Functionalized single-walled carbon nanotubes/polypyrrole composites for amperometric glucose biosensors

This article reports an amperometric glucose biosensor based on a new type of nanocomposite of polypyrrole (PPY) with p-phenyl sulfonate-functionalized single-walled carbon nanotubes (SWCNTs-PhSO₃⁻). An environmentally friendly functionalization procedure of the SWCNTs in the presence of substituted aniline and an oxidative species was adopted. The nanocomposite-modified electrode exhibited excellent electrocatalytic activities towards the reduction or oxidation of H₂O₂. This feature allowed us to use it as bioplatform on which glucose oxidase (GOx) was immobilized by entrapment in an electropolymerized PPY/SWCNTs-PhSO₃⁻ film for the construction of the glucose biosensor. The amperometric detection of glucose was assayed by applying a constant electrode potential value necessary to oxidize or reduce the enzymatically produced H₂O₂ with minimal interference from the possible coexisting electroactive compounds. With the introduction of a thin film of Prussian blue (PB) at the substrate electrode surface, the PPY/GOx/SWCNTs-PhSO₃⁻/PB system shows synergy between the PB and functionalized SWCNTs which amplifies greatly the electrode sensitivity when operated at low potentials. The biosensor showed good analytical performances in terms of low detection (0.01 mM), high sensitivity (approximately 6 μA mM⁻¹ cm⁻²), and wide linear range (0.02 to 6 mM). In addition, the effects of applied potential, the electroactive interference, and the stability of the biosensor were discussed. The facile procedure of immobilizing GOx used in the present work can promote the development of other oxidase-based biosensors which could have a practical application in clinical, food, and environmental analysis.     

Fabrication of cubic PtCu nanocages and their enhanced electrocatalytic activity towards hydrogen peroxide

Cubic PtCu nanocages (NCs) were successfully synthesized through a redox reaction using cuprous oxide (Cu₂O) as a sacrificial template and reducing agent. The porous PtCu NCs were composed of amounts of PtCu nanograins with an average particle size of 2.9 nm. The electrocatalytic performance of the PtCu NC electrode towards H₂O₂ was studied by cyclic voltammetry (CV) and chronoamperometry. The prepared PtCu NC electrode exhibited excellent electrocatalytic activity towards H₂O₂, with a wide liner range from 5 μM to 22.25 mM, a relatively high sensitivity of 295.3 μA mM^-1 cm^-2, and a low detection limit of 5 μM (S/N = 3). The hollow porous nanostructure has potential applications in biosensors.     

Glucose biosensor based on multiwalled carbon nanotubes grown directly on Si

An amperometric biosensor based on covalent immobilization of glucose oxidase (GOx) on multiwalled carbon nanotubes (MWCNTs) with potassium ferricyanide as the redox mediator was developed. The MWCNTs were grown directly on a layered structure of Co/Ti/Cr on a SiO₂/Si substrate by microwave-heated chemical vapor deposition. The mediator helps to shuttle the electrons between the immobilized GOx and the MWCNT electrode, therefore operating at a potential of 0.25 V vs. the saturated calomel electrode. This potential precludes the interfering compounds from oxidization. The sensitivity of biosensors to glucose was found to depend on the acid pretreatment and GOx reaction times. The steady-state response of the optimized biosensor exhibits a sensitivity of 20.6 μA mM⁻¹ cm⁻², a linear range of up to 8 mM, and a response time of <5 s.     

Glucose oxidase electrodes based on microstructured polypyrrole films

Highly sensitive glucose oxidase (GOD) electrodes were fabricated on the basis of microstructured polypyrrole (PPy) films. The microstructures of the PPy films had a morphology like cups and were arranged in a density of approximately 4000 units/cm². GOD was immobilized in microstructured PPy films coated on a Pt or stainless steel (SS; AISI 321) substrate electrode. The GOD/PPy/Pt electrode showed a linear response to glucose concentrations in the range of 0–17 mM at a potential of 0.4 V (vs a saturated calomel electrode). Its sensitivity was measured to be approximately 660 nA/(mM cm²) at 15°C, and the response time (t_95%) was approximately 20 s. In comparison, the sensitivity of the GOD/PPy/Pt electrode based on a flat PPy film was only approximately 330 nA/(mM cm²) under the same conditions. The sensitivity of the microstructured GOD/PPy/Pt electrode could be increased to as high as approximately 2400 nA/(mM cm²) at 37°C. The microstructured GOD/PPy/SS electrode had a sensitivity of approximately 550 nA/(mM cm²) and a t_95% value of approximately 30 s at 15°C and 0.4 V. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2550–2554, 2005     

