Quantum dot plasmon coupling : Fundamental study and applications

The dissertation focuses on the engineering of light-matter interaction using plasmonic nanoparticles and metamaterials to achieve enhanced luminescence and based on which to improve the performance of biosensing and light-emitting technologies. We designed and fabricated a spectrum of nanostructures to exhibit particular dispersion relations capable of controlling the spontaneous emission properties of quantum emitters, such as quantum dots and organic fluorophores. To realize the concept, we developed a metal-assisted focused-ion beam nanopatterning technology to fabricate the plasmonic nanostructures with high-definition. We demonstrated a silver open-ring nanoarrays (ORA) for broadband enhancement of QD emission that was further exploited to demonstrate ultrasensitive DNA sensing. The ORA design offers multiple resonance peaks to support both Purcell effect and excitation enhancement, resulting in a maximal enhancement in QD emission of greater than 100 times and significant improvement in the limit-of-detection of DNA sensing by four orders of magnitude. Another plasmonic nanostructure, aluminum dimple array, was developed to take advantage of the inherent UV plasmonic property of aluminum for broadband enhancement of QD emission. The device may find major applications in optoelectronic devices. While the small-area plasmonic devices are suitable to enhance the fluorescence-based sensors on a chip, there exists a need for large-area enhancement for several applications. For this purpose, we developed multilayered hyperbolic metamaterials accompanied with an efficient light-extraction approach to achieve enhanced quantum dot emission over a large area. Lastly, we expanded the enhancement strategy using plasmonic nanoparticles to improve carbon dot-based microLEDs. The embedded plasmonic nanoparticles were utilized to enhance carbon dot emission while minimizing the UV excitation leak–age. This research provides a set of design rules for enhanced spontaneous emission and the demonstrated applications are expected to pave the way to advanced photonic, biosensing, and optoelectronic devices

Quasi-Optical Terahertz Microfluidic Devices for Chemical Sensing and Imaging

We first review the development of a frequency domain quasi-optical terahertz (THz) chemical sensing and imaging platform consisting of a quartz-based microfluidic subsystem in our previous work. We then report the application of this platform to sensing and characterizing of several selected liquid chemical samples from 570–630 GHz. THz sensing of chemical mixtures including isopropylalcohol-water (IPA-H₂O) mixtures and acetonitrile-water (ACN-H₂O) mixtures have been successfully demonstrated and the results have shown completely different hydrogen bond dynamics detected in different mixture systems. In addition, the developed platform has been applied to study molecule diffusion at the interface between adjacent liquids in the multi-stream laminar flow inside the microfluidic subsystem. The reported THz microfluidic platform promises real-time and label-free chemical/biological sensing and imaging with extremely broad bandwidth, high spectral resolution, and high spatial resolution.Keywords: laminar flow, terahertz, chemical sensing and imaging, molecule diffusion, frequency domain, microfluidic, quasi-optical, label fre

Molecular Packing-Dependent Exciton and Polari on Dynamics in Anthradithiophene Organic Crystals

Polarization-dependent absorption spectra of two functionalized derivatives of fluorinated anthradithiophene, diF TES-ADT and diF TDMS-ADT, were studied in the crystal phase using a Holstein-like Hamiltonian. For both molecules, the primary contribution to the lowest energy absorption was found to be the S-0-S-1 excitonic transition perturbed by an intermolecular coupling of 15 meV for both TES and TDMS. A secondary contribution, consistent with that from charge-transfer states, was also found. Additionally, absorption spectra were analysed when crystals were placed inside of optical microcavities formed by two metal mirrors. Cavities exhibited a primary absorption peak determined to be an enhanced absorption from the lowest-energy S-0-S-1 transition

Quantum Dot Fullerene-Based Molecular Beacon Nanosensors for Rapid, Highly Sensitive Nucleic Acid Detection

Spherical fullerene (C₆₀) can quench the fluorescence of a quantum dot (QD) through energy-transfer and charge-transfer processes, with the quenching efficiency regulated by the number of proximate C₆₀ on each QD. With the quenching property and its small size compared with other nanoparticle-based quenchers, it is advantageous to group a QD reporter and multiple C₆₀-labeled oligonucleotide probes to construct a molecular beacon (MB) probe for sensitive, robust nucleic acid detection. We demonstrated a rapid, high-sensitivity DNA detection method using the nanosensors composed of QD–C₆₀-based MBs carried by magnetic nanoparticles. The assay was accelerated by first dispersing the nanosensors in analytes for highly efficient DNA capture resulting from short-distance three-dimensional diffusion of targets to the sensor surface and then concentrating the nanosensors to a substrate by magnetic force to amplify the fluorescence signal for target quantification. The enhanced mass transport enabled a rapid detection (<10 min) with a small sample volume (1–10 μL). The high signal-to-noise ratio produced by the QD–C₆₀ pairs and magnetic concentration yielded a detection limit of 100 fM (∼10⁶ target DNA copies for a 10 μL analyte). The rapid, sensitive, label-free detection method will benefit the applications in point-of-care molecular diagnostic technologies

Plasmonic Open-Ring Nanoarrays for Broadband Fluorescence Enhancement and Ultrasensitive DNA Detection

Fluorescence enhancement and quenching can be switched by regulating the separation distance between a fluorophore and a metal surface in the near field. The switchable luminescence provides a suitable scheme for fluorescence-based biosensing, in which the configuration of fluorescently labeled molecular probes is altered in response to molecular binding which, therefore, varies the fluorophore emission. We demonstrate the use of a unique metal nanostructure composed of open-ring nanoarrays (ORAs) engraved on silver to boost the sensing performance by magnifying both fluorescence intensity and quenching efficiency of the probes. The ORA supports multiple surface plasmon resonance peaks that overlap both absorption and emission spectra of most fluorophores or quantum dots (QDs) in the visible range. The broad spectral overlaps enable strong broadband fluorescence enhancement by enhancing both emission and excitation rates, which were experimentally and theoretically analyzed using multicolor QDs and variable excitation wavelengths. ORAs also promote fluorescence quenching when the fluorophores are brought within a few nanometers of its surface, due to efficient energy transfer. The combination of strong fluorescence enhancement and quenching amplifies the signal-to-noise ratio required for sensitive DNA detection. The sensor was integrated with a microfluidic channel to handle a low sample volume of ∼1.2 μL and yielded a detection limit of ∼300 fM concentration (equivalent to subattomoles), superior to that of the conventional sensor built on plane silver surfaces

Quasi-Optical Terahertz Microfluidic Devices for Chemical Sensing and Imaging

We first review the development of a frequency domain quasi-optical terahertz (THz) chemical sensing and imaging platform consisting of a quartz-based microfluidic subsystem in our previous work. We then report the application of this platform to sensing and characterizing of several selected liquid chemical samples from 570–630 GHz. THz sensing of chemical mixtures including isopropylalcohol-water (IPA-H2O) mixtures and acetonitrile-water (ACN-H2O) mixtures have been successfully demonstrated and the results have shown completely different hydrogen bond dynamics detected in different mixture systems. In addition, the developed platform has been applied to study molecule diffusion at the interface between adjacent liquids in the multi-stream laminar flow inside the microfluidic subsystem. The reported THz microfluidic platform promises real-time and label-free chemical/biological sensing and imaging with extremely broad bandwidth, high spectral resolution, and high spatial resolution