Anodic electrochemiluminescent behavior of lucigenin on MWNT/GCE

The electrochemiluminescent (ECL) behavior of lucigenin on a multiwall carbon nanotubes modified glassy carbon electrode (MWNT/GCE) during anodic scanning was studied. A strong and stable anodic ECL signal was found on MWNT modified electrode, which results from the oxidation reaction between lucigenin and the oxidation production of OH^-. The effects of electrode materials, pH and scan rate on the ECL intensity were studied, and the possible ECL mechanism was also proposed. Under the optimized conditions, the ECL intensity was found to be linear with concentration of lucigenin in the range of 5.0 × 10^?7–5.0 × 10^?6 mol/L with a detection limit of 2.0 × 10^?7 mol/L. Superoxide dimutase (SOD) was found to be able to inhibit this ECL system, based on which a sensitive ECL methods for detection of SOD had been established.     

Electrochemiluminescent biosensor based on multi-wall carbon nanotube/nano-Au modified electrode

The electrochemiluminescent (ECL) behavior of lucigenin on a multi-wall carbon nanotube/nano-Au modified glassy carbon electrode (MWNT/nano-Au/GCE) was studied in this paper. Compared with the bare GCE, the ECL intensity of lucigenin can be greatly enhanced at MWNT/nano-Au/GCE. Based on the fact that superoxide dimutase (SOD) could obviously inhibit the ECL of lucigenin at MWNT/nano-Au/GCE, a sensitive ECL biosensor for determination of SOD was developed with a wide linear range of 5.0 × 10⁻⁸–5.0 × 10⁻⁶ mol/L with detection limit of 2.5 × 10⁻⁸ mol/L.     

Detection of hypoxanthine based on the electrochemiluminescent of 6-(4-methoxyphenyl)-2-methylimidazo[1,2-a]pyrazin-3(7H)-one on the electrically heated indium–tin-oxide electrode

An electrochemiluminescent (ECL) enzyme biosensor was developed for detection of hypoxanthine based on ECL of 6-(4-methoxyphenyl)-2-methylimidazo[1,2-a]pyrazin-3(7H)-one (MCLA). The xanthine oxidase (XOD) was modified on the heated indium–tin-oxide (ITO) electrode, and the ECL enzyme biosensor was found to be electrode temperatures depend, this was because that both the diffusion and convection of compounds near the electrode surface and the catalytic reaction of immobilized enzyme were affected by the temperature of electrode (T_e). In this work, the highest sensitivity was gained when T_e was 36 °C. Under the optimum condition, the linear response range of hypoxanthine (HX) was found to be 0.3–27 μmol/L, and the detection limit (defined as the concentration that could be detected at the signal-to-noise ration of 3) was 0.15 μmol/L.     

Electrogenerated chemiluminescence aptamer-based biosensor for the determination of cocaine

A novel electrogenerated chemiluminescence aptamer-based (ECL-AB) biosensor for the determination of a small molecule drug is designed employing cocaine-binding aptamer as molecular recognition element for cocaine as a model analyte and ruthenium complex served as an ECL label. A 5′-terminal cocaine-binding aptamer with the ECL label at 3′-terminal of the aptamer was utilized as an ECL probe. The ECL-AB biosensors were fabricated by immobilizing the ECL probe onto a gold electrode surface via thiol-Au interactions. An enhanced ECL signal is generated upon recognition of the target cocaine, attributed to a change in the conformation of the ECL probe from random coil-like configuration on the probe-modified film to three-way junction structure, in close proximity to the sensor interface. The integrated ECL intensity versus the concentration of cocaine was linear in the range from 5.0 × 10⁻⁹ to 3.0 × 10⁻⁷ M. The detection limit was 1.0 × 10⁻⁹ M. This work demonstrates that the combination of a highly binding aptamer to analyte with a highly sensitive ECL technique to design ECL-AB biosensor is a great promising approach for the determination of small molecule drugs.     

