Yeonho Choi

Nanowire-based single-cell endoscopy

One-dimensional smart probes based on nanowires and nanotubes that can safely penetrate the plasma membrane and enter biological cells are potentially useful in high-resolution and high-throughput gene and drug delivery, biosensing and single-cell electrophysiology. However, using such probes for optical communication across the cellular membrane at the subwavelength level remains limited. Here, we show that a nanowire waveguide attached to the tapered tip of an optical fibre can guide visible light into intracellular compartments of a living mammalian cell, and can also detect optical signals from subcellular regions with high spatial resolution. Furthermore, we show that through light-activated mechanisms the endoscope can deliver payloads into cells with spatial and temporal specificity. Moreover, insertion of the endoscope into cells and illumination of the guided laser did not induce any significant toxicity in the cells.

Quantized plasmon quenching dips nanospectroscopy via plasmon resonance energy transfer

We observed quantized plasmon quenching dips in resonant Rayleigh scattering spectra by plasmon resonance energy transfer (PRET) from a single nanoplasmonic particle to adsorbed biomolecules. This label-free biomolecular absorption nanospectroscopic method has ultrahigh molecular sensitivity.

Selective and sensitive detection of metal ions by plasmonic resonance energy transfer-based nanospectroscopy

Highly selective and sensitive optical methods for the detection of metal ions have had a substantial impact on molecular biology, environmental monitoring and other areas of research. Here we demonstrate a new method for detecting metal ions that is based on selective plasmonic resonance energy transfer (PRET) between conjugated metal-ligand complexes and a single gold nanoplasmonic probe. In addition to offering high spatial resolution due to the small size of the probe, our method is 100 to 1,000 times more sensitive than organic reporter-based methods. Moreover, it can achieve high selectivity owing to the selective formation of Cu(2+) complexes and selective resonant quenching of the gold nanoplasmonic probe by the conjugated complexes. We expect that PRET-based metal ion sensing could have applications in cellular imaging, systems biology and environmental monitoring.

Self‐Organized Hexagonal‐Nanopore SERS Array

were applied for precisionnanopatterning with the advantage of high resolution withouttheneedforaphysicalmask,sincethepatterncanbechangedatany time by using computer-aided design (CAD) software.However, the disadvantages of these two methods are the longexposure time due to pixel-by-pixel scanning steps, high cost,and substantial maintenance. To overcome these limitations,phase-shift lithography,

NANOSECOND LASER ABLATION OF GOLD NANOPARTICLE FILMS

Ablation of self-assembled monolayer protected gold nanoparticle films on polyimide was explored using a nanosecond laser. When the nanoparticle film was ablated and subsequently thermally sintered to a continuous film, the elevated rim structure by the expulsion of molten pool could be avoided and the ablation threshold fluence was reduced to a value at least ten times lower than the reported threshold for the gold film. This could be explained by the unusual properties of nanoparticle film such as low melting temperature, weak bonding between nanoparticles, efficient laser energy deposition, and reduced heat loss. Finally, submicron lines were demonstrated.

Plasmonic Nanosensors: Review and Prospect

Recent progress in plasmon-based sensors has greatly overcome the limitations of conventional optical sensors, in terms of sensitivity, tunability, photostability, and in vivo applicability, by employing nanostructured materials. In this review, we summarize three types of plasmon-based nanosensors categorized by the geometries of sensing platforms as plasmonic transducers, which are planar nanofilm, periodic nanoarrays, and individual nanoparticles, respectively. We then introduce the notable accomplishments to enhance the sensing performances for each sensing platform. Additionally, we present recent works for signal enhancement strategy based on the targeted nanoassemblies of particles, which can be applied to all plasmon-based sensing platforms. The focus of this review will be on how plasmonic nanostructures can be applied to detect biological and chemical analytes, and notable approaches to improve the sensitivity.