Amperometric detection of hydrogen peroxide at nano-nickel oxide/thionine and celestine blue nanocomposite-modified glassy carbon electrodes

A simple procedure was developed to prepare a glassy carbon (GC) electrode modified with nickel oxide (NiOx) nanoparticles and water-soluble dyes. By immersing the GC/NiOx modified electrode into thionine (TH) or celestine blue (CB) solutions for a short period of time (5–120 s), a thin film of the proposed molecules was immobilized onto the electrode surface. The modified electrodes showed stable and a well-defined redox couples at a wide pH range (2–12), with surface confined characteristics. In comparison to usual methods for the immobilization of dye molecules, such as electropolymerization or adsorption on the surface of preanodized electrodes, the electrochemical reversibility and stability of these modified electrodes have been improved. The surface coverage and heterogeneous electron transfer rate constants (k_s) of thionin and celestin blue immobilized on a NiOx-GC electrode were approximately 3.5 × 10⁻¹⁰ mol cm⁻², 6.12 s⁻¹, 5.9 × 10⁻¹⁰ mol cm⁻² and 6.58 s⁻¹, respectively. The results clearly show the high loading ability of the NiOx nanoparticles and great facilitation of the electron transfer between the immobilized TH, CB and NiOx nanoparticles. The modified electrodes show excellent electrocatalytic activity toward hydrogen peroxide reduction at a reduced overpotential. The catalytic rate constants for hydrogen peroxide reduction at GC/NiOx/CB and GC/NiOx/TH were 7.96 (±0.2) × 10³ M⁻¹ s⁻¹ and 5.5 (±0.2) × 10³ M⁻¹ s⁻¹, respectively. The detection limit, sensitivity and linear concentration range for hydrogen peroxide detection were 1.67 μM, 4.14 nA μM⁻¹ nA μM⁻¹ and 5 μM to 20 mM, and 0.36 μM, 7.62 nA μM⁻¹, and 1 μM to 10 mM for the GC/NiOx/TH and GC/NiOx/CB modified electrodes, respectively. Compared to other modified electrodes, these modified electrodes have many advantages, such as remarkable catalytic activity, good reproducibility, simple preparation procedures and long-term stabilities of signal responses during hydrogen peroxide reduction.     

Melatonin as a Signaling Molecule for Metabolism Regulation in Response to Hypoxia in the Crab Neohelice granulata

Melatonin has been identified in a variety of crustacean species, but its function is not as well understood as in vertebrates. The present study investigates whether melatonin has an effect on crustacean hyperglycemic hormone (CHH) gene expression, oxygen consumption (VO₂) and circulating glucose and lactate levels, in response to different dissolved-oxygen concentrations, in the crab Neohelice granulata, as well as whether these possible effects are eyestalk- or receptor-dependent. Melatonin decreased CHH expression in crabs exposed for 45 min to 6 (2, 200 or 20,000 pmol·crab⁻¹) or 2 mgO₂·L⁻¹ (200 pmol·crab⁻¹). Since luzindole (200 nmol·crab⁻¹) did not significantly (p > 0.05) alter the melatonin effect, its action does not seem to be mediated by vertebrate-typical MT1 and MT2 receptors. Melatonin (200 pmol·crab⁻¹) increased the levels of glucose and lactate in crabs exposed to 6 mgO₂·L⁻¹, and luzindole (200 nmol·crab⁻¹) decreased this effect, indicating that melatonin receptors are involved in hyperglycemia and lactemia. Melatonin showed no effect on VO₂. Interestingly, in vitro incubation of eyestalk ganglia for 45 min at 0.7 mgO₂·L⁻¹ significantly (p < 0.05) increased melatonin production in this organ. In addition, injections of melatonin significantly increased the levels of circulating melatonin in crabs exposed for 45 min to 6 (200 or 20,000 pmol·crab⁻¹), 2 (200 and 20,000 pmol·crab⁻¹) and 0.7 (200 or 20,000 pmol·crab⁻¹) mgO₂·L⁻¹. Therefore, melatonin seems to have an effect on the metabolism of N. granulata. This molecule inhibited the gene expression of CHH and caused an eyestalk- and receptor-dependent hyperglycemia, which suggests that melatonin may have a signaling role in metabolic regulation in this crab.     

