Electrochemical Conversion of Magnetic Nanoparticles Using Disposable Working Electrode in a 3D‐Printed Electrochemical Cell

Exploration of new property/function of nanomaterials is always a strong impetus in the nanoscience field. Here, a new method of electrochemical conversion (ECC) of magnetic nanoparticles (MNPs) is proposed to endow MNPs with signal generation ability for sensing. Briefly, high potential was applied to split H₂O to generate acid, while Fe₃O₄ MNPs reacted with H⁺ and produce ferric/ferrous ions, which further reacted with K₄Fe(CN)₆ to yield Prussian blue (PB) through potential cycling. The ECC method worked well on both home‐made and commercial MNPs with different sizes. The generated PB possessed strong electrochemical activity for further applications. Interestingly, an uneven deposition of PB on working electrode and undesired contamination of the reference and counter electrodes were found when using commercial integrated three‐electrode chip. A 3D‐printed electrochemical cell was designed to facilitate the ECC and avoid drawbacks of commercial integrated electrode. The 3D‐printed electrochemical cell was proven to solve the problem above through spatial separation of electrodes and thus facilitated the ECC process. An electrochemical sensor for H₂O₂ detection based on the catalysis ability of ECC‐based PB exhibited a linear response from 5 μM to 1 mM, a high sensitivity of 269 μA mM^?1 cm^?2 and a low detection limit of 0.16 μM (S/N=3), which suggests its promising application prospect in electrochemistry‐related analysis.     

Electrochemical Behaviour and Rapid Determination of L‐Dopa at Electrochemically Pretreated Screen Printed Carbon Electrode

A simple and rapid voltammetric method based on a disposable electrochemically pretreated screen‐printed carbon electrode is proposed for the determination of L ‐dopa. Under optimum differential pulse voltammetry conditions a limit of detection of 3.6×10^?7 M for L ‐dopa was obtained. The method was successfully applied to the determination of L ‐dopa in a commercial pharmaceutical formulation.     

3D‐printed Portable Platform for Mechanized Handling and Injection of Microvolumes Coupled to Electrochemical Detection

We present a low‐cost mechanized system fabricated using fused deposition modelling 3D‐printing technology to manipulate microvolumes and perform injections on an electrochemical cell in wall‐jet configuration. As a proof‐of‐concept, the amperometric detection of paracetamol (model analyte) on a screen‐printed electrode using 0.5 μL aliquots resulted in highly reproducible responses (RSD <3 %). Moreover, handling of microliter aliquots of butylhydroxytoluene (phenolic antioxidant) and 2,2‐diphenyl‐2‐picrylhydrazyl (DPPH) to promote the radical‐scavenging reaction to determine antioxidant capacity by electrochemical detection of residual DPPH was demonstrated (time‐controlled reaction). A final application of the system was devoted to the analysis of cocaine and a common adulterant found in seized samples. The mechanized 3D‐printed analytical platform is capable to execute diverse sample preparation steps on board by handling microliter aliquots and subsequent electrochemical detection. 3D‐printing technology enabled the fabrication of a versatile and low‐cost (<U$200) mechanized system accessible to general chemistry labs.     

Graphene‐Functionalized 3D‐Carbon Fiber Electrodes – Preparation and Electrochemical Characterization

Graphene nanosheets were produced on the surface of carbon fibers by in situ electrochemical procedure including oxidative and reductive steps to yield first graphene oxide, later converted to graphene. The electrode material composed of graphene‐functionalized carbon fibers was characterized by scanning electron microscopy (SEM) and cyclic voltammery demonstrating superior electrochemical kinetics comparing with the original carbon paper. The interfacial electron transfer rate for the reversible redox process of [Fe(CN)₆]^3?/4? was found ca. 4.5‐fold higher after the electrode modification with the graphene nanosheets. The novel electrode material is suggested as a promising conducting interface for bioelectrocatalytic electrodes used in various electrochemical biosensors and biofuel cells, particularly operating in vivo.     

