The Kinetic and Analytical Aspects of Enzyme Competitive Inhibition: Sensing of Tyrosinase Inhibitors

An amperometric biosensor based on tyrosinase, immobilized onto a carbon black paste electrode using glutaraldehyde and BSA was constructed to detect competitive inhibitors. Three inhibitors were used in this study: benzoic acid, sodium azide, and kojic acid, and the obtained values for fifty percent of inhibition (IC50) were 119 µM, 1480 µM, and 30 µM, respectively. The type of inhibition can also be determined from the curve of the degree of inhibition by considering the shift of the inhibition curves. Amperometric experiments were performed with a biosensor polarized at the potential −0.15 V vs. Ag/AgCl and using 0.1 M phosphate buffer (pH 6.8) as an electrolyte. Under optimized conditions, the proposed biosensor showed a linear amperometric response toward catechol detection from 0.5 µM to 38 µM with a detection limit of 0.35 µM (S/N = 3), and its sensitivity was 66.5 mA M−1 cm−2. Moreover, the biosensor exhibited a good storage stability. Conversely, a novel graphical plot for the determination of reversible competitive inhibition was represented for free tyrosinase. The graph consisted of plotting the half-time reaction (t1/2) as a function of the inhibitor concentration at various substrate concentrations. This innovative method relevance was demonstrated in the case of kojic acid using a colorimetric bioassay relying on tyrosinase inhibition. The results showed that the t1/2 provides an extended linear range of tyrosinase inhibitors.

Investigation of Anions Effects on the Morphology of NiO Nanostructures and Their Non-Enzymatic Glucose Sensing Applications

It is essential to study the impact of anions happening the morphology of nanomaterials to prepare nanostructures with well-defined shape. This present work is based on the effect of anions (acetate, chloride, nitrate, and sulfate) on the morphology of nickel oxide nanostructures material synthesized by a simple hydrothermal method. The prepared composite material structures were studied by XRD, SEM), and TEM. The synthesized nanostructures were fabricated for the non-enzymatic glucose sensors. These sensors can be used for the non-enzymatic glucose sensors to take a fast amperometric response less time. The sensitivity for all four sensors of NiO grown using nickel acetate, nickel chloride, nickel nitrate, and nickel sulfate salts are in order of 212.71, 519, 419.57, and 79.28 μA/mM·cm2 respectively. The detection limits were estimated in the order of 0.1 to 1.0 μM. The NiO nanostructures grown with nickel chloride salt were found the most sensitive in this respect and subjected to evaluation of other competing species during glucose-sensing such as ascorbic acid, uric acid, and sucrose. The found best NiO nanomaterial remained positively used to quantify glucose levels in the blood serum of humans.

A New Possibility for Fermentation Monitoring by Electrical Driven Sensing of Ultraviolet Light and Glucose

Industrial fermentation generates products through microbial growth associated with the consumption of substrates. The efficiency of industrial production of high commercial value microbial products such as ethanol from glucose (GLU) is dependent on bacterial contamination. Controlling the sugar conversion into products as well as the sterility of the fermentation process are objectives to be considered here by studying GLU and ultraviolet light (UV) sensors. In this work, we present two different approaches of SnO2 nanowires grown by the Vapor–Liquid–Solid (VLS) method. In the GLU sensor, we use SnO2 nanowires as active electrodes, while for the UV sensor, a nanowire film was built for detection. The results showed a wide range of GLU sensing and as well as a significant influence of UV in the electrical signal. The effect of a wide range of GLU concentrations on the responsiveness of the sensor through current–voltage based on SnO2 nanowire films under different concentration conditions ranging was verified from 1 to 1000 mmol. UV sensors show a typical amperometric response of SnO2 nanowires under the excitation of UV and GLU in ten cycles of 300 s with 1.0 V observing a stable and reliable amperometric response. GLU and UV sensors proved to have a promising potential for detection and to control the conversion of a substrate into a product by GLU control and decontamination by UV control in industrial fermentation systems.

Layered Double Hydroxide-Modified Organic Electrochemical Transistor for Glucose and Lactate Biosensing

Biosensors based on Organic Electrochemical Transistors (OECTs) are developed for the selective detection of glucose and lactate. The transistor architecture provides signal amplification (gain) with respect to the simple amperometric response. The biosensors are based on a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) channel and the gate electrode is functionalised with glucose oxidase (GOx) or lactate oxidase (LOx) enzymes, which are immobilised within a Ni/Al Layered Double Hydroxide (LDH) through a one-step electrodeposition procedure. The here-designed OECT architecture allows minimising the required amount of enzyme during electrodeposition. The output signal of the biosensor is the drain current (Id), which decreases as the analyte concentration increases. In the optimised conditions, the biosensor responds to glucose in the range of 0.1–8.0 mM with a limit of detection (LOD) of 0.02 mM. Two regimes of proportionality are observed. For concentrations lower than 1.0 mM, a linear response is obtained with a mean gain of 360, whereas for concentrations higher than 1.0 mM, Id is proportional to the logarithm of glucose concentration, with a gain of 220. For lactate detection, the biosensor response is linear in the whole concentration range (0.05–8.0 mM). A LOD of 0.04 mM is reached, with a net gain equal to 400.

Enhancement of amperometric response of glucose biosensor by electrodeposition of silver nanoparticles onto chitosan-modified electrode

A highly sensitive biosensor based on silver nanoparticles (AgNPs) was fabricated for glucose detection in aqueous phase. Firstly, a platinum (Pt) electrode was modified with the mixture of glucose oxidase and chitosan. AgNPs were electrodeposited into the modified electrode by single pulse potentiostatic method at –0.4 V. The electrochemical performance of the modified electrode was evaluated by cyclic voltammetry and amperometry. The fabricated biosensor had a high sensitivity of 58.6 μA mM−1 cm−2 and detection limit of 4.4 μM glucose at a signal to noise ratio of 3. In addition, the biosensor showed a short response time less than 5 s and a wide linear range of 0.05-11.5 mM. The apparent Michaelis–Menten constant (KM) was found to be 9.14 mM. In addition, thermal stability and anti-interference ability of the biosensor were investigated. The results demonstrated that AgNPs enhanced the analytical performance of the biosensor.

Novel amperometric glucose biosensor based on MXene nanocomposite

A biosensor platform based on Au/MXene nanocomposite for sensitive enzymatic glucose detection is reported. The biosensor leverages the unique electrocatalytic properties and synergistic effects between Au nanoparticles and MXene sheets. An amperometric glucose biosensor is fabricated by the immobilization of glucose oxidase (GOx) enzyme on Nafion solubilized Au/ MXene nanocomposite over glassy carbon electrode (GCE). The biomediated Au nanoparticles play a significant role in facilitating the electron exchange between the electroactive center of GOx and the electrode. The GOx/Au/MXene/Nafion/GCE biosensor electrode displayed a linear amperometric response in the glucose concentration range from 0.1 to 18 mM with a relatively high sensitivity of 4.2 μAmM−1 cm−2 and a detection limit of 5.9 μM (S/N = 3). Furthermore, the biosensor exhibited excellent stability, reproducibility and repeatability. Therefore, the Au/MXene nanocomposite reported in this work is a potential candidate as an electrochemical transducer in electrochemical biosensors.