Film-modified Electrode Research Articles

A nanosilica/exfoliated graphene composite film-modified electrode for sensitive detection of methyl parathion

Graphene nanosheets (GS) were easily prepared through liquid-phase exfoliation of graphite powder in N,N-dimethylformamide (DMF) with the assistance of sodium citrate. Then, GS was coated onto a glassy carbon electrode (GCE) surface by drop to fabricate a GS/GCE nanointerface. Subsequently, by using tetraethylorthosilicate sol as precursor, nanosilica was electrochemically deposited onto the GS/GCE surface to produce a nanocomposite film electrode (nanosilica/GS/GCE). Electrochemical behaviors of methyl parathion (MP) on the nanosilica/GS/GCE surface were investigated thoroughly. It was found that the nanosilica/GS nanocomposites can improve the redox peak currents of MP significantly due to the synergetic effect. The oxidation peak current was linearly related to MP concentration in the range from 0.0005μmol/L to 5.6μmol/L. The detection limit was calculated to be 0.07nmol/L (S/N=3). The developed method was used to determine MP in real samples. The recoveries were in the range from 95.4% to 104.2%, demonstrating satisfactory results.

A Electrochemical Sensor based on Poly (Sulfosalicylic Acid) Film Modified Electrode and Application to Phenol Detection in Oilfield Wastewater

In this paper, a highly sensitive and selective method based on the poly (sulfosalicylic acid) modified electrode (PSA /CPE) to detect phenol was established. The morphologies and interface properties of PSA film were characterized by scanning electron microscopy and electrochemical impedance spectroscopy. It was illustrated that the PSA/CPE had an excellent electrocatalytic ability towards the oxidation of phenol. Meanwhile the influence of parameters such as pH and scan rate effect on the analytical performance of the sensor was evaluated. Moreover, the interference from o-nitrophenol can be neglected. By using differential pulse voltammetry (DPV), linear calibration curves were obtained as 5–175 and 220–555 μmol L−1 for phenol. The detection limits are 2.2 μmol L−1 for phenol. With favorable selectivity and sensitivity, the present method has been applied to the determination of phenol in oilfield wastewater.

Label-free electrochemical genosensor based on mesoporous silica thin film.

A novel label-free electrochemical strategy for nucleic acid detection was developed by using gold electrodes coated with mesoporous silica thin films as sensing interface. The biosensing approach relies on the covalent attachment of a capture DNA probe on the surface of the silica nanopores and further hybridization with its complementary target oligonucleotide sequence, causing a diffusion hindering of an Fe(CN)6 (3-/4-) electrochemical probe through the nanochannels of the mesoporous film. This DNA-mesoporous silica thin film-modified electrodes allowed sensitive (91.7A/M) and rapid (45min) detection of low nanomolar levels of synthetic target DNA (25fmol) and were successfully employed to quantify the endogenous content of Escherichia coli 16S ribosomal RNA (rRNA) directly in raw bacterial lysate samples without isolation or purification steps. Moreover, the 1-month stability demonstrated by these biosensing devices enables their advanced preparation and storage, as desired for practical real-life applications. Graphical abstract Mesoporous silica thin films as scaffolds for the development of novel label-free electrochemical genosensors to perform selective, sensitive and rapid detection of target oligonucleotide sequences. Application towards E. coli determination.

Electrocatalytic behavior of glassy carbon electrode modified with ruthenium nanoparticles and ruthenium film

The electrocatalytic behavior of glassy carbon (GC) electrode modified with ruthenium nanoparticles and ruthenium film was studied for electrochemical reduction of nicotinamide adenine dinucleotide (NAD+). The surface of GC electrode was modified via cathodic deposition of nanosized ruthenium at different potentials. Scanning electron microscopy (SEM) images showed two kinds of surface morphologies based on deposition potential: Ru nanoparticles-decorated GC at −0.3 V and Ru film-coated GC at −0.5 V versus Ag/AgCl. The electrochemical behavior of Ru nanoparticles and Ru film-modified GC electrodes in phosphate buffer solution containing NAD+ was investigated using voltammetric techniques. A prominent cathodic peak was observed on bare GC and Ru nanoparticles-modified GC at −1.2 V versus Ag/AgCl which was related to NAD+ reduction. The electrochemical response of Ru film electrode was reversible, exhibiting a reduction peak at ca. −1.0 V and an oxidation peak at ca. −0.55 V which was attributed mainly to the hydrogen evolution reaction. Electrochemical impedance analysis indicated lower charge transfer resistance of Ru film electrode for hydrogen evolution as compared to GC and Ru nanoparticle electrodes. Ru film-modified electrode was found less reactive than the nanoparticles-modified GC electrode for NAD+ reduction reaction due to hydrogen evolution reaction that proceeds exclusively on Ru film.

