Low potential detection of glucose at carbon nanotube modified glassy carbon electrode with electropolymerized poly(toluidine blue O) film

Amperometric determination of heavy metal using an HRP inhibition biosensor based on ITO nanoparticles-ruthenium (III) hexamine trichloride composite: Central composite design optimization

A novel horseradish peroxidase (HRP) enzyme inhibition biosensor based on indium tin oxide (ITO) nanoparticles, hexaammineruthenium (III) chloride (RUT), and chitosan (CH) modified glassy carbon electrode (GCE) was developed. The biosensor fabrication process was investigated using scanning electron microscopy, energy-dispersive X-ray spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. The amounts of ITO nanoparticles and RUT were optimized using a 2² central composite design for the optimization of electrode composition. The detection limits were determined as 8 nM, 3 nM, and 1 nM for Pb²⁺, Ni²⁺, and Cd²⁺, respectively. The inhibition calibration curves of the biosensor were found to be within the range of 0.009-0.301 µM with a sensitivity of 11.97 µA µM^-1 cm^-2 (0.85 µA µM^-1) for Pb²⁺, 0.011-0.368 µM with a sensitivity of 10.84 µA µM^-1 cm^-2 (0.77 µA µM^-1) for Ni²⁺, and 0.008-0.372 µM with a sensitivity of 10.99 µA µM^-1 cm^-2 (0.78 µA µM^-1) for Cd²⁺. The type of HRP inhibition by Pb²⁺, Ni²⁺ and Cd²⁺ was investigated by the Dixon and Cornish-Bowden plots. The effects of possible interfering species on the biosensor response were examined. The analysis of Pb²⁺, Ni²⁺, and Cd²⁺ in tap water was demonstrated using the HRP/ITO-RUT-CH/GCE with satisfactory experimental results. The proposed method agreed with the atomic absorption spectrometry results.

Ultrasensitive Label-free Electrochemical Immunosensor based on Multifunctionalized Graphene Nanocomposites for the Detection of Alpha Fetoprotein

In this work, a novel label-free electrochemical immunosensor was developed for the quantitative detection of alpha fetoprotein (AFP). Multifunctionalized graphene nanocomposites (TB-Au-Fe₃O₄-rGO) were applied to modify the electrode to achieve the amplification of electrochemical signal. TB-Au-Fe₃O₄-rGO includes the advantages of graphene, ferroferric oxide nanoparticles (Fe₃O₄ NPs), gold nanoparticles (Au NPs) and toluidine blue (TB). As a kind of redox probe, TB can produce the electrochemical signal. Graphene owns large specific surface area, high electrical conductivity and good adsorption property to load a large number of TB. Fe₃O₄ NPs have good electrocatalytic performance towards the redox of TB. Au NPs have good biocompatibility to capture the antibodies. Due to the good electrochemical performance of TB-Au-Fe₃O₄-rGO, the effective and sensitive detection of AFP was achieved by the designed electrochemical immunosensor. Under optimal conditions, the designed immunosensor exhibited a wide linear range from 1.0 × 10⁻⁵ ng/mL to 10.0 ng/mL with a low detection limit of 2.7 fg/mL for AFP. It also displayed good electrochemical performance including good reproducibility, selectivity and stability, which would provide potential applications in the clinical diagnosis of other tumor markers.

Electrochemical sensors and biosensors based on redox polymer/carbon nanotube modified electrodes: a review

The aim of this review is to present the contributions to the development of electrochemical sensors and biosensors based on polyphenazine or polytriphenylmethane redox polymers together with carbon nanotubes (CNT) during recent years. Phenazine polymers have been widely used in analytical applications due to their inherent charge transport properties and electrocatalytic effects. At the same time, since the first report on a CNT-based sensor, their application in the electroanalytical chemistry field has demonstrated that the unique structure and properties of CNT are ideal for the design of electrochemical (bio)sensors. We describe here that the specific combination of phenazine/triphenylmethane polymers with CNT leads to an improved performance of the resulting sensing devices, because of their complementary electrical, electrochemical and mechanical properties, and also due to synergistic effects. The preparation of polymer/CNT modified electrodes will be presented together with their electrochemical and surface characterization, with emphasis on the contribution of each component on the overall properties of the modified electrodes. Their importance in analytical chemistry is demonstrated by the numerous applications based on polymer/CNT-driven electrocatalytic effects, and their analytical performance as (bio) sensors is discussed.

Poly(brilliant green) and poly(thionine) modified carbon nanotube coated carbon film electrodes for glucose and uric acid biosensors

Poly(brilliant green) (PBG) and poly(thionine) (PTH) films have been formed on carbon film electrodes (CFEs) modified with carbon nanotubes (CNT) by electropolymerisation using potential cycling. Voltammetric and electrochemical impedance characterisation were performed. Glucose oxidase and uricase, as model enzymes, were immobilised on top of PBG/CNT/CFE and PTH/CNT/CFE for glucose and uric acid (UA) biosensing. Amperometric determination of glucose and UA was carried out in phosphate buffer pH 7.0 at -0.20 and +0.30 V vs. SCE, respectively, and the results were compared with other similarly modified electrodes existing in the literature. An interference study and recovery measurements in natural samples were successfully performed, indicating these architectures to be good and promising biosensor platforms.

