Electrodeposited poly(3,4-ethylenedioxythiophene) doped with graphene oxide for the simultaneous voltammetric determination of ascorbic acid, dopamine and uric acid

Sensitive and selective electrochemical aptasensing method for the voltammetric determination of dopamine based on AuNPs/PEDOT-ERGO nanocomposites

In this study, the effects of phosphate buffered saline (PBS) and graphene oxide (GO) as supporting electrolytes and dopants on the electropolymerization process of 3,4-ethylenedioxythiophene (EDOT) on glassy carbon electrode (GCE) were investigated. It was found that the PEDOT-ERGO nanocomposites obtained by a simple one-step electrochemical redox polymerization method using GO as the only supporting electrolyte and dopant possess excellent electrochemical properties. Then, the PEDOT-ERGO nanocomposites were used as electrode substrate to further modify with AuNPs, and an electrochemical aptasensor based on AuNPs/PEDOT-ERGO nanocomposites was successfully constructed for the sensitive and selective determination of dopamine (DA). Comparison of the cyclic voltammetric response of different neurotransmitters before and after aptamer assembly showed that the aptamer significantly improved the selectivity of the sensor for DA. The low detection limit of 1.0 μM (S/N = 3) indicated the good electrochemical performance of the PEDOT-ERGO nanocomposite film. Moreover, the aptasensor showed good recoveries in 50-fold diluted fetal bovine serum with RSD values all less than 5 % (n = 5), indicating that the PEDOT-ERGO nanocomposites and the electrochemical aptasensor have promising applications in other neurochemicals assay and biomedical analysis.

Universal Covalent Grafting Strategy of an Aptamer on a Carbon Fiber Microelectrode for Selective Determination of Dopamine In Vivo

The chemical information on brain science provided by electrochemical sensors is critical for understanding brain chemistry during physiological and pathological processes. A major challenge is the selectivity of electrochemical sensors in vivo. This work developed a universal covalent grafting strategy of an aptamer on a carbon fiber microelectrode (CFE) for selective determination of dopamine in vivo. The universal strategy was proposed by oxidizing poly(tannic acid) (pTA) to form an oxidized state (pTAox) and then coupling a nucleophilic sulfhydryl molecule of the dopamine-binding mercapto-aptamer with the o-quinone moiety of pTAox based on click chemistry for the interfacial functionalization of the CFE surface. It was found that the universal strategy proposed could efficiently graft the aptamer on a glassy carbon electrode, which was verified by using electroactive 6-(ferrocenyl) hexanethiol as a redox reporter. The amperometric method using a fabricated aptasensor for the determination of dopamine was developed. The linear range of the aptasensor for the determination of dopamine was 0.2-20 μM with a sensitivity of 0.09 nA/μM and a limit of detection of 88 nM (S/N = 3). The developed method has high selectivity originating from the specific recognition of the aptamer in concert with the cation-selective action of pTA and could be easily applicable to probe dopamine dynamics in the brain. Furthermore, complex vesicle fusion modes were first observed at the animal level. This work demonstrated that the covalently grafted immobilization strategy proposed is promising and could be extended to the in vivo analysis of other neurochemicals.

Ultrasensitive, Label-Free Voltammetric Detection of Dibutyl Phthalate Based on Poly-l-lysine/poly(3,4-ethylenedioxythiophene)-porous Graphene Nanocomposite and Molecularly Imprinted Polymers

Development of an efficient technique for accurate and sensitive dibutyl phthalate (DBP) determination is crucial for food safety and environment protection. An ultrasensitive molecularly imprinted polymers (MIP) voltammetric sensor was herein engineered for the specific determination of DBP using poly-l-lysine/poly(3,4-ethylenedioxythiophene)/porous graphene nanocomposite (PLL/PEDOT-PG) and poly(o-phenylenediamine)-imprinted film as a label-free and sensing platform. Fabrication of PEDOT-PG nanocomposites was achieved through a simple liquid-liquid interfacial polymerization. Subsequently, poly-l-lysine (PLL) functionalization was employed to enhance the dispersibility and stability of the prepared PEDOT-PG, as well as promote its adhesion on the sensor surface. In the presence of DBP, the imprinted poly(o-phenylenediamine) film was formed on the surface of PLL/PEDOT-PG. Investigation of the physical properties and electrochemical behavior of the MIP/PLL/PEDOT-PG indicates that the incorporation of PG into PEDOT, with PLL uniformly wrapping its surface, significantly enhanced conductivity, carrier mobility, stability, and provided a larger surface area for specific recognition sites. Under optimal experimental conditions, the electrochemical response exhibited a linear relationship with a logarithm of DBP concentration within the range of 1 fM to 5 µM, with the detection limit as low as 0.88 fM. The method demonstrated exceptional stability and repeatability and has been successfully applied to quantify DBP in plastic packaging materials.