Reversible Switched Detection of Dihydroxybenzenes Using a Temperature-sensitive Electrochemical Sensing Film

A composite sensing film (PGS), consisting of poly(N-isopropylacrylamide)101-b-poly(2-acrylamidoethyl benzoate)37 (PNIPAM101-b-PAAEB37), graphene oxides (GO) and short multi-walled carbon nanotubes (SMWCNs), was fabricated and modified onto a working electrode. The sensing film served as a reversible switch for electrochemical detection, with the switching behaviour responding to thermal stimuli. Cyclic voltammetry of hydroquinone (HQ) and catechol (CC) at the PGS film-modified electrode displayed large peak currents when the temperature was above the lower critical solution temperature (LCST) of PNIPAM101-b-PAAEB37. These large currents disappeared at low temperature. Interestingly, the composite film showed reversed electrochemical “on/off” behaviour as compared to previously reported switchable electrodes, which were modified only with temperature-responsive polymers. This behaviour can be attributed to the temperature-dependent phase transition of PNIPAM101-b-PAAEB37 and cooperative effects of the other two functional components (SMWCNs and GO). The repeatable “on/off” switching of the voltammetric responses of HQ/CC on the PGS-modified electrode were achieved via regulating the solution temperature. This research provides a new type of temperature-controlled switchable electrode with potential applications in the design of novel sensors, fuel cells and electronics.

Effects of alkyl chain length on film morphologies and photocurrent responses of tetrathiafulvalene-bipyridinium charge-transfer salts: a study in terms of structures

Viologen dication derivatives with a series of alkyl chains are used to assemble charge-transfer salts and films with dimethylthio-tetrathiafulvalene-bicarboxylate which aims to explore the relationship of the alkyl chain length to molecular structures and film morphologies which are important points for the design of molecular materials and manipulation of molecular devices. Four charge-transfer salts generally formulated as [(CnV)(HL)2] [n = 4(1), 8(2), 12(3) and 16(4)] are prepared and 1–3 are characterized by single-crystal X-ray structural analysis. In the short alkyl chain compound, TTF and C4V moieties are regularly arranged and effectively stacked with strong charge-transfer interactions. Lengthening the alkyl chain of the bipyridinium cation reduces the regular and close arrangement of the cations and anions in the crystals, which weakens the charge-transfer interaction while increasing the amphiphilic assembly of the films. Their film morphologies change from crystals to fused crystals, band-like structures and finally to smooth films with the increase of the alkyl chain length. The effects of alkyl chain length on photocurrent intensity are different between the crystal sample-modified electrodes (in the order of 1 > 2 > 3 = 4) and the film-modified electrodes (in the order of 2 > 1 = 3 > 4), because both inter-ion interactions and film-forming properties should be considered for the film electrodes. This is a systematic study of the effect of alkyl chain substitution on film morphologies in terms of crystal structures.

Development and Biosensor Applications of Novel Functional Electrodes.

Phenylboronic acid (PBA) derivatives have been used as alternatives to enzymes in the development of sugar-sensitive systems because the optical and electrochemical properties of these derivatives are significantly modulated upon sugar binding. This article reviews the voltammetric properties of sugar sensors prepared using dithiobis (4-butyrylamino-m-phenylboronic acid) (DTBA-PBA)-modified electrodes and PBA-appended layer-by-layer film-modified electrodes. In addition, the redox properties of reduced graphene oxide (rGO)-modified glassy carbon electrodes (GCEs) are discussed. The surface of a gold electrode was modified with a monolayer of DTBA-PBA to prepare sugar-sensitive electrodes. The modified electrodes exhibited attenuated cyclic voltammograms for Fe(CN)63-/4- in the presence of sugars at neutral pH as a result of their binding to DTBA-PBA on the electrode. Useful calibration curves were obtained for determining 3-300 mM D-glucose and 0.3-30 mM D-fructose. Similarly, gold electrodes coated with multilayer films composed of PBA-modified poly(allylamine hydrochloride) and carboxymethylcellulose exhibited a sugar-dependent response at neutral pH. The dynamic range of these modified electrodes was 0.1-300 mM for D-glucose and D-fructose. The surface of GCE was modified with rGO to evaluate the electrochemical response of the modified GCE to hydrogen peroxide (H2O2). The rGO-modified electrodes exhibited significantly higher responses in the redox reactions of H2O2 compared with the response of an unmodified GCE.

