Sang Jun Sim

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.

Pretreatment of rice straw with ammonia and ionic liquid for lignocellulose conversion to fermentable sugars.

Pretreatment technology is a prerequisite to facilitate the release of sugars from a lignocellulosic biomass prior to fermentation. Recently, some pretreatment methods have been tried with ionic liquids, but they were still expensive and unpractical. In this study, an efficient pretreatment method using ammonia and ionic liquid was developed for the recovery of bio-digestible cellulose from a lignocellulosic byproduct, rice straw, and the increase of ionic liquid utilization. The combined use of ammonia and ionic liquid ([Emim]Ac) treatment exhibited a synergy effect for rice straw with 82% of the cellulose recovery and 97% of the enzymatic glucose conversion. This cooperative effect showed over 90% of the glucose conversion even with a reduced enzyme usage and incubation time. The ionic liquid was successfully recycled more than 20 times. The 20th-recycled ([Emim]Ac) showed 74% of the cellulose recovery and 78% of the glucose conversion to rice straw. Compared with the conventional pretreatment, our combined method for lignocellulosic biomass pretreatment was an economical and eco-friendly.

Hydrocarbon production from secondarily treated piggery wastewater by the green alga Botryococcus braunii

A laboratory study was conducted on the removal of nitrogen and phosphorus from piggery wastewater during growth of Botryococcus braunii UTEX 572, together with measurements of hydrocarbon formation by the alga. The influence was tested of the initial nitrogen and phosphorus concentration on the optimum concentration range for a culture in secondarily treated piggery wastewater. A high cell density (> 7 g L−1 d. wt) was obtained with 510 mg L−1 NO3-N. Growth increased with nitrogen concentration at the basal phosphorus concentration (14 mg P L−1). The growth rate was nearly independent (μ = 0.027 ∼ 0.030 h−1) of the initial phosphate concentration, except under conditions of phosphate deficiency (μ = 0.019 h−1). B. braunii grew well in piggery wastewater pretreated by a membrane bioreactor (MBR) with acidogenic fermentation. A dry cell weight of 8.5 mgL−1 and hydrocarbon level of 0.95 gL−1 were obtained, and nitrate was removed at a rate of 620 mg NL−1. These results indicate that pretreated piggery wastewater provides a good culture medium for the growth and hydrocarbon production by B. braunii.

Ultrasensitive carbon nanotube-based biosensors using antibody-binding fragments

We report a method to build ultrasensitive carbon nanotube-based biosensors using immune binding reaction. Here carbon nanotube-field effect transistors (CNT-FETs) were functionalized with antibody-binding fragments as a receptor, and the binding event of target immunoglobulin G (IgG) onto the fragments was detected by monitoring the gating effect caused by the charges of the target IgG. Because the biosensors were used in buffer solution, it was crucial to use small-size receptors so that the charged target IgG could approach the CNT surface within the Debye length distance to give a large gating effect. The results show that CNT-FET biosensors using whole antibody had very low sensitivity (detection limit approximately 1000 ng/ml), whereas those based on small Fab fragments could detect 1 pg/ml (approximately 7 fM level). Moreover, our Fab-modified CNT-FET could successfully block the nontarget proteins and could selectively detect the target protein in an environment similar to that of human serum electrolyte. Significantly, this strategy can be applied to general antibody-based detection schemes, and it should enable the production of label-free ultrasensitive electronic biosensors to detect clinically important biomarkers for disease diagnosis.

Enhancement of sensitivity and specificity by surface modification of carbon nanotubes in diagnosis of prostate cancer based on carbon nanotube field effect transistors

This paper presents a simple and sensitive method for the real-time detection of a prostate cancer marker (PSA-ACT complex) through label-free protein biosensors based on a carbon nanotube field effect transistor (CNT-FET). Herein, the CNT-FET was functionalized with a solution containing various linker-to-spacer ratios, the binding event of the target PSA-ACT complex onto the receptor detected by monitoring the gating effect caused by charges in the target PSA-ACT complex. Since the biosensors were used in a buffer solution, it was crucial to control the distance between the receptors through introduction of linkers and spacers so that the charged target PSA-ACT complex could easily approach the CNT surface within the Debye length to give a large gating effect. The results show that CNT-FET biosensors modified with only linkers could not detect target proteins unless a very high concentration of the PSA-ACT complex solution (approximately 500 ng/ml) was injected, while those modified with a 1:3 ratio of linker-to-spacer could detect 1.0 ng/ml without any pretreatment. Moreover, our linker and spacer-modified CNT-FET could successfully block non-target proteins and selectively detect the target protein in human serum. Significantly, this strategy can be applied to general antibody-based detection schemes and enables production of very simple and sensitive electronic biosensors to detect clinically important biomarkers for disease diagnosis.

