Hyeonggon Kang

Quantitative Characterization of Quantum Dot-Labeled Lambda Phage for Escherichia coli Detection

We characterize CdSe/ZnS quantum dot (QD) binding to genetically modified bacteriophage as a model for bacterial detection. Interactions among QDs, lambda (λ) phage, and Escherichia coli are examined by several cross‐validated methods. Flow and image‐based cytometry clarify fluorescent labeling of bacteria, with image‐based cytometry additionally reporting the number of decorated phage bound to cells. Transmission electron microscopy, image‐based cytometry, and electrospray differential mobility analysis allow quantization of QDs attached to each phage (4–17 QDs) and show that λ phage used in this study exhibits enhanced QD binding to the capsid by nearly a factor of four compared to bacteriophage T7. Additionally, the characterization methodology presented can be applied to the quantitative characterization of other fluorescent nanocrystal‐biological conjugates. Biotechnol. Bioeng. 2009;104: 1059–1067. Published 2009 Wiley Periodicals, Inc.

Water-soluble DNA-wrapped single-walled carbon-nanotube/quantum-dot complexes.

In recent years, carbon nanotubes (CNTs), especially singlewalled carbon nanotubes (SWCNTs), have attracted much attention due to their unique properties and potential towards broad real-world applications. The integration of SWCNTs with other unique nanoscale luminescent materials, such as quantum dots (QDs), has enabled the manufacture of many novel nanocomposite materials with enhanced structural, mechanical, optical, and chemical properties. The performance of these composite materials strongly depends upon the properties of the individual components and additives as well as the conjugation chemistry required to assemble them into composite hybrids. Therefore, a variety of new techniques have been developed to modify the optical, mechanical, chemical, and electrical properties of SWCNTs to control the properties of the final composite materials. Among the additives to SWCNT-based composites, novel nanoparticles (NPs) have been increasingly employed. Functionalized NPs can be designed to covalently bind to the functional groups expressed on the sidewalls or ends of

Nanoparticle size determination using optical microscopes

We present a simple method for size determination of nanoparticles using conventional optical microscopes. The method, called through-focus scanning optical microscopy, makes use of the four-dimensional optical information collected at different focus positions. Low partial coherence illumination combined with analysis of through-focus optical content enables nanoparticle size determination with nanometer scale sensitivity. We experimentally demonstrate this using fabricated Si nanodots and spherical gold nanoparticles. The method is economical, as no hardware modifications to conventional optical microscopes are needed. In addition, the method also has high throughput and potential for soft nanoparticle size determination without distortion.

Multimodal, nanoscale, hyperspectral imaging demonstrated on heterostructures of quantum dots and DNA-wrapped single-wall carbon nanotubes.

A multimodality imaging technique integrating atomic force, polarized Raman, and fluorescence lifetime microscopies, together with 2D autocorrelation image analysis is applied to the study of a mesoscopic heterostructure of nanoscale materials. This approach enables simultaneous measurement of fluorescence emission and Raman shifts from a quantum dot (QD)-single-wall carbon nanotube (SWCNT) complex. Nanoscale physical and optoelectronic characteristics are observed including local QD concentrations, orientation-dependent polarization anisotropy of the SWCNT Raman intensities, and charge transfer from photoexcited QDs to covalently conjugated SWCNTs. Our measurement approach bridges the properties observed in bulk and single nanotube studies. This methodology provides fundamental understanding of the charge and energy transfer between nanoscale materials in an assembly.

A method to determine the number of nanoparticles in a cluster using conventional optical microscopes

We present a method that uses conventional optical microscopes to determine the number of nanoparticles in a cluster, which is typically not possible using traditional image-based optical methods due to the diffraction limit. The method, called through-focus scanning optical microscopy (TSOM), uses a series of optical images taken at varying focus levels to achieve this. The optical images cannot directly resolve the individual nanoparticles, but contain information related to the number of particles. The TSOM method makes use of this information to determine the number of nanoparticles in a cluster. Initial good agreement between the simulations and the measurements is also presented. The TSOM method can be applied to fluorescent and non-fluorescent as well as metallic and non-metallic nano-scale materials, including soft materials, making it attractive for tag-less, high-speed, optical analysis of nanoparticles down to 45 nm diameter.

Fluorescence intermittency and spectral shifts of single bio-conjugated nanocrystals studied by single molecule confocal fluorescence microscopy and spectroscopy

We have fabricated a combined measurement system capable of confocal microscopy and fluorescence spectroscopy to simultaneously evaluate multiple optical characteristics of single fluorescent nanocrystals. The single particle detection sensitivity is demonstrated by simultaneously measuring the dynamic excitation-time-dependent fluorescence intermittency and the emission spectrum of single cadmium selenide/zinc sulfide (CdSe/ZnS) nanocrystals (quantum dots, QDs). Using this system, we are currently investigating the optical characteristics of single QDs, the surface of which are conjugated with different ligands, such as trioctylphosphine oxide (TOPO), mercaptoundecanoicacid (MDA), and amine modified DNA (AMDNA). In this paper, we present the progress of our measurements of the time-dependent optical characteristics (fluorescence intermittency, photostability, and spectral diffusion) of single MDA-QDs and AMDNA-MDA-QDs in air in an effort to understand the effects of surface-conjugated biomolecules on the optical characteristics at single QD sensitivities.

Real-time fluorescence polarization microscopy for probing local distributions of biomolecules

We present real-time, full-field, fluorescence polarization microscopy and its calibration and validation methods to monitor the absorption dipole orientation of fluorescent molecules. A quarter-wave plate, in combination with a liquid crystal variable retarder (LCVR), provides a tunable method to rotate a linear polarized light prior to being coupled into a fluorescence microscope. A series of full-field fluorescence polarization images are obtained of fluorescent molecules interleaved into the lipid bilyaer of liposomes. With this system, the dynamic dipole orientation of the fluorescent lipid analog tetramethylindocarbocyanine (DiI)-labeled lipids inserted in liposomes are probed and found to be aligned with the liposome in a tangential manner. The dipole orientation of 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY)- labeled lipids are expected to be aligned perpendicularly in the liposome membrane. Spectral separation of fluorescent lipid analogs into separate images provide an internal control and the ability to quantitatively correlate the membrane structure and fluctuations, within an optical section, in real-time. Application of this technique to the identification of characteristic features of cellular processes such as adhesion, endocytosis, and apoptosis are being investigated.

Thermal properties of gold nanoshells in lipid vesicles studied by single particle tracking measurements

Photothermal therapy employing nanomaterials is a promising approach to selectively treat targeted tissues with abnormal characteristics such as tumors. While vital research has focused on the use of these materials in biomedical applications, net effects of these materials in biological environments are still not well understood. For reliable biomedical applications, it is crucial to quantitatively evaluate thermal properties of these materials in biological and physiological environments. To this end, we have developed a highly integrated measurement platform and examined local thermal properties of single gold shell nanocrystals in biomimetic environments. These nanoshells consist of a silica core with an outer gold coating. For quantitative measurement of the local thermal profile of gold nanoshells, we monitor lipid phase transitions triggered by gold nanoshell thermal excitation. Dried lipid layers with adsorbed gold nanoshells were placed in an aqueous environment. Photothermal excitation of the gold nanoshells induced localized liposome budding as the lipids were raised above their transition temperature. Single particle tracking of gold nanoshells in solution and within liposomes revealed larger diffusion rates for the confined nanoparticles, likely due to a raised local temperature.