Determination Of NADH Research Articles

Selective Determination of Nicotinamide Adenine Dinucleotide (NADH) on Screen-Printed Polyethylene Terephthalate (PET) Electrodes Modified with a Reduced Graphene Oxide (rGO), Gold Nanoparticle (AuNP), and Poly-Methylene Blue Nanocomposite

The present work reports the development of a disposable nanocomposite-based amperometric sensor for reduced nicotinamide adenine dinucleotide (NADH). To fabricate disposable electrodes, conductive carbon and silver ink were screen-printed on a polyethylene terephthalate (PET) film substrate. The surface of the working electrode was modified with gold nanoparticles (AuNPs) decorated reduced graphene oxide (rGO) and subsequently electro-polymerized with methylene blue for the determination of NADH. The nanocomposite modified electrode decreases the potential for NADH oxidation with a significant increase in the current due to the synergy between AuNP and rGO. The developed electrochemical sensor determined NADH at 0 V versus pseudo-Ag/AgCl with linear relationships from 25 µmol L−1 to 1.0 mmol L−1 and 1.0 mmol L−1 to 10 mmol L−1. The sensor exhibits a good sensitivity of 35.49 µA/mmol L−1/cm2 and a detection limit of 6.61 µmol L−1 based upon a signal-to-noise ratio of 3. Furthermore, interferences from electroactive substances such as ascorbic acid and uric acid are eliminated at an oxidation potential of 0 V. Thus, the modified electrode provides a simple, selective, disposable, and low-cost approach for the amperometric determination of NADH.

Non-enzymatic biosensor based on F,S-doped carbon dots/copper nanoarchitecture applied in the simultaneous electrochemical determination of NADH, dopamine, and uric acid in plasma.

This work presents the synthesis and characterization of an innovative F,S-doped carbon dots/CuONPs hybrid nanostructure obtained by a direct mixture between F,S-doped carbon dots obtained electrochemically and copper nitrate alcoholic solution. The hybrid nanostructures synthesized were characterized by absorption spectroscopy in the Ultraviolet region (UV-vis), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and different electrochemical techniques. The fluoride and sulfur-doped carbon dots/CuONPs nanostructures were used to prepare a non-enzymatic biosensor on a printed carbon electrode, exhibiting excellent electrocatalytic activity for the simultaneous determination of NADH, dopamine, and uric acid in the presence of ascorbic acid with a detection limit of 20, 80, and 400 nmol L-1, respectively. The non-enzymatic biosensors were also used to determine NADH, dopamine, and uric acid in plasma, and they did not suffer significant interference from each other.

A novel "on-off" SERS nanoprobe based on sulfonated cellulose nanofiber-Ag composite for selective determination of NADH in human serum.

A novel S-CNF-based nanocomposite was created using sulfonated cellulose nanofiber (S-CNF) to enable the detection of NADH in serum by surface-enhanced Raman spectroscopy (SERS). The numerous hydroxyl and sulfonic acid groups on the S-CNF surface absorbed silver ions and converted them to silver seeds, which formed the load fulcrum. After adding a reducing agent, silver nanoparticles (Ag NPs) were firmly adhered to the S-CNF surface to form stable 1D "hot spots." The S-CNF-Ag NP substrate demonstrated outstanding SERS performance, including good uniformity with an RSD of 6.88% and an enhancement factor (EF) of 1.23 × 107. Owing to the anionic charge repulsion effect, the S-CNF-Ag NP substrate still maintains remarkable dispersion stability after 12months of preservation. Finally, S-CNF-Ag NPs' surface was modified with 4-mercaptophenol (4-MP), a special redox Raman signal molecule, to detect reduced nicotinamide adenine dinucleotide (NADH). The results showed that the detection limit (LOD) of NADH was 0.75μM; a good linear relationship (R2 = 0.993) was establishedin the concentration range 10-6 - 10-2M. The SERS nanoprobe enabled rapid detection of NADH in human serum without any complicated sample pretreatment and provides a new potential to detect biomarkers.

