Biosensors and Carbon Nanotubes Lakshmi Jagannathan

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, 727-730.

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

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.

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

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.

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

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

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

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

References Besteman, K.; Lee, J.; Wiertz, F. G. M. ; Heering, H. A.; Dekker, C.; Nano Letters, 2003, Vol. 3, No. 6, 727-730. 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.

Thank You! Questions?

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.