Hydrogen Peroxide and Dopamine Sensors Based on Electrodeposition of Reduced Graphene Oxide/Silver Nanoparticles

In this work, silver nanoparticles (AgNPs)/reduced graphene oxide (rGO) nanocomposites were electrodeposited on glassy carbon electrodes (GCE) to construct electrochemical sensors for the detection of hydrogen peroxide (H2O2) and dopamine (DA). The AgNPs were synthesized on graphene oxide (GO) by the hydrothermal method, followed by the reduction of the GO during the electrodeposition process, resulting in the formation of the nanocomposites on the surface of the electrodes. The generation of AgNPs on the graphene sheets was verified by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The AgNPs/rGO/GCE showed a linear response to H2O2 in the range of 5 μM to 620 μM, with a sensitivity of 49 μA mM-1cm-2 and a limit of detection (LOD) of 3.19 μA. The linear response of the AgNPs/rGO/GCE to DA ranged from 1 μM to 276 μM, the sensitivity was 7.86 μA mM-1cm-2, and the LOD was 0.18 μM. Furthermore, DA and H2O2 were detected simultaneously in the same solution without interferences, and the sensors displayed good stability over time. The preparation method for the sensors is relatively eco-friendly, convenient, and efficient, exhibiting great potential for sensitive detection of DA and H2O2.

Electrochemical sensor using cobalt oxide-modified porous carbon for uric acid determination

An electrochemical sensor for the detection of uric acid was constructed using cobalt oxide-modified porous carbon@multi-walled carbon nanotube (MWCNTs) composite material for the modification of the electrode. Firstly, ZIF-67 is generated on carbon nanotubes using the surfactant cetylammonium bromide (CTAB) as template. The vesicles generated by CTAB act as nucleation sites for the in situ growth of ZIF-67. Then, cobalt oxide-modified porous carbon was obtained after high-temperature carbonization of ZIF-67, leading to the formation of cobalt oxide-modified porous carbon@MWCNT composite materials. Co-N and Co-O active sites on the composite material can improve the oxidation of uric acid on the electrode surface, leading to enhanced sensitivity and selectivity for uric acid detection. The sensor has a good linear range from 1 to 40 μM for uric acid detection with a detection limit of 0.09 μM. The sensor was utilized for determination of uric acid in actual serum samples.

Fabrication of Hybrid Electrodes by Laser-Induced Forward Transfer for the Detection of Cu2+ Ions

Composites based on poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS)-graphene oxide (GO) are increasingly considered for sensing applications. In this work we aim at patterning and prototyping microscale geometries of PEDOT:PSS: GO composites for the modification of commercially available electrochemical sensors. Here, we demonstrate the laser-induced forward transfer of PEDOT:PSS: GO composites, a remarkably simple procedure that allows for the fast and clean transfer of materials with high resolution for a wide range of laser fluences (450-750 mJ/cm²). We show that it is possible to transfer PEDOT:PSS: GO composites at different ratios (i.e., 25:75 %wt and 50:50 %wt) onto flexible screen-printed electrodes. Furthermore, when testing the functionality of the PEDOT:PSS: GO modified electrodes via LIFT, we could see that both the PEDOT:PSS: GO ratio as well as the addition of an intermediate release layer in the LIFT process plays an important role in the electrochemical response. In particular, the ratio of the oxidation peak current to the reduction peak current is almost twice as high for the sensor with a 50:50 %et PEDOT:PSS: GO pixel. This direct transfer methodology provides a path forward for the prototyping and production of polymer: graphene oxide composite based devices.

