Voltammetric sensors, signal

Figure 17. Schematic representation of the affinity biosensor construction and the proposed operational principle and voltammetric traces for affinity sensor signalling a biotin-functionalized surface before (A) and after (B) target protein (antibiotin IgG-HRP) association and precipitation reaction steps. Voltammetric measurements were performed in 0.1 M phosphate buffer (pH 7.0),containing 0.1 mM ferrocene methanol as a signal tracer. Inset charge coupled device (CCD) camera images of a sensor surface upon signalling reactions (Adapted from Refs. [176] [177]).

Finally, when the sensor array is of voltammetric type, signals coming from the sensor array are dynamic (time-varying signals) and commonly non-stationary, which implies that information is time encoded (as stated by recent investigations of neural coding in the gustatory system). 

Fig. 9.10. The signal at left was obtained with a voltammetric sensor and was processed with Matlab to compute the wavelet coefficients plotted at right. Such time-scale plotting of the coefficients is known as scalogram.

Voltammetric sensors based on chemically modified electrodes (conducting polymers, phthalocyanine complexes) with improved cross-selectivity were developed for the discrimination of bitter solutions [50], The performance and capability were tested by using model solutions of bitterness such as magnesium chloride, quinine, and four phenolic compounds responsible for bitterness in olive oils. The sensors gave electrochemical responses when exposed to the solutions. A multichannel taste sensor was constructed using the sensors with the best stabilities and cross-selectivities and PCA of the signals allowed distinct discrimination of the solutions. 

A. Gutes, F. Cespedes, S. Alegret, and M. del Valle. Sequential injection system with higher dimensional electrochemical sensor signals. Part 1. Voltammetric e-tongue for the determination of oxidizable compoimds. Talanta 66 1187-1196,2005. 

A typical feature of voltammetric sensors is fast response, linear response in a broad concentration range, non-linear dependence on the flow rate and the temperature dependence of the signal (+2 -5% C). 

The copper flow-through CL sensor comprised an anion-exchange column having luminol and cyanide coimmobilized on the resin, while copper was temporarily retained by electrochemical preconcentration on a Au electrode placed in an anodic stripping voltammetric cell [64], Injection of 0.1 mol/L NaOH through the column eluted the reagents, which then reacted with copper, stripped from the electrode to produce a CL signal. The response was linear in the 0.01-10-pg/L... 

The ability to switch the operation of electrochemical metal sensors between active and passive modes on demand offers substantial improvements in their stability in the presence of common surfactants, as demonstrated in stripping-voltammetric signals obtained from cadmium in the presence of gelatin and Tween 80. Bare electrodes display a substantial diminution of the cadmium peak in the presence of both surfactants. In contrast, the adaptive-nanowire electrode system exhibits a highly stable response with a negligible change of the peak current over multiple measurements. 

Faradaic processes of electrode reactions, which are principle mechanism of obtaining analytical signal in amperometric sensors, significantly depend on working electrode material and state of its surface. The common working electrode materials include noble and seminoble metals, solid oxides of various elements and different kinds of carbon materials including carbon nanostructures. They are employed in conventional voltammetric measurements with various modes of electrode polarization, as amperometric chemical sensors, as well as for construction of amperometric biosensors. 

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