All‐Solid‐State Chloride Sensors with Poly(3‐Octylthiopene) Matrix and Trihexadecylmethylammonium Chlorides as an Ion Exchanger Salt

All‐solid‐state chloride sensors were prepared by incorporation of trihexadecyl‐methylammonium chloride (THMACl) as an ion‐exchanger salt into a conjugated polymer membrane, poly(3‐octylthiophene) (POT). The influence of additional membrane components, such as a lipophilic anion, (potassium tetrakis[3,5‐bis(trifluoromethyl)phenyl] borate), poly(vinyl chloride) (PVC) or a plasticizer, (2‐nitrophenyl octyl ether) were studied. The membrane components were dissolved in chloroform except for PVC, which was dissolved in tetrahydrofuran (THF). The membrane solution was deposited on glassy carbon (GC) by solution casting resulting in all‐solid‐state chloride sensors. The sensor characteristics were determined potentiometrically and with impedance spectroscopy. The addition of plasticizer was found to be crucial in obtaining a well functioning Cl^?‐ISE based on POT and THMACl.     

Electrochemical Characterization of Screen‐Printed Carbon Electrodes by Modification with Chitosan Oligomers

The kinetics on the current amplification of the disposable screen‐printed carbon electrodes (SPCEs) by modification with chitosan oligomers (COs), coupled with the Fe(CN) redox system, were characterized with the variation of electron‐transfer rate constant (k°) and the electroactive area (A_ea) at electrode surface. The nonlinear response characteristics of peak currents with increase in Fe(CN) bulk concentrations complicated the estimation of A_ea in cyclic voltammetric analysis. Upon the modification with COs, the rate constant of SPCEs was not much influenced and the current amplification was characterized with the increase of a better estimated A_ea, obtained from electrochemical impedance measurements and verified with the reciprocal of electron‐transfer resistances linearly proportional to the Fe(CN) bulk concentrations. It is hereby provided for an evaluation of the carbon based electrodes with modification.     

3D‐Printed Titanium Cage with PVA‐Vancomycin Coating Prevents Surgical Site Infections (SSIs)

Many coating materials have been studied to prevent surgical site infections (SSIs). However, antibacterial coating on surfaces show weak adhesion using the traditional titanium (Ti) cage, resulting in low efficacy for preventing SSIs after spinal surgery. Herein, a 3D‐printed Ti cage combined with a drug‐releasing system is developed for in situ drug release and bacteria killing, leading to prevention of SSIs in vitro and in vivo. First, a 3D‐printed Ti cage is designed and prepared by the Electron Beam Melting (EBM) method. Second, polyvinyl alcohol (PVA) containing hydrophilic vancomycin hydrochloride (VH) is scattered across the surface of 3D‐printed porous Ti (Ti‐VH@PVA) cages. Ti‐VH@PVA cages show an efficient drug‐releasing profile and excellent bactericidal effect for three common bacteria after more than seven days in vitro. In addition, Ti‐VH@PVA cages exhibit reliable inhibition of inflammation associated with Staphylococcus aureus and effective bone regeneration capacity in a rabbit model of SSIs. The results indicate that Ti‐VH@PVA cages have potential advantages for preventing SSIs after spinal surgery.     

Electrochemical Analysis of D‐Penicillamine Using a Carbon Paste Electrode Modified with Ferrocene Carboxylic Acid

The electrochemical behavior of D ‐penicillamine (D ‐PA) studied at the surface of ferrocene carboxylic acid modified carbon paste electrode (FCAMCPE) in aqueous media using cyclic voltammetry and double step potential chronoamperometry. It has been found that under optimum condition (pH 7.00), the oxidation of D ‐PA at surface of such an electrode is occurred about 420 mV less positive than that an unmodified carbon paste electrode (CPE). The catalytic oxidation peak current was linearly dependent on the D ‐PA concentration and a linear calibration curve was obtained in the ranges 7.5×10^?5 M – 1.0×10^?3 M and 6.5×10^?6 M?1.0×10^?4 M of D ‐PA with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods respectively. The detection limits (3σ) were determined as 6.04×10^?5 M and 6.15×10^?6 M. This method was also used for the determination of D ‐PA in pharmaceutical preparation (capsules) by standard addition method.     

