Meldola blue immobilized on a new SiO2/TiO2/graphite composite for electrocatalytic oxidation of NADH

SiO2/Al2O3/C grafted 3-n propylpyridinium silsesquioxane chloride-based non-enzymatic electrochemical sensor for determination of carcinogenic nitrite in food products

The excessive uptake of nitrite is perilous and detrimental for human health that prone to cancer disease. Herein, described the synthesis of SiO₂/Al₂O₃/C material through the sol-gel procedure followed by grafting with 3-n propylpyridinium silsesquioxane chloride organic ligand for enhancing electrochemical activity. H-NMR, ¹³C NMR, and ²⁹Si studies were performed for confirmation of surface functionalization through the grafting technique. The surface morphology was evaluated through SEM and TEM techniques. The material showed an irregular and flakes-like structure that exhibited more compactness and conglomerate structure with no segregation in phase was observed after grafting. The elemental composition was confirmed from EDX analysis. The electrochemical measurements were performed with cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and chronoamperometry. The prepared hybrid inorganic-organic composite Si/C/Al/SiPy⁺Cl^- was applied for the modification of the glassy carbon (GC) electrode and assessed as a sensor for nitrite determination. The sensor showed the low limit of detection (0.01 μM), low limit of quantification (0.08 μM), wide linear response range (0.2-280 μM), and high sensitivity (410 μA·μM^-1). It gave a quick response time of <1 s in the presence of 70 μM nitrite. The fabricated sensor showed high sensitivity, chemical stability, and insignificant interference from co-existing species present in sausage meat and food industry discharges. The repeatability of the sensor was evaluated as 2.5 % R.S.D.; for n = 10 at 50 μM nitrite.

Bioengineered Polymer/Composites as Advanced Biological Detection of Sorbitol: An Application in Healthcare Sector

Bioengineered polymers and nanomaterials have emerged as promising and advanced materials for the fabrication and development of novel biosensors. Nanotechnology-enabled biosensor methods have high sensitivity, selectivity and more rapid detection of an analyte. Biosensor based methods are more rapid and simple with higher sensitivity and selectivity and can be developed for point-of-care diagnostic testing. Development of a simple, sensitive and rapid method for sorbitol detection is of considerable significance to efficient monitoring of diabetes-associated disorders like cataract, neuropathy, and nephropathy at initial stages. This issue encourages us to write a review that highlights recent advancements in the field of sorbitol detection as no such reports have been published till the date. The first section of this review will be dedicated to the conventional approaches or methods that had been playing a role in detection. The second part focused on the emerging field i.e. biosensors with optical, electrochemical, piezoelectric, etc. approaches for sorbitol detection and the importance of its detection in healthcare application. It is expected that this review will be very helpful for readers to know the different conventional and recent detection techniques for sorbitol at a glance.

Thermal Stability and Flame Retardancy of a Cured Trifunctional Epoxy Resin with the Synergistic Effects of Silicon/Titanium

An amino curing agent containing silicon/titanium flame-retardant elements (STCA) based on (3-aminopropyl)triethoxysilane (APTES) and tetrabutyl titanate was successfully prepared. The thermal decomposition and flame-retardant properties of a STCA-cured trifunctional epoxy resin, which was facilely synthesized by 1,1,1-tris(4-hydroxyphenyl)ethane and epichlorohydrin via a two-step method, were compared with those of another amino curing agent containing silicon (SCA) based on APTES and methyltrimethoxysilane. The structures of STCA and SCA were characterized by Fourier transform infrared (FT-IR), ²⁹Si NMR, and Raman spectroscopies. The STCA-cured thermoset not only had good thermal stability with an initial decomposition temperature of 344.8 °C and a char yield of 52.7% at 800 °C but also exhibited the overall improvement of flame-retardant properties. V-0 rating was achieved using the UL-94 test, and the value of limiting oxygen index reached 33.8%. From the thermogravimetry-infrared test, the yield of pyrolysis products of the STCA-cured thermoset was significantly decreased, indicating the lower toxicity in contrast to the SCA-cured thermoset. Flame-retardant performances were also investigated using the cone calorimetry test, and the flame retardancy mechanism was studied using scanning electron microscopy, FT-IR, and energy-dispersive spectrometry. The results indicate that the introduction of silicon/titanium to the system reveals the synergistic effects to promote the formation of an intumescent, sufficient, and compact char layer during combustion, which could effectively prevent heat, oxygen, and flame from penetrating into the interior structure, and lead to the retardance of further combustion.

