Sang Won Han

Mutiscale substrates based on hydrogel-incorporated silicon nanowires for protein patterning and microarray-based immunoassays

Here, protein micropatterns were prepared on micropatterned nanostructures for potential applications in microarray-based multiplex bioassays with enhanced protein-loading capacity and detection sensitivity. Vertically-aligned silicon nanowires (SiNWs) that were about 8 μm in height and 150 nm in diameter were prepared using an etching process and were surface-modified with aminopropyltriethoxysilane (APTES) to allow them to covalently immobilize proteins. The SiNW substrate was then overlaid with a micropattern of poly(ethylene glycol) (PEG) hydrogel to create defined arrays of microwells consisting of APTES-modified SiNW on the bottom of the wells, with hydrogel on the walls of the wells. Due to the non-adhesiveness of PEG hydrogels toward proteins, proteins were selectively immobilized on the surface-modified SiNW regions to create protein micropatterns. The increase in surface area increased the protein loading capacity of the SiNWs by more than 10 times the capacity of a planar silicon substrate. Immunobinding assays between IgG and anti-IgG and between IgM and anti-IgM that were performed on micropatterned SiNWs emitted stronger fluorescent signals and showed higher sensitivity than assays performed on planar silicon substrates. Finally, microfluidic channels were successfully integrated into the micropatterned SiNWs to enable the simultaneous performance of multiple immunoassays on a single microarray platform.

Preparation of photolithographically patterned inverse opal hydrogel microstructures and its application to protein patterning

Protein pattern has played an important role in biosensors, bioMEMS, tissue engineering, fundamental studies of cell biology, and basic proteomics research. Here, we developed a straightforward and effective protein patterning technique using macroporous poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogel micropatterns as a three-dimensional (3D) template for protein immobilization. Micropatterns of macroporous hydrogels with inverse opal structures were prepared on poly(ethylene glycol) (PEG)-coated silicon substrates by combining a colloidal crystal templating method with photopatterning. The resultant inverse opal hydrogel (IOH) micropatterns were modified with 3-aminopropyltriethoxysilane using the hydroxyl groups in PHEMA for the covalent immobilization of proteins. Proteins were selectively immobilized only on the hydrogel micropatterns, while the PEG regions served as an effective barrier to protein adsorption. Because of their highly ordered and interconnected 3D macroporous structures and large internal surface areas, protein loading in the IOH micropattern was about six times greater than that on a non-porous hydrogel micropattern, which consequently improved the protein activity. The porosity of the hydrogel micropatterns could be controlled using different sizes of colloidal nanoparticles, and using smaller nanoparticles produced hydrogel micropatterns with higher protein loading capacities and activities. To demonstrate the potential use of IOH micropatterns in biosensor systems, biotin was micropatterned on the hydrogels and the specific binding of streptavidin was successfully assayed using IOH micropatterns with better fluorescence signals and sensitivity than that of the corresponding non-porous hydrogel micropatterns.

Hydrogel-Framed Nanofiber Matrix Integrated with a Microfluidic Device for Fluorescence Detection of Matrix Metalloproteinases-9

Matrix metalloproteinases (MMPs) play a pivotal role in regulating the composition of the extracellular matrix and have a critical role in vascular disease, cancer progression, and bone disorders. This paper describes the design and fabrication of a microdevice as a new platform for highly sensitive MMP-9 detection. In this sensing platform, fluorescein isocyanate (FITC)-labeled MMP-9 specific peptides were covalently immobilized on an electrospun nanofiber matrix to utilize an enzymatic cleavage strategy. Prior to peptide immobilization, the nanofiber matrix was incorporated into hydrogel micropatterns for easy size control and handling of the nanofiber matrix. The resultant hydrogel-framed nanofiber matrix immobilizing the peptides was inserted into microfluidic devices consisting of reaction chambers and detection zones. The immobilized peptides were reacted with the MMP-9-containing solution in a reaction chamber, which resulted in the cleavage of the FITC-containing peptide fragments and subsequently generated fluorescent flow at the detection zone. As higher concentrations of the MMP-9 solution were introduced or larger peptide-immobilizing nanofiber areas were used, more peptides were cleaved, and a stronger fluorescence signal was observed. Due to the huge surface area of the nanofiber and small dimensions of the microsystem, a faster response time (30 min) and lower detection limit (10 pM) could be achieved in this study. The hydrogel-framed nanofiber matrix is disposable and can be replaced with new ones immobilizing either the same or different biomolecules for various bioassays, while the microfluidic system can be continuously reused.