Simultaneous Voltammetric Determination of Zn(II), Pb(II), Cu(II), and Hg(II) in Ethanol Fuel Using an Organofunctionalized Modified Graphite‐Polyurethane Composite Disposable Screen‐Printed Device

A disposable screen‐printed device containing working, auxiliary, and reference electrodes is proposed for the simultaneous voltammetric determination of Zn(II), Pb(II), Cu(II), and Hg(II) in ethanol fuel. The working electrode was printed using an ink modified with 2‐benzothiazole‐2‐thiol organofunctionalized SBA‐15 silica, in order to increase sensitivity. The performance of this electrode was compared with that of bare and SBA‐15‐modified electrodes. After optimizing the experimental parameters, the device was applied in determination of the analytes in commercial ethanol fuel samples, using 0.10 mol L^?1 KCl/ethanol ratios of 30 : 70 (v/v), with [H⁺]=10^?5 mol L^?1. After 5 min of preconcentration at ? 1.3 V (vs. pseudo‐Ag/AgCl), four well‐resolved signals were obtained, enabling simultaneous determination of the four analytes using a differential pulse anodic stripping voltammetry (DPASV) procedure. The limits of detection were 0.30, 0.065, 0.030, and 0.046 µmol L^?1 for Zn(II), Pb(II), Cu(II), and Hg(II), respectively. The results of these analyses were in agreement with those obtained using graphite furnace atomic absorption spectroscopy (GFAAS) for Pb(II), Cu(II), and Hg(II), and high‐resolution continuum source flame atomic absorption spectrometry (HR‐CS‐FAAS) for Zn²⁺, at a 95 % confidence level. Analytes originally present in the samples could be detected, and the interference of some cations and anions was evaluated.     

3D‐printed Microfluidic Device Based on Cotton Threads for Amperometric Estimation of Antioxidants in Wine Samples

The present work describes the evaluation of microfluidic electroanalytical devices constructed by a 3D printer using ABS (acrylonitrile butadiene styrene) polymer combined with cotton threads as microchannels. Screen‐printed carbon electrodes (SPCEs) were used as electrochemical detector for amperometric determination of gallic and caffeic acid in wine samples. Using optimal experimental conditions (flow rate of 0.71 μL s⁻¹, applied potential of +0.30 V and volume of injection of 2.0 μL) the proposed method presented a linear response for a concentration range of 5.0×10⁻⁶ to 1.0×10⁻³ mol L⁻¹. The detection limits for gallic and caffeic acid were found to 1.5×10⁻⁶ mol L⁻¹ and 8.0×10⁻⁷ mol L⁻¹, respectively, with a sample throughput of 43 h⁻¹. The achieved results are in agreement with those found using the official Folin‐Ciocaulteu method.     

Preparation and Characterization of Graphite‐Epoxy Composite Modified with Zinc Hexacyanoferrate and Their Electrochemical Behaviour in Presence of Substituted Anilines

The growth of zinc hexacyanoferrate (ZnHCF) hybrid film on the surface of graphite‐epoxy composite (GEC) electrodes was demonstrated by cyclic voltammetry. Surface morphology of the hybrid film was investigated by using scanning electron microscopy. The effect of the type of monovalent cations on the redox behaviour of hybrid film was also studied. This effect indicated that the radius of the hydrated cation mainly determines the ion permeability of the film.     

Nanocomposites Based on Polystyrene Sulfonate as Sensing Platforms. Comprehensive Electrochemical Study of Carbon Nanopowders and Carbon‐Nanofibers Composite Membranes

Nanocomposite membranes, prepared from carbon nano‐powders (CnP) or carbon nano‐fibers (CnF) dispersions in polystyrene sulfonate (PSS), were evaluated as sensing platforms. Composite surfaces were analyzed by scanning electron microscopy and field‐emission electron microscopy. Electrical and electrochemical properties of composite membranes were evaluated. Percolation threshold was reached at percentages higher than 5 % CnP or 0.5 % CnF. Best electrochemical responses were obtained on electrodes modified with composites containing 10 % CnP and 1 % CnF. Using a PSS‐10 % CnP composite modified electrode, a limit of detection of 0.3 µg L^?1 (1 nM) was obtained in lead determination by differential pulse anodic stripping voltammetry.     

