Effective immobilization of Ru(bpy)32+ by functional composite phosphomolybdic acid anion on an electrode surface for solid-state electrochemiluminescene to sensitive determination of NADH

Electrochemiluminescent imaging of a NADH-based enzymatic reaction confined within giant liposomes

Herein, transient releases either from NADH-loaded liposomes or enzymatic reactions confined in giant liposomes were imaged by electrochemiluminescence (ECL). NADH was first encapsulated with the [Ru(bpy)3]2+ luminophore inside giant liposomes (around 100 µm in diameter) made of DOPC/DOPG phospholipids (i.e., 1,2-dioleolyl-sn-glycero-3-phosphocholine/1,2-dioleoyl-sn-glycerol-3-phospho-(1'-rac-glycerol) sodium salt) on their inner- and outer-leaflet, respectively. Then, membrane permeabilization triggered upon contact between the liposome and a polarized ITO electrode surface and ECL was locally generated. Combination of amperometry, photoluminescence, and ECL provided a comprehensive monitoring of a single liposome opening and content release. In a second part, the work is focused on the ECL characterization of NADH produced by glucose dehydrogenase (GDH)-catalyzed oxidation of glucose in the confined environment delimited by the liposome membrane. This was achieved by encapsulating both the ECL and catalytic reagents (i.e., the GDH, glucose, NAD+, and [Ru(bpy)3]2+) in the liposome. In accordance with the results obtained, NADH can be used as a biologically compatible ECL co-reactant to image membrane permeabilization events of giant liposomes. Under these conditions, the ECL signal duration was rather long (around 10 s). Since many enzymatic reactions involve the NADH/NAD+ redox couple, this work opens up interesting prospects for the characterization of enzymatic reactions taking place notably in artificial cells and in confined environments.

Polyoxometalate Functionalized Sensors: A Review

Polyoxometalates (POMs) are a class of metal oxide complexes with a large structural diversity. Effective control of the final chemical and physical properties of POMs could be provided by fine-tuning chemical modifications, such as the inclusion of other metals or non-metal ions. In addition, the nature and type of the counterion can also impact POM properties, like solubility. Besides, POMs may combine with carbon materials as graphene oxide, reduced graphene oxide or carbon nanotubes to enhance electronic conductivity, with noble metal nanoparticles to increase catalytic and functional sites, be introduced into metal-organic frameworks to increase surface area and expose more active sites, and embedded into conducting polymers. The possibility to design POMs to match properties adequate for specific sensing applications turns them into highly desirable chemicals for sensor sensitive layers. This review intends to provide an overview of POM structures used in sensors (electrochemical, optical, and piezoelectric), highlighting their main functional features. Furthermore, this review aims to summarize the reported applications of POMs in sensors for detecting and determining analytes in different matrices, many of them with biochemical and clinical relevance, along with analytical figures of merit and main virtues and problems of such devices. Special emphasis is given to the stability of POMs sensitive layers, detection limits, selectivity, the pH working range and throughput.

Electrochemical sensing of nitrofurazone on Ru(bpy)32+ functionalized polyoxometalate combined with graphene modified electrode

Nitrofurazone is forbidden to be used in aquaculture, but it is often used illegally because of its good bactericidal effect, and its content in animals is extremely low and difficult to detect directly. Hence, a functionalized polyoxometalate combined with graphene modified electrodes through layer-by-layer assembly has achieved a sensitive detection of nitrofurazone in a pH = 6 Na₂HPO₄-citrate buffer solution and its detection limit as low as 0.08952 μM. Nitrofurazone has accelerated its electron transfer through [Ru-PMo₁₂/PDDA-GO]₃ modified electrode, thus realizing its direct detection at low levels through actual samples. This study provides a new perspective for the direct detection of nitrofurazone by electrochemical methods, which is of great significance for the supervision of nitrofurazone and the improvement of the quality and safety of aquatic products.

CsPbBr3 perovskite quantum dots/ZnO inverse opal electrodes: photoelectrochemical sensing for dihydronicotinamide adenine dinucleotide under visible irradiation

All-inorganic perovskite quantum dots (PQDs) have attracted tremendous attention due to their extraordinary optical properties, especially CsPbBr₃ QDs with their high stability and photoluminescence efficiency.

