1. Enzyme Engineering 8. Applications(2): Sensor & Fuel Cell
8.1 Biosensor
8.2 Enzyme Fuel Cells

2. 8.1 Biosensor

3. Definition of biosensor
Device for the detection of an analyte that combines a biological component with a physicochemical detector component (IUPAC)

4. Definition of biosensor
the sensitive biological element (biological material (eg. tissue, microorganisms, organelles, cell receptors, enzymes, antibodies, nucleic acids, etc), a biologically derived material or biomimic) The sensitive elements can be created by biological engineering.
the transducer or the detector element (works in a physicochemical way; optical, piezoelectric, electrochemical, etc.) that transforms the signal resulting from the interaction of the analyte with the biological element into another signal (i.e., transducers) that can be more easily measured and quantified; associated electronics or signal processors that is primarily responsible for the display of the results in a user-friendly way
Sensors 2008, 8,

5. Application Clinical: glucose, cholesterol, pregnancy
Environmental monitoring: pesticides, heavy metal
Food analysis: Salmonella, E.coli O157
Defense: airborne bacteria, organophosphate
Industry: fermentation

6. Required characteristics
Selectivity
Limit of detection (LOD)
Response time
Reproducibility
Stability

7. Amperometric biosensor
First generation: The transduction of the biological reaction is by the oxidation or reduction (redox chemistry), at the electrode surface, or an electro-active product or reactant of the biological-recognition reaction.
Second generation: Use mediator molecules to transfer the electrons from the enzyme, after it reduces or oxidizes the substrate, to the electrode.
I. Willner and E. Katz, Bioelectronics 2005
Third generation: Modified-electrode biosensor. In this generation, the surface of the electrode is modified by the addition of molecules which allow the direct oxidation or reduction of the enzyme at the electrode.

8. Amperometric biosensor
When a species is oxidized or reduced at an electrode, the current produced is directly related to the concentration of the species.

9. Immobilization of enzyme
Better contact and response
Improve enzyme stability
Electrode reusability
Less interferences
Loss of enzyme activity
Sensitivity of the electrochemical signal
/BiosensorsBioelectronics_lecture5.pdf

10. Clark oxygen electrode
O2 + 4 e− + 2 H2O → 4 OH−
Clark-type electrode: (A) Pt- (B) Ag/AgCl-electrode (C) KCl electrolyte (D) Teflon membrane (E) rubber ring (F) voltage supply (G) galvanometer
Leland C. Clark
(1918–2005)
“Father of biosensor”
A voltage of around 0.7 V is used to allow linearity between the measurements of the current and oxygen concentration.
Lifespan is limited to around 3 years due to the Teflon membrane, which becomes encoated with protein
Requires power source
Requires constant temperature

11. Glucose biosensor
In 1962, Clark described "how to make electrochemical sensors more intelligent" by adding "enzyme transducers as membrane enclosed sandwiches”.
Clark’s ideas became commercial reality in 1975 with the successful re-launch (first launch 1973) of the Yellow Springs Instrument Company (Ohio, USA) glucose analyzer based on the amperometric detection of hydrogen peroxide.
YSI 23A

12. Glucose biosensor

13. Glucose biosensor Glucose + O2 → Gluconolactone + H2O2
The oxidase enzyme is inexpensive but requires oxygen as a cosubstrate.
Consequently, as oxygen is depleted in the sample, performance decreases, whether one is monitoring oxygen depletion, or hydrogen peroxide production.
Glucose + NAD+ → Gluconolactone + NADH
NAD+ dependent GDH, on the other hand, is oxygen independent, and has the added attraction of being a well-established probe for monitoring biochemical reactions. The drawback is that the cofactors are relatively expensive.
Glucose + PQQ(ox) → Gluconolactone + PQQ(red)
PQQ-GDH is a particularly efficient enzyme system, with a rapid electron transfer rate, but it, too, is comparatively costly.

14. Glucose biosensor
Figure. Calibration curves of the glucose biosensor based on glucose oxidase immobilized tin oxide electrode: (a) at various glucose concentrations (from 0 mM to 10 mM); Inset shows typical amperometric response of the glucose biosensor. (b) at low glucose concentrations (from 0 mM to 3 mM) which shows linear response in pH 7.0 potassium phosphate buffer (100 mM).
Biotechnology and Bioprocess Engineering, 2008, 13,

16. NADH biosensor
Measuring NADH is very important because NAD(P)+ is used as a cofactor for about 250 NAD+-dependent and 150 NADP+-dependent dehydrogenases.
It can be applied to analytical detection, fermentation, clinical practices, food industry, and dairy industry.
Direct electrochemical oxidation of NAD(P)H often
occurs with high overpotential
suffers from low sensitivity
arises electrode fouling by its oxidation products

