Kyung Min Byun

Graphene-on-silver substrates for sensitive surface plasmon resonance imaging biosensors

Taking advantage of the high impermeability property of graphene and the sharp surface plasmon resonance (SPR) curve of silver, we numerically demonstrate that SPR imaging biosensors with a graphene-on-silver substrate can be used to achieve the dramatically high sensitivity as well as to prevent silver oxidation. Results of our numerical study show that a silver substrate with a few graphene layers can significantly increase the imaging sensitivity, compared to the conventional gold-film-based SPR imaging biosensor. In particular, single layered graphene deposited on the 60-nm thick silver film amplifies the SPR imaging signal more than three times. Therefore, the proposed SPR substrate could potentially open a new possibility of SPR imaging detection for sensitive and high-throughput assessment of multiple biomolecular interactions.

Experimental study of sensitivity enhancement in surface plasmon resonance biosensors by use of periodic metallic nanowires

We have experimentally confirmed sensitivity enhancement of a nanowire-based surface plasmon resonance (SPR) sensor structure. Gold nanowires with periods of 200 and 500 nm were fabricated, respectively, by electron-beam and interference lithography on a gold/SF10 substrate. Sensitivity enhancement was measured to be 44% compared with a conventional thin-film-based SPR structure for nanowires of 200 nm period and 31% for 500 nm when evaluated using ethanol at a varied concentration. This result is consistent with numerical data. Surface roughness is responsible for sensitivity reduction by more than 10%. More significant sensitivity improvement can be achieved by inducing strong localized plasmon coupling with finer nanowires.

Design study of highly sensitive nanowire-enhanced surface plasmon resonance biosensors using rigorous coupled wave analysis.

In this study, we investigated the sensitivity enhancement in nanowire-based surface plasmon resonance (SPR) biosensors using rigorous coupled wave analysis (RCWA). The enhancement, enabled by the excitation of localized surface plasmons in gold nanowires, offers improved performance in sensitivity as well as in reproducibility and customizability. Calculation results found that a T-profile provides higher sensitivity than an inverse T-profile in general and also determined optimum design parameters. Our study on a nanowire-enhanced SPR biosensor demonstrates the potential for significant improvement in the sensitivity through the nanowire-mediated localized SPR.

Enhanced NIR radiation-triggered hyperthermia by mitochondrial targeting.

Mitochondria are organelles that are readily susceptible to temperature elevation. We selectively delivered a coumarin-based fluorescent iron oxide nanoparticle, Mito-CIO, to the mitochondria. Upon 740 nm laser irradiation, the intracellular temperature of HeLa cells was elevated by 2.1 °C within 5 min when using Mito-CIO, and the treatment resulted in better hyperthermia and a more elevated cytotoxicity than HeLa cells treated with coumarin iron oxide (CIO), which was missing the mitochondrial targeting unit. We further confirmed these results in a tumor xenograft mouse model. To our knowledge, this is the first report of a near-infrared laser irradiation-induced hyperthermic particle targeted to mitochondria, enhancing the cytotoxicity in cancer cells. Our present work therefore may open a new direction in the development of photothermal therapeutics.

Grating-coupled transmission-type surface plasmon resonance sensors based on dielectric and metallic gratings

We investigated grating-coupled transmission-type surface plasmon resonance (SPR) for sensing applications. In the transmission-type SPR structure, propagating surface plasmons are outcoupled to radiation modes by dielectric and metallic gratings on a metal film. The results calculated in air and water suggest that the proposed structures present extremely linear sensing characteristics. In terms of a figure of merit, a metallic grating-based structure performs 5.4 and 3.7 times better than that of a dielectric grating in air and water, respectively.

Design for a Simplified Cochlear Implant System

A simplified cochlear implant (CI) system would be appropriate for widespread use in developing countries. Here, we describe a CI that we have designed to realize such a concept. The system implements 8 channels of processing and stimulation using the continuous interleaved sampling (CIS) strategy. A generic digital signal processing (DSP) chip is used for the processing, and the filtering functions are performed with a fast Fourier transform (FFT) of a microphone or other input. Data derived from the processing are transmitted through an inductive link using pulse width modulation (PWM) encoding and amplitude shift keying (ASK) modulation. The same link is used in the reverse direction for backward telemetry of electrode and system information. A custom receiver-stimulator chip has been developed that demodulates incoming data using pulse counting and produces charge balanced biphasic pulses at 1000 pulses/s/electrode. This chip is encased in a titanium package that is hermetically sealed using a simple but effective method. A low cost metal-silicon hybrid mold has been developed for fabricating an intracochlear electrode array with 16 ball-shaped stimulating contacts

Localized surface plasmon resonance detection of layered biointeractions on metallic subwavelength nanogratings

Enhanced detection of multiple targets such as self-assembled monolayer (SAM) formation, DNA hybridization, and ethanol ambient changes was explored using localized surface plasmon resonance (LSPR) excited by metallic surface nanogratings. The sensitivity enhancement depends on the target as well as the nanostructure with a maximum at 242% over a conventional structure when detecting an 11-mercaptoundecanoic acid SAM with an LSPR structure of 200 nm period. The measured enhancement shows smaller target-dependent variance when detecting various layered biointeractions, while structure-dependent variance was much larger. The result suggests the feasibility of the efficient detection of multiple biointeractions at enhanced sensitivity and extends the applicability of a nanostructured LSPR biosensor for diverse biomolecular events.

Sensitivity Enhancement of Surface Plasmon Resonance Imaging Using Periodic Metallic Nanowires

A nanowire-mediated surface plasmon resonance (SPR) imaging is numerically investigated for enhanced sensitivity. The results calculated by rigorous coupled-wave analysis present that interplays between localized surface plasmons and surface plasmon polaritons contribute to sensitivity enhancement. Compared to conventional thin film-based SPR imaging measurement, an optimal nanowire structure can provide sensitivity enhancement by 3.44 times as well as highly linear detection property for quantification of surface reactions of interests. This paper demonstrates the potential and limitation for a highly sensitive, label-free, and real-time SPR imaging sensor based on periodic metallic nanowires.

Enhanced infrared neural stimulation using localized surface plasmon resonance of gold nanorods.

An advanced optical activation of neural tissues is demonstrated using pulsed infrared light and plasmonic gold nanorods. Photothermal effect localized in plasma membrane triggers action potentials of in vivo neural tissues. Compared with conventional infrared stimulation, the suggested method can increase a neural responsivity and lower a threshold stimulation level significantly, thereby reducing a requisite radiant exposure and the concern of tissue damage.

Investigation on an application of silver substrates for sensitive surface plasmon resonance imaging detection

A surface plasmon resonance (SPR) imaging biosensor based on silver substrates was investigated to demonstrate that silver could be used as a substrate material for sensitive detection of biomolecular interactions, despite its poor chemical stability. The calculation results showed that oxidation of silver film may lead to a decrease in the sensitivity due to a variation in SPR characteristics such as a broader curve width and shallower minimum reflectance at resonance. The effect of a change in the refractive index of target analytes on the sensitivity was also explored. In particular, it is noteworthy that Ag/Au bimetallic substrates with a thin gold protection layer to prevent oxidation of a silver film can provide a significant amplification of SPR imaging signals in comparison with conventional gold substrates.