Won Chegal

Long-term stability of cell micropatterns on poly((3-(methacryloylamino)propyl)-dimethyl(3-sulfopropyl)ammonium hydroxide)-patterned silicon oxide surfaces

In this work, we compared the long-term stability and integrity of cell patterns on newly reported, zwitterionic poly((3-(methacryloylamino)propyl)dimethyl(3-sulfopropyl)ammonium hydroxide) (poly(MPDSAH)) films with those on widely used, poly(poly(ethylene glycol) methyl ether methacrylate) (poly(PEGMEMA)) ones. The micropatterns of both polymers were formed on a silicon oxide surface by a combination of micropattern generation of a photoresist, vapor deposition of a silane-based polymerization initiator, and surface-initiated, atom transfer radical polymerization (SI-ATRP) of each monomer, MPDSAH or PEGMEMA. The successful formation of the silane initiator SAMs, and poly(MPDSAH) and poly(PEGMEMA) micropatterns was confirmed by X-ray photoelectron spectroscopy (XPS) and imaging ellipsometry. Onto each substrate patterned with poly(MPDSAH) or poly(PEGMEMA), NIH 3T3 fibroblast cells were seeded, and the cell micropatterns were generated by the selective adhesion of cells on the cell-adhesive region of the patterned surfaces. The cell pattern formed on the poly(MPDSAH)-patterned surface was observed to have a superior ability of finely maintaining its original, line-shaped structure up to for 20 days, when compared with the cell pattern formed on the poly(PEGMEMA)-patterned surface. In order to verify the relationship between the integrity of the cell micropatterns and the stability of the underlying non-biofouling polymer layers, we also investigated the long-term stability of the polymer films themselves, immersed in the cell culture media, for one month, in the aid of ellipsometry, contact goniometry, and XPS.

Study of Cell-Matrix Adhesion Dynamics Using Surface Plasmon Resonance Imaging Ellipsometry

The interaction of cells with extracellular matrix, termed cell-matrix adhesions, importantly governs multiple cellular phenomena. Knowledge of the functional dynamics of cell-matrix adhesion could provide critical clues for understanding biological phenomena. We developed surface plasmon resonance imaging ellipsometry (SPRIE) to provide high contrast images of the cell-matrix interface in unlabeled living cells. To improve the contrast and sensitivity, the null-type imaging ellipsometry technique was integrated with an attenuated total reflection coupler. We verified that the imaged area of SPRIE was indeed a cell-matrix adhesion area by confocal microscopy imaging. Using SPRIE, we demonstrated that three different cell types exhibit distinct features of adhesion. SPRIE was applied to diverse biological systems, including during cell division, cell migration, and cell-cell communication. We imaged the cell-matrix anchorage of mitotic cells, providing the first label-free imaging of this interaction to our knowledge. We found that cell-cell communication can alter cell-matrix adhesion, possibly providing direct experimental evidence for cell-cell communication-mediated changes in cell adhesion. We also investigated shear-stress-induced adhesion dynamics in real time. Based on these data, we expect that SPRIE will be a useful methodology for studying the role of cell-matrix adhesion in important biological phenomena.

Snapshot phase sensitive scatterometry based on double-channel spectral carrier frequency concept.

Spectroscopic ellipsometry is one of the most important measurement schemes used in the optical nano-metrology for not only thin film measurement but also nano pattern 3D structure measurement. In this paper, we propose a novel snap shot phase sensitive normal incidence spectroscopic ellipsometic scheme based on a double-channel spectral carrier frequency concept. The proposed method can provide both Ψ(λ) and Δ(λ) only by using two spectra acquired simultaneously through the double spectroscopic channels. We show that the proposed scheme works well experimentally by measuring a binary grating with nano size 3D structure. We claim that the proposed scheme can provide a snapshot spectroscopic ellipsometric parameter measurement capability with moderate accuracy.

Complex object wave direct extraction method in off-axis digital holography

Off-axis digital holography generally uses a 2D-FFT based spatial filtering method to extract the complex object wave from an off-axis hologram. In this paper, we describe a novel single exposure complex object wave extraction method which can provide a faster solution than the FFT based spatial filtering approach while maintaining the reconstructed phase image quality. And also, we show that the proposed direct filtering scheme can provide more robust filtering capability to the off-axis spatial carrier frequency variation than the spatial filtering method.

