Effects of replacing wheat bran with palm kernel cake or fermented palm kernel cake on the growth performance, intestinal microbiota and intestinal health of tilapia (GIFT, Oreochromis niloticus).

A nine-week feeding trial was conducted to evaluate the effects of replacing wheat bran (WB) with palm kernel cake (PKC) or fermented palm kernel cake (FPKC) on the growth performance, intestinal microbiota and intestinal health of genetically improved farmed tilapia (GIFT, Oreochromis niloticus) (initial weight 7.00 ± 0.01 g). Eleven isonitrogenous and isolipidic experimental diets were formulated by replacing 0, 20, 40, 60, 80, and 100% of dietary WB with PKC or FPKC. Replacement of WB with PKC concentrations up to 80% had no significant effect on the growth rate of tilapia or feed utilisation (p > 0.05). FPKC improved the growth performance of tilapia, with optimum growth achieved at 40% replacement level (p < 0.05). Complete replacement with PKC significantly decreased the activity of lipase and trypsin, and reduced the height of muscularis and the height of villus (p < 0.05). However, FPKC significantly increased amylase activity and villus height (p < 0.05). The apparent digestibility of dry matter and energy decreased linearly with increasing levels of PKC substitution, while FPKC showed the opposite trend (p < 0.05). PKC replacement of WB by 20% significantly reduced serum diamine oxidase activity and endothelin levels and increased intestinal tight junctions (p < 0.05). However, FPKC significantly decreased diamine oxidase activity and increased intestinal tight junctions (p < 0.05). PKC completely replaced WB, up-regulating the expression of pro-inflammatory factors (il-1ß) (p < 0.05). When 40% of WB was replaced with FPKC, the expression of pro-inflammatory factors (il-1ß and il-6) was decreased significantly (p < 0.05). Completely replacement of WB with PKC reduced the abundance of Firmicutes and Chloroflexi, while FPKC reduced the abundance of Fusobacteriota and increased the levels of Actinobacteriota. WB can be replaced with PKC up to 80% in tilapia feeds. However, the high percentage of gluten induced intestinal inflammation, impaired gut health, and reduced dietary nutrient utilisation and growth performance. Complete replacement of WB with FPKC promoted intestinal immunity. It also improved dietary nutrient utilisation and growth performance. However, the optimal growth was achieved at a 40% replacement level.

Novel nitrite sensing using a palladium-polyphenosafranine nano-composite.

A novel palladium-polyphenosafranine nano-composite (PPS-Pd) was synthesized by electrochemical co-deposition at a glassy carbon electrode (GCE) for fabrication of a nitrite sensor, PPS-Pd/GCE. This PPS-Pd film was characterized by X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microanalysis (SEM). It was found that the PPS-Pd nano-composite consisted of Pd nanoparticles smaller than 10 nm in diameter which stick together due to the polymer, forming a Pd-embedded PPS layer structure. The sensing ability was investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and differential pulse amperometry (DPA). The PPS-Pd/GCE had excellent catalytic activity toward the oxidation of nitrite: high current sensitivity of 0.365 A/M cm(-2), good reproducibility, good stability and fast response. In neutral solutions, a linear concentration range of 1.0 x 10(-6) to 1.1 x 10(-3) M (R(2) = 0.999) with the detection limit (s/n = 3) of 3 x 10(-7) M nitrite was obtained for DPV determination.

Electrodeposition of gold nanoclusters on overoxidized polypyrrole film modified glassy carbon electrode and its application for the simultaneous determination of epinephrine and uric acid under coexistence of ascorbic acid.

