Research Three-dimensionally confined nanoparticles that harvest strong near-field interaction with light, such as colloidal quantum dots (QD) and Au nanoparticles (NP), have opened new directions in nanophotonic devices and integration, as well as applications in biomedicine such as cancer cell ablation, drug delivery, and bio-manipulation. Since its inception in January 2004, the UWEE Photonics Laboratory has ventured into the general directions of nanophotonics and biophotonics by "bridging nanoparticles with light." Utilizing the unique optoelectronic properties and surface chemistries of colloidal QDs, we have proposed QD nanophotonic integrated circuits using molecular self-assembly fabrication. The published work along this direction includes sub-diffraction QD waveguide and nanoscale QD photodetector with high sensitivity and spatial resolution. Utilizing localized surface plasmon resonance in the Au NPs, we have proposed a new plasmonic tweezers for bio-manipulation and nano-fabrication. The platform allows versatile applications, and we have demonstrated (1) high-efficiency optical manipulation of micro/nano-particles and biological cells, (2) long-range trapping of nanowires with very low optical intensity, (3) laser-controlled micro-concentrator, micro-sorter, and micro-mixer for opto-fluidics. In addition, we have also been working on new dielectrophoresis-field flow fractionation devices for DNA separation. Quantum Dot Integrated Circuit Schematic drawing of the sub-diffraction limit quantum dot integrated circuit. Quantum Dot Waveguides To create nano-scale waveguides and find an alternate means of sub-diffraction limit optical propagation, quantum dots are a potential route to success due to their high degree of quantum confinement and respective size. In particular, our group investigates QD behavior under optical stimulation in terms of absorption, emission and corresponding linear gain characteristics. A gain model for CW and pulse pumped QDs has been derived and applied to core and core/shell structures such as CdSe and CdSe/ZnS over a range of pump powers. Furthermore, the optical propagation for a 1D array of quantum dots forming a waveguide has been simulated and reveals a compensating relation between gain and coupling coefficient. In addition, work has been done to determine the field distribution between quantum dots and we have demonstrated fabrication through DNA-based and two-layer self-assembly methods. Testing of the waveguides show increasing signal out with raised pump light indicative of gain. ** Recent work may be found in our Nano Letters paper and the highlight. ** Quantum dot array nanophotonic waveguide. Poynting vector distribution of the quantum-dot waveguide. Fluorescence and atomic force micrographs of 500 nm two-layer self-assembled QD waveguides in (i) single and pair formations spaced (ii) 200 nm and (iii) 500 nm apart. Scale bar is 1 um in length. Corresponding 100 nm wide waveguide images. Quantum Dot Transistors Current research is focused on using photonic integrated circuits to solve the high-density problem, and proposing a model for a nano-scale QD phototransistor that may easily interface to a self-assembled QD integrated circuit . This optical transistor can be fabricated via DNA self-assembly using QDs and consists of a series of QDs placed between two metal electrodes. The tunneling current between the metal electrodes is mediated by the QDs and can be modulated by optically pumping the QDs at different intensities. The construction of this device requires nano-scale positioning of semiconducting QDs on a substrate and can be achieved using DNA-directed self-assembly. Quantum dot transistor. Opto-Plasmonic Tweezers Non-invasive manipulation of single micro- and nano-sized particles is an important tool for basic biological research. It allows cells, cellular components, and synthetic marker particles treated with biochemical tags to be collected, separated, concentrated, and transported without damage to the objects themselves. Among various non-invasive manipulation mechanisms, a particularly desirable one is the ability to control the orientation of the biological cells, in addition to trapping and moving them. Such capability opens the door to building structured biomaterials for potential applications in constructing biofilms and human tissue engineering. In the past, electro-rotation by dielectrophoresis has been the most widely employed method for such purpose. Such approach often requires micro-fabrication for the fixed electrodes, the manipulation area is constrained, and the resolution of rotation is limited. In this proposal, we propose a new approach for optical manipulation and rotation of micro- and nano-biological particles that utilizes polarization of light and surface plasmon excitation. In addition to flexible manipulation by scanning of the optical beam, the proposed approach is expected to achieve fine orientation control and low optical-intensity requirement compared to conventional optical tweezers. Opto-Plasmonic Tweezers. Gold coated microsphere assembly and scattering spectra necessary for plasmon effect. Particle captured by opto-plasmonic tweezers.