This paper describes the development and preparation of a new class of materials for surface-enhanced Raman scattering (SERS) consisting of gold nanoparticles coated onto hollow, buoyant silica microspheres. These materials allow for a new type of molecular assay designated as a lab-on-a-bubble (LoB). LoB materials serve as a convenient platform for the detection of analytes in solution and offer several advantages over traditional colloidal gold and planar SERS substrates, such as the ability to localize and concentrate analytes for detection. An example assay is presented using the LoB method and cyanide detection. Cyanide binds to SERS-active, gold-coated LoBs and is detected directly from the corresponding SERS signal. The abilities of LoBs and a gold colloid to detect cyanide are compared, and in both cases, a detection limit of ~170 ppt was determined. Differences in measurement error using LoBs versus gold colloid are also described, as well as an assay for 5,5'-dithiobis(2-nitrobenzoic acid) that shows the benefit of using LoBs over SERS analyses in colloids, which are often plagued by particle aggregation.

We describe a novel sandwich assay based on surface enhanced Raman scattering (SERS) comprised of buoyant silica microspheres coated with antibodies against the β subunit of the cholera toxin (CT), and gold nanoparticles tagged with a Raman reporter, shelled with silica and coated with antibodies against the β subunit of the CT. Together these components couple to form a sandwich which, after incubation, floats on the surface of the sample. The buoyant silica microparticle/nanoparticle reporter combination has been coined a lab on a bubble (LoB). LoB materials may provide a platform for rapid detection of antigen in solution and offers advantages over lateral flow or magnetic pull-down assays. The Raman reporter provides a unique and intense signal to indicate a positive analysis. Our limit of detection for the β subunit of the CT in a buffer based system is 1100 ng.

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A method for obtaining time and frequency resolved spectra with high spectral and temporal resolution over a broad spectral range is presented. Step – scan Fourier transform spectroscopy permits spectral coverage from UV to mid IR with sub nanosecond resolution making it possible to track emission from multiple manifolds with full temporal resolution in a single experiment. Data for several rare-earth doped crystalline materials exhibiting multiple emission bands and including evidence of energy transfer is shown.

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