Book of Abstracts Book of Abstracts - Universität Konstanz

Electronic structure and bonding in gold coated silica cluster: a nano
bullet for tumor
Q. Sun, Q. Wang, and P. Jena
Physics Department, Virginia Commonwealth University, Richmond, VA 23284, USA.
Recently an exciting application of gold coated silica nano-shells has been found in treating
tumor and cancer. The nano-shell consists of silica (SiO2) core of order 100 nm coated with
about 20 nm of gold. It absorbs near infrared light (NIR) and converts that light to heat, causing
irreversible thermal cellular destruction. When the nano-shells were incorporated into human
breast cancer cells in a test tube, and then exposed to NIR, 100 percent of the cancer cells were
killed. Motivated by this experiment we have investigated the coating of a small silica cluster
(of the order of a few nano-meters) with Au to understand (1) if such a small cluster can absorb
infrared radiation and (2) if so, does the mechanism for such absorption have electronic origin?
(3) How do Au atoms bind with silica core? We show for the first time that gold atoms bind to
silicon atoms with dangling bonds and serve as seeds for the growth of Au islands (Fig. 1a). The
large electron affinity of gold causes significant change in the electronic structure of silica
resulting in a substantial reduction in the HOMO-LUMO gap (Fig. 1 b), thus allowing it to
absorb near infrared radiation (Fig. 1 c). Our study suggests that a small cluster can have similar
functionality in the treatment of cancer as the large size nano-shell, but for a different
mechanism. The advantage of such small nano-bullet for targeting tumor and cancer is that it
can easily penetrate the crowded environments such as the biological milieu of cells and live
tissues for effective drug delivery.
Au
Au
References
Geometry
O
Si
Au
Energy (eV)
(a) (b) (c)
Figure 1. (a) Geometry, (b) HOMO-LUMO gap, and (c) optical spectra of Au 3-(SiO 2) 3.
[1] L.R. Hirsch, et al. PNAS 100 , 13549 (2003).
[2] Q. Sun, Q. Wang, B.K. Rao, and P. Jena, Phys. Rev. Lett. 93, 186803 (2004).
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(SiO 2 ) 3
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Energy spectra
Optical absorption (arb.units)
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Optic spectra
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