AVS 46th International Symposium
    Biomaterial Interfaces Group Friday Sessions
       Session BI-FrM

Paper BI-FrM6
Cap-shaped Gold Nano Particles for Optical Biosensing

Friday, October 29, 1999, 10:00 am, Room 613/614

Session: Interface, Properties, and Modification
Presenter: M. Himmelhaus, Hitachi, Ltd., Japan
Authors: M. Himmelhaus, Hitachi, Ltd., Japan
H. Takei, Hitachi, Ltd., Japan
Correspondent: Click to Email
Gold nano particles can be utilized for optical detection of biomolecules.@footnote 1, 2@ The approach presented here is well suited for the development of miniaturized, inexpensive biosensors for two reasons. First, the preparation of the sensing surface is easy to control and highly reproducible. Second, the unique optical properties of cap-shaped gold particles, such as a pronounced reflectivity minimum in the visible region of OD. 2.4 with a bandwidth of 100 nm, lead to a highly sensitive though simple optical read-out quantity. For preparation, a gold layer of 20 nm is first evaporated on a polystyrene (PS) substrate. Then, the gold layer is exposed to an aqueous PS nano sphere suspension containing a small amount of carbodiimide. Addition of the last chemical to the commercially available monodisperse PS sphere suspension leads to formation of a dense monolayer of randomly positioned PS nano spheres on the gold thin film. After one hour of incubation, superfluous PS spheres are simply washed off with deionized water. Finally, a gold layer of 20 nm thickness is evaporated onto the PS sphere monolayer leading to formation of cap-shaped gold particles. The resulting surface exhibits a pronounced extinction peak upon reflection of visible light. The shift of this reflectivity minimum due to changes in the refractive index of the immediate environment can be monitored with simplest optical methods and therefore is well adapted to miniaturization. We will show that a straightforward fiber-optical setup is sensitive enough to detect in-situ monolayer formation of alkanethiolates. Further, the capability of sensing biomolecular adsorption will be demonstrated utilizing the biotin/avidin functional pair as a model system. @FootnoteText@ @footnote 1@R. Elghanian, J. J. Storhoff, R. C. Mucic, R. L. Letsinger and C. A. Mirkin, Science 277 (1997) 1078-81 @footnote 2@F. Meriaudeau, T. R. Downey, A. Passian, A. Wig and T. L. Ferrell, Appl. Opt. 37 (1998) 8030-7.