The CLEIA was validated in accordance with the guidelines of immunoassay validation for bioanalysis, and all the validation criteria were acceptable. The assay's limit of detection and limit of quantitation were 12.5 and 37.5 pg mL-1, respectively, with a working dynamic range of 25-800 pg mL-1. The assay enables the accurate and precise quantitation of ATZ in human plasma samples without any interferences from endogenous substances and/or the plasma matrix. The results of the proposed CLEIA were favourably comparable with those of a pre-validated enzyme-linked immunosorbent assay using a colorimetric detection system. The CLEIA is characterized by simple and high throughput features. The CLEIA is superior to the existing analytical methodologies for ATZ. The proposed CLEIA has a great value in the quantitation of ATZ in clinical settings for assessment of its pharmacokinetics, therapeutic drug monitoring, and refining the safety profile.

Enzymatic assay for UDP-GlcNAc and its application in the parallel assessment of substrate availability and protein O-GlcNAcylation

O-linked N-acetylglucosaminylation (O-GlcNAcylation) is a ubiquitous and dynamic non-canonical glycosylation of intracellular proteins. Several branches of metabolism converge at the hexosamine biosynthetic pathway (HBP) to produce the substrate for protein O-GlcNAcylation, the uridine diphosphate N-acetylglucosamine (UDP-GlcNAc). Availability of UDP-GlcNAc is considered a key regulator of O-GlcNAcylation. Yet UDP-GlcNAc concentrations are rarely reported in studies exploring the HBP and O-GlcNAcylation, most likely because the methods to measure it are restricted to specialized chromatographic procedures. Here, we introduce an enzymatic method to quantify cellular and tissue UDP-GlcNAc. The method is based on O-GlcNAcylation of a substrate peptide by O-linked N-acetylglucosamine transferase (OGT) and subsequent immunodetection of the modification. The assay can be performed in dot-blot or microplate format. We apply it to quantify UDP-GlcNAc concentrations in several mouse tissues and cell lines. Furthermore, we show how changes in UDP-GlcNAc levels correlate with O-GlcNAcylation and the expression of OGT and O-GlcNAcase (OGA).

Smartphone-based chemiluminescence detection of aflatoxin B1 via labelled and label-free dual sensing systems

To develop a sensing platform for onsite determination of AFB₁ in foodstuffs, we developed smartphone-based chemiluminescence detection of AFB₁ via labelled and label-free dual modes. The labelled mode was characteristic of double streptavidin-biotin mediated signal amplification, obtaining limit of detection (LOD) of 0.04 ng/mL in the linear range of 1-100 ng/mL. To reduce the complexity in the labelled system, a label-free mode based on both split aptamer and split DNAzyme was fabricated. A satisfactory LOD of 0.33 ng/mL was generated in the linear range of 1-100 ng/mL. Both labelled and label-free sensing systems achieved outstanding recovery rate in AFB₁-spiked maize and peanut kernel samples. Finally, two systems were successfully integrated into smartphone-based portable device based on custom-made components and android application, achieving comparable AFB₁ detection ability to a commercial microplate reader. Our systems hold huge potential for AFB₁ onsite detection in food supply chain.

A Green-Emitting Luminol Analogue as the Next-Generation Chemiluminescent Substrate in Biochemical Analysis

Luminol and its derivatives are extensively used as chemiluminogenic substrates in bioimaging and biochemical analysis. Luminol reagents can typically emit blue chemiluminescence (CL), whose wavelength is normally outside the most sensitive detection range of human naked eyes and most CL analyzers with silicon-based charge-coupled device (CCD) detectors. Development of luminol analogues with longer wavelength emission is thus attractive. Herein, four new phthalhydrazide CL probes (GL-1/2/3/4) have been prepared through the derivatization of luminol. The most promising one, 5-(4-hydroxy-1,3-dioxoisoindolin-2-yl)-2,3-dihydrophthalazine-1,4-dione (GL-1), emits bright green CL upon oxidation and shows enhanced CL performance compared to its parent luminol. Bloodstain imaging, horseradish peroxidase (HRP)-based immunoassay, and the analysis of glucose/glucose oxidase reaction have been performed using the GL-1 reagent. These results indicate that GL-1 is a new chemiluminogenic luminol analogue with great potential in real analytical applications and will be an alternative to replace luminol in practical CL analysis.

