Nitrogen-Doped Carbon Nanotubes Supported by Macroporous Carbon as an Efficient Enzymatic Biosensing Platform for Glucose

Untangling the Effects of Doping Carbon with Diverse Heteroatoms on the Bioelectrochemistry of Glucose Oxidase

Great enthusiasm for doping carbon materials with nonmetallic heteroatoms for promoting electrical contact of redox enzymes with electrodes in bioelectronics has been aroused. However, systematic studies of different heteroatoms on enzyme activities are still lacking. Herein, choosing glucose oxidase (GOD) as a model enzyme, carbon nanotubes (CNTs) are used as electron carriers to evaluate the effects of heteroatoms' species on the direct electron transfer and catalytic activities of GOD. Experimental data demonstrate that phosphorus (P)-doped CNTs provide the most intimate electrical contact with GOD compared to other elements (B, N, and S) doping, delivering a 3-fold increase in rate constant (k_s, 2.1 s^-1) and an enhanced turnover rate (k_cat, 2.74 × 10^-9 M cm^-2 s^-1) in comparison with CNTs. Meanwhile, theoretical modeling clarifies that the active center of GOD interacts more strongly with P-doped CNTs and maintains their conformation well compared to other CNTs. This study will help to understand the mechanism of heteroatom doping of carbon on the enzymatic electron transfer and shed light on the design of efficient bioelectrocatalytic interfaces.

High-Performance, Nitrogen-Doped, Carbon-Nanotube-Based Electrochemical Sensor For Vitamin D3 Detection

With the fast changing lifestyle, vitamin D deficiency is becoming extremely common. Therefore, development of economical, efficient, and fast sensors for vitamin D is the need of the hour. Carbon-based nanomaterials are extensively explored in sensing of variety of biomolecules. In the present study, an antibody-free, highly sensitive, carbon-nanotube-based, highly responsive vitamin D3 sensor is reported. Nitrogen-doped carbon nanotubes are utilized to overcome the limiting factor of hydrophobic character of pure carbon. The synthesized N-doped CNTs showed a specific surface area of 24 m²/g. The surface charges of vitamin D3 and the vitamin D3/NCNT complex are found to be -20 and -6.4 mV, respectively, by zeta potential measurements. The sensor is able to deliver high performance in the concentration range of 0-10 nM, with a limit of detection of 16 pM. The response study indicated the sensitivity value as 0.000495 mA/cm² nM. The sensor is also able to show a higher selectivity toward vitamin D3 in comparison to other biomolecules. The long-term stability, reproducibility, good linear range, and ultralow detection capability of the sensor are also reported.

Gold Nanomaterials-Based Electrochemical Sensors and Biosensors for Phenolic Antioxidants Detection: Recent Advances

Antioxidants play a central role in the development and production of food, cosmetics, and pharmaceuticals, to reduce oxidative processes in the human body. Among them, phenolic antioxidants are considered even more efficient than other antioxidants. They are divided into natural and synthetic. The natural antioxidants are generally found in plants and their synthetic counterparts are generally added as preventing agents of lipid oxidation during the processing and storage of fats, oils, and lipid-containing foods: All of them can exhibit different effects on human health, which are not always beneficial. Because of their relevant bioactivity and importance in several sectors, such as agro-food, pharmaceutical, and cosmetic, it is crucial to have fast and reliable analysis Rmethods available. In this review, different examples of gold nanomaterial-based electrochemical (bio)sensors used for the rapid and selective detection of phenolic compounds are analyzed and discussed, evidencing the important role of gold nanomaterials, and including systems with or without specific recognition elements, such as biomolecules, enzymes, etc. Moreover, a selection of gold nanomaterials involved in the designing of this kind of (bio)sensor is reported and critically analyzed. Finally, advantages, limitations, and potentialities for practical applications of gold nanomaterial-based electrochemical (bio)sensors for detecting phenolic antioxidants are discussed.