Scanning electrochemical microscopy imaging of poly (3,4-ethylendioxythiophene)/thionine electrodes for lactate detection via NADH electrocatalysis

Herein we report the use of scanning electrochemical microscopy (SECM) together with electrochemical and spectroscopic techniques to develop and characterise a stable and uniformly reactive chemically modified platinum electrode for NADH electrocatalysis. In order to achieve this, a range of different approaches for thionine entrapment within an electropolymerised poly (3,4-ethylendioxythiophene) (PEDOT) film were evaluated using SECM imaging in the presence of NADH, demonstrating the uniformity of the reactive layer towards NADH oxidation. The effect of electrolyte type and time scale employed during PEDOT electropolymerisation was examined with respect to thionine loading and the resulting charge transport diffusion coefficient (D_CT) estimated via chronoamperometry. These studies indicated a decrease in D_CT as thionine loading increased within the PEDOT film, suggesting that charge transport was diffusion limited within the film. Additionally, thionine functionalised nanotubes were formed, providing a stable support for lactate dehydrogenase entrapment while lowering the rate of thionine leaching, determined via SECM imaging. This enabled lactate determination at E_app = 0.0 V vs Ag/AgCl over the range 0.25-5 mM in the presence of 1 mM NAD⁺.

Facile fabrication of FeN nanoparticles/nitrogen-doped graphene core-shell hybrid and its use as a platform for NADH detection in human blood serum

Herein, we present a novel strategy for the synthesis of an iron nitride nanoparticles-encapsulated nitrogen-doped graphene (FeN NPs/NG) core-shell hierarchical nanostructure to boost the electrochemical performance in a highly sensitive, selective, reproducible, and stable sensing platform for nicotinamide adenine dinucleotide (NADH). This core-shell hierarchical nanostructure provides an excellent conductive network for effective charge transfer and avoids the agglomeration and restacking of NG sheets, which provides better access to the electrode material for NADH oxidation. The FeN NPs/NG core-shell hierarchical nanostructure demonstrates direct and mediatorless responses to NADH oxidation at a low potential. This material displays a high sensitivity of 0.028μA/μMcm(2), a wide linear range from 0.4 to 718μM, and a detection limit of 25nM with a fast response time of less than 3s. The interferences from common interferents, such as glucose, uric acid, dopamine, and ascorbic acid, are negligible. The fabricated sensor was further tested for the determination of NADH in human blood serum. The resulting high sensitivity, excellent selectivity, outstanding stability, and good reproducibility make the proposed FeN NPs/NG core-shell hierarchical nanostructure as a promising candidate for biomedical applications.

Mediatorless N(2) incorporated diamond nanowire electrode for selective detection of NADH at stable low oxidation potential

The electrocatalytic properties of a N2 incorporated diamond nanowire (N-DNW) unmodified electrode towards the oxidation of nicotinamide adenine dinucleotide (NADH) was critically evaluated. The electrochemical behavior of the N-DNW unmodified electrode was examined and compared with that of boron-doped diamond, glassy carbon electrode, and graphite electrodes. The N-DNW electrode had high selectivity and high sensitivity for the differential pulse voltammetric detection of NADH in the presence of ascorbic acid at the lower and stable oxidation potential. Moreover, it exhibited strong stability after prolonged usage. The oxidation peak potential at the N-DNW electrode remained unchanged even after exposure to the solution, followed by washing, drying, and storage in laboratory air for 20 days, with minimization of surface contamination. Therefore, the N-DNW unmodified electrode shows promise for the detection of NADH and is attractive for use in a dehydrogenase based biosensor and other analytical applications.

Electrocatalytic oxidation of NADH at electrogenerated NAD+ oxidation product immobilized onto multiwalled carbon nanotubes/ionic liquid nanocomposite: application to ethanol biosensing

The multiwalled carbon nanotubes/N-butyl-N-methyl-pyrolydinium-bis(trifluoromethylsulfonyl)imide [C(4)mpyr][NTf(2)] ionic liquid (MWCNTs/IL) modified glassy carbon (GC) electrode has been utilized as a platform to immobilize electrogenerated NAD(+) oxidation products (Ox-P(NAD(+))). During potential cycling, the adenine moiety of NAD(+) molecule is oxidized and gives rise to generation of a redox active system that shows great electrocatalytic activity toward NADH oxidation. The cyclic voltammetric results indicated the ability of MWCNTs/IL/Ox-P(NAD(+)) modified GC electrode to catalyze the oxidation of NADH at a very low potential (0.05 V vs. Ag/AgCl) and subsequently, a substantial decrease in the overpotential by about 600 mV compared with the bare GC electrode. This modified electrode thus allowed highly sensitive amperometric detection of NADH with a very low limit of detection (2 × 10(-8) mol L(-1)), low applied potential (+0.05 V) at concentration range up to 4.2 × 10(-5) mol L(-1) and minimum of surface fouling. High ability of MWCNTs/IL/Ox-P(NAD(+)) to promote electron transfer between NADH and the electrode suggested a new promising biocompatible platform for development of dehydrogenase-based amperometric biosensors. With alcohol dehydrogenase (ADH) as a model enzyme, ethanol sensing ability of the proposed system was examined. The amperometric response of the biosensor increased linearly with increasing ethanol concentration in two concentration ranges, 5 × 10(-6)-6 × 10(-5) and 6 × 10(-5)-9 × 10(-4) mol L(-1) with detection limit of 5 × 10(-7) mol L(-1) and rapid response of 10s. Furthermore, the interference effects of redox active species, such as ascorbic acid, uric acid, glucose and acetaminophen for the proposed biosensor are negligible. Finally, the ability of the proposed biosensor for detection of ethanol in real complex samples was successfully demonstrated.

