Novel lateral flow assay to detect H2O2 by utilizing self-biotinylation of G-quadruplex

We herein describe a novel lateral flow assay (LFA) to detect H2O2 by utilizing self-biotinylation of G-quadruplex (G4). In this strategy, the G4 strand promotes the self-biotinylation of G4 itself in the presence of H2O2, which is then allowed to bind to the FAM-labeled complementary detector probe. The resulting biotin-labeled G4/FAM-detector probe complex is captured on the test line, producing a red-colored band during lateral flow readout. Based on this unique approach, we achieved the naked-eye detection of target H2O2 at concentrations as low as 1 μM, with reliable quantification down to 0.388 μM. This method also demonstrated exceptional specificity in distinguishing H2O2 from other non-target molecules. We further verified its versatile applicability by reliably identifying another biomolecule, choline, by coupling with choline oxidase, which generates H₂O₂ during oxidation. This novel LFA strategy holds great promise as a powerful point-of-care testing (POCT) platform for detecting a large spectrum of target biomolecules by employing their corresponding oxidases.

Mechanism of Reconstitution/Activation of the Soluble PQQ-Dependent Glucose Dehydrogenase from Acinetobacter calcoaceticus: A Comprehensive Study

The ability to switch on the activity of an enzyme through its spontaneous reconstitution has proven to be a valuable tool in fundamental studies of enzyme structure/reactivity relationships or in the design of artificial signal transduction systems in bioelectronics, synthetic biology, or bioanalytical applications. In particular, those based on the spontaneous reconstitution/activation of the apo-PQQ-dependent soluble glucose dehydrogenase (sGDH) from Acinetobacter calcoaceticus were widely developed. However, the reconstitution mechanism of sGDH with its two cofactors, i.e., pyrroloquinoline quinone (PQQ) and Ca²⁺, remains unknown. The objective here is to elucidate this mechanism by stopped-flow kinetics under single-turnover conditions. The reconstitution of sGDH exhibited biphasic kinetics, characteristic of a square reaction scheme associated with two activation pathways. From a complete kinetic analysis, we were able to fully predict the reconstitution dynamics and also to demonstrate that when PQQ first binds to apo-sGDH, it strongly impedes the access of Ca²⁺ to its enclosed position at the bottom of the enzyme binding site, thereby greatly slowing down the reconstitution rate of sGDH. This slow calcium insertion may purposely be accelerated by providing more flexibility to the Ca²⁺ binding loop through the specific mutation of the calcium-coordinating P248 proline residue, reducing thus the kinetic barrier to calcium ion insertion. The dynamic nature of the reconstitution process is also supported by the observation of a clear loop shift and a reorganization of the hydrogen-bonding network and van der Waals interactions observed in both active sites of the apo and holo forms, a structural change modulation that was revealed from the refined X-ray structure of apo-sGDH (PDB: 5MIN).

Near-infrared fluorescence probe for hydrogen peroxide detection: design, synthesis, and application in living systems

Using fluorescent probes to detect endogenous hydrogen peroxide, which is associated with many diseases in the human body, remains an essential technique. Cyanine fluorochromes are a class of dyes that have attracted much attention and are widely used in the synthesis of fluorescent probes. In this article, a novel near-infrared (NIR) fluorescence probe for the detection of hydrogen peroxide was constructed and successfully applied to imaging endogenous hydrogen peroxide in vivo. Notably, probe 1 was designed by connecting 4-(bromomethyl)benzeneboronic acid pinacol ester as the sensing unit to the IR-780 hemicyanine skeleton, which exhibits excellent properties like NIR fluorescence emission over 700 nm. Probe 1 has satisfactory sensitivity to hydrogen peroxide with a low detection limit of 0.14 μM (S/N = 3), attributed to a responding mechanism that leads to the oxidation of phenylboronic acid pinacol ester and thereby releases fluorophore 2. Moreover, probe 1 displays excellent selectivity towards hydrogen peroxide over other substances. Taking advantage of these properties, the probe proved to be cell-permeable. Based on the results of N-acetylcysteine and rotenone together, probe 1 is capable of clearly visualizing endogenously produced hydrogen peroxide in living HepG2 cells and mice. The superior performance of the probe, as a reliable chemical tool, makes it of great potential application for exploring the role played by hydrogen peroxide in biological systems.

