Da-Yeon Kang

Ultra-sensitive immunosensor for β-amyloid (1-42) using scanning tunneling microscopy-based electrical detection

An ultra-sensitive immunosensor for beta-amyloid is crucial because beta-amyloid is an important challenging marker to detect for early diagnosis of Alzheimers disease. In this study, a vertically configured electrical detection system was developed based on scanning tunneling microscopy (STM) to detect antigen-antibody binding events. This technique could be used to easily construct a multiple measurement system in a biochip. We utilized immunocomplexes comprised of the model protein, beta-amyloid (1-42), corresponding antibody fragments, and gold (Au) nanoparticles-antibody conjugates for an immunosensor for Alzheimers disease. The electrical tunneling current between the STM tip and these complexes exhibited a peak-like pulse, the frequency of which depended on the density of the bound complexes on the surface. We could therefore quantitatively measure beta-amyloid (1-42) concentrations as low as 10fg/mL using periodogram analysis of the peak frequency. Since this method accurately quantified much smaller amounts of beta-amyloid (1-42) than traditional immunosensors, this system shows promise as an ultra-sensitive immunodetection method.

Ultrasensitive immunoassay for prostate specific antigen using scanning tunneling microscopy-based electrical detection

We characterized a vertically configured electrical detection system that used scanning tunneling microscopy (STM) to detect antigen-antibody binding. This technique could be used to easily construct a multiple measurement system in a protein chip. We utilized immunocomplexes comprised of our model protein, prostate specific antigen (PSA), corresponding antibody fragments, and gold nanoparticle-antibody conjugates. The electrical tunneling current between the STM tip and these complexes exhibited a peaklike pulse, the frequency of which depended on the surface density of the bound complexes. We could therefore quantitatively measure PSA concentrations as low as 10fg∕mL using periodogram analysis of this peak frequency.

Analysis of direct immobilized recombinant protein G on a gold surface

For the immobilization of IgG, various techniques such as chemical linker, thiolated protein G methods, and fragmentation of antibodies have been reported [Y.M. Bae, B.K. Oh, W. Lee, W.H. Lee, J.W. Choi, Biosensors Bioelectron. 21 (2005) 103; W. Lee, B.K. Oh, W.H. Lee, J.W. Choi, Colloids Surf. B-Biointerfaces, 40 (2005) 143; A.A. Karyakin, G.V. Presnova, M.Y. Rubtsova, A.M. Egorov, Anal. Chem. 72 (2000) 3805]. Here, we modified the immunoglobulin Fc-binding B-domain of protein G to contain two cysteine residues at its C-terminus by a genetic engineering technique. The resulting recombinant protein, RPGcys, retained IgG-binding activity in the same manner as native protein G. RPGcys was immobilized on a gold surface by strong affinity between thiol of cysteine and gold. The orientations of both IgG layers immobilized on the base recombinant protein Gs were analyzed by fluorescence microscope, atomic force microscope (AFM), and surface plasmon resonance (SPR). Our data revealed that IgG-binding activity of RPGcys on gold surface significantly increased in comparison to wild type of protein G (RPGwild), which was physically adsorbed due to absence of cysteine residue. Immobilization of highly oriented antibodies based on cysteine-modified protein G could be useful for the fabrication of immunosensor systems.

Surface morphology and interdiffusion of LiF in Alq3-based organic light-emitting devices

Highly efficient organic light-emitting devices (OLEDs) have been realized by insertion of a thin insulating lithium fluoride (LiF) layer between aluminum (Al) cathode and an electron transport layer, tris-(8-hydroxyquinoline) aluminum (Alq(3)). In this paper, we study the surface morphology of LiF on Alq(3) by synchrotron X-ray scattering and atomic force microscopy (AFM) as a function of thickness of LiF. We also study the interdiffusion of LiF into Al cathode as well as into Alq(3) layer as a function of temperature. Initially, LiF molecules are distributed randomly as clusters on the Alq(3) layer and then gradually form a layer as increasing LiF thickness. The interdiffusion of LiF into Al occurs more actively than into Alq(3) in annealing process. LiF on Alq(3) induces the ordering of Al to (111) direction strongly with increasing LiF thickness.

Electrical detection of β-amyloid (1-40) using scanning tunneling microscopy

Numerous studies have shown that the presence of beta-amyloid (1-40) in cerebrospinal fluid can be used as a potential biomarker for Alzheimers disease. Identifying biomarkers for Alzheimers disease is highly important because these biomarkers could be used to establish the diagnosis before the disease reaches clinical severity. In this study, a vertically configured electrical detection system associated with scanning tunneling microscopy (STM) was used to characterize antigen-antibody binding interactions. The proposed technique can be easily utilized to construct a multiple measurement system in a protein chip. The immunocomplexes used in the model protein comprise beta-amyloid (1-40), corresponding antibody fragments, and gold nanoparticle-antibody conjugates. The electrical tunneling current between the STM tip and these complexes exhibited a peak-like pulse, where the frequency of these pulses was dependent on the surface density of bound complexes. Hence, a quantitative measurement of beta-amyloid concentration from a periodogram analysis of peak frequency was successfully achieved at concentrations as low as 1fg/mL.