Random Lasing Action from Biocompatible Materials

A new class of lasers has recently emerged: biolasers. Biolasers are sources of stimulated emission suitable for tissue integration. They have begun to captivate the scientific community due to their potential to harness the amplifying power of stimulated emission for biosensing, cell tracking and tagging. The main goal of this thesis is to fabricate a biocompatible random laser, study its properties and demonstrate a proof of sensing. Random lasers rely on multiple scattering to provide optical trapping necessary for lasing. Nanostructuring promotes light confinement while the gain provides light amplification. The lasing action is independent of the overall shape and in-stead relies on the device’s internal porosity; it can therefore easily adapt to biological media with the ability to withstand stretching, wetness and heat. Firstly we address how engineering light-matter interaction with a single biocompatible material can lead to increased light scattering and increased opaqueness. We demonstrate simple fabrication techniques which allow the nanostructuring of biomaterials. The gain is studied by doping biomaterials such as proteins, polysaccharides and silica and fabricating doped solid state whispering gallery mode laser. The threshold is evaluated as well as the biocompatibility. The different fabrication techniques are complementary and yield the first silk biocompatible random laser, where the technique is not limited to this material. The lasing output is studied in detail for different gain molecules. Miniature spherical random lasers are made and studied in terms of the threshold size dependence. In simultaneous we take on a different approach and develop macroporous lasers using freeze-drying. As proof of principle we explore lasing as a mechanism for enhanced sensing, demonstrating that biorandom lasing acts as a nonlinear sensor that switches off lasing at high pH values, with a sensitivity ~100 times larger than its fluorescent counterpart. Additionally we build a theoretical framework which clarifies the sensing mechanism. The combination of a natural biopolymer and random lasing offers the oppor-tunity for integration of a laser sensor within living tissue, opening a new path at the interface between nanophotonics and medicine.