Plasmonic colloidosomes: dynamic three-dimensional platform for biphasic, microfluidic and airborne surface-enhanced raman scattering applications

Abstract

The sensing of toxic pollutants in solution and hazardous vapors in air is highly important for early recognition and prevention of natural disasters, diseases, and terrorism activities. Current commercial sensing methods such as fluorescence, UV-vis and chromatography do not provide sufficient molecular fingerprints of target analytes to prevent false positives from similar molecules. As a temporary solution, surface-enhanced Raman scattering (SERS) has enabled ultratrace detection with highly specific molecular information, yet suffers the need for stringent laser alignment while only capable of static measurements due to the use of rigid 2D substrates. This thesis introduces ‘plasmonic colloidosomes’ – micron-sized water droplets coated with Ag nanoparticles – as 3D substrate-less platforms to tackle the above problems in sensing and SERS spectroscopy. These droplets possess a robust, spherical and highly SERS active plasmonic shells comprising of Ag nanoparticle clusters, allowing their establishment as the first “dual-phase tri-analyte” detection system, as demonstrated in Chapter 2. Such breakthrough in biphasic molecular sensing across liquid-liquid interface allows us to directly investigate ultrasmall interfacial reactions. In particular, Chapter 3 discusses the seamless SERS monitoring of dimethyl yellow interfacial protonation performed on plasmonic colloidosomes, which reveals the presence of two highly similar products. Chapter 4 presents the incorporation of plasmonic colloidosomes with online sensing device, realizing the rapid high through-put analysis of multiple samples. A highlight of our work, as described in Chapter 5, is the preparation of the world’s first macroscale 3D SERS ‘in-air sensing’ platform, by incorporating the colloidosomes within an liquid aerosol. These achievements also represent a giant leap towards the potential development of stand-off and substrate-less spectroscopic methodology to detect gas toxins/airborne weapons remotely.