17. amperometric detection
NADH biosensor
NAD(P)H
NAD(P)+
electrode
analyte red
analyte ox
amperometric detection

18. Electrochemical analysis
Figure. (a) Linear sweep voltammograms of the Fe2O3/CB electrode with different NADH concentrations (0 mM, 1 mM, 2 mM, 3 mM, 4 mM, and 5 mM; arranged from bottom to top, respectively) (insert: cyclic voltammograms in the absence and presence of 1 mM NADH) at a scan rate of 50 mV s−1; (b) linear sweep voltammograms of the Fe2O3/CB electrode at a scan rate of 10 mV s−1, 20 mV s−1, 30 mV s−1, 40 mV s−1, 50 mV s−1, 75 mV s−1, 100 mV s−1, 150 mV s−1, and 200 mV s−1; arranged from bottom to top, respectively (insert: dependence of the peak current on scan rate) in pH 7.5 potassium phosphate buffer (100 mM).
Biosensors and Bioelectronics, in press

19. Electrochemical analysis
Figure. (a) Nyquist plots for the Fe2O3/CB (●), GC (○), and CB () electrodes in the presence of 1 mM NADH in pH 7.5 potassium phosphate buffer (100 mM). This experiment was performed using a frequency range of 0.5–5 kHz, +0.00 V, and 5 mV amplitude. (b) Calibration curve from the amperometric response of NADH at Fe2O3/CB (●), GC (○), and CB () electrodes.

20. Amperometric detection
Figure. Calibration curve of NADH with different composition of iron oxide and carbon black 5:1 (), 10:1 (), and 15:1 ().

21. Amperometric detection
Figure. (a) Amperometric response for NADH oxidation at the Fe2O3/CB electrode after addition of different NADH concentrations into a stirred solution of 100 mM potassium phosphate buffer (pH 7.5) at +0.00 V. (b) Calibration curve from the amperometric response of NADH.
Linear range 10μM-1000μM (R2=0.993)
Limit of detection (LOD) 10μM (S/N=3)
Sensitivity 2.54 μA mM-1
Km=3.04mM

22. Stability of electrode
Figure. Amperometric response for NADH oxidation at the Fe2O3/CB electrode after addition of 1 mM NADH.

23. Response to NADPH
Figure. Calibration curve from the amperometric response of NADH () and NADPH ().

24. Performance of biosensor

25. Ethanol biosensor
Figure. (a) Effect of pH on the amperometric response to NADH oxidation (■), activity of alcohol dehydrogenase (●), and the amperometric response of the ethanol biosensor system (gray bar). (b) Calibration curve of the Fe2O3/CB electrode after addition of ethanol into a stirred solution that contained 2 mg alcohol dehydrogenase and 10 mM NADH in pH 7.5 potassium phosphate buffer at +0.00 V.

26. 8.2 Enzyme Fuel Cell

27. Fuel Cell
Fuel Cell
A device to convert chemical energy to eletrical power
Chemical Fuel Cell
BioFuel Cell
PMFC
Microbial Biofuel Cell
DMFC
Enzymatic Biofuel Cell

28. Enzyme Biofuel Cell Fuel : glucose, alcohol, glycerol
Anodic catalyst : glucose oxidase,
glucose dehydrogenase
alcohol dehydrogenase
aldehyde dehydrogenase
Cathodic catalyst : laccase
bilirubin oxidase
microperoxidase
Enzymes are selected as catalysts.
a power source for portable or implantable electronics, especially biomedical devices.
the poor power density and the short life time.

29. Efforts for Efficient Electron Transfer
Employment of the redox-mediator
The zeta potentials of the amine-terminated particles were in distilled water or pH 7 phosphate buffer slightly positive, while those of the epoxy- or carboxy-terminated particles were negative.

30. Efforts for Efficient Electron Transfer
Reconstitution of the enzyme using molecular or polymer relay unit
The zeta potentials of the amine-terminated particles were in distilled water or pH 7 phosphate buffer slightly positive, while those of the epoxy- or carboxy-terminated particles were negative.

31. Possible Solutions for Practical Use
Enzyme cascade (multienzyme system)
Three-dimensional electrode architecture
Oriented immobilization of enzyme on the electrode
The highest specific activity of CALA was obtained when it immobilized on epoxy-terminated magnetic beads, even though the maximum amount of CALA was coupled to the amine-terminated beads.

32. Enzyme Cascade
The highest specific activity of CALA was obtained when it immobilized on epoxy-terminated magnetic beads, even though the maximum amount of CALA was coupled to the amine-terminated beads.