Multi‐Compartmental Hydrogel Microparticles Fabricated by Combination of Sequential Electrospinning and Photopatterning

Multi-compartmental non-spherical hydrogel microparticles were fabricated by combining electrospinning and photopatterning. Sequential electrospinning produced multi-layered fiber matrices with different composition in which each layer became a compartment of the particle. Photopatterning of the hydrogel in the presence of the multi-layered fiber matrix generated multi-compartmental microparticles with different vertical functionalities. While the shapes of the hydrogel microparticles were determined by the design of the photomask, the chemical properties and size of each compartment were independently controlled by changing the molecules incorporated into each fiber matrix and the electrospinning times, respectively. The resultant multi-compartmental hydrogel microparticles could carry out not only the release of different growth factors with independent kinetics but also binding of multiple targets at different compartments.

Hydrophilic surface modification of poly(methyl methacrylate)-based ocular prostheses using poly(ethylene glycol) grafting

Ocular prostheses are custom-made polymeric inserts that can be placed in anophthalmic sockets for cosmetic rehabilitation. Prosthetic eye wearers have reduced tear amount, and they often experience dry eye symptoms including dryness, irritation, discomfort, and discharge. Most modern ocular prostheses are made of poly(methyl methacrylate) (PMMA), which is highly hydrophobic. Previous research has shown that improving the wettability of contact lens materials decreases its wearers discomfort by increasing lubrication. Therefore, hydrophilic modification of PMMA-based ocular prostheses might also improve patient discomfort by improving lubrication. We modified the surfaces of PMMA-based ocular prostheses using poly(ethylene glycol) (PEG), which is hydrophilic. To do this, we used two strategies. One was a grafting from method, whereby PEG was polymerized from the PMMA surface. The other was a grafting to method, which involved PEG being covalently bonded to an amine-functionalized PMMA surface. Assessments involving the water contact angle, ellipsometry, and X-ray photoelectron spectroscopy indicated that PEG was successfully introduced to the PMMA surfaces using both strategies. Scanning electron microscopy and atomic force microscopy images revealed that neither strategy caused clinically significant alterations in the PMMA surface morphology. In vitro bacterial adhesion assessments showed that the hydrophilic modifications effectively reduced bacterial adhesion without inducing cytotoxicity. These results imply that hydrophilic surface modifications of conventional ocular prostheses may decrease patient discomfort and ocular prosthesis-related infections.

A Study on Glucose Sensing Measured by Catalyst Containing Multiple Layers of Glucose Oxidase and Gold Nano Rod

In this study, we propose a catalyst structure including enzyme and metal nano rod for glucose sensing. In the catalyst structure, glucose oxidase (GOx) and gold nano rod (GNR) are alternatingly immobilized on the surface of carbon nanotube (CNT), while poly(ethyleneimine) (PEI) is inserted in between the GOx and GNR to fortify their bonding and give them opposite polarization ((GOx/GNR)nPEI/CNT). To investigate the impact of (GOx/GNR)nPEI/CNT on glucose sensing, some electrochemical measurements are carried out. Initially, their optimal layer is determined by using cyclic voltammogram and as a result of that, it is proved that (GOx/GNR/ PEI)2/CNT is the best layer. Its glucose sensitivity is 13.315 μAmM -1 cm -2 . When it comes to the redox reaction mechanism of flavin adenine dinucleotide (FAD) within (GOx/GNR/PEI)2/CNT, (i) oxygen plays a mediator role in moving electrons and protons generated by glucose oxidation reaction to those for the reduction reaction of FAD and (ii) glucose does not affect the redox reaction of FAD. It is also recognized that the (GOx/GNR/PEI)3/CNT is limited to the surface reaction and the reaction is quasi-reversible.