Joon Hyung Lee

Real-time liquid crystal-based biosensor for urea detection

A transmission electron microscopy (TEM) grid filled with 4-cyano-4′-pentylbiphenyl (5CB) on an octadecyltrichloro silane-coated glass substrate in aqueous media was developed to construct a urea biosensor by coating poly(acrylicacid-b-4-cyanobiphenyl-4-oxyundecylacrylate) (PAA-b-LCP) at the aqueous/5CB interface and immobilizing urease covalently to the PAA chains. Urea was detected from the planar to homeotropic (P–H) orientational transition of 5CB by polarized optical microscopy under crossed polarizers. This TEM grid sensor with the maximum immobilization density of urease, 0.17 molecules per nm2, enabled the detection of urea at concentrations as low as 5 mM through a P–H change with the half time of a full P–H change of 250 seconds. This TEM grid sensor could detect urea in the blood without any inference from hemoglobin and ascorbic acid. This new and sensitive urea biosensor is relatively inexpensive, allows easy naked eye detection, and may be useful for screening the urea level in the human body.

INFLUENCE OF SAMARIUM SUBSTITUTION ON IMPEDANCE DIELECTRIC AND ELECTROMECHANICAL PROPERTIES OF Pb(1-x)K2xNb2O6

Ferroelectric, hysteresis, impedance spectroscopy parameters, AC conductivity, and piezoelectric properties in the ceramics of Pb0.74K0.52Nb2O6 and Pb0.74K0.13Sm0.13Nb2O6 have been studied. X-ray diffraction study reveals single phase with the orthorhombic structure. The samples were characterized for ferroelectric and impedance spectroscopy properties from room temperature to 600°C. Cole–Cole plots (Z″ versus Z′) are drawn at different temperatures. The results obtained are analyzed to understand the conductivity mechanism in both the samples. The piezoelectric constant d33 has been found to be 96 × 10-12 C/N in PKN.

Liquid crystal-based biosensors using a strong polyelectrolyte-containing block copolymer, poly(4-cyanobiphenyl-4′-oxyundecylacrylate)- b -poly(sodium styrene sulfonate)

The interface between a nematic liquid crystal phase, 4-cyano-4′-pentylbiphenyl (5CB) and water was examined for protein detection by monitoring the formation of a complex between sodium polystyrene sulfonate (PSSNa) and a positively charged biological species on the 5CB in a transmission electron microscopy (TEM) grid cell coated with a strong anionic polyelectrolyte-containing block copolymer, LCP-b-PSSNa (LCP:poly(4-cyanobiphenyl-4′-oxyundecylacrylate)). This block copolymer was successfully synthesized by reversible addition-fragmentation chain transfer polymerization. A monolayer of LCP-b-PSSNa in a Langmuir Blodgett trough (in which PSSNa and LCP were located in and above water, respectively, in the TEM grid cell) was transferred to the 5CB/water interface in the 5CB-filled TEM grid that was already placed on octadecyltrichlorosilane-coated glass. Model proteins such as bovine serum albumin (BSA), hemoglobin (Hb), α chymotrypsinogen-A (ChTg), and lysozyme (LYZ) having different isoelectric points (pIs) were tested for non-specific protein detection. When the protein solutions were injected into the TEM grid cell, the initial homeotropic orientation of 5CB in the TEM grid cell changed to a planar one below the pIs of the proteins due to electrostatic interactions between PSSNa (- charge) and the proteins (+ charge); this did not occur above the pIs of the tested proteins. The minimum concentrations at which the homeotropic to planar configurational changes (H-P changes) occurred were 0.02, 0.04, 0.04, and 0.08 wt% for BSA, Hb, ChTg, and LYZ, respectively. Therefore, the positively charged biomaterials were visually detected at the PSSNa-coated LC/water interface during an H-P change by using polarized optical microscopy under crossed polarizers. This simple set-up for non-specific biomaterial detection paves a way for the development of efficient and excellent quality biosensors.