33. Enzyme Cascade – case study
Alcohol dehydrogenase/Aldehyde dehydrogenase system
The highest specific activity of CALA was obtained when it immobilized on epoxy-terminated magnetic beads, even though the maximum amount of CALA was coupled to the amine-terminated beads.
Ref.)
Electrochimica Acta 50 (2005)

34. Three-dimensional electrode architecture
Multidimensional and multidirectional pore structure
Small pores : high loading density, enzyme stabilization
Large pores : mass transport of liquid phase fuel
So I suggested electroenzymatic production of L-DOPA without reducing reagent to supplement previous enzymatic production.
Instead of reducing reagent such as ascorbic acid, DOPAquinone, which is by-product of serial reaction of tyrosinase, is re-converted to L-DOPA again by electrons from cathode as a reducing power.
I hope this method can reduce the production cost of L-DOPA because this method does not require the expensive reducing reagent and L-DOPA can be easily separate from reaction media. And I also hope the improved productivity during short operation time within a few hours.

35. Three-dimensional electrode architecture – case study
3-dimensional glucose oxidase/SWNT/polypyrrole composite electrode
Anode
Cathode
Power
(μW/cm2)
Ref.
Catalyst
Mediator
Glucose oxidase
HQS
Bilirubin oxidase
ABTS 42
(Habrioux, Merle et al. 2008)
1,1’-dicarboxylferrocene
Laccase
28.4
(Liu and Dong 2007)
1.38
(Wang, Yang et al. 2009) 27
(Brunel, Denele et al. 2007)
Osimium redox polymer
10.0
(Barriere, Kavanagh et al. 2006)
Fe(CN)6-3
110
(Zebda, Renaud et al. 2009)
Pt wire 10
(Zheng, Zhou et al. 2008)
Tyrosinase
158.4
(μW/cm3)
This study
So I suggested electroenzymatic production of L-DOPA without reducing reagent to supplement previous enzymatic production.
Instead of reducing reagent such as ascorbic acid, DOPAquinone, which is by-product of serial reaction of tyrosinase, is re-converted to L-DOPA again by electrons from cathode as a reducing power.
I hope this method can reduce the production cost of L-DOPA because this method does not require the expensive reducing reagent and L-DOPA can be easily separate from reaction media. And I also hope the improved productivity during short operation time within a few hours.

36. Three-dimensional electrode architecture – case study
3-dimensional glucose oxidase/SWNT/polypyrrole composite electrode
; Stability at working condition with continuous feeding of fuel
Anode
Cathode
Fuel
Power density
(μW/cm2)
Stability
(hr)
Ref.
GOx-epHOPG
MP-11-epHOPG
Glucose (2mM)
3.7
<6
(Choi, Wang et al. 2009)
Modified GC with GDH-polyBCB-SWNT
Modified GC with BOD-BSA
Glucose(40mM)
53.9
<14
(Gao, Yan et al. 2007)
GOx/SWNT/Ppy composite
Tyrosinase/CNPs/Ppy composite
Glucose(1mM)
157.4 μW/cm3 29
This study
So I suggested electroenzymatic production of L-DOPA without reducing reagent to supplement previous enzymatic production.
Instead of reducing reagent such as ascorbic acid, DOPAquinone, which is by-product of serial reaction of tyrosinase, is re-converted to L-DOPA again by electrons from cathode as a reducing power.
I hope this method can reduce the production cost of L-DOPA because this method does not require the expensive reducing reagent and L-DOPA can be easily separate from reaction media. And I also hope the improved productivity during short operation time within a few hours.

37. Orient Immobilization
Ref.)
Journal of Molecular Catalysis B: Enzymatic 59 (2009)

38. Case study - glycerol/O2 Biofuel Cell
Ref.)
Journal of Power Source 173 (2007)

39. Case study – Organell-based Biofuel Cell
Ref.)
Electrochimica Acta 53 (2008)
Electrochimica Acta 54 (2009)

40. Case study – Organell-based Biofuel Cell
Ref.)
Electrochimica Acta 53 (2008)
Electrochimica Acta 54 (2009)

41. Case study – Microfluidic Biofuel Cell
Ref.)
Electrochemistry Communications 11 (2009)
Ref.)
Journal of Power Source 178 (2008) 53-58

42. Case study – Hybrid Biofuel Cell
Ref.)
Journal of Power Source 188 (2009)

43. Case study – Hybrid Biofuel Cell
Ref.)
Biosensors and Bioelectronics 24 (2009)

44. Case study – Hybrid Biofuel Cell
Ref.)
Biosensors and Bioelectronics 24 (2009)