Surface Enhanced Raman Spectroscopy Based Biosensor with a Microneedle Array for Minimally Invasive In Vivo Glucose Measurements

To monitor blood glucose levels reliably, diabetic patients usually have to undergo frequent fingerstick tests to draw out fresh blood, which is painful and inconvenient with the potential risk of cross contamination especially when the lancet is reused or not properly sterilized. This work reports a novel surface-enhanced Raman spectroscopy (SERS) sensor for the in situ intradermal detection of glucose based on a low-cost poly(methyl methacrylate) microneedle (PMMA MN) array. After incorporating 1-decanethiol (1-DT) onto the silver-coated array surface, the sensor was calibrated in the range of 0-20 mM in skin phantoms then tested for the in vivo quantification of glucose in a mouse model of streptozocin (STZ)-induced type I diabetes. The results showed that the functional poly(methyl methacrylate) microneedle (F-PMMA MN) array was able to directly measure glucose in the interstitial fluid (ISF) in a few minutes and retain its structural integrity without swelling. The Clarke error grid analysis of measured data indicated that 93% of the data points lie in zones A and B. Moreover, the MN array exhibited minimal invasiveness to the skin as the skin recovered well without any noticeable adverse reaction in 10 min after measurements. With further improvement and proper validation, this polymeric MN array-based SERS biosensor has the potential to be used in painless glucose monitoring of diabetic patients in the future.

Electrochemical Preparation of Polyaniline- Supported Cu-CuO Core-Shell on 316L Stainless Steel Electrodes for Nonenzymatic Glucose Sensor

In this article, we reported the elaboration of a nonenzymatic glucose sensor based on the polyaniline-supported Cu-CuO core-shell structure prepared on the 316L stainless steel electrode by electrochemical methods. In the first step, polyaniline (PANI) film was electrodeposited on the 316L substrate from a solution of 0.1 M aniline and 0.5 M sulfuric acid in absolute ethanol by the cyclic voltammetry (CV) method. In the second step, the copper particles were electrodeposited on the PANI film from CuCl2·2H2O 0.01 M precursor prepared in a KCl 0.1 M solution by the CV method. In the third step, Cu particles were partially oxidized to CuO by the CV method in a NaOH 0.1 M electrolyte to form a Cu-CuO core-shell structure supported on the PANI film. The as-prepared electrode (Cu-CuO/PANI/316L) was used to detect glucose in a NaOH 0.1 M solution. The Cu-CuO/PANI/316L sensor exhibited a linear range of 0.1–5 mM (R2 = 0.995) with a detection limit of 0.1 mM (S/N = 3) and high sensitivity of (25.71 mA·mM−1·cm−2). In addition, no significant interference was observed from sucrose, maltose, lactose, and ascorbic acid. The results showed that the polyaniline-supported Cu-CuO core-shell structure has the potential to be applied as an electrode material for the nonenzymatic glucose sensor.

Designing electrochemical interfaces based on nanohybrids of avidin functionalized-carbon nanotubes and ruthenium nanoparticles as peroxidase-like nanozyme with supramolecular recognition properties for site-specific anchoring of biotinylated residues

We are reporting an original supramolecular architecture based on a rationally designed new nanohybrid with enhanced peroxidase-like activity and site-specific biorecognition properties using avidin-functionalized multi-walled carbon nanotubes (MWCNTs-Av) and Ru nanoparticles (RuNPs). The nanohybrid-electrochemical interface was obtained by drop-coating of MWCNTs-Av dispersion at glassy carbon electrodes (GCE) followed by solvent evaporation and further electrodeposition of RuNPs (50 ppm RuCl₂ for 15 s at -0.600 V). The simultaneous presence of MWCNTs and RuNPs produces a synergic effect on the non-enzymatic catatalytic reduction of H₂O₂ and allows the quantification of H₂O₂ in a wide linear range (from 5.0 × 10^-7 M to 1.75 × 10^-3 M) with a low limit of detection (65 nM). The avidin residues present in MWCNTs-Av/RuNPs hybrid nanomaterial allowed the anchoring by bioaffinity of biotinylated glucose oxidase (biot-GOx) as proof-of-concept of the analytical application of MWCNTs-Av platform for biosensors development. The resulting nanoarchitecture behaves as a bienzymatic-like glucose biosensor with a competitive analytical performance: linear range between 2.0 × 10^-5 M and 1.23 × 10^-3 M, sensitivity of (0.343 ± 0.002) μA mM^-1 or (2.60 ± 0.02) μA mM^-1 cm^-2, detection limit of 3.3 μM, and reproducibility of 5.2% obtained with five different GCE/MWCNTs-Av/RuNPs/biot-GOx bioplatforms prepared the same day using the same MWCNTs-Av dispersion, and 9.1% obtained with nine biosensors prepared in different days with nine different MWCNTs-Av dispersions. The average concentrations of glucose in Gatorade®, Red bull® and Pepsi® with the biosensor demonstrated excellent agreement with those reported in the commercial beverages.