Specific Intracellular Uptake of Herceptin-Conjugated CdSe/ZnS Quantum Dots into Breast Cancer Cells

Herceptin, a typical monoclonal antibody, was immobilized on the surface of CdSe/ZnS core-shell quantum dots (QDs) to enhance their specific interactions with breast cancer cells (SK-BR3). The mean size of the core-shell quantum dots (28 nm), as determined by dynamic light scattering, increased to 86 nm after herceptin immobilization. The in vitro cell culture experiment showed that the keratin forming cancer cells (KB) proliferated well in the presence of herceptin-conjugated QDs (QD-Her, 5 nmol/mL), whereas most of the breast cancer cells (SK-BR3) had died. To clarify the mechanism of cell death, the interaction of SK-BR3 cells with QD-Her was examined by confocal laser scanning microscopy. As a result, the QD-Her bound specifically to the membrane of SK-BR3, which became almost saturated after 6 hours incubation. This suggests that the growth signal of breast cancer cells is inhibited completely by the specific binding of herceptin to the Her-2 receptor of SK-BR3 membrane, resulting in cell death.

EFFECT OF YTTRIUM ON DIELECTRIC, PYROELECTRIC AND PIEZOELECTRIC PROPERTIES OF PBN FERROELECTRICS

Materials with batch formula Pb(1-x-3y/2)RyBaxNb2O6, where R=Y, (1-x)=0.73, 0.63, 0.53 and y=0.00, 0.02 have been prepared by the double sintering method. Substitution of yttrium (Y) restored tetragonal symmetry of PBN but reduced lattice parameters, cell volume and enhanced the density. Transition temperature of PBN has decreased due to the substitution of Y3+. Enhanced room temperature spontaneous polarization (Ps)=149.97 μC/sq. cm has been observed in PBN53, which is above MPB, whereas enhanced value of Ps=112.74 μC/sq. cm is found in Y: PBN63 at MPB region. The room temperature Pyroelectric coefficient (PRT=1.07) has been observed in the composition where maximum volume of Ps is obtained. Similarly, enhanced values of piezoelectric coefficients Kp=0.244, Kt=0.353, K31=0.131, d31=60, d33=159 and g31=3.65 have also been found in the same material PBN53. Substitution of Yttrium enhanced the stiffness constant 13.59 in PBN 73 to 14.27 of Y: PBN73.

LEAD BARIUM POTASSIUM SODIUM NIOBATE CERAMICS FOR PIEZOELECTRIC APPLICATIONS

This paper reports a systematic study of tungsten bronze morphotropic phase boundary (MPB) system Pb2-2X-3Y/2Ba2xREyK1-xNaxNb5O15, where, x = 0.20, 0.25, 0.30, RE = Pr and Bi and y = 0.05 and their structure, microstructure, hysteresis, dielectric, piezoelectric, and Pyroelectric properties. Enhanced piezoelectric constants kp, kt, k31, d31, d33, g31, g33,

FERROELECTRIC AND PIEZOELECTRIC PROPERTIES OF Gd3+ AND Y3+ MODIFIED PKN ELECTROCERAMICS

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Synthesis and Electrical Characterization of the Polymorphic Indium Tin Oxide Nanocrystalline Powders

as 30.8%, 47.6%, 18.9%, 57 × 10-12C/N, 159 × 10-12C/N, 6.89 × 10-3mV/N, 19.23 × 10-3mV/N, and 13.88 × 10-12m2/N respectively are observed in the composition for which y = 0, and x = 0.30, which is above MPB. Also, a change in thickness, 0.0159 μm has been developed for a thickness of the sample 1.2 mm, d33 = 159 × 10-12C/N and for an applied voltage of 100 V. The same material produces a length extension, 0.0475 μm for d31 = 57 × 10-12C/N, l = 10 mm, t = 1.2 mm, for an applied voltage of 100 V. Thus the material may be useful for a piezoelectric transducer. Enhanced piezoelectric coefficients, d31 = 96 × 10-12C/N and g33 = 12.95 × 10-3m...

Biosensor utilizing a liquid crystal/water interface functionalized with poly(4-cyanobiphenyl-4'-oxyundecylacrylate-b-((2-dimethyl amino) ethyl methacrylate)).

Ceramics with the composition Pb1-xK2x-3yMyNb2O6 (PKMN) with x = 0.29, y = 0.145 and M = Gd3+, Y3+ were synthesized by the solid-state reaction route between the corresponding oxides and carbonates. The crystal structure was confirmed by X-ray diffraction (XRD). The temperature dependence of dielectric properties were measured from 35 to 595°C. Well-developed P–E (polarization–electric field) hysteresis loops were observed in the materials. Determining the piezoelectric constants, Kp = 20%, Kt = 49%, d33 = 110, and quality factor, Qm = 33, reveals that the material Y3+-modified PKN can be useful for transducer applications.