A novel approach for ultrasensitive amperometric determination of NADH via graphene-based electrode obtained by electrochemical intercalation of tetraalkylammonium ions

A novel approach for ultrasensitive amperometric determination of NADH via graphene-based electrode obtained by electrochemical intercalation of tetraalkylammonium ions

Electrochemical characterization of nitrocoumarin-modified nanostructured electrode platforms: New precursors for the electrocatalysis of NADH

All synthesized nitrocoumarins, 3-acetyl-6-nitrocoumarin 6-Coum, 3-(3-nitrocinnamoyl)-coumarin 3-CinCoum, 3-(4-nitrocinnamoyl)-coumarin 4-CinCoum, and 3-(4-nitrocinnamoyl)-6-nitrocoumarin 4-Cin-6-Coum, were used to generate novel nanostructured multiwalled carbon nanotube (MWCNT) electrode platforms that were electrochemically activatable to generate the redox pair ArNHOH/ArNO. This redox pair is capable of acting as a mediator in electrocatalysis of NADH oxidation.Nitrocoumarin-modified nanostructured electrode platforms were prepared using both drop casting and buckypaper (BP) methods for comparative purposes, and they showed no differences in their electrochemical responses.It was observed that the compound most easily reduced was 4-Cin-6-Coum. The reduction occurred first at the 4-nitrocinnamoyl group due to the withdrawing electron effect exerted by the cinnamoyl carbonyl group.The heterogeneous transfer rate constant, kh, was calculated for all of the redox mediators, and they decreased in the order 4-CinCoum> 3-CinCoum> 6-Coum> 4-Cin-6-Coum (II). On the other hand, we observed no significant differences for retention of the redox pairs ArNHOH/ArNO from the nitrocoumarin precursor compounds on the electrode, and the retention values ranged from 79.6 to 91.6% after one hour of working with the nanostructured electrodes.With this electrocatalytic response, it is possible to develop an amperometric sensor for the determination of NADH that includes nanostructured platforms with nitrocoumarins. We obtained LODs of 2.95 µM and 3.43 µM for 6-Coum and 4-Cin-6-Coum (II), respectively.

MAL31, a sugar transporter involved in pullulan biosynthesis in Aureobasidium pullulans

To investigate the role of the sugar transporter MAL31 on pullulan biosynthesis, the coding gene mal31 was respectively disrupted and overexpressed in the parental strain A. pullulans CCTCC M 2012259 to construct mutants of A. pullulans Δmal31 and A. pullulans Mal31. Batch pullulan production significantly decreased by 69.1 % in A. pullulans Δmal31 but increased by 15.9 % in A. pullulans Mal31, as compared to the parental strain. We performed kinetics analysis, assays of key enzymes, determination of intracellular UDPG, NADH, and ATP contents, and measurement of transcriptional levels of genes associated with pullulan biosynthesis and excretion. The results confirmed that the mal31 disruption decreased the glucose consumption rate, decreased the formation rate and titer of pullulan, but increased the intracellular UDPG supply for β-glucan accumulation. In contrast, the mal31 overexpression increased the transcriptional levels of genes associated with pullulan biosynthesis, and accelerated the rates of glucose consumption and pullulan formation, thereby increased pullulan production. Our findings revealed that MAL31 is involved in the transport of precursors for pullulan biosynthesis. This study provides an accurate operating site for genetic modification of A. pullulans for improving pullulan production and also presents a feasible technique route for the overproduction of other polysaccharides.

