134
Conclusions and Outlooks
on the electrode surfaces to minimize the distance between electrochemicallycommunicating sites and the electrode surfaces. In addition, as a general concept, it is
important to emphasize the significance of microstructures in the interfacial electron
transfer. At the top edge of microstructures, the electric field is drastically strengthened because of the expansion of the electric double layer. In addition, the electric
charge on electrodes is accumulated on the top edge of microstructures. Further development in theoretical discussion on this issue is desired. Both of the effects appear
to accelerate the interfacial electron transfer kinetics including DET-type bioelectrocatalysis. Deglycosylation and down-sizing protein engineering of redox enzymes
have also shown successful results in the improvement of DET-type electron transfer
kinetics of redox proteins. Thanks to these understandings and improvements, redox
enzymes that are capable of DET-type communication will increase in number in near
future. On the other hand, we have to continue deep discussion on false interpretation
as DET-type bioelectrocatalysis.
This book also emphasizes the importance of a series resistance model in the
analysis of catalytic current-potential curves of bioelectrocatalysis; bioelectrocatalysis is very complicated and then the analysis of transient responses (time-dependent
responses) requires so many adjustable parameters and is very complicated. Analytical information of bioelectrocatalytic curves, especially of DET-type reactions, are
very useful for interpretation of the intramolecular electron transfer in redox enzymes,
and the knowledge will be helpful to design and improve the bioelectrocatalytic
system. Some redox enzymes such as H 2 ase, FoDH, and FNR have catalytic activity
for bidirectional reactions of the individual redox couple as the substrates. Therefore, the coupling the reactions of such redox enzymes with electrode reactions
allows bidirectional electrode reactions of the redox couples without overpotentials
in practice. Low organization energy in redox proteins is responsible for such bidirectional catalysis that is very difficult with metal-based catalysts. Fast biological
electron transfers with minimum driving force or sometime in uphill conditions
proceed thanks to low organization energy. Cascade electron transfer is also essential in the biological system to avoid decreased kinetics in the inverted region of the
Marcus theory at increased driving forces.
A huge variety of biosensor devices based on bioelectrocatalysis have been
reported. However, the practical application is limited in number, though glucose
biosensor is the most well-known and successful example of all biosensor devices.
In this book, our ideas to improve biosensor performances are introduced: METtype mass transfer-controlled biosensors with ultra thin-layered electrodes, METtype potentiometric coulometry with surface-confined redox mediators, and bienzyme biosensing by coupling DET-type peroxidase bioelectrocatalysis and oxidase
reactions without any mediators. The proposals showed some successful results,
but are not applicable to all biosensor configurations. In order to get steady-state
signals on amperometric biosensors, development of the surface coverage technique with permeable membranes in high reproducibility is desired. Furthermore,
multi-analyte detection will be getting attention in future; relative concentrations
would be more important than absolute concentrations for samples with possible
Conclusions and Outlooks
on the electrode surfaces to minimize the distance between electrochemicallycommunicating sites and the electrode surfaces. In addition, as a general concept, it is
important to emphasize the significance of microstructures in the interfacial electron
transfer. At the top edge of microstructures, the electric field is drastically strengthened because of the expansion of the electric double layer. In addition, the electric
charge on electrodes is accumulated on the top edge of microstructures. Further development in theoretical discussion on this issue is desired. Both of the effects appear
to accelerate the interfacial electron transfer kinetics including DET-type bioelectrocatalysis. Deglycosylation and down-sizing protein engineering of redox enzymes
have also shown successful results in the improvement of DET-type electron transfer
kinetics of redox proteins. Thanks to these understandings and improvements, redox
enzymes that are capable of DET-type communication will increase in number in near
future. On the other hand, we have to continue deep discussion on false interpretation
as DET-type bioelectrocatalysis.
This book also emphasizes the importance of a series resistance model in the
analysis of catalytic current-potential curves of bioelectrocatalysis; bioelectrocatalysis is very complicated and then the analysis of transient responses (time-dependent
responses) requires so many adjustable parameters and is very complicated. Analytical information of bioelectrocatalytic curves, especially of DET-type reactions, are
very useful for interpretation of the intramolecular electron transfer in redox enzymes,
and the knowledge will be helpful to design and improve the bioelectrocatalytic
system. Some redox enzymes such as H 2 ase, FoDH, and FNR have catalytic activity
for bidirectional reactions of the individual redox couple as the substrates. Therefore, the coupling the reactions of such redox enzymes with electrode reactions
allows bidirectional electrode reactions of the redox couples without overpotentials
in practice. Low organization energy in redox proteins is responsible for such bidirectional catalysis that is very difficult with metal-based catalysts. Fast biological
electron transfers with minimum driving force or sometime in uphill conditions
proceed thanks to low organization energy. Cascade electron transfer is also essential in the biological system to avoid decreased kinetics in the inverted region of the
Marcus theory at increased driving forces.
A huge variety of biosensor devices based on bioelectrocatalysis have been
reported. However, the practical application is limited in number, though glucose
biosensor is the most well-known and successful example of all biosensor devices.
In this book, our ideas to improve biosensor performances are introduced: METtype mass transfer-controlled biosensors with ultra thin-layered electrodes, METtype potentiometric coulometry with surface-confined redox mediators, and bienzyme biosensing by coupling DET-type peroxidase bioelectrocatalysis and oxidase
reactions without any mediators. The proposals showed some successful results,
but are not applicable to all biosensor configurations. In order to get steady-state
signals on amperometric biosensors, development of the surface coverage technique with permeable membranes in high reproducibility is desired. Furthermore,
multi-analyte detection will be getting attention in future; relative concentrations
would be more important than absolute concentrations for samples with possible