A novel biosensor was fabricated by electrochemical deposition of gold nanoclusters on ultrathin overoxidized polypyrrole (PPyox) film, formed a nano-Au/PPyox composite on glassy carbon electrode (nano-Au/PPyox/GCE). The properties of the nanocomposite have been characterized by field emission scanning electron microscope (FE-SEM), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD) and electrochemical investigations. The nano-Au/PPyox/GCE had strongly catalytic activity toward the oxidation of epinephrine (EP), uric acid (UA) and ascorbic acid (AA), and resolved the overlapping voltammetric response of EP, UA and AA into three well-defined peaks with a large anodic peak difference. The catalytic peak currents obtained from differential pulse voltammetry increased linearly with increasing EP and UA concentrations in the range of 3.0x10(-7) to 2.1x10(-5) M and 5.0x10(-8) to 2.8x10(-5) M with a detection limit of 3.0x10(-8) and 1.2x10(-8) M (s/n=3), respectively. The results showed that the modified electrode can selectively determine EP and UA in the coexistence of a large amount of AA. In addition, the sensor exhibited excellent sensitivity, selectivity and stability. The nano-Au/PPyox/GCE has been applied to determination of EP in epinephrine hydrochloride injection and UA in urine samples with satisfactory results.

Study of the adsorption and oxidation of antioxidant rutin by cyclic voltammetry-voltabsorptometry.

The adsorption and oxidation behavior of rutin was studied by in-situ UV spectroelectrochemistry in a long optical-path thin-layer electrochemical cell with a graphite-wax electrode. The dynamic UV spectra of rutin under potentiostatic oxidation were recorded, which indicated the formation of o-quinonic structure. During the repetitive cyclic potential scans, cyclic voltabsorptomogram was recorded at the three characteristic wavelengths 346, 254 and 296 nm, respectively. The profiles obtained showed two types of concentration fluctuation of species in solution, resulting from adsorption/desorption and redox reaction, respectively. Using derivative cyclic voltabsorptometry the contribution of the species in solution to the total current was estimated, and then the current of every step involved in the proposed redox mechanism was obtained for the first time. The result shows that rutin underwent a nearly reversible redox reaction in which the total current is mostly due to the contribution of adsorbed species. The present work developed cyclic voltabsorptometry into a useful tool for investigating redox process involving coupled adsorption/desorption steps.

Overoxidized polypyrrole film directed single-walled carbon nanotubes immobilization on glassy carbon electrode and its sensing applications.

In this paper, the films of overoxidized polypyrrole (PPyox) directed single-walled carbon nanotubes (SWNTs) have been electrochemically coated onto glassy carbon electrode (GCE). Electroactive monomer pyrrole was added into the solution containing sodium dodecyl sulfate (SDS) and SWNTs. Then, electropolymerization was proceeded at the surface of GCE, and a novel kind of conducting polymer/carbon nanotubes (CNTs) composite film with the orientation of CNTs were obtained correspondingly. Finally, this obtained polypyrrole (PPy)/SWNTs film modified GCE was oxidized at a potential of +1.8 V. It can be found that this proposed PPyox/SWNTs composite film modified GCE exhibited excellent electrocatalytic properties for some species such as nitrite, ascorbic acid (AA), dopamine (DA) and uric acid (UA), and could be used as a new sensor for practical applications. Compared with previous CNTs modified electrodes, SWNTs were oriented towards the outside of modified layer by PPyox and SDS, which made the film easily conductive. Moreover, this proposed film modified electrode was more stable, selective and applicable.

Glucose biosensor based on immobilization of glucose oxidase in poly(o-aminophenol) film on polypyrrole-Pt nanocomposite modified glassy carbon electrode.

Novel Pt nanoclusters embedded polypyrrole nanowires (PPy-Pt) composite was electrosynthesized on a glassy carbon electrode, denoted as PPy-Pt/GCE. A glucose biosensor was further fabricated based on immobilization of glucose oxidase (GOD) in an electropolymerized non-conducting poly(o-aminophenol) (POAP) film that was deposited on the PPy-Pt/GCE. The morphologies of the PPy nanowires and PPy-Pt nanocomposite were characterized by field emission scanning electron microscope (FE-SEM). Effect of experimental conditions involving the cycle numbers for POAP deposition and Pt nanoclusters deposition, applied potential used in glucose determination, temperature and pH value of the detection solution were investigated for optimization. The biosensor exhibited an excellent current response to glucose over a wide linear range from 1.5 x 10(-6) to 1.3 x 10(-2)M (r=0.9982) with a detection limit of 4.5 x 10(-7)M (s/n=3). Based on the combination of permselectivity of the POAP and the PPy films, the sensor had good anti-interference ability to ascorbic acid (AA), uric acid (UA) and acetaminophen. The apparent Michaelis-Menten constant (K(m)) and the maximum current density (I(m)) were estimated to be 23.9 mM and 378 microA/cm(2), respectively. In addition, the biosensor had also good sensitivity, stability and reproducibility.