Facile fabrication of electrochemically reduced graphene oxide/polythionine-methylene blue and its use as a platform for detection of nicotinamide adenine dinucleotide in the artificial urine sample

Here we report on a facile, rapid, selective, and stable electrochemical sensing platform for nicotinamide adenine dinucleotide (NADH) based on polythionine-methylene blue/electrochemically reduced graphene oxide modified glassy carbon electrode (PTH-MBDES-ERG/GCE). The ERG was directly formed on a glassy carbon electrode (ERG/GCE) through one-step electrochemical reduction of GO in PBS solution (10 mM, pH 7.4). In a PBS electrolyte, respectively, containing 50% (v/v) three different deep eutectic solvents (DES), thionine and methylene blue were polymerized on the surface of ERG/GCE. The electrochemical properties of the polymers polymerized in different electrolytes were investigated. The PTH-MBDES-ERG composite has a higher performance in the electrocatalytic oxidation of NADH than that of PTH-MBDES. The as-prepared PTH-MBDES-ERG/GCE demonstrated excellent direct electrocatalytic oxidation toward NADH, providing a favorable platform for electron transfer from NADH to the electrode. The sensor displayed a wide linear range from 1.52 μM to 3333.33 μM with a limit of detection of 0.51 nM. The interference from the ascorbic acid and uric acid was negligible. The prepared sensor was further tested for the determination of NADH in artificial urine samples, showing the PTH-MBDES-ERG/GCE formed by electropolymerization have promising biomedical applications.

Electrocatalytic oxidation of NADH at graphene-modified electrodes based on electropolymerized poly(thionine-methylene blue) films from nature deep eutectic solvents

• Electropolymerization of PTH-MB films in ternary nature deep eutectic solvents. • PTH-MB NADES and ERG have a synergistic effect on the oxidation of NADH. • The prepared PTH-MB NADES -ERG electrode has excellent NADH electrocatalytic oxidation performance. • Sensitive detection of NADH in artificial urine samples. In this paper, a sensing platform for the electrocatalytic oxidation of nicotinamide adenine dinucleotide (NADH) was proposed. It was prepared by the electropolymerization of poly(thionine-methylene blue) (PTH-MB) in ternary nature deep eutectic solvent (NADES) on a glassy carbon electrode (GCE) that was modified with electrochemically reduced graphene oxide (ERG). The modified electrode was denoted as PTH-MB NADES -ERG/GCE. Cyclic voltammetry (CV), chronocoulometry (CC), electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM), Raman spectroscopy, and Ultra Violet-Visible Spectroscopy (UV–Vis) were used to characterize the preparation processes. The electrochemical performances of the electrode in NADH oxidation were studied via CV and current-time methods. The NADH oxidation overpotential was lower on PTH-MB NADES -ERG/GCE compared to that on GCE, ERG/GCE, and PTH-MB NADES /GCE. The PTH-MB NADES -ERG/GCE showed excellent electrocatalytic activity for NADH oxidation with a linear range of 0.51–3333.33 µM (R 2 = 0.9534) and a detection limit of 0.159 nM. The sensor was further tested for NADH determination in artificial urine samples, showing promising biomedical applications.

An electrochemical NADH biosensor based on a nanoporous gold electrode modified with diaphorase and an osmium polymer

NADH is a cofactor used by a wide range of dehydrogenases. Measurement of the concentration of NADH is widely used to measure the activity of enzymes. Extensive efforts have been made to develop electrochemical sensors for NADH determination at low overpotentials to avoid interferences. The development of an enzymatic electrochemical biosensor for the detection of NADH is described. Nanoporous gold electrodes were utilised for the immobilization of diaphorase and osmium-based polymer Os(bpy)2(PVI). Nanoporous gold electrodes of different pore sizes were manufactured by varying the dealloying temperature. To optimise the enzymatic response, the concentrations of polymer and enzyme, average pore size and the operating temperature were examined with the optimal performance observed using 10 µL of Os(bpy)2(PVI) and 5 µL of diaphorase at concentrations of 6 and 10 mg/mL, respectively, on nanoporous gold electrodes with an average pore size of 5.9 nm. The biosensor showed a high sensitivity of 89.6 µA/cm2 mM, a low LOD of 0.8 µM and a linear range from 5 to 100 µM at a potential of 0.35 V vs Ag/AgCl at a temperature of 40 °C.

