Probing molecular interaction mechanisms of biopolymers

Department of Chemical EngineeringThe discovery and identification of biomolecular interactions have improved our understanding of the unique functions of biological systems and significantly contributed to the development of nanobiotechnology. Due to the poly-functionality of biomolecules, they often employ unique combinations of individual interactions and, as a result, can form a strong ensemble of interactions with specific molecules or matter (so called specific interaction or molecular recognition). Hence, the understanding of the molecular interactions is essential to design new molecules that bind to desired molecules and materials. There have also been several attempts to rationally design biomolecules with molecular recognition capabilities rather than relying on serendipitous findings. However, most conventional studies have relied on empirical design rules because of the lack of proper experimental analysis and understanding of these biomolecular interactions. Therefore, I investigate the biomolecular interactions and techniques. Furthermore, I report the precise measurements of various interaction forces between M13 bacteriophage (or peptide) and common functional groups. In chapter 1, I investigate various biomolecular interactions. In addition, the principles and previous research of representative techniques used to measure molecular interactions such as atomic force microscopy (AFM), quartz crystal microbalance with dissipation monitoring (QCM-D), and surface forces apparatus (SFA) are examined. In chapter 2, I select a specific type of genetically engineered M13 bacteriophage with CNT-binding polypeptide to investigate phage interactions. The interaction forces between the phage-coated surface and five different functionalized self-assembled monolayers (carboxylic, hydroxyl, amine, methyl, and phenyl) are directly measured using an SFA. Based on the results, the pH-dependent dispersion stability of M13 phage and single-walled carbon nanotubes (SWCNT) complexes was observed. In chapter 3, I study the molecular interactions of the peptide sequence (DSPHTELP) that is present in the main coat protein (pVIII) of the M13 phage used in chapter 2. The interaction forces between the peptide sequence and four different functionalized self-assembled monolayers (carboxylic, methyl, amine, and phenyl) were quantified in acidic condition via SFA. These studies provide experimental techniques for quantifying the interaction forces between biomolecules and functional groups and qualitative information on the molecular interaction mechanisms of bacteriophage and peptide. Consequently, I can suggest the direction and utilization of versatile platforms based on biomolecules.clos

Streptococcus pneumoniae Serotype 19A in Children, South Korea

A single, multidrug-resistant strain was responsible for increased incidence of this serotype before introduction of the pneumococcal 7-valent conjugate vaccine

COVID-19 diagnostics in context

The coronavirus disease 2019 (COVID-19) pandemic has highlighted the need for different types of diagnostics, comparative validation of new tests, faster approval by federal agencies, and rapid production of test kits to meet global demands. In this Perspective, we discuss the utility and challenges of current diagnostics for COVID-19

A Customizable and Low-Cost Ultraviolet Exposure System for Photolithography

For microfluidic device fabrication in the research, industry, and commercial areas, the curing and transfer of patterns on photoresist relies on ultraviolet (UV) light. Often, this step is performed by commercial mask aligner or UV lamp exposure systems; however, these machines are often expensive, large, and inaccessible. To find an alternative solution, we present an inexpensive, customizable, and lightweight UV exposure system that is user-friendly and readily available for a homemade cleanroom. We fabricated a portable UV exposure system that costs under $200. The wafer holder’s adjustable height enabled for the selection of the appropriate curing distance, demonstrating our system’s ability to be easily tailored for different applications. The high light uniformity across a 4” diameter wafer holder (light intensity error ~2.9%) was achieved by adding a light diffusing film to the apparatus. These values are comparable to the light uniformity across a 5” diameter wafer holder from a commercial mask aligner (ABM 3000HR Mask Aligner), that has a light intensity error of ~4.0%. We demonstrated the ability to perform photolithography with high quality by fabricating microfluidic devices and generating uniform microdroplets. We achieved comparable quality to the wafer patterns, microfluidic devices, and droplets made from the ABM 3000HR Mask Aligner

Anti‐cancer bioactivity of sweet basil leaf derived extracellular vesicles on pancreatic cancer cells

