Poly(N-methylaniline)/nickel modified carbon paste electrode as an efficient and cheep electrode for electrocatalytic oxidation of formaldehyde in alkaline medium

This research in finding a cheap and efficient catalyst for electrooxidation of formaldehyde give us an attempt to make and examine the behavior of poly(N-methylaniline)/nickel modified carbon paste electrode (Ni/P(NMA)/MCPE) in absence and presence of formaldehyde. This involves in situ electropolymerization of N-methylaniline at carbon paste electrode, which is following to the incorporation of Ni(II) to polymeric layer by immersion of modified electrode in 1.0 M nickel sulphate solution. The electrocatalytic oxidation of formaldehyde was studied by cyclic voltammetry and chronoamperometry methods. The effects of scan rate and formaldehyde concentration on the electrocatalytic oxidation of formaldehyde were also investigated at the surface of Ni/P(NMA)/MCPE. The diffusion coefficient (D = 14.1 × 10⁻⁵ cm² s⁻¹), and some kinetic parameters such as the transfer coefficient (α = 0.45) and also second-order rate constant (k = 8.96 × 10⁻⁴ cm³ mol⁻¹ s⁻¹) of formaldehyde were calculated.     

Electrochemistry of magnolol and interaction with DNA

The electrochemical behaviors of magnolol have been studied at glassy carbon electrode using cyclic voltammetry, linear sweep voltammetry and chronocoulometry. Moreover, its interaction with DNA was investigated in solution by electrochemical methods and ultraviolet–visible spectroscopy. The experiment results indicated that the electrochemical oxidation of magnolol was an irreversible process with one proton and one electron transfer. The electron transfer coefficient (α) was calculated to be 0.441 ± 0.001. At the scan rate from 100 mV/s to 450 mV/s, the electrode process was controlled by the adsorption step and at the range of 600–950 mV/s the electrochemical oxidation was diffusion controlled process. The corresponding electrochemical rate constant (k_s) was 0.0760 ± 0.0001 s⁻¹. Through chronocoulometry experiment, the diffusion coefficient (D) and the surface concentration (Γ) were obtained as (3.76 ± 0.01) × 10⁻⁷ cm²/s and (2.98 ± 0.01) × 10⁻¹⁰ mol/cm². In addition, the interaction of magnolol and DNA was ascribed to be electrostatic interaction and the calculated association constant (β) and Hill coefficient (m) were 1.14 × 10⁵ M⁻¹ and 0.973. At last a sensitive and convenient electrochemical method was proposed for the determination of magnolol.     

Simultaneous determination of epinephrine and uric acid at a gold electrode modified by a 2-(2,3-dihydroxy phenyl)-1, 3-dithiane self-assembled monolayer

In the present paper, the use of a gold electrode modified by 2-(2,3-dihydroxy phenyl)-1,3-dithiane self-assembled monolayer (DPDSAM) for the determination of epinephrine (EP) and uric acid (UA) was described. Initially, cyclic voltammetry was used to investigate the redox properties of this modified electrode at various scan rates. The apparent charge transfer rate constant, k_s, and transfer coefficient, α, were calculated. Next, the mediated oxidation of EP at the modified electrode was described. At the optimum pH of 8.0, the oxidation of EP occurs at a potential about 155 mV less positive than that of an unmodified gold electrode. The values of electron transfer coefficients (α = 0.356), catalytic rate constant (k = 1.624 × 10⁴ M⁻¹ s⁻¹) and diffusion coefficient (D = 1.04 × 10⁻⁶ cm² s⁻¹) were calculated for EP, using electrochemical approaches. Based on differential pulse voltammetry, the oxidation of EP exhibited a dynamic range between 0.7 and 500.0 μM and a detection limit (3σ) of 0.51 μM. Furthermore, simultaneous determination of EP and UA at the modified electrode was described. Finally, this method was used for the determination of EP in EP ampoule.     