Electrochemical Determination of Catechol Based on Cadmium Telluride Quantum Dots/Graphene Composite Film Modified Electrode

A novel electrochemical sensor of catechol based on cadmium telluride quantum dots (CdTe QDs) /graphene (GR) composite film modified electrode was prepared by using the method of electrodeposition of the GR and dispensing CdTe QDs on the glassy carbon electrode (GCE). Meanwhile, the electrochemical behavior of catechol (CC) was studied by using cyclic voltammetry (CV) and differential pulse method (DPV). The experimental results showed the oxidation peak current of the CC on the modified electrodes had a significant enhancement compared with bare GCE. The oxidation peak current exhibited a good linear relationship in the concentration range from 30 to 1000 μmol L−1 (R = 0.9904) and the detection limit (LOD) was 18.28 μmol L−1 (S/N = 3),the quantification limit (LOQ) was 60.94 μmol L−1 (S/N = 10). And the repeatability of the method was also studied, the relative standard deviation (RSD) of the oxidation peak current was 3.79%. The prepared electrode showed good reproducibility, stability and was successfully applied to the actual sample testing, the result was satisfactory.

Layer-by-layer self-assembly of polyelectrolyte functionalized MoS2 nanosheets.

Few-layered polyelectrolyte functionalized MoS2 nanosheets were obtained for the first time through in situ polymerization of MoS2 nanosheets with poly(acrylic acid) and poly(acrylamide), both of which demonstrated excellent dispersibility and stability in water. After designing and optimizing the components of this series of polyelectrolyte functionalized MoS2 nanosheets, by exploiting the electrostatic interactions present in the modified MoS2 nanosheets, we further created a series of layer-by-layer (LBL) self-assembling MoS2-based films. To this end, uniform MoS2 nanosheet-based LBL films were precisely deposited on substrates such as quartz, silicon, and ITO. The polyelectrolyte functionalized MoS2 nanosheet assembled LBL film-modified electrodes demonstrated enhanced electrocatalytic activity for H2O2. As such, they are conducive to efficient sensors and advanced biosensing systems.

Fabrication of a highly b-oriented MFI-type zeolite film-modified electrode with molecular sieving properties by Langmuir–Blodgett method

A novel highly compact and b-oriented MFI-type zeolite monolayer was obtained by assembling sec-butanol-modified rounded-coffin-shaped silicalite-1 microcrystals by Langmuir–Blodgett (LB) method. The LB monolayer was subsequently tested as a seed layer for the secondary growth of uniformly b-oriented and defect-free MFI zeolite films on stainless steel substrates and platinum electrodes. Three different methods were evaluated for identifying a suitable synthesis route to suppress the undesired a-oriented twin growth during the synthesis of MFI films. The crystal intergrowth and orientation of the MFI films were characterized by scanning electron microscopy and X-ray diffraction (XRD). The crystallographic preferred orientation indices and preferred orientation coverage values calculated using the XRD data were used to quantitatively determine the preferred orientation and surface coverage of the prepared zeolite films. The experimental results confirm that the low tetrapropylammonium hydroxide (TPAOH) method is the most effective route to suppress the undesired a-oriented twin growth, when the highly b-oriented LB monolayer was used as the seed layer for the secondary growth of the b-oriented MFI film. The highly b-oriented MFI-type zeolite film-modified electrodes were further tested as the working electrodes in electrochemical experiments. Cyclic voltammetry experimental results confirmed that the b-oriented MFI films fabricated at low TPAOH concentration were defect free and possessed a distinct molecular sieving property after calcination. The LB method, a highly reproducible and controllable method for the organization of zeolite crystals, can be further applied as an effective platform for the promotion and development of zeolite-modified electrodes as selective sensors.

Simultaneous Determination of Dopamine, Uric Acid and Guanine at Polyadenine Film Modified Electrode.

A polyadenine film (PAE) modified glassy carbon electrode (GCE) was employed for the simultaneous determination of dopamine (DA), uric acid (UA) and guanine (GA). Experimental results showed that this modified electrode had good electrocatalytic properties for the oxidation of DA, UA and GA. Under optimal conditions, DA, UA and GA reflected their electrochemical response into three separated and well-defined oxidation peaks, whose currents increased 47-, 12-, and 7-fold, respectively, compared with those at bare electrode. Moreover, their oxidation peak currents were linear proportional to their concentrations within the ranges of 2.5 - 75, 10 - 750, and 7.5 - 75 μmol L(-1), respectively, and the limits of detection (LOD) (S/N = 3) were 0.075, 0.35, and 0.025 μmol L(-1), respectively. Compared with a variety of modified electrodes, this designed sensor had a wider linear range and lower LOD. Furthermore, the sensor exhibited good stability and reproducibility.

