Hyejung Seo

Air plasma coupled with antibody-conjugated nanoparticles: a new weapon against cancer

Ambient air plasmas have been known to kill cancer cells. To enhance selectivity we have used antibody-conjugated nanoparticles. We achieved five times enhancement of melanoma cell death over the case of the plasma alone by using an air plasma with gold nanoparticles bound to anti-FAK antibodies. Our results show that this new interdisciplinary technique has enormous potential for use as a complement to conventional therapies.

Enhanced Photocatalytic Activity of Highly Crystallized and Ordered Mesoporous Titanium Oxide Measured by Silicon Resonators

Ordered mesoporous TiO(2) was synthesized using the combined assembly of soft and hard chemistries method and deposited as a film coating on a microcantilever sensor array along with two other types of TiO(2) film: one from nanoparticles and one prepared via a sol-gel reaction. After loading methylene blue molecules on the TiO(2) films, the films were exposed to ultraviolet radiation. The photocatalytic decomposition of methylene blue was monitored by measuring changes in the resonance frequency of each cantilever. The mesoporous TiO(2) film showed higher photocatalytic activity than conventional TiO(2) films fabricated from nanoparticles or via a sol-gel reaction; this difference is attributed to the purely anatase crystalline morphology of the mesoporous TiO(2) film as well as its well-organized pore structure. The three-dimensionally interconnected pore network facilitates the diffusion of methylene blue molecules to the photocatalytically active sites of the mesoporous TiO(2).

Label-Free Detection of a Biomarker with Piezoelectric Micro Cantilever Based on Mass Micro Balancing

With a piezoelectric micro cantilever sensor, a biomarker for various cancers is detected up to the concentration level required to determine a disease by using the mass micro balancing whose principle is that change of mechanical vibrant frequency is measured due to a target material attached on a sensor structure. The used piezoelectric micro cantilever sensor is designed so as to have the sufficient values of mass sensitivity and reliability. The used piezoelectric film, which acts as both sensor and actuator, is a plumbum zirconate titanate (PZT). Geometrical dimension of the micro cantilever is 100 μm (length) by 30 μm (width) by 5 μm (thickness). The 50-μm-long PZT film with thickness of 2.5 μm is covered from its root to its middle. Carcinoembryonic antigen (CEA), the biomarker for testing the sensor as label-free detection for pathological tests, is known as a biomarker for various cancers. The critical value of CEA concentration is known as 30 pM (5 ng/mL), and it is detected by the binding of antigen and antibody from high concentration to the critical concentration. From the results, the sensor could be applied to label-free detection sensors for pathological tests.

Photocatalytic silver enhancement reaction for gravimetric immunosensors

A novel microgravimetric immunosensor has been developed using TiO(2) nanoparticle-modified immunoassay and silver enhancement reaction. An antibody-conjugated TiO(2) nanoparticle is bound to the AFP antigen immobilized on a quartz resonator. When the nanoparticles are exposed to UV light in a silver nitrate solution, the photocatalytic reduction of silver ions results in the formation of metallic silver onto the nanoparticles and induces a decrease in the resonance frequency. The frequency change by this photocatalytic reduction reaction is three orders of magnitude larger than the change by antigen binding alone. The efficiency of the photocatalytic reaction has been found to increase with the fraction of anatase crystallites in the nanoparticles and the concentration of the AgNO(3) solution. The results highlight the potential of the photocatalytic nanoparticles for the detection of low concentrations of target molecules using gravimetric sensors.

A rapid and facile signal enhancement method for microcantilever-based immunoassays using the agglomeration of ferromagnetic nanoparticles

A rapid and facile signal enhancement method for detecting alpha-fetoprotein (AFP) was developed using the magnetic agglomeration of ferromagnetic nanoparticles and microcantilever sensors. The resonance frequency and deflection of the cantilevers were found to be more than 10-fold greater than that before physical agglomeration of the free nanoparticles around the magnetized nanoparticles.

Piezoelectric micro cantilever sensor for non-labeling detection of biomarker

Using the piezoelectric micro cantilever sensor, biomarkers of various diseases are detected at their critical concentration or below. The detection principle of the sensor is the mass-micro-balancing technique that utilizes the change of the mechanical resonance frequency due to an object attached on a structure. An Ohm-contact electrode is installed to remove the parasitic capacitance effects between the electrodes in the sensor. The first resonant frequency of the piezoelectric micro cantilever can be monitored by measurement of the conductance component of the admittance. The results of the bio-marker-detection experiments show that the detection sensitivity of the micro cantilever is from 2 to 3 orders of magnitude higher than that of the conventional quartz-crystal micro-balancing detection.

Influence of dissolved air on the adsorption properties and stability of vesicles on various surfaces

Large unilamellar vesicles were prepared for adsorption on quartz crystal surfaces coated with gold, mercaptoundecanoic acid, or octadecanethiol self-assembled monolayers. The adsorption of the vesicles onto these surfaces decreases the resonance frequency of the quartz crystals. We found that frequency changes due to vesicle adsorption were much lower in degassed than in air-rich water. Further, the vesicles adsorbed in air-rich water desorbed when the medium was replaced with degassed water, indicating that the presence of dissolved air in water played a key role in the adsorption and stability of vesicles.