Robert I. Nooney

Optimization of Plasmonic Enhancement of Fluorescence on Plastic Substrates

In this work, we report on the uniform deposition of tailored plasmonic coatings on polymer substrates and on the distance dependence of the plasmonic enhancement of a fluorescent dye. Silver, gold, and silver/gold alloy nanoparticles (NPs) with a range of diameters were synthesized using chemical techniques and characterized using UV-vis absorption spectroscopy, transmission electron microscopy (TEM), and atomic force microscopy (AFM). Reproducible polyelectrolyte (PEL) layers, which were deposited on plastic microwell plates using a layer-by-layer technique, served as both a stable and uniform substrate for deposition of the NPs as well as providing spacer layers of known thickness between the NPs and the fluorescent dye. A maximum enhancement factor of approximately 11 was measured for 60 nm diameter pure silver NPs, for a dye-NP separation of approximately 3 nm. A shift in the localized surface plasmon resonance (LSPR) wavelength as a function of the effective refractive index of the PEL layers was also observed, and the measured shifts show a similar trend with theoretical predictions. This work will contribute toward the rational design of optical biochip platforms based on plasmon-enhanced fluorescence.

Nanoparticle strategies for enhancing the sensitivity of fluorescence-based biochips

This article describes strategies for achieving fluorescence enhancement in optical biochips. Two strategies are discussed: plasmonic enhancement, which is due to the localized surface plasmon resonance of metal nanostructures that are adjacent to the fluorescent labels in optical immunoassays; and the use of high-brightness silica nanoparticles as enhanced labels. We present a review of the state-of-the-art in both areas, including synthesis techniques for the metal and silica nanoparticles and the use of the nanoparticles in optical immunoassays. Data are presented that highlight the key design parameters which influence the level of enhancement and model assay data are presented that illustrate potential enhancements in assay performance.

Fluorescent Cy5 silica nanoparticles for cancer cell imaging

Cancer is a leading cause of death worldwide, with metastasis responsible for the majority of cancer-related deaths. Circulating tumour cells (CTCs) play a central role in metastasis. Fluorescent silica particles (NPs), of diameter ~50 nm which contain a large concentration of Cy5 dye molecules and are extremely bright, have been developed to detect these rare CTCs. Due to this brightness, the particles have superior performance compared to single Cy5 dye molecule labels, for detecting cancer cells. Fluorescence measurements show that the NPs are almost 100 times brighter than the free dye. They do not photo bleach as readily and, due to the biocompatible silica surface, they can be chemically modified, layer-by-layer, in order to bind to cells. The choice of these chemical layers, in particular the NP to antibody linker, along with the incubation period and type of media used in the incubation, has a strong influence on the specific binding abilities of the NPs. In this work, NPs have been shown to selectively bind to the MCF-7 cell line by targeting epithelial cellular adhesion molecule (EpCAM) present on the MCF-7 cell membrane by conjugating anti-EpCAM antibody to the NP surface. Results have shown a high signal to noise ratio for this cell line in comparison to a HeLa control line. NP attachment to cells was verified qualitatively with the use of fluorescence microscopy and quantitatively using image analysis methods. Once the system has been optimised, other dyes will be doped into the silica NPs and their use in multiplexing will be investigated.