| AVS 54th International Symposium | |
| Biomaterial Interfaces | Thursday Sessions |
| Session BI-ThP |
| Session: | Biomaterial Interfaces Poster Session |
| Presenter: | T. Sherlock, University of Houston |
| Authors: | T. Sherlock, University of Houston S.M. Kemper, University of Houston P. Ruchhoeft, University of Houston R.L. Atmar, Baylor College of Medicine R.C. Willson, University of Houston |
| Correspondent: | Click to Email |
We have fabricated micron-sized retroreflectors (structures that return incident light directly back to the source) and have shown that they are extremely bright and detectable over a large range of angles when inspected with a simple optical microscope. These retroreflectors are part of an ultra-sensitive detector platform for sensing small quantities of virus particles, bacteria, DNA, RNA, or any variety of molecules of interest. In particular, we are targeting our first generation sensor to detect Norwalk virus particles. In this proposed system, the base of the retroreflector is decorated with antibodies to the virus, and, if present, the virus particles are captured by this surface. After capture, gold nanoparticles, coated with a secondary antibody, are introduced into the system, attach to the virus, and drastically reduce the retroreflector brightness with a specific, well-understood spectral signature. If no virus is present, the reflectivity is unaffected. We have measured the reflectivity versus 40nm diameter gold nanoparticle surface density and have found a 40% reduction in signal for 100 nanoparticles per square micron when illuminated with broad-band light. The base of the retroreflector is about 4 square microns in size, yielding a detection sensitivity of hundreds of particles. Further optimization of particle size and illumination wavelength is expected to increase this sensitivity substantially. Retroreflectors are fabricated by coating a silicon wafer with 2.5 microns of polyimide and 200nm of resist. A lithography step is used to generate the retroreflector pattern as openings in the resist and a 50nm thick nickel coating is deposited using thermal evaporation. After a lift-off step, which leaves behind only the nickel that coated the base of the resist openings, the patterns are transferred into the polyimide in an O2/CF4 reactive ion etch, leaving the retroreflecting structure with very straight relatively smooth walls. Next, gold is evaporated to coat the base of the structure and a directional evaporation step is used to cover all but the sensor base with aluminum. The gold is selectively functionalized with amine-reactive thiol molecules which serve as a platform for attaching antibodies, oligonucleotides, or other detector molecules.