A graphene-based electrochemical sensor for sensitive and selective determination of hydroquinone

Smart and emerging point of care electrochemical sensors based on nanomaterials for SARS-CoV-2 virus detection: Towards designing a future rapid diagnostic tool

In the recent years, researchers from all over the world have become interested in the fabrication of advanced and innovative electrochemical and/or biosensors for respiratory virus detection with the use of nanotechnology. These fabricated sensors demonstrated a number of benefits, including precision, affordability, accessibility, and miniaturization which makes them a promising test method for point-of-care (PoC) screening for SARS-CoV-2 viral infection. In order to comprehend the principles of electrochemical sensing and the role of various types of sensing interfaces, we comprehensively explored the underlying principles of electroanalytical methods and terminologies related to it in this review. In addition, it is addressed how to fabricate electrochemical sensing devices incorporating nanomaterials as graphene, metal/metal oxides, metal organic frameworks (MOFs), MXenes, quantum dots, and polymers. We took an effort to carefully compile current developments, advantages, drawbacks, possible solutions in nanomaterials based electrochemical sensors.

Electrochemical Sensor for Simple and Sensitive Determination of Hydroquinone in Water Samples Using Modified Glassy Carbon Electrode

This study addressed the use of manganese dioxide nanorods/graphene oxide nanocomposite (MnO₂ NRs/GO) for modifying a glassy carbon electrode (GCE). The modified electrode (MnO₂ NRs/GO/GCE) was used as an electrochemical sensor for the determination of hydroquinone (HQ) in water samples. Differential pulse voltammetry (DPV), cyclic voltammetry (CV), and chronoamperometry were used for more analysis of the HQ electrochemical behavior. Analyses revealed acceptable electrochemical functions with lower transfer resistance of electrons and greater conductivity of the MnO₂ NRs/GO/GCE. The small peak-to-peak separation is an indication of a rapid electron transfer reaction. Therefore, this result is probably related to the effect of the MnO₂ NRs/GO nanocomposite on the surface of GCE. In the concentration range of 0.5 μM to 300.0 μM with the detection limit as 0.012 μM, there was linear response between concentration of HQ and the current. The selectivity of the modified electrode was determined by detecting 50.0 μM of HQ in the presence of various interferent molecules. At the end, the results implied the acceptable outcome of the prepared electrode for determining HQ in the water samples.

Carbon Black Functionalized with Naturally Occurring Compounds in Water Phase for Electrochemical Sensing of Antioxidant Compounds

A new sustainable route to nanodispersed and functionalized carbon black in water phase (W-CB) is proposed. The sonochemical strategy exploits ultrasounds to disaggregate the CB, while two selected functional naturally derived compounds, sodium cholate (SC) and rosmarinic acid (RA), act as stabilizing agents ensuring dispersibility in water adhering onto the CB nanoparticles’ surface. Strategically, the CB-RA compound is used to drive the AuNPs self-assembling at room temperature, resulting in a CB surface that is nanodecorated; further, this is achieved without the need for additional reagents. Electrochemical sensors based on the proposed nanomaterials are realized and characterized both morphologically and electrochemically. The W-CBs’ electroanalytical potential is proved in the anodic and cathodic window using caffeic acid (CF) and hydroquinone (HQ), two antioxidant compounds that are significant for food and the environment. For both antioxidants, repeatable (RSD ≤ 3.3%; n = 10) and reproducible (RSD ≤ 3.8%; n = 3) electroanalysis results were obtained, achieving nanomolar detection limits (CF: 29 nM; HQ: 44 nM). CF and HQ are successfully determined in food and environmental samples (recoveries 97–113%), and also in the presence of other phenolic classes and HQ structural isomers. The water dispersibility of the proposed materials can be an opportunity for (bio) sensor fabrication and sustainable device realization.

Using photo-induced p-n junction interface effect of CoMn2O4/β-MnO2 oxidase mimetics for colorimetric determination of hydroquinone in seawater

Detection of pollutants in seawater faces a great challenge of strong interference, and the facile detection method is lacked. The CoMn₂O₄/β-MnO₂ p-n junction oxidase mimetics were successfully prepared for colorimetric detection of hydroquinone in seawater. The catalysis ability was enhanced significantly by the photo-induced p-n junction interface effect. It not only promoted the formation of H₂O₂ by suppressing the recombination of photon-generated carriers, but also provided the driving force for electron transport. The colorimetric detection of hydroquinone was achieved by fading and exhibited good adaptability in seawater. The obtained good recovery rate (97.23%-101.37%) in seawater makes it an inspiring method for practical application. The photo-induced p-n junction interface effect provides an opportunity for developing the application of colorimetric sensing in seawater detection.