Porous graphene oxide based disposable non-enzymatic electrochemical sensor for the determination of nicotinamide adenine dinucleotide

Electrochemical detection of β-nicotinamide adenine dinucleotide (NADH) has fascinated the scientific community due to its significance in pharmaceuticals, food supplements as well as in various biological reactions and pathways. Herein, a facile and low-cost disposable non-enzymatic electrochemical sensor for the selective and sensitive determination of NADH was developed using porous graphene oxide (PGO) modified screen printed carbon electrode (SPE). PGO has received growing attention owing to its high internal porosity, improved conductivity, large surface area, excellent stability, improved active sites, and hence expected to show excellent electrocatalytic activity than graphene and other derivatives of carbon. Firstly, graphene oxide (GO) sheets were synthesized, after which pores were created on these GO sheets through simple base reduction and acid treatment and the pore formation was confirmed using different characterization techniques. The PGO was directly dropcasted on the surface of SPE to form PGO/SPE and the fabricated electrode demonstrated eminent electrocatalytic activity towards NADH oxidation. Further, the fabricated sensor has shown significant response over a broad-range of concentration from 30 to 1071 μM with a good sensitivity of 21.83 μA mM −1 cm −2 and a low detection limit of 8.6 μM. Moreover, the fabricated PGO/SPE has advantages like cost-effectiveness, robustness, disposability, ease of fabrication, high stability, and excellent reproducibility. • Porous graphene oxide was synthesized via base reduction and acidification. • Fabricated a disposable electrochemical sensor by dropcasting PGO on SPE (PGO/SPE) • PGO/SPE effectively utilized for the electrocatalytic oxidation of NADH. • Compared to GO/SPE and ERGO/SPE, PGO/SPE showed superior analytical performance. • PGO/SPE exhibits good selectivity for NADH with excellent stability and sensitivity.

Highly sensitive voltammetric determination of NADH based on N-CQDs decorated SnO2/ionic liquid/carbon paste electrode

A highly sensitive and selective modified electrode was successfully developed for the monitoring of nicotinamide adenine dinucleotide (NADH) in the presence of folic acid. In this regard, a carbon paste electrode (CPE) was functionalized by the nitrogen-doped carbon quantum dots/tin oxide (N-CQDs/SnO2) nanocomposite and 1-butyl-2,3-dimethyl imidazolium hexafluorophosphate ([C4DMIM][PF6]) ionic liquid (IL). The structure and surface morphology of the nanocomposite were characterized by various methods, including field emission scanning electron microscopy, energy dispersive spectroscopy (EDS), high-resolution transmission electron microscopy (HR-TEM), and x-ray diffraction (XRD). The modified electrode displayed powerful and long-lasting electron mediating activity, with well-separated NADH and folic acid oxidation peaks. The sensing response of the developed [C4DMIM][PF6]/N-CQDs/SnO2/CPE platform was evaluated by determining NADH via the voltammetric technique under the optimized operating conditions. The current peaks of the square wave voltammograms of NADH and folic acid increased linearly with enhancing its concentrations within the ranges of 0.003–275 μM NADH and 0.4–380 μM folic acid. The detection limits for NADH and folic acid were obtained at 0.8 nM and 0.1 μM, respectively. Interference species such as glucose, urea, tryptophan, glycine, methionine, and vitamin B12 had no influence on the ability of the fabricated modified electrode to detect the target species. The low detection limit, high sensitivity, excellent selectivity, superior stability, and cost-effectiveness made it suitable for the quantification of NADH in the real biological samples with the recovery percent values in the range of 97.5%–103%.

Enzyme decorated dendritic bimetallic nanocomposite biosensor for detection of HCHO

