Electrochemical analysis of ascorbic acid using copper nanoparticles/polyaniline modified glassy carbon electrode

Environment-Friendly Ascorbic Acid Fuel Cell

Recently, ascorbic acid (AA) has been studied as an environment-friendly fuel for energy conversion devices. This review article has deliberated an overview of ascorbic acid electrooxidation and diverse ion exchange types of AA-based fuel cells for the first time. Metal and carbon-based catalysts generated remarkable energy from environment-friendly AA fuel. The possibility of using AA in a direct liquid fuel cell (DLFC) without emitting any hazardous pollutants is discussed. AA fuel cells have been reviewed based on carbon nanomaterials, alloys/bimetallic nanoparticles, and precious and nonprecious metal nanoparticles. Finally, the obstacles and opportunities for using AA-based fuel cells in practical applications have also been incorporated.

Gold Nanoparticles/Carbon Nanotubes and Gold Nanoporous as Novel Electrochemical Platforms for L-Ascorbic Acid Detection: Comparative Performance and Application

Herein, the effects of nanostructured modifications of a gold electrode surface in the development of electrochemical sensors for L-ascorbic acid detection have been investigated. In particular, a bare gold electrode has been modified by electrodeposition of gold single-walled carbon nanotubes (Au/SWCNTs) and by the formation of a highly nanoporous gold (h-nPG) film. The procedure has been realized by sweeping the potential between +0.8 V and 0 V vs. Ag/AgCl for 25 scans in a suspension containing 5 mg/mL of SWCNTs in 10 mM HAuCl4 and 2.5 M NH4Cl solution for Au/SWCNTs modified gold electrode. A similar procedure was applied for a h-nPG electrode in a 10 mM HAuCl4 solution containing 2.5 M NH4Cl, followed by applying a fixed potential of −4 V vs. Ag/AgCl for 60 s. Cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the properties of the modified electrodes. The developed sensors showed strong electrocatalytic activity towards ascorbic acid oxidation with enhanced sensitivities of 1.7 × 10−2 μA μM−1cm−2 and 2.5 × 10−2 μA μM−1cm−2 for Au/SWCNTs and h-nPG modified electrode, respectively, compared to bare gold electrode (1.0 × 10−2 μA μM−1cm−2). The detection limits were estimated to be 3.1 and 1.8 μM, respectively. The h-nPG electrode was successfully used to determine ascorbic acid in human urine with no significant interference and with satisfactory recovery levels.

Electrochemical sensing of L-ascorbic acid by using a glassy carbon electrode modified with a molybdophosphate film

Electrochemical sensing of L-ascorbic acid (AA) is reported based on the use of a redox-active molybdophosphate film on a glassy carbon electrode (GCE). Molybdophosphate is formed by reacting hydroxyapatite nanoparticles with sodium molybdate. The modified GCE can be utilized for detection of AA, typically at a working potential of 0.4 V (vs. Ag/AgCl). The GCE has a decreased overpotential and enhanced sensitivity (219 μA·mM^-1·cm^-2). Response is linear in the 1 μM to 1.5 mM AA concentration range, and the limit of detection is 4 nM. The selectivity of this sensor makes it a useful tool for accurate determination of AA in practical samples as shown for a vitamin C tablet and for spiked beverages. Graphical abstract An electrochemical sensing platform is reported that is based on the use of a redox-active molybdophosphate film that was formed via reacting hydroxyapatite nanoparticles (HAP-NPs) with sodium molybdate. Graphical abstract contains poor quality of text inside the artwork. Please do not re-use the file that we have rejected or attempt to increase its resolution and re-save. It is originally poor, therefore, increasing the resolution will not solve the quality problem. We suggest that you provide us the original format. We prefer replacement figures containing vector/editable objects rather than embedded images. Preferred file formats are eps, ai, tiff and pdf.We have uploaded the graphical abstract as PDF format.

