Jeong Hoon Lee

Dominant surface stress driven by biomolecular interactions in the dynamical response of nanomechanical microcantilevers

Nanomechanical microcantilevers have played a vital role in detecting biomolecular interactions. The ability of microcantilevers to detect biomolecular interactions is ascribed to the principle that the surface stress, caused by biomolecular interactions, dominates the dynamical response of the microcantilever. Here we have experimentally studied the correlation between biomolecular interactions and the dynamical response of microcantilevers. Moreover, the authors employed a mechanical beam model to calculate the surface stress, representing the biomolecular interactions, through measuring the resonant frequency shift. The quantitative analysis of surface stress, driven by the specific protein-protein interactions, demonstrated that microcantilevers enable the quantitative study of biomolecular interactions.

Microstructure and adhesion of Au deposited on parylene-c substrate with surface modification for potential immunoassay application

Improvement of recrystallization and adhesion of gold (Au) deposited on parylene-c (Pa-c) substrate with heat treatment and surface modification using physical and chemical treatment was investigated. Annealing of Au on Pa-c was performed to observe microstructure enhancement due to heat treatment from 100 to 250/spl deg/C. From the peak intensity and full-width at half-maximum of Au(111), its crystallinity appeared to improve as the annealing temperature increased, which can provide the surface with proper creation of monolayers. Several physical and chemical methods of surface modifications were employed to analyze surface energy and adhesion promotion, such as oxygen plasma, atmospheric plasma, ion beam, and Bovine serum albumin. These results exhibit excellent adhesion properties by exploiting oxygen plasma and ion-beam treatment, which induce carbonyl groups via the mechanical interlocking.

Wafer-scale high-resolution patterning of reduced graphene oxide films for detection of low concentration biomarkers in plasma

Given that reduced graphene oxide (rGO)-based biosensors allow disposable and repeatable biomarker detection at the point of care, we developed a wafer-scale rGO patterning method with mass productivity, uniformity, and high resolution by conventional micro-electro-mechanical systems (MEMS) techniques. Various rGO patterns were demonstrated with dimensions ranging from 5u2009μm up to several hundred μm. Manufacture of these patterns was accomplished through the optimization of dry etching conditions. The axis-homogeneity and uniformity were also measured to verify the uniform patternability in 4-inch wafer with dry etching. Over 66.2% of uniform rGO patterns, which have deviation of resistance within range of ±10%, formed the entire wafer. We selected amyloid beta (Aβ) peptides in the plasma of APP/PS1 transgenic mice as a study model and measured the peptide level by resistance changes of highly uniform rGO biosensor arrays. Aβ is a pathological hallmark of Alzheimer’s disease and its plasma concentration is in the pg mL−1 range. The sensor detected the Aβ peptides with ultra-high sensitivity; the LOD was at levels as low as 100u2009fg mL−1. Our results provide biological evidences that this wafer-scale high-resolution patterning method can be used in rGO-based electrical diagnostic devices for detection of low-level protein biomarkers in biofluids.

Electric and longitudinal piezoelectric properties of PZT(52/48) films as a function of thickness prepared by diol based sol-gel method

Abstract Piezoelectric and electrical properties were investigated in PZT (52/48) films as a function of thickness. Films are prepared by diol based sol-gel method by spin coating in order to achieve much thicker films on Si wafer. The optimized thickness of each layer individual was 0.2 μm and crack-free films could be successfully deposited on 4 inches Pt/Ti/SiO2/Si substrate. Thickness dependence of microstructure on piezoelectric and electrical properties was characterized over the range of 0.2–3.8 μm. The films exhibited (111) preferred orientation in the range of thickness below 1 μm. As the thickness increased, the (111) preferred orientation disappeared and the orientation of films became random above 3 μm. Effective longitudinal piezoelectric coefficient, d33, measured by pneumatic method, remanent polarization and dielectric constants were saturated around the value of about 300 pC/N, 45 μC/cm2 and 1400 respectively above the thickness of 1 μm.