| The focus of this research is on the development of optically barcoded silica gel microbeads, synthesized to be used in high throughput screening platforms, using suspension methods for bead synthesis developed specifically for rapid gelation. In suspension methods for particle manufacture, precursor droplets are first formed in a continuous phase immiscible with the droplet phase. The droplets are then solidified into particles. Silica is chosen as the bead material because it can very easily be functionalized to anchor probe molecules which is necessary to function as a capture element in high throughput screening applications. The optical code embedded into the microbeads consists of the spectral signature (the emission spectrum) of a collection of luminescent species. In particular, for this study, multicolor semiconductor nanocrystals or quantum dots (QDs) are used. Each type of QD emits electromagnetic waves at a set wavelength (color), and sets of QDs will be incorporated in differing quantities to form the code. The encoding QDs are dispersed in the pre-gel droplet phase, and are surface functionalized so as not to partition in the continuous phase. In this way, the QDs are effectively trapped in the droplets as they gel to microbeads, which allows for a quantitative loading necessary for optical coding.;In this study, the suspension process for encoded silica bead production is implemented using a batch stirring method for forming the emulsion, and a flow-focusing microfluidic device. The later is used to generate uniformally sized droplets of the pre-gel phase, thus insuring a monodisperse size distribution that is useful for high throughput screening platforms. The gelation of the silica precursor droplets uses an amine catalyst as an accelerant, and thus eliminates the post-production necessary in existing methodologies for obtaining silica beads.;Confocal laser scanning microscopy (CLSM) is used to record the spatial distribution of the nanocrystal fluorescence in the beads and the emission spectra (the barcode). Two colors of QDs were used to create a prototype barcode, and Forster Resonance Energy Transfer (FRET) between these colors was used in addition to the spatial distribution of the fluorescence to infer the aggregation of the nanocrystals in their new silica gel environment. A comparison of the photoluminescence (PL) profiles of the barcoded silica beads demonstrate that indeed resonant energy transfer is occurring, and the crystals do aggregate. FRET shifts in the PL profiles can be attributed to poor dispersability issues in the precursor solution and can in some instances---due to extent of unfavorable conditions for the surface molecules of QDs with the solvent---limit our ability to generate a full compliment of barcodes. Untimely ionization of catalyst, and degree of which, and poor solvability of hydrophylically surface functionalized nanocrystals leads to their poor performance as entrapped luminescing signals. |