DNA/Poly(p-aminobenzensulfonic acid) composite bi-layer modified glassy carbon electrode for determination of dopamine and uric acid under coexistence of ascorbic acid.

A nano-composite of DNA/poly(p-aminobenzensulfonic acid) bi-layer modified glassy carbon electrode as a biosensor was fabricated by electro-deposition method. The DNA layer was electrochemically deposited on the top of electropolymerized layer of poly(p-aminobenzensulfonic acid) (Pp-ABSA). Scanning electron microscopy, X-ray photoelectron spectroscopy and electrochemical impedance spectrum were used for characterization. It demonstrated that the deposited Pp-ABSA formed a 2-D fractal patterned nano-structure on the electrode surface, and which was further covered by a uniform thin DNA layer. Cyclic voltammetry and electrochemical impedance spectrum were used to characterize the deposition, and demonstrated the conductivity of the Pp-ABSA layer. The biosensor was applied to the detection of dopamine (DA) and uric acid (UA) in the presence of ascorbic acid (AA). In comparison with DNA and Pp-ABSA single layer modified electrodes, the composite bi-layer modification provided superior electrocatalytic actively towards the oxidation of DA, UA and AA, and separated the originally overlapped differential pulse voltammetric signals of UA, DA and AA oxidation at the bare electrode into three well-defined peaks at pH 7 solution. The peak separation between AA and DA, AA and UA was 176 mV and 312 mV, respectively. In the presence of 1.0 mM AA, the anodic peak current was a linear function of the concentration of DA in the range 0.19-13 microM. The detection limit was 88 nM DA (s/n=3). The anodic peak current of UA was also a linear function of concentration in the range 0.4-23 microM with a detection limit of 0.19 microM in the presence of 0.5 mM AA. The superior sensing ability was attributed to the composite nano-structure. An interaction mechanism was proposed.

Self-assembly of molybdophosphate on a glassy carbon electrode covalently modified with choline and electrocatalytic reduction of iodate.

Choline can be covalently grafted on glassy carbon electrodes using cyclic voltammetric method, forming a stable cationic monolayer-modified electrode (Ch/GCE). Keggin-type molybdophosphate anions, alpha-PMo(12)O(40)(3-), then were self-assembled on the Ch/GCE through electrostatic interactions for fabrication of an electrochemical sensor, which is denoted as alpha-PMo(12)/Ch/GCE. This two-layer modified electrode was carefully characterized by cyclic voltammetry and X-ray photoelectron spectroscopy. It was found that the sensor exhibits strong electrocatalytic activity and sensitivity toward the reduction of IO(3)(-). The content of IO(3)(-) in a table salt was determined with satisfactory results. The sensor is promising as an electrochemical sensor for the detection of IO(3)(-).

A sensitive determination of estrogens with a Pt nano-clusters/multi-walled carbon nanotubes modified glassy carbon electrode.