Two‐Stage Oxidation of Glucose by an Enzymatic Bioanode

The present study reports the design of a novel bioanode to deeply oxidize glucose in an enzymatic biofuel cell (EFC). This enzymatic glucose cell utilizes three co‐immobilized enzymes: NAD‐dependent glucose dehydrogenase (GDH), NAD(P)⁺‐dependent gluconate‐5‐dehydrogenase (Ga5DH), and diaphorase (DI). Glucose is oxidized to gluconate by NAD‐dependent GDH, gaining two electrons per glucose; the gluconate obtained as a by‐product is oxidized at the C5 carbon to 5‐keto‐gluconate by Ga5DH. Operation of our bioanode enabled the oxidation of glucose in two stages, resulting in the gain of four electrons. The three‐enzyme EFC provides a maximum power density of 10.51 ± 1.72 μW cm^–2, which is about 1.6 times higher than the maximum power density of an EFC using a bioanode based on the co‐immobilization of two enzymes (GDH and DI). Our results hold promise for increasing the current density of EFCs, and for application in glucose biosensor.     

Transport Turnover Rates for Human OCT2 and MATE1 Expressed in Chinese Hamster Ovary Cells

MATE1 (multidrug and toxin extruder 1) and OCT2 (organic cation transporter 2) play critical roles in organic cation excretion by the human kidney. The transporter turnover rate (TOR) is relevant to understanding both their transport mechanisms and interpreting the in vitro–in vivo extrapolation (IVIVE) required for physiologically-based pharmacokinetic (PBPK) modeling. Here, we use a quantitative western blot method to determine TORs for MATE1 and OCT2 proteins expressed in CHO cells. MATE1 and OCT2, each with a C-terminal V-5 epitope tag, were cell surface biotinylated and the amount of cell surface MATE1 and OCT2 protein was quantified by western analysis, using standard curves for the V5 epitope. Cell surface MATE1 and OCT2 protein represented 25% and 24%, respectively, of the total expression of these proteins in CHO cells. The number of cell surface transporters was ~55 fmol cm⁻² for MATE1 and ~510 fmol cm⁻² for OCT2. Dividing these values into the different J_max values for transport of MPP, metformin, and atenolol mediated by MATE1 and OCT2 resulted in calculated TOR values (±SE, n = 4) of 84.0 ± 22.0 s⁻¹ and 2.9 ± 0.6 s⁻¹; metformin, 461.0 ± 121.0 s⁻¹ and 12.6 ± 2.4 s⁻¹; atenolol, 118.0 ± 31.0 s⁻¹, respectively. These values are consistent with the TOR values determined for a variety of exchangers (NHEs), cotransporters (SGLTs, Lac permease), and uniporters (GLUTs, ENTs).     

Amperometric glucose biosensor with high sensitivity based on self-assembled Prussian Blue modified electrode

A glucose biosensor, which was based on self-assembled Prussian Blue (PB) modified electrode with glucose oxidase (GOD) immobilized in cross-linked glutaraldehyde matrix, was developed. Fourier-transform infrared spectroscopy shows that the immobilized GOD retains its native conformation. Cyclic voltammetry was used to examine the electrocatalytic property of the enzyme electrode. The prepared glucose biosensor exhibits fast response (<4 s) and low detection limit of 5 × 10⁻⁶ M. The calculated apparent Michaelis constant K_M was 6.3 ± 1.2 mM, indicating a high affinity between the GOD and glucose. The effects of glutaraldehyde concentration and GOD loading on the sensitivity of the glucose biosensor have also been investigated. Under the optimal conditions, the biosensor shows a high sensitivity of about 80 mA M⁻¹ cm⁻² in a concentration range up to 1 × 10⁻³ M. The relative standard deviation (RSD) for intra-electrode and inter-electrode were 4% and 5%, respectively. In addition, the anti-interferent ability and stability of the biosensor were also discussed.     