Preparation of poly N,N-dimethylaniline/ferrocyanide film modified carbon paste electrode: Application to electrocatalytic oxidation of l-cysteine

Functionalized poly N,N-dimethylaniline film was prepared by adsorption of ferrocyanide onto the polymer forming at the surface of carbon paste electrode (CPE) in aqueous solution. The electrocatalytic ability of poly N,N-dimethylaniline/ferrocyanide film modified carbon paste electrode (PDMA/FMCPE) was demonstrated by oxidation of l-cysteine. Cyclic voltammetry and chronoamperometry techniques were used to investigate this ability. In the optimum pH (6.00), the electrocatalytic ability about 480 mV and the catalytic reaction rate constant, (k_h), can be seen 3.08 × 10³ M⁻¹ s⁻¹. The catalytic oxidation peak current determined by cyclic voltammetry method was linearly dependent on the l-cysteine concentration and the linearity range obtained was 8.00 × 10⁻⁵ –2.25 × 10⁻³ M. Detection limit of this method was determined as 6.17 × 10⁻⁵ M (2σ). At a fixed potential under hydrodynamic conditions (stirred solution), the calibration plot was linear over the l-cysteine concentration range 7.40 × 10⁻⁶ M–1.38 × 10⁻⁴ M. The detection limit of the method was 6.38 × 10⁻⁶ M (2σ).     

Fabrication of functionalized carbon nanotube modified glassy carbon electrode and its application for selective oxidation and voltammetric determination of cysteamine

The functionalized carbon nanotube electrode was fabricated by electrodeposition of 1,2-naphthoquinone-4-sulfonic acid sodium (Nq) on single-wall carbon nanotube (SWNT) modified glassy carbon electrode (GCE). This electrode was characterized by scanning electron microscopy (SEM) and the results showed that Nq can rapidly and effectively be deposited on the surface of SWNT film with high stability. The electrochemical properties of functionalized SWNT/GCE with Nq (SWNT–Nq/GCE) were studied using cyclic voltammetry, double step potential chronoamperometry and differential pulse voltammetry methods. The results indicated that SWNT could improve the electrochemical behavior of Nq and greatly enhances its redox peak currents. The SWNT–Nq/GCE exhibited a pair of well-defined redox peaks. The experimental results also demonstrated that the Nq deposited species on SWNT could catalyze cysteamine oxidation and SWNT–Nq exhibited a high performance with lowering the overpotential by more than 710 mV. The effect of pH value, number of scans and Nq concentration were investigated on the electrochemical behavior of cysteamine. The selectivity of the reaction has been assessed with no interference from tyrosine, lysine, methionine, tryptophan, alanine and glutathione. The presented method has highly selectivity for voltammetric detection of cysteamine in the dynamic range from 5.0 × 10⁻⁶ M to 2.7 × 10⁻⁴ M and with a detection of limit (3σ) 3.0 × 10⁻⁶ M.     

MWNT/Nafion composite modified glassy carbon electrode as the voltammetric sensor for sensitive determination of 8-hydroxyquinoline in cosmetic

In this paper, a multiwall carbon nanotube/Nafion composite modified glassy carbon electrode (MWNT/Nafion/GCE) was used as a voltammetric sensor to determine 8-hydroxyquinoline (8-HQ) in cosmetic. This voltammetric sensor exhibited strong catalytic effect toward the oxidation of 8-HQ and caused an anodic peak at 0.97 V in HAc-NaAc buffer solution (0.2 M, pH 3.6). Under the optimized condition, the anodic peak current was linear with the concentration of 8-HQ in the range of 2 × 10⁻⁸ M–1.0 × 10⁻⁵ M. The detection limit was 9 × 10⁻⁹ M. The practical application of MWNT/Nafion/GCE was carried out for determining 8-HQ in cosmetic sample with satisfactory results. The electrode reaction mechanism was studied by cyclic voltammetry and UV–vis spectra.     

Highly temperature dependent mass-transport parameters for ORR in Nafion® 211

Nafion® 211 differs from previous versions of Nafion in that the membrane is cast from a dispersion rather than being melt-extruded. As such, the water sorption properties are different, as is the rate of increase in water content with temperature. Kinetic and mass-transport parameters for dispersion-cast Nafion® 211 were determined using solid-state electrochemistry in the temperature range 30–70 °C, 100% relative humidity, and 30 psi oxygen pressure. Exchange current densities, Tafel slopes, and transfer coefficients for ORR in Nafion® 211, are similar to those observed in Nafion® 117; mass-transport parameters are not. At 30 °C and 100% RH oxygen solubility and the diffusion coefficient is determined to be 1.16 × 10⁻⁵ mol cm⁻³ and 1.13 × 10⁻⁶ cm² s⁻¹, respectively. Oxygen permeability at 30 °C (1.28 × 10⁻¹¹ mol cm⁻¹ s⁻¹) is lower than in Nafion® 117 (5.31 × 10⁻¹¹ mol cm⁻¹ s⁻¹) by factor of 4, while at T > 60 °C the permeability of Nafion® 211 increases significantly to values higher than Nafion® 117, and is correlated with the increase in water content and hydration number (λ) with temperature.     

