My research interests cover a broad area closely related to surface chemistry/physics, particularly the surface properties of organic self-assembled films and the fundamental processes at electrode/electrolyte interfaces. Recent years, my research activities have shifted from the investigation of fundamental issues to the fabrication/characterization of nanomaterials/devices and the development of biosensors. Current research topics that I am pursuing with my colleagues at Ames Research Center are
(1) the fabrication of nanotube or nanowire assembly as electrodes for the development of ultrasensitive biosensors,
(2) the investigation of the mechanism of transducing DNA hybridization into electronic signals by electrochemical methods,
(3) the integration of nanoelectrodes into genoelectronics based genechips.
Our goal is to study methods to fabricate nanomaterials such as carbon nanotubes and mesoporous catalyst templates and to integrate these materials into useful nanodevices by the combination of nanofabrication and chemical functionalization, particularly nanoelectrode assembly interfaced with biomolecules for the development of biosensors.
Carbon nanotubes are ideal building blocks for the fabrication of nanodevices which are not easily achievable using other materials. The key for this application is to precisely control the growth of carbon nanotube at desired sites with desired structure and orientation. We are pursuing this goal with plasma assisted catalytic CVD in combination with well-defined nanoporous templating methods. Current effect is to grow micropatterned multiwalled carbon nanotube array with controlled density and purity for the application as nanoelectrode assembly.
The essential issue of the development of biosensors is to understand the mechanism that biorecognition processes are transduced into measurable physical signals. We are focused on investigating systems in which the transduction is by electrochemical mechanisms. DNA molecules are electroactive at certain potentials which can be used to identify the hybridization process. However, the redox signal from DNA itself is very weak to be detected. We are working on the amplification of the signal using metal chelates as well as indicator-free mechanisms in the combination with the design of delicately archetectured nanoelectrodes.
Our ultimate goal is to develop fast, ultrasensitive, high specific, low cost, and miniaturized biosensors using state-of-the-art nanotechnolgoies. These sensors are expected to be integrated into the next-generation genechips. Along this direction, other methods based on molecular electronics are also being pursued at this moment.
1. Structure of CH3(CH2)17SH Self-Assembled on the Ag(111) Surface: An Incommensurate Monolayer, P. Fenter, P. Eisenberger, J. Li, N. Camillone III, S. Bernasek, G. Scoles, T. A. Ramanarayanan and K. S. Liang, Langmuir, 7, 2013 (1991).
2. A Grazing Incidence X-Ray Diffraction Study of Self-Assembled Monolayers, P. Fenter, J. Li, P. Eisenberger, T. A. Ramanarayanan and K. S. Liang, in Interface Dynamics and Growth, 291 (1992).
3. Structural Defects in Self-Assembled Organic Monolayers via Combined Atomic Beam and X-ray Diffraction, N. Camillone III, C. E. D. Chidsey, P. Eisenberger, P. Fenter, J. Li, K. S. Liang, G.-Y. Liu and G. Scoles, J. Chem. Phys. 99 (1), 744 (1993).
4. Structure of Long Chain Alkane Thiols on Au(100) by the Combination of Atomic Beam and X-ray Diffraction, J. Li, K. S. Liang, N. Camillone III, B. Leung and G. Scoles, J. Chem. Phys. 102 (12), 5012 (1995).
5. The Counterion Overlayers on Self-Assembled Monolayer of HOOC(CH2)15SH on Au(111): an in situ X-Ray Reflectivity Study, J. Li, K. S. Liang, G. Scoles, A. Ulman, Langmuir, 11,4418 (1995).
6. The Coadsorption of Sulfate/Bisulfate Anions with Hg Cations during Hg Underpotential Deposition on Au(111): An In-Situ X-Ray Diffraction Study, Jun Li, H. D. Abruña, J. Phys. Chem. B, 101, 244-252 (1997).
7. The Phases of Underpotentially Deposited Hg on Au(111): An in situ X-ray Diffraction Study, Jun Li, H. D. Abruña, J. Phys. Chem. B, 101, 2907-2916 (1997).
8. Structural and Kinetics Studies of Hg (UPD) on Au(111), E. Herrero, Jun Li, and H. Abruña, in: The Electrochemical Double Laye, Eds. C. Korzeniewski, and B. E. Conway, Proc. 97 (17), 277-292, The Electrochemical Society, Pennington, New Jersey, 1997.
9. The Effects of Anions on the Underpotential Deposition of Hg on Au(111): An In-Situ X-Ray Diffraction Study, Jun Li, E. Herrero, H. D. Abruña, Colloids and Surfaces A: Physicochemical and Engineering Aspects, 134, 113-131 (1998).
10. Anion and Electrode Surface Structure Effects on the Deposition of Metal Monolayers: Electrochemical and Time-Resolved Surface Diffraction Studies, H.D. Abruña, J.M. Feliu, J.D. Brock, L.J. Buller, E. Herrerro, J. Li, R. Gómez and A.C. Finnefrock, Electrochimica . Acta, 43 (19-20), 2899-2909 (1998).
11. Electrodeposition dynamics: electrochemical and X-ray scattering studies, E. Herrero, L.J. Buller, J. Li, A. C. Finnefrock, A. B. Salomon, C. Alonso, J.D. Brock, and H.D. Abruña, Electrochimica. Acta., 44, 983-992 (1998).
12. Electrochemical, In-Situ Surface EXAFS and CTR Studies of Co Monolayers Irreversibly Adsorbed onto Pt(111), E. Herrero, Jun Li, and H. D. Abruña, Electrochimica. Acta, 44, 2385-2396 (1999).
13. In-Situ AFM Study of Pitting Corrosion of Cu Thin Films, Jun Li, D. Lampner, Colloids and Surfaces A: Physicochemical and Engineering Aspects, 154, 227-237(1999).
14. The carbon nanotube as AFM tips: Measuring DNA Molecules at the Liquid/Solid Interface, J. Li, A. Cassell, and Hongjie Dai, Surf. Interface Anal. 28, 8-11 (1999).
15. The Synthesis of Single-Walled Carbon Nanotubes by CVD Catalyzed with Mesoporous MCM-41 Powder, Jun Li, M. Foo, Y. Wang, H. T. Ng, S. Jaenicke, G.-Q. Xu, and S. F. Y. Li, Science and Application of Nanotubes, Eds. D. Tomanek, and R. J. Enbody, Kluwer Academic/Plenum Publishers, 181-194 (2000).
16. The Formation of Two-Dimensional Supramolecular Chiral Lamellae by Diamide Molecules at the Solution/Graphite Interface: a Scanning Tunneling Microscopy Study, R. Lim, J. Li, S. F. Y. Li, Z. Feng, and S. Valiyaveettil, Langmuir, 16, 7023-7030 (2000).
17. Textural Properties of Zirconia from Zirconium Propoxide Prepared at Different pH, G. K. Chuah, S. H. Liu, S. Jaenicke, and J. Li, Microporous and Mesoporous Materials, in press.
18. The Graphitization and Nanoparticulation of SiC Crystals during High Temperature Annealing, R. Lim, J. Li, S. F. Y. Li, D. Tan, and K. P. Loh, in preparation.
19. Soft-Lithography Mediated CVD Growth of Architectured Carbon Nanotubes on Elastomeric Substrates, H. T. Ng, M. L. Foo, A. P. Fang, J. Li, G. Q. Xu, S. Jaenicke, L. Chan, and S. F. Y. Li, submitted to Advanced
20. Review Article: X-ray Diffraction from Electrode Surfaces, J. Li, to be published in the Encyclopedia of Surface and Colloid Science, Ed. A. Hubbard, Marcel Dekker.