Detection with fixed working potential

When a voltammetric sensor operates with a small overpotential, the faradaic reaction rate is also small consequently, a high-precision instrument for the measurement is needed. An amperometric sensor is usually operated under limiting current or relatively small overpotential conditions. Amperometric sensors operate under an imposed fixed electrode potential. Under this condition, the cell current can be correlated with the bulk concentration of the detecting species (the solute). This operating mode is commonly classified as amperometric in most sensor work, but it is also referred to as the chronosupero-metric method, since time is involved. 

Qian et al. [31] deposited a similar polymer via the LbL technique, alternating with Au NPs, resulting in the ability to detect ascorbic acid Havens et al. [32] linked a [Os(bipy)2]Cl residue to a PVP-polyvinylpyrimidine copolymer finally anchored, through an amidic bond, to a defect of a multiple-wall CNT, trapped inside a hydrogel. This is able to swell in aqueous solvent, becoming accessible to species in solution (see Fig. 3.4). Electrocatalytic action with respect to ascorbic acid was exploited in a complete analytic work, based on amperometric measurements at a fixed potential. 

In the 19 0 s Kalousek described his well-publicized commutator (M). This work was also carried out in the Physico-Chemical Institute of Charles University. The Kalousek polarograph employed a rotating switch designed to apply alternatively a fixed potential and a second fixed potential combined with a potential changing slowly and linearly with time. The purpose was to investigate directly, by detecting products, the reversibility of electrochemical reactions on the conventional polarographic time scale. It seems unlikely that Kalousek could have been unaware of Kemula s previous work (3) yet for whatever reason he does not mention it in his paper (4). 

Amperometric sensors with the linear relationship of the current response have received great attention because of their high sensitivity, wide detection range, and short response time [5-9]. Amperometric sensors are based on the current-potential relationship of the electrochemical cell, in which a non-spontaneous reaction is driven by an external source of current. In amperometric sensors, the transduction mode works by operating the potential of the working electrode at a fixed value, relative to the reference electrode, and observing the current as a function of time. The applied potential assists to drive the electron... 

Even with a simple first generation biosensor, working in amperometric mode at a fixed detection potential of +0.7 V (high enough to directly oxidize H2O2 at the electrode surface), it is possible to achieve a linearity between 1 and 9 x 10 M (R = 0.9997) with a sensitivity of 1.11 pAmM (rsd% = 0.97%) and a limit of detection between 2.5 x 10 M (calculated as S/N = 3). Short-term stability was excellent as shown in Figure 13.19. Longterm stability results in a decrease of 34% after one month of continuous use. 

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