Simultaneous determination of adenine and guanine utilizing PbO2-carbon nanotubes-ionic liquid composite film modified glassy carbon electrode

A novel and reliable electrochemical sensor based on PbO₂-carbon nanotubes-room temperature ionic liquid (i.e., 1-butyl-3-methylimidazolium hexafluorophosphate, BMIMPF6) composite film modified glassy carbon electrode (GCE) (PbO₂–MWNT–RTIL/GCE) was proposed for simultaneous and individual determination of guanine and adenine. The guanine and adenine oxidation responses were monitored by differential pulse voltammetric (DPV) measurement. Compared with the bare electrode, the PbO₂–MWNT–RTIL/GCE not only significantly enhanced the oxidation peak currents of guanine and adenine, but also lowered their oxidation overpotentials, suggesting that the synergistic effect of PbO₂, MWNT and RTIL could dramatically improve the determining sensitivity of guanine and adenine. The PbO₂–MWNT–RTIL/GCE showed good stability, high accumulation efficiency and enhanced electrocatalytic ability for the detection of guanine and adenine. Besides, the modified electrode also exhibited good behaviors in the simultaneous detection of adenine and guanine with the peak separation of 0.29 V in 0.1 M pH 7.0 phosphate buffer solution (PBS). Under the optimal conditions, the detection limit for individual determination of guanine and adenine was 6.0 × 10⁻⁹ M and 3.0 × 10⁻⁸ M (S/N = 3), respectively. The proposed method for the measurements of guanine and adenine in herring sperm DNA was successfully applied with satisfactory results.     

Electrochemical impedimetry of electrodeposited poly(propylene imine) dendrimer monolayer

Voltammetric and electrochemical impedance spectroscopic (EIS) studies of generation one poly(propylene imine) (G1 PPI) dendrimer as an electroactive and catalytic nanomaterials both in solution and as an electrode modifier based on a simple one step electrodeposition method is presented. The G1 PPI exhibited a reversible one electron redox behaviour at E^0′ ca 210 mV in phosphate buffer pH 7.2 with diffusion coefficient and Warburg coefficient of 7.5 × 10⁻¹⁰ cm² s⁻¹ and 8.87 × 10⁻⁴ Ω s^−1/2 respectively. Cyclic voltammetric electrodeposition of a monolayer of G1 PPI on glassy carbon electrode was carried out between −100 mV and 1100 mV for 10 cycles. The nanoelectrode was electroactive in PBS at E^0′ ca 220 mV. Kinetic profiles such as time constant (4.64 × 10⁻⁵ s rad⁻¹), exchange current (1.55 × 10⁻⁴ A) and heterogeneous rate constant (4.52 × 10⁻³ cm s⁻¹) obtained from EIS showed that the dendrimer layer catalysed the redox reaction of Fe^2+/3+ in [Fe(CN)₆]^3−/4− redox probe.     

Sorption of water, ethanol or ethanol/water solutions by light-cured dental dimethacrylate resins

Objectives

This work is concerned with the study of the sorption and desorption process of water, ethanol or ethanol/water solution 50% (v/v) or 75% (v/v) by the dental resins prepared by light curing of Bis-GMA, Bis-EMA, UDMA, TEGDMA or D₃MA.

Methods

A thin resin disc is placed in a bath of time to obtain the sorption curve m_t = f(t). Then the liquid is desorbed until a constant mass for the disc is reached and the desorption curve is recorded. These experimental curves help in the determination of the sorbed/desorbed liquid amount at equilibrium, the percentage of the extracted mass of unreacted monomer known as “solubility”, and the sorption/desorption diffusion coefficient which expresses correspondingly the rate of the liquid sorption/desorption.