Facile preparation of carbon nanotube-conducting polymer network for sensitive electrochemical immunoassay of Hepatitis B surface antigen in serum

A novel electrochemical immunosensor built on three dimensional carbon nanotube-conducting polymer (CNT-CP) network is reported for detection of Hepatitis B surface antigen (HBsAg) in human serum. The CNT-CP network is prepared by drop-drying of CNT solution on glassy carbon electrode, followed by electrochemical polymerization of poly (pyrrole propionic acid) (pPPA) film to crosslink and stabilize the CNTs, wherein the CNTs form the backbone of the network, and offer great specific surface areas for antibody attachment, and confer good conductivity for electrochemical detection, while the conducting film integrates the carbon nanotubes into a stable network due to its self-limiting growth behavior and provides abundant carboxyl groups for covalent immobilization of probe proteins. As a unique matrix, the CNT-CP network enables sensitive electrochemical detection of HBsAg biomarker by using alkaline phosphatase (ALP)-conjugated secondary antibodies under sandwich format coupling with the ALP substrate solution, p-aminophenyl phosphate (PAPP), reaching a detection limit of 0.01ng/mL with a dynamic range of 5 orders of magnitude.

Stabilization role of a phenothiazine derivative on the electrocatalytic oxidation of hydrogen via Aquifex aeolicus hydrogenase at graphite membrane electrodes

The [NiFe] membrane-bound hydrogenase from the microaerophilic, hyperthermophilic Aquifex aeolicus bacterium (Aa Hase) presents oxygen, carbon monoxide, and temperature resistances. Since it oxidizes hydrogen with high turnover, this enzyme is thus of particular interest for biotechnological applications, such as biofuel cells. Efficient immobilization of the enzyme onto electrodes is however a mandatory step. To gain further insight into the parameters governing the interfacial electron process, cyclic voltammetry was performed combining the use of a phenothiazine dye with a membrane electrode design where the enzyme is entrapped in a thin layer. In the absence of the phenothiazine dye, direct electron transfer (DET) for H(2) oxidation is observed due to Aa Hase adsorbed onto the PG electrode. An unexpected loss of the catalytic current with time is however observed. The effect of toluidine blue O (TBO) on the catalytic process is first studied with TBO in solution. In addition to the expected mediated electron transfer process (MET), TBO is demonstrated to reconnect directly some Aa Hase molecules possibly released from the electrode but still entrapped in the thin layer. On adsorbed TBO the two same processes occur demonstrating the ability of the TBO film to connect Aa Hase via a DET process. Loss of activity is however observed due to the poor stability of adsorbed TBO at high temperatures. Aa Hase immobilization is then studied on electropolymerized TBO (pTBO). The effect of film thickness, temperature, presence of inhibitors and pH is evaluated. Given a film thickness less than 20 nm, H(2) oxidation proceeds via a mixed DET/MET process through the pTBO film. A high and very stable H(2) oxidation activity is reached, showing the potential applicability of the bioelectrode for biotechnologies. Finally, the multifunctional roles of TBO-based matrix are underlined, including redox mediator, Aa Hase anchor, but also buffering and ROS scavenger capabilities to drive pH local changes and avoid oxidative damage.

Advances in carbon nanotube based electrochemical sensors for bioanalytical applications

Electrochemical (EC) sensing approaches have exploited the use of carbon nanotubes (CNTs) as electrode materials owing to their unique structures and properties to provide strong electrocatalytic activity with minimal surface fouling. Nanofabrication and device integration technologies have emerged along with significant advances in the synthesis, purification, conjugation and biofunctionalization of CNTs. Such combined efforts have contributed towards the rapid development of CNT-based sensors for a plethora of important analytes with improved detection sensitivity and selectivity. The use of CNTs opens an opportunity for the direct electron transfer between the enzyme and the active electrode area. Of particular interest are also excellent electrocatalytic activities of CNTs on the redox reaction of hydrogen peroxide and nicotinamide adenine dinucleotide, two major by-products of enzymatic reactions. This excellent electrocatalysis holds a promising future for the simple design and implementation of on-site biosensors for oxidases and dehydrogenases with enhanced selectivity. To date, the use of an anti-interference layer or an artificial electron mediator is critically needed to circumvent unwanted endogenous electroactive species. Such interfering species are effectively suppressed by using CNT based electrodes since the oxidation of NADH, thiols, hydrogen peroxide, etc. by CNTs can be performed at low potentials. Nevertheless, the major future challenges for the development of CNT-EC sensors include miniaturization, optimization and simplification of the procedure for fabricating CNT based electrodes with minimal non-specific binding, high sensitivity and rapid response followed by their extensive validation using "real world" samples. A high resistance to electrode fouling and selectivity are the two key pending issues for the application of CNT-based biosensors in clinical chemistry, food quality and control, waste water treatment and bioprocessing.

Review: Carbon nanotube based electrochemical sensors for biomolecules

Carbon nanotubes (CNTs) have been incorporated in electrochemical sensors to decrease overpotential and improve sensitivity. In this review, we focus on recent literature that describes how CNT-based electrochemical sensors are being developed to detect neurotransmitters, proteins, small molecules such as glucose, and DNA. Different types of electrochemical methods are used in these sensors including direct electrochemical detection with amperometry or voltammetry, indirect detection of an oxidation product using enzyme sensors, and detection of conductivity changes using CNT-field effect transistors (FETs). Future challenges for the field include miniaturizing sensors, developing methods to use only a specific nanotube allotrope, and simplifying manufacturing.