Abstract Most living organisms secrete tiny lipid bilayer particles encapsulating various biomolecular entities, including nucleic acids and proteins. These secreted extracellular vesicles (EVs) are shown to aid in communication between cells and their environment. EVs are mainly involved in the signalling and manipulation of physiological processes. Plant EVs display similar functional activity as seen in mammalian EVs. Medicinal plants have many bioactive constituents with potential applications in cancer treatment. Particularly, Basil (Ocimum basilicum), has wide therapeutic properties including anti‐inflammatory, anti‐cancer, and anti‐infection, among others. In this study, we focused on using EVs purified from Apoplast Washing Fluid (AWF) of Basil plant leaves as a biological therapeutic agent against cancer. Characterization of Basil EVs revealed a size range of 100–250 nm, which were later assessed for their cell uptake and apoptosis inducing abilities in pancreatic cancer cells. Basil plant EVs (BasEVs) showed a significant cytotoxic effect on pancreatic cancer cell line MIA PaCa‐2 at a concentration of 80 and 160 μg/mL in cell viability, as well as clonogenic assays. Similarly, RT‐PCR and western blot analysis has shown up regulation in apoptotic gene and protein expression of Bax, respectively, in BasEV treatment groups compared to untreated controls of MIA PaCa‐2. Overall, our results suggest that EVs from basil plants have potent anti‐cancer effects in pancreatic cancer cells and can serve as a drug delivery system, demanding an investigation into the therapeutic potential of other medicinal plant EVs

A Versatile Microchannel Array Device for Portable and Parallel Droplet Generation

The efficient generation of monodispersed droplets holds great promise for micro‐/nanoparticle synthesis and biochemical analysis. However, it remains a challenge to achieve high‐throughput generation of monodispersed droplets in a portable and/or parallel manner in nonexpert biomedical laboratories. Herein, a versatile microchannel array (μCA) device is reported that is portable, multifaceted, reliable, and mass‐manufacturable, supporting the high‐throughput generation of monodispersed droplets in different ways. This device consists of a silicon‐based μCA chip based on the step emulsification principle, as well as two matching plastic containers, both of which can be mass‐manufactured by traditional microfabrication methods at low material costs. With the μCA device, aqueous solution can be dispersed into emulsion droplets by various modes, such as mechanical pump‐based large‐scale, handheld syringe‐based portable, and gas pump‐based highly parallel droplet generation. Furthermore, it is demonstrated that our cost‐effective device can be applied for digital polymerase chain reaction analysis, supporting the need for more accessible microfluidic systems. Thus, the present device is expected to have a significant impact on both benchside and bedside applications

Probing Nanomechanical Interaction at the Interface between Biological Membrane and Potentially Toxic Chemical

Various xenobiotics interact with biological membranes, and precise evaluations of the molecular interactions between them are essential to foresee the toxicity and bioavailability of existing or newly synthesized molecules. In this study, surface forces apparatus (SFA) measurement and Langmuir trough based tensiometry are performed to reveal nanomechanical interaction mechanisms between potential toxicants and biological membranes for ex vivo toxicity evaluation. As a toxicant, polyhexamethylene guanidine (PHMG) was selected because PHMG containing humidifier disinfectant and Vodka caused lots of victims in both S. Korea and Russia, respectively, due to the lack of holistic toxicity evaluation of PHMG. Here, we measured strong attraction (Wad similar to 4.2 mJ/m(2)) between PHMG and head group of biological membranes while no detectable adhesion force between the head group and control molecules was measured. Moreover, significant changes in pi-A isotherm of 1,2-Dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) monolayers were measured upon PHMG adsorption. These results indicate PHMG strongly binds to hydrophilic group of lipid membranes and alters the structural and phase behavior of them. More importantly, complementary utilization of SFA and Langmuir trough techniques are found to be useful to predict the potential toxicity of a chemical by evaluating the molecular interaction with biological membranes, the primary protective barrier for living organisms

Detection rate and clinical impact of respiratory viruses in children with Kawasaki disease

PurposeThe purpose of this prospective case-control study was to survey the detection rate of respiratory viruses in children with Kawasaki disease (KD) by using multiplex reverse transcriptase-polymerase chain reaction (RT-PCR), and to investigate the clinical implications of the prevalence of respiratory viruses during the acute phase of KD.MethodsRT-PCR assays were carried out to screen for the presence of respiratory syncytial virus A and B, adenovirus, rhinovirus, parainfluenza viruses 1 to 4, influenza virus A and B, metapneumovirus, bocavirus, coronavirus OC43/229E and NL63, and enterovirus in nasopharyngeal secretions of 55 KD patients and 78 control subjects.ResultsVirus detection rates in KD patients and control subjects were 32.7% and 30.8%, respectively (P=0.811). However, there was no significant association between the presence of any of the 15 viruses and the incidence of KD. Comparisons between the 18 patients with positive RT-PCR results and the other 37 KD patients revealed no significant differences in terms of clinical findings (including the prevalence of incomplete presentation of the disease) and coronary artery diameter.ConclusionA positive RT-PCR for currently epidemic respiratory viruses should not be used as an evidence against the diagnosis of KD. These viruses were not associated with the incomplete presentation of KD and coronary artery dilatation