On the top of a multi-walled carbon nanotubes (MWNTs) modified glassy carbon electrode (MWNTs/GCE), Pt nanoclusters were electrochemically deposited, fabricating a Pt/MWNTs composite modified electrode, Pt/MWNTs/GCE. X-ray photoelectron spectroscopy, powder X-ray diffraction and field emission scanning electron microscope were used for the surface characterization of the electrode, and demonstrated the formation and distribution of Pt clusters of Pt nanoparticles of 8.4 nm in averaged size in the MWNTs matrix. The preliminary study found that this composite modified electrode has strong electrocatalytic activity toward the oxidation of estrogens involving estradiol, estrone and estriol. The voltammetric behavior of estrogens on this electrode was investigated by cyclic voltammetry, linear sweep voltammetry and square-wave voltammetry. In comparison with the MWNTs/GCE or a Pt nanoparticles modified GCE prepared in the similar way, this composite modified electrode exhibited much higher current sensitivity and catalytic activity. This electrode is also stable. The linear range of square-wave voltammetric determination was 5.0 x 10(-7)-1.5 x 10(-5)mol/L for estradiol, 2.0 x 10(-6)-5.0 x 10(-5)mol/L for estrone, and 1.0 x 10(-6)-7.5 x 10(-5)mol/L for estriol. Under an assumption that the concentration ratio of estradiol:estrone:estriol is 2:2:1, the real sample of blood serums was tested for the determination using this electrode. Satisfactory result was obtained with averaged recovery of 105%.

Voltammetry of the interaction of metronidazole with DNA and its analytical applications.

Voltammetric methods were used to probe the interaction of antimicrobial drug metronidazole (MTZ) with calf thymus DNA. Binding constants (K) and binding site sizes (s) were determined from the voltammetric data, i.e., shifts in potential and changes in limiting current with the addition of DNA. MTZ showed appreciable electrostatic binding to DNA in solution with K=2.2(+/- 1.3) x 10(4) M(-1) and s=0.34 bp. One reduction peak of MTZ at the bare glassy carbon electrode (GCE) split into two peaks at the DNA modified GCE (DNA/GCE). These changes in the cyclic voltammogram can only be due to the interaction of MTZ with the surface-confined DNA. In addition, the peak current of MTZ at the DNA/GCE was nearly 8-fold of the response at the bare GCE. The low detection limit of 2.0 x 10(-8) M made the DNA/GCE a promising biosensor for MTZ determination. And this method was successfully applied with high precision and accuracy compared with spectroscopic methods (relative error < 6%) for estimation of the total MTZ drug content in pharmaceutical dosage forms.

Development of a new electrochemical hydride generator with tungsten wire cathode for the determination of As and Sb by atomic fluorescence spectrometry.

A novel electrochemical hydride generator has been developed for the determination of As and Sb. This newly devised hydride generator is constructed from a flowing electrolytic cell, in which the tungsten wire is selected as cathode. Compared with some cathode material usually used in electrochemical hydride generator, the tungsten cathode is of better interference tolerance, corrosion-resistant and longer working time. The characteristics of the cathode material, hydride generating efficiency and interferences of concomitant have been studied in detail. The detection limits (3sigma) of As and Sb in sample solution were 0.10mugL(-1) and 0.15mugL(-1), the precisions for 11 replicate measurements of 20mugL(-1) As and Sb were 1.3% and 1.7%. The electrochemical hydride generator coupled with atomic fluorescence spectrometry has been applied to the determination of total As and Sb in tobacco samples.

[In situ UV-visible absorption spectrum monitoring the electrochemical degradation of PAn films].

Kinetic degradation process of PAn films during aniline polymerization was in situ monitored by UV-Visible absorption spectrum. The effects of anodic potential, acidity and monomer concentration on the degradation process were also investigated. The experiment results displayed that the more positive the anodic potential, the higher the acidity of the solution, the higher the concentration of aniline, the faster the PAn films degradation speed. Which was similar to the results obtained when the kinetic degradation process of PAn films was studied in blank solutions by cyclic voltammetry.

Electrochemical behavior of a covalently modified glassy carbon electrode with aspartic acid and its use for voltammetric differentiation of dopamine and ascorbic acid.