Facile preparation of CoMoO4 nanorods at macroporous carbon hybrid electrocatalyst for non-enzymatic glucose detection

Glucose is a popular biosensor target due to its closely with diabetes or hypoglycemia in blood. Designing efficiency electrocatalysts for the determination of glucose is vital to develop glucose detection devices. CoMoO₄, as a kind of bimetallic oxide material, exhibits unique electrochemical properties. 3D macroporous carbon (MPC) has large specific surface area and excellent electrical conductivity, providing an effective support for loading other nano-entities to form novel composite with good synergetic effects. Herein, nanorod-like CoMoO₄ anchored onto MPC support was synthesized for the development of a promising electrochemical sensing platform for glucose. Attributing to the synergic effects between the good electrocatalytic performance of CoMoO₄ nanorods and the extraordinary electrical conductivity of 3D layered MPC, the novel CoMoO₄/MPC composites non-enzymatic sensor shows excellent electrocatalytic performance for oxidation of glucose. Under the optimum conditions, the proposed CoMoO₄/MPC hybrids provided a reliable linear range of 5 × 10^-7 to 1.08 × 10^-4 M with a low limit of detection (0.13 μM) for the detection of glucose. Meanwhile, the CoMoO₄/MPC sensing platform shows fast response time of 1.76 s, good stability and selectivity for detecting glucose. Moreover, this non-enzymatic sensor also has been successfully applied to measure glucose level in human blood samples. Therefore, the developed sensor holds a new promise for the construction of facile and sensitive non-enzymatic glucose analytical platform.

Optofluidic microcapillary biosensor for label-free, low glucose concentration detection

We demonstrate label-free detection of low glucose concentration based on whispery gallery mode resonance in an optofluidic microcapillary (OFMC) biosensor. The wall surface of the OFMC is bio-chemically functionalized to detect cellular-level glucose concentration as low as 2.78 mM. The measured sensitivity is 0.966 pm/mM. The fabricated microcapillary has a thin wall thickness of 2 μm and a Q factor of 1.3 × 10⁶, corresponding to a bulk refractive index sensitivity of 23.36 nm/RIU. The OFMC biosensor has advantages such as high resistance to environmental perturbation, small sample volume down to 90 nL and cost-effectiveness. Theoretical analysis shows the sensor sensitivity depends on the microcapillary wall thickness and liquid core refractive index.

Simple and Large-Scale Strategy to Prepare Flexible Graphene Tape Electrode

A simple and large-scale strategy to prepare flexible graphene tape electrode (GTE) was proposed. The flexible GTE was prepared by a facile peeling method in which a piece of commercial graphite foil was first covered by a commercial acrylic transparent tape and then the transparent adhesive tape was quickly torn off from the graphite foil. Scanning electron microscopy results showed that some folded and wrinkled graphene layers stood up on the GTE surface to form three-dimensional (3D) porous graphene foam. The 3D porous flexible GTE was proposed as a novel supporting matrix to load Ni-Co nanoparticles (Ni-CoNPs) and glucose oxidase (GOD) as examples to test its applications for electrochemical glucose sensing. The Ni-CoNPs/GTE showed the linear range of 0.6 μM-0.26 mM and 1.360-5.464 mM with a detection limit of 0.16 μM. The GOD/AuNPs-CHIT/GTE had a linear range of 0.616-14.0 mM and a detection limit of 0.202 mM. These results were similar or superior to the printable electrodes by nanocarbon and electrodes modified with graphene, carbon nanotubes, or porous carbon materials, but the flexible GTE was more easier to prepare in large-scale and the 3D porous graphene foam were not easy to drop off from the tape because they were glued on acrylic transparent tape firmly. Therefore, the 3D porous flexible GTE should be promising candidates for electrochemical sensors and other electrochemical applications.

