Our group is composed of people interested and enthusiastic about light, photons, optical devices and systems. We have been interested in three-dimensionally confined nanoparticles such as colloidal quantum dots (QD) and plasmonic nanoparticles. These materials harvest strong near-field interaction with light, and have opened new directions in nanophotonic devices and integration, as well as various applications in biomedicine and nanotechnology. We also utilize photonic crystal nanostructures to modulate light fields and enhance the efficiency of optical tweezers. In addition, we pursue device integration in micro-scale utilizing optical MEMS technologies.
Nanostructure-enhanced laser tweezers (NELT)Optical manipulation of particles has broad applications in nanoscience, biological study, and biomedicine. Conventional optical tweezers require high optical intensity to achieve sufficient force due to low efficiency in direct conversion from optical energy to mechanical energy. The challenge becomes more severe as the particle size decreases to sub-micron regime. We explore the enhanced field from plasmonic or photonic crystal nanostructures to increase the trapping efficiency and functionality of optical tweezers. Using these approaches, we have demonstrated efficient trapping and rotation of micro- and nano-particles, nanowires, cells and nuclei with low optical intensity. In addition, trapping and concentration of DNA, micro-fluidic mixing, and scalable assembly of nanoparticles have also been achieved using the platform.
NELT-integrated MEMS for high-accuracy mass sensingIn this NSF-sponsored project, we integrate photonic crystal optical tweezers and microfluidic structures with MEMS resonators. By precisely trap and position the particles on the surface of the MEMS resonators, the mass of the particles can be measured and monitored with high accuracy and repeatability. The technology can be used for living cells and nanoparticles, for example, understanding how cell mass change under various cemo-mechanical stimuli and monitoring nanoparticle growth in nanofabrications. Its broader impacts include the fields of cell biology, tissue engineering, cancer and disease research, as well as nanotechnology.
Quantum dot nanophotonics
Quantum dots have unique optical and electrical properties that arise from the very small size of the particles, resulting in quantization of electron-hole energy levels in the particle. This leads to their various properties that are far superior to the corresponding materials in bulk form, such as high quantum efficiency, size-dependent tunable emission, and high sensitivity. In addition, they have flexible surface chemistry that can be modified for various self-assembly fabrication, which provides a powerful route to integrated fabrication on a wide range of substrates. We have demonstrated sub-diffraction limit QD waveguides, nanogap QD photodetectors with high sensitivity and spatial resolution, plasmonic-enhanced QD photodetectectors with color selectivity, Si QDs with high photoluminescence quantum yield. We have also demonstrated photostimulation of cells and neurons through QDs with extremely low optical intensities.
At our spare time, we enjoy turning our research into fun stuff. For example, the logo on the uppper-left corner is the red fluorescence of CdSe QDs patterned using self-assembly fabrication process.
Micro-instrumentation by optical MEMSWe have developed a scanning micro-mirror with an adjustable focal length for endoscope applications. A miniaturized scanner integrated with the distal end of an endoscope and advanced optical imaging technologies such as optical conherence tomography and confocal fluorescence endomicroscopy allows imaging of the gastrointestinal (GI) system with high controlability. A MEMS scanning micro-mirror is an outstanding candidate technology for such an application. With active focus tracking capability, it allows high-resolution 3-D imaging to be achieved with the endoscope system, which can significantly improve our currently limited ability for detecting early and pre-cancers.