Selective Electrochemical Determination of Dopamine with Molecularly Imprinted Poly(Carbazole‐co‐Aniline) Electrode Decorated with Gold Nanoparticles

Dopamine (DA) is a significant neurotransmitter in the central nervous system, coexisting with uric acid (UA) and ascorbic acid (AA). UA and AA are easily oxidizable compounds having potentials close to that of DA for electrochemical analysis, resulting in overlapping voltammetric response. In this work, a novel molecularly imprinted (MI) electrochemical sensor was proposed for selective determination of DA (in the presence of up to 80‐fold excess of UA and AA), relying on gold nanoparticles (Au_nano)‐decorated glassy carbon (GC) electrode coated with poly(carbazole (Cz)‐co‐aniline (ANI)) copolymer film incorporating DA as template (DA imprinted‐GC/P(Cz‐co‐ANI)‐Au_nano electrode, DA‐MIP‐Au_nano electrode). The DA recognizing sensor electrode showed great electroactivity for analyte oxidation in 0.2 mol L^?1 pH 7 phosphate buffer. Square wave voltammetry (SWV) was performed within 10^?4–10^?5 mol L^?1 of DA, of which the oxidation peak potential was observed at 0.16 V. The limit of detection (LOD) and limit of quantification (LOQ) were 2.0×10^?6 and 6.7×10^?6 mol L^?1, respectively. Binary and ternary synthetic mixtures of DA‐UA, DA‐AA and DA‐UA‐AA yielded excellent recoveries for DA. Additionally, DA was quantitatively recovered from a real sample of bovine serum spiked with DA, and determined in concentrated dopamine injection solution. The developed SWV method was statistically validated against a literature potentiodynamic method using a caffeic acid modified‐GC electrode.     

Electrochemical Determination of Tetracycline Using Molecularly Imprinted Polymer Modified Carbon Nanotube‐Gold Nanoparticles Electrode

This paper reports the use of a tetracycline (TC) sensor constructed from a combination of molecularly imprinted polymer (MIP) and gold nanoparticles modified multiwall carbon nanotubes (MWNTs‐GNPs). The results demonstrated that the amount of recognition sites in the polymer was significantly increased and the electron transfer ability of the sensor was improved. The relationship between the peak current and the TC concentration was linear in the range from 0.1 to 40 mg L^?1, and the detection limit was 0.04 mg L^?1 (S/N=3). The peak current to TC was 4.3, 6.2 and 6.8 times larger than that of oxytetracycline, chloramphenicol and nafcillin, respectively. Thus, the combination of MIP and MWNTs‐GNPs provides a sensitive and selective electrochemical detection method for tetracycline.     

Tailoring Coordination Polymers by Substituent Effect: A Bifunctional CoII‐Doped 1D‐Coordination Network with Electrochemical Water Oxidation and Nitroaromatics Sensing

Three Cd^II coordination polymers (CPs) were synthesized with a tripodal ligand N,N‘,N‘ ‘‐tris(4‐pyridinylmethyl)‐1,3,5‐benzenetricarboxamide in combination with three different substituted isophthalic acids with general formulas {[Cd₂( L )(NIP)₂(H₂O)₂].4H₂O}_n, (CP‐ 1 ), {[Cd₂( L )(AIP)₂(H₂O)₂].4H₂O}_n, (CP‐ 2 ) and {[Cd( L )(BIP) (H₂O)].4H₂O}_n, (CP‐ 3 ). The substituent groups on the co‐ligand had profound effect on the network topologies of the corresponding CPs as well as their properties. Out of the three, CP‐ 1 and 2 were found to form 3D networks whereas CP‐ 3 was a 1D linear chain with uncoordinated pyridyl sites. Due to its structural features CP‐ 3 was found to show interesting properties. The 1D CP containing uncoordinated pyridyl site exhibited an excellent ability for doping with Co^II which in turn acts as an efficient water oxidation electrocatalyst with required overpotential of 380 mV for an anodic current density of 1 mA cm^?2. The CP also exhibited luminescence‐based detection of nitroaromatics (LOD: 0.003 mm ) without any significant interference in presence of other organic compounds.     