Aspartic acid was covalently grafted on to a glassy carbon electrode (GCE) by amine cation radical formation in the electrooxidation of the amino-containing compound. X-ray photoelectron spectroscopic (XPS) measurement and cyclic voltammetric experiments proved the aspartic acid was immobilized as a monolayer on the GCE. Electron transfer to Fe(CN)6(4-) in solution of different pH was studied by cyclic voltammetry. Changes in solution pH resulted in the variation of the charge state of the terminal group; surface pK(a) values were estimated on the basis of these results. Because of electrostatic interactions between the negatively charged groups on the electrode surface and dopamine (DA) and ascorbic acid (AA), the modified electrode was used for electrochemical differentiation between DA and AA. The peak current for DA at the modified electrode was greatly enhanced and that for AA was significantly reduced, which enabled determination of DA in the presence of AA. The differential pulse voltammetric (DPV) peak current was linearly dependent on DA concentration over the range 1.8 x 10(-6)-4.6 x 10(-4) mol L(-1) with slope (nA micromol(-1) L) and intercept (nA) of 47.6 and 49.2, respectively. The detection limit (3delta) was 1.2 x 10(-6) mol L(-1). The high selectivity and sensitivity for dopamine was attributed to charge discrimination and analyte accumulation. The modified electrode has been used for determination of DA in samples, in the presence of AA, with satisfactory results.

An integrated dual ultramicroelectrode with lower solution resistance applied in ultrafast cyclic voltammetry.

A method for calculating the solution resistance of an integrated dual ultramicroelectrode was introduced, and then tested by experiments using dummy cells. Then, with the reduction of anthracene on a gold ultramicroelectrode in a 0.1 M tetraethylammonium tetrafluoroborate/acetonitrile solution as the test system, it could be found that the solution resistance of this integrated dual ultramicroelectrode was much lower than that of the two-electrode system conventionally used. Thus, the compensation level could be improved up to nearly 100% at a scan rate of 1.34 MV s(-1), while the latter could not. This showed that the integrated dual ultramicroelectrode was more suitable for acting as the electrode system in ultrafast cyclic voltammetry, especially in a high-resistance solution.

DNA deposition on carbon electrodes under controlled dc potentials.

The native calf-thymus DNA molecule fully dispersed in solution was deposited onto highly oriented pyrolytic graphite, carbon fiber column and disk electrodes under controlled dc potentials. X-ray photoelectron spectroscopy, atomic force microscopy and electrochemical investigations indicated that network structures of DNA could be formed on various carbon electrode surfaces resulting in significant surface enlargement. The conformation, conductivity and stability of the deposited DNA layer largely depended on the concentration of the DNA deposition solution, the applied dc potential and the mode of electric field. The optimal condition for deposition of the DNA on carbon fiber disk electrode was determined as a deposition potential of 1.8 +/- 0.3 V versus 50 mM NaCl-Ag/AgCl and a deposition DNA solution of 0.1 mg ml(-1). Under this condition, the DNA was covalently bonded on the electrode surface forming a three-dimensional modified layer, generating a 500-fold enlarged effective electrode surface area and similarly enlarged current sensitivity for redox species, such as Co(phen)3(3+). A possible mechanism for the formation of DNA networks is proposed.

Immobilization of DNA on carbon fiber microelectrodes by using overoxidized polypyrrole template for selective detection of dopamine and epinephrine in the presence of high concentrations of ascorbic acid and uric acid.

The overoxidized polypyrrole (PPyox) film as a template for DNA immobilization has been demonstrated in this paper. The DNA molecules inserted into the micropores of the ultrathin PPyox matrix under the driving forces of an electric field and were firmly immobilized on the carbon fiber electrode (CFE). Such a DNA-PPyox biocomposite layer exhibited more effective rejection of anionic ascorbate (AA) and uric acid (UA) and more preferential collection of the cationic dopamine (DA) and epinephrine (EP) than pure PPyox and DNA coatings. The DPV peak currents increased linearly with increasing DA and EP concentrations in the range of 3.0 x 10(-7) to 1.0 x 10(-5) M and 5.0 x 10(-7) to 2.0 x 10(-5) M with the lowest detected concentrations of 8.0 x 10(-8) M and 6.0 x 10(-8) M, respectively. The electrochemical signal of AA could be totally suppressed under a concentration of 20 mM and beyond this concentration, the overlapped responses of AA, DA/EP and UA could be resolved into three well-defined voltammetric peaks. The selectivity factors k(DA/AA) and k(EP/AA) were about 5000 and 2000 for an equal concentration in the presence of 0.5 mM UA. The properties of the biocomposite film have been characterized by atomic force microscopy and electrochemical investigations.