Sandwich-structured nanoparticles-grafted functionalized graphene based 3D nanocomposites for high-performance biosensors to detect ascorbic acid biomolecule

We present a highly sensitive and selective nano-biosensor for rapid, stable and highly reproducible detection of ascorbic acid (AA) in the presence of dopamine, uric acid and other interferences by a three-layer sandwich arrangement of nitrogen-doped functionalized graphene (NFG), silver nanoparticles (AgNPs) and nanostructured polyaniline (PANI) nanocomposite. The enhanced AA electrochemical properties of the NFG/AgNPs/PANI electrode is attributed to the superior conductivity of the NFG-PANI and the excellent catalytic activity of AgNPs. The critical modification of the AgNPs-grafted NFG-PANI coated on very low-cost fluorine doped tin oxide electrode (FTOE) increased the charge transfer conductivity of the electrode (the resistance drops down from 11,000 Ω to 6 Ω). The nano-biosensor was used to accurately detect AA in vitamin C tablets with the recovery of 98%. The sensor demonstrated a low detection limit of 8 µM (S/N = 3) with a very wide linear detection range of 10–11,460 µM, good reproducibility and excellent selectivity performance for AA detection. The results demonstrate that this nanocomposite is a promising candidate for rapid and selective detection of AA in practical clinical samples.

Synthesis of CuNP-Modified Carbon Electrodes Obtained by Pyrolysis of Paper

A one-step approach for the synthesis and integration of copper nanoparticles (CuNPs) onto paper-based carbon electrodes is herein reported. The method is based on the pyrolysis (1000 °C under a mixture of 95% Ar / 5% H₂ for 1 hour) of paper strips modified with a saturated solution of CuSO₄ and yields to the formation of abundant CuNPs on the surface of carbonized cellulose fibers. The resulting substrates were characterized by a combination of scanning electron microscopy, EDX, Raman spectroscopy as well as electrical and electrochemical techniques. Their potential application, as working electrodes for nonenzymatic amperometric determination of glucose, was then demonstrated (linear response up to 3 mM and a sensitivity of 460 ± 8 μA·cm^-2·mM^-1). Besides being a simple and inexpensive process for the development of electrochemically-active substrates, this approach opens new possibilities for the in-situ synthesis of metallic nanoparticles without the traditional requirements of solutions and adjuvants.

Enhancement of electrogenerated chemiluminescence of luminol by ascorbic acid at gold nanoparticle/graphene modified glassy carbon electrode

Gold nanoparticle/graphene (GNP/GR) nanocomposite was one-pot synthesized from water soluble graphene and HAuCl₄ by hydrothermal method and characterized by TEM, Raman spectroscopy, XRD, XPS, UV-vis spectroscopy, and electrochemical impedance spectroscopy (EIS). Electrogenerated chemiluminescence (ECL) of luminol was investigated at the GNP/GR modified glassy carbon electrode (GNP/GR/GCE) and the GNP modified glassy carbon electrode (GNP/GCE) in aqueous solution respectively. The results revealed that one strong anodic ECL peak could be observed at ∼0.8 V at two modified electrodes compared with that at the bare electrode. The intensity of the anodic ECL at the GNP/GR/GCE is weaker than that at the GNP/GCE, which should be due to the synergic effect of the enhancing effect of gold nanoparticles and the inhibiting effect of graphene on anodic luminol ECL. One strong cathodic ECL peak located at ∼-0.8 V could be observed at the GNP/GR/GCE but not at the GNP/GCE, which should be result from the adsorbed oxygen at the graphene film. In the presence of ascorbic acid, the anodic ECL at the GNP/GR/GCE was enhanced more than 8-times, which is more apparent than that at the GNP/GCE. Whereas, the cathodic ECL peak was seriously inhibited at the GNP/GR/GCE. The enhanced ECL intensity at the GNP/GR/GCE varied linearly with the logarithm of ascorbic acid concentration in the range of 1.0 × 10(-8) to 1.0 × 10(-6)mol L(-1) with a detection limit of 1.0 × 10(-9) mol L(-1). The possible ECL mechanism was also discussed.

