Paired pulse voltammetry for differentiating complex analytes.

Department of Neurologic Surgery, Mayo Clinic, Rochester, MN 55905, USA.
The Analyst (Impact Factor: 3.91). 02/2012; 137(6):1428-35. DOI: 10.1039/c2an15912k
Source: PubMed

ABSTRACT 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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    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.
    Biomedical Engineering Letters. 3(2).
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    ABSTRACT: In this paper is presented an overview of the technological barriers faced by the in vivo brain analysis with microelectrodes. Numerous microsensors and enzymatic microbiosensors have been developed for the real time monitoring of neurotransmitters, neuromodulators, drugs and diverse other biological relevant substances. A clear understanding of the working principle, advantages and limitations is essential for the acquisition of valid data in neurological investigations. Some of the aspects presented here refer to: microelectrode insertion and positioning related to possibilities to minimize tissue damage, spatial and temporal resolution of the measurements, actual controversies in data interpretation and sensor calibration, simultaneous detection of multiple analytes, interferences and state of the art in the development of wireless devices.
    Current Neuropharmacology 09/2012; 10(3):197-211. · 2.35 Impact Factor
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    ABSTRACT: Purpose Deep Brain Stimulation (DBS) has been effective in treating various neurological and psychiatric disorders; however, its underlying mechanism hasn’t been completely understood. Fast scan cyclic voltammetry (FSCV) is a valuable tool to elucidate underlying neurotransmitter mechanisms of DBS, due to its sub-second temporal resolution and direct identification of analytes. However, since DBS-like high frequency stimulation evokes neurotransmitter release as well as extracellular pH shift, it is hard to isolate the neurotransmitter signal from the complex environment. Here we demonstrate the efficacy of a modified FSCV technique, Paired Pulse Voltammetry (PPV), in detecting dopamine (DA) release in the caudate nucleus during long-term electrical stimulation of the medial forebrain bundle (MFB) in the rat. Methods Unlike traditional FSCV applying a single triangular waveform, PPV employs a binary waveform with a specific time gap (2.2 ms) in between the comprising pulses. DA measurement was performed with a carbon fiber microelectrode placed in the caudate nucleus and a twisted bipolar stimulating electrode in the MFB. PPV data was collected with the Wireless Instantaneous Neurochemical Concentration Sensing System (WINCS). Results Using PPV, the detection of DA was evident throughout the long-term stimulation (5 minutes); however, without PPV, in vivo environmental changes including pH shift eventually obscured the characteristic oxidation current of DA at 0.6V. Conclusions These results indicate that PPV can be a valuable tool to accurately determine DA dynamics in a complex in vivo environment during long-term electrical stimulation.
    Biomed. Eng. Lett. 03/2013; 3(1):22-31.

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