Ms. Suehyun K. Cho Profile

Suehyun K. Cho

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Proceedings Article | 15 March 2018 Presentation

Multifunctional nanocluster composed of gold nanorod and upconversion nanoparticle for simultaneous imaging and treatment (Conference Presentation)

Suehyun Cho, Lih-Jen Su, Thomas Flaig, Wounjhang Park

Proceedings Volume 10509, 1050909 (2018) https://doi.org/10.1117/12.2290371

KEYWORDS: Upconversion, Bladder cancer, Gold, Nanorods, Nanoparticles, Surface plasmons, Photons, Receptors, Luminescence, Confocal microscopy

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Upconverting nanophosphors (UCNPs) absorb two or more photons at 980nm and emit a higher energy photon in the visible range. UCNPs provide distinct advantages as biological imaging agents in that they have no autofluorescence, don’t photobleach, are capable of deep tissue imaging, exhibit no blinking, and are physically robust. Through surface modifications with an amphiphilic polymer, we can not only functionalize UCNPs for targeted imaging, but also tether them to plasmonic nanoparticles such as gold nanorods (AuNRs) for enhanced upconversion and multifunctionality. We developed a process to construct UCNP-AuNR nanoclusters using polyethylene glycol. The UCNP-AuNR nanocluster is further modified with an anti-epidermal growth factor receptor (aEGFR), allowing specific binding to bladder cancer cells that highly express epidermal growth factor receptor. Once the nanoclusters bind to the cell membrane we can (1) perform targeted and high contrast imaging of the bladder cancer cells and (2) utilize localized surface plasmon of AuNRs to selectively kill the cells in situ upon detection by UCNP fluorescence. Successful conjugation and integrity of the UCNP-AuNR nanoclusters were confirmed via electron microscopy. Then, through a combination of brighftield, confocal upconversion fluorescence, and infrared darkfield microscopy we demonstrate selective binding and high-contrast upconversion imaging of the bladder cancer cells. Finally, through a series of in vitro studies, we demonstrate two different methods of cell killing. First, with a continuous wave laser, we demonstrate effective thermal ablation of cells. Second, with a femtosecond pulse laser, we demonstrate optoporation of the cell membrane that allows increased uptake of drugs.

Proceedings Article | 19 April 2017 Presentation

Design and fabrication of high-Q chalcogenide glass micro-disk resonators (Conference Presentation)

Gumin Kang, Suehyun Cho, Molly Krogstad, Juliet Gopinath, Won Park

Proceedings Volume 10106, 1010609 (2017) https://doi.org/10.1117/12.2252509

KEYWORDS: Photoresist materials, Optical components, Resonators, Photonics, Infrared radiation, Chalcogenide glass, Edge roughness, Silica, Infrared materials, Optical lithography

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Chalcogenide glass (ChG) which contain one or more chalcogen elements is one of the most interesting material for infrared (IR) photonics owing to its unique optical properties, such as high refractive index, strong optical nonlinearity, and wide infrared transparency. In this paper, we experimentally demonstrate high-quality ChG micro-disk resonators on oxidized silicon wafers fabricated by the standard UV photolithography and lift-off. Quality factor of micro-disk resonators are often limited by optical scattering loss induced by lithographically defined edge roughness. Thermal reflow of chalcogenide itself may significantly reduce edge roughness, but thermal shrinkage and deformation of the material during the reflow make it hard to precisely control the overall size and shape of the fabricated device. Instead, we reduce the sidewall roughness using thermal reflow of photoresist and modified bi-layer lift-off process. Typically, the thermal reflow of resist destroys the undercut or vertical sidewall profile of developed resist layer, making it extremely difficult or impossible to subsequently use lift-off or etching for patterning. We address this issue by first wet etching the silica substrate to undercut the reflowed photoresist, creating an overhang required for lift-off. ChG film is then deposited to produce a micro-disk resonator with much improved edge roughness. To finally create a micro-disk resonator on a silica pillar, we adopt vapor etching of the silica substrate. With optimized conditions of reflow and undercut, we obtained high quality ChG disk-resonators with extremely smooth edge profile, operating in the infrared region. Complete characterization results will be presented at the conference. The new method is compatible with traditional CMOS process and thus expected to have great potentials for fabricating high quality photonic integrated devices.

Proceedings Article | 3 November 2016 Presentation

Gold nanorods coupled with upconverting nanophosphors for targeted thermal ablation and imaging of bladder cancer cells (Conference Presentation)

Suehyun Cho, Lih-Jen Su, Thomas Flaig, Wounjhang Park

Proceedings Volume 9930, 99300H (2016) https://doi.org/10.1117/12.2238365

KEYWORDS: Bladder cancer, Luminescence, Near infrared, Gold, Upconversion, Photons, Confocal microscopy, Nanoparticles, Energy transfer, Nanorods

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NaYF4:Yb3+,Er3+ upconverting nanophosphors (UCNPs) are robust and stable nanoparticles that absorb near-infrared (NIR) photons and emit green and red visible photons through energy transfer upconversion. This mechanism provides UCNPs several advantages as a bioimaging agent over traditional fluorescence imaging agent in that NIR excitation allows high-contrast imaging without autofluorescence and that they can be used for deep-tissue imaging. However, additional surface modification of UCNPs is necessary for them to be biocompatible. We use an amphiphilic polymer (poly(maleic anhydride-alt-octadecene) (PMAO) and a hetero-functional polyethylene glycol with amine and thiol ends (NH2-PEG-SH)) to make the UCNPs water-soluble. This reaction yields a carboxylic group that allows functionalization with anti-epidermal growth factor receptor (aEGFR), which provides specific binding of UCNPs to EGFR-expressing bladder cancer cells. Additionally, the thiol ends of the PEGylated UCNPs are able to bind with gold nanorods (AuNRs) to create UCNP-AuNR complexes. The localized surface plasmon of the AuNR then allow localized heating of HTB9 bladder cancer cells, enabling in situ cell killing upon detection by UCNP fluorescence. Here, we report a successful synthesis, surface modification and conjugation of aEGFR functionalized UCNP-AuNR complexes and in vitro imaging and thermal ablation studies using them. Synthesis and surface modification of UCNP-AuNR complexes are confirmed by electron microscopy. Then, a combination of brightfield, NIR confocal fluorescence, and darkfield microscopy on the UCNP-AuNR treated bladder cancer cells revealed successful cancer targeting and imaging capabilities of the complex. Finally, cell viability assay showed that NIR irradiation of UCNP-AuNR conjugated cells resulted highly selective cell killing.

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