An updated view on horseradish peroxidases: recombinant production and biotechnological applications

Horseradish peroxidase has been the subject of scientific research for centuries. It has been used exhaustively as reporter enzyme in diagnostics and histochemistry and still plays a major role in these applications. Numerous studies have been conducted on the role of horseradish peroxidase in the plant and its catalytic mechanism. However, little progress has been made in its recombinant production. Until now, commercial preparations of horseradish peroxidase are still isolated from plant roots. These preparations are commonly mixtures of various isoenzymes of which only a small fraction has been described so far. The composition of isoenzymes in these mixed isolates is subjected to uncontrollable environmental conditions. Nowadays, horseradish peroxidase regains interest due to its broad applicability in the fields of medicine, life sciences, and biotechnology in cancer therapy, biosensor systems, bioremediation, and biocatalysis. These medically and commercially relevant applications, the recent discovery of new natural isoenzymes with different biochemical properties, as well as the challenges in recombinant production render this enzyme particularly interesting for future biotechnological solutions. Therefore, we reviewed previous studies as well as current developments with biotechnological emphasis on new applications and the major remaining biotechnological challenge—the efficient recombinant production of horseradish peroxidase enzymes.

Heterogeneous reconstitution of the PQQ-dependent glucose dehydrogenase immobilized on an electrode: a sensitive strategy for PQQ detection down to picomolar levels

A highly sensitive electroanalytical method for determination of PQQ in solution down to subpicomolar concentrations is proposed. It is based on the heterogeneous reconstitution of the PQQ-dependent glucose dehydrogenase (PQQ-GDH) through the specific binding of its pyrroloquinoline quinone (PQQ) cofactor to the apoenzyme anchored on an electrode surface. It is shown from kinetics analysis of both the enzyme catalytic responses and enzyme surface-reconstitution process (achieved by cyclic voltammetry under redox-mediated catalysis) that the selected immobilization strategy (i.e., through an avidin/biotin linkage) is well-suited to immobilize a nearly saturated apoenzyme monolayer on the electrode surface with an almost fully preserved PQQ binding properties and catalytic activity. From measurement of the overall rate constants controlling the steady-state catalytic current responses of the surface-reconstituted PQQ-GDH and determination of the PQQ equilibrium binding (Kb = 2.4 × 10(10) M(-1)) and association rate (kon = 2 × 10(6) M(-1) s(-1)) constants with the immobilized apoenzyme, the analytical performances of the method could be rationally evaluated, and the signal amplification for PQQ detection down to the picomolar levels is well-predicted. These performances outperform by several orders of magnitude the direct electrochemical detection of PQQ in solution and by 1 to 2 orders the detection limits previously achieved by UV-vis spectroscopic detection of the homogeneous PQQ-GDH reconstitution.

Sensitive detection of H2O2 and H2O2-related reactant with Ru(bipy)(2)(7,8-dimethyl-dipyridophenazine)2+ and oligodeoxyribonucleotide

A sensor for H(2)O(2) and H(2)O(2)-related reactant was constructed with oligonucleotides and Ru(bipy)(2)dppx(2+) (bipy = 2,2'-bipyridine, dppx = 7,8-dimethyl-dipyridophenazine), which was performed by converting the H(2)O(2)-induced DNA cleavage into the change of luminescence. The 'DNA light switch' Ru(bipy)(2)dppx(2+) could emit strong luminescence in the presence of dsDNA. DNA cleavage occurred upon addition of H(2)O(2) due to the Fenton reaction, which resulted in the decrease of the luminescence of Ru(bipy)(2)dppx(2+). Therefore, the luminescence intensity depended on the concentration of H(2)O(2) and H(2)O(2)-related reactants, and the detection limits for H(2)O(2), uric acid and cholesterol were 0.20 μM, 0.46 μM and 1.25 μM, respectively. The recovery varied between 94.0% and 105.0% when the assay was applied to the determination of uric acid and cholesterol in biological samples, which demonstrated the good practicability of the assay.