Jeongjin Lee

Bacterial cytotoxicity of the silver nanoparticle related to physicochemical metrics and agglomeration properties

Silver particles are used in various consumer products due to their positive effects, which include sterilization and antibacterial properties. However, it has been reported that silver nanoparticles (AgNPs) have strongly acute toxic effects on various cells. Therefore, the cytotoxicity of AgNPs was investigated, using Escherichia coli as a model organism, from the standpoint of three key metrics (ionic ratio, size, and agglomeration) that are the most relevant physicochemical properties. The findings indicated that cytotoxicity is depressed by the agglomeration of AgNPs. The order of toxic sensitivity was as follows: total Ag concentration  >  ionic ratio  >  size, the order of which was inversely related to the extent of agglomeration.

Simple technique for the simultaneous measurements of the four-probe resistivity and the thermoelectric power

We propose simple configurations to measure the thermoelectric power and the four-probe resistivity simultaneously for different types of samples.

Dependence of image distortion in a liquid-cell atomic force microscope on fluidic properties

When the standard grating sample was tested in seven different fluids using a liquid atomic force microscope, it was observed that the images were significantly distorted. It was proposed as a modified squeeze-drag superposition model for the elucidation of image distortion. This model considers the net force between the cantilever and the sample for scanning with the y direction. It was found that the net force between the cantilever and the sample was strongly dependent on the kinematic viscosity of fluids. These image distortion phenomena were proven by the proposed model with the experiments.

Multifunctionalization of organosilanes on submicron-sized island-type electrodes for the selective detection of metal ions

A submicron-sized metal ion detector with two electrodes was fabricated by atomic force microscopy lithography. Two detection zones were functionalized with thiol (SH) and amine (NH2) groups, which have a high affinity for mercury and copper, respectively. Conductance with metal adsorption was measured by the forced contact of the tip (mobile electrode) with the gold-deposited center (fixed electrode) at a constant repulsive force (38nN). In Cu2+∕Hg2+ binary solutions, one electrode (thiol group) showed a high affinity for mercury, and the other for copper. This two-electrode system immobilized with different functional groups was used in the selective adsorption and detection of target materials.

Fabrication of submicron size electrode via nonetching method for metal ion detection

A metal ion detector with a submicron size electrode was fabricated by atomic force microscopy lithography using a pre-programmed voltage and a nonetching method. The square frame of the mesa pattern was functionalized by (aminopropyl)triethoxysilane for the metal ion detection, and the remaining portion was used as an electrode by the self-assembly of (3-mercaptopropyl)trimethoxysialne for Au metal deposition. In this module, no metal lining or lead line was required, because the conductive tip (mobile electrode) was in direct contact with the gold-deposited mesa portion (fixed electrode). The conductance changed with the quantity of adsorbed copper ions, due to electron tunneling between the mobile and surface electrodes.

Synthesis oftrans-substituted porphyrin building blocks containing two S-trityl or thiol groups

The synthesis of some linear structuredtrans-porphyrin bearing functional groups (S-trityl or thiol) was described. The rational synthetic pathway consisted of 6 reaction steps (up to S-trityl derivatized porphyrin, 5 steps), constituting a MacDonald-type 2+2 condensation and amine-carboxylic acid coupling. The completion of each step was confirmed by1H-NMR, UV/Vis adsorption, and FAM-MS. The resulting porphyrins would be applicable to the study of self-assembled gold-thiol structures, due to the reactive nature of the molecules with a gold surface.

Fabrication of submicron-sized copper structures on pre-patterned self-assembled monolayer and Langmuir-Blodgett films

The fabrication of a metal microstructure on pre-patterned organic templates, prepared using SAM and LB techniques is described. The OTS derivatized substrate was oxidized by AFM anodic oxidation at the threshold voltage. Site-selective copper structure was then fabricated on the locally modified monolayer based on pre-designed patterns. The sequential adsorption-reduction of copper ion was carried out, leading to improved metal coverage and a reduction in defects.

Construction of pcAFM module to measure photoconductance with a nanoscale spatial resolution.

A photoconductive atomic force microscopy (pcAFM) module was designed and the performance was tested. This module consisted of three units: the conductive mirror-plate, the steering mirror and the laser source. The module with a laser irradiation unit was equipped to a conventional conducting probe atomic force microscopy (CP-AFM) instrument to measure photoconductance in a nanoscale resolution. As a proof-of-concept experiment, the photoconductance of aggregated fullerene on indium tin oxide (ITO) substrate was measured with this module. The electrical signals (currents) of aggregated fullerene under the conditions of laser on/off at about -10 V sample bias voltage were -100 to -160 nA and 0 to -20 nA, respectively. Results indicated that the pcAFM with this module allowed one to observe photoinduced changes of electrical properties in nanodevices with nanoscale spatial resolution.

Biomimetic sensors for the heavy metal detection

Specific interactions between heavy metal ions and biomaterials have advantages in the sensitive and selective detection of the metal ions. In this study, Cu-demetallated form of Cu/Zn-superoxide dismutase (SOD1) protein was applied as a sensing probe in order to detect Cu(II) ions selectively via surface plasmon resonance (SPR) analysis. Because demetallated metalloproteins have vacant specific metal-binding sites in their own structures, Cu-demetallated SOD1 protein can successfully form stable complex with Cu(II) ion. By applying the properties as a sensing principle, we designed the Cu(II)-selective sensor chip with Cu-demetallated SOD1 protein. When Cu(II) ions were exposed to the fabricated sensor chips, their interaction was quantitatively measured via SPR analysis, and it was proportional to the concentrations of Cu(II) ions. This result reveals successful development of biosensor for the label-free selective detection of Cu(II) ions.

Fabrication of 3D functionalized microstructure via scanning probe lithography and self-assembly methods.

A type of 2-dimensional planar pattern with spatial resolution can be easily produced using scanning probe lithography (SPL). However, it has not been used successfully for fabricating 3-dimensional (3D) structures due to the low aspect ratio of the resulting structure. Herein, we describe a method for fabricating a 3D functionalized structure via a combination of SPL and self-assembly techniques. In this study, a 3D structure was established on a Si surface with a passivated monolayer via SPL. The patterned layer was modified using a omega-functionalized organosilane. Lateral force microscopy (LFM) was applied to discriminate the chemical functionalities and gold nanoparticles were also used to clearly identify the modified layer.