Femtosecond laser microfabricated devices for biophotonic applications

Abstract

Femtosecond Laser DirectWriting has emerged as a key enabling technology for realising miniaturised biophotonic applications offering clear advantages over competing soft-lithography, ion-exchange and sol-gel based fabrication techniques. Waveguide writing and selective etching with three-dimensional design flexibility allows the development of innovative and unprecedented optofluidic architectures using this technology. The work embodied in this thesis focuses on utilising the advantages offered by direct laser writing in fabricating integrated miniaturised devices tailored for biological analysis. The first application presented customised the selective etching phenomenon in fused silica by tailoring the femtosecond pulse properties during the writing process. A device with an embedded network of microchannels with a significant difference in aspect-ratio was fabricated, which was subsequently applied in achieving the high-throughput label-free sorting of mammalian cells based on cytoskeletal deformability. Analysis on the device output cell population revealed minimal effect of the device on cell viability. The second application incorporated an embedded microchannel in fused silica with a monolithically integrated near-infrared optical waveguide. This optofluidic device implemented the thermally sensitive emission spectrum of semiconductor nanocrystals in undertaking remote thermometry of the localised microchannel environment illuminated by the waveguide. Aspects relating to changing the wavelength of illumination from the waveguide were analysed. The effect of incorporating carbon nanotubes as efficient heaters within the microchannel was investigated. Spatio-thermal imaging of the microchannel illuminated by the waveguide revealed the thermal effects to extend over distances appreciably longer than the waveguide cross-section. On the material side of direct laser writing, ultra-high selective etching is demonstrated in the well-known laser crystal Nd:YAG. This work presents Nd:YAG as a material with the potential to develop next-generation optofluidic devices.