On-Chip Electromembrane Surrounded Solid Phase Microextraction for Determination of Tricyclic Antidepressants from Biological Fluids Using Poly(3,4-ethylenedioxythiophene)-Graphene Oxide Nanocomposite as a Fiber Coating

In the present study, on-chip electromembrane surrounded solid phase microextraction (EM-SPME) was employed in the determination of tricyclic antidepressants (TCAs), including amitriptyline, nortriptyline, imipramine, desipramine, maprotiline, and sertraline, from various biological fluids. In this regard, poly(3,4-ethylenedioxythiophene)-graphene oxide (PEDOT-GO) was electrodeposited on an SPME fiber as a conductive coating, then the fiber played the acceptor-electrode role during the extraction. Thus, the immigration of the analytes under the influence of an electric field and their absorption onto the fiber coating were accomplished simultaneously. Under the optimized conditions, the limits of detection for the target analytes were acquired in the range of 0.005-0.025 µg L^-1 using gas chromatography-mass spectrometry. The linearity of the method was 0.010-500 µg L^-1 for the imipramine and sertraline, 0.025-500 µg L^-1 for the amitriptyline, nortriptyline, and desipramine, and 1.000-250 µg L^-1 for the maprotiline (R² ≥ 0.9984). Moreover, this method provided suitable precision and fiber-to-fiber reproducibility, with RSDs ≤ 8.4%. The applicability of the proposed setup was eventually investigated for extraction of the drugs from human bone marrow aspirate, urine, plasma, and well water samples, in which satisfactory relative recoveries, from 93-105%, were obtained.

Functionalization of Graphene Derivatives with Conducting Polymers and Their Applications in Uric Acid Detection

In this article, we review recent progress concerning the development of sensorial platforms based on graphene derivatives and conducting polymers (CPs), alternatively deposited or co-deposited on the working electrode (usually a glassy carbon electrode; GCE) using a simple potentiostatic method (often cyclic voltammetry; CV), possibly followed by the deposition of metallic nanoparticles (NPs) on the electrode surface (ES). These materials have been successfully used to detect an extended range of biomolecules of clinical interest, such as uric acid (UA), dopamine (DA), ascorbic acid (AA), adenine, guanine, and others. The most common method is electrochemical synthesis. In the composites, which are often combined with metallic NPs, the interaction between the graphene derivatives-including graphene oxide (GO), reduced graphene oxide (RGO), or graphene quantum dots (GQDs)-and the CPs is usually governed by non-covalent functionalization through π-π interactions, hydrogen bonds, and van der Waals (VW) forces. The functionalization of GO, RGO, or GQDs with CPs has been shown to speed up electron transfer during the oxidation process, thus improving the electrochemical response of the resulting sensor. The oxidation mechanism behind the electrochemical response of the sensor seems to involve a partial charge transfer (CT) from the analytes to graphene derivatives, due to the overlapping of π orbitals.

Precise and quick detection of ascorbic acid and eugenol in fruits, pharmaceuticals and medicinal herbs using hydroxyapatite-titanium dioxide nanocomposite-based electrode

Ascorbic acid (AA) and eugenol (EUG) are well-known antioxidants found in several fruits, spices and herbs. In particular, the EUG, one of the major phytocompounds present in clove, acts as pro-oxidant or anti-oxidant depending on its concentration. Considering the medical importance of AA and EUG and its extensive usage in the form of food and medicine, we have developed a voltammetric sensor based on hydroxyapatite-TiO₂ composite modified GCE for their selective and simultaneous determination over very wide linear range of 2.78-2490 µM for AA and 1.4-78 µM for EUG with the LODs of 63.3 nM and 94 nM respectively. Practical applicability of the prepared electrode has been demonstrated by detecting AA and EUG in lemon juice, vitamin tablet, clove oil and Kabasura Kudineer, an herbal decoction used as an immunity booster against number of diseases including Covid-19. The proposed HAP-TiO₂/GCE shall be useful for food and pharmaceutical industries.

