Youngho Cho

Ultra-Wideband Multi-Dye-Sensitized Upconverting Nanoparticles for Information Security Application

Multi-dye-sensitized upconverting nanoparticles (UCNPs), which harvest photons of wide wavelength range (450-975 nm) are designed and synthesized. The UCNPs embedded in a photo-acid generating layer are integrated on destructible nonvolatile resistive memory device. Upon illumination of light, the system permanently erases stored data, achieving enhanced information security.

Broadband supercontinuum generation using a hollow optical fiber filled with copper-ion-modified DNA

We experimentally demonstrated supercontinuum generation through a hollow core photonic bandgap fiber (HC-PBGF) filled with DNA nanocrystals modified by copper ions in a solution. Both double-crossover nano DNA structure and copper-ion-modified structure provided a sufficiently high optical nonlinearity within a short length of hollow optical fiber. Adding a higher concentration of copper ion into the DNA nanocrystals, the bandwidth of supercontinuum output was monotonically increased. Finally, we achieved the bandwidth expansion of about 1000 nm to be sufficient for broadband multi-spectrum applications.

Enhanced nonlinear optical characteristics of copper-ion-doped double crossover DNAs

The modification of deoxyribonucleic acid (DNA) samples by sequencing the order of bases and doping copper ions opens the possibility for the design of novel nanomaterials exhibiting large optical nonlinearity. We investigated the nonlinear characteristics of copper-ion doped double crossover DNA samples for the first time to the best of our knowledge by using Z-scan and four-wave mixing methods. To accelerate the nonlinear characteristics, we prepared two types of unique DNA nanostructures composed of 148 base pairs doped with copper ions with a facile annealing method. The outstanding third-order nonlinear optical susceptibility of the copper-ion-doped DNA solution, 1.19 × 10(-12) esu, was estimated by the conventional Z-scan measurement, whereas the four-wave mixing experiment was also investigated. In the visible spectral range, the copper-ion-doped DNA solution samples provided competent four-wave mixing signals with a remarkable conversion efficiency of -4.15 dB for the converted signal at 627 nm. The interactions between DNA and copper ions contribute to the enhancement of nonlinearity due to structural and functional changes. The present study signifies that the copper-ion-doped double crossover DNA is a potential candidate as a highly efficient novel material for further nonlinear optical applications.

Artificial Rod and Cone Photoreceptors with Human-Like Spectral Sensitivities

Photosensitive materials contain biologically engineered elements and are constructed using delicate techniques, with special attention devoted to efficiency, stability, and biocompatibility. However, to date, no photosensitive material has been developed to replace damaged visual-systems to detect light and transmit the signal to a neuron in the human body. In the current study, artificial nanovesicle-based photosensitive materials are observed to possess the characteristics of photoreceptors similar to the human eye. The materials exhibit considerably effective spectral characteristics according to each pigment. Four photoreceptors originating from the human eye with color-distinguishability are produced in human embryonic kidney (HEK)-293 cells and partially purified in the form of nanovesicles. Under various wavelengths of visible light, electrochemical measurements are performed to analyze the physiological behavior and kinetics of the photoreceptors, with graphene, performing as an electrode, playing an important role in the lipid bilayer deposition and oxygen reduction processes. Four nanovesicles with different photoreceptors, namely, rhodopsin (Rho), short-, medium-, and longwave sensitive opsin 1 (1SW, 1MW, 1LW), show remarkable color-dependent characteristics, consistent with those of natural human retina. With four different light-emitting diodes for functional verification, the photoreceptors embedded in nanovesicles show remarkably specific color sensitivity. This study demonstrates the potential applications of light-activated platforms in biological optoelectronic industries.

Generation of Broadband Supercontinuum through Nonlinear Interaction in DNA Materials

We demonstrated supercontinuum generation through DNA materials. The DNA material, which is modified copper ion, provided optical nonlinearity within a hollow optical fiber. The supercontinuum spectrum is optimized by fiber length and copper ion concentration for the bandwidth of more than 800nm.

Metal ion sensing solution containing double crossover DNA

The current study describes metal ion sensing with double crossover DNAs (DX1 and DX2), artificially designed as a platform of doping. The sample for sensing is prepared by a facile annealing method to grow the DXs lattice on a silicon/silicon oxide. Adding and incubating metal ion solution with the sensor substrate into the micro-tube lead the optical property change. Photoluminescence (PL) is employed for detecting the concentration of metal ion in the specimen. We investigated PL emission for sensor application with the divalent copper. In the range from 400 to 650 nm, the PL features of samples provide significantly different peak positions with excitation and emission detection. Metal ions contribute to modify the optical characteristics of DX with structural and functional change, which results from the intercalation of them into hydrogen bonding positioned at the center of double helix. The PL intensity is decreased gradually after doping copper ion in the DX tile on the substrate.

Supercontinuum generation through DNA-filled hollow core fiber for broadband absorption spectroscopy

In this study, we successfully generated the large bandwidth of supercontinuum spectra through hollow fibers filled with DNA. Also, by observing that spectra bandwidth was the widest in the order of the hollow core fiber filled with DNA modified by copper ion, the hollow core fiber with only DNA, and the bulk hollow core fiber, we demonstrated that DNA material modified with copper ions can further enhance the spectral bandwidth of supercontinuum. As a result, we anticipate that the SCG as a broadband light source can be used in analytical methods to demonstrate a wide range of biological and environmental questions.