Functionalized carbon nanotube-bienzyme biocomposite for amperometric sensing

An approach to design a biocomposite bienzyme biosensor with the aim of evaluating its suitability as an amperometric sensor using functionalized multiwalled carbon nanotubes (MWCNTs) is presented. The biosensor is based on a bienzyme-channelling configuration, employing the enzymes glucose oxidase (GOx) and horseradish peroxidase (HRP), which were immobilized with toluidine blue (TB) functionalized MWCNTs. The proposed method demonstrates an easy electron transfer between the immobilized enzymes and the electrode via functionalized MWCNTs in a Nafion matrix. Co-immobilization of GOx and HRP was employed to establish the feasibility of fabricating highly effective bienzyme-based biosensors for low-level glucose determination. Bienzyme immobilized TB functionalized MWCNTs were attached to a glassy carbon electrode, and the electrochemical behavior of the sensor was studied using electrochemical impedance spectroscopy, cyclic voltammetry and chronoamperometry. The excellent electrocatalytic activity of the biocomposite film resulted in the detection of glucose under reduced over potential with a wider range of determination from 1.5 × 10⁻⁸ M to 1.8 × 10⁻³ M and with a detection limit of 3 × 10⁻⁹ M. The sensor showed a short response time (within 2 s), good stability and anti-interferant ability. The proposed biosensor exhibits good analytical performance in terms of repeatability, reproducibility and shelf-life stability.     

Preparation and Characterization of a Chloroperoxidase-like Catalytic Antibody

The small molecule, meso-tetra(α,α,α,α-o-phenylacetamidophenyl) porphyrin (Mr1147.0) was used as complete antigen to elicit MAb through the immunization and cell fusion techniques. The MAb 1F2 obtained was demonstrated to be very pure by MALDI/TOFMS. The subtype of MAb 1F2 is IgG2a, which has a relative molecular weight of 156,678.8 Da.No significant change in the intensity of absorption peaks in UV and CD spectra was observed over a pH range between 6 and 12. The high stability of the abzyme and the tight binding between Fe porphyrin and antibody were also demonstrated. V_max, K_m, κcat, κcat/K_m for abzyme are 5.18 × 10⁻⁸ Ms⁻¹, 1.50 × 10⁻⁸ M, 0.518 s⁻¹, 3.45 × 10⁷ M⁻¹s⁻¹, respectively. The data obtained indicate that catalytic antibody has high catalytic activity. The chloroperoxidase activity of MAb 1F2-Fe porphyrin complex is stable from 10 °C to 60 °C.     

Nitric Oxide Does Not Inhibit but Is Metabolized by the Cytochrome bcc-aa3 Supercomplex

Nitric oxide (NO) is a well-known active site ligand and inhibitor of respiratory terminal oxidases. Here, we investigated the interaction of NO with a purified chimeric bcc-aa₃ supercomplex composed of Mycobacterium tuberculosis cytochrome bcc and Mycobacterium smegmatis aa₃-type terminal oxidase. Strikingly, we found that the enzyme in turnover with O₂ and reductants is resistant to inhibition by the ligand, being able to metabolize NO at 25 °C with an apparent turnover number as high as ≈303 mol NO (mol enzyme)⁻¹ min⁻¹ at 30 µM NO. The rate of NO consumption proved to be proportional to that of O₂ consumption, with 2.65 ± 0.19 molecules of NO being consumed per O₂ molecule by the mycobacterial bcc-aa₃. The enzyme was found to metabolize the ligand even under anaerobic reducing conditions with a turnover number of 2.8 ± 0.5 mol NO (mol enzyme)⁻¹ min⁻¹ at 25 °C and 8.4 µM NO. These results suggest a protective role of mycobacterial bcc-aa₃ supercomplexes against NO stress.     

