1. Brett Goldsmith, Ye Lu, Nicholas Kybert, A.T. Charlie Johnson University of Pennsylvania Department of Physics and Astronomy

2. Graphene Transistors Vb Silicon Gate SiO 2 c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c Vg initial

3. Graphene Transistors Vb c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c Vg Vb c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c Vg 400  C anneal Ishigami et al. Nano Letters (2007) Yaping Dan, A.T.C. Johnson et al, Nano Letters, 2009 initialclean

4. Effect of Cleaning on Sensing Cleaning causes: - Reduction in carrier density here from 3.3×10 12 /cm 2 to 6.2×10 11 /cm 2 - Increase in mobility here from 1000 cm 2 /V-s to 2600 cm 2 /V-s - Decrease in chemical sensitivity Yaping Dan, A.T.C. Johnson et al, Nano Letters, 2009

5. Why ssDNA? Chemical sensing is moving beyond “single type” sensors – focus on useful diversity and “electronic nose” approaches Diverse chemistry (e.g., 4 20 ~ 10 12 sequences for 20- mer) Existing literature on ssDNA functionalized sensors. White J, et. al., PLoS Biol 2008 Zuniga C, et. al., APL. 2009 Staii C, A.T.C. Johnson et. al., Nano Lett., 2005 mechanical optical electronic

6. DNA Deposition Sequence 1: 5’ GAG TCT GTG GAG GAG GTA GTC 3’ Sequence 2: 5’ CTT CTG TCT TGA TGT TTG TCA AAC 3’ - 200  g/mL single stranded DNA solution - non-covalent functionalization - graphene is exposed to DNA for 45 minutes - DNA code is used to alter the chemical properties of the applied bio-polymer 1m1m

7. DNA-graphene interaction initialcleanssDNA ssDNA deposition leads to - expected gate shift - lowered mobility Vb c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c Vg

8. DNA-graphene interaction modeling would predict around 1.5×10 14 bases/cm 2 at 100% coverage we measure an increase in doping of around 6.2×10 11 /cm 2 carriers direction is consistent with negatively charged adsorbates ssDNA deposition leads to - expected gate shift - lowered mobility graphene CNT Johnson, R. R.; Johnson, A. T. C., et. al., Nanoletters 2008

9. Sensing Results - DMMP DMMP - no response with clean graphene - response with ssDNA is concentration dependent - response changes depending on sequence of applied ssDNA Sequence 1: 5’ GAG TCT GTG GAG GAG GTA GTC 3’ Sequence 2: 5’ CTT CTG TCT TGA TGT TTG TCA AAC 3’ 2%4%6%8%10%12%

10. Chemically Gating in Two Directions DMMP Propionic Acid Chemical gating response, probably mediated by water – direction and magnitude is similar to ssDNA-CNT responses 2%4%6%8%10%12% 4%6%8%10%

11. Similar Molecule Sensing sequence 2 sequence 1 2%6%9%12%15% 2%6% 9%12% 15% - Changes in sequence show a dramatic ability to change chemical sensitivity - demonstrates differentiation between very similar chemicals

12. Summary - Clean graphene makes a poor chemical sensor - Graphene can be easily functionalized with ssDNA, with a predictable gate shift - ssDNA-graphene devices show vastly improved chemical sensing over pristine graphene - Changing ssDNA sequence does alter chemical sensitivity of graphene

13. Thank You Johnson Group UPenn Prof. A.T. Charlie Johnson Matthew Berck Dan Singer Nicholas Kybert Thomas Ly Jen Daily Dr. Zhengtang Luo Dr. Brett Goldsmith Luke Somers Ye Lu Mitch Lerner *Supported by the Intelligence Community Postdoctoral Fellowship Program, JSTO DTRA, The Nano/Bio Interface Center