Shadow Overlap Ion-beam Lithography for Nanoarchitectures

Precisely constructed nanoscale devices and nanoarchitectures with high spatial resolution are critically needed for applications in high-speed electronics, high-density memory, efficient solar cells, optoelectronics, plasmonics, optical antennas, chemical sensors, biological sensors, and nanospectroscopic imaging. Current methods of classical optical lithography are limited by the diffraction effect of light for nanolithography, and the state of art of e-beam or focused ion beam lithography limit the throughput and further reduction less than few nanometers for large-area batch fabrication. However, these limits can be surpassed surprisingly by utilizing the overlap of two shadow images. Here we present shadow overlap of ion-beam lithography (SOIL), which can combine the advantages of parallel processing, tunable capability of geometries, cost-effective method, and high spatial resolution nanofabrication technique. The SOIL method relies on the overlap of shadows created by the directional metal deposition and etching angles on prepatterned structures. Consequently, highly tunable patterns can be obtained. As examples, unprecedented nanoarchitectures for optical antennas are demonstrated by SOIL. We expect that SOIL can have a significant impact not only on nanoscale devices, but also large-scale (i.e., micro and macro) three-dimensional innovative lithography.

Graphene Nanopore with a Self-Integrated Optical Antenna

We report graphene nanopores with integrated optical antennae. We demonstrate that a nanometer-sized heated spot created by photon-to-heat conversion of a gold nanorod resting on a graphene membrane forms a nanoscale pore with a self-integrated optical antenna in a single step. The distinct plasmonic traits of metal nanoparticles, which have a unique capability to concentrate light into nanoscale regions, yield the significant advantage of parallel nanopore fabrication compared to the conventional sequential process using an electron beam. Tunability of both the nanopore dimensions and the optical characteristics of plasmonic nanoantennae are further achieved. Finally, the key optical function of our self-integrated optical antenna on the vicinity of graphene nanopore is manifested by multifold fluorescent signal enhancement during DNA translocation.

Self-Assembled Three-Dimensional Nanocrown Array

Although an ordered nanoplasmonic probe array will have a huge impact on light harvesting, selective frequency response (i.e., nanoantenna), and quantitative molecular/cellular imaging, the realization of such an array is still limited by conventional techniques due to the serial processing or resolution limit by light diffraction. Here, we demonstrate a thermodynamically driven, self-assembled three-dimensional nanocrown array that consists of a core and six satellite gold nanoparticles (GNPs). Our ordered nanoprobe array is fabricated over a large area by thermal dewetting of thin gold film on hexagonally ordered porous anodic alumina (PAA). During thermal dewetting, the structural order of the PAA template dictates the periodic arrangement of gold nanoparticles, rendering the array of gold nanocrown. Because of its tunable size (i.e., 50 nm core and 20 nm satellite GNPs), arrangement, and periodicity, the nanocrown array shows multiple optical resonance frequencies at visible wavelengths as well as angle-dependent optical properties.

Three-Dimensional Reduced-Symmetry of Colloidal Plasmonic Nanoparticles

Owing to their novel optical properties, three-dimensional plasmonic nanostructures with reduced symmetry such as a nanocrescent and a nanocup have attracted considerable current interest in biophotonic imaging and sensing. However, their practical applications have been still limited since the colloidal synthesis of such structures that allows, in principle, for in vivo application and large-scale production has not been explored yet. To date, these structures have been fabricated only on two-dimensional substrates using micro/nanofabrication techniques. Here we demonstrate an innovative way of breaking symmetry of colloidal plasmonic nanoparticles. Our strategy exploits the direct overgrowth of Au on a hybrid colloidal dimer consisting of Au and polystyrene (PS) nanoparticles without the self-nucleation of Au in an aqueous solution. Upon the overgrowth reaction, the steric crowding of PS leads to morphological evolution of the Au part in the dimer ranging from half-shell, nanocrescent to nanoshell associated with the appearance of the second plasmon absorption band in near IR. Surface-enhanced Raman scattering signal is obtained directly from the symmetry-broken nanoparticles solution as an example showing the viability of the present approach. We believe our concept represents an important step toward a wide range of biophotonic applications for optical nanoplasmonics such as targeting, sensing/imaging, gene delivery, and optical gene regulations.