Research in our group falls into two areas that at first glance appear to be rather different, but that are in reality closely related through the common thread of interface chemistry. In short, we aim to develop new chemical procedures to join together, at the molecular level, dissimilar materials that, once assembled, form the basis of novel devices. As chemists, we think of systems on the molecular level; this provides us with a perspective that is different from that of engineers or biologists, two groups with whom we collaborate extensively. Because we do operate on the “molecular level,“ we can often propose solutions to scientific problems that are not on the “radar screen” of these colleagues.
Most of our work is based on self-assembled monolayers of organophosphonates, which we have nicknamed SAMPs. We have synthesized and characterized these monolayers on a variety of surfaces, including metals, oxides, and several organic polymers. We have shown that SAMPs form with molecular level surface density on many substrates, which makes them especially important in areas where film quality and homogeneity are critical.
Molecular electronics is our first area of interest. In particular, we aim to control electrode surface properties using designed SAMPs. In our initial investigations, we prepared SAMPs for the activation of electrodes for “hole” injection in organic light emitting diodes (OLEDs). We made OLEDs in our own lab, and we tested them for brightness and current density in collaboration with groups in Electrical Engineering. OLEDs using our SAMP electrode modification matched some of the best devices prepared in the Electrical Engineering department using traditional means. We then turned our attention to organic thin film transistors (OTFTs). Our goal was to prepare SAMPs that could be formed on the gate dielectric material of a transistor device. The role of the SAMP was to improve growth of the organic semiconductor pentacene on it; this was intended to improve a range of transistor characteristics. We designed and prepared a family or aromatic SAMPs on the SiO2 dielectric formed on a Si electrode and, in collaboration with a group at Dalhousie University in Halifax, we had OTFTs built. In this way we have built models that at least equal and in critical ways surpass reported OTFT behavior; some of our new substrates even appear to enable us to turn what are traditionally 2-dimensional monolayers into 3-dimensional templates for further semiconductor growth.
Cell-surface interactions are our second area of focus. In particular, we aim to learn how to control cell behavior on a surface to enable tissue integration with a synthetic of interest in the biomedical area. We collaborate extensively with the group of Prof. Jean Schwarzbauer in Molecular Biology at Princeton. We originally developed our SAMP techniques to address the issue of surface activation of titanium alloys, which are commonly used orthopedic and dental prosthesis materials. We showed that our treatments gave not only excellent in vitro cell growth, but also demonstrated efficacy for promoting bone growth in two in vivo studies, which contrasted our SAMP treatments with highly regarded models from both academia and industry. We have now turned our attention to examining surface activation of otherwise bioinert polymeric materials that have mechanical and degradative properties that are superior to metals. We have shown that a simple adhesion layer can be deposited onto these polymers from the vapor phase, and that these layers can be used to bond phosphonic acids to the polymer surfaces. In an especially interesting ramification, we have found that our adhesion layer can be applied to a variety of surfaces through a photolithographic mask. In this way, patterns of cell adhesive molecules can be prepared on these surfaces. Recently, we showed that patterns with dimensions on the order of a single cell can be prepared, and that these patterns control the shape of cell spreading within them. Applications to the control of stem cell differentiation are now in progress.
Selected Recent Publications
- Advanced Surface Modification of Indium Tin Oxide for Improved Charge Injection in Organic Devices, Hanson, E. L.; Guo, J.; Koch, N.; Schwartz, J.; Bernasek, S. L., J. Am. Chem. Soc. 2005, 127, 10058-10062.
- Organophosphonate Self-Assembled Monolayers for Gate Dielectric Surface Modification of Pentacene-Based Organic Thin-Film Transistors: A Comparative Study, McDermott, J. E.; McDowell, M.; Hill, I. G.; Hwang, J.; Kahn, A.; Bernasek, S. L.; Schwartz, J. J. Phys. Chem. 2007, 111, 12333-12338.
- A Novel Surface Treatment of Porous Metallic Implants that Improves the Rate of Bony Ingrowth, Shannon, F.; Cottrell, J. M.; Deng, X.-H.; Crowder, K. N.; Doty, S. B.; Avaltroni, M. J.; Warren, R. F.; Wright, T. M., Schwartz, J., J. Biomed. Mater. Res. A. 2008, 86A, 857-864.
- Surface activation of Polyurethanes Via Zirconium Carbamate Complex Interfaces Dennes, T. J.; Schwartz, J. Soft Matter, 2008, 4, 86-89.
- Organophosphonate based PNA-functionalization of silicon nanowires for label-free DNA detection, Tornow, M.; Cattani-Scholz, A.; Pedone, D.; Dubey, M.; Neppl, S.; Nickel, B.; Feulner, P.; Schwartz, J.; Abstreiter, G., ACS Nano 2008, 8, 1653-1660.
- A Modular Monolayer Coating Enables Cell Targeting by Luminescent Yttria Nanoparticles, Traina, C. A. Traina; Dennes, T. J.; Schwartz, J., Bioconjugate Chemistry 2009, 20, 437-439.
- A Nanoscale Adhesion Layer to Promote Cell Growth on PEEK, Dennes, T. J., Schwartz, J. J. Am. Chem. Soc. 2009, 131, 3456-3457.
- A Nanoscale Metal Alkoxide/Oxide Adhesion Layer Enables Spatially Controlled Metallization of Polymer Surfaces, Dennes, T. J., Schwartz, J. ACS Appl. Mater. Interfaces, 2009, 1, 2119-2122.
- Silicon Surface Passivation by an Organic Overlayer of 9,10-Phenanthrenequinone, Avasthi, S.; Qi,Y.; Vertelov, G.; Schwartz, J.; Kahn, A.; Sturm, J. C. Appl. Phys. Lett., 2010, 96, 222109.
- Designed Organophosphonate Self-Assembled Monolayers Enhance Device Performance of Pentacene-Based Organic Thin-Film Transistors, Liao, K.-C.; Ismail, A. G.; Kreplak, L.; Schwartz, J.; Hill, I. G. Adv. Mater., 2010, in press.