Effective and reliable platform for nonenzymatic nanomolar-range quinol detection in water samples using ceria doped polypyrrole nanocomposite embedded on graphitic carbon nitride nanosheets

A glassy carbon electrode modification by a novel ternary nanocomposite of advantageously united ceria, polypyrrole, and graphitic carbon nitride (CeO₂/Ppy@g-C₃N₄) is reported here. It can be used to tailor the sensor surface for the electrochemical detection of nanomolar-level quinol (Qnl), a chemical widely used as a developing agent in photography and lithography, as a cosmetic, and as an antioxidant in rubber and food industries. The occupational exposure of Qnl may occur by inhalation or dermal contact, leading to lot of health hazards. The synthesized nanocomposite was characterized by various analytical techniques such as UV-Vis, Fourier transformed infrared (FTIR), X-ray powder diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy, Raman, thermogravimetric analysis, energy-dispersive X-ray spectroscopy, selected area electron diffraction, and elemental mapping analyses. The oxidation current of Qnl is linear to its concentration in the range of 0.01-260 μM and the lowest detection and quantification limit are found to be 1.5 nM and 0.004 μM, respectively, with a sensitivity of 283.33 μA mM^-1 cm^-2. The performance of the modified electrode was compared with those of high-performance liquid chromatography, which indicates that the proposed sensor can be used as an effective and reliable platform for nano-molar detection of Qnl in various environmental and biological fluids.

Carbon Nanomaterials: Synthesis, Functionalization and Sensing Applications

Recent advances in nanomaterial design and synthesis has resulted in robust sensing systems that display superior analytical performance. The use of nanomaterials within sensors has accelerated new routes and opportunities for the detection of analytes or target molecules. Among others, carbon-based sensors have reported biocompatibility, better sensitivity, better selectivity and lower limits of detection to reveal a wide range of organic and inorganic molecules. Carbon nanomaterials are among the most extensively studied materials because of their unique properties spanning from the high specific surface area, high carrier mobility, high electrical conductivity, flexibility, and optical transparency fostering their use in sensing applications. In this paper, a comprehensive review has been made to cover recent developments in the field of carbon-based nanomaterials for sensing applications. The review describes nanomaterials like fullerenes, carbon onions, carbon quantum dots, nanodiamonds, carbon nanotubes, and graphene. Synthesis of these nanostructures has been discussed along with their functionalization methods. The recent application of all these nanomaterials in sensing applications has been highlighted for the principal applicative field and the future prospects and possibilities have been outlined.

Facile synthesis of doped CxNy QDs as photoluminescent matrix for direct detection of hydroquinone

In this work, we are reporting facile hydrothermal synthesis of a highly photoluminescent doped carbon nitride quantum dots (C_xN_yQDs) and implied it for direct detection of hydroquinone (H₂Q) by photoluminescence quenching phenomenon. Oxygen and sulphur moieties are regarded as dopant species in C_xN_yQDs and sourced from cheap solid precursors viz. cysteine and maleic acid. Morphological studies of C_xN_yQDs have done by SEM and TEM techniques, while structural analysis has carried out using FTIR, XPS, EDS and UV-Visible spectroscopy. The strong tendency of dispersivity of this QD in water has revealed by its zeta potential value of -32.4 mV. Optical properties of the as-prepared QDs have optimized at different excitation wavelengths. The photoluminescence stability of the dispersion is tested in various pH solutions and under continuous UV irradiation (365 nm). After that, sensing property is observed in quenching of photoluminescence feature of as-prepared QDs by direct addition of various concentrations of H₂Q. We obtained lower detection limit (LOD) of 50 nM (S/N = 3) in linear range from 12 to 57.5 μM. The reduction in photoluminescence of QDs may be attributed to electron transfer from QDs to oxidized H₂Q via -S^- and -COO^- groups present at its surface. Further, as-prepared QDs matrix exhibited high selectivity for hydroquinone over a range of potential interfering agents. Thus, the present work shows cost-effective facile synthesis of highly stable O- and S-doped carbon nitride (C_xN_y) quantum dots as promising photoluminescent sensor for pollutant hydroquinone without help of any enzyme or polymer assisted system.