Electrochemical aptasensor based on electrodeposited poly(3,4-ethylenedioxythiophene)-graphene oxide coupled with Au@Pt nanocrystals for the detection of 17β-estradiol

An electrochemical aptasensor is reported for the sensitive and specific monitoring of 17β-estradiol (E2) based on the modification of electrodeposited poly(3,4-ethylenedioxythiophene) (PEDOT)-graphene oxide (GO) coupled with Au@Pt nanocrystals (Au@Pt). With excellent conductivity, chemical stability and active sites, the PEDOT-GO nanocomposite film was firstly in situ polymerized on the glassy carbon electrode by cyclic voltammetry. Subsequently, one-step synthesized Au@Pt were decorated on the conductive polymer, providing a platform for immobilizing the aptamer and enhancing the detecting sensitivity. With the addition of E2, since the interfacial electron transfer process was retarded by the E2-aptamer complex, the differential pulse voltammetry signal decreased gradually. Under optimum conditions, the calibration curve of E2 exhibited a linear range between 0.1 pM and 1 nM, with a low detection limit (S/N = 3) of 0.08 pM. The developed aptasensor showed admiring selectivity, stability, and reproducibility. It was tested in human serum, lake water and tap water samples after low-cost and simple pretreatment. Consequently, the developed platform could provide a new design thought for ultrasensitive detection of E2 in clinical and environmental samples.

Overoxidized poly(3,4-ethylenedioxythiophene)-gold nanoparticles-graphene-modified electrode for the simultaneous detection of dopamine and uric acid in the presence of ascorbic acid

An innovative, ternary nanocomposite composed of overoxidized poly(3,4-ethylenedioxythiophene) (OPEDOT), gold nanoparticles (AuNPs), and electrochemically reduced graphene oxide (ERGO) was prepared on a glassy carbon electrode (GCE) (OPEDOT–AuNPs–ERGO/GCE) through homogeneous chemical reactions and heterogeneous electrochemical methods. The morphology, composition, and structure of this nanocomposite were characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The electrochemical properties of the OPEDOT–AuNPs–ERGO/GCE were investigated by cyclic voltammetry using potassium ferricyanide and hexaammineruthenium(III) chloride redox probe systems. This modified electrode shows excellent electro-catalytic activity for dopamine (DA) and uric acid (UA) under physiological pH conditions, but inhibits the oxidation of ascorbic acid (AA). Linear voltammetric responses were obtained when DA concentrations of approximately 4.0–100 μM and UA concentrations of approximately 20–100 μM were used. The detection limits (S/N=3) for DA and UA were 1.0 and 5.0 μM, respectively, under physiological conditions and in the presence of 1.0 mM of AA. This developed method was applied to the simultaneous detection of DA and UA in human urine, where satisfactory recoveries from 96.7% to 105.0% were observed. This work demonstrates that the developed OPEDOT–AuNPs–ERGO ternary nanocomposite, with its excellent ion-selectivity and electro-catalytic activity, is a promising candidate for the simultaneous detection of DA and UA in the presence of AA in physiological and pathological studies.

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Facile preparation of graphene-based hybrid composite OPEDOT–AuNPs–ERGO onto GCE.

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The OPEDOT–AuNPs–ERGO/GCE was endued with excellent electrocatalytic activity and ion-selectivity.

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The OPEDOT–AuNPs–ERGO/GCE was found highly selective and sensitive determination of DA and UA in the presence of AA.

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The method is expected to be applied to the detection of DA and UA under physiological and pathological conditions.

Construction of cationic polyfluorinated azobenzene/reduced graphene oxide for simultaneous determination of dopamine, uric acid and ascorbic acid

A highly sensitive cationic polyfluorinated azobenzene/reduced graphene oxide (C₃F₇-azo⁺/RGO) nanocomposite electrochemical sensor for simultaneous detection of dopamine (DA), ascorbic acid (AA) and uric acid (UA) was successfully synthesized using a facile exfoliation/restacking method. The nanocomposite is self-assembled from oppositely charged graphene oxide nanosheets (GO) and polyfluorinated azobenzene cations (C₃F₇-azo⁺), and then obtained by electrochemical reduction. The structure and electrochemical properties were characterized by X-ray diffraction (XRD), energy dispersive spectrometer analysis (EDS), transmission electron microscope (TEM) and scanning electron microscope (SEM). The electrochemical property of C₃F₇-azo⁺/RGO was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). It can be clearly seen from experimental results that C₃F₇-azo⁺/RGO-modified electrode (C₃F₇-azo⁺/RGO/GCE) can detect DA, AA and UA simultaneously, and has good stability and anti-interference performance. The detection limits are 65 nM, 8 nM and 11 nM for DA, AA and UA in the ranges 57.28-134.28 μM, 0.04-6.01 μM, 9.23-23.45 μM, respectively.