Low potential detection of NADH based on Fe₃O₄ nanoparticles/multiwalled carbon nanotubes composite: fabrication of integrated dehydrogenase-based lactate biosensor

Fe(3)O(4) magnetic nanoparticles were in situ loaded on the surface of multiwalled carbon nanotubes (MWCNTs) by a simple coprecipitation procedure. The resulting Fe(3)O(4)/MWCNTs nanocomposite brings new capabilities for electrochemical sensing by combining the advantages of Fe(3)O(4) magnetic nanoparticles and MWCNTs. It was found that Fe(3)O(4) has redox properties similar to those of frequently used mediators used for electron transfer between NADH and electrode. The cyclic voltammetric results indicated the ability of Fe(3)O(4)/MWCNTs modified GC electrode to catalyze the oxidation of NADH at a very low potential (0.0 mV vs. Ag/AgCl) and subsequently, a substantial decrease in the overpotential by about 650 mV compared with the bare GC electrode. The catalytic oxidation current allows the stable and selective amperometric detection of NADH at an applied potential of 0.0 mV (Ag/AgCl) with a detection limit of 0.3 μM and linear response up to 300 μM. This modified electrode can be used as an efficient transducer in the design of biosensors based on coupled dehydrogenase enzymes. Lactate dehydrogenase (LDH) and NAD(+) were subsequently immobilized onto the Fe(3)O(4)/MWCNTs nanocomposite film by covalent bond formation between the amine groups of enzyme or NAD(+) and the carboxylic acid groups of the Fe(3)O(4)/MWCNT film. Differential pulse voltammetric detection of lactate on Fe(3)O(4)/MWCNT/LDH/NAD(+) modified GC electrode gives linear responses over the concentration range of 50-500 μM with the detection limit of 5 μM and sensitivity of 7.67 μA mM(-1). Furthermore, the applicability of the sensor for the analysis of lactate concentration in human serum samples has been successfully demonstrated.

Meldola’s Blue — doped titania sol-gel sensor for NADH determination

Titania layers obtained by a sol-gel technique doped with redox mediator, Meldola’s Blue, were employed for construction of a new NADH senor. Optimization of preparation process as well as experimental conditions affecting the response of the sensor were examined. Under optimal conditions NADH could be determined in the wide linear range from 90 to 2300 µM with detection limit 12 µM and a high sensitivity 12.5 nA µM−1. The usefulness of developed sensor was preliminarily checked in determination of NADH forming during enzymatic oxidation of ethanol catalyzed by alcohol dehydrogenase (ADH).

SiO2/SnO2/Sb2O5 microporous ceramic material for immobilization of Meldola's blue: application as an electrochemical sensor for NADH

The mixed oxide SiO(2)/SnO(2), containing 25 wt% of SnO(2), determined by X-ray fluorescence, was prepared by the sol-gel method and the porous matrix obtained was then grafted with Sb (V), resulting the solid designated as (SiSnSb). XPS indicated 0.7% of Sb atoms on the surface. Sb grafted on the surface contains Brønsted acid centers (SbOH groups) that can immobilize Meldola's blue (MB(+)) cationic dye onto the surface by an ion exchange reaction, resulting the solid designated as (SiSnSb/MB). In the present case a surface concentration of MB(+)=2.5×10(-11) mol cm(2) on the surface was obtained. A homogeneous mixture of the SiSnSb/MB with ultra pure graphite (99.99%) was pressed in disk format and used to fabricate a working electrode that displayed an excellent specific electrocatalytic response to NADH oxidation, with a formal potential of -0.05 V at pH 7.3. The electrochemical properties of the resulting electrode were investigated thoroughly with cyclic voltammetric and chronoamperometry techniques. The proposed sensor showed a good linear response range for NADH concentrations between 8×10(-5) and 9.0×10(-4) mol L(-1), with a detection limit of 1.5×10(-7) mol L(-1). The presence of dopamine and ascorbic acid did not show any interference in the detection of NADH on this modified electrode surface.

Recent advances in NADH electrochemical sensing design

NADH electrochemical sensor development has been one of the most studied areas of bioelectroanalysis because of the ubiquity of NAD(P)H based enzymatic reactions in nature. The different solutions proposed are still far from the realisation of the "ideal" NADH sensor and the research area is still challenging. The principles and the recent approaches in NADH electrochemical sensing design are reported in this review. An overview of selected examples and novel sensor materials for the electrocatalysis of NADH is given with emphasis on the appropriate design to obtain improved performances. The literature data taken in consideration has been grouped depending on the strategy used in: surface modified electrodes for NADH sensing, surface redox mediated NADH probes, and bulk modified electrodes for the electrocatalytic oxidation of NADH. A list of already reported dehydrogenase-based biosensors is also given.