In recent times, bi- and tri-metallic nanocomposites are being extensively studied to improve the catalytic surface and sensitivity of detection. In this study, we designed a formaldehyde dehydrogenase decorated Cys-AuPd-ErGO nanocomposite with fern like AuPd dendrites deposited on reduced graphene oxide (ErGO) on screen printed electrode (SPE) for determination of NADH and successfully demonstrated its application for detection of HCHO. This biosensor exhibited direct electron transfer by lowering the oxidation potential of NADH from +0.63 V to 0.32 V vs Ag/AgCl, avoiding usage of electron mediators. The sensor LOD was 0.3 μM HCHO with excellent sensitivity of 70 μA/μM/cm2 and linear detection range between 1 μM and 100 μM during chronoamperometric studies at applied over potential of +0.35 V vs Ag/AgCl. The sensor was tested for its performance in simulated HCHO adulterated samples of fish and milk, and appreciable recoveries (88–104%) at tested concentrations indicated good sensor performance. It was also validated against conventional method of HPLC with highly acceptable correlation coefficient of 0.99, indicating successful fabrication of a simple, “on site” disposable sensor for HCHO detection. The developed biosensor can also find wide application in quantitative measurement of NADH and analytes involved in reactions with the co-enzyme.

(+)-Catechin-assisted graphene production by sonochemical exfoliation in water. A new redox-active nanomaterial for electromediated sensing.

A new green and effective sonochemical liquid-phase exfoliation (LPE) is proposed wherein a flavonoid compound, catechin (CT), promotes the formation of conductive, redox-active, water-phase stable graphene nanoflakes (GF). To maximize the GF-CT redox activity, the CT concentration and sonication time have been studied, and the best performing nanomaterial-fraction selected. Physicochemical and electrochemical methods have been employed to characterize the morphological, structural, and electrochemical features of the GF-CT nanoflakes. The obtained GF intercalated with CT exhibits fully reversible electrochemistry (ΔEp = 28mV, ipa/ipc = ⁓1) because of the catecholic adducts. GF-CT-integrated electrochemistry was generated directly during LPE of graphite, with no need of graphene oxide production, nor activation steps, electropolymerization, or ex-post functionalization. The GF-CT electro-mediator ability has been proven towards hydrazine (HY) and β-nicotinamide adenine dinucleotide (NADH) by simply drop-casting the redox-material onto screen-printed electrodes. GF-CT-based electrodes by using amperometry exhibited high sensitivity and extended linear ranges (HY: LOD = 0.1µM, L.R. 0.5-150µM; NADH: LOD = 0.6µM, L.R. 2.5-200µM) at low overpotential (+ 0.15V) with no electrode fouling. The GF-CT electrodes are performing significantly better than commercial graphite electrodes and graphene nanoflakes exfoliated with a conventional surfactant, such as sodium cholate. Recoveries of 94-107% with RSD ≤ 8% (n = 3) for determination of HY and NADH in environmental and biological samples were achieved, proving the material functionality also in challenging analytical media. The presented GF-CT is a new functional redox-active material obtainable with a single-pot sustainable strategy, exhibiting standout properties particularly prone to (bio)sensors and cutting-edge device development.

Rapid microfluidic analysis detection system for sodium dehydroacetate in foods

Sodium dehydroacetate (NADH) has good antibacterial effects and is widely used as a preservative in dairy products. However, NADH is toxic in large amounts, so it must be added to food in accordance with regulations. Accordingly, the current study has developed a microfluidic analysis detection (MAD) system for the determination of NADH in foods incorporating a microfluidic PMMA-paper chip and a smart analysis device. In this system, the extracted NADH sample is dropped into the sample chamber of the microfluidic PMMA-paper chip and is then wicking/filtering through paper strips and transferred to a detection zone embedded with Fe-Alum reagent. The chip is heated at 35 °C for 5 min to produce a compound reaction and the color compound image acquired by a camera is then transmitted wirelessly to a smartphone, where the NADH concentration is obtained by the intensity inversion of RGB analysis. A standard calibration curve is determined using NADH control samples with concentrations in the range of 30–5000 ppm. The feasibility of the proposed MAD system is then evaluated by analyzing the NADH concentrations of 15 commercial dairy products. It is shown that the measured values deviate from those obtained using an official high performance liquid chromatography (HPLC) method by no more than 5.0%.

