Paired pulse voltammetry for differentiating complex analytes

Department of Neurologic Surgery, Mayo Clinic, Rochester, MN 55905, USA.
The Analyst (Impact Factor: 4.11). 02/2012; 137(6):1428-35. DOI: 10.1039/c2an15912k
Source: PubMed


Although fast-scan cyclic voltammetry (FSCV) has contributed to important advances in neuroscience research, the technique is encumbered by significant analytical challenges. Confounding factors such as pH change and transient effects at the microelectrode surface make it difficult to discern the analytes represented by complex voltammograms. Here we introduce paired-pulse voltammetry (PPV), that mitigates the confounding factors and simplifies the analytical task. PPV consists of a selected binary waveform with a specific time gap between each of its two comprising pulses, such that each binary wave is repeated, while holding the electrode at a negative potential between the waves. This allows two simultaneous yet very different voltammograms (primary and secondary) to be obtained, each corresponding to the two pulses in the binary waveform. PPV was evaluated in the flow cell to characterize three different analytes, (dopamine, adenosine, and pH changes). The peak oxidation current decreased by approximately 50%, 80%, and 4% for dopamine, adenosine, and pH, in the secondary voltammogram compared with the primary voltammogram, respectively. Thus, the influence of pH changes could be virtually eliminated using the difference between the primary and secondary voltammograms in the PPV technique, which discriminates analytes on the basis of their adsorption characteristics to the carbon fiber electrode. These results demonstrate that PPV can be effectively used for differentiating complex analytes.

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    • "Lee et al. recently introduced pair–pulse voltammetry (PPV) in which a selected binary waveform with a defined time lapse is applied to an electrode which is held at a negative potential between each of two pulses [141]. This enables recording of two simultaneous, yet different, voltammograms, and enables discrimination of analytes on the basis of their adsorption behavior on the electrode [141]. More detailed information about electrochemical techniques as bioanalytical tools for in-vivo and in-vitro experiments can be found in several excellent recent reviews [142–148]. "
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    • "The peak oxidation/reduction currents are correlated with two time dependent phenomena: analyte transport from solution to the electrode surface and subsequent adsorption. The monitoring of three different analytes (dopamine, adenosine and pH) was possible based on the specific kinetics of these phenomena corresponding to each analyte and the variable time periods between FSCV [65]. "
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    ABSTRACT: Purpose Although paired-pulse voltammetry (PPV) has significantly reduced the effects of confounding factors such as pH changes, its appliance has been limited to triangular waveforms. Here, we extend PPV to N-waveform, known to be effective in differentiating serotonin (5-HT) from other analytes. Methods Unlike previous PPV that employs a triangular binary waveform with a specified time gap between the comprising pulses, this study experiments PPV with Nwaveform. N-waveform, the most conventional waveform for detecting 5-HT, sweeps from 0.2 V to 1.0 V to −1.0 V and back to 0.2 V at a sweep rate of 1000 V/s, while the electrode is held at a holding potential of +0.2 V between the voltammetric pulses. After experimenting with various gap times (2 ms, 10 ms, 30 ms, and 45 ms), N-shape PPV was optimized to the parameter of 100 ms repetition time (2 Hz) and 2 ms gap time that displayed the highest sensitivity. 5-HT measurement was performed with a carbon fiber microelectrode placed in the flow cell. PPV data was collected with the Wireless Instantaneous Neurochemical Concentration Sensing System. Results At the optimized parameter, the oxidation peak in secondary pulse of N-waveform PPV recorded about 68% of the peak of the primary pulse. In addition, the fitting of peak currents in primary, secondary, and primary-secondary in Nshape PPV in relation to the concentration level between 0.25 μM to 2 μM displayed high reliability (R-squared values = 0.9823, 0.9895, 0.9914, respectively). When 5-HT 3 μM and 0.1 ΔpH is mixed, the 10 nA artifact created by 0.1 ΔpH in P-S voltammogram was almost completely removed while the oxidative peak by 5-HT was detected. Conclusions These results demonstrate that N-shape PPV will enable more accurate measures of real-time serotonin changes, especially in complex environment.
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