Results

The highest liquid uptake by dental resins was 13.3 wt% ethanol for Bis-GMA-resin, 12.0 wt% ethanol for UDMA-resin, 10.10 wt% ethanol/water solution for TEGDMA-resin, 7.34 wt% ethanol for D₃MA-resin and 6.61 wt% ethanol for Bis-EMA-resin. The diffusion coefficient for all resins was higher in water than in ethanol/water solution or ethanol. Bis-GMA-resin showed the highest diffusion coefficient (11.01 × 10⁻⁸ cm² s⁻¹) followed by Bis-EMA-resin (7.43 × 10⁻⁸ cm² s⁻¹), UDMA-resin (6.88 × 10⁻⁸ cm² s⁻¹), D₃MA-resin (6.22 × 10⁻⁸ cm² s⁻¹) and finally by TEGDMA-resin (1.52 × 10⁻⁸ cm² s⁻¹).

Significance

All studied dental resins, except TEGDMA-resin, absorbed higher amount of pure ethanol than water or ethanol water solution. TEGDMA-resin absorbed higher amount of ethanol/water solution (50/50 or 75/25 (v/v)) than water or ethanol. For all studied dental resins the diffusion coefficient was higher in water than in ethanol/water solution or ethanol.     

Voltammetric sensor based on ordered mesoporous carbon for folic acid determination

With ordered mesoporous carbon (OMC) as the modifier, a voltammetric sensor for folic acid (FA) was constructed on a glassy carbon electrode (GCE). Due to the good characteristics of OMC, FA exhibited an enhanced electrochemical response and lower reduction potential in the neutral solution. In addition, the experimental parameters such as pH values, accumulation time and potential were optimized. Using the differential pulse voltammetry (DPV) measurement, the peak current was found to be linear with FA concentration in the range from 5.0 × 10⁻¹⁰ to 1.0 × 10⁻⁷ M with a lower detection limit of 6.0 × 10⁻¹¹ M (S/N = 3). Also, in real samples analysis, the as-prepared sensor successfully gives satisfying results.     

A differential pulse voltammetric method for simultaneous determination of ascorbic acid,dopamine, and uric acid using poly (3-(5-chloro-2-hydroxyphenylazo)-4,5-dihydroxynaphthalene-2,7-disulfonic acid) film modified glassy carbon electrode

A stable modified glassy carbon electrode based on the poly 3-(5-chloro-2-hydroxyphenylazo)-4,5-dihydroxynaphthalene-2,7-disulfonic acid (CDDA) film was prepared by electrochemical polymerization technique to investigate its electrochemical behavior by cyclic voltammetry. The properties of the electrodeposited films, during preparation under different conditions, and their stability were examined. The homogeneous rate constant, k_s, for the electron transfer between CDDA and glassy carbon electrode was calculated as 5.25(±0.20) × 10² cm s⁻¹. The modified electrode showed electrocatalytic activity toward ascorbic acid (AA), dopamine (DA), and uric acid (UA) oxidation in a buffer solution (pH 4.0) with a diminution of their overpotential of about 0.12, 0.35, and 0.50 V for AA, DA, and UA, respectively. An increase could also be observed in their peak currents. The modified glassy carbon electrode was applied to the electrocatalytic oxidation of DA, AA, and UA, which resolved the overlapping of the anodic peaks of DA, AA, and UA into three well-defined voltammetric peaks in differential pulse voltammetry (DPV). This modified electrode was quite effective not only for detecting DA, AA, and UA, but also for simultaneous determination of these species in a mixture. The separation of the oxidation peak potentials for ascorbic acid–dopamine and dopamine–uric acid were about 0.16 V and 0.17 V, respectively. The final DPV peaks potential of AA, DA and UA were 0.28, 0.44, and 0.61 V, respectively. The calibration curves for DA, AA, and UA were linear for a wide range of concentrations of each species including 5.0–240 μmol L⁻¹ AA, 5.0–280 μmol L⁻¹ DA, and 0.1–18.0 μmol L⁻¹ UA. Detection limits of 1.43 μmol L⁻¹ AA, 0.29 μmol L⁻¹ DA and 0.016 μmol L⁻¹ UA were observed at pH 4. Interference studies showed that the modified electrode exhibits excellent selectivity toward AA, DA, and UA.     