Enzymes Encapsulated within Alginate Hydrogels: Bioelectrocatalysis and Electrochemiluminescence Applications

A simple procedure to incorporate enzymes (horseradish peroxidase, HRP, and lactate oxidase, LOx) within alginate hydrogels is reported with electrochemiluminescence (ECL) used to detect the enzymatic reactions with the corresponding substrates. First, HRP and LOx were successfully immobilized into CaCO3 microspheres, followed by the electrostatic layer-by-layer deposition of a nanoshell onto the microspheres, and finally by their dispersion into alginate solution. The as-prepared dispersion was drop cast onto the glassy carbon electrodes and cross-linked by the external and internal gelation methods using Ca2+ cations. The enzymes encapsulated within the alginate hydrogels were characterized using cyclic voltammetry and kinetic studies performed using ECL. The results showed that the enzymatic activity was significantly maintained as a result of the immobilization, with values of the apparent Michaelis-Menten constants estimated as 7.71 ± 0.62 and 8.41 ± 0.43 μM, for HRP and LOx, respectively. The proposed biosensors showed good stability and repeatability with an estimated limit of detection of 5.38 ± 0.05 and 0.50 ± 0.03 μM for hydrogen peroxide and lactic acid, respectively. The as-prepared enzymes encapsulated within the alginate hydrogels showed good stability up to 28 days from their preparation. The sensitivity and selectivity of the enzymes encapsulated within the alginate hydrogels were tested in real matrices (HRP, hydrogen peroxide, in contact lens solution; LOx, lactic acid in artificial sweat) showing the sensitivity of the ECL detection methods for the detection of hydrogen peroxide and lactic acid in real samples.

Luminol-hydrogen peroxide-horseradish peroxidase chemiluminescence intensification by kosmotrope ammonium sulfate

The kosmotropic effect induced by ammonium sulfate (AS) at concentrations greater than approximately 2.8 M allows the marked intensification of chemiluminescence (CL) arising from a conventional luminol-hydrogen peroxide (H2O2)-horseradish peroxidase (HRP) reaction. Because of the kosmotropic effect, CL is intensified by at least three orders of magnitude than that from the conventional HRP-catalyzed luminol reaction with no AS; the linear relationship between the CL intensity and the HRP concentration is established over the range of 0.3 pM to several tens of pM. The novel CL intensification effect on the HRP-catalyzed luminol CL can be stably and reproducibly induced.

A sensitive biosensor for glucose determination based on the unique catalytic chemiluminescence of sodium molybdate

Chemiluminescent (CL) reaction between hydrogen peroxide (H₂O₂) and luminol was dramatically enhanced by sodium molybdate (Na₂MoO₄) for 284-fold. CL mechanism investigation indicated that Na₂MoO₄ increased the production of hydroxyl radical (•OH) and superoxide anion (•O₂^-) in the H₂O₂-luminol system, which could attribute to the enhanced-CL intensity and gave us new insights into the CL-enhanced property of Na₂MoO₄. The CL intensity of Na₂MoO₄-H₂O₂-luminol system increased with the concentration of H₂O₂, based on which, a convenient and sensitive CL determination method could be developed for H₂O₂ in the concentration ranging from 0.5 to 60 μmol/L, with a detection limit of 0.25 μmol/L. Combining with glucose oxidase, the Na₂MoO₄-H₂O₂-luminol system could also be applied for glucose detection. Glucose in human serum has been successfully detected with satisfied recoveries in the range of 96.7 % to 105.4 %.

Determination of tyrosine by sodium fluorescein-enhanced ABEI–H2O2–horseradish peroxidase chemiluminescence

In this study, N-(4-aminobutyl)-N-ethylisoluminol (ABEI) was used as an energy donor, while sodium fluorescein was used as an enhancer and energy acceptor, which resulted in it producing resonance energy transfer and greatly increasing the strength of chemiluminiscence (CL). When horseradish peroxidase (HRP) is added, hydrogen peroxide (H2O2) will quickly separate into hydroxyl radicals (·OH) and superoxide ions (O2·−). If tyrosine (Tyr) is present in the system, the hydroxyl group on the benzene ring of Tyr robs ·OH and O2·− in the CL system, thereby reducing the intensity of CL. Based on this phenomenon, a luminescence system of ABEI and sodium fluorescein system was established to detect Tyr for the first time. This method has an ultra-low detection limit and a wide linear range, and is cheap and easy to operate. Under various optimal conditions, the linear range is from 3.0×10−8 to 3.0×10−5 mol/L, and the limit of detection is 2.4×10−8 mol/L. It has been successfully used in the detection of dairy products with satisfactory results.

Magnetic Nanoparticle-Based Ligand Replacement Strategy for Chemical Luminescence Determination of Cholesterol

Determination of serum cholesterol (Chol) is important for disease diagnosis, and has attracted great attention during the last few decades. Herein, a new magnetic nanoparticle-based ligand replacement strategy has been presented for chemical luminescence detection of Chol. The detection depends on ligand replacement from ferrocene (Fc) to Chol through a β-cyclodextrin (β-CD)-based host-guest interaction, which releases Fc-Hemin as a catalyst for the luminol/hydrogen peroxide chemical luminescence system. More importantly, the luminescence signal can be captured by the camera of a smartphone, thus realizing Chol detection with less instrument dependency. The limit of detection of this method is calculated to be 0.18 μM, which is comparable to some of the developed methods. Moreover, this method has been used successfully to quantify Chol from serum samples with a simple extraction process.

