Inseon Lee

Immobilization of glucose oxidase into polyaniline nanofiber matrix for biofuel cell applications

Glucose oxidase (GOx) was immobilized into the porous matrix of polyaniline nanofibers in a three-step process, consisting of enzyme adsorption, precipitation, and crosslinking (EAPC). EAPC was highly active and stable when compared to the control samples of enzyme adsorption (EA) and enzyme adsorption and crosslinking (EAC) with no step of enzyme precipitation. The GOx activity of EAPC was 9.6 and 4.2 times higher than those of EA and EAC, respectively. Under rigorous shaking at room temperature for 56 days, the relative activities of EA, EAC and EAPC, defined as the percentage of residual activity to the initial activity, were 22%, 19% and 91%, respectively. When incubated at 50°C under shaking for 4h, EAPC showed a negligible decrease of GOx activity while the relative activities of EA and EAC were 45% and 48%, respectively. To demonstrate the feasible application of EAPC in biofuel cells, the enzyme anodes were prepared and used for home-built air-breathing biofuel cells. The maximum power densities of biofuel cells with EA and EAPC anodes were 57 and 292 μW/cm(2), respectively. After thermal treatment at 60°C for 4h, the maximum power density of EA and EAPC anodes were 32 and 315 μW/cm(2), representing 56% and 108% of initially obtained maximum power densities, respectively. Because the lower power densities and short lifetime of biofuel cells are serious problems against their practical applications, the present results with EAPC anode has opened up a new potential for the realization of practical biofuel cell applications.

Enzyme precipitate coatings of glucose oxidase onto carbon paper for biofuel cell applications.

Enzymatic biofuel cells (BFC) have a great potential as a small power source, but their practical applications are being hampered by short lifetime and low power density. This study describes the direct immobilization of glucose oxidase (GOx) onto the carbon paper in the form of highly stable and active enzyme precipitation coatings (EPCs), which can improve the lifetime and power density of BFCs. EPCs were fabricated directly onto the carbon paper via a three‐step process: covalent attachment (CA), enzyme precipitation, and chemical crosslinking. GOx‐immobilized carbon papers via the CA and EPC approaches were used as an enzyme anode and their electrochemical activities were tested under the BFC‐operating mode. The BFCs with CA and EPC enzyme anodes produced the maximum power densities of 50 and 250 µW/cm2, respectively. The BFC with the EPC enzyme anode showed a stable current density output of >700 µA/cm2 at 0.18 V under continuous operation for over 45 h. When a maple syrup was used as a fuel under ambient conditions, it also produced a stable current density of >10 µA/cm2 at 0.18 V for over 25 h. It is anticipated that the direct immobilization of EPC on hierarchical‐structured electrodes with a large surface area would further improve the power density of BFCs that can make their applications more feasible. Biotechnol. Bioeng. 2012; 109:318–324.

Fabrication of enzyme-based coatings on intact multi-walled carbon nanotubes as highly effective electrodes in biofuel cells

CNTs need to be dispersed in aqueous solution for their successful use, and most methods to disperse CNTs rely on tedious and time-consuming acid-based oxidation. Here, we report the simple dispersion of intact multi-walled carbon nanotubes (CNTs) by adding them directly into an aqueous solution of glucose oxidase (GOx), resulting in simultaneous CNT dispersion and facile enzyme immobilization through sequential enzyme adsorption, precipitation, and crosslinking (EAPC). The EAPC achieved high enzyme loading and stability because of crosslinked enzyme coatings on intact CNTs, while obviating the chemical pretreatment that can seriously damage the electron conductivity of CNTs. EAPC-driven GOx activity was 4.5- and 11-times higher than those of covalently-attached GOx (CA) on acid-treated CNTs and simply-adsorbed GOx (ADS) on intact CNTs, respectively. EAPC showed no decrease of GOx activity for 270 days. EAPC was employed to prepare the enzyme anodes for biofuel cells, and the EAPC anode produced 7.5-times higher power output than the CA anode. Even with a higher amount of bound non-conductive enzymes, the EAPC anode showed 1.7-fold higher electron transfer rate than the CA anode. The EAPC on intact CNTs can improve enzyme loading and stability with key routes of improved electron transfer in various biosensing and bioelectronics devices.

Effects of propofol or desflurane on post-operative spirometry in elderly after knee surgery: a double-blind randomised study

Intravenous or volatile agents reduce respiratory function, which can result in respiratory complications in geriatric patients. We hypothesised that there would be no differences in lung function between anaesthesia established using either drug.

