Hollow Gold Nanoparticles Are Very Sensitive Sensors Mostafa A. El-Sayed, Georgia Tech Research Corporation, DMR Sensing of biological materials, dangerous substances or explosive substances is presently a very important field of research. Although many sensing techniques have been used, improving the accuracy and sensitivity is still in need. Each molecule has a Raman fingerprint, but the challenge in using Raman measurement is to enhance its weak signal. Silver and gold nanoparticles have plasmon fields which are responsible for greatly enhancing the Raman signal. During our research in this current grant we prepared gold nanocages which we have shown to have the strongest plasmon field ever reported for a nanoparticle. We used these nanoparticles to sense thiophenol vapor with very great sensitivity. Our theoretical calculations show gold nanocages to have a high plasmon field. Many sizes and shapes of nanoparticles have been used as a Raman substrate. Some conditions have to be met to observe a strong Raman signal quantitatively. The plasmonic nanoparticles should be kept at fixed separation distances during the measurement. The plasmon field intensity depends on the inter-particle separation, so if the distance is varied during the SERS measurement or from one analyte to another, the SERS spectrum will not be an accurate analytical technique. In order to solve this problem we used a Langmuir-Blodgett technique to assemble the nanoparticles into a monolayer of fixed average separation which can be changed and controlled by this technique. Mahmoud M A, Snyder, B., El-Sayed, M A; J Phys. Chem.(2010), 114, Surface-enhanced Raman Scattering of Thiophenol vapor adsorbed on gold nanocages monolayer of different percent surface coverage by using the Langmuir-Blodgett technique. SEM images of 50 nm gold nanocages monolayer assembled on the surface of quartz substrate by use of the Langmuir-Blodgett. The field enhancement map contour for 50 nm gold nanocage with wall thickness of 5 nm as calculated by the DDA method.

SERS of peptide adsorbed on the surface of AuNCs assembled at different percent of coverage of a Langmuir-Blodgett. High-throughput protein detection has been identified as a critical emerging technology in biology and impacts several key scientific and technical research thrust goals identified by NSF including discovery and preservation of biodiversity, high-resolution structure of biological molecules, biological influences on global cycles, and enhanced waste treatment and bioremediation. The accomplishment in this funding period is that, we are able to detect peptides with Raman spectroscopy. The measurement is based on adsorbing the peptide on the surface of a monolayer of gold nanocages assembled by Langmuir-Blodgett technique. Development of new materials for sensitve biological detection is a very important field of research for medical applications. One out of four people die of cancer worldwide. If detected early, it can be cured. Thus the development of sensitive detectors of protein markers for cancer is a very important area of material research. Thus the application of nanotechnology in this direction is also of vital importance to human health. Hollow Nanoparticles are Very Sensitive Sensors Mostafa A. El-Sayed, Georgia Tech Research Corporation, DMR