Amperometric biosensing of glutamate using carbon nanotube based electrode

Amperometric biosensing of glutamate using nanobiocomposite derived from multiwall carbon nanotube (CNT), biopolymer chitosan (CHIT), redox mediator meldola’s blue (MDB) and glutamate dehydrogenase (GlDH) is described. The CNT composite electrode shows a reversible voltammetric response for the redox reaction of MDB at −0.15 V; the composite electrode efficiently mediates the oxidation of NADH at −0.07 V, which is 630 mV less positive than that on an unmodified glassy carbon (GC) electrode. The CNTs in the composite electrode facilitates the mediated electron transfer for the oxidation of NADH. The CNT composite electrode is highly sensitive (5.9 ± 1.52 nA/μM) towards NADH and it could detect as low as 0.5 μM of NADH in neutral pH. The CNT composite electrode is highly stable and does not undergo deactivation by the oxidation products. The electrode does not suffer from the interference due to other anionic electroactive compounds such as ascorbate (AA) and urate (UA). Separate voltammetric peaks have been observed for NADH, AA and UA, allowing the individual or simultaneous determination of these bioanalytes. The glutamate biosensor was developed by combining the electrocatalytic activity of the composite film and GlDH. The enzymatically generated NADH was electrocatalytically detected using the biocomposite electrode. Glutamate has been successfully detected at −0.1 V without any interference. The biosensor is highly sensitive, stable and shows linear response. The sensitivity and the limit of detection of the biosensor was 0.71 ± 0.08 nA/μM and 2 μM, respectively.     

Enhanced electrochemiluminescence based on Ru(bpy)32+-doped silica nanoparticles and graphene composite for analysis of melamine in milk

A sensitive electrochemiluminescence (ECL) sensor for melamine analysis was fabricated based on Ru(bpy)₃²⁺-doped silica (Ru(bpy)₃²⁺@SiO₂) nanoparticles and graphene composite. Spherical Ru(bpy)₃²⁺@SiO₂ nanoparticles with uniform size about 55 nm were prepared by the reverse microemulsion method. Since per Ru(bpy)₃²⁺@SiO₂ nanoparticle encapsulated a great deal of Ru(bpy)₃²⁺, the ECL intensity has been greatly enhanced, which resulted in high sensitivity. Due to its extraordinary electric conductivity, graphene improved the conductivity and accelerated the electron transfer rate. In addition, graphene could work as electronic channel improving the efficient luminophor amount participating in the ECL reaction, which further enhanced the ECL signal. This proposed sensor was used to melamine analysis and the ECL intensity was proportional to logarithmic melamine concentration range from 1 × 10⁻¹³ M to 1 × 10⁻⁸ M with the detect limit as low as 1 × 10⁻¹³ M. In application to detect melamine in milk, satisfactory recoveries could be obtained, which indicated this sensor having potential application in melamine analysis in real samples.     

Review on applications of carbon nanomaterials for simultaneous electrochemical sensing of environmental contaminant dihydroxybenzene isomers

Carbonaceous nanostructures stand out as an excellent electrode material to enhance the electrocatalytic, electroconductivity, and long-term stability of the electrochemical sensor in recent years. This review article focus on the important advancement in developing carbonaceous nanomaterials-based electrochemical sensors for simultaneous electrochemical sensing (binary and ternary mixtures) of environmental contaminants dihydroxybenzene isomers. The fabrication of electrochemical sensors such as graphene/carbon nanotubes hybrid composite, graphene/ carbon nanotubes supported nanomaterials, mesoporous carbon, carbon nanofiber, carbon nano-fragment and biochar modified electrode was presented coupled with suitable applications. This review discussed the selective reports on the application of dihydroxybenzene sensors during the period from 2015 to 2020.     