A glassy carbon electrode modified with cerium phosphate nanotubes for the simultaneous determination of hydroquinone, catechol and resorcinol

A nafion film containing cerium phosphate nanotubes was pasted onto a glassy carbon electrode (GCE) to obtain a sensor for hydroquinone (HQ). The morphologies and components of the coating were characterized by transmission electron microscopy, scanning electron microscopy and energy-dispersive spectroscopy. Cyclic voltammetry and differential pulse voltammetry (DPV) showed the specific surface of the electrode to be significantly increased and the electron transfer rate to be accelerated. The modified GCE was applied to the determination of hydroquinone (HQ) via DPV. The oxidation current increases linearly in the 0.23 μM to 16 mM HQ concentration range which is as wide as five orders of magnitude. The limit of detection is 0.12 μM (based on a signal-to-noise ratio of 3), and the sensitivity is 1.41 μA·μM^-1 cm^-2. The method was further applied to the simultaneous determination of HQ, catechol and resorcinol. The potentials for the three species are well separated (20, 134, and 572 mV vs SCE). Average recoveries from (spiked) real water samples are between 95.2 and 107.0%, with relative standard deviations of 0.9~2.7% (for n = 3) at three spiking levels. The method was validated by independent assays using HPLC. Graphical abstract ᅟ.

Sensitive detection of hydroquinone using exfoliated graphene-Au/glassy carbon modified electrode

Graphene nanosheets (EGr) were electrochemically prepared through one-step exfoliation of a graphite rod in a mixture of H₂SO₄:HNO₃ (3:1) at low bias (4 V). Subsequently, gold nanoparticles were attached to the graphene surface (EGr-Au) by the reduction of the metal precursor (HAuCl₄) in aqueous solution containing dispersed graphene sheets. According to the XRD investigation, the synthesized material consists of a mixture of few-layer (86%) and multi-layer (14%) graphene. The interlayer distance was found to be in the range of 0.466-0.342 nm, which is larger than the interlayer distance in graphite (0.335 nm). The average size of gold nanoparticles in the EGr-Au sample was 24 nm, in excellent agreement with the TEM results. The synthesized material was then employed to modify a glassy carbon (GC) substrate, in order to obtain a modified electrode (GC/EGr-Au). Next, the electrochemical behavior of hydroquinone (HQ) in the presence and absence of interfering species, catechol (CAT) and bisphenol A (BPA) was studied and the corresponding calibration curves were plotted. Thus, in solutions without interfering species, the GC/EGr-Au electrode has a wide linear range (3 × 10^-7-10^-4 M), high sensitivity (0.089 A M^-1) and low detection limit (LOD = 10^-7 M; S/N = 3). The presence of either catechol or bisphenol A leads to the increase of LOD to 2 × 10^-7 M, and in addition changes the electrode sensitivity, up to 0.146 A M^-1.

Ecofriendly preparation of graphene sheets decorated with an ethylenediamine copper(ii) complex composite modified electrode for the selective detection of hydroquinone in water

A reduced graphene oxide decorated copper(ii) ethylenediamine complex composite modified electrode was applied for the electrochemical determination of hydroquinone.

Kinetic and Mechanistic Investigation of Electrochemical Oxidation of Hydroquinones in the Absence and Presence of 2-acetyl-gamma-butyrolactone

Electrochemical oxidation of hydroquinones (1a,b) was studied in the presence of 2-acetyl-gamma-butyrolactone (3) as nucleophile in phosphate buffer solution (pH 7.0 and c = 0.15 mol L−1):ethanol (80: 20), using cyclic voltammetry and controlled potential coulometry. The results indicated that the p-benzoquinone derived from (1a,b) participates in 1,4-Michael addition reaction with 3 via an EC mechanism which produces the relatively new hydroquinone derivatives (5a,b). The electrochemical synthesis of (5a,b) has been successfully performed on carbon rod electrodes in an undivided cell. Furthermore, the observed homogeneous rate constants of the reaction between hydroquinones and 2-acetyl-gamma-butyrolactone were estimated by comparing the experimental cyclic voltammograms curves with those digitally simulated.

A graphene-based electrochemical sensor for rapid determination of phenols in water

A glassy carbon electrode (GCE) coated with a graphene/polymer film was fabricated for rapid determination of phenols in aqueous solutions. The electrochemical behavior of different phenols at the graphene/polymer-coated GCE was also investigated. In PBS buffer solution with a pH of 6.5, hydroquinone exhibits a well-defined reduction peak at the modified GCE. Based on this, an electrochemical method for the direct determination of phenols is proposed. Investigating different parameters revealed the optimized detection conditions for the electrode are a scan rate of 50 mV/s, dosage of graphene-polyaniline of 8 μL, dosage of tyrosinase of 3 μL, and pH of 6.5. Under the optimal conditions, the reduction peak current varies linearly with the concentration of phenols, with a linear regression equation of I (10(-6)A) = -4.887 × 10(-4)C (mol/L)-5.331 × 10(-6) with a correlation coefficient of 0.9963 and limit of detection (S/N = 3) of 2.00 × 10(-4) mol/L. The electrochemical sensor is also used to detect phenols in actual samples, where it shows great promise for rapid, simple and quantitative detection of phenols.