A simplistic approach to green future with eco-friendly luminescent carbon dots and their application to fluorescent nano-sensor 'turn-off' probe for selective sensing of copper ions

Zero-dimensional fluorescent nanoparticles having specificity as molecular probe appears to be strategically balanced fluorescent nano-probes. In this work, purified lemon extract and l-arginine have been thermally coupled for the extremely acute detection of Cu²⁺ in aqueous medium. The Cu²⁺ ions may be captured by the amino groups on the surface of the nano-sensor to form cupric ammine complex resulting in quenched fluorescence via an inner filter effect. Our proposed nano-probe is N-doped carbon dots (NCDs) which are efficiently selective as fluorescent chemosensor due to enormous binding affinity towards Cu²⁺ in a wide range of concentration (0.05-300μM) within a few minutes.

Synthesis of nickel(ii) coordination polymers and conversion into porous NiO nanorods with excellent electrocatalytic performance for glucose detection

Porous NiO nanostructures are fabricated by calcinating the Ni(SA)₂(H₂O)₄coordination polymers and used as electrocatalysts for the detection of glucose in a nonenzymatic electrochemical sensor.

Gold–platinum bimetallic nanoclusters with enhanced peroxidase-like activity and their integrated agarose hydrogel-based sensing platform for the colorimetric analysis of glucose levels in serum

Bimetallic Au–PtNCs with enhanced peroxidase-like activity were integrated into agarose hydrogels for direct visualization of glucose in human serum.

Sensitive determination of chlorogenic acid in pharmaceutical products based on the decoration of 3D macroporous carbon with Au nanoparticles via polyoxometalates

A simple and sensitive electrochemical sensor is constructed for the detection of chlorogenic acid (CGA).

Hierarchically mesostructured porous TiO2 hollow nanofibers for high performance glucose biosensing

Effective immobilization of enzymes on an electrode surface is of great importance for biosensor development, but it still remains challenging because enzymes tend to denaturation and/or form close-packed structures. In this work, a free-standing TiO₂ hollow nanofibers (HNF-TiO₂) was successfully prepared by a simple and scalable electrospun nanofiber film template-assisted sol-gel method, and was further explored for glucose oxidase (GOD) immobilization and biosensing. This porous and nanotubular HNF-TiO₂ provides a well-defined hierarchical nanostructure for GOD loading, and the fine TiO₂ nanocrystals facilitate direct electron transfer from GOD to the electrode, also the strong interaction between GOD and HNF-TiO₂ greatly enhances the stability of the biosensor. The as-prepared glucose biosensors show good sensing performances both in O₂-free and O₂-containing conditions with good sensitivity, satisfactory selectivity, long-term stability and sound reliability. The novel textile formation, porous and hierarchically mesostructured nature of HNF-TiO₂ with excellent analytical performances make it a superior platform for the construction of high-performance glucose biosensors.

Facile and green decoration of Pd nanoparticles on macroporous carbon by polyoxometalate with enhanced electrocatalytic ability

A well-defined Pd nanoparticles@polyoxometalates/macroporous carbon (Pd@POMs/MPC) tri-component nanohybrid has been developed using a facile, green, and one-pot synthesis method.

Microperoxidase-11/metal–organic framework/macroporous carbon for detecting hydrogen peroxide

Schematic illustrating of the fabrication and sensing principle of the newly develpoed H₂O₂ biosensor.