Enhanced PEC characteristics of pre-annealed CuS film electrodes by metalloporphyrin/polymer matrices

High conversion efficiency (η) values have been obtained from modified CuS film electrodes electrochemically deposited onto Glass/FTO. The modification involved pre-annealing the film followed by coating with tetra(-4-pyridyl)porphyrinato manganese (MnTPyP+) ions embedded inside a polyethylene (PE) matrix. The Glass/FTO/CuS/MnTPyP/PE electrodes exhibited enhanced photo-electrochemical (PEC) characteristics under solar simulated illumination (5.6mW/cm−2) in aqueous media, compared to the as-prepared Glass/FTO/CuS films which showed no PEC activity. Up to 17.4% efficiency and 85% fill factor (FF) values were obtained from the modified film electrodes. Such characteristics have not been widely known for metal chalcogenide based film electrodes before. Different pre-annealing temperatures were attempted and the 250°C temperature, followed by quenching, showed favorable results. Different aqueous redox couples were studied and the environmentally safe FeCl2/FeCl3 aqueous system showed highest PEC characteristics. Effect of pre-annealing on film electrode characteristics is discussed. The MnTPyP/PE matrix behaves as charge transfer catalyst for the holes across the CuS film/liquid junction.

Reusable electrochemical sensor for bisphenol A based on ionic liquid functionalized conducting polymer platform

The toxicity of bisphenol A (BPA) has attracted considerable attention, and the reported electrochemical sensors for BPA need further improvement in reusability due to serious surface fouling. In this study, a composite film is designed aiming to provide both an accurate and repeatable platform for BPA determination. The conducting poly(3,4-ethylenedioxythiophene) film (PEDOT) and ionic liquid 1-butyl-3-methylimidazolium bromide (BMIMBr) were modified onto screen-printed carbon electrodes (SPCE) by electropolymerization and drop/spin methods, respectively. The surface characteristics of the composite film were characterized by field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and surface water contact angle experiments. The composite film-modified electrodes exhibited a linear response to BPA in the range of 0.1–500µM in pH 7.0 phosphate buffer solution (PBS) under optimized flow-injection amperometry. The method sensitivity and detection limit (S/N=3) were 0.2661μAμM−1 (2.419μAμM−1cm−2) and 0.02µM, respectively. A relative standard deviation of 1.95% was obtained for 77 successive measurements of 10µM BPA, and the repeatability outperformed previously reported work. The proposed method was applied to detect BPA released from plastic water bottles using the standard addition method, and satisfactory recoveries were obtained. The electrochemical assay was validated by comparison with the chromatographic method, and the results showed good agreement between the two methods.

Simultaneous electrochemical determination of ascorbic acid, epinephrine, and uric acid using a polymer film-modified electrode based on Au nanoparticles/poly(3,3′,5,5′-tetrabromo-m-cresolsulfonphthalein)

A new polymer film-modified electrode based on the Au nanoparticles/poly(3,3′,5,5′-tetrabromo-m-cresolsulfonphthalein)/glassy carbon electrode (Au-NPs/poly(BCG)/GCE) was prepared for the simultaneous determination of ascorbic acid (AA), epinephrine (EP), and uric acid (UA). The prepared electrode, Au-NPs/poly(BCG)/GCE, was characterized by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR). The poly(BCG) film showed an efficient electrocatalytic activity for the oxidation of AA, UA, and EP. In addition, the prepared electrode separates the oxidation peak potential of AA-EP by 140 mV, and EP-UA by 140 mV, while the bare GCE cannot resolve them.

SDS/poly(alanine) Modified Carbon Paste Electrode based Voltammetric Sensors for the Detection of Norfloxacin

Electrochemical oxidation of norfloxacin (NX) at SDS/poly(alanine) film-modified carbon paste electrode (SPAMCPE) was studied by voltammetric technique in 0.2 M acetate buffer solution at pH 4.2. The modified electrode exhibited strong promoting effect and stability towards the detection of norfloxacin. From the studies of scan rate effect the overall electrode process was found to be adsorption controlled. The concentration effect reveals that the detection limit and quantification limit of norfloxacin were 6.6810-8 M and 2.2270-7 M respectively. The effect of pH suggested that equal number of protons and electrons were involved in the electrochemical oxidation of norfloxacin. The presence of SDS on the poly(alanine)film-modified carbon paste electrode showed excellent electrocatalytic effect towards the detection of norfloxacin.

