Electroanalytical Determination of Paracetamol Using Pd Nanoparticles Deposited on Carboxylated Graphene Oxide Modified Glassy Carbon Electrode

The study presents a novel paracetamol (PA) sensor based on Pd nanoparticles (PdNPs) deposited on carboxylated graphene oxide (GO?COOH) and nafion (Nf) modified glassy carbon electrode (GCE). The morphologies of the as prepared composites were characterized using high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), and fourier transform infrared spectroscopy (FTIR). The experimental results demonstrated that Nf/GO?COOPd displayed excellent electrocatalytic response to the oxidation PA. The linear range was 0.04–800 μM for PA with limit of detection of 0.012 μM and excellent sensitivity of 232.89 μA mM^?1 cm^?2. By considering the excellent performance of Nf/GO?COOPd composite such as wider linear range, lower detection, better selectivity, repeatability, reproducibility, and storage stability, the prepared composite, especially GO?COOH support, with satisfactory electrocatalytic properties was a promising material for the modification of electrode material in electrochemical sensor and biosensor field.     

Pd‐Nanoparticle‐Supported,PDDA‐Functionalized Graphene as a Promising Catalyst for Alcohol Oxidation

Poly(diallyldimethylammonium chloride) (PDDA) has been employed as a modifying material for the development of new functional materials; then, the functionalized graphene was employed as a support for Pd nanoparticles through a facile method. The structures and morphologies of the as‐synthesized Pd/PDDA–graphene composites were extensively characterized by Raman spectroscopy, XRD, XPS, and TEM. Morphological observation showed that Pd NPs with average diameters of 4.4 nm were evenly deposited over the functionalized graphene sheets. Moreover, the electrochemical experiments indicated that the Pd/PDDA–graphene catalyst showed improved electrocatalytic activity toward alcohol‐oxidation reactions compared to the Pd/graphene and commercial Pd/C systems, as well as previously reported Pd‐based catalysts. This study demonstrates the great potential of PDDA‐functionalized graphene as a support for the development of metal–graphene nanocomposites for important applications in fuel cells.     

Synthesis of a Palladium-Graphene Material and Its Application for Formaldehyde Determination

A novel electrochemical sensor for formaldehyde determination was fabricated by using the Pd-graphene nanohybrides. Pd-graphene nanohybrids were prepared via a concise chemical reduction method. Raman spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM) were used for the characterization of structure and morphology of the nanohybrids. The result showed that Pd nanoparticles were uniformly dispersed and were well-separated on the graphene sheets. The Pd-graphene nanohybrids were dissolved in Nafion and modified on the glassy carbon electrode to fabricate the electrochemical sensor. This proposed electrochemical sensor performed excellent electrocatalytic activity toward formaldehyde oxidation in alkaline medium. The peak current was linearly related to the formaldehyde concentration in the range of 7.75 µM to 62.0 µM with the detection limit of 3.15 µM. The highly sensitive and robust graphene based Pd nanohybrids sensor offers a promising and practical tool for formaldehyde sensing and chemical analysis.     

An enhanced Nonenzymatic Electrochemical Glucose Sensor Based on Copper‐Palladium Nanoparticles Modified Glassy Carbon Electrodes

Novel copper‐palladium nanoparticles modified glassy carbon electrodes (Cu−Pd/GC) with enhanced nonenzymatic sensing for glucose were facilely prepared by one‐step electrodeposition. The structure and composition of the prepared nanoparticles were characterized by XRD, SEM, TEM and EDS, respectively. The electrode modified process was characterized by electrochemical impedance spectroscopy. Cyclic voltammetry and chronoamperometric experiments were used to evaluate the electrocatalytic activities of the electrodes toward glucose. The surface morphology and the electrocatalytic activities of Cu−Pd/GC was compared to Pd and Cu nanoparticles modified glassy carbon electrodes (Pd/GC and Cu/GC), respectively. Thanks to homogeneous distribution of Cu−Pd nanoparticles and the synergistic effect of Cu and Pd atoms, Cu−Pd/GC exhibited the highest sensitivity (298 μA mM⁻¹ cm⁻²) and the widest linear amperometric response (0.01 mM to 9.6 mM, R²=0.996) toward glucose compared to Pd/GC and Cu/GC. The detection limit of Cu−Pd/GC was 0.32 μM (S/N=3). In addition, the as‐prepared Cu−Pd/GC glucose sensor also exhibited exceptional capabilities of anti‐interference, reproducibility and long‐term stability. The as‐prepared sensor was also evaluated for determination of glucose concentration in human blood serum samples, which exhibited high reliability and accuracy, having great potential in clinical application.     

