Electrochemical Detection of Dihydroxybenzene Isomers at a Pencil Graphite Based Electrode

In this work, an HB pencil electrode (HBPE) was electrochemically modified by amino acids (AAs) glycine (GLY) and aspartic acid (ASA) and designated as GLY-HB and ASA-HB electrodes. They were used in the detection of dihydroxybenzene isomers (DHBIs) such as hydroquinone (HQ), catechol (CC), and resorcinol (RS), by cyclic voltammetry (CV), and by differential pulse voltammetry. HBPE was characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy. These three electrodes showed a linear relationship of current with concentration of DHBIs, and the electrochemical processes were diffusion controlled in all cases. In simultaneous detection, the limit of detection, based on signal-to-noise ratio (S/N = 3), for HQ, CC, and RS was 12.473, 16.132, and 25.25 μM, respectively, at bare HBPE; 5.498, 7.119, and 14.794 μM, respectively, at GLY-HB; and 22.459, 25.478, and 38.303 μM, respectively, at ASA-HB. The sensitivity for HQ, CC, and RS was 470.481, 363.781, and 232.416 μA/mM/cm², respectively, at bare HBPE; 364.785, 282.712, and 135.560 μA/mM/cm², respectively, at GLY-HB; and 374.483, 330.108, and 219.574, respectively, at ASA-HB. The interference studies clarified the suitability and reliability of the electrodes for the detection of HQ, CC, and RS in an environmental system. Real sample analysis was done using tap water, and the proposed electrodes expressed recovery with high reproducibility. Meanwhile, these three electrodes have excellent sensitivity and selectivity, which can be used as a promising technique for the detection of DHBIs simultaneously.

Catechol sensor based on pristine and transition metal embedded holey graphyne: a first-principles density functional theory study

To develop a highly sensitive and selective biosensor for detecting noxious biomolecules from the environment, we examined catechol (Cc) adsorption in pristine and transition metal (TM = Sc, Cu, and Pd) embedded 2D holey graphyne (hGY) monolayers using the first-principles density functional theory method. The interaction between Cc and the pristine hGY is purely weak, and hence the response of the sensing device will be difficult to detect. Therefore, the TM doping strategy is adopted to improve the sensitivity. According to our findings, Sc binds strongly to the hGY monolayer, with a binding energy of -4.09 eV and a charge transfer of 1.89e from the valence orbitals of Sc to the C 2p orbitals. Later on, the Cc adsorption on the TM-embedded hGY was investigated. The interaction of Cc with the transition metal involves charge transfer from Cc to the metal d orbital. A large binding energy of -3.22 eV and a significant charge transfer of about 0.9e from the O 2p orbitals of Cc to the valence orbital of Sc suggest that the Sc embedded hGY monolayer is a good choice for the efficient sensing of Cc molecules. Furthermore, ab initio MD simulations confirmed the structural stability of the Sc + hGY system at room temperature. We strongly believe that this theoretical work will aid the experimentalists in designing and developing 2D semiconducting nanolayer-based biosensors for commercial purposes.

Recent Developments in Polymer Nanocomposite-Based Electrochemical Sensors for Detecting Environmental Pollutants

The human population is generally subjected to diverse pollutants and contaminants in the environment like those in the air, soil, foodstuffs, and drinking water. Therefore, the development of novel purification techniques and efficient detection devices for pollutants is an important challenge. To date, experts in the field have designed distinctive analytical procedures for the detection of pollutants including gas chromatography/mass spectrometry and atomic absorption spectroscopy. While the mentioned procedures enjoy high sensitivity, they suffer from being laborious, expensive, require advanced skills for operation, and are inconvenient to deploy as a result of their massive size. Therefore, in response to the above-mentioned limitations, electrochemical sensors are being developed that enjoy robustness, selectivity, sensitivity, and real-time measurements. Considerable advancements in nanomaterials-based electrochemical sensor platforms have helped to generate new technologies to ensure environmental and human safety. Recently, investigators have expanded considerable effort to utilize polymer nanocomposites for building the electrochemical sensors in view of their promising features such as very good electrocatalytic activities, higher electrical conductivity, and effective surface area in comparison to the traditional polymers. Herein, the first section of this review briefly discusses the most important methods for polymer nanocomposites synthesis, such as in situ polymerization, direct mixing of polymer and nanofillers (melt-mixing and solution-mixing), sol-gel, and electrochemical methods. It then summarizes the current utilization of polymer nanocomposites for the preparation of electrochemical sensors as a novel approach for monitoring and detecting environmental pollutants which include heavy metal ions, pesticides, phenolic compounds, nitroaromatic compounds, nitrite, and hydrazine in different mediums. Finally, the current challenges and future directions for the polymer nanocomposites-based electrochemical sensing of environmental pollutants are outlined.