Simultaneous determination of ascorbic acid,epinephrine, and uric acid by differential pulse voltammetry using poly(p-xylenolsulfonephthalein) modified glassy carbon electrode

A novel poly(p-xylenolsulfonephthalein) modified glassy carbon electrode was prepared for the simultaneous determination of ascorbic acid (AA), epinephrine (EP) and uric acid (UA). Cyclic voltammetric, chronoamperometric, and differential pulse voltammetric methods were used to investigate the modified electrode for the electrocatalytic oxidation of EP, AA, and UA in aqueous solutions. The separation of the oxidation peak potentials for AA–EP and EP–UA was about 200 and 130 mV, respectively. The calibration curves obtained for AA, EP, and UA were in the ranges of 10–1343, 2–390, and 0.1–560 μmol L⁻¹, respectively. The detection limits (S/N = 3) were 4, 0.1, and 0.08 μmol L⁻¹ for AA, EP and UA, respectively. The diffusion coefficient and the catalytic rate constant for the oxidation of EP at the modified electrode were calculated as 1.40(±0.10) × 10⁻⁴ cm² s⁻¹ and 1.06 × 10³ mol⁻¹ L s⁻¹, respectively. The present method was applied to the determination of EP in pharmaceutical and urine samples, AA in commercially available vitamin C tablet, and EP plus UA in urine samples.     

Amperometric determination of NADH at a Nile blue/ordered mesoporous carbon composite electrode

A novel amperometric NADH sensor was presented based on a Nile blue A (NB)/ordered mesoporous carbon (OMC) composite (NB/OMC) electrode. Cyclic voltammetric tests revealed the NB/OMC displayed a new well defined redox couple in the potential range of ?250 to 50 mV in pH 6.85 phosphate buffer. Interestingly, we found that only the new redox couple exhibited significant catalytic activity towards the oxidation of NADH. Under a lower operation potential of ?0.1 V, NADH could be linearly detected up to 350 μM with an extremely lower detection limit of 1.2 μM (S/N = 3).     

Selective determination of uric acid with DNA doped polymers modified carbon fiber microelectrode

New biocomposite materials, based on the incorporation of DNA doped p-aminobenzensulfonic acid, was fabricated by electrochemical method. A carbon fiber microelectrode modified by this thin film was fabricated for selective determination of uric acid (UA) in the presence of a larger amount of ascorbic acid (AA). It was found that the voltammetric oxidation peak separation between UA and AA is about 260 mV at the modified electrode. A linear response of the peak current versus the concentration was found in the range of 8 × 10⁻⁷–6 × 10⁻⁴ M with correlation coefficient of 0.9991 and the detection limit was 5 × 10⁻⁷ M (s/n = 3) at the 5 × 10⁻⁴ M AA. The presence of high concentration AA did not interference the determination. The electropolymerized film was characterized by SEM techniques. The modified electrode shows good sensitivity, selectivity and stability.     

Highly efficient electrogenerated chemiluminescence of natural chlorophyll a

Highly efficient electrogenerated chemiluminescence (ECL) of natural chlorophyll a (Chl a) was observed in acetonitrile with 1-butyl-3-methylimidazolium hexafluorophosphate as electrolyte and tri-n-propylamine (TPrA) as a coreactant. The collected ECL spectrum displayed a maximum emission peak at ca. 670 nm, suggesting that the same excited states with the photo-excitation processes were generated. The possible ECL reaction mechanism of this Chl a–TPrA system was discussed and established. ECL intensity of Chl a was proportional to its concentration over the range of 0.1–11 μM, and a high ECL efficiency (Φ_ecl) of 0.86 was calculated using Ru(bpy)₃^2 + as the standard (Φ_ecl = 1). Herein, an important property of natural Chl a was expanded and a new kind of ECL luminophores was developed. Moreover, it is expected that this high ECL efficiency of natural porphyrin complex has great potential to expand its ECL sensing application.     

Electrochemical investigation of platinum-coated gold nanoporous film and its application for Escherichia coli rapid measurement

Pt-nanoparticle-coated gold nanoporous film (PGNF) was synthesized via a simple nonpolluting approach and PGNF modified electrode was also constructed successfully for the rapid measurement of Escherichia coli (E. coli) in this work. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) images showed that the resulting PGNF electrode had highly ordered arrangement and large surface area. Furthermore, the electrochemical characteristics of the PGNF electrode were investigated by cyclic voltammetry (CV) and amperometric i-t curve. The PGNF electrode showed excellent electrocatalytic activity to E. coli and the current responses were in good linear from 2 × 10¹ cfu/ml to 1 × 10⁶ cfu/ml with the detection limit of 10 cfu/ml (S/N = 3) without pretreatment. The high sensitivity, wider linear range and good reproducibility make this PGNF a promising candidate for portable amperometric E. coli sensor.     