Eco-synthesis of graphene and its use in dihydronicotinamide adenine dinucleotide sensing

In this paper, we report a green and eco-friendly approach to synthesize reduced graphene oxide (rGO) via a mild hydrothermal process using malt as a reduced agent. The proposed method is based on the reduction of graphene oxide (GO) in malt solution by making use of the reducing capability of phenolic compounds contained in malt solution. The obtained rGO was characterized by atomic force microscopy (AFM), ultraviolet-visible (UV-vis) absorption spectroscopy, X-ray diffraction spectroscopy (XRD), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Electrochemical impedance spectroscopy analysis revealed that the charge transfer resistance of rGO modified glassy carbon (GC) electrode was much lower than that of the GC electrode. The electrochemical behavior of dihydronicotinamide adenine dinucleotide (NADH) on rGO modified GC electrode was investigated by cyclic voltammetry and amperometry. Electrochemical experiments indicated that rGO/GC electrode exhibited excellent electrocatalytic activity toward the NADH, which can be attributed to excellent electrical conductivity and high specific surface area of the rGO composite. The resulting biosensor showed highly sensitive amperometric response to NADH with a low detection limit (0.33μM).

Polyoxometalate@magnetic graphene as versatile immobilization matrix of Ru(bpy)3(2+) for sensitive magneto-controlled electrochemiluminescence sensor and its application in biosensing

We demonstrated here the exploration of polyoxometalate (POM) coated magnetic Fe3O4/reduced graphene oxide (POM@mrGO) composite as the versatile immobilization matrix for the electrochemiluminescence (ECL) agent Ru(bpy)3(2+). The effective modification of Ru(bpy)3(2+)/POM@mrGO hybrid simply involved using magnetic electrode showed 10-fold ECL intensity increase than that observed for Ru(bpy)3(2+)/Nafion@mrGO to the same concentration of nicotinamide adenine dinucleotide (NADH), which is largely due to POM׳s good electrocatalytic activity towards NADH oxidation. These findings allowed the stable and ultrasensitive ECL detection of NADH as low as 0.1 nM. The good stability and high sensitivity of the magneto-controlled ECL sensor enabled us to explore the feasibility of applying the sensing platform to fabricating the ECL biosensors in which the NADH was produced from the dehydrogenase-based enzymatic reaction in the presence of NAD(+) cofactor. With L-lactate dehydrogenase as a model, a L-lactate biosensor was successfully constructed where we showed that the ECL intensity of the biosensor increased with the increasing L-lactate concentration. Excellent performance of the presented biosensor has been achieved including a wide linear range extended from 5.0×10(-9) M to 5.0×10(-4) M and an extremely low detection limit of 0.4 nM. Such sensing strategy combines enzymatic selectivity with simple sensor preparation can be used as a new and biocompatible platform for dehydrogenase-based ECL biosensing.

Electrocatalytic activity of nickel oxide nanoparticles as mediatorless system for NADH and ethanol sensing at physiological pH solution

The glassy carbon (GC) electrode modified by nickel oxide nanoparticles (NiOxNPs) is proposed as a novel electrocatalytic system for the oxidation of NADH without using any electron transfer mediator. Here, chronoamperometry was used not only as a simple method for the deposition of NiOxNPs onto the GC electrode but also as an efficient tool in the controlling of nanoparticles size and efficient electrocatalytic activity. The surface morphology and electrochemical properties of the NiOxNPs/GC electrode was investigated using scanning electron microscopy and cyclic voltammetry techniques, respectively. The NPs are deposited uniformly across the GC surface and the size of NiOxNPs varies from 20 to less than 100 nm. The NiOxNPs/GC electrode shows excellent electrocatalytic activity toward oxidation of NADH at reduced overvoltage. The detection limit and sensitivity of the modified electrode toward NADH were estimated to be 106 nM (S/N=3) and 0.052 μAμM(-1), respectively at a concentration range up to 1mM. Due to the biocompatibility of NiOxNPs toward biomolecules, this modified electrode can be used as an efficient transducer in the design of an ethanol biosensor based on the coupled alcohol dehydrogenase enzyme(ADH). Hydrodynamic amperometric detection of ethanol on the ADH-Nafion/NiOxNPs/GC modified electrode gives linear responses over the concentration range of 0.2-6mM with a detection limit of 6.4 μM and sensitivity of 36 nA mM(-1). Applicability of the proposed biosensor for ethanol detection in real samples, easy and simple preparation, being mediator free, high sensitivity and biocompatibility are the major advantages of the proposed biosensor.