Microelectrode glucose biosensor based on nanoporous platinum/graphene oxide nanostructure for rapid glucose detection of tomato and cucumber fruits

Microelectrode glucose biosensor based on three-dimensional hybrid nanoporous platinum/graphene oxide nanostructure was developed for rapid glucose detection of tomato and cucumber fruits. The nanostructure was fabricated by a two-step modification method on microelectrode for loading a larger amount of glucose oxidase. The nanoporous structure was prepared on the surface of the platinum microelectrode by electrochemical etching, and then graphene oxide was deposited on the prepared nanoporous electrode by electrochemical deposition. The nanoprorous platinum/graphene oxide nanostructure had the advantage of improving the effective surface area of the electrode and the loading quantity of glucose oxidase. As a result, the biosensor achieved a wide range of 0.1-20.0 mM in glucose detection, which had the ability to accurately detect the glucose content. It was found that the three-dimensional hybrid nanostructure on the electrode surface realized the rapid direct electrochemistry of glucose oxidase. Therefore, the biosensor achieved high glucose detection sensitivity (11.64 μA mM -1cm -2), low detection limit (13 μM) and rapid response time (reaching 95% steady-state response within 3 seconds), when calibrating in glucose standard solution. In agricultural application, the as-prepared biosensor was employed to detect the glucose concentration of tomato and cucumber samples. The results showed that the relative deviation of this method was less than 5% when compared with that of HPLC, implying high accuracy of the presented biosensor in glucose detection in plants.

Glucose oxidase as a model enzyme for antidiabetic activity evaluation of medicinal plants: In vitro and in silico evidence

Diabetes mellitus is a major public health problem in the world. In Africa, more than 80% of patients use plants for their treatment. However, the methods of validation of endogenous knowledge usually used are costly. The alternative method developed in this study aims at creating hyperglycemia <i>in vitro</i> and exploiting the metabolic pathway involving glucose oxidase for UV-visible spectrophotometric screening of medicinal plants’ antidiabetic activity. The evolution of glucose oxidation as a function of drug concentration is followed by UV-visible spectrophotometry. The formation of the stable complex between the enzyme and the inhibitor is studied using molecular docking. Drugs used (Gliben) and plant extracts exhibited an <i>in vitro</i> hypoglycemic effect by reducing exponentially, <i>in vitro</i>, the level of free glucose. The results also showed that <i>L. multiflora</i> is more active than <i>V. amygdalina</i> (IC₅₀: 1.36 ± 0.09 mg/mL Vs IC₅₀: 3.00 ± 0.54 mg/mL). Gliben (0.5 mg/mL) and <i>L. multiflora</i> (2 mg/mL) reduced both the rate of oxidation of glucose by glucose oxidase (catalytic power V_max: 0.84 ± 0.11 mg*mL^-1*min^-1 for Gliben and 1.72 ± 0.13 mg*mL^-1*min^-1 for ^{L. multiflora}); and the affinity of this enzyme for its substrate-glucose (K_M: 15.11 ± 2.72 mg*mL^-1 for Gliben and 9.17 ± 1.56 mg*mL^-1 for <i>L. multiflora</i>) when these results are compared to enzyme catalysis in the absence of inhibitor (V_max: 2.86 ± 0.44 mg*mL^-1*min-1; K_M: 8.07 ± 1.96 mg*mL^-1). The binding of GOX (1GAL) to selected phytocompounds derived from <i>L. multiflora</i> was confirmed by molecular docking. The most stable complexes were obtained for four compounds; <b>8</b> (-10.1±0.0 Kcal/mol), <b>6</b> (-9.5±0.1 Kcal/mol), <b>3</b> (-8.3±0.0 Kcal/mol) and <b>9</b> (-8.2±0.1 Kcal/mol). Among these, compounds <b>8</b> and <b>6</b> formed complexes with the enzyme stabilized by hydrogen bonds, the compound <b>8</b> forms 5 hydrogen bonds (<b>ASN514</b>, <b>ASP424</b>, <b>ARG95</b>, <b>TYP68</b>, <b>LEU65</b>) while compound <b>6</b> forms 2 hydrogen bonds (<b>ASN514</b> and <b>SER422</b>). However, no H-bonding interaction occurs in the complex that involves ligands <b>9</b> and <b>3</b> despite their high binding energy (-8.2±0.1 Kcal/mol and -8.3±0.0 Kcal/mol respectively). Glucose oxidase can serve as a marker enzyme for<i> in vitro</i> antidiabetic activity evaluation of medicinal plants.

pH-switchable nanozyme cascade catalysis: a strategy for spatial–temporal modulation of pathological wound microenvironment to rescue stalled healing in diabetic ulcer

The management of diabetic ulcer (DU) to rescue stalled wound healing remains a paramount clinical challenge due to the spatially and temporally coupled pathological wound microenvironment that features hyperglycemia, biofilm infection, hypoxia and excessive oxidative stress. Here we present a pH-switchable nanozyme cascade catalysis (PNCC) strategy for spatial–temporal modulation of pathological wound microenvironment to rescue stalled healing in DU. The PNCC is demonstrated by employing the nanozyme of clinically approved iron oxide nanoparticles coated with a shell of glucose oxidase (Fe3O4-GOx). The Fe3O4-GOx possesses intrinsic glucose oxidase (GOx), catalase (CAT) and peroxidase (POD)-like activities, and can catalyze pH-switchable glucose-initiated GOx/POD and GOx/CAT cascade reaction in acidic and neutral environment, respectively. Specifically, the GOx/POD cascade reaction generating consecutive fluxes of toxic hydroxyl radical spatially targets the acidic biofilm (pH ~ 5.5), and eradicates biofilm to shorten the inflammatory phase and initiate normal wound healing processes. Furthermore, the GOx/CAT cascade reaction producing consecutive fluxes of oxygen spatially targets the neutral wound tissue, and accelerates the proliferation and remodeling phases of wound healing by addressing the issues of hyperglycemia, hypoxia, and excessive oxidative stress. The shortened inflammatory phase temporally coupled with accelerated proliferation and remodeling phases significantly speed up the normal orchestrated wound-healing cascades. Remarkably, this Fe3O4-GOx-instructed spatial–temporal remodeling of DU microenvironment enables complete re-epithelialization of biofilm-infected wound in diabetic mice within 15 days while minimizing toxicity to normal tissues, exerting great transformation potential in clinical DU management. The proposed PNCC concept offers a new perspective for complex pathological microenvironment remodeling, and may provide a powerful modality for the treatment of microenvironment-associated diseases. Graphical Abstract

Highly sensitive urine glucose detection by graphene field-effect transistors functionalized with electropolymerized nanofilms.

We introduce a new approach for glucose oxidase (GOx) immobilization on graphene field-effect transistors (gFETs) to fabricate highly sensitive glucose sensors. The strategy relies on the electropolymerization of a layer...