Amperometric ascorbic acid biosensor based on carbon nanoplatelets derived from ground cherry husks

In this work, a novel amperometric biosensor based on carbon nanoplatelets derived from ground cherry (Physalis peruviana) husks (GCHs-CNPTs) is reported for the sensitive and selective detection of ascorbic acid (AA). The structure of the nanoplatelets, the oxygen-containing groups and edge-plane-like defective sites (EPDSs) on the GCHs-CNPTs were characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The presence of GCHs-CNPTs with a high density of EPDSs effectively enhances the electron transfer between AA and the glassy carbon electrode (GCE), and thus induces a substantial decrease in the overvoltage for AA oxidation compared with both a bare GCE and a GCE modified with carbon nanotubes (CNTs/GCE). In particular, an amperometric biosensor based on GCHs-CNPTs exhibited a wider linear range (0.01–3.57 mM), higher sensitivity (208.63 μA mM^− 1 cm^− 2), a lower detection limit (1.09 μM, S/N = 3) and better resistance to fouling for AA determination compared to a CNTs/GCE. The great potential of the GCHs-CNPTs/GCE for practical and reliable AA analysis was demonstrated by the successful determination of AA in samples taken from a medical injection dose and a soft drink.     

Synergistic contributions of multiwall carbon nanotubes and gold nanoparticles in a chitosan–ionic liquid matrix towards improved performance for a glucose sensor

We report an ingenious approach for the fabrication of a promising glucose sensor, GOx/Au/CS–IL–MWNT(SH), that exploits the synergistic beneficial characteristics of multiwalled-carbon nanotubes (MWNTs), gold nanoparticles (AuNPs), chitosan (CS) and room temperature ionic liquid (RTIL). Direct electron transfer between glucose oxidase (GOx) and electrode was achieved. Scanning electron microscopy and atomic force microscopy images of GOx/Au/CS–IL–MWNT(SH) reveal that MWNTs and AuNPs are dispersed in CS–IL matrix. Cyclic voltammetry, impedance spectroscopy and chronoamperometry were used to evaluate the performance of biosensor. The GOx/Au/CS–IL–MWNT(SH) biosensor exhibits a linear current response to glucose concentration (1–10 mM) at a low potential of 0.10 V and precludes interferences from uric acid and ascorbic acid. The GOx/Au/CS–IL–MWNT(SH) biosensor has superior performances over GOx/CS–IL–MWNT(SH).     

Ultrasonic-electrodeposition of gold–platinum alloy nanoparticles on multi-walled carbon nanotubes – ionic liquid composite film and their electrocatalysis towards the oxidation of nitrite

We report here for the first time on the electrochemical co-deposition of gold–platinum (AuPt) nanoparticles on multi-walled carbon nanotubes (MWNT) – ionic liquid (i.e. trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide, [P_6,6,6,14][NTf₂]) composite surface in ultrasonic field. The obtained AuPt nanoparticles were characterized by scanning electron microscope, X-ray diffraction and X-ray photoelectron spectroscopy. It was found that they were well-dispersed on the composite surface, with particle size about 10 nm. Furthermore, they exhibited alloy features. Electrochemical impedance spectroscopy and voltammetric experiments showed that the resulted AuPt-MWNT-[P_6,6,6,14][NTf₂] modified electrode possessed rather small electron transfer resistance and good catalytic activity towards nitrite oxidation. Under the optimized conditions, the oxidation current of nitrite was linear to its concentration in the range of 5–200 nM and the detection limit was down to 1.0 nM (S/N = 3).     