Improved Sensing of Capsaicin with TiO2 Nanoparticles Modified Epoxy Graphite Electrode

The presented research focuses on the electrochemical determination of capsaicin, a lipophilic alkaloid which originates hotness in chili peppers. An electrochemical sensor based on epoxy‐graphite composite with the modification of titanium dioxide (TiO₂) nanoparticles is developed for the determination of this alkaloid. The measurements were carried out in glycine buffer at pH 2.5 using cyclic voltammetry. Two linear concentration ranges were obtained from 6 to 75 μM (R=0.99) and from 12 to 138 μM, with a detection limit of 5.34 μM and 11.3 μM capsaicin, for 1^st and 2^nd oxidation peak, respectively. The main advantage of developed sensor is its repeatability and robustness against fouling; the relative standard deviation (RSD) value was 2.53 % (n=10). This voltammetric sensing procedure has successfully been applied to quantify capsaicin in various real samples such as hot chili sauce and pharmaceutical preparations.     

Synthesis of Ferrosoferric Oxide‐graphene Oxide Nanocomposite by Isoelectric Point Method for the Detection of Catechol

Ferrosoferric oxide functionalized graphene oxide nanocomposite with layer by layer structure was synthesized by isoelectric point method in this work. The prepared material was characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. Then the material was used to modify a glassy carbon electrode to fabricate an electrochemical sensor for the detection of catechol. The electrochemical sensor exhibited excellent electrochemical performance towards the detection of catechol with a linear response in the range of 5–205 μM and a detection limit of 2.32 μM. Furthermore, the electrochemical sensor showed excellent selectivity, stability and repeatability. These results revealed ferrosoferric oxide functionalized graphene oxide nanocomposite has potential applications in the fabrication of electrochemical sensors.     

Enhanced Electrochemical Determination of Catechol and Hydroquinone Based on Pd Nanoparticles/Poly(Taurine) Modified Glassy Carbon Electrode

Here, Pd nanoparticles and poly(taurine) film was prepared on the glassy carbon electrode surface (Pd/Poly(TAU)/GCE) by the rapid electrochemical technique. The proposed composite surface was characterized by scanning electron microscopy(SEM), X‐ray photoelectron spectroscopy(XPS) and electrochemical impedance spectroscopy(EIS). Enhanced electron transfer ability and higher electroactive surface area were achieved at Pd/Poly(TAU)/GCE as compared to the bare GCE and polymer film electrode. The new and highly stable Pd/Poly(TAU)/GCE was employed for the individual and simultaneous determination of hydroquinone and catechol which were environmentally toxic. Under the optimized conditions, HQ and CC were individually determined by using the differantial pulse voltammetry in the linear ranges of 0.008–100 μM and 0.001–100 μM with the detection limits of (LOD) 2.1 nM and 0.68 nM, respectively. In case of simultaneous determination, LODs were found as 10 nM and 0.88 nM for HQ and CC, respectively. The content of both analytes in the real sample analysis was evaluated in the river water and tap water successfully.     

