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Calibration Factors for Cationic and Anionic Neurochemicals at Carbon‐Fiber Microelectrodes are Oppositely Affected by the Presence of Ca 2+ and Mg 2+
Author(s) -
Chen Billy T.,
Rice Margaret E.
Publication year - 1999
Publication title -
electroanalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.574
H-Index - 128
eISSN - 1521-4109
pISSN - 1040-0397
DOI - 10.1002/(sici)1521-4109(199905)11:5<344::aid-elan344>3.0.co;2-k
Subject(s) - microelectrode , chemistry , electrode , neurochemical , cyclic voltammetry , adsorption , metabolite , analytical chemistry (journal) , biophysics , chromatography , biochemistry , organic chemistry , electrochemistry , medicine , biology , endocrinology
Carbon‐fiber microelectrodes and voltammetric methods have been used extensively for detection of neurochemical substances in brain tissue. We previously reported that calibration factors for dopamine obtained with these electrodes and fast‐scan cyclic voltammetry are 2–3‐fold higher in nonphysiological phosphate‐buffered saline (PBS) than in artificial cerebrospinal fluid (ACSF) containing Ca 2+ and Mg 2+ . In the present report, we describe the media‐dependence of calibration factors for other neurochemicals. Strikingly, whereas electrode sensitivities to dopamine and the indoleamine serotonin were lower in ACSF than in PBS, those for the acid metabolites of these neuro‐transmitters were roughly 2‐fold higher in ACSF than PBS. The data are consistent with adsorption or repulsion of these molecules by a negatively charged carbon‐fiber electrode surface. One consequence of this pattern is that electrodes calibrated in PBS, rather than Ca 2+ ‐ and Mg 2+ ‐containing media, will have a 2–6‐fold lower amine‐to‐metabolite selectivity ratio in brain tissue than expected from in vitro calibration. More generally, the data suggest that the sensitivity of carbon‐fiber‐based microsensors to many organic molecules will be media‐dependent. Thus, calibration in appropriate physiological media is essential for accurate tissue measurements.