Electrochemical sensor formed from poly(3,4-ethylenedioxyselenophene) and nitrogen-doped graphene composite for dopamine detection

In this study, an electrochemical sensor for dopamine (DA) detection has been developed by a composite of poly(3,4-ethylenedioxyselenophene) (PEDOS) and nitrogen-doped graphene (PEDOS/N-Gr) using an in situ polymerization method. Its structure and properties were then compared with those of the composites of poly(3,4-ethylenedioxythiophene) (PEDOT)/nitrogen-doped graphene (PEDOT/N-Gr), which were prepared by the same methods. FT-IR, Raman, UV-vis, XPS, mapping and SEM investigated the structure and morphology of these composites. These revealed that PEDOS/N-Gr had a higher conjugation degree than PEDOT/N-Gr. The synergetic effect between PEDOS and N-Gr was beneficial for the formation of a homogenous surface coating. The cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods were conducted for electrochemical detection of DA. Compared with PEDOT/N-Gr, the PEDOS/N-Gr displayed an enhanced sensitivity and electrocatalytic performance for DA detection with linear ranges of 0.008-80 μM (PEDOT/N-Gr: 0.04-70 μM) and limits of detection (LOD) of 0.0066 μM (S/N = 3) (PEDOT/N-Gr: 0.018 μM (S/N = 3)).

Flexible sensor with electrophoretic polymerized graphene oxide/PEDOT:PSS composite for voltammetric determination of dopamine concentration

We demonstrate a novel, flexible sensor with graphene oxide/PEDOT:PSS (GO/PEDOT:PSS) composite for voltammetric determination of selective low levels of dopamine. The well-distributed GO and EDOT:PSS suspension in water were deposited simply and polymerized. Consequently, the EDOT:PSS provided a strong interaction between GO and PEDOT:PSS, and it also had well-tailored interfacial properties that allowed the highly selective and sensitive determination of DA. Since the interfacial net charge is well-constructed, the sensor satisfies both the requirements of selectivity and the highly sensitive detection of low amounts of DA. In the results, the sensor with the GO/PEDOT:PSS composite exhibited a low interfacial impedance of about 281.46 ± 30.95 Ω at 100 Hz and a high charge storage capacity (53.94 ± 1.08 µC/cm²) for the detection of dopamine. In addition, the interference from ascorbic acid was reduced effectively to a minimum by electrostatic charge repelling of the AA and the distinct difference for the oxidation peak of the UA. Due to the fact that the GO/PEDOT:PSS composite had a net negative charge and, enhanced interfacial properties, the sensor showed a dopamine detection limit of 0.008 μM and a sensitivity of 69.3 µA/µMcm².

E-Tongues/Noses Based on Conducting Polymers and Composite Materials: Expanding the Possibilities in Complex Analytical Sensing

Conducting polymers (CPs) are extensively studied due to their high versatility and electrical properties, as well as their high environmental stability. Based on the above, their applications as electronic devices are promoted and constitute an interesting matter of research. This review summarizes their application in common electronic devices and their implementation in electronic tongues and noses systems (E-tongues and E-noses, respectively). The monitoring of diverse factors with these devices by multivariate calibration methods for different applications is also included. Lastly, a critical discussion about the enclosed analytical potential of several conducting polymer-based devices in electronic systems reported in literature will be offered.

