Electrochemical Behavior of Amino Acids and their Influence on the Anodic Oxidation of Glucose in Neutral Media

Abstract

Body fluids contain a large number of amino acids along with glucose. Therefore, the electrochemical behavior of amino acids should be considered in studying the anodic oxidation reaction of glucose for biological applications. Potential-sweep and steady-state measurements with different platinum electrodes under neutral conditions have shown that the oxidation of amino acids is basically possible. However, their presence, especially as a mixture, has a remarkable influence on the glucose oxidation and the anodic reaction is strongly inhibited. With respect to the degree of inhibition, they can be classified into two groups. The inhibiting effect is particularly drastic in the case of basic and unsaturated amino acids as well as the ones containing sulphur because of their strong absorption at the electrode surface. The glucose currents are inhibited by about 90% under steady-state. In addition to the direct electrochemical inhibition, the following bacterial decomposition of amino acids is probably also responsible for the drastic effect. However, about 10% of the glucose currents still remain measurable indicating that glucose is detectable at physiological concentrations even under extremly unfavorable conditions. This result is of basic importance in operating a biofuel cell or in measuring glucose concentrations.

Abiotic (Nonenzymatic) Implantable Biofuel Cells

“…Already in buffered solution a degradation of electrode performance can be noticed, attributed to the selfpoisoning of the platinum catalyst. Upon addition of amino acids the oxidation current is further reduced, which is attributed to the adsorption of amino acids on the platinum surface and the associated blockage of reaction sites for glucose oxidation [84]. As can be seen, the poisoning strength of the individual amino acids differs significantly.…”

“…Of particular relevance for long-term operation in a physiological environment is the adsorption of endogenous amino acids [84], which are known to quickly and drastically decrease the glucose oxidation activity of platinum-based catalysts. In contrast to larger molecules such as proteins, the amino acids are of similar size as glucose and can thus not be effectively shielded from the electrode by the use of, for example, dialysis membranes.…”

An implantable artificial pancreas

“…The insulin-delivery system comprising piezoelectric pump and valves is designed around a 24-hour clock that can be programmed to deliver insulin in To increase the safety of the implantable infusion system, the control of the piezoelectric pumping valve (SCHUBERT et al, 1979) is realised by a system operating on three levels with decreasing priority. Reliable operation is guaranteed by a data check performed at each level for the data coming from the next higher level.…”

“…This type of sensor acts as a transducer for the quantitative measurement of glucose in a diffusionlimited 6urrent mode. Since this sensor is relatively nonspecific, membranes have to be incorporated in order to minimise contributions from various monosaccharides, endogenous substances such as urea, proteins and amino acids (MARINCIC, 1979;RAO, 1978). Besides a lengthening of the response time due to the membranes, these interfering substances cause a deactivation of the platinum electrode.…”

“…However, results have shown that the poisoning effects are not totally eliminated (RAo, 1978). Thus, the 'fuel cell' sensor seems to be out of the question for use as an implantable glucose sensor.…”