Activation of the phagocyte NADPH oxidase/NOX2 and myeloperoxidase in the mouse brain during pilocarpine-induced temporal lobe epilepsy and inhibition by ketamine

Excessive reactive oxygen species (ROS) production can induce tissue injury involved in a variety of neurodegenerative disorders such as neurodegeneration observed in pilocarpine-induced temporal lobe epilepsy. Ketamine, a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist has beneficial effects in pilocarpine-induced temporal lobe epilepsy, when administered within minutes of seizure to avoid the harmful neurological lesions induced by pilocarpine. However, the enzymes involved in ROS productions and the effect of ketamine on this process remain less documented. Here we show that during pilocarpine-induced epilepsy in mice, the expression of the phagocyte NADPH oxidase NOX2 subunits (NOX2/gp91^phox, p22^phox, and p47^phox) and the expression of myeloperoxidase (MPO) were dramatically increased in mice brain treated with pilocarpine. Interestingly, treatment of mice with ketamine before or after pilocarpine administration decreased this process, mainly when injected before pilocarpine. Finally, our results showed that pilocarpine induced p47^phox phosphorylation and H₂O₂ production in mice brain and ketamine was able to inhibit these processes. Our results show that pilocarpine induced NOX2 activation to produce ROS in mice brain and that administration of ketamine before or after the induction of temporal lobe epilepsy by pilocarpine inhibited this activation in mice brain. These results suggest a key role of the phagocyte NADPH oxidase NOX2 and MPO in epilepsy and identify a novel effect of ketamine.

Optimized bioluminescence analysis of adenosine triphosphate (ATP) released by platelets and its application in the high throughput screening of platelet inhibitors

Activated platelets release adenosine trisphosphate (ATP) and bioluminescence analysis of ATP release is usually used to monitor activation of platelets induced by various stimulants. However, bioluminescence analysis of ATP possesses poor linearity, the signal is quickly attenuated, and the accuracy of ATP release from platelets is hard to determine accurately enough to be used in a high throughput screening of platelet inhibitors. The present study was designed to optimize bioluminescence analysis of ATP released by platelets and expand its application in high throughput screening of platelet inhibitors. The results showed that accuracy of ATP analysis was significantly improved by adding coenzyme A (CoA) and signal attenuation of ATP analysis was greatly postponed by adding bovine serum albumin (BSA) both in Hank’s balanced salt solution (HBSS) and Tyrode’s buffer. Furthermore, ATP release of activated platelets and inhibitory effects of Ly294002 and Staurosporine on platelet activation were accurately determined by our optimized bioluminescence analysis of ATP. Thus, we have successfully constructed an optimized bioluminescence analysis of ATP which can be used in high throughput screening of platelet inhibitors.

Determination of sulfonamides in meat with dummy-template molecularly imprinted polymer-based chemiluminescence sensor

In this study, a molecularly imprinted polymer capable of recognizing 15 sulfonamides was first synthesized with sulfabenz as the dummy template. The calculation results from computation simulation showed that the specific 3D conformation of the template had an important influence on the polymer's recognition ability. Then, the polymer was used as recognition reagent to prepare a chemiluminescence sensor on a conventional 96-well microplate for the determination of the residues of 15 sulfonamides in meat (chicken and pork). Due to the 4-(imidazol-1-yl)phenol-enhanced luminol-H₂O₂ system, the limits of detection for the 15 analytes were in the range of 1.0-12 pg/mL. The recoveries from the standard fortified blank samples were in the range of 72.7-99%. Furthermore, one assay could be finished within 30 min, and the sensor could be reused 4 times. Therefore, this sensor could be used as a very useful tool for routine screening of residues of sulfonamides in meat samples. Graphical abstract Assay procedures of the molecularly imprinted polymer-based chemiluminescence sensor for determination of sulfonamides.

Lyophilization of chemiluminescent substrate reagents for high-sensitive microchannel-based lateral flow assay (MLFA) in point-of-care (POC) diagnostic system

A new method towards successful lyophilization and reconstitution of chemiluminescent substrate while restoring the substrate functionality is reported in this work.

Redox Modulators Determine Luminol Luminescence Generated by Porphyrin-Coordinated Iron and May Repress "Suicide Inactivation"

Iron porphyrin catalysts of the luminol reaction (horseradish peroxidase, hemoglobin, cytochrome c, and hemin) interact with diverse reducing compounds. Here, it is demonstrated how the chemiluminescence yield is modulated by such interactions. The compounds accepted as substrates protect the catalyst against the "suicide inactivation" caused by high peroxide concentrations. The reducing agents not accepted by the catalyst inhibit light production either by generating a futile redox cycle of the luminophore or by irreversibly inactivating the catalytic center. In the case of a futile cycle, light emission resumes as soon as the reducing agents in the reaction are consumed, whereas with an irreversible inactivation, light emission does not recover. The characteristics of luminescence enhancement and quenching depending on interfering agents are also reported here. They reveal details about the relative redox potentials of the involved compounds. It is discussed how this should be considered when the luminol reaction is used for quantitative analyses and when unpurified samples with a broad compound matrix are to be assayed.