A Sensitive and Selective Nitrite Detection in Water Using Graphene/Platinum Nanocomposite

A glassy carbon electrode modified with reduced graphene oxide and platinum nanocomposite film was developed simply by electrochemical method for the sensitive and selective detection of nitrite in water. The electrochemical reduction of graphene oxide (GO) efficiently eliminates oxygen‐containing functional groups. Pt nanoparticles were electrochemically and homogeneously deposited on the ErGO surface. Field emission scanning electron microscopy (FE‐SEM), Raman spectroscopy, attenuated total reflectance‐fourier transform infrared spectroscopy (ATR‐FTIR), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) were used to examine the surface morphology and electrocatalytic properties of the Pt‐ErGO nanocomposite film‐modified electrode surface. The fabricated nitrite sensor showed good electrochemical performance with two linear ranges; one from 5 to 100 µM (R²=0.9995) and the other from 100 to 1000 µM (R²=0.9972) and a detection limit of 0.22 µM. The proposed sensor was successfully applied for the detection of nitrite in tap water samples which proves performance of the Pt‐ErGO nanocomposite films.     

A novel nitrite sensor based on graphene/polypyrrole/chitosan nanocomposite modified glassy carbon electrode

A novel nitrite sensor was fabricated based on a graphene/polypyrrole/chitosan nanocomposite film modified glassy carbon electrode. The nanocomposite film was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and Raman spectroscopy. The electron transfer behaviour of the modified electrodes was investigated in [Fe(CN)(6)](3-)/(4-) redox probe using cyclic voltammetry and electrochemical impedance spectroscopy. Differential pulse voltammetry and amperometry were used to study the electrochemical properties of the proposed sensor. Under optimum conditions, the sensor exhibited good reproducibility and stability for nitrite determination. Linear response was obtained in the range of 0.5-722 μM with a detection limit of 0.1 μM (S/N = 3) for nitrite determination.     

Electrocatalysis of Cu−MOF/Graphene Composite and its Sensing Application for Electrochemical Simultaneous Determination of Dopamine and Paracetamol

A nanocomposite of HKUST‐1 (MOF) and electroreduction graphene oxide (ERGO) is prepared and applied as an electrochemical sensor for the simultaneous determination of paracetamol and dopamine by means of one‐step electrodeposition. The MOF/ERGO composite displays excellent electrochemical catalytic activities towards the paracetamol and dopamine, which is attributed to the synergistic effect of big surface area, porosity and high electrocataytic activity of the MOF and good conductivity of ERGO. The modified electrode could be applied to determine simultaneously paracetamol and dopamine in biochemical samples with wide linear ranges (0.2 μM to 160 μM for paracetamol and 0.2 μM to 300 μM for dopamine) and low detection limits (0.016 μM for paracetamol and 0.013 μM for dopamine). Meanwhile, the proposed sensor still displays high sensitivity, good selectivity and excellent stability.     

An Electrochemical Sensor Based on Gold Nanoparticles Incorporated in Mesoporous MFI Zeolite for Determination of Purine Bases in DNA

An electrochemical sensor was developed based on gold nanoparticles incorporated in mesoporous MFI zeolite for the determination of purine bases. Au nanoparticles (AuNPs) were incorporated into the mesoporous MFI zeolite (AuNPs/m‐MFI) by post‐grafting reaction. The composite materials were characterized by transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS) and electrochemical methods. Au nanoparticles with a size of 5‐20 nm are uniformly dispersed in the pores of mesoporous MFI zeolite. And the morphology of MFI zeolite can be perfectly kept after pore expansion and Au nanoparticles incorporation. The electrocatalytic oxidation of purine bases (guanine and adenine in DNA) is investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The surface‐confined Au nanoparticles provide the good catalytic activity for oxidation of purine bases. The simultaneous detection of guanine and adenine can be achieved at AuNPs/m‐MFI composites modified glassy carbon electrode (GCE). The electrochemical sensor based on AuNPs/m‐MFI exhibits wide linear range of 0.5–500 μM and 0.8–500 μM with detection limit of 0.25 and 0.29 μM for guanine and adenine, respectively. Moreover, the electrochemical sensor is applied to evaluation of guanine and adenine in herring sperm DNA samples with satisfactory results.     