Nickel-N,N’–bis(salicylidene)-1,3-propanediamine (Ni-Salpn) film-modified electrodes. Influence of electrodeposition conditions and of electrode material on electrochemical behaviour in aqueous solution

Modified electrodes based on films of Schiff base complexes are excellent candidates for sensing applications. The influence of the electrode material, glassy carbon, platinum, gold or indium tin oxide, on the electrodeposition of nickel-N,N’–bis(salicylidene)-1,3-propanediamine (Ni-Salpn) films in 1,2-dichloroethane (DCE) was investigated, and their electrochemical behaviour was evaluated by cyclic voltammetry and electrochemical impedance spectroscopy. The effect of the electrodeposition potential and electrodeposition time on the electrochemical behaviour of Ni-Salpn was examined using glassy carbon as substrate. The film growth process was investigated using the electrochemical quartz crystal microbalance and UV-vis absorption spectroscopy and structural differences between the Ni-Salpn complex and the Ni-Salpn film were examined by micro-Raman spectroscopy. The results demonstrate that the electrodeposition mechanism is independent of the electrode material, but that the nature of the substrate material influences the rate of film growth, the electrochemical behaviour and the stability of the film-modified electrodes in aqueous solution. Counteranion insertion during oxidation can break the bonds between the complexes in the stacked Ni-Salpn film structure and cause both mass loss and blockage of the redox metal centre activity, but these effects are small in thin films.

Amperometric Determination of Ascorbic Acid on an Au Electrode Modified by a Composite Film of Poly(3,4-ethylenedioxythiophene) and Superconductive Carbon Black.

A new composite film-modified electrode was prepared by the electropolymerisation of poly(3,4-ethylenedioxythiophene) (PEDOT) and superconductive carbon black (SCB) on a gold electrode. The PEDOT-SCB/Au electrode exhibited excellent ability towards the electrocatalytic oxidation of ascorbic acid, in terms of a 480 mV shift of the oxidation potential in the negative direction, and a dramatically enhanced oxidation current. Under the optimum conditions, the amperometric detection of ascorbic acid provided a wide linear detection range from 1.0 × 10(-7) to 8.0 × 10(-4) M, and a detection limit of 5.0 × 10(-8) M (S/N = 2) as well as good reproducibility and stability.

Evaluation of nicotine sensor based on copper nanoparticles and carbon nanotubes

An electrochemical sensor was prepared to de- tect nicotine by depositing copper nanoparticles (Cu NPs) on the surface of a glassy carbon electrode (GCE) modified with multi-walled carbon nanotubes (MWNTs). The mod- ified electrode was characterized by scanning electron mi- croscopy and cyclic voltammetry. The novel-modified sensor exhibited effective electrocatalytic activities toward anodic oxidation of nicotine. Calibration plot showed two linear regions with different sensitivity, 1.121 (r 2 = 0.982) in the range from 1 9 10 -6 to 9 9 10 -5 M and 0.164 (r 2 = 0.982) from 1 9 10 -4 Mu p to 19 10 -3 M. The detection limit was 1 lM. For six parallel detections of 1 mM nicotine, the relative standard deviation was 5.68 %, suggesting that the film-modified electrode had good re- producibility. Experimental parameters affecting the sensor response such as pH, modifier concentration and electro- deposition scan rate were found to be optimum at 7.0, 2m g mL -1 and 80 mV s -1 , respectively.

An electrochemical biosensor based on DNA tetrahedron/graphene composite film for highly sensitive detection of NADH.

Dihydronicotinamide adenine dinucleotide (NADH) is a major biomarker correlated with lethal diseases such as cancers and bacterial infection. Herein, we report a graphene-DNA tetrahedron-gold nanoparticle modified gold disk electrode for highly sensitive NADH detection. By assembling the DNA tetrahedron/graphene composite film on the gold disk electrode surface which prior harnessed electrochemical deposition of gold nanoparticles to enhance the effective surface area, the oxidation potential of NADH was substantially decreased to 0.28V (vs. Ag/AgCl) and surface fouling effects were successfully eliminated. Furthermore, the lower detection limit of NADH by the presented platform was reduced down to 1fM, with an upper limit of 10pM. Both the regeneration and selectivity of composite film-modified electrode are investigated and proved to be robust. The novel sensor developed here could serve as a highly sensitive probe for NADH detection, which would further benefit the field of NADH related disease diagnostics.

Determination of 4-nitrophenol at Iron Phthalocyanine Decorated Graphene Nanosheets Film Modified Electrode

Determination of 4-nitrophenol at Iron Phthalocyanine Decorated Graphene Nanosheets Film Modified Electrode