1. Biosensors and Carbon Nanotubes
Lakshmi Jagannathan

2. Enzyme-Coated Carbon Nanotubes as Single-Molecule Bionsensors1
Introduction and Motivation
Physical Immobilization of Protein
Method/Experimentation
Result/Evidence of Immobilization (AFM)
Electrical Characteristics
Results and Electrical Characteristics
Conclusion
1Koen Besteman, Jeong-O Lee, Frank G. M. Wiertz, Hendrik A. Heering, and Cees Dekker, Nano Letters, 2003, Vol. 3, No. 6,

3. Introduction and Motivation
Unique properties of single-wall carbon nanotubes can be used for biosensors
Detection of Glucose Oxidase:
important enzyme that catalyzes glucose
necessary to detect the presence of glucose in body fluids
enzyme as an electrode to detect current
Potential applications: highly sensitive, cheap, and smaller glucose monitors and other applications
Tiny, lightweight, record-high elastic modulus, capillary properties that help with catalysis, and exceptional electrical properties

4. Physical Immobilization- Method
LINKING MOLECULE: 1-Pyrenebutanoic acid succinimidyl ester– absorbing into the SWNT when left in DMF or dimethylformamide
(van der Waals coupling)
Amine bond in protein reacts with amide group from linking molecule and immobilizes (covalent bond)
Source: Chen, R. J.; Zhang, Y.; Wang, D.;
Dai, H. J. Am. Chem. Soc. 2001, 123, 3838.

5. Physical Immobilization- Results (AFM)
A and C: Laser-ablated
and CVD growth,
respectively; before GOX
immobilization
B and D: After
immobilization of GOX-
difference in height before
and after= height of GOX
molecule
Roughly half of SWNT surface is covered with Gox after immobilization

6. Electrical Measurements- Method
Electrolyte-gated carbon nanotube transistors
Measurements done in aqueous solution at room temperature
Liquid gate voltage applied between an Ag/AgCl 3M NaCl standard reference electrode and SWNT
Conductance:
Liquid Electrolyte Gate: The high mobilities, low contact resistances, and excellent gate coupling
Ct= tube capacitance per unit length dominated by the quantum capacitance and Cd (tube-liquid interface capacitance) is negligible
Source: Rosenblatt, S.; Yaish, Y.; Park, J.; Gore, J.; Sazonova, V.; McEuen,
P. L. Nano Lett. 2002, 2, 869.

7. Electrical Characteristics- Results
Black: bare SWNT
Green/Red: 2h and 4h in DMF
Electron-donating power of DMF
Dark Blue: With linking molecule on surface
Light Blue: After Gox immobilization
DMF: dimethylformamide

8. Electrical Characteristics- Results
SWNT as an excellent nanosize pH sensor
Without Gox Immobilization, cannnot tell difference between different pH
After Gox, conductance increases for higher pH
Gate voltage changes by 20mV- conductance changes
Sensitivity due to charged groups on Gox that become more negative with increasing pH

9. Electrical Characteristics- Results
Real time electronic response
Adding water  no conductance shift
Adding Glucose and after activity of Gox conductance shifts
Inset a– another device
Inset b– bare SWNT without immobilization of Gox, but just the addition of glucose

10. Conclusion SWNT can be used as an enzymatic-activity sensor
SWNT can also be used as a pH sensor
This first demonstration of biosensors provides a new tool for enzymatic studies and highlights the potential for SWNT to be used for biomolecular diagnostics

11. References
Besteman, K.; Lee, J.; Wiertz, F. G. M. ; Heering, H. A.; Dekker, C.; Nano Letters, 2003, Vol. 3, No. 6,
Rosenblatt, S.; Yaish, Y.; Park, J.; Gore, J.; Sazonova, V.; McEuen, P. L. Nano Lett. 2002, 2, 869.
Chen, R. J.; Zhang, Y.; Wang, D.; Dai, H. J. Am. Chem. Soc. 2001, 123, 3838.

12. Thank You! Questions?

13. Extra Slides pH sensor:
Figure 3. The pH was set by using 0.1 mM HCl in milli-Q water (pH 4) and 0.1 mM KCl in milli-Q water (pH 5.5). For all measurements the source-drain voltage was kept at 9.1 mV. It is seen that the conductance increases with increasing pH and that pH changes induce a reversible change in the conductance.