Electrochemical Determination of Adrenaline Using MXene/Graphite Composite Paste Electrodes

MXene/graphite composite paste electrode (MXene/GCPE)-based electrochemical sensor has been fabricated for the detection of adrenaline. The electrode exhibits a sensitive response to adrenaline in phosphate buffer solution of pH 7.4, and its catalytic activity is much higher than that of the bare graphite paste electrode. The electron-transfer reaction of MXene/GCPE is a diffusion controlled process. The graph of concentration of adrenaline with the peak current exhibits two linearities, one in the lower and other in the higher concentration range with a detection limit of 9.5 nM. The simultaneous analyses of adrenaline, ascorbic acid, and serotonin reveal that the fabricated electrode could separate the overlapped cyclic voltammetric peaks of these ternary mixtures. This electrode has been further employed in the detection of adrenaline in pharmaceutical samples with 99.2-100.8% recoveries.

Gold atomic cluster mediated electrochemical aptasensor for the detection of lipopolysaccharide

We have constructed an aptamer immobilized gold atomic cluster mediated, ultrasensitive electrochemical biosensor (Apt/AuAC/Au) for LPS detection without any additional signal amplification strategy. The aptamer self-assemble onto the gold atomic clusters makes Apt/AuAC/Au an excellent platform for the LPS detection. Differential pulse voltammetry and EIS were used for the quantitative LPS detection. The Apt/AuAC/Au sensor offers an ultrasensitive and selective detection of LPS down to 7.94 × 10^-21M level with a wide dynamic range from 0.01 attomolar to 1pM. The sensor exhibited excellent selectivity and stability. The real sample analysis was performed by spiking the diluted insulin sample with various concentration of LPS and obtained recovery within 2% error value. The sensor is found to be more sensitive than most of the literature reports. The simple and easy way of construction of this sensor provides an efficient and promising detection of an even trace amount of LPS.

Flow injection amperometric sandwich-type aptasensor for the determination of human leukemic lymphoblast cancer cells using MWCNTs-Pdnano/PTCA/aptamer as labeled aptamer for the signal amplification

In this research, we demonstrated a flow injection amperometric sandwich-type aptasensor for the determination of human leukemic lymphoblasts (CCRF-CEM) based on poly(3,4-ethylenedioxythiophene) decorated with gold nanoparticles (PEDOT-Au_nano) as a nano platform to immobilize thiolated sgc8c aptamer and multiwall carbon nanotubes decorated with palladium nanoparticles/3,4,9,10-perylene tetracarboxylic acid (MWCNTs-Pd_nano/PTCA) to fabricate catalytic labeled aptamer. In the proposed sensing strategy, the CCRF-CEM cancer cells were sandwiched between immobilized sgc8c aptamer on PEDOT-Au_nano modified surface electrode and catalytic labeled sgc8c aptamer (MWCNTs-Pd_nano/PTCA/aptamer). After that, the concentration of CCRF-CEM cancer cells was determined in presence of 0.1 mM hydrogen peroxide (H₂O₂) as an electroactive component. The attached MWCNTs-Pd_nano nanocomposites to CCRF-CEM cancer cells amplified the electrocatalytic reduction of H₂O₂ and improved the sensitivity of the sensor to CCRF-CEM cancer cells. The MWCNT-Pd_nano nanocomposite was characterized with transmission electron microscopy (TEM) and energy dispersive X-ray (EDX). The electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used to confirm the stepwise changes in the electrochemical surface properties of the electrode. The proposed sandwich-type electrochemical aptasensor exhibited an excellent analytical performance for the detection of CCRF-CEM cancer cells ranging from 1.0 × 10¹ to 5.0 × 10⁵ cells mL^-1. The limit of detection was 8 cells mL^-1. The proposed aptasensor showed high selectivity toward CCRF-CEM cancer cells. The proposed aptasensor was also applied to the determination of CCRF-CEM cancer cells in human serum samples.

