Redox current

SCHEME 3 The electrochemical gene sensing system based on the formation of complementary sandwich-type complex, (a) Target DNA combines the ferrocenyl ODN with the probe ODN on the electrode. Redox currents due to the surface-confined ferrocenyl units should reflect the concentration of the target, (b) Ferrocenyl units are not deposited onto the electrode using nontarget DNA. 

In principle the ISO-NOP sensor works as follows. The sensor is immersed in a solution containing NO and a positive potential of —860 mV (vs Ag/AgCl reference electrode) is applied. NO diffuses across the gas permeable/NO-selective membrane and is oxidized at the working electrode surface producing a redox current. This oxidation proceeds via an electrochemical reaction followed by a chemical reaction. The electrochemical reaction is a one-electron transfer from the NO molecule to the electrode, resulting in the formation of the nitrosonium cation ... 

The nanostructured Au and AuPt catalysts were found to exhibit electrocatalytic activity for ORR reaction. The cyclic voltammetric (CV) curves at Au/C catalyst reveal an oxidation-reduction wave of gold oxide at +200 mV in the alkaline (0.5 M KOH) electrolyte but little redox current in the acidic (0.5 M H2SO4) electrolyte. Under saturated with O2, the appearance of the cathodic wave is observed at -190 mV in the alkaline electrolyte and at +50 mV in the acidic electrolyte. This finding indicates that the Au catalyst is active toward O2 reduction in both electrolytes. From the Levich plots of the limiting current vs. rotating speed data, one can derive the electron transfer number (w). We obtained n = 3.1 for ORR in 0.5 M KOH electrolyte, and 2.9 for ORR in 0.5 M H2SO4 electrolyte. The intermittent n-value between 2 and 4 indicates that the electrocatalytic ORR at the Au/Ccatalyst likely involved mixed 2e and 4e reduction processes. 

Fig. 8-16. Electron state density in a semiconductor electrode and in hjrdrated redox partides, rate constant of electron tunneling, and exchange redox current in equilibrium with a redox electron transfer reaction for which the Fermi level is close to the conduction band edge eF(sc) = Fermi level of intrinsic semiconductor at the flat band potential 1. 0 (tp.o) = exchange reaction current of electrons (holes) (hvp)) - tunneling rate constant of electrons (holes).

Interestingly, when the fourth-generation molecule was complexed with one equivalent of SnCl2, the redox current increased and the capacitance became smaller. It was concluded that SnCl2 complexation facilitated the electron transfer. 

Figure 4.8-8 Internal redox reaction and chemical structure of PANI (a), change of bcH Raman lines as a result of protonation (b), according to (Bartonek et al, 1990). Redox current (C), spin concentration (ESR), and Raman cross section of the polaron type ring mode at 1630 cm (RCS) vs. oxidation potential (c), according to Kuzmany and Bartonek, 1990a.

In several cases it has been found that the oxidation of the redox system occurs entirely via hole transfer directly from the valence band to the reduced form of the couple. Then both processes, oxidation of the redox system and corrosion, proceed independently. This is usually not visible from measurements with an n-type electrode, because the photocurrent is entirely determined by the light intensity. As already mentioned above, p-type electrodes are more suitable, because the current is determined by majority carrier transfer (reaction rate Vf, in Fig. 21). From the thermodynamic point of view, the oxidation of Cu at GaAs is an interesting case. The corresponding current-potential curves are given in Fig. 22 [93]. The corrosion current is not changed upon addition of Cu, i.e. corrosion and redox process are completely independent. In this case, the kinetics of the direct hole transfer is obviously very fast, i.e. the redox current is considerably larger than the corrosion current. Both processes occur indepen-... 

CV of 4-nitropyridine shows a similar pattern [96]. The current consists of two parts, a surface redox current and a diffusion controlled current the latter is dominant at slow sweep rate whereas the former becomes important at fast sweep rates. The reduction path is illustrated by a bicubic reaction diagram. 

Another important case is the comparison of anodic currents at n-type electrodes under illumination with the dark current at p-type, as illustrated in Fig. 7.44. The anodic dark current at the p-electrode is composed of corrosion (dashed curve) and the redox currents (dotted curve). The total current at the n-type electrode (solid... 

The direct detection of DNA via conformational changes of ferrocene-conjugated DNA stem-loop (or hair-pin) structure onto electrode surface induced by the hybridization was also proposed (Fig. 11.1c) [4, 20]. The conformational change induces the displacement of ferrocene molecules from the electrode surface, resulting in a drop in peak redox current measured by cyclic voltametry. The detection limits were 115 fM for 24-base oligonucleotide [20] and 10 pM for 17-base oligonucleotide [4], respectively. Furthermore, the difference between... 

Cyclic voltammograms of luminol at different electrodes in 0.1 mol/L phosphate buffer (PBS, pH=7.5) were obtained (Fig. 3A). Similarly, an enhancement of redox current from the analyte was observed at the PDDA-chitosan modified GCE, compared with the response at the bare GCE. This is due to the good permselectivity and highly positive charge density of the PDDA-chitosan composite layer. The negatively charged luminol could be easily absorbed on the surface of modified GCE through electrostatic interaction, which was supported by the linear increase of oxidation current vs. scan rates. 

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