Sensitive Electrochemical Determination of NADH Using an Electrode Fabricated by Intercalation of Tetrabutylammonium Ions Into Graphite Electrode

AbstractIn this study, we present a strategy for the specific electrochemical detection of NADH in human blood serums using modified electrode fabricated by intercalation of tetrabutylammonium ions (TBA+) into pencil graphite electrode (TBA+/PGE). In order to implement this protocol, a modification process in the potential range (−0.2) to (−2.75) V was performed in DMSO containing 0.1 M TBAP by CV method. The characterization processes of the prepared sensor were carried out using CV, EIS, FT‐IR, XPS, and SEM methods. The electrode fabricated by intercalation of TBA+ was found to be able to analyze NADH at +0.32 V applied potential by the amperometric method. The LOD was detected as 0.46 μM. The analysis results of human blood serums which are taken from healthy individuals show that TBA+/PGE can be used for real samples. The results indicated that TBA+/PGE can be easily fabricated by one‐step and one‐pot electrochemical method and TBA+/PGE can be used as a potential sensor for the NADH determination.

Determination of NADH by Surface Enhanced Raman Scattering Using Au@MB@Ag NPs

Nicotinamide adenine dinucleotide (NADH) is an important coenzyme involved in various metabolic processes of living cells. As an important biomarker, NADH is associated with breast cancer and Alzheimer’s disease. In this paper, silver plated gold core–shell nanoparticles containing Raman signal molecules were synthesised on the basis of bare gold. Using the Raman peak corresponding to the 4-mercaptobenzonitrile (MB) silent region C≡N vibration for quantification, while avoiding competition with the precious metal surface binding site to be measured, it can also be free from the interference of endogenous biomolecules. On the one hand, it can correct the working curve, on the other hand, it can avoid competing with the binding site. Compared with the core–shell structure prepared here, the limit of detection (LOD) for NADH was only 10−5 M for bare gold and the LOD for the core–shell structure prepared on the basis of bare gold was 3.3 × 10−7 M. In terms of correction, with Rhodamine 6G (R6G) as a Raman signalling molecule, the R2 value before SERS detection and correction is only 0.9405, and the R2 value after correction increases to 0.9853. The unique fingerprint peak of SERS was used to realise the quantitative detection of NADH, which realizes the detection of NADH in complex biological samples of serum and provides the possibility for expanding the early diagnosis of breast cancer.

An efficient and rapid synthesis route to highly fluorescent copper microspheres for the selective and sensitive excitation wavelength-dependent dual-mode sensing of NADH

Fluorescent copper microspheres (CMS) with high quantum yield (72.9 %) were synthesized by an efficient, one-pot, and rapid aggression-induced mechanism. The CMS was bright brick-red luminescent under UV light and have shown an excitation independent emission at 670 nm. The emission intensity of CMS was significantly quenched by the addition of nicotinamide adenine dinucleotide (NADH) when excited at 275 nm, providing a linear range with the logarithmic concentration of NADH, suitable for the detection of low concentrations of NADH. Similarly, the emission intensity at 670 nm was enhanced when excited at 340 nm, providing a linear range for NADH determination in the higher concentration. Thus, a dual-mode sensing platform for the determination of NADH was established by utilizing the fluorescent quenching and enhancement properties of NADH over CMS. Addition of other common interfering molecules and ions induced only a meager change in the fluorescent intensity of CMS, suggesting the high selectivity of the sensor. The linear range observed for NADH by exploring the fluorescent quenching properties was from 24.8−575.2 μM (R2 = 0.99) with a L.O.D of 2.4 μM. Meanwhile, the linear range observed for NADH by utilizing the fluorescent enhancing properties was from 625 μM-2.30 mM (R2 = 0.98) with a L.O.D of 322.5 μM.