Molecular Pathomechanisms of Impaired Flow-Induced Constriction of Cerebral Arteries Following Traumatic Brain Injury: A Potential Impact on Cerebral Autoregulation

(1) Background: Traumatic brain injury (TBI) frequently occurs worldwide, resulting in high morbidity and mortality. Here, we hypothesized that TBI impairs an autoregulatory mechanism, namely the flow-induced constriction of isolated rat middle cerebral arteries (MCAs). (2) Methods: TBI was induced in anaesthetized rats by weight drop model, and then MCAs were isolated and transferred into a pressure-flow chamber. The internal diameter was measured by a video-microscopy. (3) Results: In MCAs from intact rats, increases in flow and pressure + flow elicited constrictions (−26 ± 1.9 µm and −52 ± 2.8 µm, p < 0.05), which were significantly reduced after TBI or in the presence of thromboxane-prostanoid (TP receptor) antagonist SQ 29,548. Flow-induced constrictions were significantly reduced by HET0016, inhibitor of cytochrome P450 4A (CYP450 4A). Arachidonic acid, (AA, 10⁻⁷ M), and CYP-450 4A metabolite 20-hydroxyeicosatetraenoic acid (20-HETE) elicited constrictions of intact MCA (−26 ± 2.3% and −31 ± 3.6%), which were significantly reduced after TBI (to 11 ± 1.3% and −16 ±2.5%). The TP receptor agonist U46619 (10⁻⁷ M) elicited substantial constrictions of MCA from intact rats (−21 ± 3.3%), which were also significantly reduced, after TBI (to −16 ± 2.4%). (4) Conclusions: Flow-induced constrictor response of MCA is impaired by traumatic brain injury, likely due to the reduced ability of cytochrome P450 4A to convert arachidonic acid to constrictor prostaglandins and the mitigated sensitivity of thromboxane-prostanoid receptors.     

Development of a Novel Electrochemical Biosensor Based on Carbon Nanofibers–Cobalt Phthalocyanine–Laccase for the Detection of p-Coumaric Acid in Phytoproducts

The present paper developed a new enzymatic biosensor whose support is a screen-printed electrode based on carbon nanofibers modified with cobalt phthalocyanine and laccase (CNF-CoPc-Lac/SPE) to determine the p-coumaric acid (PCA) content by cyclic voltammetry and square wave voltammetry. Sensor modification was achieved by the casting and cross-linking technique, using glutaraldehyde as a reticulation agent. The biosensor’s response showed the PCA redox processes in a very stable and sensitive manner. The calibration curve was developed for the concentration range of p-coumaric acid of 0.1–202.5 μM, using cyclic voltammetry and chronoamperometry. The biosensor yielded optimal results for the linearity range 0.4–6.4 μM and stood out by low LOD and LOQ values, i.e., 4.83 × 10⁻⁷ M and 1.61 × 10⁻⁶ M, respectively. PCA was successfully determined in three phytoproducts of complex composition. The results obtained by the voltammetric method were compared to the ones obtained by the FTIR method. The amount of p-coumaric acid determined by means of CNF-CoPc-Lac/SPE was close to the one obtained by the standard spectrometric method.     

Continuous glucose monitoring using enzyme-immobilized platinized diamond microfiber electrodes

A sensitive and stable glucose biosensor for in vivo monitoring has been developed using boron-doped diamond microfiber (BDDMF) electrodes. The electrodes were modified with platinum nano-particles to detect H₂O₂, which was enzymatically produced by glucose oxidase (GOx) immobilized on the electrode surface. The platinum-modified BDDMF (Pt-BDDMF) electrodes exhibited much higher sensitivity compared to Pt-microfiber electrodes, Pt electrodes and Pt-modified diamond thin film electrodes. Deposition conditions for Pt nano-particles on the BDDMF electrodes and immobilization of GOx were optimized. GOx/overoxidized polypyrrole (OPPy)/Pt-modified BDDMF electrodes were applied for continuous interference-free glucose monitoring. Amperometric measurements of glucose showed a linear response in the range of 1-70 mM, with an R.S.D. of 3.7% for five injections of 100 μM glucose. The electrodes exhibited good stability over 3 months with no detected anodic current for ascorbic acid (AA), which is an interfering compound.     