Fabrication of Electrochemical Sensor Based on CeO2−SnO2 Nanocomposite Loaded on Pd Support for Determination of Nitrite at Trace Levels

Here, an electrochemical sensor based on CeO₂‐SnO₂/Pd was prepared and used for highly selective and sensitive determination of nitrite in some real samples. This nanocomposite was characterized by various methods like X‐ray photoelectron spectroscopy, X‐ray diffraction, energy dispersive spectroscopy, Fourier‐transform infrared spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. The electrochemical behavior of the sensor was evaluated by cyclic voltammetry. The results showed excellent catalytic property of the nanocomposite as a an electrocatalyst for nitrite oxidation. In the following, the experimental parameters affecting the analytical signal for nitrite were optimized. Under the optimal conditions, the limit of detection and sensitivity of the sensor were calculated as 0.10 μM and 652.95 μA.mM^?1.cm^?2, respectively. Also, the response of the sensor was linear in the range of 0.36 to 2200 μM of nitrite. Finally, some of the inherent features of the sensor such as repeatability, reproducibility and stability were examined after evaluation of the sensor selectivity in the presence of several interfering species.     

Pt‐Pd Bimetallic Nanoparticles Decorated Nanoporous Graphene as a Catalytic Amplification Platform for Electrochemical Detection of Xanthine

The nanoporous graphene papers (NGPs) was prepared by the hard‐template method. The Pt−Pd modified NGPs hybrid was prepared by the self‐assembly method. Then a glassy carbon electrode (GCE) modified with Pt−Pd bimetallic nanoparticles‐functionalized nanoporous graphene composite has been prepared for the electrochemical determination of Xanthine (XA). The Pt−Pd/NGPs hybrid was characterized by transmission electron microscopy, scanning electron microscope and X‐ray diffraction. The electrochemical behavior of XA on Pt−Pd/NGPs/GCE was investigated by cyclic voltammetry and amperometric i‐t. The Pt−Pd/NGPs modified electrode exhibited remarkably electrocatalytic activity towards the oxidation reaction of XA in phosphate buffer solution (pH=5.5). Under the optimal conditions, the determination of XA was accomplished by using amperometric i‐t, the linear response range from 1.0×10⁻⁵∼1.2×10⁻⁴ M. The detection limit was 3.0×10⁻⁶ M (S/N=3). The proposed modified electrode showed good sensitivity, selectivity, and stability with applied to determine XA in human urine.     

Fabrication of Non‐enzymatic Electrochemical Glucose Sensor Based on Pd−Mn Alloy Nanoparticles Supported on Reduced Graphene Oxide

Mixed metals alloy nanoparticles supported on carbon nanomaterial are the most attractive candidates for the fabrication of non‐enzymatic electrochemical sensor with enhanced electrochemical performance. In this study, palladium‐manganese alloy nanoparticles supported on reduced graphene oxide (Pd?Mn/rGO) are prepared by a simple reduction protocol. Further, a novel enzyme‐free glucose sensing platform is established based on Pd?Mn/rGO. The successful fabrication of Pd?Mn alloy nanoparticles and their attachment at rGO are thoroughly characterized by various microscopic and spectroscopic techniques such as XRD, Raman, TEM and XPS. The electrochemical activity and sensing features of designed material towards glucose detection are explored by amperometric measurments in 0.1 M NaOH at the working voltage of ?0.1 V. Thanks to the newly designed Pd?Mn/rGO nanohybrid for their superior electrorochemical activity towards glucose comprising the admirable sensing features in terms of targeted selectivity, senstivity, two linear parts and good stability. The enhanced electrochemical efficacy of Pd?Mn/rGO electrocatalyst may be credited to the abundant elecrocatalytic active sites formed during the Pd?Mn alloying and the electron transport ability of rGO that augment the electron shuttling phenomenon between the electrode material and targeted analyte.     

