Biofuel cells allow for constructing sensors that leverage the specificity of enzymes without the need for an external power source. In this work, we design a self-powered glucose sensor based on a biofuel cell. The redox enzymes glucose dehydrogenase (NAD-GDH), glucose oxidase (GOx), and horseradish peroxidase (HRP) were immobilized as biocatalysts on the electrodes, which were previously engineered using carbon nanostructures, including multi-wall carbon nanotubes (MWCNTs) and reduced graphene oxide (rGO). Additional polymers were also introduced to improve biocatalyst immobilization. The reported design offers three main advantages: (i) by using glucose as the substrate for the both anode and cathode, a more compact and robust design is enabled, (ii) the system operates under air-saturating conditions, with no need for gas purge, and (iii) the combination of carbon nanostructures and a multi-enzyme cascade maximizes the sensitivity of the biosensor. Our design allows the reliable detection of glucose in the range of 0.1–7.0 mM, which is perfectly suited for common biofluids and industrial food samples.

The determination of paracetamol is a common need in pharmaceutical and environmental samples for which a low-cost, rapid, and accurate sensor would be highly desirable. We develop a novel pencil graphite lead electrode (PGE) modified with single-wall carbon nanotubes (SWCNTs) and polyvinylpyrrolidone (PVP) polymer (PVP/SWCNT/PGE) for the voltammetric quantification of paracetamol. The sensor shows remarkable analytical performance in the determination of paracetamol at neutral pH, with a limit of detection of 0.38 μM and a linear response from 1 to 500 μM using square-wave voltammetry (SWV), which are well suited to the analysis of pharmaceutical preparations. The introduction of the polymer PVP can cause dramatic changes in the sensing performance of the electrode, depending on its specific architecture. These effects were investigated using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). The results indicate that the co-localization and dispersion of PVP throughout the carbon nanotubes on the electrode are key to its superior electrochemical performance, facilitating the electrical contact between the nanotubes and with the electrode surface. The application of this sensor to commercial syrup and tablet preparations is demonstrated with excellent results.

The simultaneous and cost-effective determination of Dopamine (DA), Acetaminophen (APAP), and Caffeine (CAF) could be useful in several areas such as pain management, clinical diagnostics, and pharmaceutical quality control. In this study, reduced graphene oxide (rGO) was synthesized from graphite and graphene oxide (GO) using ascorbic acid as reducing agent. The rGO was characterized using FT-IR spectroscopy, Raman spectroscopy, scanning electron microscopy, and thermogravimetry. rGO and polyvinylpyrrolidone (PVP) were then combined to modify a glassy carbon electrode (rGO-PVP/GCE), which was studied using cyclic voltammetry, electrochemical impedance spectroscopy, and square-wave voltammetry (SWV). The modified electrode rGO-PVP/GCE exhibited favorable electron transfer kinetics and electrocatalytic activity in the oxidation of DA, APAP, and CAF compared to GO/GCE, PVP/GCE, and rGO/GCE. The SWV results showed three distinct anodic peaks at 0.44, 0.63, and 1.49 V (vs Ag/AgCl 3 M KCl), corresponding to the oxidation of DA, APAP, and CAF, respectively. The responses showed good linearity in the investigated concentration ranges and the limits of detection for DA, APAP, and CAF were 0.81, 0.16, and 19.6 μM, respectively. Finally, the proposed sensor was applied to simultaneously determine DA, APAP, and CAF in artificial urine, a pharmaceutical syrup, and an energy beverage.

We designed and optimized a glucose biosensor system based on a screen-printed electrode modified with the NAD-GDH enzyme. To enhance the electroactive surface area and improve the electron transfer efficiency, we introduced graphene oxide (GO) and ferrocene-modified linear poly(ethylenimine) (LPEI-Fc) onto the biosensor surface. This strategic modification exploits the electrostatic interaction between graphene oxide, which possesses a negative charge, and LPEI-Fc, which is positively charged. This interaction results in increased catalytic current during glucose oxidation and helps improve the overall glucose detection sensitivity by amperometry. We integrated the developed glucose sensor into a flow injection (FI) system. This integration facilitates a swift and reproducible detection of glucose, and it also mitigates the risk of contamination during the analyses. The incorporation of an FI system improves the efficiency of the biosensor, ensuring precise and reliable results in a short time. The proposed sensor was operated at a constant applied potential of 0.35 V. After optimizing the system, a linear calibration curve was obtained for the concentration range of 1.0–40 mM (R² = 0.986). The FI system was successfully applied to determine the glucose content of a commercial sports drink.

We develop an electrochemical sensor for the determination of bromhexine hydrochloride (BHC), a widely use mucolytic drug. The sensor is prepared by electrodeposition of cobalt oxides (CoO_x) on a glassy carbon electrode modified with carboxylated single-walled carbon nanotubes (SWCNT). A synergistic effect between CoO_x and SWCNT is observed, leading to a significant improvement in the BHC electrooxidation current. Based on cyclic voltammetry studies at varying scan rates, we conclude that the electrochemical oxidation of BHC is under mixed diffusion–adsorption control. The proposed sensor allows the amperometric determination of BHC in a linear range of 10–500 µM with a low applied voltage of 0.75 V. The designed sensor provides reproducible measurements, is not affected by common interfering substances, and shows excellent performance for the analysis of BHC in pharmaceutical preparations.

Dihydro-1,3,2H-benzoxazine dimer derivatives or dihydro-benzoxazine dimers are a class of compounds typically prepared by ring-opening reactions between dihydro-benzoxazines and phenols. Dihydro-benzoxazine dimers act as chelating agents for several transition and rare-earth cations. To better understand the chelating properties, it is necessary to examine their structural features and electrochemical characteristics thoroughly. However, the electrochemical properties of dihydro-benzoxazine dimers have not been tremendously examined. Herein, eight derivatives of dihydro-benzoxazine dimers possessing different substituents on the benzene ring and the tertiary-amine nitrogen were synthesized as model compounds to investigate their influences on crystal structures and electrochemical properties. The crystal structure of the dihydro-benzoxazine dimer, namely 2,2′-(cyclohexylazanediyl)bis(methylene)bis(4-methoxyphenol) (7), is identified for the first time and further used to compare with the crystal structures of other derivatives reported previously. For all the derivatives, intermolecular O–H⋅⋅⋅O hydrogen bonds are the significant interactions to hold the crystal packing of (7) and also the other derivatives. Hirshfeld surface analyses confirm the presence of intermolecular O–H⋅⋅⋅O hydrogen bonds. Redox behavior of the eight dihydro-benzoxazine dimers was studied by cyclic voltammetry. An oxidation peak observed at 0.25–0.47 V corresponds to the oxidation of the phenolic –OH group to the phenoxonium intermediate. The shift in the electrochemical peak positions is due to the different abilities of the substituents to stabilize the phenoxonium cation intermediate. The stabilizing power is ranged in the following order: methoxy > dimethyl > ethyl ≈ methyl, and N-cyclohexyl > N-methyl. Thus, the derivative (7), which contains both the methoxy and N-cyclohexyl groups, has the lowest oxidation potential. Our work elucidates the effect of the substituents on the crystal structures and electrochemical properties of the dihydro-benzoxazine dimers.