A Disposable Amperometric Sensor Based on High-Performance PEDOT:PSS/Ionic Liquid Nanocomposite Thin Film-Modified Screen-Printed Electrode for the Analysis of Catechol in Natural Water Samples

A conducting polymer-based composite material of poly(3,4-ethylenedioxythiophene) (PEDOT): poly(4-styrenesulfonate) (PSS) doped with different percentages of a room temperature ionic liquid (IL), 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF₄]), was prepared and a very small amount of the composite (2.0 µL) was drop-coated on the working area of a screen-printed carbon electrode (SPCE). The SPCE, modified with PEDOT:PSS/IL composite thin-film, was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), profilometry and sessile contact angle measurements. The prepared PEDOT:PSS/IL composite thin-film exhibited a nano-porous microstructure and was found to be highly stable and conductive with enhanced electrocatalytic properties towards catechol, a priority pollutant. The linear working range for catechol was found to be 0.1 µM-330.0 µM with a sensitivity of 18.2 mA·mM·cm^-2 and a calculated limit of detection (based on 3× the baseline noise) of 23.7 µM. When the PEDOT:PSS/IL/SPCE sensor was used in conjunction with amperometry in stirred solution for the analysis of natural water samples, the precision values obtained on spiked samples (20.0 µM catechol added) (n = 3) were 0.18% and 0.32%, respectively, with recovery values that were well over 99.0%.

A novel Laccase Biosensor based on Laccase immobilized Graphene-Cellulose Microfiber Composite modified Screen-Printed Carbon Electrode for Sensitive Determination of Catechol

In the present work, we demonstrate the fabrication of laccase biosensor to detect the catechol (CC) using laccase immobilized on graphene-cellulose microfibers (GR-CMF) composite modified screen printed carbon electrode (SPCE). The direct electrochemical behavior of laccase was investigated using laccase immobilized different modified SPCEs, such as GR/SPCE, CMF/SPCE and GR-CMF/SPCE. Compared with laccase immobilized GR and CMF modified SPCEs, a well-defined redox couple of Cu^I/Cu^II for laccase was observed at laccase immobilized GR-CMF composite modified SPCE. Cyclic voltammetry results show that the as-prepared biosensor has 7 folds higher catalytic activity with lower oxidation potential towards CC than SPCE modified with GR-CMF composite. Under optimized conditions, amperometric i-t method was used for the quantification of CC, and the amperometric response of the biosensor was linear over the concertation of CC ranging from 0.2 to 209.7 μM. The sensitivity, response time and the detection limit of the biosensor for CC is 0.932 μMμA⁻¹ cm⁻², 2 s and 0.085 μM, respectively. The biosensor has high selectivity towards CC in the presence of potentially active biomolecules and phenolic compounds. The biosensor also accessed for the detection of CC in different water samples and shows good practicality with an appropriate repea.

An electrochemically aminated glassy carbon electrode for simultaneous determination of hydroquinone and catechol

A simple strategy based on the easy modification of GCE by pre-electrolyzing it in ammonium carbamate aqueous solution was employed for the simultaneous determination of HQ and CC.

Glucose sensing by a glassy carbon electrode modified with glucose oxidase and a magnetic polymeric nanocomposite

Glucose sensing by using of glucose oxidase and a biocompatible poly(p-phenylenediamine)-based nanocomposite.

Investigation of morphologies and characterization of rare earth metal samarium hexacyanoferrate and its composite with surfactant intercalated graphene oxide for sensor applications

Different morphologies of electrochemically deposited samarium hexacyanoferrate.