Semiconductor nanolasers in living cells

Abstract

In recent years there have been significant advancements in the miniaturisation of semiconductor laser devices, with optimised structures reaching extremely low thresholds, and operating at room temperature. This progress has enabled the demonstration of intracellular lasers, where miniaturised lasers are operated within living cells. Further developments in this new field focused on the optimisation of laser geometries as a potential method to increase the intensity and spectral resolution provided, over conventional biophotonic imaging approaches, using e.g. fluorophores and quantum dots. These intracellular lasers provide opportunities for sensing and multiplexing that were not possible with established techniques.

The focus of this PhD was on integrating these two research frontiers. It involved the fabrication, characterisation, and application of III-V, semiconductor nanodisk whispering gallery mode (WGM) lasers. These were processed to be biocompatible and applied as a biophotonic tool. The tiny resonator volumes - substantially smaller than the nucleus of a cell - could be easily integrated into a variety of cell types, including neurons and immune T-cells that had not been previously capable of internalising lasers. The minimal resonator volume allowed inserting multiple lasers within cells, as they moved through confined environments, such as micro-pore epithelial analogues. Furthermore, the unique properties of WGM lasers were exploited to investigate cell dynamics as an intracellular local refractive index sensor.

The realised lasers exhibited excellent properties, with high signal to noise ratios and very low laser thresholds (~0.13pJ). This was achieved by exploiting the large optical gain and high refractive index of GaInP/AlGaInP multi-quantum wells. In this work, the versatility of these lasers as a photonic platform was demonstrated by embedding them into transferable membranes. This was applied as a sensor for investigating epsilon near zero (ENZ) metamaterials and their optical enhancement properties, and additionally allowed the fabrication of different laser cavity designs such as a random network laser, to investigate the properties of random lasing.