Angle-resolved annular data acquisition method for microellipsometry

An ellipsometric data acquisition method is introduced to measure the optical properties of sample. It is based on a microellipsometer hardware layout integrated a high numerical aperture objective lens, which is aligned in the normal direction of sample surface. This technique enables to achieve ellipsometric data at multiple incident angle with a sub-mum probe beam size, moreover real-time measurement is possible due to no moving parts. The experimental results of different SiO(2) thin film are demonstrated, also calibration technique is described.

Enhancement of biomolecular detection sensitivity by surface plasmon resonance ellipsometry

We present the application of ellipsometry to the phase measurement of surface plasmon resonance (SPR) in biomolecular detection. In this configuration, the phase measurement gives a large enhancement of detection sensitivity in comparison to traditional SPR techniques. In this work, the experimental setup for SPR ellipsometry is based on both custom-built rotating analyzer ellipsometer and an imaging ellipsometer which are equipped with a SPR-cell and a flow system, respectively. We investigate the adequate thickness of the gold layer used for SPR cell and the resolution of the phase detection using two ellipsometric methods under the SPR condition. The rotating analyzer method yields higher sensitivity sufficient to detect changes in the effective thickness of biomolecular layers of less than 1 pm. In comparison to conventional SPR the simultaneous measurement of ellipsometric parameters, Δ and ψ, yields more information which is useful for quantitative analysis based on fitting theoretical solutions to experimental results.

Calibration of a snapshot phase-resolved polarization-sensitive spectral reflectometer

This Letter describes a universal calibration theory by which conventional interferometry can be extended to vibration robust snapshot polarization-sensitive spectral reflectometry without any complicated optical components or active devices. Experiments for verifying the proposed calibration theory have been conducted by using a Michelson-interferometer-based normal incidence spectroellipsometric system, and also some key system design considerations for object 3D pose tolerant measurement capability have been drawn. The proposed solution enables us to extract the spectroscopic ellipsometric parameter Δ(k) of an anisotropic object within 10 ms with high accuracy.

Ultrasensitive, label-free detection of cardiac biomarkers with optical SIS sensor

Acute myocardial infarction (MI) is the leading cause of high mortality and morbidity rate worldwide, early and accurate diagnosis can increase the chances of survival. In this work, we report a simple, ultrasensitive, label-free, and high-throughput solution immersed silicon (SIS) immunosensor based on non-reflection condition (NRC) for p-polarized wave for early diagnosis of MI. SIS sensor chips are just a thin dielectric polymer layer on the silicon surface, which can be functionalized for specific application. At NRC, SIS sensors are extremely sensitive to the growing thickness of a bio-layer on the sensor surface while independent of refractive index change of the surrounding medium. Therefore, SIS signal is free from thermal noise, unlike surface plasmon resonance based sensor. Also, there is no need of reference signal which facilitates fast and accurate interaction measurement. Here, SIS technology is applied to tackle two issues in MI diagnosis: high sensitivity with the direct assay and the ability to measure in human serum. Myoglobin, creatine kinase-MB, and cardiac troponin I (cTnI) proteins were used as the MI biomarkers. We were able to measure over a broad concentration range with the detection limit of 5 and 10pg/ml for cTnI in PBS and blood serum, respectively. The response time is about 5min. This novel technique is a suitable candidate for cost effective point-of-care application.

Stokes vector measurement based on snapshot polarization-sensitive spectral interferometry

This paper describes a Stokes vector measurement method based on a snapshot polarization-sensitive spectral interferometry. We measure perpendicular linearly polarized complex wave information of an anisotropic object in the spectral domain from which an accurate Stokes vector can be extracted. The proposed Stokes vector measurement method is robust to the object plane 3-D pose variation and external noise, and it provides a reliable snapshot solution in numerous spectral polarization-related applications.

A new spectral imaging ellipsometer for measuring the thickness of patterned thin films

We proposed spectral imaging ellipsometry that uniquely combines one-dimensional imaging and spectroscopic ellipsometry. This type of ellipsometry enables the measurement of the optical parameters and dimensional structures of patterned or multilayered thin films. We demonstrated the result of the measurement of the thickness of patterned SiO2 layers with 3 nm accuracy and 200 µm spatial resolution.