Endothelium-Derived Hyperpolarizing Factor (EDHF) Mediates Acetylsalicylic Acid (Aspirin) Vasodilation of Pregnant Rat Mesenteric Arteries

Acetylsalicylic acid (aspirin) exhibits a broad range of activities, including analgesic, antipyretic, and antiplatelet properties. Recent clinical studies also recommend aspirin prophylaxis in women with a high risk of pre-eclampsia, a major complication of pregnancy characterized by hypertension. We investigated the effect of aspirin on mesenteric resistance arteries and found outdiscovered the molecular mechanism underlying this action. Aspirin (10⁻¹²–10⁻⁶ M) was tested on pregnant rat mesenteric resistance arteries by a pressurized arteriography. Aspirin was investigated in the presence of several inhibitors of: (a) nitric oxide synthase (L-NAME 2 × 10⁻⁴ M); (b) cyclooxygenase (Indomethacin, 10⁻⁵ M); (c) Ca²⁺-activated K⁺ channels (Kca): small conductance (SKca, Apamin, 10⁻⁷ M), intermediate conductance (IKca, TRAM34, 10⁻⁵ M), and big conductance (BKca, paxilline, 10⁻⁵ M); and (d) endothelial-derived hyperpolarizing factor (high KCl, 80 mM). Aspirin caused a concentration-dependent vasodilation. Aspirin-vasodilation was abolished by removal of endothelium or by high KCl. Furthermore, preincubation with either apamin plus TRAM-34 or paxillin significantly attenuated aspirin vasodilation (p < 0.05). For the first time, we showed that aspirin induced endothelium-dependent vasodilation in mesenteric resistance arteries through the endothelial-derived hyperpolarizing factor (EDHF) and calcium-activated potassium channels. By activating this molecular mechanism, aspirin may lower peripheral vascular resistance and be beneficial in pregnancies complicated by hypertension.     

Bis-Aniline-Crosslinked Enzyme–Metal Nanoparticle Composites on Electrodes for Bioelectronic Applications

The electrical contacting of redox enzymes with electrodes is the most fundamental requirement for the development of amperometric biosensors and biofuel cell elements. We describe a novel method to prepare electrically contacted metallic nanoparticles (NPs) or carbon nanotubes (CNTs)/enzyme hybrid composites on electrodes that act as amperometric biosensors or as the constituents of biofuel cells. Au NPs or Pt NPs were modified with thioaniline electropolymerizable groups, and so were the enzymes glucose oxidase (GOx) or bilirubin oxidase (BOD). Electrochemical polymerization of the thioaniline-functionalized Pt NPs and GOx on a thioaniline monolayer-modified Au surface led to the formation of a bis-aniline-bridged Pt NPs/GOx composite electrode that enabled the analysis of glucose through the electrocatalyzed reduction of H₂O₂. Similarly, a Pt NPs/BOD composite-functionalized electrode showed electrocatalytic activity toward the reduction of O₂ to H₂O. Also, a Au NPs/GOx composite-functionalized electrode revealed direct electrical contacting between the enzyme and the electrode through the electrocatalytic reduction of the bis-aniline bridges, and this enabled the bioelectrocatalytic oxidation and the amperometric sensing of glucose. Finally, a biofuel cell consisting of an anode modified with Nile blue/NAD⁺/alcohol dehydrogenase on carbon nanotubes, and a cathode composed of the bis-aniline-crosslinked Pt NPs/BOD composite was constructed. The biofuel cell operates with a power output corresponding to 200 μW cm^-2.     