Electrocatalytic determination of NADH by means of electrodes modified with MWCNTs and nitroaromatic compounds

In this work, we have both synthesized and studied 4-phenylbutyl-3,5-dinitrobenzoate (3,5-DNBPh) as a potential precursor of an electrocatalytic mediator for the oxidation of NADH, with the di-nitro compound immobilized in a three-dimensional network of glassy carbon electrodes modified with MWCNTs. This di-nitro compound is activated electrochemically to selectively generate one nitroso-hydroxylamine redox pair, which ultimately acts as a redox mediator of NADH oxidation. Thus, NADH electrocatalysis displaces the oxidation potential of NADH with the formation of a single voltammetric peak, the displacement occurs from Ep = +0.374 V in GCE/MWCNT to +0.001 V in GCE/MWCNT/3,5-DNBPh (very close to 0 V, ΔEp = 0.373 V). The 4-phenylbutyl-3,5-dinitrobenzoate mediator is sensitive to NADH concentration, and a linear regression between 0.1 and 0.6 mM NADH (r2 = 0.99) was obtained, with a detection limit of 22.3 μM (S/N = 3) and a quantification limit of 74.2 μM (S/N = 10). The developed modified electrode presents low NADH electrocatalytic oxidation potentials, and an interesting and novel advantage is that the preparation of the electrodes is fast, clean and effective, allowing biosensors to be obtained in a few steps.

Electrocatalytic NADH Sensing using Electrodes Modified with 2‐[2‐(4‐Nitrophenoxy)ethoxy]ethylthio‐Substituted Porphyrazine/Single‐Walled Carbon Nanotube Hybrids

AbstractThe electrochemical properties of a modified electrode covered with 2‐[2‐(4‐nitrophenoxy)ethoxy]ethylthio‐substituted porphyrazine/single‐walled carbon nanotube hybrids were investigated. The electrochemical study revealed that the electrode mechanism is more complex in acidic conditions in comparison to neutral buffer. According to our study, the nitro groups constituting the part of porphyrazine substituents can be electrochemically reduced to the corresponding hydroxylamine moieties; surprisingly, however, the latter can be additionally transformed to o‐aminophenol/o‐iminoquinone groups, but only in acidic conditions. The electrode covered with hybrid material was used in the electrocatalytic oxidation of NADH. According to these results, it seems that after the electrochemical activation of the electrode material, 2‐[2‐(4‐nitrophenoxy)ethoxy]ethylthio‐substituted porphyrazine reveals strong electrocatalytic behavior towards NADH oxidation, owing to the appearance of reversible surface‐anchored o‐aminophenol/o‐iminoquinone intermediate redox couples. In the amperometric determination, the limit of detection (LOD) and limit of quantification (LOQ) of NADH were calculated and found to be LOD=0.16 and LOQ=0.48 μM. Moreover, the relative standard deviation of the response was 3.32 %, indicating excellent reproducibility. Thus, the novel electrode based on 2‐[2‐(4‐nitrophenoxy)ethoxy]ethylthio‐substituted porphyrazine and single‐walled carbon nanotubes present an interesting opportunity in the fields of electroanalytical and biosensing applications, and can be considered for amperometric NADH determination.

A new disposable amperometric NADH sensor based on screen-printed electrode modified with reduced graphene oxide/polyneutral red/gold nanoparticle

ABSTRACTA new amperometric NADH sensor was developed based on screen-printed electrode (SPCE) modified with reduced graphene oxide (RGO), polyneutral red (PNR) and gold nanoparticles (AuNP). Electrochemical behaviour of NADH on SPCE/RGO/PNR/AuNP was investigated. The prepared sensor showed a high electrocatalytic effect on the oxidation of NADH. The sensor response for NADH was investigated as a function of pH and working potential. Optimum values of these parameters in the NADH determination were found as 7.0 for pH and +0.15 V for working potential. Sensitivity, linear range, limit of detection and limit of quantification of the sensor were found to be 8.72 μAmM−1, 5 to 3170 μM, 0.384 μM and 1.18 μM, respectively. The relative standard deviation (RSD) was calculated to be 1.93% (for n = 10). The operational stability studies have shown that the initial amperometric response of sensor to NADH decreased by 56.15% at the 60th day. Storage life studies have shown that the sensitivity of the biosensor decreased by 48.72% at the end of 12 weeks. The developed sensor has been tested for NADH determination in the human serum sample. The developed NADH sensor is promising to be used for NADH analysis in human serum samples as simple, practical and disposable device without requiring laborious sample pre-treatment producers.