Target-specific delivery of siRNA by stabilized calcium phosphate nanoparticles using dopa-hyaluronic acid conjugate

Low cytotoxicity and high cellular gene delivery capability are among the most important prerequisites for the selection of a non-viral carrier. Although calcium phosphate (CAP) nanoparticles have been long used for animal cell transfection, its rapid and uncontrollable crystal growth and lack of tissue specificity are among the most challenging problems that limit its use in the clinic. In this study, we report the development of CAP nanoparticles stabilized by a conjugate of the mussel-inspired adhesive molecule, 3,4-dihydroxy-l-phenylalanine (dopa), and a nontoxic hydrophilic natural polymer, hyaluronic acid (HA), for targeted siRNA delivery to tumors. CAP/siRNA/dopa-HA can form compact nanoparticles that effectively protect siRNA from enzymatic degradation despite the structural drawbacks of siRNA, such as low charge density and short and rigid structure. In addition, stabilized CAP nanoparticles were able to maintain their colloidal stability in a physiological salt condition for over a week. The superior ability of CAP/siRNA/dopa-HA to maintain the integrity of encapsulated siRNA and the stability in solution of the nanoparticles allow this formulation to achieve improved intratumoral accumulation of siRNA and a high level of target gene silencing in solid tumors after systemic administration. Considering its biocompatibility, transfection efficacy, and tumor targeting capability, this stabilized calcium phosphate nanoparticle-based gene delivery platform should be considered a promising candidate carrier for systemic siRNA delivery and targeted cancer therapy.

Sensitive DNA biosensor based on a long-period grating formed on the side-polished fiber surface.

We demonstrate a sensitive DNA biosensor based on a long period grating (LPG) formed by a photolithograph process on the surface of a side-polished fiber. The biomolecules of the biosensor were immobilized on the silica surface between LPG patterns. The resonance wavelength was red-shifted after the binding of the poly-L-lysine, probe ssDNA and target ssDNA to the sensor surface. The overall wavelength shift after the successful DNA hybridization was 1.82 nm. The proposed LPG-based DNA biosensor is approximately 2.5 times more sensitive than the previously reported fiber grating-based DNA biosensors.

Hydrogen production of the hyperthermophilic eubacterium, Thermotoga neapolitana under N2 sparging condition.

Gas sparging was found to be a useful technique to reduce hydrogen partial pressure in the liquid phase to enhance the hydrogen yields of strictly anaerobically fermentative bacteria. The effect of nitrogen (N(2)) sparging on hydrogen yield was investigated in sterile and non-sterile conditions using a pure strain of the hyperthermophilic eubacteria, Thermotoga neapolitana with glucose or xylose as a carbon source. The maximum hydrogen accumulations reached 41% of the gaseous mixtures after 30-40 h. Two applications of N(2) sparging after the H(2) content in the headspace reached the maximum levels gave an increase of H(2) production by 78% from 1.82 to 3.24 mol H(2)/mol glucose and by 56% from 1.41 to 2.20 mol H(2)/mol xylose. This result suggested that the removal of the produced H(2) from the gas headspace of the limited-volume, closed culture vial when it achieves the maximum level of H(2) tolerance of the bacterium is a necessary technique to improve its H(2) yield.

High cell density culture of Anabaena variabilis using repeated injections of carbon dioxide for the production of hydrogen

Cyanobacteria have the unique characteristic of using CO 2 in the air as a carbon source and solar energy as an energy source. Reducing equivalents from the fermentation of carbohydrates are used as the primary electron donors in cyanobacteria for the hydrogen producing enzymes. The cells take up CO 2 first to produce cellular substances, which are subsequently used for H 2 production. Since the optimal operating conditions for the CO 2 uptake and H 2 production are different, a two-stage system can be effectively employed to separate these two phases. In this study, for the efficient production of H 2 in the second stage, the conditions for the effective CO 2 uptake and cell growth in the first stage were characterized, and high cell density culture was carried out using repeated injections of CO 2 . The specific growth rate and growth yield based on CO 2 decreased with an increase in light intensity or CO 2 concentration. However, the effect of CO 2 concentration on the growth yield was much smaller than that of a light intensity. A CO 2 uptake rate per unit cell decreased linearly with the initial CO 2 concentration in the gas phase. With repeated injections of CO 2 , the CO 2 was continuously consumed and the cell concentration reached 3.7 g dry cell/l in 20 days, which is 6.7 times higher than that in a batch culture without further supply of CO 2 . The CO 2 injection in the cell growth phase increased not only the cell concentration but also the hydrogen production per gram cell.

Rational aspect ratio and suitable antibody coverage of gold nanorod for ultra-sensitive detection of a cancer biomarker

We report a simple, ultra-sensitive, and straightforward method for non-labeling detection of a cancer biomarker, using Rayleigh light scattering spectroscopy of the individual nanosensor based on antibody-antigen recognition and localized surface plasmon resonance (LSPR) λ(max) shifts. By experimentally measuring the refractive index sensitivity of Au nanorods, the Au nanorod with an aspect ratio of ~3.5 was proven optimal for the LSPR sensing. To reduce the steric hindrance effect as well as to immobilize a large amount of ligand on the nanoparticle surface, various mixtures containing different molar ratios of HS(CH(2))(11)(OCH(2)CH(2))(6)OCH(2)COOH and HS(CH(2))(11)(OCH(2)CH(2))(3)OH were applied to form different self-assembled monolayer surfaces. The results showed that the best molar ratio for antibody conjugation was 1 : 10. When using individual Au nanorod sensors for the detection of prostate specific antigen (PSA), the lowest concentration recorded was ~1 aM (~6 × 10(5) molecules), corresponding to LSPR λ(max) shifts of ~4.2 nm. These results indicate that sensor miniaturization down to the nanoscale level, the reduction of steric hindrance, and optimization of size, shape, and aspect ratio of nanorods have led to a significant improvement in the detection limit of sensors.