To obtain a coding system for multiplex detection, we have developed a method to synthesize a new type of nanomaterial called composite organic-inorganic nanoparticles (COINs). The method allows the incorporation of a broad range of organic compounds into COINs to produce surface enhanced Raman scattering (SERS)-like spectra that are richer in variety than fluorescence-based signatures. Preliminary data suggest that COINs can be used as Raman tags for multiplex and ultrasensitive detection of biomolecules.

Surface-enhanced Raman-scattering (SERS) substrates fabricated on the nanoscale offer new ways of detecting low concentrations of chemicals by bringing target molecules close to the metallic surface to generate large SERS signals. The vast surface area of porous silicon and its open porous structure are two key material properties we used to fabricate highly sensitive SERS substrates for the detection of chemical and biological molecules. Introduction of silver into the silicon nanoscale pores form a nanocomposite material that uniquely combines the ability of metal surfaces to amplify Raman scattering signals with an enlarged surface area that allows ten orders of magnitude enhancement for the detection of rhodamine 6G. Our enhancement factor is comparable to other substrates commonly used by researchers in the field, such as chemically synthesized metal colloids. We also report the detection of biological molecules, such as adenine, on a metalcoated silicon nanostructured surface. The ability for a silicon substrate to detect low concentrations of target molecules opens the door to applications where it can be used as the detection tool for integrated, on-chip devices.Development of efficient and reliable SERS substrates is important for biological analysis applications because Raman spectroscopy provides highly resolved vibrational information at room temperature and does not suffer from rapid photobleaching commonly observed in fluorescence spectroscopy. However, Raman scattering is an extremely inefficient process with low scattering cross-sections which are approximately fourteen orders of magnitude smaller than the absorption cross-sections (~10 ±16 cm 2 per molecule) of fluorescent dye molecules.[1] To achieve high sensitivity, the Raman scattering efficiency must be enhanced. Several research groups have explored different types of substrates to provide this enhancement using silver and gold nanoparticles.[2±6] The use of silver colloid solutions [2] is the most popular method for generating SERS signals from target molecules. However, the chemical synthesis of such nanoparticles is typically unstable, difficult to reproduce, and not suitable for high-volume production. Over the past 10 years, extensive research efforts have been devoted to the determination and understanding of the sources of Raman enhancement in the SERS effect. Although still debatable, based on experimental data, the origin of the SERS enhancement can be explained by two supporting theories: [7] 1) electromagnetic resonances occurring near the metal surface generate large localized fields, also referred to as ªhot spotsº, and 2) chemical interactions between the molecules and the metal surface allow the molecules to effectively scatter light. This communication reports on a new method to produce efficient and reliable SERS substrates using a nanoporous material coated homogeneously with a metal layer. Our focus is on integrating novel substrate synthesis and conformal metal deposition in silicon nanopores to create SERS-active nanost...

No abstract

Composite organic-inorganic nanoparticles (COINs) are novel optical labels for detection of biomolecules. We have previously developed methods to encapsulate COINs and to functionalize them with antibodies. Here we report the first steps toward application of COINs to the detection of proteins in human tissues. Two analytes, PSA and CK18, are detected simultaneously using two different COINs in a direct binding assay, and two different COINs are shown to simultaneously label PSA in tissue samples.