A Self‐assembled L‐Cysteine and Electrodeposited Gold Nanoparticles‐reduced Graphene Oxide Modified Electrode for Adsorptive Stripping Determination of Copper

Glassy carbon electrode (GCE) modified with L‐cysteine and gold nanoparticles‐reduced graphene oxide (AuNPs‐RGO) composite was fabricated as a novel electrochemical sensor for the determination of Cu²⁺. The AuNPs‐RGO composite was formed on GCE surface by electrodeposition. The L‐cysteine was decorated on AuNPs by self‐assembly. Physicochemical and electrochemical properties of L‐cysteine/AuNPs‐RGO/GCE were characterized by scanning electron microscopy, atomic force microscopy, energy dispersive spectroscopy, Raman spectroscopy, X‐ray diffraction, cyclic voltammetry and adsorptive stripping voltammetry. The results validated that the prepared electrode had many attractive features, such as large electroactive area, good electrical conductivity and high sensitivity. Experimental conditions, including electrodeposition cycle, self‐assembly time, electrolyte pH and preconcentration time were studied and optimized. Stripping signals obtained from L‐cysteine/AuNPs‐RGO/GCE exhibited good linear relationship with Cu²⁺ concentrations in the range from 2 to 60 μg L⁻¹, with a detection limit of 0.037 μg L⁻¹. Finally, the prepared electrode was applied for the determination of Cu²⁺ in soil samples, and the results were in agreement with those obtained by inductively coupled plasma mass spectrometry.     

Design and Development of Ultrafast Sinapic Acid Sensor Based on Electrochemically Nanotuned Gold Nanoparticles and Solvothermally Reduced Graphene Oxide

We report for the first time sinapic acid (SA) sensing based on nanocomposite comprising electrochemically tuned gold nanoparticles (EAuNPs) and solvothermally reduced graphene oxide (rGO). The synthesized EAuNPs, rGO, and EAuNPs‐rGO nanocomposite were characterized using X‐ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), particle size analysis, and Raman spectroscopy. A proof‐of‐concept electrochemical sensor for SA was developed based on synthesized EAuNPs‐rGO nanocomposite, which was characterized by electrochemical techniques such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The developed sensor detected SA with a linear dynamic range (LDR) between 20 μM and 200 μM and detection limit (DL) of 33.43 (±0.21) nM (RSD<3.32 %). To show the useful purpose of the sensor probe in clinical applications, SA was detected in human urine samples, which showed the percentage recovery between 82.6 % and 92.8 %. Interferences due to various molecules such as L‐cystine, glycine, alanine, serum albumin, uric acid, citric acid, ascorbic acid, and urea were tested. Long‐term stability of the sensor probe was examined, which was found to be stable up to 6 weeks. The sensor fabricated using EAuNPs‐rGO nanocomposite has many attractive features such as; simplicity, rapidity, and label‐free detection; hence, it could be a method of choice for SA detection in various matrices.     

石墨烯负载的空心银钯纳米粒子的制备及其在过氧化氢检测中的应用

制备了在石墨烯上修饰的AgPd合金纳米粒子,并将其应用于对过氧化氢(H2O2)的电化学检测。通过两步合成得到此纳米复合物:利用柠檬酸钠作为保护剂和还原剂,合成石墨烯负载的Ag纳米粒子(Ag/GO);在100℃下,通过Ag与Pd2+之间的置换反应得到石墨烯负载的具有空心结构的AgPd合金纳米粒子(AgPd/GO)。用紫外-可见光谱(UV-vis),电子显微镜(TEM)等对此纳米复合物的结构及其吸收光谱和形貌进行了表征。电化学循环伏安法(CV)和计时安培法(i-t)的研究结果表明,修饰在石墨烯上的空心AgPd合金纳米粒子对H2O2还原具有显著的催化活性,对H2O2检测的线性范围为0.01～1.4 mmol/L(R=0.990);检出限为1.4μmol/L。     

Molecularly Imprinted Electrochemical Sensor Based on Modified Reduced Graphene Oxide‐gold Nanoparticles‐polyaniline Nanocomposites Matrix for Dapsone Determination

