In vivo electrochemical measurements

The first in vivo electrochemical measurements were performed in 1973 Since then bioelectrocheraists have spent much effort in developing in vivo methods of analysis. A major reason for this effort is the rapidity with which in vivo techniques... 

M. Mas, A. Escrig and J.L. Gonzalez-Mora, In vivo electrochemical measurement of nitric oxide in corpus cavernosum penis. J. Neurosci. Methods 119, 143-150 (2002). 

For in vivo electrochemical measurement, the placement of the electrodes is important. In the potentiometric measurement (e.g., measurement of the pH of gastric juices) both the working electrode and the reference electrode are placed in the stomach. On the other hand, when amperometric measurement is done, the working electrode is in the place where you are getting the information from, but the auxiliary (reference) electrode can be anywhere, even on the skin. 

Luthman J, Friedemann MN, Hoffer BJ, Gerhardt GA. In vivo electrochemical measurements of exogenous dopamine clearance in normal and neonatal 6-hydroxydopamine-treated rat striatum. Exp. Neurol. 1993 122 273-282. 

It has been stated that if 6-hydroxydopamine and 6-aminodopamine are to be selective in their neurotoxic behavior the damaging process must occur intraneuronally following uptake and hence concentration of the neurotoxin within the neuron. In vivo electrochemical measurements have shown that about 20% of 6-hydroxydopamine is converted to its p-quinone within a few minutes after injection into rat brain. " The redox equilibrium between 6-hydroxydopamine and its p-quinone or 6-aminodopamine and its p-quinoneimine is apparently maintained by an active redox buffer, probably ascorbate-dehydroascorbate, which exists in brain tissue. The potential of this redox buffer is apparently close to -0.200 V vs. SCE. 

This section is intended as an overview of the current applications of in vivo electrochemical measurements and, since the field is relatively new, to categorize types of work already done and evaluate the directions taken. The details of each of the studies are contained in the literature cited and they are not repeated here. 

Cheng, H.-Y., White, W., and Adams, R. N., 1980, Microprocessor-controlled apparatus for in vivo electrochemical measurement. Anal. Chem. 52 2445-2448. 

Factors Which Affect In Vivo Electrochemical Measurements... 

Robinson, D.L., Volz, T.J., Schenk, J.O., and Wightman, R.M., Acute ethanol decreases dopamine transporter velocity in rat striatum in vivo and in vitro electrochemical measurements, Alcohol Clin. Exp. Res., 29, 746, 2005. 

With regard to in vivo gas-sensing devices, the majority of the work reported to date has involved oxygen-sensitive devices which operate as an electrolytic, not galvanic, type of electrochemical cell (i.e., current measured, not potential). Since such oxygen-sensing catheters are not based on ISEs, they will not be considered in this review. There has been, however, some limited work concerning the development of potentiometric sensors, particularly for in vivo COg measurements. One approach has been to devise... 

Second, the in vivo electrochemical technique measures dynamic changes in concentration of electroactive species near the electrode induced by some physical or drug stimulation. In spite of the complexity of brain interactions, one can expect that not all of the electroactive species will necessarily change simultaneously. Selectivity based on the time of appearance of electroactive response is possible. 

In vivo electrochemical testing is possible in humans (in the oral cavity) under restricted conditions [77,78]. Open circuit potentials and galvanic currents between dissimilar metals have been measured. Linear polarization and AC impedance tests have been conducted. The paramount concern for these measurements is obtaining accurate data under conditions that present no hazard to the human subjects. 

Beissenhirtz MK, Kwan RCH, Ko KM, Renneberg R, Scheller FW, Lisdat F (2004) Comparing an In vitro electrochemical measurement of superoxide scavenging activity with an in vivo assessment of antioxidant potential in Chinese tonifying heibs. Phyt Res 18 149-153... 

Detection and calibration methods identified to be suitable for BGM and CGM systems are not identical. BGM systems are based either on photometric [71] or electrochemical [288] detection approaches, whereas CGM systems which have shown advanced clinical performance rely exclusively on electrochemical sensors. While BGM systems routinely rely on factory-based calibration of test element batches, only one continuous glucose measurement system [233] advertises the possibility of renouncing reference-based in vivo calibration measurements. Other CGM systems rely on the daily use of a BGM system for calibration of filtered CGM data [289, 290]. 

In Vivo Biosensing. In vivo biosensing involves the use of a sensitive probe to make chemical and physical measurements in living, functioning systems (60—62). Thus it is no longer necessary to decapitate an animal in order to study its brain. Rather, an electrochemical biosensor is employed to monitor interceUular or intraceUular events. These probes must be small, fast, sensitive, selective, stable, mgged, and have a linear response. 

Electrochemical techniques in vivo use the standard three electrode voltammetric system described earlier with the electrodes implanted in the brain of the animal subject. Measurements are made by acquiring some stable baseline signal and then stimulating release of the biogenic amine neurotransmitters. The change in signal is then a measure of the concentration of neurotransmitter in the extracellular fluid. 

Grant S.A., Bettencourt K., Krulevich P., Hamilton J., Glass S.R., In vitro and in vivo measurements of fiber optic and electrochemical sensors to monitor brain tissue pH, Sensors and Actuat.B 2001 72 174. 

To date, electrochemical (amperometric) detection of NO is the only available technique sensitive enough to detect relevant concentrations of NO in real time and in vivo and suffers minimally from potential interfering species such as nitrite, nitrate, dopamine, ascorbate, and L-arginine. Also, because electrodes can be made on the micro- and nano-scale these techniques also have the benefit of being able to measure NO concentrations in living systems without any significant effects from electrode insertion. 

R. Cespuglio, H. Faradji, Z. Hahn, and M. Jouvet, Voltammetric detection of brain 5-hydroxyindo-lamines by means of electrochemically treated carbon fiber electrodes chronic recordings for up to one month with movable cerebral electrodes in die sleeping or waking rat, in Measurements of Neurotransmitters Release in Vivo (C.A. Marsden, ed.), Wiley, Chichester (1984). 

L. Mao, J. Jin, L. Song, K. Yamamoto, and L. Jin, Electrochemical microsensor for in vivo measurements of oxygen based on Nafion and methylviologen modified carbon fiber microelectrode. Electroanalysis. 11, 499-504 (1999). 

J.B. Zimmerman and R.M. Wightman, Simultaneous electrochemical measurements of oxygen and dopamine in vivo. Anal. Chem. 63, 24-28 (1991). 

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