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.
The major trends driving optical chemical sensor technology are miniaturisation and multi-parameter functionality on a single platform (so-called multi-analyte sensing). A multi-analyte sensor chip device based on miniature waveguide structures, porous sensor materials and compact optoelectronic components has been developed. One of the major challenges in fluorescence-based optical sensor design is the efficient capture of emitted fluorescence from a fluorophore and the effective detection of the signal. In this work, the sensor platform has been fabricated using poly(methyl methacrylate), PMMA, as the waveguide material. These platforms employ a novel optical configuration along with rapid prototyping technology, which facilitates the production of an effective sensor platform.
Sensing films for oxygen, carbon dioxide and humidity have been developed. These films consist of a fluorescent indicator dye entrapped in a porous immobilisation matrix. The analyte diffuses through the porous matrix and reacts with the indicator dye, causing changes in the detected fluorescence. The reaction between the dye and the analyte is completely reversible with no degradation of the signal after detection of different concentrations of the analyte. A single LED excitation source is used for all three analytes, and the sensor platform is housed in a compact unit containing the excitation source, filters and detector.
The simultaneous detection of several analytes is a major requirement for fields such as food packaging, environmental quality control and biomedical diagnostics. The current sensor chip is designed for use in indoor air-quality monitoring.
In this paper, we report on a strategy, which produces enhancement of fluorescence using the so-called plasmonic effect whereby the presence of adjacent metallic nanoparticles can dramatically alter the fluorescence emission and absorption properties of a fluorophore. The effect, which is a result of the surface plasmon resonance of the metal surface, can lead to increases in quantum efficiency, radiative decay rates and photostability of the fluorophore, and depends very sensitively on parameters such as geometry of the nanoparticles, nanoparticle-fluorophore separation and fluorophore type. The work is aimed at improving the efficiency of optical biochips. Key benefits from this enhancement include lower limits of detection, reduced reagent requirements and better resolution. This study is part of a comprehensive investigation of plasmonic enhancement using a range of metal nanoparticle (NP) fabrication techniques and a range of measurement configurations. The focus here is on the fabrication of chemically prepared silver-gold alloy spherical NP with a variable thickness silica shell on the surface of which is immobilised a layer of fluorescent dye molecules. The variable thickness shell serves to control the dye-NP separation, which plays a key role in the enhancement mechanism. Transmission electron microscopy (TEM) was used to characterise the NP. The dye used here was the ruthenium polypyridyl complex [Ru(II)-tris(4,7-diphenyl-1,10-phenanthroline)], abbreviated to [Ru(dpp)<sub>3</sub>]<sup>2+</sup>. This paper reports the tuning of the NP plasmon resonance via NP size and alloy composition. The wavelength of the plasmon peak as a function of NP size and composition correlated very well with theoretical predictions based on the Mie scattering theory. Preliminary fluorescence enhancement measurements on this system yielded an enhancement factor of approximately 5.