Yukeun Eugene Pak

Development of an SH-SAW sensor for detection of DNA immobilization and hybridization

We have developed SH (shear horizontal) surface acoustic wave (SAW) sensors for detection of the immobilization and hybrdization of DNA (deoxyribonucleic acid) on the gold coated delay line of transverse SAW devices. The experiments of DNA immobilization and hybridization were performed with 15-mer oligonucleotides (probe and complementary target DNA). The sensor consists of twin SAW delay line oscillators (sensing channel and reference channel) operating at 100 MHz fabricated on 36° rotated Y-cut X-propagation LiTaO3 piezoelectric single crystals. The relative change in the frequency of the two oscillators was monitored to detect the immobilization of probe DNA with thiol group on the Au coated delay line and the hybridization between target DNA and immobilized probe DNA in a pH 7.4 PBS (phosphate buffered saline) solution. The measurement results showed a good response of the sensor to the mass loading effects of the DNA immobilization and hybridization with the sensitivity up to 1.5 ng/ml/Hz.

SAW sensor for anti-human-immuno-globulin G molecule detection

We developed SAW sensors to detect human-immuno-globulin G (HigG) molecules by applying a particular antibody thin film on the delay line of transverse SAW devices. The mass loading effect was given by the antibody-antigen bonding of the target molecules on the delay line. The sensor consists of twin SAW delay lines operating at 100 MHz fabricated on 36/spl deg/ rotated Y-cut X-propagation LiTaO/sub 3/ piezoelectric single crystals. The sensitive channel of the SAW sensor was coated with a gold film on which an antibody layer was immobilized. Protein A molecules were coupled with the HigG molecules to work as an immobilizer layer to hold the antigens (anti-HigG). For proper immobilization of the detection molecules, bovine serum albumin worked as a blocking layer to prevent the adhesion of any other molecules different from the anti-HigG. The relative change in the frequency of the two oscillators was monitored to measure the anti-HigG concentration in the protein solution. The sensor showed linear response to the mass loading effects of the anti-HigG molecules with a sensitivity up to 10.7 ng/ml/Hz.

An application of polarized domains in ferroelectric thin films using scanning probe microscope

The feasibility of utilizing PZT films as future data storage media has been investigated using a modified AFM. Applying voltages between a conductive AFM tip and the PZT films causes the switching of ferroelectric domains. The domains are observed using an EFM imaging technique. The experimental results and calculations revealed that the electrostatic force generated between the polarized area and the tip is a main contributor for the imaging of the polarized domains. The written features on ferroelectric films were less than 100 nm in diameter, implying the possibility of realizing data storage devices with ultrahigh areal density. The disappearance of the polarized images without any applied voltage spontaneous reversal polarization was observed, which is a drawback in this application of PZT thin films.