Ultrasensitive immunoassay based on electrochemical measurement of enzymatically produced polyaniline

A novel ultrasensitive immunoassay method was developed based on the electrochemical measurement of polyaniline, which was catalytically produced by horseradish peroxidase-functionalized gold nanoparticle (HRP-Au NP) probe at an immunosensor. The immunosensor was prepared step-wise by first modifying the electrode with reduced graphene oxide (rGO)/Au NPs nanocomposite followed by the immobilization of capture antibodies on its surface. After performing a sandwich immunoreaction, the quantitatively captured HRP-Au NP nanoprobes could catalyze oxidation of aniline to produce electroactive polyaniline on the immunosensor surface. The electrochemical measurement of polyaniline enabled a novel detection strategy for HRP-based immunoassay. Both the signal amplification of the HRP-Au NP nanoprobe and the electron transfer acceleration of rGO/Au NPs on the immunosensor surface greatly improved the detection sensitivity of the immunoassay method. With the use of human IgG as a model analyte, this method showed a wide linear range over 4 orders of magnitude with a detection limit of 9.7 pg/mL. In addition, the immunosensor had low cost, satisfactory reproducibility and stability, and acceptable reliability. The relatively positive potential range for the polyaniline measurement completely excluded the conventional interference from dissolved oxygen. Thus, this method provides a promising potential for practical applications.

Fabrication of a novel and simple microcystin-LR photoelectrochemical sensor with high sensitivity and selectivity

Microcystin-LR (MC-LR), an inert electrochemical species, is difficult to be detected by a simple and direct electrochemical method. In the present work, a novel photoelectrochemical sensor is developed on highly ordered and vertically aligned TiO(2) nanotubes (TiO(2) NTs) with convenient surface modification of molecularly imprinted polymer (MIP) (denoted as MIP@TiO(2) NTs) for highly sensitive and selective determination of MC-LR in solutions. Molecularly imprinted polypyrrole (PPy) of MC-LR is chosen as the recognition element. The designed MIP@TiO(2) NTs photoelectrochemical sensor presents excellent applicability in MC-LR determination, with linear range from 0.5 to 100 μg L(-1) and limit of detection of 0.1 μg L(-1). Moreover, the sensor exhibits outstanding selectivity while used in coexisting systems containing 2,4-dichorophenoxyacetic acid, atrazine, paraquat, or monosultap with high concentration, 100 times that of MC-LR. The sensor presents good photoelectric conversion efficiency and detection sensitivity, as well as broad linear detection range, mainly because of the high specific surface area and photoelectric activity of TiO(2) NTs and the π bond delocalized electron system of PPy that promotes the separation of electron-holes. The prominent selectivity is from the MIP by forming multiple hydrogen bonds between PPy and MC-LR. Mechanisms for photoelectrochemical analysis and selective recognition are also discussed.

An ascorbic acid amperometric sensor using over-oxidized polypyrrole and palladium nanoparticles composites

We constructed a highly responsive ascorbic acid (AA) sensor utilizing over-oxidized polypyrrole (OPPy) and Palladium nanoparticles (PdNPs) composites (OPPy-PdNPs). In the presence of PdNPs, polypyrrole (PPy) was coated on a gold (Au) electrode through cyclic voltammetry (CV) and over-oxidized at a fixed potential in NaOH solution. The PdNPs were characterized using ultraviolet-visible (UV-vis) spectrum and transmission electron microscopy (TEM). The surface of OPPy-PdNPs on the Au electrode was investigated using field-emission scanning electron microscopy (FE-SEM). Results revealed that the OPPy-PdNPs-modified Au electrode (OPPy-PdNPs/Au) has the capacity to catalyze the oxidation of AA by lowering its oxidation potential to 0 V. The OPPy-PdNPs/Au electrode exhibited 2 different linear concentration ranges. In the low concentration range (1-520 μM), OPPy-PdNPs/Au exhibited a direct linear relation with current responses and had high sensitivity (570 μA mM(-1)cm(-2)) and a high correlation coefficient (0.995). In contrast, in the higher concentration range (120-1600 μM), the relationship between current responses and concentration of AA can be represented by a two-parameter sigmoidal equation. In addition, the sensor exhibited a short response time (less than 2s) and a very low limit of detection of 1 μM. The electrochemical AA sensor constructed in this study was simple, inexpensive, reproducible, sensitive, and resistant to interference. Thus, the proposed sensor has great potential for detecting AA in complex biosystems and can be applied in various fields, particularly neuroscience.