Selective Killing of Pathogenic Bacteria by Antimicrobial Silver Nanoparticle—Cell Wall Binding Domain Conjugates

Broad-spectrum antibiotics indiscriminately kill bacteria, removing nonpathogenic microorganisms and leading to evolution of antibiotic resistant strains. Specific antimicrobials that could selectively kill pathogenic bacteria without targeting other bacteria in the natural microbial community or microbiome may be able to address this concern. In this work, we demonstrate that silver nanoparticles, suitably conjugated to a selective cell wall binding domain (CBD), can efficiently target and selectively kill bacteria. As a relevant example, CBDBA from Bacillus anthracis selectively bound to B. anthracis in a mixture with Bacillus subtilis, as well in a mixture with Staphylococcus aureus. This new biologically-assisted hybrid strategy, therefore, has the potential to provide selective decontamination of pathogenic bacteria with minimal impact on normal microflora.

In vitro gene expression-coupled bacterial cell chip for screening species-specific antimicrobial enzymes

Targeting infectious bacterial pathogens is important for reducing the evolution of antibiotic‐resistant bacteria and preserving the endogenous human microbiome. Cell lytic enzymes including bacteriophage endolysins, bacterial autolysins, and other bacteriolysins are useful antibiotic alternatives due to their exceptional target selectivity, which may be used to lysins rapidly kill target bacteria and their high specificity permit the normal commensal microflora to be left undisturbed. Genetic information of numerous lysins is currently available, but the identification of their antimicrobial function and specificity has been limited because most lysins are often poorly expressed and exhibit low solubilities. Here, we report the development of bacterial cell chip for rapidly accessing the function of diverse genes that are suggestive of encoding lysins. This approach can be used to evaluate rapidly the species‐specific antimicrobial activity of diverse lysins synthesized from in vitro transcription and translation (TNT) of plasmid DNA. In addition, new potent lysins can be assessed that are not expressed in hosts and display low solubility. As a result of evaluating the species‐specific antimicrobial function of 11 (un)known lysins with an in vitro TNT‐coupled bacterial cell chip, a potent recombinant lysin against Staphylococcus strains, SA1, was identified. The SA1 was highly potent against not only S. aureus, but also both lysostaphin‐resistant S. simulans and S. epidermidis cells. To this end, the SA1 may be applicable to treat both methicillin‐resistant S. aureus (MRSA) and lysostaphin‐resistant MRSA mutants. Biotechnol. Bioeng. 2017;114: 1648–1657.

Sensitive Multiplex Detection of Whole Bacteria Using Self-Assembled Cell Binding Domain Complexes

Detecting bacterial cells at low levels is critical in public health, the food industry and first response. Current processes typically involve laborious cell lysis and genomic DNA extraction to achieve 100-1000 CFU mL-1 levels for detecting gram-positive bacteria. As an alternative to DNA-based methods, cell wall binding domains (CBDs) derived from lysins having a modular structure with an N-terminal catalytic domain and a C-terminal CBD, can be used to detect bacterial pathogens as a result of their exceptionally specific binding to target bacteria with great avidity. We have developed a highly sensitive method for multiplex detection of whole bacterial cells using self-assembled CBD complexes. Self-assembled CBD-SA-reporter complexes were generated using streptavidin (SA), biotin-CBDs, and biotinylated reporters, such as glucose oxidase (GOx) and specific DNA sequences. The simultaneous detection of three test bacteria, Staphylococcus aureus, Bacillus anthracis-Sterne, and Listeria innocua cells in PBS could be accomplished with a 96-well plate-based sandwich method using CBD-SA-GOx complex-coupled spectrophotometric assay to achieve a detection limit of >100 CFU mL-1. To achieve greater detection sensitivity, we used CBD-SA-DNA complexes and qPCR of specific DNA barcodes selectively bound to the surface of target bacterial cells, which resulted in a detection sensitivity as low as 1-10 CFU mL-1 without cross-reactivity. This sensitive multiplex detection of bacterial pathogens using both CBD-SA-GOx and CBD-SA-DNA complexes has the potential to be quickly combined with point-of-care compatible diagnostics for the rapid detection of pathogens in test samples.

Use of Terlipressin in an Elderly Patient With Moderate Aortic Valve Stenosis Accompanied by Episodic Atrial Fibrillation During Liver Transplantation: A Case Report

Anesthesia for patients with moderate aortic stenosis accompanied by atrial fibrillation during high-risk surgery such as liver transplantation remains a challenge in maintaining control of heart rate and maintenance of cardiac output. The action of terlipressin on vasopressin receptors (mainly V1 receptors) leads to splanchnic vasoconstriction and is the key mechanism responsible for increasing systemic vascular resistance and reducing heart rate. We report successful anesthetic management using low-dose terlipressin infusion in an elderly patient who had moderate aortic stenosis with atrial fibrillation during urgent deceased-donor liver transplantation.