Reduced Graphene Oxide/Carbon Nanotube/Gold Nanoparticles Nanocomposite Functionalized Screen‐Printed Electrode for Sensitive Electrochemical Detection of Endocrine Disruptor Bisphenol A

We fabricated a highly sensitive electrochemical sensor for the determination of bisphenol A (BPA) in aqueous solution by using reduced graphene oxide (RGO), carbon nanotubes (CNT), and gold nanoparticles (AuNPs)‐modified screen‐printed electrode (SPE). GO/CNT nanocomposite was directly reduced to RGO/CNT on SPE at room temperature. AuNPs were then electrochemically deposited in situ on RGO/CNT‐modified SPE. Under optimized conditions, differential pulse voltammetry (DPV) produced linear current responses for BPA concentrations of 1.45 to 20 and 20 to 1,490 nM, with a calculated detection limit of an ultralow 800 pM. The sensor response was unaffected by the presence of interferents such as phenol, p‐nitrophenol, pyrocatechol, 2,4‐dinitrophenol, and hydroquinone.     

Beta‐lactoglobulin Electrochemical Detection Based with an Innovative Platform Based on Composite Polymer

In this work, we present a new electrochemical disposable platform based on poly(aniline‐co‐anthranilic acid) (PANI/PAA) composite polymer coupled with an aptamer for sensitive detection of β‐lactoglobulin. Firstly, PANI/PAA film was electrodeposited on the graphite screen‐printed electrode surface by cyclic voltammetry. The co‐polymer modified electrode was then employed as platform for the covalent immobilization of an amino‐modified aptamer. Various β‐lactoglobulin solutions, with a fixed amount of biotinylated oligonucleotide complementary sequence, were dropped onto the aptasensor surface. A streptavidin‐alkaline phosphatase conjugate was then employed to trace the affinity reaction. After the addition of 1‐naphthyl‐phosphate enzymatic substrate, 1‐naphthol electroactive product was detected by differential pulse voltammetry. A decrease in the signal was obtained when the target concentration was increased, in according to a signal‐off approach. After optimization of key experimental parameters, a dose‐response curve was obtained between 0.01–1.0 μg mL^?1 β‐lactoglobulin concentration range. The limit of detection of 0.053 μg L^?1 was obtained. Milk samples spiked with β‐lactoglobulin were analyzed.     

Graphite‐Nanoplate‐Coated Bi2S3 Composite with High‐Volume Energy Density and Excellent Cycle Life for Room‐Temperature Sodium–Sulfide Batteries

Graphite‐nanoplate‐coated Bi₂S₃ composite (Bi₂S₃@C) has been prepared by a simple, scalable, and energy‐efficient precipitation method combined with ball milling. The Bi₂S₃@C composite was used as the cathode material for sodium–sulfide batteries. It delivered an initial capacity of 550 mAh g^?1 and high stable specific energy in the range of 275–300 Wh kg^?1 at 0.1 C, with an enhanced capacity retention of 69 % over 100 cycles. The unique structure demonstrates superior cycling stability, with a capacity drop of 0.3 % per cycle over 100 cycles, compared with that of bare Bi₂S₃. The sodium storage mechanism of Bi₂S₃ was investigated based on ex situ X‐ray diffraction and scanning transmission electron microscopy.     

Rapid and Sensitive Determination of Dinotefuran Residue Based on Electrochemical Enhancement of β‐cyclodextrin‐Graphene Composite

A rapid method for sensitive voltammetric determination of dinotefuran residue was reported. The proposed method was based on the electrocatalytic reduction of dinotefuran on β‐cyclodextrin‐graphene composite modified glassy carbon electrode (β‐CD‐rGO/GCE), giving rise to a higher reduction signal to dinotefuran relative to the bare (GCE) and graphene modified electrode (rGO/GCE). Moreover, a further signal enhancement was observed when the modified electrode incubated in solution at low temperature (0 °C) for a short time. The reduction mechanism and binding affinity were also discussed. The external standard calibration curve was obtained from linear sweep voltammetry in the range of 0.5 to 16.0 μM with a detection limit of 0.10 μM. In addition to optimization of pretreatment, this electrochemical method has been applied to the dinotefuran residue determination in millet samples with the detection limit of 0.01 mg kg^?1 and compared with an high performance liquid chromatography method. The proposed electrode and analysis methods were proven to be sensitive, accurate and rapid under the used conditions.