Attachment of DNA to the carbon fiber microelectrode via gold nanoparticles for simultaneous determination of dopamine and serotonin.

A novel biochemical sensor was fabricated on a carbon fiber microelectrode, which consisted of an inner layer of electrodeposited gold nanoparticles, as a nano-array electrode, and an outer layer of electrodeposited calf thymus ds-DNA at +1.5 V vs. SCE. This modified electrode was characterized by X-ray photoelectron spectroscopy, scanning electron microscope, atomic force microscopy, cyclic voltammetry and differential pulse voltammetry (DPV). It was found that this electrochemical sensor exhibits a strong catalytic activity toward the oxidation of dopamine (DA), serotonin (5-HT) and ascorbic acid (AA), as a result of resolving the anodic voltammetric peaks of DA, 5-HT and AA into three well-defined peaks. Simutaneous DPV determination of DA and 5-HT can be achieved in the presence of 2000-fold AA. The modified electrode shows good sensitivity, selectivity and stability.

Electrochemical determination of serotonin and the competitive adsorption with dopamine at 5,5-ditetradecyl-2-(2-trimethylammonioethyl)-1,3-dioxane bromide lipid film modified by glassy carbon electrode.

A novel and effective approach to sensitively determine serotonin, known as 5-hydroxytryptamine (5-HT), has been proposed based on a 5,5-ditetradecyl-2-(2-trimethylammonioethyl)-1,3-dioxane bromide (DTDB) self-assembled lipid bilayer membrane modified glassy carbon electrode (DTDB/GCE). A DTDB/GCE shows the strong electrocatalysis for the oxidation of 5-HT, with the peak potential shifted to less positive value of 0.376 V vs. SCE, and effectively eliminates the interference from ascorbic acid (AA), even in the presence of 100-fold concentration of AA. Differential pulse voltammetry (DPV) gave a linear current for 5-HT from 2.0 x 10(-7) to 1.0 x 10(-5) M. At the DTDB/GCE, the oxidation of 5-HT was controlled by the adsorption process; for 5-HT coexisting with DA, the competitive adsorption was observed.

Glassy carbon electrode modified with gold nanoparticles and DNA for the simultaneous determination of uric acid and norepinephrine under coexistence of ascorbic acid.

A novel biochemical sensor was assembled on a glass carbon electrode by a electrodeposition process. Gold nanoparticles were deposited by potential +1.5 V on the glass carbon electrode. CT-DNA was deposited by potential +1.5 V on the gold nanoparticles array electrode. The properties of the modified electrode were characterized by electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Our results showed that gold nanoparticles increase the DNA membrane capacitance and reduce the membrane resistance. This modified electrode can selectively determine uric acid and norepinephrine in the presence of a larger amount of ascorbic acid. The fabricated electrode showed good sensitivity, reproducibility, and stability.

Effect of pH on inhibition and enhancement of luminol-H2O2-Co2+ chemiluminescence by phenolic compounds and amino acids.

The effect of pH on inhibition and enhancement of luminol-H2O2-Co2+ chemiluminescence (CL) by 18 phenolic compounds and 20 amino acids was studied. It was found that most of the tested compounds showed an inhibiting effect at lower pH and an enhancing effect at higher pH. At a midrange pH, for some phenolic compounds with two ortho-position -OH, both an inhibiting and an enhancing peak were simultaneously observed. UV-visible spectra of the tested phenolic compounds at different pH values were studied. The mechanism for CL inhibition and enhancement was proposed. It is likely that the competition of the -OH or the -NH2 group and other reducing groups in the molecules with luminol for O2*- led to the CL inhibition. A reaction of -COO(-) and quinone or ketone formed by phenolic compounds at higher pH via deprotonation with O2*- also resulted in the CL enhancement.