Amperometric sensing of dopamine using a single-walled carbon nanotube covalently attached to a conical glass micropore electrode

A single-walled carbon nanotube (SWNT) is covalently attached to the interior surface of a conical glass micropore electrode (GME) to create a novel amperometric dopamine sensor (SWNT/NH-GME). The SWNT/NH-GME combines the advantages of excellent transport properties of the cone-shaped micropore with the characteristics of a SWNT, exhibiting a dramatic electrocatalytic effect on the oxidation of dopamine (DA). Cyclic voltammetry and amperometric methods were employed to study the electrochemical behavior of the SWNT/NH-GME. The results showed that the SWNT/NH-GME sensor exhibited an excellent immunity from ascorbic acid interference and was able to measure DA concentrations with a detection limit of 4.2 × 10^?7 mol/L (S/N = 3).     

Determination of hydrogen sulfide in gasoline by Au nanoclusters modified glassy carbon electrode

A promising hydrogen sulfide (H₂S) sensor was prepared by electrodeposition of Au nanoclusters on glassy carbon electrode (GCE) and the surface structure was characterized by SEM and EDAX. These flower-like form Au nanoclusters, which were made up of highly dense clustering Au nanorods with an average diameter of 20 nm and length up to 80 nm, had an average size about 600 nm and uniformly distributed on the GCE surface. The electrocatalytic oxidation of H₂S in gasoline was performed on this modified electrode, which had a satisfactory liner response to H₂S in the range of 1–80 ppm and a detection limit of 0.45 ppm (s/n = 3). This sensor was sensitive, selective and stable.     

CtrA gene based electrochemical DNA sensor for detection of meningitis

Electrochemical DNA sensor has been fabricated by immobilizing thiolated single stranded oligonucleotide (ssDNA) probe onto gold (Au) coated glass electrode for meningitis detection using hybridization with complementary DNA (CtrA) in presence of methylene blue (MB). These electrodes (ssDNA/Au and dsDNA/Au) have been characterized using atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT-IR), electrochemical impedance spectroscopy (EIS) and cyclic voltammetric (CV) technique. The DNA/Au electrode can detect the complementary DNA in the range of 7–42 ng/μl in 5 min (hybridization) with response time 60 s and electrode is stable for about 4 months when stored at 4 °C. The sensitivity of dsDNA/Au electrode is 115.8 μA/ng with 0.917 regression coefficient (R).     

A new composite electrode of Ni-Ferrite/TiOx/Si(111): Preparations and photoelectrochemical studies

A composite electrode of Ni-ferrite/TiO_x/Si(111) was synthesized by grafting Ni²⁺Fe²⁺Fe³⁺–LDH–TiCl₃ (LDH: Layered Double Hydroxides) on n-Si(111) surface and calcined under 1100 °C. Photoelectric research results indicated that the electrode had good photovoltaic effects in an electrolyte solution containing 7.6 M HI and 0.05 M I₂, while platinum plate was used as counter-electrode. The observed photo-voltages (U_pv) and photocurrent densities (j_pc) of the electrode were at ?0.75 V and 5.35 mA/cm², respectively. Compared with electrodes of oxidized n-Si(111) crystal and n-Si(111) wafer covered by Ni-ferrites, j_pc of the electrode Ni-ferrite/TiO_x/Si(111) was increased greatly.     

Bismuth nano-powder electrode for trace analysis of heavy metals using anodic stripping voltammetry

In the present work, a more sensitive and conveniently usable electrode sensor for a trace analysis of heavy metal was developed by using Bi nanopowder synthesized by levitational gas condensation (LGC) method. It was observed from the TEM image that the Bi nanopowder is spherical in shape with a size of nearly 50 nm. The XRD pattern revealed intense peaks which can be indexed as a rhombohedral structure of Bi without any other diffraction peaks corresponding to an oxide or an impurity. This indicates that the resulting nanopowder synthesized by the LGC method is a highly crystallized Bi with a high purity. The square wave anodic stripping voltammograms (SWASV), experimentally measured for the Bi nanopowder electrode, showed well-defined and highly reproducible electrochemical responses relating to the stripping of Cd and Pb. The detection limit of the electrode was estimated to be 0.15 μg/l and 0.07 μg/l for Cd and Zn, respectively, on the basis of the signal-to-noise characteristics (S/N = 3) of the response for the 1.0 μg/l solution under a 10 min accumulation.