Scanning electrochemical microscope studies of dye regeneration in indoline (D149)-sensitized ZnO photoelectrochemical cells

A scanning electrochemical microscope (SECM) in the feedback and generation-collection modes was used to investigate the regeneration of photoexcited dye cations at the semiconductor/electrolyte interface in a dye-sensitized solar cell (DSSC) based on ZnO/D149. An effective dye regeneration rate constant k_ox of 9.55 × 10⁷ cm^9/2 mol^−3/2 s⁻¹ was obtained from feedback mode experiments at different wavelengths and light intensities on ZnO/D149 electrodes. Illuminated regions of the dye-sensitized electrodes could be differentiated from non-illuminated regions by local imaging in SECM generation-collection experiments with I^- as redox mediator. We also report SECM feedback measurements on non-illuminated dye-sensitized electrodes to investigate the electron transfer kinetics of dissolved redox couples at the underlying FTO substrate.     

EIS characterization of tantalum and niobium oxide films based on a modification of the point defect model

Electrochemical impedance spectroscopy (EIS) studies were performed to analyze the passive properties of tantalum and niobium oxides films potentiostatically formed in a 0.1 M KOH solution. The quantitative characterization of these passive materials was carried out through a transfer function previously developed by our research group, which is based on the point defect model (PDM) framework considering the formation of molecular hydrogen. According to the PDM prediction criteria, Ta₂O₅ and Nb₂O₅ films exhibited an inherent n-type semiconductor behavior, which was confirmed by the parameters obtained from the fit to the transfer function. The diffusion coefficients of the oxygen vacancies were 0.53 ± 0.14 × 10⁻¹⁶ and 2.18 ± 0.14 × 10⁻¹⁶ cm² s⁻¹, for Ta₂O₅ and Nb₂O₅, respectively. And a slight increase of the corresponding hydroxyl vacancies diffusion (2.73 ± 0.02 and 2.23 ± 0.65 × 10⁻¹⁶ cm² s⁻¹) was obtained, suggesting the favorable diffusion of these defects due to the alkaline conditions.     

Development of a carbon nanotubes paste electrode modified with crosslinked chitosan for cadmium(II) and mercury(II) determination

A functionalized carbon nanotubes paste electrode modified with cross-linked chitosan for the determination of trace amounts of cadmium(II) and mercury(II) by linear anodic stripping voltammetry is described. Under optimal experimental conditions, the peak current was linear in the Cd(II) concentration range from 5.9 × 10⁻⁸ to 1.5 × 10⁻⁶ mol L⁻¹ with a detection limit of 9.8 × 10⁻⁹ mol L⁻¹ and, for Hg(II) from 6.7 × 10⁻⁹ to 8.3 × 10⁻⁸ mol L⁻¹with a detection limit of 2.4 × 10⁻⁹ mol L⁻¹. The proposed method was successfully applied for the determination of Hg(II) in natural and industrial wastewater samples, and Cd(II) in sediments, human urine, natural, and industrial wastewater samples.     

Electrochemical detection of ethidium bromide by using pure single-walled carbon nanotube sheet as the electrode

Sheets consisted of entire single-walled carbon nanotubes (SWNTs) were used as the working electrode for electrochemical measurement of ethidium bromide by covering a glassy carbon electrode (GCE) using the SWNT-sheet. This SWNT-sheet based electrode exhibited a fast electron transfer process on the electrode surface via the cyclic voltammetry with K₄Fe(CN)₆ as electrochemical probes. This SWNT-sheet based electrode showed also a high sensitivity toward ethidium bromide, a typically harmful, aromatic backboned chemical. The SWNT-sheet based electrode was capable of accumulating ethidium bromide to a higher concentration and therefore was capable of detecting ethidium bromide with a detection limit of 1.0 × 10⁻⁸ M.     

Silver nanoparticles modified carbon nanotube paste electrode for simultaneous determination of dopamine and ascorbic acid

A novel modified carbon-paste electrode was employed for the simultaneous determination of dopamine (DA) and ascorbic acid (AA) with good selectivity and high sensitivity. Silver nanoparticle and carbon nanotube modified carbon-paste electrode (Ag/CNT–CPE) displayed excellent electrochemical catalytic activities towards dopamine (DA) and ascorbic acid (AA). The oxidation overpotentials of DA and AA were decreased significantly compared with those obtained at the bare CPE. Differential pulse voltammetry was used for the simultaneous determination of DA and AA. The peak separation between DA and AA was 67 mV. The calibration curves for DA and AA were obtained in the range of 8.0 × 10⁻⁷–6.4 × 10⁻⁵ M and 3.0 × 10⁻⁵–2.0 × 10⁻³ M, respectively. The lowest detection limits (S/N = 3) were 3.0 × 10⁻⁷ M and 1.2 × 10⁻⁵ M for DA and AA, respectively. Method was applied to the determination of DA and AA in real samples.     

