Seung Phill Choi

Enzymatic pretreatment of Chlamydomonas reinhardtii biomass for ethanol production

The production of ethanol from feedstock other than agriculture materials has been promoted in recent years. Some microalgae can accumulate a high starch content (about 44% of dry base) via photosynthesis. Algal biomass, Chlamydomonas reinhardtii UTEX 90, was converted into a suitable fermentable feedstock by two commercial hydrolytic enzymes. The results showed that almost all starch was released and converted into glucose without steps for the cell wall disruption. Various conditions in the liquefaction and saccharification processes, such as enzyme concentration, pH, temperature, and residence time, have been investigated to obtain an optimum combination using the orthogonal analysis. As a result, approximately 235 mg of ethanol was produced from 1.0 g of algal biomass by a separate hydrolysis and fermentation (SHF) method. The main advantages of this process include the low cost of chemicals, short residence time, and simple equipment system, all of which promote its large-scale application.

NMR-based metabolic profiling and differentiation of ginseng roots according to cultivation ages

Ginseng is an important herbal resource worldwide, and the adulteration or falsification of cultivation age has been a serious problem in the commercial market. In this study, ginseng (Panax ginseng) roots, which were cultivated for 2-6 years under GAP standard guidelines, were analyzed by NMR-based metabolomic techniques using two solvents. At first, ginseng root samples were extracted with 50% methanol, and analyzed by NMR with D(2)O as the NMR dissolution solvent. The 2-, 3-, 4-, and 5/6-year-old ginseng root samples were separated in PLS-DA-derived score plots. However, 5- and 6-year-old ginseng roots were not separated by the solvent system. Therefore, various solvents were tested to differentiate the 5- and 6-year-old ginseng root samples, and 100% methanol-d(4) was chosen as the direct extraction and NMR dissolution solvent. In the PLS model using data from the 100% methanol-d(4) solvent, 5- and 6-year-old ginseng roots were clearly separated, and the model was validated using internal and external data sets. The obtained RMSEE and RMSEP values suggested that the PLS model has strong predictability for discriminating the age of 5- and 6-years-old ginseng roots. The present study suggests that the age of ginseng could be successfully predicted using two solvents, and the developed method in this study can be used as a standard protocol for discriminating and predicting the ages of ginseng root samples.

Signal Amplification by Magnetic Force on Polydiacetylene Supramolecules for Detection of Prostate Cancer

A method in which a permanent magnet is introduced onto polydiacetylene (PDA) vesicle chips is introduced for enhancement of the fluorescence of PDA vesicles. This strategy can be applied to general antibody-based PDA vesicle chips to detect clinically important biomarkers for disease diagnosis.

Amplification of Resonant Rayleigh Light Scattering Response Using Immunogold Colloids for Detection of Lysozyme

A strategy for attomolar-level detection of small molecule-size proteins is reported based on Rayleigh light scattering spectroscopy of individual nanoplasmonic aptasensors by exploiting the outstanding characteristics of gold colloids to amplify the nontransparent resonant signal at ultralow analyte concentrations. The fabrication method utilizes thiol-mediated adsorption of a DNA aptamer on the immobilized Au nanoparticle surface, the interfacial binding characteristics of the aptamer with its target molecules, and the antibody-antigen interaction through plasmonic resonance coupling of the Au nanoparticles. Using lysozyme as a model analyte for disease detection, the detection limit of the aptasensor is ∼7 × 10(3) aM, corresponding to the LSPR λmax shift of ∼2.25 nm. Up to a 380% increase in the localized resonant λmax shift is demonstrated upon antibody binding to the analyte compared to the primary response during signal amplification using immunogold colloids. This enhancement leads to a limit of detection of ∼7 aM, which is an improvement of three orders of magnitude. The results demonstrate substantial promise for developing coupled plasmonic nanostructures for ultrasensitive detection of various biological and chemical analytes.

Real‐Time, Sensitive, and Specific Detection of Promoter‐Polymerase Interactions in Gene Transcription Using a Nanoplasmonic Sensor

Molecular interactions between proteins (e.g., promoters and transcription factors) and nucleic acids (DNA and RNA) play crucial roles in controlling normal cellular processes as well as development and progress of diseases. Despite enormous importance not only in basic biology but also in medicine, identifying proteins binding to the target nucleic acid sequence and understanding underlying mechanisms at a molecular level still remain a major challenge. For example, binding of RNA polymerase to the promoter region of the gene determines gene transcription and, hence, control gene expression. [ 1 ] The degree of gene expression is greatly affected by the promoter sequence which controls the binding and initiating effi ciency of polymerase (i.e., promoter activity). However, investigating the effi cacy and specifi city of promoters by examining endpoint biochemical products such as RNA and proteins is timeconsuming and often very complicated. [ 2 ] Therefore, development of a technique that enables fast (ideally in real-time), ultrasensitive, and direct monitoring of promoter activity by quantifying protein binding to DNA and transcription process is of great interest. In this study, a new strategy based on the optical property of single gold nanoparticle (AuNP) was introduced to attain fast (almost in real time), sensitive, and simple monitoring of the molecular interactions between nucleic acids and promoters. The nanoplasmonic sensor detects the incident photon frequency oscillation that is generated by the collective polarized electrons of the nanometer-sized metallic nanoparticles (e.g., AuNPs) upon excitation by the electric fi eld of the incoming light, which is also called localized surface plasmon resonance (LSPR). [ 3,4 ] It was hypothesized that sequence-specifi c binding of polymerases on the promoter generate distinct LSPR signal

Dynamics of membrane fatty acid composition of succinic acid-producing Anaerobiospirillum succiniciproducens

The dynamics of the membrane fatty acid composition of a succinic acid-producing bacterium, Anaerobiospirillum succiniciproducens, was studied using continuous and batch cultures. In both batch and chemostat continuous culture conditions, A. succiniciproducens grown on glucose or glycerol responded to acid stress by lowering the content of saturated fatty acids (SFAs) and increasing the content of unsaturated fatty acids (UFAs). Notably, A. succiniciproducens elongated C16:0 (SFA) and converted it to C18:1 (UFA) in the pH-uncontrolled culture, which is a common bacterial adaptation strategy to combat acid stress. Interestingly, A. succiniciproducens did not exhibit a significant increase in cyclic FA content, which is another common strategy to cope with acidic conditions.