Jiseok Lee

Polydiacetylene Liposome Arrays for Selective Potassium Detection

Potassium is an important cation in biology, and quantitative detection of the extracellular potassium level is important. However, selective detection of extracellular physiological potassium is a challenging task due to the presence of sodium in a much higher concentration. In this contribution, we describe the development of practical polydiacetylene (PDA) liposome-based microarrays to selectively detect potassium even in the presence of sodium. We utilize the fact that the G-rich ssDNA can fold into a G-quadruplex via intramolecular hydrogen bonding by wrapping around a potassium ion exclusively. We rationally design the PDA liposome in such a way that the G-rich ssDNA probes are presented densely at the liposome surface and form bulky quadruplexes upon binding with K+. The resulting bulky quadruplexes are sterically hindered and repulse each other and impose mechanical stress on the PDA backbone, resulting in the conformational change of the ene-yne backbone of the PDA. As a result, polydiacetylene liposomes turn into the emissive red phase from the nonfluorescent blue phase.

Conjugated Polyelectrolyte-Antibody Hybrid Materials for Highly Fluorescent Live Cell-Imaging

Conjugated polyelectrolyte-antibody hybrid materials promise to enhance the utility of conjugated polymers in bioimaging field. Polymer-antibody conjugates that are biologically safe and highly sensitive and selective to cells are designed to image human T or B lymphocytes. In the clear state, the observed efficiency of luminescence is superior to that of commercially available FITC-antibody probe.

Polydiacetylene Liposome Microarray Toward Influenza A Virus Detection: Effect of Target Size on Turn-On Signaling

Target size effect on the sensory signaling intensity of polydiacetylene (PDA) liposome microarrays was systematically investigated. Influenza A virus M1 peptide and M1 antibody were selected as a probe-target pair. While red fluorescence from the PDA liposome microarrays was observed when the larger M1 antibody was used as a target, when the same M1 antibody was used as a probe to detect the smaller M1 peptide sensory signal did not appear. The results reveal that the intensity of the PDA sensory signal is mainly related to the steric repulsion between probe-target complexes not the strength of the probe-target binding force. Based on this finding, we devised a PDA sensory system that directly detects influenza A whole virus as a larger target, and confirmed the target size effect on the signaling efficiency of PDA.

Design of Polydiacetylene-Phospholipid Supramolecules for Enhanced Stability and Sensitivity

We present polydiacetylene (PDA) liposome assemblies with various phospholipids that have different headgroup charges and phase transition temperatures (T(m)). 10,12-Pentacosadiynoic acid (PCDA)-epoxy was used as a base PDA monomer and the insertion of highly charged phospholipids resulted in notable changes in the size of liposome and reduction of the aggregation of PDA liposome. Among the various phospholipids, the phospholipid with a moderate T(m) demonstrated enhanced stability and sensitivity, as measured by the size and zeta potential over storage time, thermochoromic response, and transmission electron microscopy images. By combining these results, we were able to detect immunologically an antibody of bovine viral diarrhea virus over a wide dynamic range of 0.001 to 100 μg/mL.

Biomimetic detection of aminoglycosidic antibiotics using polydiacetylene–phospholipids supramolecules

We rationally designed highly sensitive and selective polydiacetylene (PDA)-phospholipids liposomes for the facile detection of aminoglycosidic antibiotics. The detecting mechanism mimics the cellular membrane interactions between neomycin and phosphatidylinositol-4,5-bisphosphate (PIP(2)) phospholipids. The developed PDA-PIP(2) sensory system showed a detection limit of 61 ppb for neomycin and was very specific to aminoglycosidic antibodies only.

Nonpolymeric thermosensitive benzenetricarboxamides.

A new class of nonpolymeric thermosensitive materials based on the benzene-1,3,5-tricarboxamide (BTC) structural platform are described. We observed that the benzocrown ether-substituted BTC derivatives undergo an unusual temperature-dependent reversible solubility change in aqueous solution. Thus, a clear nonfluorescent solution of BTC derivatives becomes turbid and generates fluorescent aggregates above the LCST temperature. The aggregates disappear, and a clear solution is reformed when the solution is cooled to 20 °C. It is believed that the LCST behavior of BTC derivatives results from the removal of water molecules from crown ether moieties at elevated temperature. Thus, BTC derivatives exist in fully hydrated forms below the LCST. Heating the BTC derivatives solutions causes the expulsion of water and induces the formation of aggregates. At room temperature, the removal of water from BTC derivatives occurs slowly and leads to the formation of long nanofibers.

High-Throughput Contact Flow Lithography

High‐throughput fabrication of graphically encoded hydrogel microparticles is achieved by combining flow contact lithography in a multichannel microfluidic device and a high capacity 25 mm LED UV source. Production rates of chemically homogeneous particles are improved by two orders of magnitude. Additionally, the custom‐built contact lithography instrument provides an affordable solution for patterning complex microstructures on surfaces.

Governing Principles of Alginate Microparticle Synthesis with Centrifugal Forces

A controlled synthesis of polymeric particles is becoming increasingly important because of emerging applications ranging from medical diagnostics to self-assembly. Centrifugal synthesis of hydrogel microparticles is a promising method, combining rapid particle synthesis and the ease of manufacturing with readily available laboratory equipment. This method utilizes centrifugal forces to extrude an aqueous polymer solution, sodium alginate (NaALG) through a nozzle. The extruded solution forms droplets that quickly cross-link upon contact with aqueous calcium chloride (CaCl2) solution to form hydrogel particles. The size distribution of hydrogel particles is dictated by the pinch-off behavior of the extruded solution through a balance of inertial, viscous, and surface tension stresses. We identify the parameters dictating the particle size and provide a numerical correlation predicting the average particle size. Furthermore, we create a phase map identifying different pinch-off regimes (dripping without satellites, dripping with satellites, and jetting), explaining the corresponding particle size distributions, and present scaling arguments predicting the transition between regimes. By shedding light on the underlying physics, this study enables the rational design and operation of particle synthesis by centrifugal forces.

Rapid Light-Driven Color Transition of Novel Photoresponsive Polydiacetylene Molecules

We developed new photoresponsive polydiacetylene (PR-PDA) molecules by incorporating a photocleavable moiety, 6-nitropiperonyl alcohol (NP) or 4,5-dimethoxy-2-nitrobenzyl alcohol (DMN), into a self-assembling diacetylene molecule. Inducing steric disordering of the assembled PDA molecules by the cleavage of the photoresponsive moiety under 365 nm UV irradiation results in color transition from blue to red and development of red fluorescence, allowing convenient photo patterning. Further writing and erasing of fluorescence patterns are demonstrated toward novel secure information communication and anticounterfeiting applications.