Biosensores y bioelectrónica

A bioanode with improved enzyme orientation was developed to achieve an efficient enzyme reaction and electron transfer on an electrode surface. A highly stable PQQ-dependent glucose dehydrogenase (PQQ-GDH) isolated from a hyper-thermophilic archaeon was employed as an electron conversion element. PQQ-GDH is expected to maintain battery properties and to have a long battery life. To immobilize the enzyme onto the electrode with appropriate orientation, we introduced a His-tag to the N-terminal of PQQ-GDH by a genetic technique and utilized the affinity bond between His-tag and Cu atoms. The catalytic current density in the presence of substrate was 18.6 μA/cm2 without a mediator. The current density of the oriented electrode was approximately 90 times higher than that of the non-oriented electrode. By immobilizing the enzyme with orientation, the accessibility between the enzyme and substrate for enzyme reaction increased because the active site of PQQ-GDH is located opposite the electrode. Because enzymes have different orientations at the surface of the non-orientated electrode, the efficiency of the electrode was lower than that of the high-orientation electrode. The results of the present study present a potentially promising finding for application to practical bioelectric devices, such as bio-fuel cells and biosensors.

Reasons for performing study: Electrotherapy is used in human medicine and successively also in veterinary practice, but relatively little is known about the mechanisms of action in detail.This study is focused on identifying the physiological effects of micro-pulse stimulation, a new method designed for equine electrotherapy, using the thermodynamic sensing.
Objectives: To establish on the basis of measurement with the Thermo Dynamic Sensors, if the micro-pulse stimulation has any effect on blood circulation.
Methods: Twenty horses participated in this study. Two miniature Thermo Dynamic Sensors (TDS), working on the principle of the balance energy equilibrium and special designed for the measurement on horses, were placed on both forelimbs and monitored the changes in thermal activity. Micro-pulse stimulation of specified parameters was applied for a defined time only on one limb and the other was just considered as a reference. The measured responses were statistically processed, compared and evaluated.
Results: The measured data were processed by basic and multivariate statistical analysis (correlation, Wilcoxon test, multidimensional scaling, and cluster analysis) which identified a significant difference between signals from stimulated and reference limb. A considerable increase of thermal activity is evident in signals from stimulated limb during the applied micro-pulse stimulation.
Conclusions: Based on the results, it seems the micro-pulse stimulation really has physiological effect consisting in an increased blood perfusion which is associated with the warming-up of the stimulated area and this is detectable by the thermodynamic sensor.
Potential relevance: Comparison and statistical evaluation of the measured signals provided a more detailed view on the thermal changes within the stimulated area, which is significantly related to blood circulation in limbs, and also with the support of the reduction of edema which could be one of the practical applications of micro-pulse stimulation (also tested parallel to this study).