Seongjin Hong

Thermo-optic characteristic of DNA thin solid film and its application as a biocompatible optical fiber temperature sensor

We report unique thermo-optical characteristics of DNA-Cetyl tri-methyl ammonium (DNA-CTMA) thin solid film with a large negative thermo-optical coefficient of -3.4×10-4/°C in the temperature range from 20°C to 70°C without any observable thermal hysteresis. By combining this thermo-optic DNA film and fiber optic multimode interference (MMI) device, we experimentally demonstrated a highly sensitive compact temperature sensor with a large spectral shift of 0.15 nm/°C. The fiber optic MMI device was a concatenated structure with single-mode fiber (SMF)-coreless silica fiber (CSF)-single mode fiber (SMF) and the DNA-CTMA film was deposited on the CSF. The spectral shifts of the device in experiments were compared with the beam propagation method, which showed a good agreement.

Irreversible denaturation of DNA: a method to precisely control the optical and thermo-optic properties of DNA thin solid films

The denaturation of double-stranded deoxyribonucleic acid (ds-DNA) has been well known to break nucleobase bonds, resulting in single-stranded deoxyribonucleic acid (ss-DNA) in solutions, which can recombine to form ds-DNA in a reversible manner. We developed an efficient process to irreversibly maintain various DNA denaturation levels in thin solid films in order to investigate the impacts of the denaturation on the optical properties of DNA films. By adding NaOH in an aqueous solution of salmon testis DNA, we flexibly controlled the level of denaturation in the solution, which was then spin-coated on Si and silica substrates to irreversibly bind ss-DNAs in a thin solid film. The denaturation of DNA in thin solid films was experimentally confirmed by ultraviolet-visible and Fourier transform infrared spectroscopic investigations, whose level could be controlled by the NaOH content in the aqueous solution precursor. By this irreversible denaturation process, we developed a new method to flexibly vary the refractive index of DNA thin solid films in a wide range of Δn>0.02 in the visible to near-infrared range. Thermo-optic coefficients dn/dT of the films were also experimentally measured in the temperature range from 40°C to 90°C to confirm the significant impacts of denaturation. Detailed thin film processes and optical characterizations are discussed.

High sensitivity temperature measurement via mask-free hybrid polymer long period fiber grating

Long-period fiber gratings (LPFGs) are useful for environmental sensing under conditions of high corrosiveness and electromagnetic interference. Most LPFGs are fabricated by coherent or high-power UV illumination of an optical fiber under an amplitude mask, resulting in narrow and environmentally-dependent band rejection. We present a hybrid LPFG waveguide fabricated without an amplitude mask through polymer self-assembly under low-power incoherent UV illumination, which demonstrates high-temperature sensitivity in its transmission spectrum compared to LPFG sensors based purely on silica waveguides. A sensitivity of 1.5 nm °C -1 is obtained experimentally for attenuation near 1180 nm, and a sensitivity of 4.5 nm °C -1 with a low random error was obtained with a composite of attenuation bands. Finite element method simulations and coupling mode theory reveal this to be due to a thermo-optic coefficient one order of magnitude greater than that of fused silica. The device has potential for a simple and inexpensive transmission intensity based temperature sensor consisting of an infrared light source, the LPFG, a bandpass filter, and a photodiode.

DNA based thin solid film and its application to optical fiber temperature sensor

Temperature dependent refractive index of DNA-cetyltrimethylammonium chloride (CTMA) thin-solid-film was measured 20 to 90°C to obtain its thermo-optic coefficient of −3.6× 10−4 (dn/dT). DNA-CTMA film has high thermosoptic coefficient than other polymers. The film was deposited on coreless silica fiber (CSF) to serve as a multimode interferometer optical fiber temperature sensor. It is immersed in a water that changed temperature from 40 to 90°C. It has sensitivity of 0.25nm/°C.

Optical study of light-emitting bioploymer based on deoxyribonucleic acid-cetylmethyammonium chloride doped with riboflavin

We research light emission properties of the optical gain medium based on biopolymer for biocompatible laser system. The deoxyribonucleic acid-cetyltrimethylammonium chloride surfactant (DNA-CTMA) doped with riboflavin has been measured by UV-vis spectroscopy and confirmed by photoluminescence measurement for the five different composition doping rates (100–2000 ppm of riboflavin) of the blended solution with hexafluoro-2-propanol (HFIP). The riboflavin-doped DNA-CTMA:HFIP solid-state thin-films are achieved by spin-coating method and the doping behavior has been studied by Raman spectroscopy.

Cationic lipid binding control in DNA based biopolymer and its impacts on optical and thermo-optic properties of thin solid films

Biomaterials based on deoxyribonucleic acid (DNA) have shown notable potential in optoelectronic and photonic devices. In order to further investigate the optical properties of a DNA-based lipid complex such as DNA-cetyltrimethylammonium (CTMA), which is widely used in current DNA thin film research, a new refinement process was developed to minimize the relative bound water content and control binding of CTMA onto the DNA backbone. The water contents and CTMA binding in the DNA-CTMA precipitates were identified by spectrometric measurements to quantify effects of our refinement process. Dissolving these refined DNA-CTMAs in organic solvents, thin solid films were deposited on Si and quartz substrate using the spin coating process. Their refractive indices and absorbance were measured to quantitatively assess the impact of our refinement process on the optical properties of the DNA-CTMA films. In addition, thermo-optic coefficients, dn/dT, were also measured in a temperature range from 30 to 100°C to observe differences among refined DNA-CTMAs. Detailed quantitative spectroscopic analyses and optical measurements are reported.