This work was designed to develop an electrochemical sensor based on molecular imprinted polyaniline membranes onto reduced graphene oxide (RGO) and gold nanoparticles (AuNPs) modified glassy carbon (GC) electrode for dapsone (DDS) determination. The prepared RGO/AuNPs/PANI‐MIPs nanocomposite was characterized by Ultra‐Violet‐Visible (UV‐Vis), Fourier transform infrared spectroscopy (FT‐IR) and scanning electronic microscopy (SEM) images. The feature of the imprinted electrode was evaluated by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and impedance spectroscopy (IS). Throughout this study several analytical parameters, such as incubation time, pH value, concentration of monomer/template molecules and electro‐polymerization cycles were investigated. Under the optimized conditions, the experimental results showed best analytical performances for DDS detection with a sensitivity of 0.188 Ω/mol L^?1, a linear range from 1.0×10^?7 M to 1.0×10^?3 M and a detection limit of 6.8×10^?7 M. The bioanalytical sensor was applied to the determination of dapsone in real samples with high selectivity and recovery.     

Direct Electrochemistry of Cytochrome c Based on Poly(diallyldimethylammonium Chloride)‐ Graphene Nanosheets/Gold Nanoparticles Hybrid Nanocomposites and Its Biosensing

A novel biosensor was developed by entrapping cytochrome c (Cyt c) in thin films of the room temperature ionic liquid (RTIL) containing nanocomposites of poly(diallyldimethylammonium chloride)‐graphene nanosheets‐gold nanoparticles (PDDA‐Gp‐AuNPs) at a 11‐mercaptoundecanoic acid‐6‐mercapto‐1‐hexanol modified gold electrode. The synthesized PDDA‐Gp‐AuNPs hybrid nanocomposites were characterized by UV‐vis spectroscopy, Raman spectroscopy, scanning electron microscopy and atomic force microscopy. The PDDA‐Gp‐AuNPs nanocomposites could increase the effective surface of the electrode, enhance the fixed amount of Cyt c on the electrode surface, promote the electron transfer and facilitate the catalytic activity of Cyt c. The RTIL could provide a biocompatible microenvironment to keep Cyt c biological activities, act as an effective mediator to immobilize a large number of Cyt c on the electrode and have good conductivity to improve electron transfer. Therefore, the resultant electrode exhibited good electrochemical performance and electrocatalytic activity. It could be used for electrochemical detection of H₂O₂ with rapid response, high sensitivity, wide linear range and low detection limit, as well as good stability, repeatability and selectivity. The sensor might be promising for practical application.     

Differential Pulse Voltammetry Determination of Ofloxacin in Human Serum and Urine Based on a Novel Tryptophan‐graphene Oxide‐carbon Nanotube Electrochemical Sensor

The highly sensitive determination of ofloxacin (OFL) in human serum and urine was achieved on a novel tryptophan‐graphene oxide‐carbon nanotube (Trp‐GO‐CNT) composite modified glassy carbon electrode (Trp‐GO‐CNT/GCE). The Trp‐GO‐CNT composite was fabricated, and its morphologies and surface functional groups were characterized by field emission scanning electron microscopy (FE‐SEM) and Fourier transform infrared (FT‐IR) spectroscopy. The electrochemical properties of Trp‐GO‐CNT/GCE were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The superior electrochemical behaviors of Trp‐GO‐CNT/GCE toward OFL can be mainly assigned to the excellent electrocatalytic activity of Trp, the great conductivity and high surface area of GO and CNT, and the synergistic effect between Trp, GO and CNT. Under optimum conditions, a wide and valuable linear range (0.01–100 μM), a low detection limit (0.001 μM, S/N=3), a good linear relationship (R2>0.999), good stability and repeatability were obtained for the quantitative determination of OFL. Furthermore, the Trp‐GO‐CNT electrochemical sensor was successfully applied to the determination of OFL in human serum and urine samples, and satisfactory accuracy and recovery could be obtained.