Selective determination of dopamine in the presence of ascorbic acid at a multi-wall carbon nanotube-poly(3,5-dihydroxy benzoic acid) film modified electrode

A sensitive and selective method for determination of dopamine (DA) using multi-wall carbon nanotube (MWCNT)-poly(3,5-dihydroxy benzoic acid) [poly(DBA)] modified electrode is developed. The modified electrode shows excellent electrocatalytic activity toward the oxidation of dopamine in phosphate buffer solutions at pH 7.4. Using cyclic voltammetry, the linear range of 1 × 10⁻⁷–7.0 × 10⁻⁵ M in the interference of 500 μM ascorbic acid (AA) and the detection limit of 1.0 × 10⁻⁸ M were estimated for the measurement of DA in pH 7.4 phosphate buffer solutions. The value of DA current retained 98.36% of the initial response current after the modified electrode exposed to the air for one week. The interference studies showed that the modified electrode excludes effectively large excess of AA. The kinetic characteristics of the transfer of DA demonstrated that the electron propagation between DA and electrode was accelerated at MWCNT-poly(DBA) modified electrode. The work provided a valid and simple approach to selectively detect dopamine in the presence of AA in physiological environment.     

Simultaneous determination of dopamine,ascorbic acid and uric acid on ordered mesoporous carbon/Nafion composite film

Here we report the selective, sensitive and simultaneous determination of dopamine (DA), ascorbic acid (AA) and uric acid (UA) on ordered mesoporous carbon (OMC)/Nafion composite film. Insoluble OMC was dispersed into ethanol in the presence of 0.5% Nafion, resulting in a stable and well-distributed OMC/Nafion suspension. After evaporation of ethanol, a uniform OMC/Nafion composite film-coated glassy carbon electrode (GCE) was achieved by simple casting deposition. The OMC/Nafion electrode shows ideal reversibility in 5 mM K₃[Fe(CN)₆] in the range of 0.02–0.50 V s⁻¹, indicating a fast electron-transfer kinetics. Moreover, due to the strong catalytic function of OMC, the overlapping voltammetric response of DA, AA and UA is well-resolved from each other with lowered oxidation potential and enhanced oxidation currents. The mechanism for the oxidation of AA, DA and UA at the OMC/Nafion film was also studied. By using differential pulse voltammetry (DPV), detection limits of 0.5, 20 and 4.0 μM were obtained for DA, AA and UA, respectively. The practical application of the electrode is successfully demonstrated for the determination of DA, AA and UA simultaneously in standard and real samples, without any preliminary treatment.     

Electrodeposited indigotetrasulfonate film onto glutaraldehyde-cross-linked poly-l-lysine modified glassy carbon electrode for detection of dissolved oxygen

The nano composited film of indigotetrasulfonate (ITS) electrodeposited onto poly-l-lysine (PLL)–glutaraldehyde (GA) (ITS/PLL–GA) was modified on glassy carbon electrode (GCE) by multiple scan cyclic voltammetry. Composited of the proposed film was characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), electrochemical quartz crystal microbalance (EQCM), electrochemical impedance spectroscopy (EIS), and UV–vis spectrum for the absorption at λ_max at 566 nm. For the electrocatalytic reduction of dissolved oxygen, ITS/PLL–GA film modified electrodes was determined in 0.1 M acetate buffer solution (pH 5.6) by cyclic voltammetry and rotating disk electrode voltammetry. This dissolved oxygen electrochemical sensor exhibited a linear response range (from 0 to 178.4 μM, R² = 0.9949), lowest detection limit (2.2 μM), lowest overpotential at −0.09 V, high sensitivity (906 μA mM⁻¹) and relative standard deviation (RSD) for determining dissolved oxygen (n = 3) was 4.2%. In addition, the ITS/PLL–GA/GCE was advantageous in terms of its simple preparation, specificity, stability and the ability of regeneration.