An ultrasensitive electrochemical biosensor for glucose using CdTe-CdS core–shell quantum dot as ultrafast electron transfer relay between graphene-gold nanocomposite and gold nanoparticle

The paper reported an ultrasensitive electrochemical biosensor for glucose which was based on CdTe-CdS core–shell quantum dot as ultrafast electron transfer relay between graphene-gold nanocomposite and gold nanoparticle. Since efficient electron transfer between glucose oxidase and the electrode was achieved, the biosensor showed high sensitivity (5762.8 nA nM⁻¹ cm⁻²), low detection limit (S/N = 3) (3 × 10⁻¹² M), fast response time (0.045 s), wide calibration range (from 1 × 10⁻¹¹ M to 1 × 10⁻⁸ M) and good long-term stability (26 weeks). The apparent Michaelis–Menten constant of the glucose oxidase on the medium, 5.24 × 10⁻⁶ mM, indicates excellent bioelectrocatalytic activity of the immobilized enzyme towards glucose oxidation. Moreover, the effects of omitting graphene-gold nanocomposite, CdTe-CdS core–shell quantum dot and gold nanoparticle were also investigated. The result showed sensitivity of the biosensor is 7.67-fold better if graphene-gold nanocomposite, CdTe-CdS core–shell quantum dot and gold nanoparticle are used. This could be ascribed to improvement of the conductivity between graphene nanosheets due to introduction of gold nanoparticles, ultrafast charge transfer from CdTe-CdS core–shell quantum dot to graphene nanosheets and gold nanoparticle due to unique electrochemical properties of the CdTe-CdS core–shell quantum dot and good biocompatibility of gold nanoparticle for glucose oxidase. The biosensor is of best sensitivity in all glucose biosensors based on graphene nanomaterials up to now and has been satisfactorily applied to determination of the glucose in human saliva samples.     

A conducting polymer/ferritin anode for biofuel cell applications

An enzyme anode for use in biofuel cells (BFCs) was constructed using an electrically connected bilayer based on a glassy carbon (GC) electrode immobilized with the conducting polymer polypyrrole (Ppy) as electron transfer enhancer, and with horse spleen ferritin protein (Frt) as electron transfer mediator. The surface-coupled redox system of nicotinamide adenine dinucleotide (NADH) catalyzed with diaphorase (Di) was used for the regeneration of NAD⁺ in the inner layer and the NAD⁺-dependent enzyme catalyst glucose dehydrogenase (GDH) in the outer layer. The outer layer of the GC-Ppy-Frt-Di-NADH-GDH electrode effectively catalyzes the oxidation of glucose biofuel continuously; using the NAD⁺ generated at the inner layer of the Di-catalyzed NADH redox system mediated by Frt and Ppy provides electrical communication with enhancement in electron transport. The electrochemical characteristics of the electrodes were investigated by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). This anode provides a current density of 1.2 mA cm⁻² in a 45 mM glucose solution and offers a good possibility for application in biofuel cells.     

Electrochemical detection of avian influenza virus H5N1 gene sequence using a DNA aptamer immobilized onto a hybrid nanomaterial-modified electrode

A sensitive electrochemical method for the detection of avian influenza virus (AIV) H5N1 gene sequence using a DNA aptamer immobilized onto a hybrid nanomaterial-modified electrode was developed. To enhance the selectivity and sensitivity, the modified electrode was assembled with multi-wall carbon nanotubes (MWNT), polypyrrole nanowires (PPNWs) and gold nanoparticles (GNPs). This electrode offered a porous structure with a large effective surface area, highly electrocatalytic activities and electronic conductivity. Therefore, the amount of DNA aptamer immobilized onto the electrode was increased while the accessibility of the detection target was maintained. The biosensor is based on the hybridization and preferred orientation of a DNA aptamer immobilized onto a modified electrode surface with its target (H5N1 specific sequence) present in solution. It is selective for the H5N1 specific sequence, and the signal of the indicator was approximately linear to log(concentration) of the H5N1 specific sequence from 5.0 × 10⁻¹² to 1.0 × 10⁻⁹ M (R = 0.9863) with a detection limit of 4.3 × 10⁻¹³ M. These studies showed that the new hybrid nanomaterial (MWNT/PPNWs/GNPs) and the DNA aptamer could be used to fabricate an electrochemical biosensor for gene sequence detection. Furthermore, this design strategy is expected to have extensive applications in other biosensors.