Lithium cobalt phosphate electrode for the simultaneous determination of ascorbic acid, dopamine, and serum uric acid by differential pulse voltammetry

Lithium cobalt phosphate (LCP) was prepared and modified on the surface of glassy carbon electrode (GCE) to fabricate the electrochemical sensor (LCP/GCE) for the simultaneous determination of ascorbic acid (AA), dopamine (DA), and serum uric acid (UA). The homogenous incorporation of carbon improved the conductivity of LCP. Benefiting from the small particle size distribution, LCP/GCE has a large active surface and responds to AA, DA, and UA sensitively and rapidly. For the simultaneous detection with differential pulse voltammetry the anodic peaks of AA, DA, and UA were well-separated and appeared at ~0 V, ~0.19 V, and ~ 0.33 V (vs. Ag/AgCl), respectively. The linear responses toward AA, DA, and UA were in the range 10 μM-8.0 mM, 10 nM-10 μM, and 0.020 μM-25 μM; the detection limits were estimated to be 8.10 μM, 7.50 nM, and 22.7 nM (S/N = 3), respectively. The excellent selectivity and reproducibility of LCP/GCE enable serum UA to be detected without the interference of AA and DA. The recoveries of DA and AA in the serum sample were in the range 95 to 111%. The results indicate that LCP has the potential to be developed as the sensing devices to be applied to in vitro diagnosis. The lithium-ion battery cathodic material, LCP with the excellent adsorption and catalytic behavior, was utilized to fabricate the electrochemical sensor for the sensitive and simultaneous detection of AA, DA, and UA, which achieved the low detection limits and the wide concentration ranges. LCP/GCE can be used for the quantitative detection of serum UA without the interference of DA and AA. In addition, the recoveries of DA and AA in human serum were satisfactory, which illustrate the reliability of LCP/GCE to be applied to in vitro diagnosis.

Electrodeposition of poly-ethylenedioxythiophene-graphene oxide nanocomposite in a stainless steel tube for solid-phase microextraction of letrozole in plasma samples

Coated stainless steel was used as an in-tube solid-phase microextraction for the extraction of letrozole from plasma samples. The coating process on the inner surface of the stainless steel was conducted by a simple electrodeposition process. The coated composite was prepared from 3,4-ethylenedioxythiophene and graphene oxide. In this composite, graphene oxide acts as an anion dopant and sorbent. The coated nanostructured polymer was characterized using different techniques. The operational factors affecting the extraction process, including pH, adsorption, and desorption time, the recycling flow rate of the sample solution, sample volume, desorption solvent type and its volume, and ionic strength were optimized to achieve the best extraction efficiency of the analyte. The total extraction time including adsorption and desorption steps was about 15.0 min. The developed method demonstrated a linear range of 5.0-1500.0 μg/L with a limit of detection of 1.0 μg/L. The repeatability of the developed extraction approach in terms of intraday, interday, and fiber to fiber was attained in the range of 4.9-8.3%. After finding the optimal conditions, the potential of the described approach for letrozole quantitation was investigated in plasma samples, and satisfactory results were obtained.

Nanocomposite based on Poly (para-phenylene)/Chemical Reduced Graphene Oxide as a Platform for Simultaneous Detection of Ascorbic Acid, Dopamine and Uric Acid

In this study, an efficient and simple designed nanohybrid created for individual and simultaneous detection of ascorbic acid (AA), dopamine (DA) and uric acid (UA). This nanohybrid is a combination of reduced graphene oxide (CRGO) and redox poly(para-phenylene) (Fc-ac-PP) modified in a lateral position with ferrrocenyl group CRGO/Fc-ac-PPP. The CRGO/Fc-ac-PPP nanohybrid demonstrated a synergistic effect resulting in a large conductivity, surface area and catalytic properties provided by the redox attached ferrocene. Moreover, this nanocomposite is able to detect individually as well as simultaneously AA, DA and UA in a co-existence system with defined and separated redox peaks oxidation. The linear response ranges for AA, DA and UA, when detected simultaneously, are 0.1-10000 μM, 0.0001-1000 μM and 0.1-10000 μM, respectively, and the detection limits (S/N = 3) are 0.046 μM, 0.2 nM and 0.013 μM, respectively. The proposed sensor shown satisfactory results when applied to real spiked urine samples for measuring the abnormal high or lowconcentration of AA, DA and UA in vivo.